Photochemical Properties Research Articles

Visible Light Excitation of Poly‐(para‐Phenylene Ethynylene) Enables Heterogeneous Photocatalytic Oxidations of Amines in Flow

AbstractHeterogeneous visible light photocatalysis is a compelling approach to address sustainability in synthetic photochemistry. However, the use of solid‐state photocatalysts remains very unpopular in organic synthesis because of their limited accessibility and the black‐box effect associated to the lack of rational between their molecular structure and their photochemical properties. Herein, we disclose the synthesis, characterization, photocatalytic properties and synthetic applications of a simple and readily available solid‐state conjugated organic polymer, poly‐(para‐phenylene ethynylene) 1, which exhibits a strong oxidative power upon irradiation with visible light (E(1*/1⋅−)=+1.67 V vs SCE). Comparisons with structural analogues highlighted the superior photocatalytic activity of this linear semiconductor, on account of its fully conjugated architecture. The associated excited‐state reactivity enabled the transformation of various amines into imines in batch and continuous flow reactors together with straightforward photocatalyst recycling. Mechanistic investigations revealed concomitant photoredox and energy transfer pathways, that led to the formation of the desired products. Ultimately, the inline generation of imines was exploited in telescoped three‐component Ugi reactions (3CR) in batch and flow toward biologically relevant α‐acylaminoamides.

Liposomal Formulations of Novel BODIPY Dimers as Promising Photosensitizers for Antibacterial and Anticancer Treatment

Synthesis, photochemical properties, liposomal encapsulation, and in vitro photodynamic activity studies of novel BODIPY dimer connected at meso-meso positions and its brominated and iodinated analogs were described. UV-Vis measurements indicated that the dimeric structure of obtained BODIPYs did not significantly influence the positions of the absorption maxima. Emission properties and singlet oxygen generation studies revealed a strong heavy atom effect of brominated and iodinated BODIPY dimers, manifested by fluorescence intensity reduction and increased singlet oxygen generation ability compared to analog without halogen atoms. For the in vitro photodynamic activity studies, dimers were incorporated into two different types of liposomes: positively charged DOTAP:POPC and negatively charged POPG:POPC. The photoinactivation studies revealed high activity of brominated and iodinated dimers incorporated into DOTAP:POPC liposomes on both Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli. Anticancer studies on human breast adenocarcinoma MDA-MB-231 and human ovarian carcinoma A2780 cells revealed that DOTAP:POPC liposomes containing brominated and iodinated dimers were active even at low nanomolar concentrations. In addition, they were more active against MDA-MB-231 cells than A2780 cells, which is particularly important since the MDA-MB-231 cell line represents triple-negative breast cancer, which has limited therapeutic options.

Advances in Lanthanide-Based NIR-IIb Probes for In Vivo Biomedical Imaging.

The past decades have witnessed the significant development and practical interest of in vivo biomedical imaging technologies and optical materials in the second-near infrared (NIR-II, 1000-1700 nm) window. Imaging with the extended emission wavelength toward the long-wavelength end (NIR-IIb, 1500-1700 nm) further offers micrometer imaging resolution and centimeter tissue penetration depth by taking advantage of the much-reduced photon scattering and near-zero tissue autofluorescence background, which have become a very hot research area. This review focuses on the recent advances in the development of lanthanide-based NIR-IIb probes for in vivo biomedical applications. The progress including ratiometric imaging, multiplexed imaging for wide-field and microscopy, lifetime multiplexing and sensing, persistent luminescence, and multimodal imaging is summarized. Challenges and future directions concerning the investigation of the photophysical and photochemical properties of NIR-IIb probes, the selection of near-infrared cameras as well as the potential extension of the NIR-IIb imaging sub-window are pointed out. This review will inspire readers who have a strong interest in developing optical imaging technology and long-wavelength fluorescence probes for high-contrast in vivo biomedical applications.

Meta-connected Oligo-Azobenzenes Outperform Their Para Counterparts.

Systems with multiple photoswitchable units in one molecule have attracted considerable attention in the past years as they are useful for a broad variety of possible applications. Especially, linked azobenzenes sharing one benzene ring are of high interest since their direct linkage introduces an additional photoswitchable unit at only small increase in molecular weight. In this spirit, linear oligoazobenzenes had been synthesized, though their photochemical properties have only been investigated for short chain lengths. In this study, we use (time-dependent) density functional methodology for the evaluation of the excitations of meta- and para-connected oligo-azobenzenes to predict their switching ability. It becomes apparent, that the meta connection pattern enables each azobenzene subunit to act as an individual switchable unit, whereas they are strongly coupled and loose their individuality in para connection. Therefore, meta-oligo-azobenzenes are ideal candidates for future studies of azobenzene-based functional polymers, while para-oligo-azobenzenes are not.

Gas Phase Reactions of Pristine and Single-Atom-Doped Copper and Silver Clusters: Probing Size-Dependent Stability and Novel Superatoms.

Gas phase reactions have been a subject of research interest, enabling reliable strategies to explore the stability and reactivity of metal clusters as well as to probe novel superatoms that form the building blocks to assemble new materials with tailored properties. Coinage metal clusters have attracted great research attention due to their simple electronic shell structures and rich photochemical and catalytic properties at relatively low cost. This perspective focuses on the recent progress made in studying the gas phase reactions of undamaged and single-atom-doped Cun±,0 and Agn±,0 clusters with O2, CO, and NO molecules. It covers various aspects, such as reaction mechanisms, relationships between structure and activity, control of reactivity by changing cluster size and composition, and the identification of novel superatoms (Cu18-, Ag13-, Ag17-, and Ag15O+). Lastly, we provide a detailed account of the obstacles and prospective avenues for future research in order to establish a connection between these findings and nanocluster systems that have practical applications.

Photoinduced On and Off Polymeric Room Temperature Phosphorescence Based On Polycyclic Aromatic Hydrocarbon Isomers.

As family members of polycyclic aromatic hydrocarbons, compound anthracene (Ant) and phenanthrene (Phe) as isomers are widely used in organic optical materials and electronic materials. But their photochemical and physical properties are very different. In this work, the room temperature phosphorescence (RTP) properties of PVA-B-Ant and PVA-B-Phe are discussed carefully which are prepared by B-O click reaction through polyvinyl alcohol (PVA) with 9-anthraceneboronic acid (B-Ant) and 9-phenanthrenylboronic acid (B-Phe), respectively. PVA-B-Phe 1 % film exhibits excellent fluorescence (FL) emission at 374 nm and RTP emission at 523 nm with green afterglow and around 1.9 s phosphorescence lifetime. However, PVA-B-Ant 1 % film only shows strong blue FL emission at 414 nm, and the emission intensity decreases seriously with the extension of irradiation time. Experimental and theoretical calculations results suggest that the photodimer of Ant which is formed in PVA matrix under the UV light irradiation would be competitive with the process of RTP emission. This work demonstrates that the RTP properties of organic molecules might be probably affected by the photostability of the organic phosphor under UV irradiation.

Current Context of Designing Phototheranostic Cyclometalated Iridium (III) Complexes to Open a New Avenue in Cancer Therapy.

Photo-induced chemotherapy offers the best option for the selective treatment of cancer among all the prevailing modalities. Iridium (III) complexes, flourished with excellent photophysical and photochemical properties, have been considered to be superior for undergoing photo-responsive cancer therapy. Large Stokes shift, long-lived triplet excited state, photostability, and tuneable emission have rendered its excellence as a phototheranostic agent. In particular, the cyclometalated Ir (III) complexes and their respective nanoparticles have made a strong niche in the arena of cancer therapy. In recent years, Ir (III) based complexes have shown promising utilities as both imaging and therapeutic agents as well. Therefore, this review summarises the recent advances in the strategic designing of cyclometalated Ir(III) complexes to augment their phototheranostic applications in precision medicine.

All-Visible-Light-Activated Diarylethene Photoswitches.

Photochromic compounds have attracted much attention for their potential applications in photo-actuators, optoelectronic devices and optical recording techniques. This interest is driven by their key photochemical and photophysical properties, which can be reversibly modulated by light irradiation. Among them, diarylethene compounds have garnered extensive investigation due to their excellent thermal stability of both open- and closed-form isomers, robust fatigue resistance, high photocyclization quantum yield and good photochromic performance in both solution and solid phases. However, a notable limitation in expanding the utility of diarylethene compounds is the necessity for ultraviolet light to induce their photochromism. This requirement poses challenges, as ultraviolet light can be detrimental to biological tissues, and its penetration is often restricted in various media. This review provides an overview of design strategies employed in the development of visible-light-responsive diarylethene compounds. These design strategies serve as a guideline for molecular design, with the potential to significantly broaden the applications of all-visible-light-activated diarylethene compounds in the realms of materials science and biomedical science.

The new metal-free, zinc, magnesium, indium ball-type phthalocyanines and their hybrids with graphene oxide: Synthesis, investigation of photophysical, photochemical properties and theoretical studies

In this study, four ball-type phthalocyanines (BTPc-H2-4, BTPc-Zn-5, BTPc-Mg-6, BTPc-In-7) were synthesized from 3,3,′((3,5-di-tert-butyl-1,2-phenylene)bis(oxy)diphthalonitrile in a single reaction step. Non-covalent ball-type phthalocyanine (BTPc)-graphene oxide (GO) hybrids (BTPc-GO) were prepared by simple sonication method. The structures were confirmed by elemental analysis, ultraviolet–visible (UV–Vis), fourier-transform infrared (FT-IR), proton nuclear magnetic resonance (1H NMR), MALDI-TOF MS spectroscopies, elemental analysis and scanning electron microscope (SEM). The photophysical and photochemical properties of ball-type phthalocyanines were investigated in dimethyl sulfoxide (DMSO) and tetrahydrofuran (THF). In this way, the contribution of solution polarity to these properties was compared. The contribution of GO was examined by examining the singlet oxygen quantum yields of BTPc-GO hybrids in DMSO. In addition, the structural properties of ball-type phthalocyanines were examined through theoretical studies and the effect of structural properties on experimentally determined band gaps was examined. Interestingly, we also report that ball-type thalocyanines are both photostable and exhibit extremely high singlet oxygen quantum yields. In addition, we can state that hybrids of these compounds with GO also show the ability to increase the singlet oxygen quantum yield, depending on the degree of interaction.

Enabling the Photochromism of 4’-Aminoflavylium Compounds in Water by Host-Guest Interaction with β-Cyclodextrin.

Aminoflavylium compounds are known to display poor photochemical properties in water precluding their application in aqueous medium. In this work, we show that the host-guest encapsulation with β-cyclodextrin (β-CD) significantly improves the photochemical performance of 4’-aminoflavylium enabling their operation in aqueous solution. The pH-dependent thermodynamics and kinetics of two aminoflavylium compounds 4’-(N,N-dimethylamino)-7-hydroxylflavylium (4’NMe27OH) and 4’-(N,N-diethylamino)-7-hydroxylflavylium (4’NEt27OH) were studied in water in the absence and presence of β-CD. The association constants follow the order trans-chalcone > quinoidal base > flavylium cation, resulting in β-CD lowering both pKa and pK’a. All species in the 4’NEt27OH multistate system interact more strongly than those in 4’NMe27OH. The pH-dependent kinetics toward the equilibrium follows a bell-shaped curve at moderately acidic pH and increases in the presence of β-CD in both compounds. At highly acidic pH, protonation of trans-chalcone accelerates the kinetics, particularly for 4’NEt27OH due to the easier protonation of the trans-chalcone. In the presence of β-CD this effect is reduced, because protonation of trans-chalcone becomes more difficult.Upon irradiation of trans-chalcone in both compounds in the presence of β-CD, the pale yellow trans-chalcones convert into a purple, less-bound mixture of the flavylium cation and quinoidal base, with a quantum yield of ∼ 0.01.

Pentamethine cyanine dyes with alkynyl group as perspective structure for conjugation with targeting moiety

We report a modified carbocyanine-based asymmetric fluorescent dye, suitable for the azide-alkyne cycloaddition reaction, that possesses promising photochemical properties (Φfl = 0,49). As an example of usage of the new fluorophore, it was conjugated to a ligand targeting prostate-specific membrane antigen (PSMA), one of the widely utilized prostate cancer markers.

Polyoxometalate‐Derived Photocatalysts Enabling Progress in Hydrogen Evolution Reactions

AbstractPhotocatalytic water splitting is capable of converting abundant solar energy into environmentally friendly and renewable chemical energy, presenting a promising solution to alleviate the energy crisis and combat environmental pollution. The development of high‐performance photocatalysts is crucial for significantly improving the efficiency of the hydrogen evolution reaction (HER) involved. Polyoxometalate (POM)‐derived materials, known for their tunable compositions, diverse structures, electron storage/release capabilities, as well as quasi‐semiconductor photochemical properties, serve as highly efficient catalysts in sustainable photosynthesis. This comprehensive review navigates the latest advancements in the assembly strategies and HER performance of POM‐based crystalline materials. It also discusses the composite materials formed by infiltrating POM into metal‐organic frameworks (MOF) and examines the roles of transition metal compounds derived from polyoxometalates, such as sulfides and carbides, in photocatalytic HER. Emphasis is placed on the prospects for the future development of POM‐based compounds as photocatalysts, along with several strategies and outlooks that could facilitate their progress. POM‐derived materials are believed to have significant potential to enhance hydrogen production efficiency while maintaining thermal stability in HER processes.

Electrospinning as a Method for Fabrication of Nanofibrous Photocatalysts Based on Gallium Oxide

Photocatalysts are currently widely used in various research and industrial fields, from water and air purification to solar energy, from self‐cleaning surfaces to wearable biosensors and electronic devices. Among semiconductors, the growing interest is attracted to gallium oxide, especially β‐Ga2O3, due to the unique physical, chemical (especially acid‐resistance), physical–chemical, photochemical properties, and redox potential. These photocatalysts can be used not only as suspended mixture, but also in the form of films, nanoparticles, and nanofibers. The last one is more challenging due to the high level of surface‐to‐volume ratio, porousness, air and water permeability, and excellent morphological and physical–mechanical properties. Moreover, electrospinning techniques, in comparison with fabrication of nanoparticles, allow to obtain photocatalytic devices without usage of additional carrying base, which simplify the industrial process. However, to date there are limited publications related to the Ga2O3 electrospun nanofibers. The aim of this review is to summarize current results of gallium oxide electrospun nanofibers preparation. Special attention is given to the technological parameters of the electrospinning, the polymer solution receipts, and the properties of such nanomaterials and its potential application. Despite the limited number of publications related to Ga2O3 fibers fabrications, that data collected in this review article demonstrate great potential for practical applications.

Visible Light Excitation of Poly-(para-Phenylene Ethynylene) Enables Heterogeneous Photocatalytic Oxidations of Amines in Flow.

Heterogeneous visible light photocatalysis is a compelling approach to address sustainability in synthetic photochemistry. However, the use of solid-state photocatalysts remains very unpopular in organic synthesis because of their limited accessibility and the black-box effect associated to the lack of rational between their molecular structure and their photochemical properties. Herein, we disclose the synthesis, characterization, photocatalytic properties and synthetic applications of a simple and readily available solid-state conjugated organic polymer, poly-(para-phenylene ethynylene) 1, which exhibits a strong oxidative power upon irradiation with visible light (E(1*/1•-) = +1.67 V vs SCE). Comparisons with structural analogues highlighted the superior photocatalytic activity of this linear semiconductor, on account of its fully conjugated architecture. The associated excited-state reactivity enabled the transformation of various amines into imines in batch and continuous flow reactors together with straightforward photocatalyst recycling. Mechanistic investigations revealed concomitant photoredox and energy transfer pathways, that led to the formation of the desired products. Ultimately, the inline generation of imines was exploited in telescoped three-component Ugi reactions (3CR) in batch and flow toward biologically relevant α-acylaminoamides.

Novel phthalocyanines bearing fluoro-methylquinolin substituents: Synthesis, characterization, photophysical and photochemical properties

The novel 4-((6-fluoro-2-methylquinolin-4-yl)oxy)phthalonitrile (3a), 3-((6-fluoro-2-methylquinolin-4-yl)oxy)phthalonitrile (3b), tetra 6-fluoro-2-methylquinolin-4-yl)oxy substituted zinc(II) phthalocyanines (4a and 4b) and their water soluble derivatives (5a and 5b) were prepared. The proposed structures of novel compounds were comfirmed via FT-IR, 1HNMR , UV–Vis and MALDI-TOF mass data. The aggregation tendency, fluorescence quantum yield, singlet oxygen quantum yield and photodegradation measurements were performed to examine the photodynamic therapy potential of both peripherally tetra substituted zinc(II) phthalocyanines (4a and 4b) and the water soluble quaternized tetra substituted zinc(II) phthalocyanines (5a and 5b). The result showed that both the novel tetra 6-fluoro-2-methylquinolin-4-yl)oxy substituted zinc(II) phthalocyanines (4a and 4b) and their water soluble derivatives (5a and 5b) could be used as photosensitizer agents in PDT thanks to their lack of aggregation tendency, having sufficient fluorescence emission for monitoring and produce high amount of singlet oxygen to destroy cancerous tissues and having moderate photostability.

Targeted Modulation of Photocatalytic Hydrogen Evolution Activity by Nickel-Substituted Rubredoxin through Functionalized Ruthenium Phototriggers.

Light-driven hydrogen evolution is a promising means of sustainable energy production to meet global energy demand. This study investigates the photocatalytic hydrogen evolution activity of nickel-substituted rubredoxin (NiRd), an artificial hydrogenase mimic, covalently attached to a ruthenium phototrigger (RuNiRd). By systematically modifying the para-substituents on Ru(II) polypyridyl complexes, we sought to optimize the intramolecular electron transfer processes within the RuNiRd system. A series of electron-donating and electron-withdrawing groups were introduced to tune the photophysical, photochemical, and electrochemical properties of the ruthenium complexes. Our findings reveal that electron-donating substituents can increase the hydrogen evolution capabilities of the artificial enzyme to a point; however, the complexes with the most electron-donating substituents suffer from short lifetimes and inefficient reductive quenching, rendering them inactive. The present work highlights the intricate balance required between driving force, lifetime, and quenching efficiency for effective light-driven catalysis, providing valuable insights into the design of artificial enzyme-photosensitizer constructs.

Platinum(II)-Salphen Complexes as DNA Binders and Photosensitisers.

Current anticancer therapies suffer from issues such as off-target side effects and the emergence of drug resistance; therefore, the discovery of alternative therapeutic approaches is vital. These can include the development of drugs with different modes of action, and the exploration of new biomolecular targets. For the former, there has been increasing interest in drugs that are activated by an external stimulus (e. g. light irradiation) to generate cytotoxic chemicals such as reactive oxygen species (ROS). For the latter, significant efforts are being directed to explore non-canonical DNA and RNA structures (e. g. guanine-quadruplexes), as alternative biomolecular targets. Herein we report the synthesis of a library of 21 new platinum(II)-Salphen complexes (square planar platinum(II) complexes coordinated to tetradentate O,N,N,O-Schiff base ligands), and the investigation, for all complexes, of their photophysical and photochemical properties, their interactions with duplex and quadruplex DNA, and their cytotoxicity against HeLa cancer cells both in the dark and upon light irradiation. Thanks to the intrinsic phosphorescence of the platinum(II) complexes, confocal microscopy was used for six of the complexes to determine their cellular permeability and localisation in two cancer cell lines (HeLa and U2OS). Altogether, these studies have allowed us to identify two lead platinum(II) complexes with high guanine-quadruplex DNA affinity and selectivity, good cell permeability and nuclear localisation, and high cytotoxicity against HeLa cancer cells upon irradiation with no detected cytotoxicity in the dark.

Synthesis and Photochemical Properties of Heterometallic Ti-Cu Ring Clusters Constructed from Myo-Inositol Ligand.

Incorporating heterometals into titanium-oxygen clusters represents an effective approach to adjusting the band gap and absorption properties. Herein, a family of heterometallic Ti-Cu clusters was synthesized under solvothermal conditions. The unique structural feature of these clusters is the formation of ring clusters with myo-inositol ligands serving as structure-directing ligands. The myo-inositol ligand, as a typical polyol ligand, demonstrates flexible and distinctive coordination modes capable of chelating up to eight transition metal ions simultaneously. Compounds 4 and 5 show significant absorption in the visible region, indicating that the incorporation of Cu ions can efficiently tune the band gap of titanium-oxygen clusters.

Application and Challenge of Metalloporphyrin Sensitizers in Noninvasive Dynamic Tumor Therapy

Dynamic tumor therapies (mainly including photodynamic therapy (PDT) and sonodynamic therapy (SDT)) offer new approaches to cancer treatment. They are often characterized by their noninvasive nature, high selectivity, and low toxicity. Sensitizers are crucial for dynamic therapy. Developing efficient sensitizers with good biocompatibility and controllability is an important aim in dynamic therapy. Porphyrins and metalloporphyrins attract great attention due to their excellent photophysical properties and low cytotoxicity under non-light. Compared to porphyrins, metalloporphyrins show greater potential for dynamic therapy due to their enhanced photochemical and photophysical properties after metal ions coordinate with porphyrin rings. This paper reviews some metalloporphyrin-based sensitizers used in photo/sonodynamic therapy and combined therapy. In addition, the probable challenges and bottlenecks in clinical translation are also discussed.

Achievement of biochar photocatalytic performance by synergistic oxidation of sulfuric acid/hydrogen peroxide: Towards revealing the mechanism of synergistic oxidation on photocatalytic performance

The oxygen-containing functional groups of biochar have great potential in tailoring photochemical properties, but the content of oxygen-containing functional groups of pristine biochar is insufficient to support photocatalytic reactions. In this study, a synergistic oxidation of H2SO4 and H2O2 was innovatively proposed to prepare biochar photocatalysts (OGPC400). The results showed that the synergistic oxidation of H2SO4 and H2O2 increased the contents of hydroxyl and carboxyl groups of biochar with the degree of oxidation, and the total concentration of acidic functional groups was about 4 mmol/g higher than that of the oxidation with H2SO4 or H2O2 alone, which was attributed to the synergistic oxidation to promote the conversion of CH and C-OH on the benzene ring. The achievement of electron exchange among hydroxyl and carboxyl groups and internal electron transfer within biochar by the benzene ring as a medium resulted in 100 % degradation of rhodamine b (RhB) and 25 times reaction rate constant higher than that of pristine biochar, as compared to only 45 % or 37 % degradation by oxidation with H2SO4 or H2O2 alone. The exciting results confirmed the positive availability of H2SO4 and H2O2 synergistic oxidation on biochar photocatalysts, which is expected to be applied in environmental remediation.