Photochem

Under solvothermal conditions, the Zn(II) complexes formed from salophen-based ligands with N and O donor atoms are reported. These Zn(II) complexes were initially confirmed through elemental analysis and supported by mass spectral data. The purity of the ligands and Zn(II) complexes was confirmed by using NMR spectral studies. The functional group complexation was established by FT-IR analysis. Additional supportive information about the complexes is also reported through molar conductance and thermal studies. The bandgap energies of the ligands and Zn(II) complexes are estimated with UV-visible DRS studies. The rate of recombination of hole–electron pairs is directly related to photocatalytic activity, which is confirmed by using emission spectral analysis. The surface metaphors for ligands and complexes are obtained from FESEM analysis. These new sequences of Zn(II) complexes were used for the photooxidation of 2,2′-(ethyne-1,2-diyl)dianiline and its derivatives. Mechanistic studies on the fast degradation of dyes were supported in the presence of several scavengers. The rapid photooxidation process in the presence of [Zn(CPAMN)] has been demonstrated, and a highly efficient photocatalyst for the photooxidation of 2,2′-(ethyne-1,2-diyl) dianiline has been proposed. Furthermore, the experimental findings are supported by the DFT studies. Full article

This paper describes the photophysical properties of a series of seven selected examples of 5-(alkyl/aryl/heteroaryl)-2-methyl-7-(trifluoromethyl)pyrazolo[1,5-a]pyrimidines (3), which contain alkyl, aryl, and heteroaryl substituents attached to the scaffolds of 3. Given the electron-donor groups and -withdrawing groups, the optical absorption and emission in the solid state and solution showed interesting results. Absorption UV–Vis and fluorescence properties in several solvents of a pyrazolo[1,5-a]pyrimidines series were investigated, and all derivatives were absorbed in the ultraviolet region despite presenting higher quantum emission fluorescence yields in solution and moderate emission in the solid state. Moreover, the solid-state thermal stability of compounds 3a–g was assessed using thermogravimetric analysis. The thermal decomposition profile showed a single step with almost 100% mass loss for all compounds 3. Additionally, the values of T_0.05 are considerably low (72–187 °C), especially for compound 3a (72 °C), indicating low thermal stability for this series of pyrazolo[1,5-a]pyrimidines. Full article

We report herein the linear optical properties of some extended 2,4,6-triphenyl-s-triazines of formula 2,4,6-[(1,4-C₆H₄)C≡C(4-C₆H₄X)]₃-1,3,5-(C₃H₃N₃) (3-X; X = NO₂, CN, OMe, NMe₂, NPh₂) and related analogues 4 and 7-X (X = H, NPh₂), before briefly discussing their two-photon absorption (2PA) cross-sections. Their 2PA performance is discussed in relation to 2PA values previously measured for closely related octupoles such as N,N′,N″-triphenylisocyanurates (1-X, 5, and 6-X) or 1,3,5-triphenylbenzenes (2-X). While s-triazines are usually much better two-photon absorbers in the near-IR range than these molecules, especially when functionalised by electron-releasing substituents at their periphery, they present a decreased transparency window in the visible range due to their red-shifted first 1PA peak, in particular when compared with corresponding isocyanurates analogues. In contrast, due to their significantly larger two-photon brilliancy, 2,4,6-triphenyl-s-triazines appear more promising than the latter for two-photon fluorescence bio-imaging purposes. Rationalisation of these unexpected outcomes is proposed based on DFT calculations. Full article

A synthesis is provided of the roles of the carotenoids zeaxanthin and/or lutein in opposing (i) photodamage in plants, (ii) photodamage to the human eye as well as cognitive dysfunction and a host of human diseases and disorders, and (iii) damage to extremophile microorganisms in the most inhospitable environments on earth. Selected examples are used to examine microenvironments and basic biological structures with which these xanthophylls associate as well as the effect of the organisms’ external environment. An overview is presented of the multiple principal mechanisms through which these xanthophylls can directly or indirectly impact organisms’ internal redox (oxidant/antioxidant) balance that provides input into the orchestration of growth, development, and defense in prokaryotic microorganisms, plants, and humans. Gaps in the research are identified, specifically with respect to the need for further in vivo assessment of the mechanisms. Full article

The kinetics of relaxation of high-lying electronic states of porphycene (porphyrin isomer) embedded in different cryogenic matrices were studied using picosecond time-resolved fluorescence (TRF) and transient absorption (TA) techniques. The molecule was excited into the Soret band, i.e., with a large energy excess compared to that of the lowest (Q) excited state. The TRF and TA time profiles obtained for porphycene embedded in argon and methane matrices were remarkably different: the overall relaxation in argon occurred in 64 ps, whereas the corresponding value for methane matrix was 18 ps. Analysis of the evolution over time of different spectral ranges of TRF spectra indicates the multidimensional character of relaxation kinetics. Full article

The solar motivated photoelectrochemical (PEC), used in water splitting systems, shows superior talent in converting solar energy in the form of cleaning and in sustaining a chemical energy evolution. PEC systems present by integrating a photoelectrode, which involves light-harvesting to absorb solar energy, thereby introducing an interlayer for the transformation of photogenerated electrons and holes, along with a co-catalyst to trigger oxidation and reduce the chemical reactions. In this review, we describe a variety of two-dimensional (2D) layered photoanodes and photocathodes, such as graphitic carbon nitrides, transition metal dichalcogenides, layered double hydroxides, MXenes, and co-catalysts for the assembly of combined photoelectrodes belonging to oxygen evolution and/or hydrogen evolution chemical reactions. The basic principles of PEC water splitting associated with physicochemical possessions relating to photoelectrodes unified with catalytic chemical reactions have been investigated. Additionally, the mechanisms attributing to a relationship with 2D photoelectrodes have been incorporated as a supplementary discussion. The improvement strategies, which include the construction of heterostructures, surface functionalization, and formations of heterojunctions, have also been discussed. The issues and challenges relevant to the field have been acknowledged for facilitating future research, indicating optimized conversion activity corresponding to PEC water splitting. Full article

Phosphorescence of C₅N⁻ was discovered following the ArF-laser (193 nm) photolysis of cyanodiacetylene (HC₅N) isolated in cryogenic argon, krypton, and xenon matrices. This visible emission, with an origin around 460 nm, is vibrationally resolved, permitting the measurement of frequencies for eight ground-state fundamental vibrational modes, including the three known from previous IR absorption studies. Phosphorescence lifetime amounts to tens or even hundreds of ms depending on the matrix host; it is five times longer than in the case of HC₅N. Full article

The interaction of polycyclic aromatic hydrocarbons (PAHs) with water is of paramount importance in atmospheric and astrophysical contexts. We report here a combined theoretical and experimental study of corannulene-water interactions in low temperature matrices and of the matrix’s influence on the photoreactivity of corannulene with water. The theoretical study was performed using a mixed density functional based tight binding/force field approach to describe the corannulene-water clusters trapped in an argon matrix, together with Born-Oppenheimer molecular dynamics to determine finite-temperature IR spectra. The results are discussed in the light of experimental matrix isolation FTIR spectroscopic data. We show that in the solid phase, $\pi$ isomers of (C${}_{20}$H${}_{10}$)(H${}_2$O)${}_n$, with n = 2 or 3, are energetically favored. These $\pi$ complexes are characterized by small shifts in corannulene vibrational modes and large shifts in water bands. These $\pi$ structures, particularly stable in the case of the water trimer where the water cluster is trapped “inside” the corannulene bowl, may account for the difference in photoreactivity of non-planar–compared to planar–PAHs with water. Indeed, planar PAHs such as pyrene and coronene embedded in H${}_2$O:Ar matrices form $\sigma$ isomers and react with water to form alcohols and quinones under low energy UV irradiation, whereas no photoreactivity was observed for corannulene under the same experimental conditions. Full article

An effective way to obtain the optimal parameters of a process or experiment is the response surface method. Using the Box–Behnken design further decreases the number of experiments needed to obtain sufficient data to obtain a reliable equation. From the equation, it is possible to predict the behavior of the response with respect to the combination of variables involved. In this study we evaluated the photocatalytic activity of the synthesized TiO₂ for the degradation of acetaminophen, a frequently used and uncontrolled drug that has been detected with increasing frequency in wastewater effluents. The variables used for this study were pH, contaminant concentration (acetaminophen) and catalyst dose. We found, with a 95% confidence level, that 99% of the contaminant can be degraded to pH 10, contaminant to 35 mg/L and a catalyst dose of 0.15 g TiO₂. Full article

Matrix isolation studies were carried out for porphycene, an isomer of porphyrin, embedded in solid nitrogen and xenon. The external heavy atom effect resulted in nearly a 100% population of the triplet state and in the appearance of phosphorescence, with the origin located at 10163 cm⁻¹. This energy is much lower than that corresponding to the T₁ position in porphyrin. This difference could be explained by postulating that the orbital origin corresponds in both isomers to the second excited singlet state, which lies much closer to S₁ in porphycene. Most of the vibrational frequencies observed in the phosphorescence spectrum correspond to totally symmetric modes, but several ones were assigned to the out-of-plane Bg vibrations. These bands are not observed in fluorescence, which suggests their possible role in vibronic-spin-orbit coupling. Full article

The rational design of cyanine dyes for the fine-tuning of their photophysical properties undoubtedly requires theoretical considerations for understanding and predicting their absorption and fluorescence characteristics. The present study aims to assess the applicability and accuracy of several DFT functionals for calculating the absorption and fluorescence maxima of monomethine cyanine dyes. Ten DFT functionals and different basis sets were examined to select the proper theoretical model for calculating the electronic transitions of eight representative molecules from this class of compounds. The self-aggregation of the dyes was also considered. The pure exchange functionals (M06L, HFS, HFB, B97D) combined with the triple-zeta basis set 6-311+G(2d,p) showed the best performance during the theoretical estimation of the absorption and fluorescent characteristics of cyanine dyes. Full article

Laser-ablated polyyne molecules, H(C≡C)_nH, were separated by size in solutions and co-condensed with excess hexane molecules at a cryogenic temperature of 20 K in a vacuum system. The solid matrix samples containing C₈H₂, C₁₀H₂, and C₁₂H₂ molecules were irradiated with UV laser pulses and the phosphorescence 0–0 band was observed at 532, 605, and 659 nm, respectively. Vibrational progression was observed for the symmetric stretching mode of the carbon chain in the ground state with increments of ~2190 cm⁻¹ for C₈H₂, ~2120 cm⁻¹ for C₁₀H₂, and ~2090 cm⁻¹ for C₁₂H₂. Temporal decay analysis of the phosphorescence intensity revealed the lifetimes of the triplet state as ~30 ms for C₈H₂, ~8 ms for C₁₀H₂, and ~4 ms for C₁₂H₂. The phosphorescence excitation spectrum reproduces UV absorption spectra in the hexane solution and in the gas phase at ambient temperature, although the excitation energy was redshifted. The symmetry-forbidden vibronic transitions were observed for C₁₀H₂ by lower excitation energies of 25,500–31,000 cm⁻¹ (320–390 nm). Detailed phosphorescence excitation patterns are discussed along the interaction of the polyyne molecule and solvent molecules of hexane. Full article

The treatment and prognosis of cancers of the nervous system remain unfavorable to the patient, which makes it necessary to study alternative therapies as primary or adjuvant treatments to existing methods. Photodynamic Therapy (PDT) is a method that consists of combining a photosensitizer (PS), a light source at the appropriate wavelength, and molecular oxygen, forming reactive oxygen species (ROS), leading to death in the target cell. The objective of this work was to compare the effects of PDT with two chlorins, Photodithazine (PDZ) and Fotoenticine (FTC), in 9L/lacZ gliosarcoma cell lines. Both chlorins, together with an LED device at 660 nm with a fluence of 10 J/cm², were included in the study. It was observed that the response to therapy depends on the concentration and type of PS used. In addition, PDZ showed a higher quantum yield of singlet oxygen generation than FTC. Full article

Each olefin (ethylene, trans-1,3-butadiene, isoprene, dimethyl butadiene (DMB)) and ozone molecules were codeposited on a CsI window at cryogenic temperature, and the products of photolysis with ultraviolet–visible light were observed using Fourier-transform infrared spectroscopy. The products of the C₂H₄–O₃ system could be assigned to glyoxal (CHO–CHO), ethylene oxide (c–C₂H₄O), CO, and CO₂. The formation of CHO–CHO and c–C₂H₄ and the absence of H₂CO and HCOOH indicated that the main reaction channels did not involve C–C bond breaking. Based on this simple scheme, the photoproducts of different olefin–O₃ systems were assigned, and the vibrational features predicted by density functional theory calculations were compared with the observed spectra. Regarding butadiene, spectral matches between the observations and calculations seemed reasonable, while assignments for isoprene ambiguities of and DMB remain, mainly because of the limited availability of authentic sample spectra. Full article

TiO₂ thin films are promising as photocatalysts to decompose organic compounds. In this study, TiO₂ thin films were deposited by reactive radio-frequency (RF) magnetron sputtering under various flow rates of oxygen and argon gas. The results show that the photocatalytic activity decreases as the oxygen-gas ratio is increased to 30% or less, while the activity increases under oxygen-rich conditions. It was observed that the crystal structure changed from anatase to a composite of anatase and rutile, where the oxygen-gas ratio during RF sputtering is more than 40%. Interestingly, the oxygen vacancy concentration increased under oxygen-rich conditions, where the oxygen-gas ratio is more than 40%. The sample prepared under the most enriched oxygen condition, 70%, among our experiments exhibited the highest concentration of oxygen vacancy and the highest photocatalytic activity. Both the oxygen vacancies and the composite of anatase and rutile structure in the TiO₂ films deposited under oxygen-rich conditions are considered responsible for the enhanced photocatalysis. Full article

Under photoirradiation, Sc₃[email protected]I_h-C₈₀ reacted readily with disilirane 1, silirane 4, and digermirane 7 to afford the corresponding 1:1 adducts, whereas Sc₃[email protected]D_5h-C₈₀ was recovered without producing those adducts. Based on these results, we described a novel method for the exclusive separation of I_h and D_5h isomers of Sc₃[email protected]₈₀. The method includes three procedures: selective derivatization of Sc₃[email protected]I_h-C₈₀ using 1, 4, and 7, facile HPLC separation of pristine Sc₃[email protected]D_5h-C₈₀ and Sc₃[email protected]I_h-C₈₀ derivatives, and thermolysis of Sc₃[email protected]I_h-C₈₀ derivatives to collect pristine Sc₃[email protected]I_h-C₈₀. In addition, laser flash photolysis experiments were conducted to elucidate the reaction mechanism. Decay of the transient absorption of ³Sc₃[email protected]I_h-C₈₀^* was observed to be enhanced in the presence of 1, indicating the quenching process. When Sc₃[email protected]D_5h-C₈₀ was used, the transient absorption was much less intensive. Therefore, the quenching of ³Sc₃[email protected]D_5h-C₈₀^* by 1 could not be confirmed. Furthermore, we applied time-dependent density functional theory (TD-DFT) calculations of the photoexcited states of Sc₃[email protected]₈₀ to obtain insights into the reaction mechanism. Full article

In this work, 2-F-4-OH benzoic acid was isolated in Ar matrices and conformational changes were induced by near-IR irradiating the sample. Upon deposition, three conformers could be observed in the matrix, denoted as A1, A2, and D1, respectively. A1 and A2 are trans carboxylic acids, i.e., there is an intramolecular H bond between the H and the carbonyl O atoms in the COOH group, whereas D1 is a cis carboxylic acid with an intramolecular H bond between the F atom and the H atom in the COOH group, which otherwise has the same structure as A1. The difference between A1 and A2 is in the orientation of the carbonyl O atom with regard to the F atom, i.e., whether they are on the opposite or on the same side of the molecule, respectively. All three conformers have their H atom in their 4-OH group, facing the opposite direction with regard to the F atom. The stretching overtones of the 4-OH and the carboxylic OH groups were selectively excited in the case of each conformer. Unlike A2, which did not show any response to irradiation, A1 could be converted to the higher energy form D1. The D1 conformer spontaneously converts back to A1 via tunneling; however, the conversion rate could be significantly increased by selectively exciting the OH vibrational overtones of D1. Quantum efficiencies have been determined for the ‘local’ or ‘remote’ excitations, i.e., when the carboxylic OH or the 4-OH group is excited in order to induce the rotamerization of the carboxylic OH group. Both ‘local’ and ‘remote’ conformational switching are induced by the same type of vibration, which allows for a direct comparison of how much energy is lost by energy dissipation during the two processes. The experimental findings indicate that the ‘local’ excitation is only marginally more efficient than the ‘remote’ one. Full article

Many sunscreen chemical agents are designed to absorb UVB radiation (and in some cases UVA) to protect the skin from sunlight, but UV absorption is often accompanied by photodissociation of the chemical agent, which may reduce its UV absorption capacity. Therefore, it is important to understand the photochemical processes of sunscreen agents. In this study, the photolysis of para-aminobenzoic acid (PABA), one of the original sunscreen chemical agents, at three different UV ranges (UVA: 355 nm, UVB: >280 nm, and UVC: 266 nm and 213 nm) was investigated using parahydrogen (pH${}_2$) matrix isolation Fourier-Transform Infrared (FTIR) Spectroscopy. PABA was found to be stable under UVA (355 nm) irradiation, while it dissociated into 4-aminylbenzoic acid (the PABA radical) through the loss of an amino hydrogen atom under UVB (>280 nm) and UVC (266 nm and 213 nm) irradiation. The radical production supports a proposed mechanism of carcinogenic PABA-thymine adduct formation. The infrared spectrum of the PABA radical was analyzed by referring to quantum chemical calculations, and two conformers were found in solid pH${}_2$. The PABA radicals were stable in solid pH${}_2$ for hours after irradiation. The trans-hydrocarboxyl (HOCO) radical was also observed as a minor secondary photoproduct of PABA following 213 nm irradiation. This work shows that pH${}_2$ matrix isolation spectroscopy is effective for photochemical studies of sunscreen agents. Full article

A comparative study of amino phenoxide zirconium catalysts in the hydrophosphination of alkenes with diphenylphosphine reveals enhanced activity upon irradiation during catalysis, with conversions up to 10-fold greater than reactions in ambient light. The origin of improved reactivity is hypothesized to result from substrate insertion upon an n→d charge transfer of a Zr–P bond in the excited state of putative phosphido (Zr–PR₂) intermediates. TD-DFT analysis reveals the lowest lying excited state in the proposed active catalysts are dominated by a P 3p→Zr 4d MLCT, presumably leading to enhanced catalysis. This hypothesis follows from triamidoamine-supported zirconium catalysts but demonstrates the generality of photocatalytic hydrophosphination with d⁰ metals. Full article