An Approach to Developing Cyanines with Simultaneous Intersystem Crossing Enhancement and Excited-State Lifetime Elongation for Photodynamic Antitumor Metastasis

Pyrazolo[1,5-a]pyrimidine-Based Type-I Photosensitizer as an Efficient Pyroptosis Inducer for Tumor Ablation

Pyroptosis is a proinflammatory and lytic programmed cell death form, which can promote cytotoxic T lymphocyte (CTL) maturation and tumor infiltration through the release of damage-associated molecular patterns (DAMPs). Therefore, the induction of pyroptosis by small molecules is a promising strategy to activate antitumor immunity. In this work, we report the design of a new class of pyrazolo[1,5-a]pyrimidine-based type-I photosensitizers (PSs) as efficient pyroptosis inducers for cancer photodynamic therapy (PDT). Among the compounds, ZS-3 exhibited the most excellent reactive oxygen species (ROS) generation ability and phototoxicity in vitro. It was found that ZS-3 induced cell pyroptosis through the caspase-3/gasdermin E (GSDME) pathway under light irradiation, characterized by bubble formation and damage-associated molecular pattern release. Furthermore, ZS-3 lipid nanoparticles significantly inhibited tumor growth and evoked antitumor immune responses in vivo.

Type I BODITh Photosensitizers with Twisted Conformation for Augmented Photodynamic Therapy and FOXO1-Involved Apoptosis

Developing targeted type I photosensitizers with low oxygen-dependence is essential to overcome tumor hypoxia and address the short diffusion radius of free radicals in photodynamic therapy (PDT). Herein, two Boron dithiazolemethene (BODITh)-derivatives, SBDP-1 and SBDP-2 with different numbers of thiophene units, were designed as mitochondria-targeted type I photosensitizers with significant ·OH generation. Through theoretical calculations, the additional thiophene unit in SBDP-2 induced a torsional conformation with a smaller overlap integral of holes and electrons than SBDP-1, resulting in an increased spin-orbit coupling (SOC) constant with a decreased singlet-triplet energy gap (ΔEST), thereby promoting the intersystem crossing (ISC) process. Moreover, through a molecular docking study, SBDP-2 NPs could bind to miR-96 via hydrophobic interaction and trigger the forkhead box protein O1 (FOXO1) involved pathway to accelerate cell apoptosis. This work presented innovative type I photosensitizers with twisted conformation for efficient cancer PDT to conquer tumor hypoxia.

Pyrazolone-Modified Photosensitizers for Precise Cell Membrane Rupture to Enhance Cancer Immunotherapy

The advancement of immunotherapy aims to achieve complete tumor eradication. However, several critical challenges hinder the efficacy of conventional phototherapy-mediated immune responses, including insufficient immunogenicity and the presence of an immunosuppressive tumor microenvironment. Nonprogrammed cell death, as a highly immunogenic pathway, offers a promising strategy to enhance immune responses. Herein, a membrane-anchored photodynamic immunotherapy agent, PNBSe, was developed by conjugating a selenium-substituted benzophenothiazine photosensitizer with a pyrazolone group, enabling membrane targeting via pyrazolone-protein interactions. Upon light irradiation, PNBSe induced rapid and intense cell necrosis characterized by significant cell membrane rupture, organelle swelling, and content leakage. Further investigations demonstrated that PNBSe activated inflammatory signaling pathways, induced immunogenic cell death, and reshaped the immunosuppressive tumor microenvironment, ultimately promoting systemic antitumor immune responses in vivo. This membrane-anchored small molecule provides a novel perspective for promoting cancer photodynamic immunotherapy.

Spin Manipulation Engineering of Photodynamic Intermediates: Magnetic Amplification of Oxyradicals Generation for Enhanced Antitumor Phototherapeutic Efficacy

Improving the photosensitization efficiency represents a critical challenge in photodynamic therapy (PDT) research. While cyanines exhibit potential as photosensitizers (PSs) due to their large extinction coefficients and excellent biocompatibility, the inherent limitations in intersystem crossing severely affect therapeutic efficacy. Herein, we proposed a bottom-up magnetically enhanced photodynamic therapy (magneto-PDT) paradigm employing fluorobenzene-substituted pentamethine cyanine as type-I reactive oxygen species generators. Based on the radical pair mechanism and magnetic field effect, the notable difference in g-factors (Δg) between PSs and oxyradicals enabled magnetically responsive amplification of Cy5-3,4,5-3F-mediated hydroxyl radical (•OH) and superoxide anion radical (O2•-) production, achieving maximum yield enhancements of 66.9 and 28.0% respectively at 500 mT. This magnetically augmented oxyradicals generation exhibited universal cytotoxicity superiority over conventional PDT protocols in various cancer cell models. Notably, the semi-inhibitory concentration (IC50) of murine mammary carcinoma 4T1 cells demonstrated a remarkable reduction under both normoxic and hypoxic conditions, with the most pronounced decrease observed in normoxia from 0.91 μM (PDT alone) to 0.38 μM (magneto-PDT). The significantly magneto-enhanced therapeutic performance effectively inhibited orthotopic tumor growth. This magneto-PDT paradigm established a novel strategy for manipulating spin-dependent photosensitization processes in biological applications.

A base-stacking-driven ratiometric electrochemical biosensor using dsDNA-mediated MB-and-cholesterol co-immobilization: A model of hydrophobic versatile platform for biosensing

It remains a huge challenge to integrate the stability, reproducibility, and sensitivity of electrochemical DNA biosensors (E-sensors) for practical applications in a simplistic yet cost-effective way. In this work, we present a versatile and inclusive hexanethiol self-assembled monolayer (HT SAM) platform that strategically recruits cholesterol and methylene blue (MB) through double-stranded DNA (dsDNA) coordination, incorporating immobilization and reference functionalities onto the HT SAM. Systematically augmented anchoring sites substantially enhanced interfacial DNA probe immobilization stability and efficiency. Additionally, co-immobilized MB functions as an intrinsic reference signal, effectively mitigating the precision limitations arising from reproducibility issues inherent in conventional E-sensors. The upright dsDNA and the coaxial base-stacking promote the target-probe interactions and improve both hybridization efficiency and rate for the interface DNA probes. The tightly packed hydrophobic HT SAM facilitates [Fe(CN)6]3‒-mediated cascade electrocatalytic amplification, further increasing E-sensor sensitivity. As a proof-of-concept, the designed base-stacking-driven ratiometric E-sensor using dsDNA-mediated MB-and-cholesterol co-immobilization successfully detected severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) N gene-related fragments, demonstrates a wide dynamic range (10 fM to 10 nM) with a low detection limit of 1.32 fM, exhibiting excellent reproducibility and selectivity. With its high detection performance, ease of operation and low cost, this E-sensor is well-suited for point-of-care testing in large-scale disease screening. Above all, the hydrophobic HT SAM as a versatile and inclusive platform combined with the ease of modification of DNA structures to recruit functional molecules and maximize their contributions is key to synergistically enhancing the overall performance of E-sensors.

Turning Lemons into Lemonade: One-Step Synthesized Dual-Acceptor Organic Photosensitizer to Boost the Photodynamic Therapy

Reactive oxygen species (ROS) are crucial in photodynamic therapy (PDT), but their generation is highly dependent on the S-T bandgap (ΔEST), spin-orbit coupling (SOC), intersystem crossing rate (kISC), and also excited triplet-states lifetime (τTriplet) in organic photosensitizers (PSs). In contrast to the widely reported donor-acceptor-donor (D-A-D) type PSs, D-A-A-D typed PSs are seldomly developed for the time-consuming and complicated synthesis, but show great potential in enhancing ROS generation in phototheranostics. This work here presents a one-step synthetic procedure of D-A-A-D type 2DMeTPA-2BT with a high yield of 47%, which is significantly different from the previously reported dual-acceptor cases. In contrast to 2DMeTPA-BT, the dual-acceptor PSs of 2DMeTPA-2BT display a much smaller ΔEST value but large SOC constants. Also, the intersystem crossing (ISC) dynamics indicate that fast kISC, long τTriplet, and large triplet population are observed in 2DMeTPA-2BT-based nanoparticles (NPs), contributing to a superior generation of ROS. 2DMeTPA-2BT NPs are then finally utilized for the imaging-guided PDT in vivo with a tumor inhibition rate of 90%. This method offers an efficient way to produce dual-acceptor typed PSs via a one-step reaction, providing new avenues in high-performance phototheranostics.

A Lanthanide Nanoparticle-Aggregation-Induced Emission Photosensitizer Complex System Drives Coupled Triplet Energy Transfer for Enhanced Radio-Photodynamic Therapy

Cerenkov light (CL), utilized as an internal excitation source for photodynamic therapy (PDT), addresses the limitations of laser penetration and has substantial potential for seamlessly integrating clinical radiotheranostics with phototheranostics. Nevertheless, the effectiveness of CL-mediated PDT is significantly hindered by challenges, such as the low intensity of CL and inadequate energy transfer between the CL donor and photosensitizers (PSs). In this study, a novel approach is introduced for enhanced radionuclide-activated radio-photodynamic therapy utilizing a hybrid nanoparticle system composed of lanthanide nanoparticles and an aggregation-induced emission photosensitizer (AIE PS), designated LnNP-TQ NPs. This system enables lanthanide nanoparticles to optimize the decay energy of radionuclides, effectively sensitizing the AIE PS through triplet energy transfer (TET)-mediated processes with an efficiency approaching 100%. When activated by the clinical radionuclide 18F for positron emission tomography imaging, the LnNP-TQ NPs substantially inhibited tumor growth via effective singlet oxygen (1O2) generation. This strategy, which optimally harnesses radionuclide energy and achieves efficient energy transfer, offers a promising pathway for enhancing radiotherapy-phototherapy efficacy in tumor treatment.

Tumor-Targeted Exosome-Based Heavy Atom-Free Nanosensitizers With Long-Lived Excited States for Safe and Effective Sono-Photodynamic Therapy of Solid Tumors

Theranostic nanosensitizers with combined near-infrared (NIR) fluorescence imaging and sono-photodynamic effects have great potential for use in the personalized treatment of deep-seated tumors. However, developing effective nanosensitizers for NIR fluorescence image-guided sono-photodynamic therapy remains a considerable challenge, including the low generation efficacy of reactive oxygen species (ROS), poor photostability, and the absence of cancer specificity. Herein, a novel heavy atom-free nanosensitizer is developed, which exhibits intense NIR fluorescence, high ROS generation efficiency, and improved aqueous stability. By conjugating a bulky and electron-rich group, 4-(1,2,2-triphenylvinyl)-1,1'-biphenyl (TPE), to the IR820 backbone, the resulting IR820 bearing TPE (IR820-TPE) effectively generates ROS via type I and II photochemical mechanisms under 808 nm laser irradiation. Moreover, TPE conjugation considerably increases the sono-photodynamic performance of IR820. To improve the intracellular delivery and tumor-targeting ability of IR820-TPE, biotin-conjugated exosome (B-Exo) is used as a natural nanocarrier. In vitro studies demonstrate the outstanding therapeutic performance of IR820-TPE-loaded B-Exo (IR820-TPE@B-Exo) in synergistic sono-photodynamic cancer therapy. In vivo studies reveal that IR820-TPE@B-Exo shows enhanced tumor accumulation, strong fluorescence signals, and effective sono-photodynamic therapeutic activity with high biosafety. This work demonstrates that IR820-TPE@B-Exo is a promising sono-phototheranostic agent for safe and targeted cancer therapy and NIR fluorescence imaging.

Albumin Modulated Homodimer as an Efficient Photosensitizer for Long-Term Imaging-Guided Tumor Therapy Directed with Sunlight Irradiation

The reactive oxygen species (ROS) amplification caused by inevitable plasma albumin encapsulation is still a challenge to circumvent the systemic adverse effects in the photodynamic therapy (PDT) process. Herein, a disulfide bond linked homodimer, Cy1280, which is modulated by albumin to accurately balance the fluorescence and ROS generation and exhibit a weak fluorescence and sealed PDT effect during blood circulation, is exploited. Cy1280 can be specifically internalized and dispersed at the tumor site via Organic Anion Transporter Proteins (OATPs) and thiol-disulfide exchange mediated synergistic uptake and activated after mild sunlight irradiation (100 ± 5 Klx) to sensitize neighboring oxygen in cellular mitochondria to execute direct protein dysfunction effect. The dynamic covalent chemistry (DCC) facilitates prolonged and sustained retention in tumors (>336 h) and demonstrates the efficacy of imaging-guided solid-tumor therapy in tumor-bearing BALB/C mice. This study resolves the inevitable stubborn impotent tumor penetration caused by bulky-sized nanoparticles and high interstitial pressure of tumor with synergistic uptake manner, the long-term circulation and sealed PDT manipulated with albumin also improve the whole body phototoxic symptom. The advantageous feature of Cy1280 provides a promising candidate for overcoming the off-target phototoxicity and inadequate accumulation challenges in clinical translation with photosensitizers (PSs).

Organelle-Specific Thiochromenocarbazole Imide Derivative as a Heavy-Atom-Free Type I Photosensitizer for Biomolecule-Triggered Image-Guided Photodynamic Therapy

Modern photodynamic therapy (PDT) demands next-generation photosensitizers (PSs) that overcome heavy-atom dependency and enhance efficacy beyond traditional, highly oxygen-dependent type II mechanisms. We introduce herein TCI-NH, as a thiochromenocarbazole imide derivative designed for type I photodynamic action. Upon light activation, TCI-NH efficiently favors superoxide (O2•-) and PS-centered radical formation instead of singlet oxygen (1O2) generation. Its high luminescence efficiency and selective localization in both the endoplasmic reticulum and mitochondria enable precise, image-guided PDT. Notably, interactions with biomolecules, such as serum albumin or DNA, enhance TCI-NH's emission by up to 40-fold and amplify radical generation by up to 5-fold. With negligible dark toxicity, this results in ∼120 nM photocytotoxicity along with an impressive phototherapeutic index exceeding 200. Real-time live-cell imaging revealed rapid, light-triggered cytotoxicity characterized by apoptotic body formation and extensive cellular damage. With its small size, heavy-atom-free structure, exceptional, organelle specificity, and therapeutic efficacy, TCI-NH sets a new benchmark for anticancer type I PDT.

Heterodimeric Photosensitizer as Radical Generators to Promoting Type I Photodynamic Conversion for Hypoxic Tumor Therapy

Photodynamic therapy (PDT) using traditional type II photosensitizers (PSs) has been limited in hypoxic tumors due to excessive oxygen consumption. The conversion from type II into a less oxygen-dependent type I PDT pathway has shown the potential to combat hypoxic tumors. Herein, the design of a heterodimeric PS, NBSSe, by conjugating a widely used type I PS NBS and a type II PS NBSe via molecular dimerization, achieving the aggregation-regulated efficient type I photodynamic conversion for the first time is reported. Electrochemistry characterizations and theoretical calculations elucidate that NBSSe tends to form a S+·/Se-· radical pair via intramolecular electron transfer in the co-excited NBSSe* aggregate, realizing 7.25-fold O2 -· generation compared to NBS and 80% suppression of 1O2 generation compared to NBSe. The enhanced O2 -· generation of NBSSe enables excellent anti-hypoxia PDT efficiency and inhibition of pulmonary metastasis. Additionally, the incorporation of electron-rich bovine serum albumin accelerates the recycling of cationic PS radical NBSSe+·, further boosting photostability and O2 -· generation. The resultant BSA@NBSSe nanoparticles demonstrate successful tumor-targeting PDT capability. This work provides an appealing avenue to convert ROS generation from the type II pathway to the type I pathway for efficient cancer phototherapy in hypoxia.

Fluorescence probe for the fast and sensitive detection and imaging of ONOO-via regulation of charge distribution

A rapid, sensitive and selective ONOO- probe L-C-CH3-Cy5 was developed using a cyanine dye bearing a meso-quinolinium group. The quinolinium group plays a pivotal role in the performance, as it modulates the signal-to-noise ratio and the reactivity of L-C-CH3-Cy5 towards ONOO-, thereby substantially improving both sensitivity and selectivity.

Recent Advances in Strategies to Enhance Photodynamic and Photothermal Therapy Performance of Single-Component Organic Phototherapeutic Agents

Photodynamic therapy (PDT) and photothermal therapy (PTT) have emerged as promising treatment options, showcasing immense potential in addressing both oncologic and nononcologic diseases. Single-component organic phototherapeutic agents (SCOPAs) offer advantages compared to inorganic or multicomponent nanomedicine, including better biosafety, lower toxicity, simpler synthesis, and enhanced reproducibility. Nonetheless, how to further improve the therapeutic effectiveness of SCOPAs remains a challenging research area. This review delves deeply into strategies to improve the performance of PDT or PTT by optimizing the structural design of SCOPAs. These strategies encompass augmenting reactive oxygen species (ROS) generation, mitigating oxygen dependence, elevating light absorption capacity, broadening the absorption region, and enhancing the photothermal conversion efficiency (PCE). Additionally, this review also underscores the ideal strategies for developing SCOPAs with balanced PDT and PTT. Furthermore, the potential synergies are highlighted between PDT and PTT with other treatment modalities such as ferroptosis, gas therapy, chemotherapy, and immunotherapy. By providing a comprehensive analysis of these strategies, this review aspires to serve as a valuable resource for clinicians and researchers, facilitating the wider application and advancement of SCOPAs-mediated PDT and PTT.

Aggregation control of anionic pentamethine cyanine enabling excitation wavelength selective NIR-II fluorescence imaging-guided photodynamic therapy

Near-infrared (NIR)-II fluorescence imaging-guided photodynamic therapy (PDT) has shown great potential for precise diagnosis and treatment of tumors in deep tissues; however, its performance is severely limited by the undesired aggregation of photosensitizers and the competitive relationship between fluorescence emission and reactive oxygen species (ROS) generation. Herein, we report an example of an anionic pentamethine cyanine (C5T) photosensitizer for high-performance NIR-II fluorescence imaging-guided PDT. Through the counterion engineering approach, a triphenylphosphine cation (Pco) modified with oligoethylene glycol chain is synthesized and adopted as the counterion of C5T, which can effectively suppress the excessive and disordered aggregation of the resulting C5T-Pco by optimizing the dye amphipathicity and enhancing the cyanine-counterion interactions. Dynamic tuning of fluorescence characteristics and ROS generation is achieved at the aggregate level, resulting in an impressive type I ROS generation under 760 nm light irradiation, accompanied by efficient NIR-II fluorescence emission excited at 808 nm. As a result, excitation wavelength selective NIR-II fluorescence imaging-guided PDT has been successfully demonstrated for tumor diagnosis and therapeutics of female mice.

Alleviating hypoxia by integrating MnO2 with metal-organic frameworks coated upconversion nanocomposites for enhanced photodynamic therapy in vitro

Photodynamic therapy (PDT) requires the participation of abundant oxygen while the hypoxic tumor microenvironment limits the efficacy of PDT. Here, upconversion luminescent nanocomposites coated with metal-organic frameworks (MOFs) were synthesized and modified with MnO2 (named UMMnP) to alleviate hypoxia of the tumor microenvironment. Under 980 nm light irradiation, the upconversion nanoparticles (UCNPs) achieve upconversion emission to excite porphyrin MOFs, which then transfer energy to oxygen to produce singlet oxygen for PDT. At the same time, the MnO2 in the UMMnP nanocomposites can catalyze the generation of O2 from H2O2, which could increase singlet oxygen production in a hypoxic environment, thus enhancing the PDT effect. The HeLa cell viability assay shows that the UMMnP nanocomposites possess good biocompatibility, while after irradiation with 980 nm light, the cell viability decreases dramatically, demonstrating efficient PDT. Furthermore, the nanocomposites can be successfully applied for upconversion luminescence imaging in vitro. Thus, this work provides a promising application of bioimaging and enhanced photodynamic therapy by alleviating hypoxia in tumor treatment.

Design strategies and applications of cyanine dyes in phototherapy

Cyanine dyes have been widely used in phototherapy in recent years due to their excellent optical properties and diverse modifiable structures. This review provides detailed descriptions of the basic structures of various cyanines and their derivatives as well as their optical properties. It summarizes the strategies for constructing cyanine dyes for phototherapy and discusses their structure-effect relationship. Furthermore, a comprehensive classification and summary of the applications of cyanine dyes in phototherapy are presented. Importantly, this review also addresses both the advances made in this field as well as the challenges that need to be overcome. We hope that these profound insights into phototherapy using cyanine dyes will facilitate the design of future systems for clinical applications based on these compounds.

Divergent Syntheses of Near-Infrared Light-Activated Molecular Jackhammers for Cancer Cell Eradication

Aminocyanines incorporating Cy7 and Cy7.5 moieties function as molecular jackhammers (MJH) through vibronic-driven action (VDA). This mechanism, which couples molecular vibrational and electronic modes, results in picosecond-scale concerted stretching of the entire molecule. When cell-associated and activated by near-infrared light, MJH mechanically disrupts cell membranes, causing rapid necrotic cell death. Unlike photodynamic and photothermal therapies, the ultrafast vibrational action of MJH is unhindered by high concentrations of reactive oxygen species scavengers and induces only a minimal temperature increase. Here, the efficient synthesis of a library of MJH is described using a practical approach to access a key intermediate and facilitating the preparation of various Cy7 and Cy7.5 MJH with diverse side chains in moderate to high yields. Photophysical characterization reveals that structural modifications significantly affect molar extinction coefficients and quantum yields while maintaining desirable absorption and emission wavelengths. The most promising compounds, featuring dimethylaminoethyl and dimethylcarbamoyl substitutions, demonstrate up to sevenfold improvement in phototherapeutic index compared to Cy7.5 amine across multiple cancer cell lines. This synthetic strategy provides a valuable platform for developing potent, light-activated therapeutic agents for cancer treatment, with potentially broad applicability across various cancer types.

Devising Biocompatible, NIR-Activated Helical Pyroptosis Agents via 𝛑-Twisting Strategy for Promoting Antitumor Immunity

Specifically controlling cell pyroptosis is advantageous for oncotherapy as it allows simultaneous ablation of primary tumors and activation of immunogenicity of tumor environment. Herein, a facile and robust strategy is presented to construct efficient NIR-activated helical pyroptosis agents (PyroAs) with negligible dark cytotoxicity. It is demonstrated that the construction of four intramolecular B-X bonds (X = O or N) within the BODIPY chromophore enforces a significant twisting of its π-conjugation, yielding a variety of helical HBD molecules with desired high photosensitivity and negligible dark toxicity. A robust approach is established to extend HBD into the near-infrared (NIR) region through site-selective incorporation of an electron-withdrawing ester moiety. It is also proved that targeted delivery of the NIR-activated HBD-ER to the endoplasmic reticulum (ER) specifically activates pyroptosis pathway by equipping it with an ER-targeting moiety. Finally, the favorable biocompatibility, excellent antitumor efficacy, and remarkable systematic immune response of this unique NIR-activated helical PyroAs are shown in vivo, demonstrating its potential application in solid tumor immunotherapy.

Near-Infrared Heptamethine Cyanine Photosensitizers with Efficient Singlet Oxygen Generation for Anticancer Photodynamic Therapy

Near-infrared photosensitizers are valuable tools to improve treatment depth in photodynamic therapy (PDT). However, their low singlet oxygen (1O2) generation ability, indicated by low 1O2 quantum yield, presents a formidable challenge for PDT. To overcome this challenge, the heptamethine cyanine was decorated with biocompatible S (Scy7) and Se (Secy7) atom. We observe that Secy7 exhibits a redshift in the main absorption to ~840 nm and an ultra-efficient 1O2 generation capacity. The emergence of a strong intramolecular charge transfer effect between the Se atom and polymethine chain considerably narrows the energy gap (0.51 eV), and the heavy atom effect of Se strengthens spin-orbit coupling (1.44 cm-1), both of which greatly improved the high triplet state yield (61 %), a state that determines the energy transfer to O2. Therefore, Secy7 demonstrated excellent 1O2 generation capacity, which is ~24.5-fold that of indocyanine green, ~8.2-fold that of IR780, and ~1.3-fold that of methylene blue under low-power-density 850 nm irradiation (5 mW cm-2). Secy7 exhibits considerable phototoxicity toward cancer cells buried under 12 mm of tissue. Nanoparticles formed by encapsulating Secy7 within amphiphilic polymers and lecithin, demonstrated promising antitumor and anti-pulmonary metastatic effects, exhibiting remarkable potential for advancing PDT in deep tissues.

Counterion Exchange Enhances the Brightness and Photostability of a Fluorous Cyanine Dye

Fluorofluorophores are a unique class of fluorophores that can be solubilized in perfluorocarbons (PFCs) and used to study biological systems. However, because of the low dielectric constant and high oxygen solubility in the fluorous phase, the brightness and photostability of the fluorofluorophores are significantly diminished. Here, we leveraged the tight ion pairing in the fluorous phase to improve the photophysical properties of a fluorous soluble pentamethine dye (FCy5) via counterion exchange. We found that larger, softer, fluorinated, aryl borate counterions promote the ideal polymethine state where charge delocalization across the polymethine chain increases the brightness (6-fold) and photostability (55-fold) of FCy5.

Harnessing Dual Phototherapy and Immune Activation for Cancer Treatment: The Development and Application of BODIPY@F127 Nanoparticles

Conventional phototherapeutic agents are typically used in either photodynamic therapy (PDT) or photothermal therapy (PTT). However, efficacy is often hindered by hypoxia and elevated levels of heat shock proteins in the tumor microenvironment (TME). To address these limitations, a formylated, near-infrared (NIR)-absorbing and heavy-atom-free Aza-BODIPY dye is presented that exhibits both type-I and type-II PDT actions with a high yield of reactive oxygen species (ROS) and manifests efficient photothermal conversion by precise adjustments to the conjugate structure and electron distribution, leading to a large amount of ROS production even under severe hypoxia. To improve biosafety and water solubility, the dye with an amphiphilic triblock copolymer (Pluronic F-127), yielding BDP-6@F127 nanoparticles (NPs) is coated. Furthermore, inspired by the fact that phototherapy triggers the release of tumor-associated antigens, a strategy that leverages potential immune activation by combining PDT/PTT with immune checkpoint blockade (ICB) therapy to amplify the systemic immune response and achieve the much-desired abscopal effect is developed. In conclusion, this study presents a promising molecular design strategy that integrates multimodal therapeutics for a precise and effective approach to cancer therapy.

TADF-Guiding Modification of Endoplasmic Reticulum-Targeted Photosensitizers for Efficient Photodynamic Immunotherapy

Pharmacological activation of the immunogenic cell death (ICD) pathway by endoplasmic reticulum (ER) targeted photosensitizer (PS) has become a promising strategy for tumor immunotherapy. Despite a clear demand for ER-targeted PS, the sluggish intersystem crossing (ISC) process, unstable excited state, insufficient ROS production, and immunosuppressive tumor microenvironment (ITME) combined to cause the high-efficiency agents are still limited. Herein, three groups commonly used in thermally activated delayed fluorescence (TADF) molecular design are used to modify the excited state characteristics of xanthene-based cyanine PS (obtained the XCy-based PS). The electronic and geometric modulation effectively optimize the excited state characteristics, facilitating the ISC process and prolonging the excited state life for boosting ROS generation. Among them, car-XCy showed 100 times longer excited state life and 225% higher ROS yield than that of original XCy. The satisfactory ROS production and ER-targeted ability of car-XCy arouse intense ER stress to activate the ICD. Adequate antigen presentation promotes the dendritic cell maturation and infiltration of cytotoxic T lymphocytes (CTLs), ultimately reversing the ITME to realize efficient immunotherapy. As a result, significant inhibition is observed in both primary and distant tumors, underscoring the efficacy of this TADF-guiding excited state characteristics modulation strategy for developing photodynamic immunotherapy drugs.

Dissecting Exciton Dynamics in pH-Activatable Long-Wavelength Photosensitizers for Traceable Photodynamic Therapy

Tumor-specific activatable long-wavelength (LW) photosensitizers (PSs) show promise in overcoming the limitations of traditional photodynamic therapy (PDT), such as systemic phototoxicity and shallow tissue penetration. However, their insufficient LW light absorption and low singlet oxygen quantum yield (Φ 1O2) usually require high laser power density to produce thermal energy and synergistically enhance PDT. The strong photothermal radiation causing acute pain significantly reduces patient compliance and hinders the broader clinical application of LW PDT. Through the exciton dynamics dissection strategy, we have developed a series of pH-activatable cyanine-based LW PSs (LET-R, R = H, Cl, Br, I), among which the activated LET-I exhibits strong light absorption at 808 nm and a remarkable 3.2-fold enhancement in Φ 1O2 compared to indocyanine green. Transient spectroscopic analysis and theoretical calculations confirmed its significantly promoted intersystem crossing and simultaneously enhanced LW fluorescence emission characteristics. These features enable the activatable fluorescence and photoacoustic dual-modal imaging-escorted complete photodynamic eradication of tumors by the folic acid (FA)-modified LET-I probe (LET-I-FA), under the ultralow 808 nm laser power density (0.2 W cm-2) for irradiation, without the need for photothermal energy synergy. This research presents a novel strategy of dissecting exciton dynamics to screen activatable LW PSs for traceable PDT.

Reversible pH-switchable NIR-II nano-photosensitizer for precise imaging and photodynamic therapy of tumors

Photodynamic therapy (PDT) has attracted widespread attention from researchers as an emerging cancer treatment method. There have been many reports on various types of NIR-II photosensitizers for imaging and treatment of tumor sites. However, there are few reports on the development of NIR-II organic small molecule photosensitizers that have intelligent response to the tumor microenvironment, precise imaging, real-time treatment, and high biocompatibility. In this work, we developed a series of NIR-II photosensitizers (RBTs) with near-infrared excitation, good photostability, and large Stokes shift. Among them, RBT-Br exhibited higher reactive oxygen species (ROS) generation efficiency due to the introduction of halogen heavy atoms to enhance intersystem crossing (ISC). It is noteworthy that RBT-Br can generate singlet oxygen (1O2) and superoxide anion radicals (•O2-) simultaneously under 730 nm laser. Subsequently, we used molecular engineering technology to construct three pH-responsive NIR-II photosensitizers (RBT-pHs) by utilizing the closure of the lactam ring, among which RBT-pH-1 (pKa = 6.78) is able to be directionally activated under the stimulation of tumor micro-acid environment, with its fluorescence emission window reaching 933 nm. Subsequently, RBT-pH-1 NPs encapsulated in DSPE-mPEG5k were applied for PDT treatment of mouse tumors. The results showed that RBT-pH-1 NPs were activated by the acidic tumor microenvironment and generated ROS under laser excitation, exhibiting precise tumor imaging and significant tumor growth inhibition. We look forward to these multifunctional NIR-II organic small molecule photosensitizers providing a more efficient approach for clinical treatment of tumors. STATEMENT OF SIGNIFICANCE: A reversible pH-switchable NIR-II nano-photosensitizer RBT-pH-1 NPs (pKa = 6.76) is developed for precise imaging and PDT therapy of mouse tumors, which can be effectively used for targeted enrichment and activation of tumor micro-acid environments. The results show that this NIR-II photosensitizer generates ROS through tumor micro-acid environment stimulation and laser triggering, showing precise tumor imaging guidance and significant tumor growth inhibition.

Red-Light Triggered H-Abstraction Photoinitiators for the Efficient Oxygen-Independent Therapy of Hypoxic Tumors

The clinical application of photodynamic therapy (PDT) is limited by oxygen-dependence and side effects caused by photosensitizer residues. Photoinitiators based on the H-abstraction reaction can address these challenges because they can generate alkyl radical-killing cells independently of oxygen and undergo rapid bleaching following H-abstraction. Nonetheless, the development of photoinitiators for PDT has been impeded by the absence of effective design strategies. Herein, we have developed aryl-ketone substituted cyanine (ACy-R), the first red-light triggered H-abstraction photoinitiators for hypoxic cancer therapy. These ACy-R molecules inherited the near-infrared absorption of cyanine dye, and aryl-ketone modification imparted H-abstraction capability. Experimental and quantum calculations revealed that modifying the electron-withdrawing groups of the aryl (e.g., ACy-5F) improved the contribution of the O atom to the photon excitation process promoting intersystem crossing and H-abstraction ability. Particularly, ACy-5F rapidly penetrated cells and enriched in the endoplasmic reticulum. Even under severe hypoxia, ACy-5F initiated red-light induced H-abstraction with intracellular biomolecules, inducing necroptosis and ferroptosis. Moreover, ACy-5F was degraded after H-abstraction, thus avoiding the side effects of long-term phototoxicity after therapy. This study not only provides a crucial molecular tool for hypoxic tumors therapy, but also presents a promising strategy for the development of multifunctional photosensitizers and photoinitiators.

Exploring the triplet state properties of thio-benzothioxanthene imides with applications in TTA-upconversion and photopolymerization

Thio-benzothioxanthene imide (BTXI) exhibits long excited state lifetime (τT = 17.7 μs) and high ISC efficiency (ΦΔ = 97%). For the first time, BTXI derivatives were used as photosensitizers for triplet-triplet annihilation upconversion, achieving the highest efficiency of 13.8%. In addition, thio-BTXI derivatives were used as photoinitiators for photopolymerization, resulting in a series of green light-activated radical polymerization systems.

Deep near infrared light-excited stable synergistic photodynamic and photothermal therapies based on P-IR890 nano-photosensitizer constructed via a non-cyanine dye

The cyanine dyes represented by IR780 can achieve synergistic photodynamic therapy (PDT) and photothermal therapy (PTT) under the stimulation of near-infrared (NIR) light (commonly 808 nm). Unfortunately, the stability of NIR-excited cyanine dyes is not satisfactory. These cyanine dyes can be attacked by self-generated reactive oxygen species (ROS) during PDT processes, resulting in structural damage and rapid degradation, which is fatal for phototherapy. To address this issue, a novel non-cyanine dye (IR890) was elaborately designed and synthesized by our team. The maximum absorption wavelength of IR890 was located in the deep NIR region (ca. 890 nm), which was beneficial for further improving tissue penetration depth. Importantly, IR890 exhibited good stability when continuously illuminated by deep NIR light. To improve the hydrophilicity and biocompatibility, the hydrophobic IR890 dye was grafted onto the side chain of hydrophilic polymer (POEGMA-b-PGMA-g-C[bond, triple bond]CH) via click chemistry. Then, the synthesized POEGMA-b-PGMA-g-IR890 amphiphilic polymer was utilized to prepare P-IR890 nano-photosensitizer via self-assembly method. Under irradiation with deep NIR light (850 nm, 0.5 W/cm2, 10 min), the dye degradation rate of P-IR890 was less than 5%. However, IR780 was almost completely degraded with the same light output power density and irradiation duration. In addition, P-IR890 could stably generate a large number of ROS and heat at the same time. It was rarely reported that the stable synergistic combination therapy of PDT and PTT could be efficiently performed by a single photosensitizer via irradiation with deep NIR light. P-IR890 exhibited favorable anti-tumor outcomes through apoptosis pathway. Therefore, the P-IR890 could provide a new insight into the design of photosensitizers and new opportunities for synergistic combination therapy of PDT and PTT.

Regulating Charge Transfer in Cyanine Dyes: A Universal Methodology for Enhancing Cancer Phototherapeutic Efficacy

Due to the advantages of spatiotemporal selectivity and inherent noninvasiveness, cancer phototherapy, which includes both photodynamic therapy (PDT) and photothermal therapy (PTT), has garnered significant attention in recent years as a promising cancer treatment. Despite the commendable progress in this field, persistent challenges remain. In PDT, limitations in dyes manifest as low intersystem crossing (ISC) efficiency and oxygen-dependent photoactivity, resulting in unsatisfactory performance, particularly under hypoxic conditions. Similarly, PTT encounters consistent insufficiencies in the photothermal conversion efficiency (PCE) of dyes. Additionally, the suboptimal phototherapeutic efficacy often exhibits a limited immune response. These factors collectively impose significant constraints on phototherapy in oncological applications, leading to limited tumor inhibition, tumor recurrence, and even metastasis. Unlike strategies that rely on external assistance with complicated systems, manipulating excited-state deactivation pathways in biocompatible dyes offers a universal way to systematically address these challenges. Our group has devoted considerable effort to achieving this goal. In this Account, we present and discuss our journey in optimizing excited-state energy-release pathways through regulating molecular charge transfer based on cyanine dyes, which are renowned for their exceptional photophysical properties and harmonious biocompatibility. The investigation begins with the introduction of amino groups in the meso position of a heptamethine cyanine dye, where the intramolecular charge transfer (ICT) effect causes a significant enlargement of the Stokes shift. Subsequently, ICT induced by introducing functional electron-deficient groups in cyanines is found to decrease the overlap of electron distribution or narrow the energy gaps of molecular frontier orbitals. Such modifications result in a reduction of the energy gaps between singlet and triplet states or an improvement in internal conversion, ultimately promoting phototherapy efficacy in both primary and distant tumors. Furthermore, with the intensification of the charge transfer effect aided by light, photoinduced intramolecular electron transfer occurs in some cyanines, leading to complete charge separation in the excited state. This process enhances the transition to the ground or triplet states, improving tumor phototherapy and inhibiting metastasis by increasing the PCE or the yield of reactive oxygen species, respectively. Shifting focus from intramolecular to intermolecular interactions, we successfully constructed and explored cyanines based on intermolecular charge transfer. These dyes, with excited-state dynamics mimicking natural photosynthesis, generate radicals and facilitate oxygen-independent hypoxic tumor PDT. Finally, we outlined the existing challenges and future directions for optimizing phototherapeutic efficacy by regulating molecular charge transfer. This Account provides molecular-level insights into improving phototherapeutic performance, offering valuable perspectives, and inspiring the development of functional dyes in other application fields.

Heavy-atom-free π-twisted photosensitizers for fluorescence bioimaging and photodynamic therapy

As the field of preclinical research on photosensitizers (PSs) for anticancer photodynamic therapy (PDT) continues to expand, a focused effort is underway to develop agents with innovative molecular structures that offer enhanced targeting, selectivity, activation, and imaging capabilities. In this context, we introduce two new heavy-atom-free PSs, DBXI and DBAI, characterized by a twisted π-conjugation framework. This innovative approach enhances the spin-orbit coupling (SOC) between the singlet excited state (S1) and the triplet state (T1), resulting in improved and efficient intersystem crossing (ISC). Both PSs are highly effective in producing reactive oxygen species (ROS), including singlet oxygen and/or superoxide species. Additionally, they also demonstrate remarkably strong fluorescence emission. Indeed, in addition to providing exceptional photocytotoxicity, this emissive feature, generally lacking in other reported structures, allows for the precise monitoring of the PSs' distribution within specific cellular organelles even at nanomolar concentrations. These findings underscore the dual functionality of these PSs, serving as both fluorescent imaging probes and light-activated therapeutic agents, emphasizing their potential as versatile and multifunctional tools in the field of PDT.

A de novo zwitterionic strategy of ultra-stable chemiluminescent probes: highly selective sensing of singlet oxygen in FDA-approved phototherapy

Singlet oxygen (1O2), as a fundamental hallmark in photodynamic therapy (PDT), enables ground-breaking clinical treatment in ablating tumors and killing germs. However, accurate in vivo monitoring of 1O2 remains a significant challenge in probe design, with primary difficulties arising from inherent photo-induced side reactions with poor selectivity. Herein, we report a generalizable zwitterionic strategy for ultra-stable near-infrared (NIR) chemiluminescent probes that ensure a highly specific [2 + 2] cycloaddition between fragile electron-rich enolether units and 1O2 in both cellular and dynamic in vivo domains. Innovatively, zwitterionic chemiluminescence (CL) probes undergo a conversion into an inert ketone excited state with an extremely short lifetime through conical intersection (CI), thereby affording sufficient photostability and suppressing undesired photoreactions. Remarkably, compared with the well-known commercial 1O2 probe SOSG, the zwitterionic probe QMI exhibited an ultra-high signal-to-noise ratio (SNR, over 40-fold). Of particular significance is that the zwitterionic CL probes demonstrate excellent selectivity, high sensitivity, and outstanding photostability, thereby making a breakthrough in real-time tracking of the FDA-approved 5-ALA-mediated in vivo PDT process in living mice. This innovative zwitterionic strategy paves a new pathway for high-performance NIR chemiluminescent probes and high-fidelity feedback on 1O2 for future biological and medical applications.

Quasi-intrinsic thiobase derivatives as potential targeted photosensitizers in two-photon photodynamic therapy

In this study, a set of potential quasi-intrinsic photosensitizers for two-photon photodynamic therapy (PDT) are proposed based on the unnatural 2-amino-8-(1'-β-ᴅ-2'-deoxyribofuranosyl)-imidazo[1,2-ɑ]-1,3,5-triazin-4(8H)-one (P), which is paired with the 6-amino-5-nitro-3-(1'-β-ᴅ-2'-deoxyribofuranosyl)-2(1H)-pyridone (Z) and can specifically recognize breast and liver cancer cells. Herein, the effects of sulfur substitution and electron-donating/electron-withdrawing groups on the photophysical properties in aqueous solution are systematically investigated. The one- and two-photon absorption spectra evidence that the modifications could result in red-shifted absorption wavelength and large two-photon absorption cross-section, which contributes to selective excitation and provides effective PDT for deep-seated tissues. To ensure the efficient triplet state population, the singlet-triplet energy gaps and spin-orbit coupling constants were examined, which is responsible for a rapid intersystem crossing rate. Furthermore, these thiobase derivatives are characterized by the long-lived T1 state and the large energy gap for radiationless transition to ensure the generation of cytotoxic singlet oxygen.

Constructing Heavy-Atom-Free Photosensitizers for Hypoxic Tumor Phototherapy Based on Donor-Excited Photoinduced Electron-Transfer-Driven Type-I and Type-II Mechanisms

The spin-orbit charge transfer intersystem crossing (SOCT-ISC) photophysical process has shown great potential for constructing heavy-atom-free photosensitizers (PSs) for photodynamic therapy (PDT) of tumors. However, for almost all such PSs reported to date, the SOCT-ISC is driven by the acceptor-excited photoinduced electron transfer (a-PeT). In this work, for the first time the donor-excited photoinduced electron transfer (d-PeT)-driven SOCT-ISC mechanism is utilized to construct the heavy-atom-free PSs for PDT of tumors by directly installing the electron-deficient N-alkylquinolinium unit (as an electron acceptor) into the meso-position of the near-infrared (NIR) distyryl Bodipy chromophore (as an electron donor). In the less polar environment, the PSs exist as the monomer and promote the production of singlet oxygen (1O2) (Type-II) relying on the d-PeT-driven population of the triplet excited state via SOCT-ISC, whereas in the aqueous environment, they exist as nanoaggregates and induce the generation of superoxides (O2-•) and hydroxyl radicals (HO•) (Type-I) via the d-PeT-driven formation of the delocalized charge-separated state. The PSs could rapidly be internalized into cancer cells and induce the simultaneous production of intracellular 1O2, O2-•, and HO• upon NIR light irradiation, endowing the PSs with superb photocytotoxicity with IC50 values up to submicromolar levels whether under normoxia or under hypoxia. Based on the PSs platform, a tumor-targetable PS is developed, and its abilities in killing cancer cells and in ablating tumors without damage to normal cells/tissues under NIR light irradiation are verified in vitro and in vivo. The study expands the design scope of PSs by introducing the d-PeT conception, thus being highly valuable for achieving novel PSs in the realm of tumor PDT.

Activating Iterative Revolutions of the Cancer-Immunity Cycle in Hypoxic Tumors with a Smart Nano-Regulator

The activation of sequential events in the cancer-immunity cycle (CIC) is crucial for achieving effective antitumor immunity. However, formidable challenges, such as innate and adaptive immune resistance, along with the off-target adverse effects of nonselective immunomodulators, persist. In this study, a tumor-selective nano-regulator named PNBJQ has been presented, focusing on targeting two nonredundant immune nodes: inducing immunogenic cancer cell death and abrogating immune resistance to fully activate endogenous tumor immunity. PNBJQ is obtained by encapsulating the immunomodulating agent JQ1 within a self-assembling system formed by linking a Type-I photosensitizer to polyethylene glycol through a hypoxia-sensitive azo bond. Benefiting from the Type-I photosensitive mechanism, PNBJQ triggers the immunogenic cell death of hypoxic tumors under near-infrared (NIR) light irradiation. This process resolves innate immune resistance by stimulating sufficient cytotoxic T-lymphocytes. Simultaneously, PNBJQ smartly responds to the hypoxic tumor microenvironment for precise drug delivery, adeptly addressing adaptive immune resistance by using JQ1 to downregulate programmed death ligand 1 (PD-L1) and sustaining the response of cytotoxic T lymphocytes. The activatable synergic photoimmunotherapy promotes an immune-promoting tumor microenvironment by activating an iterative revolution of the CIC, which remarkably eradicates established hypoxic tumors and suppresses distal lesions under low light dose irradiation.

Expanded ROS Generation and Hypoxia Reversal: Excipient-free Self-assembled Nanotheranostics for Enhanced Cancer Photodynamic Immunotherapy

The efficacy of photodynamic therapy (PDT)-related cancer therapies is significantly restricted by two irreconcilable obstacles, i.e., low reactive oxygen species (ROS) generation capability and hypoxia which constrains the immune response. Herein, this work develops a self-assembled clinical photosensitizer indocyanine green (ICG) and the HSP90 inhibitor 17-dimethylaminoethylamino-17-demethoxygeldanamycin (17-DMAG) nanoparticles (ISDN) without any excipient. This work discovers that the hydrophobic interaction forces between ICG and 17-DMAG promote the photostability of ICG and its intersystem crossing (ISC) process, thereby improving the ROS quantum yield from 0.112 to 0.46. Augmented ROS generation enhances PDT efficacy and further enhances immunogenic cell death (ICD) effects. 17-DMAG inhibits the HSP90/hypoxia-inducible factor 1α (HIF-1α) axis to dramatically reverse the immunosuppressive tumor microenvironment caused by PDT-aggravated hypoxia. In a mouse model of pancreatic cancer, ISDN markedly improve cytotoxic T lymphocyte infiltration and MHC I and MHC II activation, demonstrating the superior ICD effects in situ tumor and the powerful systematic antitumor immunity generation, eventually achieving vigorous antitumor and recurrence resistance. This study proposes an unsophisticated and versatile strategy to significantly improve PDT efficacy for enhancing systemic antitumor immunity and potentially extending it to multiple cancers.

Newly Designed Quasi-intrinsic Photosensitizers for Fluorescence Image-Guided Two-Photon Photodynamic Therapy with Type I/II Photoreactions

In this work, a set of quasi-intrinsic photosensitizers are theoretically proposed based on the 2-amino-8-(1'-β-d-2'-deoxyribofuranosyl)-imidazo[1,2-α]-1,3,5-triazin-4(8H)-one (P), which could pair with the 6-amino-5-nitro-3-(1'-β-d-2'-deoxyribofuranosyl)-2(1H)-pyridone (Z) and keep the essential structural characters of nucleic acid. It is revealed that the ring expansion and electron-donating/electron-withdrawing substitution bring enhanced two-photon absorption and bright photoluminescence of these monomers, thereby facilitating the selective excitation and tumor localization through fluorescence imaging. However, instead of undergoing radiative transition (S1 → S0), the base pairing induced fluorescence quenching and rapid intersystem crossing (S1 → Tn) are observed and characterized by the reduced singlet-triplet energy gaps and large spin-orbit coupling values. To ensure the phototherapeutic properties of the considered base pairs in long-lived T1 state, we examined the vertical electron affinity as well as vertical ionization potential for production of superoxide anions via Type I photoreaction, and their required T1 energy (0.98 eV) to generate singlet oxygen 1O2 via Type II mechanism.

Near-infrared photocatalysis with cyanines: synthesis, applications and perspectives

Cyanines are organic dyes bearing two aza-heterocycles linked by a polymethine chain. Excited states, fluorescence, redox activity, and energy transfer are interesting properties of cyanines which have been used by chemists. Moreover, they are easily accessible and highly tunable. For all these reasons, cyanines are often selected for applications like fluorescent probes, phototherapy and photovoltaics. However, considering cyanines as photocatalysts is a new field of investigation and has been sparsely reported in the literature. This field of research has been launched on the basis of near-infrared light photocatalysis. With a deeper NIR light penetration, the irradiation is compatible with biological tissues. Due to the longer wavelengths that are involved, the safety of the operator can be guaranteed. In this perspective review, the photophysical/redox properties of cyanines are reported as well as their preparations and applications in modern synthetic approaches. Finally, recent examples of cyanine-based NIR-photocatalysis are discussed including photopolymerization and organic synthesis.

"Three Musketeers" Enhances Photodynamic Effects by Reducing Tumor Reactive Oxygen Species Resistance

Photodynamic therapy (PDT) based on upconversion nanoparticles (UCNPs) has been widely used in the treatment of a variety of tumors. Compared with other therapeutic methods, this treatment has the advantages of high efficiency, strong penetration, and controllable treatment range. PDT kills tumors by generating a large amount of reactive oxygen species (ROS), which causes oxidative stress in the tumor. However, this killing effect is significantly inhibited by the tumor's own resistance to ROS. This is because tumors can either deplete ROS by high concentration of glutathione (GSH) or stimulate autophagy to eliminate ROS-generated damage. Furthermore, the tumor can also consume ROS through the lactic acid metabolic pathway, ultimately hindering therapeutic progress. To address this conundrum, we developed a UCNP-based nanocomposite for enhanced PDT by reducing tumor ROS resistance. First, Ce6-doped SiO2 encapsulated UCNPs to ensure the efficient energy transfer between UCNPs and Ce6. Then, the biodegradable tetrasulfide bond-bridged mesoporous organosilicon (MON) was coated on the outer layer to load chloroquine (CQ) and α-cyano4-hydroxycinnamic acid (CHCA). Finally, hyaluronic acid was utilized to modify the nanomaterials to realize an active-targeting ability. The obtained final product was abbreviated as UCNPs@MON@CQ/CHCA@HA. Under 980 nm laser irradiation, upconverted red light from UCNPs excited Ce6 to produce a large amount of singlet oxygen (1O2), thus achieving efficient PDT. The loaded CQ and CHCA in MON achieved multichannel enhancement of PDT. Specifically, CQ blocked the autophagy process of tumor cells, and CHCA inhibited the uptake of lactic acid by tumor cells. In addition, the coated MON consumed a high level of intracellular GSH. In this way, these three functions complemented each other, just as the "three musketeers" punctured ROS resistance in tumors from multiple angles, and both in vitro and in vivo experiments had demonstrated the elevated PDT efficacy of nanomaterials.

Self-Adaptive Photodynamic-to-Photothermal Switch for Smart Antitumor Photoimmunotherapy

Photodynamic therapy (PDT) and photothermal therapy (PTT) possess different merits in cancer phototherapy, but the tumor microenvironment becomes unfavorable during the phototheranostic progress. Herein, we report a self-adaptive cyanine derivative Cy5-TPA with the PDT-dominated state to PTT-dominated state autoswitch feature for enhanced photoimmunotherapy. The incorporation of rotatable triphenylamine (TPA) moiety renders Cy5-TPA with the temperature or intramolecular-motion regulated photoactivities, which shows preferable reactive oxygen species (ROS) generation at lower temperature while stronger photothermal conversion at higher ones. Such a promising feature permits the in situ switch from PDT-dominated state to PTT-dominated state along with intratumoral temperature increase during laser irradiation, which also works in line with the concurrently reduced intratumoral oxygen level, exhibiting a self-adaptive phototherapeutic behavior to maximize the phototherapeutic antitumor outcome. Most importantly, the self-adaptive PDT-dominated state to PTT-dominated state switch also facilitates the sequential generation and release of damage-associated molecular patterns during immunogenic cell death (ICD). Hence, Cy5-TPA demonstrates excellent photoimmunotherapy performance in ICD induction, dendritic cell maturation, and T cell activation for tumor eradication and metastasis inhibition.

A smart cysteine-activated and heavy-atom-free nano-photosensitizer for photodynamic therapy to treat cancers

A smart and heavy-atom-free photoinactive nano-photosensitizer capable of being activated by cysteine at the tumor site to generate highly photoactive nano-photosensitizers that show strong NIR absorption and fluorescence with a good singlet oxygen quantum yield (16.8%) for photodynamic therapy is reported.

Cationized orthogonal triad as a photosensitizer with enhanced synergistic antimicrobial activity

Single-molecule-based synergistic phototherapy holds great potential for antimicrobial treatment. Herein, we report an orthogonal molecular cationization strategy to improve the reactive oxygen species (ROS) and hyperthermia generation of heptamethine cyanine (Cy7) for photodynamic and photothermal treatments of bacterial infections. Cationic pyridine (Py) is introduced at the meso‑position of the asymmetric Cy7 with intramolecular charge transfer (ICT) to construct an atypical electron-transfer triad, which reduces ΔES1-S0, circumvents rapid charge recombination, and simultaneously enhances intersystem crossing (ISC) based on spin-orbit charge-transfer ISC (SOCT-ISC) mechanism. This unique molecular construction produces anti-Stokes luminescence (ASL) because the rotatable CN bond enriched in high vibrational-rotational energy levels improves hot-band absorption (HBA) efficiency. The obtained triad exhibits higher singlet oxygen quantum yield and photothermal conversion efficiency compared to indocyanine green (ICG) under irradiation above 800 nm. Cationization with Py enables the triad to target bacteria via intense electrostatic attractions, as well as biocidal property against a broad spectrum of bacteria in the dark. Moreover, the triad under irradiation can enhance biofilm eradication performance in vitro and statistically improve healing efficacy of MRSA-infected wound in mice. Thus, this work provides a simple but effective strategy to design small-molecule photosensitizers for synergistic phototherapy of bacterial infections. STATEMENT OF SIGNIFICANCE: We developed an orthogonal molecular cationization strategy to enhance the reactive oxygen species and thermal effects of heptamethine cyanine (Cy7) for photodynamic and photothermal treatments of bacterial infections. Specifically, cationic pyridine (Py) was introduced at the meso‑position of the asymmetric Cy7 to construct an atypical electron-transfer triad, which reduced ΔES1-S0, circumvented rapid charge recombination, and simultaneously enhanced intersystem crossing (ISC). This triad, with a rotatable CN bond, produced anti-Stokes luminescence due to hot-band absorption. The triad enhanced antimicrobial performance and statistically improved the healing efficacy of MRSA-infected wounds in mice. This site-specific cationization strategy may provide insights into the design of small molecule-based photosensitizers for synergistic phototherapy of bacterial infections.

A Silicon-Rhodamine-Based Heavy-Atom-Free Photosensitizer for Mitochondria-targeted Photodynamic Therapy

Silicon-xanthene derivatives (SiXs) have gained popularity in the field of bioimaging due to their advantageous far-red to near-infrared (NIR) absorption and emission wavelengths, notable brightness (ε × Φ), inherent mitochondrial targeting properties and high photo-stability, making them an excellent candidate for photodynamic therapy (PDT). Nevertheless, the utilization of SiXs as photosensitizers (PSs) for PDT in cancer treatment remains largely unexplored, primarily due to their limited capacity to generate cytotoxic reactive oxygen species (ROS). However, the potential of SiXs in PDT warrants further investigation. In this study, utilizing the spin-orbit charge transfer-induced intersystem crossing (SOCT-ISC) mechanism, we reported one novel heavy-atom-free, mitochondria-targeted, silicon-rhodamine-based photosensitizer (SiR-PXZ), which demonstrated excellent biocompatibility, minimal dark toxicity, favorable water-solubility and stability, and considerable singlet oxygen quantum yield under 660 nm light irradiation (ΦΔ = 0.16 in air-saturated PBS). Moreover, SiR-PXZ could be rapidly taken up by the mitochondria and efficiently induced apoptosis of cancer cells with an IC50 value of 1.2 μM. The in vivo studies showed that SiR-PXZ exhibited excellent anti-tumor effects, making it potentially valuable for clinical application. This study offers a source of ideas for the construction of SiXs-based photosensitizers for photodynamic cancer treatment in the future.

Leveraging Radiation-triggered Metal Prodrug Activation Through Nanosurface Energy Transfer for Directed Radio-chemo-immunotherapy

Metal-based drugs currently dominate the field of chemotherapeutic agents; however, achieving the controlled activation of metal prodrugs remains a substantial challenge. Here, we propose a universal strategy for the radiation-triggered activation of metal prodrugs via nanosurface energy transfer (NSET). The core-shell nanoplatform (Ru-GNC) is composed of gold nanoclusters (GNC) and ruthenium (Ru)-containing organic-inorganic hybrid coatings. Upon X-ray irradiation, chemotherapeutic Ru (II) complexes were released in a controlled manner through a unique NSET process involving the transfer of photoelectron energy from the radiation-excited Ru-GNCs to the Ru-containing hybrid layer. In contrast to the traditional radiation-triggered activation of prodrugs, such an NSET-based system ensures that the reactive species in the tumor microenvironment are present in sufficient quantity and are not easily quenched. Additionally, ultrasmall Ru-GNCs preferably target mitochondria and profoundly disrupt the respiratory chain upon irradiation, leading to radiosensitization by generating abundant reactive oxygen species. Consequently, Ru-GNC-directed radiochemotherapy induces immunogenic cell death, resulting in significant therapeutic outcomes when combined with the programmed cell death-ligand 1 (PD-L1) checkpoint blockade. This NSET strategy represents a breakthrough in designing radiation-triggered nanoplatforms for metal-prodrug-mediated cancer treatment in an efficient and controllable manner.

Enhancing near-infrared II photodynamic therapy with nitric oxide for eradicating multidrug-resistant biofilms in deep tissues

Nitric oxide (NO) enhanced photodynamic therapy (PDT) is a promising approach to overcome drug tolerance and resistance to biofilm but is limited by its short excitation wavelengths and low yield of reactive oxygen species (ROS). Herein, we develop a compelling degradable polymer-based near-infrared II (NIR-II, 1000-1700 nm) photosensitizer (PNIR-II), which can maintain 50 % PDT efficacy even under a 2.6 cm tissue barrier. Remarkably, PNIR-II is synthesized by alternately connecting the electron donor thiophene to the electron acceptors diketopyrrolopyrrole (DPP) and boron dipyrromethene (BODIPY), where the intramolecular charge transfer properties can be tuned to increase the intersystem crossover rate and decrease the internal conversion rate, thereby stabilizing the NIR-II photodynamic rather than photothermal effect. For exerting a combination therapy to eradicate multidrug-resistant biofilms, PNIR-II is further assembled into nanoparticles (NPs) with a synthetic glutathione-triggered NO donor polymer. Under 1064 nm laser radiation, NPs precisely release ROS and NO that triggered by over-expressed GSH in the biofilm microenvironment, thereby forming more bactericidal reactive nitrogen species (RNS) in vitro and in vivo in the mice model that orderly destroy biofilm of multidrug-resistant Staphylococcus aureus cultures from clinical patients. It thus provides a new outlook for destroy the biofilm of deep tissues.

Photoinduced Cuproptosis with Tumor-Specific for Metastasis-Inhibited Cancer Therapy

Cuproptosis is a novel form of regulated cell death which guarantees to increase the efficacy of existing anticancer treatments that employ traditional apoptotic therapeutics. However, reducing the amount of undesirable Cu ions released in normal tissue and maximizing Cu-induced cuproptosis therapeutic effects at tumor sites are the major challenges. In this study, exploiting the chemical properties of copper ionophores and the tumor microenvironment, a novel method is developed for controlling the valence of copper ions that cause photoinduced cuproptosis in tumor cells. CJS-Cu nanoparticles (NPs) can selectively induce cuproptosis after cascade reactions through H2 O2 -triggered Cu2+ release, photoirradiation-induced superoxide radical (∙O2 - ) generation, and reduction of Cu2+ to Cu+ by ∙O2 - . The generated reactive oxygen species can result in glutathione depletion and iron-sulfur cluster protein damage and further augmented cuproptosis. CJS-Cu NPs effectively suppressed tumor growth and downregulated the expression of metastasis-related proteins, contributing to the complete inhibition of lung metastasis. Ultimately, this study suggests novel avenues for the manipulation of cellular cuproptosis through photochemical reactions.

Accidental triplet harvesting in donor-acceptor dyads with low spin-orbit coupling

We present an accidental mechanism for efficient intersystem crossing (ISC) between singlet and triplet states with low spin-orbit coupling (SOC) in molecules having donor-acceptor (D-A) moieties separated by a Sigma bond. Our study shows that SOC between the lowest singlet excited state and the higher-lying triplet states, together with nuclear motion-driven coupling of this triplet state with lower-lying triplet states during the free rotation about a Sigma bond, is one of the possible ways to achieve the experimentally observed ISC rate for a class of D-A type photoredox catalysts. This mechanism is found to be the dominant contributor to the ISC process with the corresponding rate reaching a maximum at a dihedral angle in the range of 72°-78° between the D-A moieties of 10-(naphthalen-1-yl)-3,7-diphenyl-10H-phenoxazine and other molecules included in the study. We have further demonstrated that the same mechanism is operative in a specific spirobis[anthracene]dione molecule, where the D and A moieties are interlocked near to the optimal dihedral angle, indicating the plausible effectiveness of the proposed mechanism. The present finding is expected to have implications in strategies for the synthesis of new generations of triplet-harvesting organic molecules.

Aryl-Modified Pentamethyl Cyanine Dyes at the C2' Position: A Tunable Platform for Activatable Photosensitizers

Pentamethyl cyanine dyes are promising fluorophores for fluorescence sensing and imaging. However, advanced biomedical applications require enhanced control of their excited-state properties. Herein, a synthetic approach for attaching aryl substituents at the C2' position of the thio-pentamethine cyanine (TCy5) dye structure is reported for the first time. C2'-aryl substitution enables the regulation of both the twisted intramolecular charge transfer (TICT) and photoinduced electron transfer (PET) mechanisms to be regulated in the excited state. Modulation of these mechanisms allows the design of a nitroreductase-activatable TCy5 fluorophore for hypoxic tumor photodynamic therapy and fluorescence imaging. These C2'-aryl TCy5 dyes provide a tunable platform for engineering cyanine dyes tailored to sophisticated biological applications, such as photodynamic therapy.

Molecularly Engineered Room-Temperature Phosphorescence for Biomedical Application: From the Visible toward Second Near-Infrared Window

Phosphorescence, characterized by luminescent lifetimes significantly longer than that of biological autofluorescence under ambient environment, is of great value for biomedical applications. Academic evidence of fluorescence imaging indicates that virtually all imaging metrics (sensitivity, resolution, and penetration depths) are improved when progressing into longer wavelength regions, especially the recently reported second near-infrared (NIR-II, 1000-1700 nm) window. Although the emission wavelength of probes does matter, it is not clear whether the guideline of "the longer the wavelength, the better the imaging effect" is still suitable for developing phosphorescent probes. For tissue-specific bioimaging, long-lived probes, even if they emit visible phosphorescence, enable accurate visualization of large deep tissues. For studies dealing with bioimaging of tiny biological architectures or dynamic physiopathological activities, the prerequisite is rigorous planning of long-wavelength phosphorescence, being aware of the cooperative contribution of long wavelengths and long lifetimes for improving the spatiotemporal resolution, penetration depth, and sensitivity of bioimaging. In this Review, emerging molecular engineering methods of room-temperature phosphorescence are discussed through the lens of photophysical mechanisms. We highlight the roles of phosphorescence with emission from visible to NIR-II windows toward bioapplications. To appreciate such advances, challenges and prospects in rapidly growing studies of room-temperature phosphorescence are described.

Ru(II)-Cyanine Complexes as Promising Photodynamic Photosensitizers for the Treatment of Hypoxic Tumours with Highly Penetrating 770 nm Near-Infrared Light

Light-activated treatments, such as photodynamic therapy (PDT), provide temporal and spatial control over a specific cytotoxic response by exploiting toxicity differences between irradiated and dark conditions. In this work, a novel strategy for developing near infrared (NIR)-activatable Ru(II) polypyridyl-based photosensitizers (PSs) was successfully developed through the incorporation of symmetric heptamethine cyanine dyes in the metal complex via a phenanthrimidazole ligand. Owing to their strong absorption in the NIR region, the PSs could be efficiently photoactivated with highly penetrating NIR light (770 nm), leading to high photocytotoxicities towards several cancer cell lines under both normoxic and hypoxic conditions. Notably, our lead PS (Ru-Cyn-1), which accumulated in the mitochondria, exhibited a good photocytotoxic activity under challenging low-oxygen concentration (2 % O2 ) upon NIR light irradiation conditions (770 nm), owing to a combination of type I and II PDT mechanisms. The fact that the PS Protoporphyrin IX (PpIX), the metabolite of the clinically approved 5-ALA PS, was found inactive under the same challenging conditions positions Ru-Cyn-1 complex as a promising PDT agent for the treatment of deep-seated hypoxic tumours.

An Activatable Prodrug Nanosystem for Ultrasound-Driven Multimodal Tumor Therapy and Metastasis Inhibition

Ultrasound, featuring deep tissue penetration and noninvasiveness, offers a new opportunity to activate functional materials in a tumor-selective manner. However, very few direct ultrasound-responsive redox systems are applicable under therapeutic ultrasound (1 MHz). Herein, the investigations on nanoprodrug of DHE@PEG-SS-DSPE are reported, which exhibit glutathione-activated release of dihydroethidium (DHE) in tumor cells. DHE is stable with good biosafety and is transformed into cytotoxic ethidium to induce DNA damage under medical ultrasound irradiation, accompanied by the generation of reactive oxygen species. Further, DHE@PEG-SS-DSPE could effectively induce ferroptosis through glutathione depletion, lipid peroxide accumulation, and downregulation of glutathione peroxidase 4. In vivo studies confirmed that DHE@PEG-SS-DSPE nanoparticles effectively inhibit both the growth of solid tumors and the expression of metastasis-related proteins in mice, thus effectively inhibiting lung metastasis. This DHE-based prodrug nanosystem could lay a foundation for the design of ultrasound-driven therapeutic agents.

Near-Infrared Self-Assembled Hydroxyl Radical Generator Based on Photoinduced Cascade Electron Transfer for Hypoxic Tumor Phototherapy

The hydroxyl radical (•OH) is an extremely potent reactive oxygen species that plays a crucial role in photooxidations within the realm of hypoxic tumor therapy. However, the current methods for •OH photogeneration typically rely on inorganic materials that require UV/vis light excitation. Consequently, photogenerators based on organic molecules, especially those utilizing near-infrared (NIR) light excitation, are rare. In this study, the concept of photoinduced cascade charge transfer (PICET), which utilizes NIR heavy-atom-free photosensitizers (ANOR-Cy5) to generate •OH is introduced. The ANOR-Cy5 photosensitizer, with its flexible hydrophobic structure, enables the formation of nanoparticles in aqueous solutions through molecular assembly. PICET involves a symmetry-breaking charge separation-induced localized charge-separated state, transitioning to a delocalized charge-separated state, which governs the efficiency of •OH generation. Thanks to the oxygen-independent nature of •OH generation and its robust oxidative properties, the ANOR-Cy5-based photosensitizer demonstrates highly effective photoinduced anti-cancer effects, even under severely hypoxic conditions. This discovery emphasizes the potential for achieving •OH photogeneration using a single organic molecule through the engineering of molecular self-assembly, thereby opening up new possibilities for phototherapy and beyond.