Photochem

Due to its favorable excited-state physicochemical properties, indium oxide (In₂O₃) has widely captured attention as a potentially great photocatalyst. However, an inferior charge separation efficiency limits its application. Recently, an increasing amount of evidence has demonstrated that the construction of surface defects is an effective strategy to boost photocatalytic performances. In this work, a ruthenium (Ru) species was successfully introduced into the lattice of In₂O₃ nanoparticles through co-precipitation and thermal treatment. It was found that the content of surface oxygen vacancies was directly related to the amount of Ru³⁺ doping, which further determines the separation efficiency of photogenerated carriers. As a result, the 0.5% Ru-In₂O₃ samples enriched with oxygen vacancies exhibit dramatically enhanced photocatalytic dehalogenation performances of decabromodiphenyl ether and hexabromobenzene, about four times higher than that of the pure In₂O₃ nanoparticles. This study emphasized the significance of the surface defects of the photocatalyst and may provide a valuable strategy to prepare highly active photocatalysts for photocatalytic dehalogenation reactions. Full article

In the continuation of our sustained interest in porphyrin-based dendrimers and their use as luminescent photosensitizers for two-photon photodynamic therapy (2P-PDT), we wondered about the effect of changing the connectors in our macromolecular structures. We also wanted to initiate preliminary studies on meso-tetraarylporphyrins decorated with more electron-releasing arms. Thus, various meso-tetrafluorenylporphyrin-cored star-shaped and dendrimeric derivatives have been synthesized and characterized, as well as their zinc(II) complexes. In the new dendrimeric derivatives, the peripheral fluorenyl units of the dendrons are linked to the inner core either by N-phenylcarbazole (C_Cbz) or triphenylamine (C_Tpa) connectors instead of the more classic 1,3,5-phenylene (C_Ph) linkers previously used by us. Selected linear and non-linear optical (LO and NLO) properties were then determined for these compounds via absorption or emission studies and by two-photon excited fluorescence (TPEF) measurements. It was found that the C_Cbz-containing dendrimer, which has the most rigid structure, exhibits a significantly lower two-photon absorption (2PA) cross-section than its C_Tpa analog, presenting a more flexible structure while rather similar luminescence and singlet oxygen activation quantum yields are found for both. The origin of this unexpected discrepancy is briefly discussed based on our photophysical data. It is then demonstrated that the latter dendrimer also outperforms several closely related dendrimers in terms of 2PA action cross-section and 2PA-oxygen sensitization, making its molecular architecture quite appealing for developing new 2PA photosensitizers suited to theranostic uses. Full article

When volatile alkenes are emitted into the atmosphere, they are rapidly removed by oxidizing agents such as hydroxyl radicals and ozone. The latter reaction is termed ozonolysis and is an important source of Criegee intermediates (CIs), i.e., carbonyl oxides, that are implicated in enhancing the oxidizing capacity of the troposphere. These CIs aid in the formation of lower volatility compounds that typically condense to form secondary organic aerosols. CIs have attracted vast attention over the past two decades. Despite this, the effect of their substitution on the ground and excited state chemistries of CIs is not well studied. Here, we extend our knowledge obtained from prior studies on CIs by CF₃ substitution. The resulting CF₃CHOO molecule is a CI that can be formed from the ozonolysis of hydrofluoroolefins (HFOs). Our results show that the ground state unimolecular decay should be less reactive and thus more persistent in the atmosphere than the non-fluorinated analog. The excited state dynamics, however, are predicted to occur on an ultrafast timescale. The results are discussed in the context of the ways in which our study could advance synthetic chemistry, as well as processes relevant to the atmosphere. Full article

A Sn(IV) meso-tetra(4-methylthiolphenyl) N-confused porphyrin (4-Sn) complex was prepared to facilitate a comparison of the photophysicochemical and singlet oxygen photosensitiser properties of a series of Sn(IV) complexes of meso-4-methylthiolphenyl-substituted porphyrin, corrole, chlorin, and N-confused porphyrin. 4-Sn has an unusually high singlet oxygen quantum (Φ_Δ) yield of 0.88, markedly higher than the Φ_Δ values of the other complexes in this series. A Thorlabs M660L4 LED (280 mW · cm⁻²) was used to study the photodynamic activity of Sn-4 against the MCF-7 cancer cell line through irradiation at 660 nm for 30 min. The IC₅₀ value was calculated to be 1.4 (± 0.8) µM, markedly lower than the previously reported values for the rest of the series. Photodynamic antimicrobial activity was also determined against Staphylococcus aureus and Escherichia coli, and 4-Sn was found to deactivate both Gram-(+) and Gram-(−) bacteria despite the absence of cationic charges on the ligand structure. Full article

The potential of E–Z photoisomerization in molecular organic light-to-thermal conversion and storage in an E–styryl merocyanine system was studied in a polar acidic medium. A photoswitchable styryl merocyanine dye (E)-2-(2-(2-hydroxynaphthalen-1-yl)vinyl)-3,5-dimethylbenzo[d]thiazol-3-ium iodide was synthesized for the first time. The reversible E–Z photoisomerisation of the dye was investigated using UV-Vis spectroscopy and DFT calculations. E–Z isomerization was induced through the use of visible light irradiation (λ = 450 nm). The obtained experimental and theoretical results confirm the applicability of the Z and E isomers for proton-triggered light harvesting. Full article

Benzophenones (BPs) frequently occur in water environments, and they are able to both screen UV light and to sensitize reactive intermediate (RI) production. However, BPs have largely been overlooked as a background water component when studying photodegradation of co-existing organic micropollutants (OMPs). Therefore, in this study, we investigated the influence of BP and its derivative oxybenzone (BP3) on the degradation of the co-existing model OMP sulfamethoxazole (SMX). A series of photodegradation experiments were conducted covering a range of BPs concentrations in μg/L levels, and the degradation of 1.00 μM of SMX was studied. The addition of BP at 0.10 μM, 0.25 μM, and 0.30 μM, and BP3 at 0.10 μM and 0.25 μM, significantly increased the first order degradation rate constant of 1.00 μM of SMX (k_obs(BP)) by 36.2%, 50.0%, 7.3%, 31.5%, and 36.2% respectively, compared to that in the absence of any BPs. The maximum indirect photodegradation induced by BP and BP3 reached 33.8% and 27.7%, respectively, as a percentage of the observed SMX degradation rate at the [BPs]/[SMX] ratio of 0.25. In general, triplet excited dissolved organic matter (³SMX*, ³BP*, and ³BP3*) played the major role in the photosensitizing ability of BPs. The results further implied that the increase of SMX degradation at the molar ratio of 0.25 was possibly due to ³BP* for the mixture of SMX and BP. Overall, this study revealed the sensitizing ability of BP and BP3 on the co-existing OMP, SMX, in water for the first time. Our findings can be applied to other BP type UV filters which are similar to BP and PB3 in molecular structure. Full article

We have reported tetradentate ligands (salophen) coordinated with N and O atoms that led to the Cu (II) complexes. These Cu (II) complexes (C-1 and C-2) were firstly established by using elemental analysis and confirmed by mass spectra. At the same time, the characterization of C-1 and C-2 complexes is performed by using several spectroscopic methods and morphological analysis. The bandgap values of the C-1 and C-2 complexes are evaluated with UV-vis DRS spectra. The PL spectral data and photocurrent curves clearly indicated the small recombination rate of the hole–electron pair. The synthesized C-1 and C-2 complexes’ photocatalytic properties were examined for the degradation of cationic dyes such as methylene blue (MB λ_max.= 654 nm) and methyl violet (MV λ_max.= 590 nm) below visible-light action. The C-2 complex is more active than the C-1 complex because of its high photostability, small band-gap energy, and low recombination rate for hole–electron pair separation, and improved visible-light character, which encourages the generation of hydroxyl radical species throughout the photodegradation process. Scavenger probes were used to identify the dynamic species for the photodegradation of dyes, and a mechanism investigation was established. Full article

In this tutorial review, we intend to provide the reader with a comprehensive introduction to the photophysical properties of organic compounds with a specific focus on anthracene and its derivatives. Anthracene-based building blocks have attracted the attention of chemists due to their intrinsic luminescent properties. A deep understanding of their interaction with light, including the mechanisms of emission (luminescence, i.e., fluorescence or phosphorescence) and quenching, is crucial to design and generate compounds with precise properties for further applications. Thus, the photophysical properties of different types of aggregates, both in the ground state (J- and H-type) and in the exited state (e.g., excimer, exciplex) will be discussed, finishing with a few examples of dyads and triads. Full article

Acridine orange (AO) is a metachromatic fluorescent dye that stains various cellular compartments, specifically accumulating in acidic vacuoles (AVOs). AO is frequently used for cell and tissue staining (in vivo and in vitro), mainly because it marks different cellular compartments with different colors. However, AO also forms triplet excited states and its role as a photosensitizer is not yet completely understood. Human immortalized keratinocytes (HaCaT) were incubated for either 10 or 60 min with various concentrations (nanomolar range) of AO that were significantly lower than those typically used in staining protocols (micromolar). After incubation, the cells were irradiated with a 490 nm LED. As expected, cell viability (measured by MTT, NRU and crystal violet staining) decreased with the increase in AO concentration. Interestingly, at the same AO concentration, altering the incubation time with HaCaT substantially decreased the 50% lethal dose (LD₅₀) from 300 to 150 nM. The photoinduced cell death correlated primarily with lysosomal disfunction, and the correlation was stronger for the 60 min AO incubation results. Furthermore, the longer incubation time favored monomers of AO and a distribution of the dye to intracellular sites other than lysosomes. Studies with mimetic systems indicated that monomers, which have higher yields of fluorescence emission and singlet oxygen generation, are favored in acidic environments, consistent with the more intense emission from cells submitted to the longer AO incubation period. Our results indicate that AO is an efficient PDT photosensitizer, with a photodynamic efficiency that is enhanced in acidic environments when multiple intracellular locations are targeted. Consequently, when using AO as a probe for live cell tracking and tissue staining, care must be taken to avoid excessive exposure to light to avoid undesirable photosensitized oxidation reactions in the tissue or cell under investigation. Full article

Ultraviolet-induced photodissociation and photo-isomerization of the three most stable conformers (SSC, GAC, and AAT) of glycolic acid are investigated in a low-temperature solid argon matrix using FTIR spectroscopy and employing laser radiation with wavelengths of 212 nm, 226 nm, and 230 nm. The present work broadens the wavelength range of photochemical studies of glycolic acid, thus extending the understanding of the overall photochemistry of the compound. The proposed kinetic model for the photodissociation of glycolic acid proceeds from the lowest energy conformer (SSC). The model suggests that ultraviolet light induces isomerization only between the SSC and GAC conformers and between the SSC and AAT conformers. The relative reaction rate coefficients are reported for all proposed reactions. These results suggest that the direct photodissociation of GAC and AAT conformer does not occur in an argon matrix. The main photodissociation channel via the SSC conformer produces formaldehyde–water complexes. The proposed photodissociation mechanism emphasizes that the conformers’ relative abundancies can significantly affect the photodissociation rate of the molecule. For example, in the case of high relative GAC and AAT concentrations, the ultraviolet photodissociation of glycolic acid requires the proceeding photo-isomerization of GAC and AAT to SSC. Full article

Under simulated light irradiation, the aerobic oxidation of benzylamine to N,N-benzylidenebenzylamine was carried out as a model reaction to investigate the photocatalytic activity of a hydrothermally prepared composite based on BiOF and BiFeO₃ materials. The prepared photocatalysts were characterized using several spectroscopic techniques, such as powder X-ray diffraction (PXRD), diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and Fourier transform infrared spectroscopy (FTIR). Band gap analysis showed that the composite exhibits a band gap that lies in the UV region (3.5 eV). Nonetheless, pristine BiOF and BiFeO₃ exhibited band gaps of 3.8 eV and 2.15 eV, respectively. N,N-benzylidenebenzylamine was selectively achieved with a high conversion yield of ~80% under atmospheric conditions in which the product was confirmed using ¹H-NMR, ¹³C-NMR, and FTIR spectroscopic techniques. Various control experiments were conducted to further confirm the enhanced photocatalytic performance of the reported composite. Full article

Multidrug resistance of pathogenic microflora is a serious threat to the modern community looking for new approaches to treating superinfections. In this sense, antimicrobial photodynamic therapy (aPDT) is an effective and safe technique considered to be a promising alternative or an important supplement to the traditional clinically applied methods for inactivating antibiotic resistant pathogens. Macroheterocyclic photosensitizers (PS) of three generations are proposed for clinical practice. They are known as the key compounds for PDT able to be localized selectively in microbial cells and to be activated with the red light producing toxic reactive oxygen species (ROS). However, these neutral and anionic PSs possess low affinity towards the outer lipopolysaccharide membrane of Gram-negative bacteria and, consequently, poor ability to kill these pathogens under irradiation. In contrast, cationic PSs containing one or more charged groups, especially those bound to an appropriate carrier, provide efficient inactivation of microorganisms. In this paper, we focus on the study of photophysics, aggregation and photoinduced antimicrobial activity of the water-soluble derivative of deuteroporphyrin-IX, a blood group porphyrin, bearing two cationic trialkylammonium fragments. This potential photosensitizing agent is found to generate singlet oxygen in a non-polar environment and forms stable nano-sized molecular complexes with passive non-ionic carrier Tween 80, localizing in an aqueous surfactant solution as a non-aggregated form in the surface micellar layer. Two different modes of PS/Tween 80 binding characterized by their own stability constants and interaction stoichiometry are observed. Microbiological experiments clearly demonstrate that the increased permeability of the outer bacterial membrane caused by the application of the intramicellar form of the photosensitizer or addition of some potentiation agents leads to pronounced light phototoxicity of the pigment against antibiotic-resistant nosocomial strains of Gram-negative bacterial pathogens. Full article

The application domain of deep learning (DL) has been extended into the realm of nanomaterials, photochemistry, and optoelectronics research. Here, we used the combination of a computer vision technique, namely convolutional neural network (CNN), with multilayer perceptron (MLP) to obtain the far-field optical response at normal incidence (along cylinder axis) of concentric cylindrical plasmonic metastructures such as nanorods and nanotubes. Nanotubes of Si, Ge, and TiO₂ coated on either their inner wall or both their inner and outer walls with a plasmonic noble metal (Au or Ag) were thus modeled. A combination of a CNN and MLP was designed to accept the cross-sectional images of cylindrical plasmonic core-shell nanomaterials as input and rapidly generate their optical response. In addition, we addressed an issue related to DL methods, namely explainability. We probed deeper into these networks’ architecture to explain how the optimized network could predict the final results. Our results suggest that the DL network learns the underlying physics governing the optical response of plasmonic core-shell nanocylinders, which in turn builds trust in the use of DL methods in materials science and optoelectronics. Full article

The linear and nonlinear optical properties of two quadrupolar bithiophenes and two quadrupolar cyclopentadithiophenes have been investigated. At the 5,5′ positions of the central bi/dithiophene units, the molecules possess 1,4-phenylalkynyl groups that bear either electron-donating (NPh₂) or electron-withdrawing (SO₂CF₃) groups. The optical properties were experimentally studied and modelled via quantum chemistry computations of key configurations and conformations. All the compounds show good light harvesting efficiency due to their strong absorption in the visible range. These fluorescent compounds are also good two-photon absorbers in the NIR range that can photosensitize oxygen in toluene. DFT calculations reveal that the mixtures of conformers in a solution show similar linear optical properties. TD-DFT calculations reproduce the experimental spectroscopic data fairly well, including vibronic couplings in the fluorescence spectra. The lowest excited state for two-photon absorption corresponds to the S₂ state. The roles of the SO₂CF₃ and NPh₂ terminal groups on the nonlinear response were analyzed for possible bio-oriented applications, with the cyclopentadithiophenes showing the most promising figures of merit. Full article

Here we present simple fluorophores based on the pyridine core, obtained with straightforward synthetic methodologies. These compounds present in solution absorption maxima in the UV region and fluorescence emission of between 300 and 450 nm, depending on the solvent and chemical structure of the fluorophore. The nature of the solvent was shown to play a fundamental role in their excite-state deactivation, which allowed successful exploration of these compounds as optical sensors for benzene and fuel adulteration in gasoline. In ethanolic solution, upon the addition of benzene, in general the fluorophores presented fluorescence quenching, where a linear correlation between the emission intensity and the amount of benzene (quencher) was observed. In addition, the application of an optical sensor for the detection of fuel adulteration in commercial standard and premium gasoline was successfully presented and discussed. Theoretical calculations were also applied to better understand the solvent–fluorophore interactions. Full article

In the present study, we investigated the photooxidation of the biomimetic model of C-terminal methionine, N-Acetyl-Methionine (N-Ac-Met), sensitized by a 3-Carboxybenzophenone (3CB) excited triplet in neutral and basic aqueous solutions. The short-lived transient species that formed in the reaction were identified and quantified by laser flash photolysis and the final stable products were analyzed using liquid chromatography coupled with high-resolution mass spectrometry (LC-MS) and tandem mass spectrometry (MSMS). Based on these complementary methods, it was possible to calculate the quantum yields of both competing reactions, and the deprotonation was found to be favored over decarboxylation (for neutral pH: ϕ_-H = 0.23 vs. ϕ_-CO2 = 0.09, for basic pH: ϕ_-H = 0.23 vs. ϕ_-CO2 = 0.05). Findings on such a model system, which can possibly mimic the complex protein environment, are important in understanding complicated biological systems, for example, the studied compound, N-Ac-Met, can, to some extent, mimic the methionine in the C-terminal domain of β-amyloid, which is thought to be connected with the pathogenesis of Alzheimer’s disease. Full article

Gliosarcoma (GS) is a primary malignant neoplasm of the central nervous system, treated with an unfavorable prognosis with surgery, radiotherapy, and chemotherapy. The treatment for GS consists of surgical resection, almost always accompanied by radiotherapy and/or chemotherapy, given the invasive behavior of the tumor. Photodynamic Therapy (PDT) is studied as an alternative method that combines light, a photosensitizer (PS), and molecular oxygen. This study aimed to compare the effects of PDT using the photosensitizers Fotoenticine (FTC) and Photodithazine (PDZ) at low concentrations and fluences. For this study, 9 L/lacZ cells, concentrations of 1.55 µg mL⁻¹, 12.5 µg mL⁻¹, and 50 µg mL⁻¹ of chlorins and fluences of 1, 5, and 10 J/cm² were used. A test was also carried out with Trypan Blue in L929 cells at the mentioned concentrations at 5 J/cm². Both chlorins were internalized in the cytoplasm, with a significant reduction in viability (>95%) in almost all groups and altered cell adhesion and morphology after PDT. HSP70 expression decreased in both PS, while HSP27 increased only in PDT with FTC, and although there was a change in cell adhesion in the 9 L/LacZ lineage it was not observed in the L929 fibroblast lineage. Both chlorins were effective, highlighting the concentration of 50 µg mL⁻¹ at the fluence of 5 J/cm²; according to the present study, the PDZ showed better results. Full article

A combined spectroscopic and computational approach has been used to study in detail the complexation between Ga(III) and ARS in solution. The NMR results revealed the formation of four Ga(III)/ARS complexes, at pH 4, differing in their metal:ligand stoichiometries or configuration, and point to a coordination mode through the ligand positions C-1 and C-9. For equimolar metal:ligand solutions, a 1:1 [Ga(ARS)(H₂O)₄]⁺ complex was formed, while for 1:2 molar ratio solutions, a [Ga(ARS)₂(H₂O)₂]⁻ complex, in which the two ligands are magnetically equivalent, is proposed. Based on DFT calculations, it was determined that this is a centrosymmetric structure with the ligands in an anti configuration. For solutions with a 1:3 molar ratio, two isomeric [Ga(ARS)₃]³⁻ complexes were detected by NMR, in which the ligands have a mer and a fac configuration around the metal centre. The DFT calculations provided structural details on the complexes and support the proposal of a 1,9 coordination mode. The infrared spectroscopy results, together with the calculation of the infrared spectra for the theoretically proposed structures, give further support to the conclusions above. Changes in the UV/vis absorption and fluorescence spectra of the ligand upon complexation revealed that ARS is a highly sensitive fluorescent probe for the detection of Ga(III). Full article