Photochem, Volume 2, Issue 4 (December 2022) – 9 articles

Atomically precise metal nanoclusters are a new kind of nanomaterials that appeared in recent years; a pair of isomer nanoclusters have the same metal types, numbers of metal atoms, and surface-protected organic ligands but different metal atom arrangements. This article summarizes the structure features of isomer nanoclusters and concentrates on synthesis methods that could lead to isomer structure. The pairs of isomer inorganic nanoclusters’ conversion to each other and their applications in catalyst and photoluminescence are also discussed. We found that the structure conversions are relevant to their stability. However, with the same molecule formulas, different atom arrangements significantly influence their performance in applications. Finally, the existing challenges and some personal perspectives for this novel field in the nano-science investigation are proposed. We hope this minireview can offer a reference for researchers interested in inorganic isomer nanoclusters. Full article

The photo-induced electron transfer has been under intensive investigation for a few decades already, and a good understanding of the reaction was developed based on thorough study of the molecular donor–acceptor (DA) system. The recent shift to hybrid DA systems opens the question of transferring the knowledge to analyze and design these new materials. One of the apparent differences is the size increase of the donor or acceptor entities. The electronic wave functions of larger entities occupy a larger volume, but since these are still one-electron wave functions, their amplitudes are lower. A simple analysis proposed here demonstrates that this leads to roughly inverse third power dependence of the electron transfer rate constant on the donor or acceptor size, $k_{ET}\propto R^{-3}$. This dependence can be observed upon switching from molecular to quantum dot donor in DA systems with a fullerene acceptor. Full article

The mesoporous zirconia/alumina composites were synthesized via a sol–gel method, followed by heat treatment at 500 °C for 5 h. The effect of the ZrO₂/Al₂O₃ ratio on the structural and textural properties of the obtained composites was explored. Sorption analysis has confirmed that all samples have a mesoporous structure whose parameters (S_BET, V_p and D_max) strongly depend on the ZrO₂/Al₂O₃ ratio. The XRD pattern of composites has shown that the addition of zirconia disrupts the crystallinity of alumina. The composites with higher zirconia content (50% ZrO₂ and 67% ZrO₂) are characterized by peaks related only to the zirconia phase. UV/Vis diffuse reflection spectra of all samples revealed that composites have more intensive absorption compared to pure oxides for wavelengths larger than 250 nm and similar band gaps. Photoluminescence measurements showed presence of defects in all samples, which are responsible for photocatalytic activity. All samples showed significant adsorption/photocatalytic efficacy for the removal/degradation of 2,4,6 -trichlorophenol (TCP). Results obtained using HPLC and TOC techniques showed that between 70 and 80% of the initial TCP concentration was removed/degraded after 4 h of illumination. These results were corelated with flat, conduction and valence band potentials of synthesized pure and binary oxides, calculated using Mott–Schottky plots. Full article

Photodynamic inactivation of microorganisms has emerged as a promising strategy to kill and eradicate pathogens. In this work, two polymers, TCP-P and ZnTCP-P, were synthesized by oxidative polymerization of 5,10,15,20-tetrakis [3-(N-ethylcarbazoyl)]porphyrin and its complex with Zn(II). Solid polymers consist of rods (diameter 100 nm, length ~100–500 nm) that form microporous structures on a surface. UV-visible absorption spectra in solution showed the Soret and Q bands characteristic of the corresponding constitutional porphyrins. In addition, the polymers presented two red emission bands with quantum yields Φ_F = 0.11 for TCP-P and Φ_F = 0.050 for ZnTCP-P. These compounds sensitized the production of singlet molecular oxygen with quantum yields of Φ_Δ~0.3. Thus, the spectroscopic and photodynamic properties of the porphyrin units were maintained in the conjugates. The photodynamic activity induced by both polymers was tested to inactivate S. aureus. In cell suspensions, TCP-P was more effective than ZnTCP-P in killing bacteria. Viable S. aureus cells were not detected using 4 µM TCP-P after 20 min of irradiation. Moreover, both polymers showed a high photocytotoxic activity to eradicate S. aureus cells attached to a surface. The results indicate that these conjugated polymers can act as effective antimicrobial agents to photoinactivate pathogens. Full article

Photostabilization is an important methodology to ensure both the quality and quantity of photodegradable pharmaceuticals. The purpose of our study is to develop a photostabilization strategy focused on the addition of photostabilizers. In this study, the protective effects of selected polyphenols and antioxidants on naproxen (NPX) photodegradation in the solid state were evaluated. Residual amounts of NPX were determined by high-performance liquid chromatography (HPLC), and the protective effects of tested additives on NPX photodegradation induced by ultraviolet light (UV) irradiation were evaluated. As a result, quercetin, curcumin, and resveratrol suppressed NPX photodegradation completely. When they were mixed with NPX, the residual amounts of NPX after UV irradiation were significantly higher compared to that without additives, and comparable to those of their control samples. In addition, to clarify the mechanisms of the highly protective effects of these additives on NPX photodegradation, their antioxidative potencies, and UV filtering potencies were determined. There was no correlation between photoprotective effects and antioxidative potencies among selected polyphenols and antioxidants although photoprotective additives showed more significant UV absorption compared to NPX. From these results, it is clarified that a higher UV filtering activity is necessary for a better photostabilizer to photodegradable pharmaceuticals in the solid state. Full article

Bismuth vanadate (BiVO₄ or BVO) is one of the most studied photocatalysts for water oxidation because of its excellent visible light absorption and appropriate band energy positions. However, BVO presents a low charge mobility and a high electron–hole recombination rate. To address these fundamental limitations, this study proposes the coating of previously synthesized phase-pure monoclinic scheelite BVO with different amounts of naked cobalt (further oxidized to cobalt hydroxide) nanoparticles (NPs) via a modified magnetron sputtering deposition. The resulting BVO/Co photocatalysts were investigated for methylene blue (MB) photodegradation, photocatalytic oxygen evolution, and photoelectrochemical (PEC) water oxidation. In the MB photodegradation tests, the BVO/Co sample prepared with a deposition time of 5 min (BVO/Co(5 min)) presented the highest photoactivity (k = 0.06 min⁻¹) compared with the other sputtering investigated times (k = 0.01–0.02 min⁻¹), as well as the pristine BVO sample (k = 0.04 min⁻¹). A similar trend was evidenced for the PEC water oxidation, where a photocurrent density of 23 µA.cm⁻² at 1.23 V (vs. RHE) was observed for the BVO/Co(5 min) sample, a value 4.6 times higher compared with pristine BVO. Finally, the BVO/Co(5 min) presented an O₂ evolution more than two times higher than that of the pristine BVO. The increased photocatalytic performance was ascribed to increased visible-light absorption, lesser electron–hole recombination, and enhanced charge transfer at the liquid/solid interface. The deposition of Co(OH)₂ NPs via magnetron sputtering can be considered an effective strategy to improve the photocatalytic performance of BVO for different target catalytic reactions, including oxygen evolution, water oxidation, and pollutant photodegradation. Full article

Research in photochemistry is always looking for novel compounds that can serve a role in applications ranging from medicine to environmental science. Push–pull compounds with protonable groups represent an interesting class of molecules in this sense, as they can prove to be sensitive to changes in both the acidity and polarity of the medium, becoming valuable as sensors and probes. Hence, in this work, a new dinitrophenyl-hydrazinylidene derivative with multiple protonable centers has been specifically designed and synthesized. The molecule showed an important acidochromism in the visible, with three differently-protonated species under acidic, neutral, and basic conditions, each characterized by a peculiar absorption spectrum. The photophysical characterization of this compound revealed an ultrafast excited-state deactivation, as described by femtosecond transient absorption experiments, and the hints of charge-transfer dynamics, as supported by the observed solvatochromism and quantum-mechanical calculations. These properties led to almost undetectable fluorescence that, together with negligible intersystem crossing and the absence of reactive pathways, points to the preference for a total non-radiative deactivation mechanism, i.e., internal conversion. This intriguing behavior stimulates interest in light of possible applications of the investigated acidochromic dye as a probe in photoacoustic imaging, which offers an alternative to classical fluorescence imaging. Full article

Herein, we present the synthesis, characterization, and light-driven hydrogen evolution activity of two dinuclear Ru-Pt complexes, Rup(ph)pPtX₂ (X = Cl, I), comprising a new phenyl-spaced 5,5′-bis-phenanthroline p(ph)p bridging ligand. The two complexes only differ in the nature of the halide ligand at the catalytic center. Structural, photophysical, electrochemical, as well as photochemical characterization techniques revealed that the variations of single components of the intramolecular system provide a strong influence on the stability even in non-catalytic conditions. Interestingly, varying electron density at the catalytic center, mainly influenced by the coordinating halide at the catalytic center, as shown by ¹⁹⁵Pt NMR spectroscopy, strongly influences the photocatalytic efficiency. Furthermore, intensive investigations on the potential catalytic mechanism showed that small structural variations (e.g., halide exchange) not only affect catalytic activity but can also switch the main catalytic mechanism from an initially molecular one to a fully heterogeneous, colloid-driven hydrogen evolution. Full article

Photo-thermal catalysis is among the most effective alternative pathways used to perform chemical reactions under solar irradiation. The synergistic contributions of heat and light during photo-thermal catalytic processes can effectively improve reaction efficiency and alter design selectivity, even under operational instability. The present review focuses on the recent advances in photo-thermal-driven chemical reactions, basic physics behind the localized surface plasmon resonance (LSPR) formation and enhancement, pathways of charge carrier generation and transfer between plasmonic nanostructures and photo-thermal conversion, critical aspects influencing photo-thermal catalytic performance, tailored symmetry, and morphology engineering used to design efficient photo-thermal catalytic systems. By highlighting the multifield coupling benefits of plasmonic nanomaterials and semiconductor oxides, we summarized and discussed several recently developed photo-thermal catalysts and their catalytic performance in energy production (CO₂ conversion and H₂ dissociation), environmental protection (VOCs and dyes degradation), and organic compound synthesis (Olefins). Finally, the difficulties and future endeavors related to the design and engineering of photo-thermal catalysts were pointed out to draw the attention of researchers to this sustainable technology used for maximum solar energy utilization. Full article