A metallaphotoredox C−O coupling reaction was optimized through the use of High Throughput Experimentation (HTE) and Design of Experiment (DoE) techniques. The resulting methodology utilizes more sustainable and cost effective materials than previously reported conditions, and has been demonstrated on a range of substrates from 300 μL up to 500 mL scales.

Abstract

Using High-Throughput Experimentation (HTE), a visible light-mediated etherification method was developed, employing the organic photocatalyst thioxanthen-9-one (TXO) and a commercially available, air-stable nickel source. Design of Experiments (DoE) techniques were utilized in conjunction with HTE to identify optimal reaction conditions which are mild, cost-effective, robust and therefore suitable for use in an industrial setting. A diverse substrate scope was prepared via parallel synthesis and selected examples were demonstrated on a 4.2 mmol scale in batch. Furthermore, the reaction was successfully performed on an 83 mmol scale, utilizing a standard jacketed reactor and Kessil PR160 L lamps.

Forming TiO₂ mesoporous microspheres with small particle size and can provide abundant active sites for photocatalytic hydrogen production due to their high surface area and mesoporous structure. In addition, graphene is selected as a co-catalyst for photocatalytic hydrogen production due to the excellent conductivity and high specific surface area of graphene materials, which has excellent enrichment effect on photogenerated electrons of the photocatalyst and can effectively inhibit the recombination of photogenerated carriers and improve the photocatalytic hydrogen production activity.

Abstract

The regulation of surface active sites and structures is a key factor affecting the performance of photocatalysts. In order to prepare monodisperse anatase TiO₂ mesoporous microspheres with higher specific surface area, smaller pore size and particle size, a dual-surfactant orientation assembly method was selected. Graphene (NG) was selected as a cocatalyst to compound with mesoporous TiO₂ and nickel doping was performed on the cocatalyst to improve the photocatalytic hydrogen production activity of the semiconductor photocatalyst. Through proper regulation and rational design, the semiconductor photocatalyst with desired properties was prepared. SEM characterization of mesoporous titanium dioxide (TiO₂/Ni-NG) with graphene cocatalyst proved that TiO₂ nanospheres have good monodispersion, and TiO₂ nanospheres are well supported on graphene cocatalyst. The composite material belonged to mesoporous group with the pore size being mainly distributed between 10–20 nm. The loading of graphene and Ni-NG cocatalyst increased the absorption band edge by 9 nm and 38 nm, respectively, and the band gap decreased by 0.07 eV and 0.16 eV, respectively. The selection of graphene as cocatalyst improved the hydrogen production activity of photocatalyst and nickel doping was very effective in the modification of graphene. For reaction time of 2.5 h, the H₂ production of TiO₂/Ni-NG material reached 1.767 mmol/g which was 7.27 times that of TiO₂/NG composite material.

Based on appropriate PES data, the Interacting Quantum Atoms method (IQA) allows to quantify the atomic and pair contributions that promote the relaxation of an excited electronic state, thus providing mechanistic information useful for rationalising photophysical processes in molecular systems.

Abstract

A theoretical study of the non-radiative photophysical relaxation mechanisms of the first singlet excited state of benzene, cyclobutadiene and fulvene is presented. For these molecules, the calculation of the Minimum Energy Path (MEP) leading from the Franck–Condon region to the surface crossing with the ground state is carried out. Subsequently, the decomposition of the electronic energies into atomic and pair contributions is performed using the Interacting Quantum Atom (IQA) method. The IQA approach provides the important mechanistic information necessary to rationalise some relevant aspects of the processes, such as the components that explain the appearance of an energy barrier or that favour the crossing between potential energy surfaces (PES); it also allows to quantify the direct effect on the MEP due to the inclusion of a substituent. In particular, it is shown how the IQA energies allow measuring the extent to which the formation of biradicaloid structures affects the crossing of the PES. The analysis of electron density functions suggests that aromaticity is not a driving force on the relaxation processes. Overall, this work shows the potential of the IQA method as a useful tool for the detailed description of photophysical processes.

The PCE of 18.43 % and 17.84 % are achieved in LbL and BHJ PSCs with polymer donor PM6 and small acceptor L8-BO. Over 3 % PCE improvement can be obtained in LbL PSC, benefiting from the enhanced exciton dissociation, charge collection efficiency and charge transport in LbL active layer.

Abstract

Two kinds of polymer solar cells (PSCs) were fabricated with polymer donor PM6 and small molecule non-fullerene acceptor L8-BO as accepted based on bulk heterojunction (BHJ) or layer-by-layer (LbL) structure. The power conversion efficiency (PCE) of 18.43 % and 17.84 % can be achieved from the PSCs based on BHJ and LbL structure, respectively. Two kinds of PSCs exhibit the same open circuit voltage (V_OC ) of 0.88 V, which can be well explained from the same donor and acceptor materials and the same electrodes. The LbL based PSCs exhibit a relatively large short circuit current density (J_SC ) of 26.97 mA cm⁻² and fill factor (FF) of 77.64 % in comparison with J_SC of 26.64 mA cm⁻² and FF of 76.07 % for BHJ based PSCs. The relatively high PCE of LbL based PSCs should be attributed to the sufficient exciton dissociation and charge collection efficiency, as well as the more balanced charge transport, which can be confirmed from the photogenerated current density dependence on the effective bias. This work demonstrates that layer-by-layer structure may have great potential in preparing highly efficient PSCs.

A novel organic dye featuring an indacenodithieno[3,2-b]thiophene unit as the π-bridge, labeled as YB6, has been designed for p-type dye-sensitized solar cells (p-DSCs) and photoelectrochemical H₂O₂ production. Remarkably, it exhibits superior performance compared to the reference PB6 dye.

Abstract

Efficient photosensitizers are crucial for advancing solar energy conversion and storage technologies. In this study, we designed and synthesized a novel organic dye, denoted as YB6, for p-type dye-sensitized solar cells (p-DSCs) and photoelectrochemical H₂O₂ production. YB6 features an extended conjugated π-bridge derived from indacenodithieno[3,2-b]thiophene and exhibits notable advantages: a two-fold higher molar extinction coefficient at its main absorption peak and a broader absorption as compared to the PB6 dye. In p-type dye-sensitized NiO photoelectrochemical cells, the YB6-based device demonstrated superior performance as compared to the PB6-based device. It delivered nearly a 50 % higher H₂O₂ production over 5 hours. Furthermore, when fabricated into p-DSCs, the YB6-based device exhibited a 33 % higher power conversion efficiency. This enhancement is caused by suppressed charge recombination from the dye structure, which in turn may be traced to a larger thermodynamic up-hill process for recombination losses in the YB6-based system.

Photoswitching of hydroxy azobenzene derivatives was studied in different solvents. It was observed that in polar solvents, showed unexpectedly very slow trans⇆cis isomerization. Studies showed that aggregation⇆dispersion was the cause of unusual stabilities. The presence of ionic species was found to promote photoisomerization. Regular photoswitching was observed under non-polar conditions.

Abstract

Hydroxy azo-benzenes are very well known for their rapid trans⇆cis photoisomerization under polar solvents. In contrast, we synthesized two hydroxymethylated- hydroxyazobenzene derivatives and investigated their light-triggered photoisomerization and stability under polar solvents. The result showed just opposite behavior and very slow trans⇆cis isomerization was observed (minutes-days). Thus, the UV-vis spectrum revealed a very low decrease in the absorbance of π–π* transition. Surprisingly, the isomerization process became faster with the addition of ionic species. Here, we attempted to understand the underlying cause of the unusual photo-switching behavior. The presence of hydroxymethyl and fluorine substituents was found to have a significant effect on the stability of the trans and photo-isomerized cis products. Here, it was confirmed with NMR and DLS studies that the unusual photostability of trans compounds was caused by polar solvent-assisted aggregation (hydrodynamic radius, R_H 5660–1720 nm) which underwent dispersion (R_H, 220–68 nm) and formed a significant stable solvated photoproduct under photoirradiation. Furthermore, this aggregation-dispersion was found to be very slowly reversible. Further, the fluorescence emission demonstrated a characteristic dispersion-induced quenching. Regular photoswitching was observed under non-polar conditions in benzene where an expected blue shift of π–π* transition and an increase in the intensity of n–π* transitions.

Estimating the kinetics of electron transfer (ET) processes in biologically relevant systems using theoretical-computational methods remains a formidable task. This challenge arises from the inherent complexity of these systems, which makes it impractical to apply a fully quantum-mechanical treatment. Hybrid quantum mechanical/classical mechanical computational approaches have been devised to enable the explicit simulation of electron transfer kinetics. This concept article focuses on a specific theoretical-computational method employed in this context, namely the Perturbed Matrix Method (PMM), which has the merit of being able to include large-scale conformational effects in the ET kinetics and potential multiple, alternative, ET channels. We describe its underlying physical principles, examine its advantages and limitations, and offer insights into its applications. Examples of the approach are discussed in the context of estimating photo-induced electron transfer kinetics in proteins. The non-exponential behavior observed in the presented case studies arises mainly from an active coupling with the environment fluctuations, but partly also stems from the presence of branching ET pathways.

We discovere that when methylation occurs in a DNA dimer, a low-energy emissive species is induced and it is distinct from the previously reported monomer-like species as well as the charge-transfer exciplex species.

Abstract

Methylation of adenine at the N6 position is a crucial epigenetic modification that profoundly influences gene regulation and expression. Moreover, this modification intricately alters the excited state dynamics of adenine nucleobases. To explore the impact of N6-methyladenine on the excited state dynamics within oligonucleotides, we conducted a comprehensive investigation of two dinucleotides containing N6-methyladenosine, in conjunction with adenosine or guanosine. Using steady-state and time-resolved absorption and fluorescence spectroscopy techniques, we not only observed the customary monomer-like and charge transfer emissive states, as reported in previous dinucleotides, but also identified an additional low-energy emissive state. This unique state exhibits an extraordinary Stokes Shift exceeding 2.3 eV and has a relatively long lifetime of 4–5 ns. We propose that this state corresponds to a bonded exciplex state, governed by ground-state geometries.

The employment of carbon nitride as a photocatalyst is conditional to understanding its response to light and the nature of all the photogenerated species. Amongst the characterisation techniques, EPR spectroscopy occupies a central role since it permits to detect paramagnetic states and follow their fate. Here we aim to provide guidelines to employ EPR spectroscopy in the research on carbon nitride.

Abstract

As a metal-free semiconductor, carbon nitride is a promising material for sustainable photocatalysis. From the large number of studies, it seems apparent that the photocatalytic activity is related to the number and type of defects present in the structure. Many defects are paramagnetic and photoresponsive and, for these reasons, Electron Paramagnetic Resonance (EPR) spectroscopy is a powerful method to derive fundamental information on the structure – local, extended and electronic – of such defects which in turn impact the optical, magnetic and chemical properties of a material. This review aims at critically discussing the interpretation of EPR data of native and photoinduced radical defects in carbon nitride research highlighting strengths and limitations of this spectroscopic technique.

By encapsulating photosensitizers and reactants in tailored supramolecular assemblies, preservation of photoreactivity even in the presence of molecular oxygen can be observed. The focus of this concept article has been dedicated to aqueous solutions of supramolecular assemblies as potential reaction media as they present an underdeveloped and attractive solution for photochemical reaction development.

Abstract

Oxygen removing protocols have long been the standard approach to perform photoreactions. By encapsulating photosensitizers and reactants in tailored supramolecular assemblies, preservation of photoreactivity even in the presence of molecular oxygen can be observed. Herein, we showcase some of the solutions that could render time-consuming oxygen removal redundant in photochemical synthesis. A focus has been dedicated to aqueous solutions of supramolecular assemblies as potential reaction media. They present an attractive solution possibly useful not only for synthetic photochemical transformations, but also for water purification, bio-applications or biocatalysis. The included media are membranes, hydrogels, deep eutectic solvents and peptide assemblies.