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

Efficient Intersystem Crossing and Long-lived Charge-Separated State Induced by Through-Space Intramolecular Charge Transfer in a Parallel Geometry Carbazole-Bodipy Dyad

The design of efficient heavy atom-free triplet photosensitizers (PSs) based on through bond charge transfer (TBCT) features is a formidable challenge due to the criteria of orthogonal donor-acceptor geometry. Herein, we propose using parallel (face-to-face) conformation carbazole-bodipy donor-acceptor dyads (BCZ-1 and BCZ-2) featuring through space intramolecular charge transfer (TSCT) process as efficient triplet PS. Efficient intersystem crossing (ΦΔ =61 %) and long-lived triplet excited state (τT =186 μs) were observed in the TSCT dyad BCZ-1 compared to BCZ-3 (ΦΔ =0.4 %), the dyad involving TBCT, demonstrating the superiority of the TSCT approach over conventional donor-acceptor system. Moreover, the transient absorption study revealed that TSCT dyads have a faster charge separation and slower intersystem crossing process induced by charge recombination compared to TBCT dyad. A long-lived charge-separated state (CSS) was observed in the BCZ-1 (τCSS =24 ns). For the first time, the TSCT dyad was explored for the triplet-triplet annihilation upconversion, and a high upconversion quantum yield of 11 % was observed. Our results demonstrate a new avenue for designing efficient PSs and open up exciting opportunities for future research in this field.

Metal-Coordination-Mediated H-Aggregates of Cyanine Dyes for Effective Photothermal Therapy

Integration of cyanine dyes and metal ions into one nanoplatform via metal-coordination interactions is an effective strategy to build multimodality phototheranostics. The multifunctionalities of the formed nanoscale metal-organic particles (NMOPs) have been widely explored. However, the effect of metal-coordination interaction on the aggregation behavior of cyanine dyes is rarely reported. Herein, we reported the H-aggregation behavior of cyanine dye Cy-3COOH induced by different metal ions M (Fe2+ or Mn2+ ). Moreover, the extent of H-aggregates varied with different metal-coordination interactions. Upon NIR irradiation, H-aggregates of Cy-3COOH remarkably promoted photothermal conversion efficiency. Interestingly, we also find that H-aggregates of Cy-3COOH induced by metal ions can generate the reactive oxygen species (ROS) involving singlet oxygen (1 O2 ) and superoxide anion radical (O2 - ⋅) upon light irradiation. In addition, the ROS efficiency varies depending on the extent of H-aggregates. Additionally, the photoinduced ROS could disassemble aggregates and decompose cyanine dye Cy-3COOH, which limits the photothermal capability of Cy-3COOH/M NPs. Therefore, the photothermal performance of Cy-3COOH/M NPs could be manipulated by the degree of H-aggregation. This would provide a new insight to develop efficient phototheranostics NMOPs for cancer treatment.

Highly Efficient Photosensitizers with Molecular Vibrational Torsion for Cancer Photodynamic Therapy

The development of highly effective photosensitizers (PSs) for photodynamic therapy remains a great challenge at present. Most PSs rely on the heavy-atom effect or the spin-orbit charge-transfer intersystem crossing (SOCT-ISC) effect to promote ISC, which brings about additional cytotoxicity, and the latter is susceptible to the interference of solvent environment. Herein, an immanent universal property named photoinduced molecular vibrational torsion (PVT)-enhanced spin-orbit coupling (PVT-SOC) in PSs has been first revealed. PVT is verified to be a widespread intrinsic property of quinoid cyanine (QCy) dyes that occurs on an extremely short time scale (10-10 s) and can be captured by transient spectra. The PVT property can provide reinforced SOC as the occurrence of ISC predicted by the El Sayed rules (1ππ*-3nπ*), which ensures efficient photosensitization ability for QCy dyes. Hence, QTCy7-Ac exhibited the highest singlet oxygen yield (13-fold higher than that of TCy7) and lossless fluorescence quantum yield (ΦF) under near-infrared (NIR) irradiation. The preeminent photochemical properties accompanied by high biosecurity enable it to effectively perform photoablation in solid tumors. The revelation of this property supplies a new route for constructing high-performance PSs for achieving enhanced cancer phototherapy.

Tumor-Targeting Probe for Dual-Modal Imaging of Cysteine In Vivo

Cysteine (Cys) is a crucial biological thiol that has a vital function in preserving redox homeostasis in organisms. Studies have shown that Cys is closely related to the development of cancer. Thus, it is necessary to design an efficient method to detect Cys for an effective cancer diagnosis. In this work, a novel tumor-targeting probe (Bio-Cy-S) for dual-modal (NIR fluorescence and photoacoustic) Cys detection is designed. The probe exhibits high selectivity and sensitivity toward Cys. After reaction with Cys, both NIR fluorescence and photoacoustic signals are activated. Bio-Cy-S has been applied for the dual-modal detection of Cys levels in living cells, and it can be used to distinguish normal cells from cancer cells by different Cys levels. In addition, the probe is capable of facilitating dual-modal imaging for monitoring changes in Cys levels in tumor-bearing mice. More importantly, the excellent tumor-targeting ability of the probe greatly improves the signal-to-noise ratio of imaging. To the best of our knowledge, this is the first Cys probe to combine targeting and dual-modal imaging performance for cancer diagnosis.

Fluorescent dyes based on rhodamine derivatives for bioimaging and therapeutics: recent progress, challenges, and prospects

Since their inception, rhodamine dyes have been extensively applied in biotechnology as fluorescent markers or for the detection of biomolecules owing to their good optical physical properties. Accordingly, they have emerged as a powerful tool for the visualization of living systems. In addition to fluorescence bioimaging, the molecular design of rhodamine derivatives with disease therapeutic functions (e.g., cancer and bacterial infection) has recently attracted increased research attention, which is significantly important for the construction of molecular libraries for diagnostic and therapeutic integration. However, reviews focusing on integrated design strategies for rhodamine dye-based diagnosis and treatment and their wide application in disease treatment are extremely rare. In this review, first, a brief history of the development of rhodamine fluorescent dyes, the transformation of rhodamine fluorescent dyes from bioimaging to disease therapy, and the concept of optics-based diagnosis and treatment integration and its significance to human development are presented. Next, a systematic review of several excellent rhodamine-based derivatives for bioimaging, as well as for disease diagnosis and treatment, is presented. Finally, the challenges in practical integration of rhodamine-based diagnostic and treatment dyes and the future outlook of clinical translation are also discussed.

Photosensitizers-Loaded Nanocarriers for Enhancement of Photodynamic Therapy in Melanoma Treatment

Malignant melanoma poses a significant global health burden. It is the most aggressive and lethal form of skin cancer, attributed to various risk factors such as UV radiation exposure, genetic modifications, chemical carcinogens, immunosuppression, and fair complexion. Photodynamic therapy is a promising minimally invasive treatment that uses light to activate a photosensitizer, resulting in the formation of reactive oxygen species, which ultimately promote cell death. When selecting photosensitizers for melanoma photodynamic therapy, the presence of melanin should be considered. Melanin absorbs visible radiation similar to most photosensitizers and has antioxidant properties, which undermines the reactive species generated in photodynamic therapy processes. These characteristics have led to further research for new photosensitizing platforms to ensure better treatment results. The development of photosensitizers has advanced with the use of nanotechnology, which plays a crucial role in enhancing solubility, optical absorption, and tumour targeting. This paper reviews the current approaches (that use the synergistic effect of different photosensitizers, nanocarriers, chemotherapeutic agents) in the photodynamic therapy of melanoma.

Single Component Organic Photosensitizer with NIR-I Emission Realizing Type-I Photodynamic and GSH-Depletion Caused Ferroptosis Synergistic Theranostics

Phototheranostic agents have thrived as prominent tools for tumor luminescence imaging and therapies. Herein, a series of organic photosensitizers (PSs) with donor-acceptors (D-A) are elaborately designed and synthesized. In particular, PPR-2CN exhibits stable near infrared-I (NIR-I) emission, excellent free radicals generation and phototoxicity. Experimental analysis and calculations imply that a small singlet-triplet energy gap (ΔES1-T1 ) and large spin-orbit coupling (SOC) constant boost the intersystem crossing (ISC), leading to type-I photodynamic therapy (PDT). Additionally, the specific glutamate (Glu) and glutathione (GSH) consumption abilities of PPR-2CN inhibit the intracellular biosynthesis of GSH, resulting in redox dyshomeostasis and GSH-depletion causing ferroptosis. This work first realizes that single component organic PS could be simultaneously used as a type-I photodynamic agent and metal-free ferroptosis inducer for NIR-I imaging-guided multimodal synergistic therapy.

ON-OFF Fluorescent Cyanine Dye Based on a Benzothiophenyl Rotor Enables Selective Illumination of G-Quadruplexes in Mitochondria

Conventional cyanine dyes exist as "always-on" fluorescent probes leading to inevitable background signals which often limit their performance and scope of applications. To develop specific fluorescent probes with high sensitivity and robust OFF/ON switching for targeting G4s, we introduced aromatic heterocycles through conjugation with polymethine chains to construct a rotor-π system. Here, a universal strategy is presented to synthesize pentamethine cyanines with different aromatic heterocycle substituents on the meso-polymethine chain. In these probes, SN-Cy5-S is self-quenched in aqueous solution due to H-aggregation. The structure indicates that SN-Cy5-S with a flexible meso-benzothiophenyl rotor conjugated to the cyanine backbone matches adaptively with G-tetrad planes, enhancing π-π stacking and resulting in triggered fluorescence. This allows recognition of G-quadruplexes due to the synergy of disaggregation-induced emission (DIE) and inhibited twisted intramolecular charge-transfer effects. This combination leads to a robust lighting-up fluorescence response for c-myc G4 with superior fluorescence enhancement (98-fold), allowing for a low detection limit of 1.51 nM, which is much more sensitive than the previously reported DIE-based G4 probes (22-83.5 nM). In addition, the superior imaging properties and rapid internalization time (5 min) in mitochondria allow SN-Cy5-S to also have a high potential for mitochondrially targeting anti-cancer therapy.

Spin-Vibronic Control of Intersystem Crossing in Iodine-Substituted Heptamethine Cyanines

Spin-orbit coupling between electronic states of different multiplicity can be strongly coupled to molecular vibrations, and this interaction is becoming recognized as an important mechanism for controlling the course of photochemical reactions. Here, we show that the involvement of spin-vibronic coupling is essential for understanding the photophysics and photochemistry of heptamethine cyanines (Cy7), bearing iodine as a heavy atom in the C3' position of the chain and/or a 3H-indolium core, as potential triplet sensitizers and singlet oxygen producers in methanol and aqueous solutions. The sensitization efficiency was found to be an order of magnitude higher for the chain-substituted than the 3H-indolium core-substituted derivatives. Our ab initio calculations demonstrate that while all optimal structures of Cy7 are characterized by negligible spin-orbit coupling (tenths of cm^-1) with no dependence on the position of the substituent, molecular vibrations lead to its significant increase (tens of cm^-1 for the chain-substituted cyanines), which allowed us to interpret the observed position dependence.

BODIPY as a Multifunctional Theranostic Reagent in Biomedicine: Self-Assembly, Properties, and Applications

The use of boron dipyrromethene (BODIPY) in biomedicine is reviewed. To open, its synthesis and regulatory strategies are summarized, and inspiring cutting-edge work in post-functionalization strategies is highlighted. A brief overview of assembly model of BODIPY is then provided: BODIPY is introduced as a promising building block for the formation of single- and multicomponent self-assembled systems, including nanostructures suitable for aqueous environments, thereby showing the great development potential of supramolecular assembly in biomedicine applications. The frontier progress of BODIPY in biomedical application is thereafter described, supported by examples of the frontiers of biomedical applications of BODIPY-containing smart materials: it mainly involves the application of materials based on BODIPY building blocks and their assemblies in fluorescence bioimaging, photoacoustic imaging, disease treatment including photodynamic therapy, photothermal therapy, and immunotherapy. Lastly, not only the current status of the BODIPY family in the biomedical field but also the challenges worth considering are summarized. At the same time, insights into the future development prospects of biomedically applicable BODIPY are provided.

All-in-one bioactive properties of photothermal nanofibers for accelerating diabetic wound healing

Diabetic wound healing has attracted widespread attention in biomedical engineering. However, the harsh hypoxic microenvironment (HME) comprising high glucose levels, local bleeding, and bacterial infection often leads to the formation of hyperplastic scars, increasing the clinical demand for wound dressings. Here, we report a comprehensive strategy using near-infrared NIR-assisted oxygen delivery combined with the bioactive nature of biopolymers for remodeling the HME. Black phosphorus (BP) nanosheets and hemoglobin (Hb) were self-assembled layerwise onto electrospun poly-l-lactide (PLLA) nanofibers using charged quaternized chitosan (QCS) and hyaluronic acid. BP converts NIR radiation into heat and stimulates Hb to release oxygen in situ. QCS is a hemostatic and broad-spectrum antibacterial material. Moderate BP-derived photothermal therapy can increase the sensitivity of bacteria to QCS. A series of composite wound dressings (coded as PQBH-n) with different numbers of layers were fabricated, and the in vivo diabetic wound healing potentials were tested. The molecular mechanism can be partly attributed to the cytokine-cytokine receptor interaction. Notably, this comprehensive strategy based on NIR-assisted oxygen delivery combined with the bioactive properties of biopolymers is not only applicable for fabricating multifunctional wound dressings but also has a great potential in expanding biomedical engineering fields.

Immuno-photodynamic Therapy (IPDT): Organic Photosensitizers and Their Application in Cancer Ablation

Photosensitizer-based photodynamic therapy (PDT) has been considered as a promising modality for fighting diverse types of cancers. PDT directly inhibits local tumors by a minimally invasive strategy, but it seems to be incapable of achieving complete eradication and fails to prevent metastasis and recurrence. Recently, increasing events proved that PDT was associated with immunotherapy by triggering immunogenic cell death (ICD). Upon a specific wavelength of light irradiation, the photosensitizers will turn the surrounding oxygen molecules into cytotoxic reactive oxygen species (ROS) for killing the cancer cells. Simultaneously, the dying tumor cells release tumor-associated antigens, which could improve immunogenicity to activate immune cells. However, the progressively enhanced immunity is typically limited by the intrinsic immunosuppressive tumor microenvironment (TME). To overcome this obstacle, immuno-photodynamic therapy (IPDT) has come to be one of the most beneficial strategies, which takes advantage of PDT to stimulate the immune response and unite immunotherapy for inducing immune-OFF tumors to immune-ON ones, to achieve systemic immune response and prevent cancer recurrence. In this Perspective, we provide a review of recent advances in organic photosensitizer-based IPDT. The general process of immune responses triggered by photosensitizers (PSs) and how to enhance the antitumor immune pathway by modifying the chemical structure or conjugating with a targeting component was discussed. In addition, future perspectives and challenges associated with IPDT strategies are also discussed. We hope this Perspective could inspire more innovative ideas and provide executable strategies for future developments in the war against cancer.

Highly Twisted Conformation Thiopyrylium Photosensitizers for In Vivo Near Infrared-II Imaging and Rapid Inactivation of Coronavirus

Despite significant effort, a majority of heavy-atom-free photosensitizers have short excitation wavelengths, thereby hampering their biomedical applications. Here, we present a facile approach for developing efficient near-infrared (NIR) heavy-atom-free photosensitizers. Based on a series of thiopyrylium-based NIR-II (1000-1700 nm) dyads, we found that the star dyad HD with a sterically bulky and electron-rich moiety exhibited configuration torsion and significantly enhanced intersystem crossing (ISC) compared to the parent dyad. The electron excitation characteristics of HD changed from local excitation (LE) to charge transfer (CT)-domain, contributing to a ≈6-fold reduction in energy gap (ΔEST ), a ≈10-fold accelerated ISC process, and a ≈31.49-fold elevated reactive oxygen species (ROS) quantum yield. The optimized SP@HD-PEG2K lung-targeting dots enabled real-time NIR-II lung imaging, which precisely guided rapid pulmonary coronavirus inactivation.

Modification of a SOCT-ISC type triphenylamine-BODIPY photosensitizer by a multipolar dendrimer design for photodynamic therapy and two-photon fluorescence imaging

In this study, a series of multipolar triphenylamine-BODIPY photosensitizers T-BDP_n (n = 1, 2, 3) was synthesized. Compared with T-BDP₁ of D-A configuration, the multipolar T-BDP₃ dendrimer have higher singlet oxygen efficiency (44%), better fluorescence quantum yield (7.45%), and could be used in the simulated photodynamic therapy in A-549 cells and two-photon fluorescence imaging in zebrafish. The theoretical calculation and fs-transient absorption spectra indicated that the reason of its higher singlet oxygen efficiency was that the multipolar T-BDP₃ dendrimer could generate more nearly degenerate charge transfer (CT) states and triplet states, which could further increase the possibility of spin-orbit charge-transfer intersystem crossing (SOCT-ISC) process. In the simulated photodynamic therapy of A-549 cells, T-BDP₃ shows good cytocompatibility, great phototoxicity with its IC₅₀ value of 3.17 μM, and could kill cancer cells effectively with the dosage of 5 μM under 10 min irradiation in the AO/EB double-staining experiment. In the fluorescence imaging of zebrafish, the experiment results indicate that T-BDP₃ could generate superoxide radical (O₂˙^-) in the body of zebrafish and could be applied to the two-photon fluorescence imaging under 800 nm excitation. The above experiment results shown that the multipolar dendrimer design was an effective approach to improve the key parameters of SOCT-ISC-type BODIPY photosensitizer and was ready for further two-photon photodynamic therapy in organisms.

Tumor-Targeting Near-Infrared Dimeric Heptamethine Cyanine Photosensitizers With an Aromatic Diphenol Linker for Imaging-Guided Cancer Phototherapy

Phototherapy is considered a promising alternative to conventional tumor treatments due to its noninvasive modality and effective therapeutic effect. However, designing a photosensitizer with satisfactory therapeutic effect and high security remains a considerable challenge. Herein, a series of dimeric heptamethine cyanine photosensitizers with an aromatic diphenol linker at the meso position is developed to improve the photothermal conversion efficiency (PCE). Thanks to the extended conjugate system and high steric hindrance, the screened 26NA-NIR and 44BP-NIR exhibit high PCE (≈35%), bright near-infrared (NIR) fluorescence, excellent reactive oxygen species (ROS) generation capability, and improved photostability. Furthermore, their outstanding performance on imaging-guided PDT-PTT synergistic therapy is demonstrated by in vivo and in vitro experiments. In conclusion, this study designs a series of dimeric heptamethine cyanine photosensitizers and presents two compounds for potential clinical applications. The strategy provides a new method to design NIR photosensitizers for imaging-guided cancer treatment.

Tumor Cell-Responsive Photodynamic Immunoagent for Immunogenicity-Enhanced Orthotopic and Remote Tumor Therapy

Combining photodynamic therapy (PDT) and immune checkpoint blockades is an efficient method to maximize immunotherapeutic outcome by boosting tumor immunogenicity and modulating the immunosuppressive tumor microenvironment. However, the always-on bioactivity of photosensitizers or immune checkpoint inhibitors leads to uncontrollable side effects, limiting the in vivo therapeutic efficacy of treatments. An activatable strategy is of great importance for improving the selectivity during cancer therapy. In this study, a photodynamic immunomodulator, ICy-NLG, is developed by conjugating the photosensitizer ICy-NH2 with the indoleamine 2,3-dioxygenase 1 inhibitor NLG919 through a glutathione (GSH)-cleavable linker to achieve activatable photodynamic immunotherapy. The conjugation considerably suppresses both the PDT effect and the activity of the inhibitor. After ICy-NLG is activated by high levels of GSH in tumor cells, the PDT effect is restored and leads to immunogenic tumor cell death. The released tumor-associated antigens in conjunction with the activated immune checkpoint inhibitor induce a synergistic antitumor immune response, resulting in the growth inhibition of primary and distant tumors and the prevention of lung metastasis in mouse xenograft models.

Rational Design of Asymmetric Polymethines to Attain NIR(II) Bioimaging at >1100 nm

Organic molecules having emission in the NIR(II) region are emergent and receiving enormous attention. Unfortunately, attaining accountable organic emission intensity around the NIR(II) region is hampered by the dominant internal conversion operated by the energy gap law, where the emission energy gap and the associated internal reorganization energy λ_int play key roles. Up to the current stage, the majority of the reported organic NIR(II) emitters belong to those polymethines terminated by two symmetric chromophores. Such a design has proved to have a small λ_int that greatly suppresses the internal conversion. However, the imposition of symmetric chromophores is stringent, limiting further development of organic NIR(II) dyes in diversity and versatility. Here, we propose a new concept where as far as the emissive state of the any asymmetric polymethines contains more or less equally transition density between two terminated chromophores, λ_int can be as small as that of the symmetric polymethines. To prove the concept, we synthesize a series of new polymethines terminated by xanthen-9-yl-benzoic acid and 2,4-diphenylthiopyrylium derivatives, yielding AJBF1112 and AEBF1119 that reveal emission peak wavelength at 1112 and 1119 nm, respectively. The quantum yield is higher than all synthesized symmetric polymethines of 2,4-diphenylthiopyrylium derivatives (SC1162, 1182, 1185, and 1230) in this study. λ_int were calculated to be as small as 6.2 and 7.3 kcal/mol for AJBF1112 and AEBF1119, respectively, proving the concept. AEBF1119 was further prepared as a polymer dot to demonstrate its in vitro specific cellular imaging and in vivo tumor/bone targeting in the NIR(II) region.

Mitochondrial Targeting and Imaging with Small Organic Conjugated Fluorophores: A Review

The last decade has seen an increasingly large number of studies reporting on the development of novel small organic conjugated systems for mitochondrial imaging exploiting optical signal transduction pathways. Mitochondria are known to play a critical role in a number of key biological processes, including cellular metabolism. Importantly, irregularities on their working function are nowadays understood to be intimately linked to a range of clinical conditions, highlighting the importance of targeting mitochondria for therapeutic benefits. In this work we carry out an in-depth evaluation on the progress to date in the field to pave the way for the realization of superior alternatives to those currently existing. The manuscript is structured by commonly used chemical scaffolds and comprehensively covers key aspects factored in design strategies such as synthetic approaches as well as photophysical and biological characterization, to foster collaborative work among organic and physical chemists as well as cell biologists.

Near-Infrared Dyes: Towards Broad-Spectrum Antivirals

Broad antiviral activity in vitro is known for many organic photosensitizers generating reactive oxygen species under irradiation with visible light. Low tissue penetration of visible light prevents further development of antiviral therapeutics based on these compounds. One possible solution to this problem is the development of photosensitizers with near-infrared absorption (NIR dyes). These compounds found diverse applications in the photodynamic therapy of tumors and bacterial infections, but they are scarcely mentioned as antivirals. In this account, we aimed to evaluate the therapeutic prospects of various NIR-absorbing and singlet oxygen-generating chromophores for the development of broad-spectrum photosensitizing antivirals.

An injectable vitreous substitute with sustained release of metformin for enhanced uveal melanoma immunotherapy

Uveal melanoma (UM) is the most prevalent primary intraocular malignant tumor in adults with a high rate of metastasis. Conventional treatments have limited effects on metastasis and cause permanent ocular tissue defects. Here, a novel strategy based on an injectable vitreous substitute with sustained metformin release ability (IVS-Met) was reported for efficient UM therapy as well as for repairing vitreous deficiency and preserving visual function. IVS-Met showed an excellent long-term anti-tumor effect by direct tumor attack and modulation of the tumor microenvironment (TME). IVS-Met reduced the proportion of pro-tumor M2 tumor-associated macrophages and induced the pro-inflammatory M1 phenotype, thus reversing the immunosuppressive TME and eliciting robust anti-tumor immune responses. Notably, IVS-Met demonstrated high performance in the inhibition of UM metastasis and significantly extended the survival time of mice. In addition, the vitreous substitute achieved facile administration via direct injection and exhibited excellent rheological and optical properties with the key parameters very close to those of the vitreous body to repair vitreous deficiency and preserve visual function. In summary, this strategy has realized effective UM treatment while retaining eyeballs and vision for the first time, revealing great potential for translation to clinical practice.

Three Birds with One Stone: Acceptor Engineering of Hemicyanine Dye with NIR-II Emission for Synergistic Photodynamic and Photothermal Anticancer Therapy

It is challenging to develop a near-infrared (NIR) small molecular photosensitizer for synergistic phototherapy in deep tissues. Herein, first, a heavy-atom-free NIR hemicyanine photosensitizer (BHcy) for 808 nm light-mediated synergistic photodynamic therapy/photothermal therapy (PDT/PTT) anticancer therapy by leveraging the acceptor engineering strategy is reported. This strategy endows BHcy with a more planar and larger π-conjugated structure, resulting in long NIR absorption/emission at 770/915-1200 nm as well as enhanced singlet oxygen (¹ O₂ ) generation ability and photothermal effect, which is ascribed to the reduced energy levels of excited singlet/triplet states and the promoted intersystem crossing process. Notably, BHcy-based nanoparticles (BHcy-NPs) exhibit efficient ¹ O₂ yield (12.9%) and high photothermal conversion efficiency (55.1%). More importantly, BHcy-NPs are able to significantly kill cancer cells by destroying main organelles and inhibit tumor growth in vivo after a single irradiation. Overall, this study provides a strategy to design new heavy-atom-free PDT/PTT agents for potential clinical applications.

An Approach to Developing Cyanines with Upconverted Photosensitive Efficiency Enhancement for Highly Efficient NIR Tumor Phototheranostics

Upconverted reactive oxygen species (ROS) photosensitization with one-photon excitation mode is a promising tactic to elongate the excitation wavelengths of photosensitive dyes to near-infrared (NIR) light region without the requirement of coherent high-intensity light sources. However, the photosensitization efficiencies are still finite by the unilateral improvement of excited-state intersystem crossing (ISC) via heavy-atom-effect, since the upconverted efficiency also plays a decisive role in upconverted photosensitization. Herein, a NIR light initiated one-photon upconversion heavy-atom-free small molecule system is reported. The meso-rotatable anthracene in pentamethine cyanine (Cy5) is demonstrated to enrich the populations in high vibrational-rotational energy levels and subsequently improve the hot-band absorption (HBA) efficiency. Moreover, the spin-orbit charge transfer intersystem crossing (SOCT-ISC) caused by electron donated anthracene can further amplify the triplet yield. Benefiting from the above two aspects, the ¹ O₂ generation significantly increases with over 2-fold improved performance compared with heavy-atom-modified method under upconverted light excitation, which obtains efficient in vivo phototheranostic results and provides new opportunities for other applications such as photocatalysis and fine chemical synthesis.

Molecular Tailoring Based on Forster Resonance Energy Transfer for Initiating Two-Photon Theranostics with Amplified Reactive Oxygen Species

The fabrication of multifunctional photosensitizers (PSs) with abundant Type I/II ROS for efficient theranostics in the "therapeutic window" (700-900 nm) is an appealing yet significantly challenging task. We herein report a molecular tailoring strategy based on intramolecular two-photon Forster Resonance Energy Transfer (TP-FRET) to obtain a novel theranostic agent (Lyso-FRET), featuring the amplified advantage of energy donor (NH) and acceptor (COOH), because of the reuse of fluorescence energy with high efficiency of FRET (∼83%). Importantly, under the excitation by the near-infrared (840 nm) window, Lyso-FRET can not only penetrate the deeper tissue with a higher resolution for fluorescence imaging due to the nonlinear optical (NLO) nature, but also generate more Type I (superoxide anion) and Type II (singlet oxygen) reactive oxygen species for hypoxic PDT. Moreover, Lyso-FRET targeting lysosomes further promotes the effect of treatment. The experiments in vitro and in vivo also verify that the developed TP-FRET PS is conducive to treating deep hypoxic tumors. This strategy provides new and significant insights into the design and fabrication of advanced multifunctional PSs.

A novel active mitochondrion-selective fluorescent probe for the NIR fluorescence imaging and targeted photodynamic therapy of gastric cancer

The annual morbidity and mortality due to gastric cancer are still high across the world, posing a serious threat to public health. Improving the diagnosis rate of gastric cancer and exploring new treatments are urgent issues in the clinical field. In recent years, photosensitizer (PS)-based photodynamic therapy (PDT) has proven to be an effective cancer treatment strategy and can be used to treat a variety of cancers. Developing PSs with tumor-targeting ability and high singlet oxygen yield (Φ(¹O₂)) is the key to improving the PDT effect. Herein, we developed a novel diagnosis and treatment system (Cy₁₃₉₅-NPs). Our active thio-photosensitizer is based on the sulfur substitution strategy as it can reduce the S1-T1 energy gap, which can promote the process of intersystem crossing (ISC), thus resulting in high ROS generation efficiency. Cy₁₃₉₅-NPs exhibited stable spectral characteristics, satisfactory biocompatibility and high ¹O₂ yield under laser irradiation due to the introduction of the sulfur atom. In cellular studies, Cy₁₃₉₅-NPs could specifically target MKN45 cells via integrin α_vβ₃-mediated cRGD endocytosis and selectively aggregate in the mitochondria. Cy₁₃₉₅-NPs had no obvious cytotoxicity for MKN45 cells and exerted obvious phototoxicity due to the production of ¹O₂ under laser irradiation. The in vivo results showed that the fluorescence signal from the tumor site was obviously enhanced in 16-48 h, and Cy₁₃₉₅-NPs could selectively target solid tumors with a retention time of about 32 h. Under laser irradiation, Cy₁₃₉₅-NPs significantly inhibited tumor growth and led to significant tumor suppression and apoptosis. In summary, the developed Cy₁₃₉₅-NPs could actively target tumors and exert mitochondrial selectivity, showing an excellent fluorescence imaging effect. Under the irradiation of an 808 nm laser, Cy₁₃₉₅-NPs achieved good inhibition of gastric cancer cells both in vitro and in vivo, thus displaying the functions of tumor targeting, mitochondrial selectivity, fluorescence imaging and tumor inhibition. Our strategy provides a new diagnostic and treatment method for gastric cancers in clinical settings.

Proton-Driven Transformable 1 O2 -Nanotrap for Dark and Hypoxia Tolerant Photodynamic Therapy

Despite the clinical potential, photodynamic therapy (PDT) relying on singlet oxygen (¹ O₂ ) generation is severely limited by tumor hypoxia and endosomal entrapment. Herein, a proton-driven transformable ¹ O₂ -nanotrap (ANBDP NPs) with endosomal escape capability is presented to improve hypoxic tumor PDT. In the acidic endosomal environment, the protonated ¹ O₂ -nanotrap ruptures endosomal membranes via a "proton-sponge" like effect and undergoes a drastic morphology-and-size change from nanocubes (≈94.1 nm in length) to nanospheres (≈12.3 nm in diameter). Simultaneously, anthracenyl boron dipyrromethene-derived photosensitizer (ANBDP) in nanospheres transforms to its protonated form (ANBDPH) and switches off its charge-transfer state to achieve amplified ¹ O₂ photogeneration capability. Upon 730 nm photoirradiation, ANBDPH prominently produces ¹ O₂ and traps generated-¹ O₂ in the anthracene group to form endoperoxide (ANOBDPH). Benefitting from the hypoxia-tolerant ¹ O₂ -release property of ANOBDPH in the dark, the ¹ O₂ -nanotrap brings about sustained therapeutic effect without further continuous irradiation, thereby achieving remarkable antitumor performance.

The biological activities of 5,15-diaryl-10,20-dihalogeno porphyrins for photodynamic therapy

PURPOSE

Esophageal cancer is the most common gastrointestinal tumor and is difficult to be eradicated with conventional treatment. Porphyrin-based photosensitizers (PSs) mediated photodynamic therapy (PDT) could kill tumor cells with less damage to normal cells. As the most widely used porphyrin-based photosensitizer in clinics, Photofrin II has excellent anti-tumor effect. However, it has some disadvantages such as weak absorption at near infrared region, the complexity of components and prolonged skin photosensitivity. Here series novel 5,15-diaryl-10,20-dihalogeno porphyrin derivatives were afforded and evaluated to develop more effective and safer photosensitizers for tumor therapy.

METHODS

The photophysical properties and singlet oxygen generation rates of 5,15-diaryl-10,20-dihalogeno porphyrins (I_1-6, II_1-4) were tested. The cytotoxicity of I_1-6 and II_1-4 were measured by MTT assay. The pathway of cell death was studied by flow cytometry. In vivo photodynamic efficacy of I₃ and II_2-4 in Eca-109 tumor-bearing BABL/c nude mice were measured and histopathological analysis were examined.

RESULTS

5,15-Diaryl-10,20-dihalogeno porphyrins I_1-6 and II_1-4 were synthesized. The longest absorption wavelength of these halogenated porphyrins (λ_max = 660 nm) displayed a red shift around 30 nm compared to the unhalogenated porphyrins PS₁ (λ_max = 630 nm). The singlet oxygen generation rates of I_1-6 and II_1-4 were significantly higher than PS₁ and HMME. All PSs mediated PDT showed obvious cytotoxic effect against Eca-109 cells compared to HMME in vitro and in vivo. Among these PSs, II₄ exhibited appropriate absorption in the phototherapeutic window, higher ¹O₂ generation rate (k = 0.0061 s^-1), the strongest phototoxicity (IC₅₀ = 0.4 μM), lower dark toxicity, high generation of intracellular ROS in Eca-109 cells and excellent photodynamic anti-tumor efficacy in vivo. Besides, cell necrosis was induced by compound II₄ mediated PDT.

CONCLUSION

All new compounds have obvious photodynamic anti-esophageal cancer effects. Among them, the photosensitizer II₄ showed excellent efficacy in vitro and in vivo, which has the potential to become a photodynamic anti-tumor drug.

Universal "Three-in-One" Matrix to Maximize Reactive Oxygen Species Generation from Food and Drug Administration-Approved Photosensitizers for Photodynamic Inactivation of Biofilms

Biofilms, an accumulation of microorganisms, cause persistent bacterial infection and low cure rate due to the remarkable drug resistance. Photodynamic inactivation (PDI) is a promising treatment modality for bacterial infections, but the formation of biofilms raises new challenges for photosensitizers (PSs), particularly the reactive oxygen species (ROS) generation efficiency. Herein, through targeting the Jablonski energy diagram, we proposed a universal "three-in-one" matrix of Gd³⁺-ADP assembly for encapsulation and fixing of PSs to inhibit non-radiative transitions and promoting intersystem crossing (ISC) by the heavy atom and paramagnetic effects of Gd³⁺, eventually resulted in boosted ROS generation from the existing PSs (1.5-9.0-fold). Particularly, photophysical studies indicated that the matrix resulted in simultaneous ISC promotion and triplet-state lifetime lengthening, which is essential for ROS boosting. The PDI performance of the matrix was confirmed through fast and effective elimination of bacterial biofilms in 10-30 min. Moreover, successful therapy of a Pseudomonas aeruginosa biofilm-infected all-thickness third-degree burn wound was achieved within 11 days with Ce 6@CNs (matrix) but not feasible for matrix-free PSs (Ce 6 only), which highlighted the role of "three-in-one" matrix in ROS boosting.

A Descriptor for Accurate Predictions of Host Molecules Enabling Ultralong Room-Temperature Phosphorescence in Guest Emitters

Although doping can induce room-temperature phosphorescence (RTP) in heavy-atom free organic systems, it is often challenging to match the host and guest components to achieve efficient intersystem crossing for activating RTP. In this work, we developed a simple descriptor ΔE to predict host molecules for matching the guest RTP emitters, based on the intersystem crossing via higher excited states (ISCHES) mechanism. This descriptor successfully predicted five commercially available host components to pair with naphthalimide (NA) and naphtho[2,3-c]furan-1,3-dione (2,3-NA) emitters with a high accuracy of 83 %. The yielded pairs exhibited bright yellow and green RTP with the quantum efficiency up to 0.4 and lifetime up to 1.67 s, respectively. Using these RTP pairs, we successfully achieved multi-layer message encryption. The ΔE descriptor could provide an efficient way for developing doping-induced RTP materials.

Visible Light Generation of a Microsecond Long-Lived Potent Reducing Agent

Photoexcitation of molecular radicals can produce strong reducing agents; however, the limited lifetimes of the doublet excited states preclude many applications. Herein, we propose and demonstrate a general strategy to translate a highly energetic electron from a doublet excited state to a ZrO₂ insulator, thereby increasing the lifetime by about 6 orders of magnitude while maintaining a reducing potential less than -2.4 V vs SCE. Specifically, red light excitation of a salicylic acid modified perylene diimide radical anion PDI^•- anchored to a ZrO₂ insulator yields a ZrO₂(e^-)|PDI charge separated state with an ∼10 μs lifetime in 23% yield. The ZrO₂(e^-)s were shown to drive CO₂ → CO reduction with a Re catalyst present in micromolar concentrations. More broadly, this strategy provides new opportunities to reduce important reagents and catalysts at low concentrations through diffusional electron transfer.

Orthogonally aligned cyclic BODIPY arrays with long-lived triplet excited states as efficient heavy-atom-free photosensitizers

In photosensitizers, long triplet excited state lifetimes are key to their efficient electron transfer or energy transfer processes. Herein, we report a novel class of cyclic trimeric BODIPY arrays which were efficiently generated from easily accessible meso-mesityldipyrrinone and arylboronic acids in one pot. Arylboronic acid, for the first time, was used to provide a boron source for BODIPY derivatives. Due to the well-defined and orthogonally aligned BODIPY cores as verified by X-ray crystallography, these BODIPY arrays show strong exciton coupling effects and efficient intersystem crossings, and are novel heavy-atom-free photosensitizers with a long-lived triplet excited state (lifetime up to 257.5 μs) and good reactive oxygen species generation efficiency (up to 0.72) contributed by both 1O2 and O2 -˙ under light irradiation.

1,7-Di-tert-butyl-Substituted aza-BODIPYs by Low-Barrier Rotation to Enhance a Photothermal-Photodynamic Effect

1,7-Di-tert-butyl-substituted aza-BODIPYs (tBu-azaBDP) were successfully obtained for the first time. The structures of tBu-azaBDP and Ph-azaBDP were confirmed by X-ray crystal analysis, and tBu-azaBDP 2 is more twisted than Ph-azaBDP 5. tBu-azaBDPs have significant photo-stability and enhanced water solubility. tBu-azaBDPs possess excellent optical properties, such as high molar extinction coefficients, broad full width half maxima, and large Stokes shifts, which is comparable to those of the parent dye Ph-azaBDP. Although the low-barrier rotation of the distal -tBu groups in tBu-azaBDPs results in low quantum yield, photothermal conversion efficiency and singlet oxygen generation ability of tBu-azaBDPs are more effective than those of Ph-azaBDP, which is highly desirable for a photothermal-photodynamic therapy agent.

Strategic Construction of Sulfur-Bridged BODIPY Dimers and Oligomers as Heavy-Atom-Free Photosensitizers

An efficient strategy for building sulfur-bridged oligo-BODIPYs based on the S_NAr reaction is described. These oligo-BODIPYs showed broadband and strong visible-near-infrared (NIR) light absorption, strong intramolecular exciton coupling, and efficient intersystem crossing (ISC). Generation of ¹O₂ as well as O₂^•- under irradiation was found to give high reactive oxygen species generation efficiencies for those oligomers.