Photosensitization Mechanism Research Articles

Assessing the Influence of Illumination on Ion Conductivity in Perovskite Solar Cells.

Whether illumination influences the ion conductivity in lead-halide perovskite solar cells containing iodide halides has been an ongoing debate. Experiments to elucidate the presence of a photoconductive effect require special devices or measurement techniques and neglect possible influences of the enhanced electronic charge concentrations. Here, we assess the electronic-ionic charge transport using drift-diffusion simulations and show that the well-known increase in capacitance at low frequencies under illumination is caused by electronic currents that are amplified due to the screening of the alternating electric field by the ions. We propose a novel characterization technique to detect a potential photoinduced increase in ionic conductivity based on capacitance measurements on fully integrated devices. The method is applied to a range of perovskite solar cells with different active layer materials. Remarkably, all measured samples show a clear signature of photoenhanced ion conductivity, posing fundamental questions on the underlying nature of the photosensitive mechanism.

Phthalocyanine-enabled technologies for water treatment and disinfection strategies

Water treatment and disinfection are critical factors in ensuring a safe and sustainable water supply. Phthalocyanines (Pcs), a class of versatile and robust organic compounds, have garnered significant attention for their application in various water treatment processes. This review paper offers a groundbreaking investigation of Pc-enabled technologies within the domain of water treatment applications. The core aim of this review is to meticulously analyze the chemical and optical properties of Pcs, elucidate their photosensitization mechanism and establish the crucial connection between their chemical structure and photodynamic efficacy. The various modes of Pcs application in water treatment processes - whether in solution, immobilized, or integrated into water treatment membranes - emphasizing the strategies for their integration and effectiveness in disinfection and decontamination has also been extensively investigated. Moreover, it sheds light on the latest advancements and challenges in the field, providing valuable insights into future research for employing Pcs in environmentally sustainable water treatment methods.

High-precision BaTiO3 piezoelectric ceramics via vat photopolymerization 3D printing

BaTiO3 ceramics with high precision and superior performance are fabricated by vat photopolymerization 3D printing technology. The curing behaviors and photosensitive mechanisms are systematically investigated. Through the optimization of printing parameters, BaTiO3 ceramics with a high relative density of 95 % and few defects are obtained. Notably, the sintered BaTiO3 ceramics exhibit impressive properties, including a high piezoelectric coefficient d33 of 201 pC/N and strong ferroelectric characteristics with a maximum polarization Pmax of 31.4 μC/cm2 and residual polarization Pr of 18.5 μC/cm2. More importantly, a series of complex BaTiO3 structures including the body-centered cubic lattice and triply periodic minimal surface (TPMS) structures are created perfectly with the feature size as fine as 75 μm. Compared with other reported BaTiO3 structures printed by vat photopolymerization and material extrusion technologies, this work realizes a much higher printing resolution. The excellent performance and high precision of these BaTiO3 ceramics make them great potential for practical applications in piezoelectric components.

Photosensitive Ag-contained CeO2-ZnO composites with non-stoichiometric matrix: Aspects of formation

It was shown the forming of Ag-contained ZnO-CeO2 composites occurs due to the complex decomposition and structure transformation of oxide materials and Ag-complexes. It allows us to realise one synthesised approach for obtaining photosensitive materials with different particle sizes, defects and kinds of architecture. The possible mechanisms of photosensitivity of these materials are determined. For composite nanoparticles (NP) with sizes up to 30 nm, the photosensitivity is connected with an abnormal decrease of bandgap energies at reducing NP sizes and an effective charge separation due to electron stocks on [Се3+…O2] centres and surface [Ce4+…O2-] oxidative centres formation. The appearance of the hyperfine structure pattern of six lines centred at g =2.002 and split by 93–94 G in the ESR spectra of the composite structure confirms the realization of this mechanism. For more big NP sizes of this composite, the surface plasmon resonance plays a more significant role in the material's photosensitive properties. The position of surface plasmon resonance depends on the kind of realised structure. The phase composition, temperature and reduction determine the type of structure (NPs/AgNPs ore core/Ag shell) that will be recognised in the Ag-contained CeO2-ZnO system.

Photosensitization mechanisms and detoxification effect of extracellular organic matters and intracellular organic matters in antibiotics photodegradation: A case of Microcystis aeruginosa

Although studies on algae-mediated photodegradation for antibiotic removal in exploring cleaner environmental systems have been reported, the specific mechanism of algal organic matter for improving antibiotic photodegradation remains unclear. Herein, we proposed the enhanced efficiency mechanism of extracellular organic matter (EOM) and intracellular organic matter (IOM) in Microcystis aeruginosa for promoting tetracycline (TC) photodegradation. The degradation efficiencies of EOM and IOM on TC were found to obtain 74.5 and 83.3%, respectively. Three-dimensional excitation emission matrix fluorescence spectroscopy combined with parallel factor analysis and Fourier transform infrared confirmed that the carbonyl compounds exhibited a significant contribution to the photosensitivity of EOM and IOM. Mechanistic investigation showed that 3EOM* and 3IOM* were identified as the principal active species in the photodegradation of TC. The EOM and IOM showed excellent detoxification ability for TC removal and remarkable tolerance in real water backgrounds, highlighting strong potential for applications. This study refined the photosensitization mechanism of algal organic matter degradation antibiotics, and offered methods and theoretical basis for environment-friendly and sustainable control of antibiotic pollutants.

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.

XMECP: Reaching State-of-the-Art MECP Optimization in Multiscale Complex Systems.

The Python-based program, XMECP, is developed for realizing robust, efficient, and state-of-the-art minimum energy crossing point (MECP) optimization in multiscale complex systems. This article introduces the basic capabilities of the XMECP program by theoretically investigating the MECP mechanism of several example systems including (1) the photosensitization mechanism of benzophenone, (2) photoinduced proton-coupled electron transfer in the cytosine-guanine base pair in DNA, (3) the spin-flip process in oxygen activation catalyzed by an iron-containing 2-oxoglutarate-dependent oxygenase (Fe/2OGX), and (4) the photochemical pathway of flavoprotein adjusted by the intensity of an external electric field. MECPs related to multistate reaction and multistate reactivity in large-scale complex biochemical systems can be well-treated by workflows suggested by the XMECP program. The branching plane updating the MECP optimization algorithm is strongly recommended as it provides derivative coupling vector (DCV) with explicit calculation and can equivalently evaluate contributions from non-QM residues to DCV, which can be nonadiabatic coupling or spin-orbit coupling in different cases. In the discussed QM/MM examples, we also found that the influence on the QM region by DCV can occur through noncovalent interactions and decay with distance. In the example of DNA base pairs, the nonadiabatic coupling occurs across the π-π stacking structure formed in the double-helix system. In contrast to general intuition, in the example of Fe/2OGX, the central ferrous and oxygen part contribute little to the spin-orbit coupling; however, a nearby arginine residue, which is treated by molecular mechanics in the QM/MM method, contributes significantly via two hydrogen bonds formed with α-ketoglutarate (α-KG). This indicates that the arginine residue plays a significant role in oxygen activation, driving the initial triplet state toward the productive quintet state, which is more than the previous knowledge that the arginine residue can bind α-KG at the reaction site by hydrogen bonds.

Positive profile of natural small molecule organic matters on emerging antivirus pharmaceutical elimination in advance reduction process: A deep dive into the photosensitive mechanism of triplet excited state compounds

Natural small molecular organic matter (NSOM), ubiquitous in natural waters and distinct from humic acid or fulvic acid, is a special type of dissolved organic matter (DOM) which is characterized as strong photosensitivity and simple molecular structure. However, little study had been directed on the role of NSOM in eliminating emerging contaminants in advanced reduction process (ARP). This study took three small molecular isomeric organic acids (p−hydroxybenzoic acid, pHBA; salicylic acid, SA; m−hydroxybenzoic acid, mHBA) as the representative substances of NSOM to explore these mechanisms on promoting Ribavirin (RBV, an anti COVID−19 medicine) degradation in ultraviolet activated sulfite (UV/Sulfite) process. The results demonstrated that the observed degradation rate constant of RBV (kobs-RBV) was 7.56 × 10−6 s−1 in UV/Sulfite process, indicating that hydrated electron (eaq−) from UV/Sulfite process could not effectively degrade RBV, while it increased by 178 and 38 times when pHBA and SA were introduced into UV/Sulfite process respectively, suggesting that pHBA and SA strongly promoted RBV degradation while mHBA had no promotion on RBV abatement in UV/Sulfite process. Transient absorption spectra and reactive intermediates scavenging experiment indicated that the triplet excited state pHBA and SA (3pHBA* and 3SA*) contributed to the degradation of RBV through non−radical process. Notably, eaq− played the role of key initiator in transforming pHBA and SA into their triplet states. The difference of kobs-RBV in UV/Sulfite/pHBA and UV/Sulfite/SA process was attributed to different generation pathways of 3pHBA* and 3SA* (high molar absorptivity at the wavelength of 254 nm and photosensitive cycle, respectively) and their second order rate constants towards RBV (kRBV-3pHBA* = 8.60 × 108 M−1 s−1 and kRBV-3SA* = 6.81 × 107 M−1 s−1). mHBA could not degrade RBV for its lack of intramolecular hydrogen bond and low molar absorptivity at 254 nm to abundantly transform into its triplet state. kobs-RBV increased as pH increased from 5.0 to 11.0 in UV/Sulfite/SA process, due to the high yield of eaq− in alkaline condition which promoted the generation of 3SA* and the stable of the absorbance of SA at 254 nm. By contrast, kobs-RBV underwent a process of first increasing and then decreasing in UV/Sulfite/pHBA process as the increase of pH, and its highest value achieved in a neutral condition. This lied in the exposure of eaq− increased as the increase of pH which promoted the generation of 3pHBA*, while the molar absorptivity of pHBA at 254 nm decreased as the increase of pH in an alkaline condition which inhibited the yield of 3pHBA*. The RBV degradation pathways and products toxicity assessment indicated that UV/Sulfite/pHBA had better detoxification performance on RBV than UV/Sulfite/SA process. This study disclosed a novel mechanism of emerging contaminants abatement through non-radical process in NSOM mediated ARP, and provide a wide insight into positive profile of DOM in water treatment process, instead of only taking DOM as a quencher of reactive intermediates.

Trap-Mediated Sensitization Governs Near-Infrared Emission from Yb3+-Doped Mixed-Halide CsPbClxBr3-x Perovskite Nanocrystals.

Understanding the photosensitization mechanisms in Yb3+-doped perovskite nanocrystals is crucial for developing their anticipated photonic applications. Here, we address this question by investigating near-infrared photoluminescence of Yb3+-doped mixed-halide CsPbClxBr3-x nanocrystals as a function of temperature and revealing its strong dependence on the stoichiometry of the host perovskite matrix. To explain the observed experimental trends, we developed a theoretical model in which energy transfer from the perovskite matrix to Yb3+ ions occurs through intermediate trap states situated beneath the conduction band of the host. The developed model provides an excellent agreement with experimental results and is further validated through the measurements of emission saturation at high excitation powers and near-infrared photoluminescence quantum yield as a function of the anion composition. Our findings establish trap-mediated energy transfer as a dominant photosensitization mechanism in Yb3+-doped CsPbClxBr3-x nanocrystals and open up new ways of engineering their optical properties for light-emitting and light-harvesting applications.

Preparation of N-Si-P-GaSe Heterojunctions Based on an Amorphous GaSe Layer Without Impurities and Study of Their Electrical Properties

The electrical and photoelectric properties of anisotype n-Si−p-GaSe heterojunctions obtained as a result of the deposition of a GaSe thin layer on a cold n-Si single crystal substrate by the thermal evaporation method were studied. It was determined that the height of the potential barrier in thermal annealing structures at T = 200 °C during t = 3 hours occurs due to the decrease in the density of states of local levels located near the Fermi level in the amorphous layer. The mechanism of photosensitivity in an isotype heterostructures was analyzed and it was found that the photosensitivity of the heterojunction increases as a result of a decrease in the surface density of state at the contact boundary of the components, by thermal means. The spectral distribution of the quantum efficiency in the n‑Si – p‑GaSe heterojunction was studied and their perspective was determined.

Lime Dermatitis.

Phytophotodermatitis are skin eruptions caused by contact with a plant substance and exaggerated by exposure to sunlight. They are due to the presence of furocoumarins (psoralens, xanthotoxins, and bergaptenes) in the plant and involve 2 mechanisms of skin photosensitivity: phototoxicity or photoallergy.

Irradiation of ZnPPIX Complexed with Bovine β-Lactoglobulin Causes Chemical Modifications and Conformational Changes of the Protein

Photosensitization of proteins mediated by chromophores is a mechanism commonly employed by nature and mimicked in a broad array of laboratory research and applications. Nature has evolved specialized complexes of proteins and photosensitizers (PS) that assemble to form photoreceptor proteins (PRP). These are used by many organisms in diverse processes, such as energy conversion, protection against photodamage, etc. The same concept has been used in laboratory settings for many applications, such as the stimulation of neurons or the selective depletion of proteins in a signaling pathway. A key issue in laboratory settings has been the relationship between the photooxidation of proteins and conformational changes in host proteins. For several years, we have been interested in creating non-native PRP using porphyrin PS. In this study, we investigated the self-assembled complex between zinc protoporphyrin IX (ZnPPIX) and bovine β-lactoglobulin (BLG) as a model of non-native PRP. Since BLG undergoes a significant conformational transition near physiological pH, the study was carried out at acidic (pH 5) and alkaline (pH 9) conditions where the two conformations are respectively prevalent. We employed a series of steady-state and time-resolved optical spectroscopies as well as gel electrophoresis to experimentally characterize the photosensitization mechanisms and their effect on the host protein. Our results show that ZnPPIX prompts light-dependent modifications of BLG, which appear to be much more significant at alkaline pH. The modifications seem to be driven by photooxidation of amino acid residues that do not lead to the formation of cross-links or protein fragmentation.

High-Performance Planar Field-Emission Photodetector of Monolayer Tungsten Disulfide with Microtips.

Monolayer tungsten disulfide (ML WS2 ) is believed as an ideal photosensitive material due to its small direct bandgap, large exciton/trion binding energy, high carrier mobility, and considerable quantum conversion efficiency. Compared with other photosensitive devices, planar field emission (FE)-type photodetectors with a full-plane structure should simultaneously have rapider switching speed and lower power consumption. In this work, ML WS2 microtips are fabricated by electron beam lithography (EBL) way and used to construct a planar FE-type photodetector. By optimization design, ML WS2 with three microtips can exhibit the maximum current density as high as 52 A cm-2 (@300V µm-1 ), and the largest photoresponsivity is up to 6.8 × 105 A W-1 under green light irradiation, superior to that of many other ML transition metal dichalcogenide (TMDC) detectors. More interestingly, ML WS2 devices with microtips can effectively solve the contradictory problem between large photoresponsivity and rapid switching speed. The excellent photoresponse performances of ML WS2 with microtips should be attributed to their high carrier mobility, sharp emission edge, ultrahigh quantum yield, and unique planar FE device structure. Ourresearch may shed new light on exploring the fabrication technology and photosensitive mechanism of two dimensional (2D) material-based planar FE photodetectors.

Spectroscopic study of methylene blue photophysical properties in biological media

A spectroscopic study of the photophysical properties of methylene blue (MB) in aqueous solutions was carried out. Absorption and fluorescence spectra as well as fluorescence lifetime were recorded. The concentration dependence of the intensity and shape of the spectra allowed establishing the ranges of MB concentrations for in vitro and in vivo studies at which aggregation is not observed (up to 0.01 mM, which corresponds to 3.2 mg/kg). Studies of photodegradation in biological media showed that photobleaching of more than 80% in plasma and culture media is observed already at a dose of 5 J/cm2 , while in water at this concentration and dose photobleaching is not yet observed, and at a dose of 50 J/cm2 photobleaching of MB is about 30%. It was found that in media containing proteins and having an alkaline pH, photobleaching occurs significantly faster than in neutral aqueous media. The ionic strength of the solution has no effect on the photobleaching rate. Such photobleaching is caused by the photodegradation of MB rather than the transition to the leucoform.The efficiency of singlet oxygen generation and photodynamic activity were evaluated in vitro. In the investigated range of MB concentrations, the efficiency of singlet oxygen generation is rather low, because positively charged MB binds to negatively charged cell membranes, which leads to a change in the type of photodynamic reaction. The emergence of other reactive oxygen species (ROS), different from singlet oxygen, in cells has been demonstrated. The generation of ROS and the low quantum yield of singlet oxygen generation indicate the tendency of MB to provide the type I photosensitization mechanism (electron transfer with the formation of semi-reduced and semi-oxidized MB+ radicals) rather than to the type II mechanism (energy transfer to oxygen with the formation of singlet oxygen) in biological media and in vivo.

Algal organic matter accelerates the photodegradation of tetracycline: Mechanisms, degradation pathways and product toxicity

Algae are ubiquitous in eutrophic surface waters and they play important roles in the sunlight-driven transformation of environmental contaminants. The present study aims to investigate the role of algal organic matter (AOM) separated from Microcystis aeruginosa at different growth stages in tetracycline photodegradation along with the related photosensitive mechanisms. The results showed that AOM, both extracellular organic matter (EOM) and intracellular organic matter (IOM) at different growth phases all promote tetracycline photodegradation, but in different ways and performances. EOM exerts greater photolysis effectiveness than IOM with logarithmic phase (LP) organic matter more effective than that from the algae’s declining growth phase (DP). The promoting efficiencies of tetracycline photodegradation by four AOM types follow the order of LP-EOM > DP-EOM > LP-IOM > DP-IOM, accounting for 1.0420 h−1, 0.8281 h−1, 0.6527 h−1 and 0.4974 h−1, respectively. Such discrepant effectiveness is related to the different chemical constituents and structures of EOM and IOM. Scavenger experiments further demonstrated that triplet-state AOM (3AOM*) contributes the most to tetracycline degradation (30.01%∼48.51%), followed by OH (1.68%∼10.66%) and 1O2 (1.34%∼10.08%). The steady-state concentrations of 3AOM*, OH and 1O2 were measured with probe compounds in the range of 13.950 ∼ 155.234 L/mol, 2.494 × 10−17 ∼ 27.636 × 10−17 M and 1.410 × 10−14 ∼ 26.493 × 10−14 M, respectively. Interestingly, the photolytic intermediates show increasing toxicity to Photobacterium phosphoreum at first which then decreases with the extension of irradiation. These results provide comprehensive insight into the transport and environmental behavior of antibiotics in a eutrophic aqueous environment.

Front Cover: Unveiling Photodegradation and Photosensitization Mechanisms of Unconjugated Pterins (Chem. Eur. J. 29/2023)

Pterins can be considered as biological jacks-of-all-trades. Firstly identified as pigments in butterfly wings, they are nowadays well-known cofactors in the synthesis of NO, nucleotides, and amino acids, markers in cell-mediated immune responses. Yet, not all of their properties are beneficial. Some of these pterins contribute to the photochemical evolution of vitiligo, a depigmentation disorder. Enhanced oxidative stress and cytotoxicity lead to melanocyte destruction and tissue damage. More information can be found in the Research Article by E. M. Arpa and I. Corral (DOI: 10.1002/chem.202300519).

Unveiling Photodegradation and Photosensitization Mechanisms of Unconjugated Pterins

Invited for the cover of this issue are Enrique M. Arpa (Linköping University) and Inés Corral (Universidad Autónoma de Madrid). The image depicts two examples where pterin chemistry is relevant, the wing coloration of some butterflies and the cytotoxic action in vitiligo. Read the full text of the article at 10.1002/chem.202300519.

Unveiling Photodegradation and Photosensitization Mechanisms of Unconjugated Pterins.

Unconjugated pterins are ubiquitous molecules participating in countless enzymatic processes and potentially involved in the photosensitization of singlet oxygen, amino acids, and nucleotides. Following electronic excitation with UV-A light, some of these pterins degrade, producing hydrogen peroxide as the main side product. This process, that is known to take place in vivo, contributes to oxidative stress and melanocyte destruction in vitiligo. In this work, we present for the first time mechanistic insight to the formation of transient triplet species which simultaneously trigger Type I and Type II photosensitizing processes and the initiation of degradation processes. Our calculations reveal that photodegradation of 6-biopterin, which accumulates in the skin of vitiligo patients, leads to 6-formylpterin via retro-aldol reaction, and subsequently to 6-carboxypterin through a water-mediated aldehyde oxidation. Additionally, we show that the changes in the photosensitizing potential of these systems with pH come from the modulation of their excited-state redox potentials.

An intercommunicated nanosystem for dual delivery.

Here, we describe the design of a novel particle-to-particle intercommunicated nanosystem for dual delivery, triggered by physical and chemical inputs. The nanosystem was composed of an Au-mesoporous silica Janus nanoparticle loaded with paracetamol, mechanized with light-sensitive supramolecular gates at the mesoporous face and functionalized on the metal surface with the enzyme acetylcholinesterase. The second component was a mesoporous silica nanoparticle loaded with rhodamine B and gated with thiol-sensitive ensembles. Upon irradiation of this nanosystem with a near-UV light laser, an analgesic drug was released from the Janus nanomachine due to disassembling of the photosensitive gating mechanism. Further addition of N-acetylthiocholine leads to the enzymatic production of thiocholine at the Janus nanomachine, thus acting as a "chemical messenger" causing the disruption of the gating mechanism at the second mesoporous silica nanoparticle with the subsequent dye release.

Application of Antimicrobial Photodynamic Therapy for Inactivation of Acinetobacter baumannii Biofilms.

Acinetobacter baumannii is a dangerous hospital pathogen primarily due to its ability to form biofilms on different abiotic and biotic surfaces. The present study investigated the effect of riboflavin- and chlorophyllin-based antimicrobial photodynamic therapy, performed with near-ultraviolet or blue light on the viability of bacterial cells in biofilms and their structural stability, also determining the extent of photoinduced generation of intracellular reactive oxygen species as well as the ability of A. baumannii to form biofilms after the treatment. The efficacy of antimicrobial photodynamic therapy was compared with that of light alone and the role of the photosensitizer type on the photosensitization mechanism was demonstrated. We found that the antibacterial effect of riboflavin-based antimicrobial photodynamic therapy depends on the ability of photoactivated riboflavin to generate intracellular reactive oxygen species but does not depend on the concentration of riboflavin and pre-incubation time before irradiation. Moreover, our results suggest a clear interconnection between the inactivation efficiency of chlorophyllin-based antimicrobial photodynamic therapy and the sensitivity of A. baumannii biofilms to used light. In summary, all the analyzed results suggest that riboflavin-based antimicrobial photodynamic therapy and chlorophyllin-based antimicrobial photodynamic therapy have the potential to be applied as an antibacterial treatment against A. baumannii biofilms or as a preventive measure against biofilm formation.