ChemPhotoChem最新文献

Azobenzene compounds are putative solar thermal fuels (STF) due to the excellent photostability and structural control of isomerization rates. Azobenzenes, in which both Z- and E-isomers are liquid at room temperature, are promising candidates for STF flow technology. A literature survey of melting points led to the synthesis and isomer separation of ortho- and meta-monosubstituted azobenzenes with fluoro, methyl, ethyl, trifluoromethyl and methoxy substituents and several dimethyl substituted azobenzenes. Four of the compounds are liquid azobenzenes with higher specific energy than literature work with higher molar mass, liquid compounds. Eight of the compounds unexpectedly displayed a higher melting point for the Z-isomer which is rarely observed. Intermolecular close contacts in the crystal lattice of the Z-isomer are the main factor responsible for the higher melting temperatures.

9-Phenylacridine (9-PA) is an important acridine-based medicine that has been proven to possess significant anticancer activity and can be used as a photodynamic therapy (PDT) agent. Meanwhile, the possible twisting of the C−C single bond at the C9 position after photo-excitation makes it a potential probe responsive to changes in the viscosity of living cells. However, the photophysical properties of 9-PA is poorly understood. In this study, we utilized femtosecond time-resolved spectroscopy combined with quantum chemical calculation methods to investigate the excited state dynamics of 9-PA in solutions with different viscosities. Notably, we demonstrated that the viscosity could strongly influence the deactivation pathway of the initially populated S₁ (ππ*) state of 9-PA. In low-viscosity solutions, the single bond at the C9 could twist after photo-excitation, leading to a conformation that shows efficient intersystem crossing. However, such process is suppressed in high-viscosity solutions, resulting a ~2.5 times higher internal conversion (IC) yield. A full picture of the excited state deactivation mechanism of 9-PA is proposed.

Selective synthesis of furfuryl alcohol from furfural conversion via semiconductor photocatalytic route has appeared as a promising solution for transforming biomass into high-value-added products under mild temperature and pressure conditions. Titanium dioxide (TiO₂) photocatalysts were prepared by a simple sol-gel method followed by a calcination treatment ranging from 500–1000 °C, resulting in materials with distinct physicochemical properties. The photocatalytic efficiency of the TiO₂ samples was examined in the selective production of furfuryl alcohol from furfural under UV-LED irradiation. The influence of various organic solvents, including ethanol, methanol, 2-propanol, and acetonitrile, was evaluated to optimise the selectivity towards furfuryl alcohol production. Photocatalysts with larger anatase to rutile ratio and increased density of oxygen vacancies (defects) exhibited superior performance for furfuryl alcohol production. The presence of these defects on the catalyst surface leads to a significant enhancement in the photocatalytic efficiency by acting as crucial active sites. Among the TiO₂ samples, the highest conversion of furfural into furfuryl alcohol was observed with the TiO₂ sample calcined under an air atmosphere at 600 °C (TiO₂-600), achieving 85 % yield and 100 % selectivity for furfural after 30 min reaction using ethanol as solvent.

A series of methoxylated bis(pentafluorophenyl)boron-β-diketonates (dkB(C₆F₅)₂) with intense emission has been synthesized and characterized by a variety of physicochemical methods. The photophysical properties of the synthesized compounds were thoroughly investigated by electronic absorption, steady-state, and time-resolved fluorescence spectroscopy in both solution and solid state. The studied compounds exhibit solvatochromic behavior attributed to the intramolecular charge transfer (ICT) nature of the first excited state. The formation of exciplexes between DBMB(C₆F₅)₂ and benzene derivatives was also studied. Notably, the studied compounds display a complex luminescence profile in the solid state, featuring fluorescence, delayed fluorescence and phosphorescence emission. Furthermore, the hydrolytical stability of the complexes was assessed, demonstrating excellent resistance to hydrolysis. Estimated rate constants, determined at 60 °C, are significantly lower (90-2000 times) than those observed for the well-studied dibenzoylmethanatoboron difluoride (DBMBF₂). The incorporation of pentafluorophenyl substituents at the boron atom enables the synthesis of highly fluorescent and hydrolytically stable boron chelate complexes, suitable for sensing and bioimaging applications in water-containing environments.

RNA-based tools for biological and pharmacological research are raising an increasing interest. Among these, RNA aptamers whose biological activity can be controlled via illumination with specific wavelengths represent an important target. Here, we report on a proof-of-principle study supporting the viability of a systematic use of Morita-Baylis-Hillman adducts (MBHAs) for the synthesis of light-responsive RNA building blocks. Accordingly, a specific acetylated MBHA derivative was employed in the functionalization of the four natural RNA bases as well as two unnatural bases (5-aminomethyl uracil and 5-methylaminomethyl uracil). The results reveal a highly selective functionalization for both unnatural bases. The conjugation products were then investigated spectroscopically, photochemically and computationally. It is shown that when a single light-responsive unit is present (i. e. when using 5-methylaminomethyl uracil), the generated unnatural uracil behaves like a cinnamic-framework-based photochemical switch that isomerizes upon illumination through a biomimetic light-induced intramolecular charge transfer mechanism driving a barrierless and, therefore, ultrafast reaction path.

A case study, detailing the effect of different DNA oligomers on a NIR-emitting DNA-stabilized silver nanocluster (DNA-AgNC), is reported. The presence of single-stranded DNA oligomers was found to adversely affect the chemical stability of (DNA)₂[Ag₁₆Cl₂]⁸⁺ with distinct degrees of destruction depending on the DNA sequence. To increase the chemical stability of the DNA-AgNC, we implemented two protection strategies. First, hybridization of the bare DNA strands with the corresponding complementary sequences dramatically reduced the destruction of (DNA)₂[Ag₁₆Cl₂]⁸⁺, as demonstrated by the decreased drops in both the absorption and emission spectra. Secondly, saturation of the free DNA oligomers with silver cations left (DNA)₂[Ag₁₆Cl₂]⁸⁺ intact. Our investigation can thus provide an easy-to-implement approach to discover DNA sequences that are intrinsically less reactive towards preformed DNA-AgNCs, and give an idea on how to protect DNA-AgNCs from bare DNA strands.

Understanding thermally activated delayed fluorescence (TADF) in solid-state environments is crucial for practical applications. However, limited research focuses on how the medium affects TADF properties of hot-exciton-based emitters. In our study, we calculated and compared reverse intersystem crossing, radiative, and non-radiative decay rates of TADF emitters in gas, solvent, and solid phases. The designed emitters have a donor-acceptor-donor (D-A-D) structure, with donors such as triphenylamine (TPA) and diphenylamine thiophene (ThPA), combined with acceptors such as benzothiadiazole (BT), pyridine thiadiazole (PT) and thiadiazolobenzopyridine (NPT). We model the solvent and solid phases with the polarizable continuum model (PCM) and quantum mechanical/molecular mechanics (QM/MM) methods, respectively. Using density functional theory (DFT) and time-dependent DFT, we analyze how TADF emitters′ geometrical, electronic, and excited-state properties vary in these phases. Our results show that the solid-state environment significantly influences the geometry and TADF properties of emitters. In the presence of solid medium, our study indicates that non-radiative decay rates tend to be slower. On the other hand, radiative emission rates were found to be less influenced by the properties of the surrounding medium. Overall, our study connects emitter chemical structure and the surrounding environment‘s impact on excited-state characteristics and photochemical properties.

The photoreforming reaction, which can produce hydrogen simultaneously with the decomposition of organic waste, is a promising method for resolving longstanding global issues such as the depletion of energy resources and climate change. However, ZnS photocatalysts, one of the most optimal catalysts for such reactions, has an inadequate visible-light response; thus, the extensibility of the reaction is limited. In this study, CdS photocatalysts are prepared from metal–organic framework (MOF) precursors, that is, Cd-MOFs. The prepared CdS exhibits high hydrogen production activity in the photoreforming of lignocellulosic biomass under quasi-sunlight conditions. This activity is approximately 13.4 times that of the CdS prepared via the conventional hydrothermal method. Further, CdS can utilize light energy in the visible region of sunlight, providing a high quantum yield and demonstrating the potential for the extensibility of the reaction. The results of this study will facilitate the fabrication of novel materials for sustainable and efficient hydrogen production.

Eumelanin is a natural pigment found in many organisms that provides photoprotection from harmful UV radiation. As a redox-active biopolymer, the structure of eumelanin is thought to contain different redox states of quinone, including catechol subunits. To further explore the excited state properties of eumelanin, we have investigated the catechol/o-quinone redox couple by spectroelectrochemical means, in a pH 7.4 aqueous buffered solution, and using a boron doped diamond mesh electrode. At pH 7.4, the two proton, two electron oxidation of catechol is promoted, which facilitates continuous formation of the unstable o-quinone product in solution. Ultrafast transient absorption (femtosecond to nanosecond) measurements of o-quinone species involve initial formation of an excited singlet state followed by triplet state formation within 24 ps. In contrast, catechol in aqueous buffer leads to formation of the semiquinone radical Δt>500 ps. Our results demonstrate the rich photochemistry of the catechol/o-quinone redox couple and provides further insight into the excited state processes of these key building blocks of eumelanin.

The Front Cover shows “blueprints” of the photocatalytic reaction design that is mediated by graphitic carbon nitride. A combination of physical chemistry and organic chemistry in carbon nitride photocatalysis allows for rational design of photocatalytic reactions. Cover design by Prof. Oleksandr Savateev. More information can be found in the Review by Oleksandr Savateev and Jingru Zhuang.