Photo-Catalyzed α-Arylation of Enol Acetate Using Recyclable Silica-Supported Heteroleptic and Homoleptic Copper(I) Photosensitizers

Earth-abundant photosensitizers are highly sought after for light-mediated applications, such as photoredox catalysis, depollution and energy conversion schemes. Homoleptic and heteroleptic copper(I) complexes are promising candidates in this field, as copper is abundant and the corresponding complexes are easily obtained in smooth conditions. However, some heteroleptic copper(I) complexes suffer from low (photo)stability that leads to the gradual formation of the corresponding homoleptic complex. Such degradation pathways are detrimental, especially when recyclability is desired. This study reports a novel approach for the heterogenization of homoleptic and heteroleptic Cu complexes on silica nanoparticles. In both cases, the photophysical properties upon surface immobilization were only slightly affected. Excited-state quenching with aryl diazonium derivatives occurred efficiently (108 -1010  M-1  s-1 ) with heterogeneous and homogeneous photosensitizers. Moderate but almost identical yields were obtained for the α-arylation of enol acetate using the homoleptic complex in homogeneous or heterogeneous conditions. Importantly, the silica-supported photocatalysts were recycled with moderate loss in photoactivity over multiple experiments. Transient absorption spectroscopy confirmed that excited-state electron transfer occurred from the homogeneous and heterogeneous homoleptic copper(I) complexes to aryl diazonium derivatives, generating the corresponding copper(II) center that persisted for several hundreds of microseconds, compatible with photoredox catalysis applications.

Fluorescence-informed photoacoustic discrimination of multiple chromophores by lifetime mapping optically gated responses

Synchronously Amplified Photoacoustic Image Recovery (SAPhIRe) offers improved background suppression using non-linear properties of modulatable contrast agents. Using SAPhIRe, multiple contrast agents in the same absorption window can be detected independently based on their unique triplet-state lifetimes. Here, we have demonstrated the unmixing of rose bengal and eosin Y signals from solution based on triplet-state lifetime mapping using both fluorescence and photoacoustics. Varying the pump-probe delay enables resolution and recovery of fast-decaying rose bengal and of slowly decaying eosin Y modulated photoacoustic signals, resulting from optically gated triplet state residence. Distinct images were reconstructed within tissue-mimicking phantom using the fitting coefficients of triplet-state lifetimes. Fluorescence was used to screen for modulation prior to photoacoustic imaging. The results suggest that lifetime unmixing can be utilized to simultaneously detect multiple pathologies with overlapping spectra using photoacoustic imaging.

Sequential Two-Photon Delayed Fluorescence Anisotropy for Macromolecular Size Determination

Time-resolved fluorescence anisotropy (FA) uses the fluorophore depolarization rate to report on rotational diffusion, conformation changes, and intermolecular interactions in solution. Although FA is a rapid, sensitive, and nondestructive tool for biomolecular interaction studies, the short (∼ns) fluorescence lifetime of typical dyes largely prevents the application of FA on larger macromolecular species and complexes. By using triplet shelving and recovery of optical excitation, we introduce optically activated delayed fluorescence anisotropy (OADFA) measurements using sequential two-photon excitation, effectively stretching fluorescence anisotropy measurement times from the nanosecond scale to hundreds of microseconds. We demonstrate this scheme for measuring slow depolarization processes of large macromolecular complexes, derive a quantitative rate model, and perform Monte Carlo simulations to describe the depolarization process of OADFA at the molecular level. This setup has great potential to enable future biomacromolecular and colloidal studies.

Novel Oxygen- and Curcumin-Laden Ionic Liquid@Silica Nanocapsules for Enhanced Antimicrobial Photodynamic Therapy

The efficiency of photodynamic therapy is often limited by the scarcity of oxygen at the target site. To address this problem, this work proposes the development of a new nanosystem for antimicrobial photodynamic therapy applications (aPDT) where the natural-origin photosensitizer curcumin (CUR) is immersed in an oxygen-rich environment. Inspired by the perfluorocarbon-based photosensitizer/O2 nanocarriers reported in the literature, we developed a new type of silica nanocapsule containing curcumin dissolved in three hydrophobic ionic liquids (ILs) with high oxygen dissolving capacities. The nanocapsules (CUR-IL@ncSi), prepared by an original oil-in-water microemulsion/sol-gel method, had a high IL content and exhibited clear capacities to dissolve and release significant amounts of oxygen, as demonstrated by deoxygenation/oxygenation studies. The ability of CUR-IL solutions and of CUR-IL@ncSi to generate singlet oxygen (1O2) upon irradiation was confirmed by the detection of 1O2 phosphorescence at 1275 nm. Furthermore, the enhanced capacities of oxygenated CUR-IL@ncSi suspensions to generate 1O2 upon irradiation with blue light were confirmed by an indirect spectrophotometric method. Finally, preliminary microbiological tests using CUR-IL@ncSi incorporated into gelatin films showed the occurrence of antimicrobial effects due to photodynamic inactivation, with their relative efficiencies depending on the specific IL in which curcumin was dissolved. Considering these results, CUR-IL@ncSi has the potential to be used in the future to develop biomedical products with enhanced oxygenation and aPDT capacities.

Rose bengal-decorated rice husk-derived silica nanoparticles enhanced singlet oxygen generation for antimicrobial photodynamic inactivation

Rice husks are well known for their high silica content, and the RH-derived silica nanoparticles (RH NPs) are amorphous and biocompatible; therefore, they are suitable raw materials for biomedical applications. In this study, rose bengal-impregnated rice husk nanoparticles (RB-RH NPs) were prepared for their potential photosensitization and ¹O₂ generation as antimicrobial photodynamic inactivation. RB is a halogen-xanthene type's photosensitizer showing high singlet oxygen efficiency, and the superior photophysical properties are desirable for RB in the antimicrobial photodynamic inactivation of bacteria. To enhance the binding of anionic RB to RH NPs, we conducted cationization for the RH NPs using polyethyleneimine (PEI). The control of the RB adsorption state on cationic PEI-modified RH NPs was essential for RB RH-NP photosensitizers to obtain efficient ¹O₂ generation. Minimizing RB aggregation allowed highly efficient ¹O₂ production from RB-RH NPs at the molar ratio of RB with the PEI, X_RB/PEI. = 0.1. The RB-RH NPs have significant antimicrobial activity against Streptococcus mutans compared to free RB after white light irradiation. The RB-RH NP-based antimicrobial photodynamic inactivation can be employed effectively in treating Streptococcus mutans for dental applications.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10853-023-08194-z.

Microwave-assisted direct synthesis of BODIPY dyes and derivatives

A microwave-assisted one-pot synthesis of BODIPY dyes from pyrroles and acyl chlorides is reported. This protocol features short reaction times, low temperatures, minimum amount of solvent, scalability, versatility, and good yields of the products. These simple, efficient and sustainable conditions can be also applied to the synthesis of derivatives such as BOPHY, BOAHY and BOPAHY.

Photoactive Red Fluorescent SiO2 Nanoparticles Based on Controlled Methylene Blue Aggregation in Reverse Microemulsions

We present a reverse microemulsion synthesis procedure for incorporating methylene blue (MB), a known FDA-approved type-II red-absorbing photosensitizer and ¹O₂ generator, into the matrix of hydrophobic-core/hydrophilic-shell SiO₂ nanoparticles. Different synthesis conditions were explored with the aim of controlling the entrapped-dye aggregation at high dye loadings in the hydrophobic protective core; minimizing dye aggregation ensured highly efficient photoactive nanoentities for ¹O₂ production. Monitoring the synthesis in real time using UV-vis absorption allowed tracking of the dye aggregation process. In particular, silica nanoparticles (MB@SiO₂ NPs) of ∼50 nm diameter size with a high local entrapped-MB concentration (∼10^-2 M, 1000 MB molecules per NP) and a moderate proportion of dye aggregation were obtained. The as-prepared MB@SiO₂ NPs showed a high singlet oxygen photogeneration efficiency (Φ_Δ = 0.30 ± 0.05), and they can be also considered as red fluorescent probes (Φ_F ∼ 0.02, λ_max ∼ 650 nm). The distinctive photophysical and photochemical characteristics of the synthesized NPs reveal that the reverse microemulsion synthesis procedure offers an interesting strategy for the development of complex theranostic nano-objects for photodynamic therapy.

Photosensitizer Encryption with Aggregation Enhanced Singlet Oxygen Production

Chromophores that generate singlet oxygen (¹O₂) in water are essential to developing noninvasive disease treatments using photodynamic therapy (PDT). A facile approach for formation of stable colloidal nanoparticles of ¹O₂ photosensitizers, which exhibit aggregation enhanced ¹O₂ generation in water toward applications as PDT agents, is reported. Chromophore encryption within a fuchsonarene macrocyclic scaffold insulates the photosensitizer from aggregation induced deactivation pathways, enabling a higher chromophore density than typical ¹O₂ generating nanoparticles. Aggregation enhanced ¹O₂ generation in water is observed, and variation in molecular structure allows for regulation of the physical properties of the nanoparticles which ultimately affects the ¹O₂ generation. In vitro activity and the ability of the particles to pass through the cell membrane into the cytoplasm is demonstrated using confocal fluorescence microscopy with HeLa cells. Photosensitizer encryption in rigid macrocycles, such as fuchsonarenes, offers new prospects for the production of biocompatible nanoarchitectures for applications involving ¹O₂ generation.

A porphyrin-based metal-organic framework with highly efficient adsorption and photocatalytic degradation of organic dyes

Organic dye pollution has become an urgent issue due to their toxicity to humans and potential for damage to the environment. However, achieving highly efficient adsorption and degradation materials for...

Preparation of 1, 3, 6, 8-Pyrenesulfonic Acid Tetrasodium Salt Dye-Doped Silica Nanoparticles and Their Application in Water-Based Anti-Counterfeit Ink

In order to improve the luminescent stability of water-based anti-counterfeit ink, a new fluorescent material is prepared by doping dye into silica nanoparticles. Water soluble anionic dye 1, 3, 6, 8-pyrenesulfonic acid sodium salt (PTSA) is selected as the dopant. In this work, PTSA is successfully trapped into silica nanoparticles (SiNPs) by the reverse microemulsion method using cationic polyelectrolyte poly (dimethyl diallyl ammonium chloride; PDADMAC) as a bridge. The UV absorption spectra, fluorescence emission spectra and fluorescent decay curves are used to describe the luminescent properties of the PTSA-doped silica nanoparticles (PTSA-SiNPs). In addition, the as-prepared PTSA-SiNPs and polyurethane waterborne emulsion are used to prepare water-based anti-counterfeit ink, and fluorescent patterns are successfully printed through screen-printing. The samples printed by the ink exhibit desirable fluorescence properties, heat stability, robust photostability, and a fluorescent anti-counterfeit effect, which makes the PTSA-SiNPs promising luminescent materials for anti-counterfeit applications.

Constructing a Local Hydrophobic Cage in Dye-Doped Fluorescent Silica Nanoparticles to Enhance the Photophysical Properties

Aggregation-caused quenching (ACQ) and poor photostability in aqueous media are two common problems for organic fluorescence dyes which cause a dramatic loss of fluorescence imaging quality and photodynamic therapy (PDT) failure. Herein, a local hydrophobic cage is built up inside near-infrared (NIR) cyanine-anchored fluorescent silica nanoparticles (FSNPs) in which a hydrophobic silane coupling agent (n-octyltriethoxysilane, OTES) is doped into FSNPs for the first time to significantly inhibit the ACQ effect and inward diffusion of water molecules. Therefore, the obtained optimal FSNP-C with OTES-modification can provide hydrophobic repulsive forces to effectively inhibit the π-π stacking interaction of cyanine dyes and simultaneously reduce the formation of strong oxidizing species (•OH and H₂O₂) in reaction with H₂O, resulting in the best photostability (fluorescent intensity remained at 90.1% of the initial value after 300 s of laser scanning) and a high PDT efficiency on two- and three-dimensional (spheroids) HeLa cell culture models. Moreover, through molecular engineering (including increasing covalent anchoring sites and steric hindrance groups of cyanine dyes), FSNP-C exhibits the highest fluorescent intensity both in water solution (12.3-fold improvement compared to free dye) and living cells due to the limitation of molecular motion. Thus, this study provides an effectively strategy by combining a local hydrophobic cage and molecular engineering for NIR FSNPs in long-term bright fluorescence imaging and a stable PDT process.

Exploring BODIPY Derivatives as Singlet Oxygen Photosensitizers for PDT

This minireview is devoted to honoring the memory of Dr. Thomas Dougherty, a pioneer of modern photodynamic therapy (PDT). It compiles the most important inputs made by our research group since 2012 in the development of new photosensitizers based on BODIPY chromophore which, thanks to the rich BODIPY chemistry, allows a finely tuned design of the photophysical properties of this family of dyes to serve as efficient photosensitizers for the generation of singlet oxygen. These two factors, photophysical tuning and workable chemistry, have turned BODIPY chromophore as one of the most promising dyes for the development of improved photosensitizers for PDT. In this line, this minireview is mainly related to the establishment of chemical methods and structural designs for enabling efficient singlet oxygen generation in BODIPYs. The approaches include the incorporation of heavy atoms, such as halogens (iodine or bromine) in different number and positions on the BODIPY scaffold, and also transition metal atoms, by their complexation with Ir(III) center, for instance. On the other hand, low-toxicity approaches, without involving heavy metals, have been developed by preparing several orthogonal BODIPY dimers with different substitution patterns. The advantages and drawbacks of all these diverse molecular designs based on BODIPY structural framework are described.

The construction of an AIE-based controllable singlet oxygen generation system directed by a supramolecular strategy

An aggregation-induced emission based controllable singlet oxygen generation system has been successfully fabricated in an aqueous phase based on supramolecular host–guest assembly.

Organo metal halide perovskites effectively photosensitize the production of singlet oxygen (1Δg)

Using the steady state and time resolved NIR emission and specific chemical trapping techniques, we show for the first time that metal halide perovskite quantum dots can effectively generate singlet oxygen with a quantum yield of up to 0.34, the highest among nano semiconductor/nano metal singlet oxygen photosensitizers. The mechanism is concluded to be due to energy transfer from triplet excitons to molecular oxygen.

Three-in-One Functional Silica Nanocarrier with Singlet Oxygen Generation, Storage/Release, and Self-Monitoring for Enhanced Fractional Photodynamic Therapy

At present, the intermittent photodynamic therapy (fractional PDT) for overcoming tumor hypoxia still have their own defects, such as irradiation-dependence and rapid metabolism of organic photosensitizers. Therefore, it is still a really formidable challenge to achieve efficient fractional PDT. Herein, a three-in-one functional silica nanocarrier (FSNC) with singlet oxygen (¹O₂) generating unit (protoporphyrin IX derivative), ¹O₂ storage/release unit (2-pyridone derivative), and ¹O₂ self-monitoring unit (cyanine derivative) was prepared by reverse microemulsion method. Also, it could be efficiently internalized in the HeLa cells because of an appropriate particle size (∼44.8 nm). In the presence of light, the endoperoxide is formed to achieve ¹O₂ storage together with ¹O₂ generated by ¹O₂ generating unit for traditional PDT. In the absence of light, the endoperoxide produces ¹O₂ through cycloreversion for continuous PDT. As a result, the fractional PDT process of the FSNC on the HeLa cells performed a higher phototoxicity than traditional photosensitizer protoporphyrin IX. Furthermore, this real-time release behavior of ¹O₂ can be visually captured by confocal laser scanning microscope via monitoring fluorescent bleaching of ¹O₂ self-monitoring unit. Therefore, this fluorescent imaging-guided fractional PDT process could effectively enhance the PDT effect compared with traditional PDT.

Achieving long-lived thermally activated delayed fluorescence in the atmospheric aqueous environment by nano-encapsulation

Fluorescent silica nanoparticles which encapsulated dye DCF-BYT with thermally activated delayed fluorescence (TADF) were fabricated by a simple synthetic method.

Singlet oxygen partition between the outer-, inner- and membrane-phases of photo/chemotherapeutic liposomes

Herein, we developed a strategy to quantify the fraction of singlet oxygen lifetime spent in the three distinct local liposomal environments through the combination of direct and indirect singlet oxygen detection approaches.