The Front Cover highlights one of the main ultrafast spectroscopic techniques used to study the light-induced molecular processes in transparent solar cells based on diketo pyrrolopyrrole dyes. A near-IR pump pulse excites the molecules, and photoproducts like cations and excited dye aggregates are probed by a white-light pulse. Cover design by J. Valanciunaite (Strasbourg). More information can be found in the Research Article by Frédéric Sauvage, Fabrice Odobel, Stefan Haacke and co-workers.
The non-zwitterionic merocyanine derivative 2MeMC is a photoswitch with outstanding photoisomerization efficiency, photostability, especially in protic environment, and high switching rates, whose ring closure reaction to the spiropyran is inhibited by methylation of the phenolate oxygen. Ultrafast spectroscopy and quantum chemical calculations reveal the photoisomerization mechanism of this trans(TTT)-cis (CCT)-only merocyanine.
Merocyanines (MC) usually adopt ring opened zwitterionic structures that are interconvertible with their ring-closed spiropyran photoisomers. By methylating the phenolate oxygen, and thereby blocking the ring-closure reaction, a cis/trans-only MC photoswitch was obtained, yielding a perfect candidate for a detailed examination of the cis/trans isomerization mechanism for this class of compounds. This photoswitch displays outstanding properties including excellent photoreaction quantum yields and photoswitching turnovers. Due to the central polymethine bridge of MC, in principle eight cis (C)/trans/(T) isomers are possible. Density Functional Theory (DFT) calculations revealed the CCT and TTT-isomers of the studied compound as most stable cis and trans ground state isomers, respectively. UV/vis transient absorption studies combined with conical intersection computations with the complete active space self-consistent field (CASSCF) method show that both trans/cis- and cis/trans-photoisomerizations are initiated by a rotation of the central doubled bond fragment. A hot ground state species is then formed, which undergoes a second isomerization. Thus, the cis/trans reaction proceeds via a CCT-CTT-TTT sequence and the reverse reaction via TTT-TCT-CCT.
The photocyclization reactivity of an inverse type diarylethene derivative decreased by inclusion into β-cyclodextrin. From the detailed investigation using job-plots, NOESY spectra and DFT calculations, it was elucidated that this is ascribed to the restriction of the rotational motion between thiophene and phenyl rings. These results would provide useful information for the photochromic reaction dynamics of inverse type diarylethenes.
Diarylethene derivatives are one of the promising compounds for practical applications including optical memory, display, sensor, and photoactuator. In this work, we newly designed and synthesized an inverse type diarylethene derivative bearing sodium carbonate groups at the p-position of the lateral phenyl ring and investigated the photochromic behavior in the presence and absence of cyclodextrins (CDs) (αCD, βCD, and γCD). Interestingly, only in the presence of βCD, the photocyclization reactivity decreased. From the results of job-plots, NOESY spectra, and quantum chemical calculations, it was suggested that the distinctive interaction between the diarylethene and βCD leads to the restriction of molecular geometrical change, resulting in the suppression of the photocyclization reactivity. These results provide information on the rational designing of inverse type diarylethenes with advanced properties.
This review provides an overview on the recent research progress in the photocatalytic methane conversion to syngas and chemicals including photocatalytic reforming, photocatalytic partial oxidation and photocatalytic coupling of methane.
As a primary constituent of natural gas and shale gas, direct conversion of methane has attracted significant attention due to its potential to reduce energy consumption and CO2 emissions. Compared with thermal catalysis, photocatalysis has the capacity to transcend thermodynamic constraint and enable the conversion of sustainable solar energy into chemical energy under mild reaction condition, which contributes to optimize the utilization of methane. In this review, we undertake a comparative analysis of various strategies for photocatalytic methane conversion to syngas and chemicals, including photocatalytic reforming of methane, photocatalytic partial oxidation of methane and photocatalytic coupling of methane. The distinct reaction systems with corresponding catalysts and underlying mechanisms are expounded in detail to foster a profound comprehension of solar-driven methane conversion. Finally, the challenges and prospectives in photocatalytic methane conversion are discussed.
The investigation of photo-induced effects is profoundly influenced by the characteristics of photo-excitation sources. We present here a comprehensive analysis of the structures of two photoinduced linkage isomers (PLI) in a ruthenium nitrosyl complex trans-[Ru(py)4F(NO)](ClO4)2, following irradiation with both pulsed and continuous wave (CW) light sources under low temperature conditions.
The investigation of photo-induced effects is profoundly influenced by the characteristics of photo-excitation sources. In this study, we present a comprehensive analysis of the structures of two photoinduced linkage isomers (PLI) in a ruthenium nitrosyl complex, trans-[Ru(py)4F(NO)](ClO4)2, following irradiation with both pulsed and continuous wave (CW) light sources under low temperature conditions. The X-ray (photo)diffraction analysis shows that the resulting PLI generated from the two types of irradiation sources, an isonitrosyl configuration of the nitrosyl ligand in the so-called metastable state MS1, and a side-on configuration of the nitrosyl ligand in the metastable state MS2, are identical. In-situ optical absorption spectroscopy was employed during CW and pulsed irradiation, enabling the monitoring of the population process of these PLI. The results obtained from the infrared spectroscopic analysis after pulsed irradiation give insight into the population mechanism illustrating that the generation of the isonitrosyl MS1 occurs through a two-step process, via the second PLI, the side-on configuration MS2.
Near-IR dyes for transparent dye-sensitized solar cells: The effects of small driving forces (−ΔG) and excited state quenching by energy transfer to aggregates studied by femtosecond differential absorption and fluorescence spectroscopy for two DPP cyanine dyes.
In the context of developing transparent near-IR absorbing dye-sensitized solar cells, diketopyrrolopyrrole (DPP) cyanine dyes have recently emerged as an alternative to strongly aggregating linear cyanines. In our efforts to increase both the power conversion efficiency (PCE) and the average visible transmittance (AVT), a thienylated version, called TB202, that shows a red-shifted absorption with respect to our champion dye TB207 was designed. However, the lower energy LUMO level of TB202 brings along a lower driving force (−ΔG) for carrier injection, which we recently identified as the main parameter limiting the PCE to 1.5 % in the best device conditions. In the present paper, we publish a detailed account of the effect of the de-aggregating cheno-deoxycholic acid (CDCA) for both TB207 and TB202. Both transient absorption (TAS) and fluorescence up-conversion (FLUPS) data are presented, which allow to quantitively compare the effect of −ΔG and the CDCA concentration, in terms of the kinetic competition of ensemble averaged carrier injection and monomer-to-aggregate energy transfer (ET) rates. A comprehensive picture emerges on how ET is reduced by higher CDCA concentrations, leading in the best device conditions to injection efficiencies in the range of 65 % for TB207 and only 35 % for TB202.
Double-dipole bi-tetraphenylphosphonium bromide exhibits excellent cathode modification effect for organic solar cell, HOMO level down to −7.32 eV.
Nowadays, amine containing electrode interface material destroy the non-fullerene acceptor becomes a hard nut to crack for organic solar cells. Developing water-soluble interface material which is no chemical reaction with non-fullerene acceptor is an important research theme. Here, we report two bi-triangular pyramidal electronic configuration organic-phosphonium bromides as non-amine cathode interfacial layer for fabricating high-efficiency stable organic solar cells. The power conversion efficiency (PCE) of inverted device structure with PBDB-T/ITIC as active layer is up to 11.58 % which is great larger than control device PCE (9.35 %). Same device structure with PM6/Y6 as active layer, the PCE is up to 15.26 % and also is dramatically higher than the referred device PCE 14.36 %. Meanwhile, the devices show greatly improved stability by organic-phosphonium bromide interlayer.
The C10a-acetoxylated tetrahydroazepino[1,2-a]indole-6,11-diones are a class of tricyclic oxindoles that feature an α-keto-N,O-acetal substructure, rendering them highly susceptible to SET reduction followed by fragmentation. In protic medium, they undergo a PCET-assisted two-step reduction including an interposed C-O bond cleavage that can be initiated photocatalytically as well as by cathodic reduction, and which generates nucleophilic ketyl radicals. In the presence of acrylonitrile and DIPEA as additional reactants, the photoinduced reaction unfolds as a tandem C-O bond reduction / ketyl radical conjugate addition, to furnish C10a-reduced, C11-cyanoethyl-substituted tricyclic azepino-[1,2-a]indole derivatives with high stereoselectivity.
Changes in farming techniques have facilitated the movement of nitrogen-containing species, making converting nitrate into ammonia (fertilizer) highly desirable. Recently, we introduced a photosystem comprising NiO/Au plasmon/TiO2 that can selectively convert nitrate to ammonia at neutral pH and room temperature using visible light in a photo-electrochemical approach. The study evaluated the role of adding alcohol to the overall process activity and selectivity. Adding small quantities of alcohol to the electrolyte leads to changes in the catalytic behaviour, which cannot be attributed exclusively to improvement in counter-electrode reaction kinetics. Analysis of product Faradaic efficiency and photo-current measurements revealed that alcohols act as proton donors in nitrate/nitrite reduction, possibly through a concerted proton-couple electron transfer mechanism. These initial findings offer new handles for nitrate reduction to ammonia efficacy at neutral pH. Ultimately, this opens up avenues for agricultural practices that recycle nutrients, improve process circularity, and reduce fertilizer costs, thus contributing to economic sustainability.
The introduction of L-phenylalanine resulting in a notable optimization of the bandgap structure, the utilization of photocarriers and the generation of ROS of HCPs H3LP-HCPs, and achieving close to 100 % conversion efficiency and 100 % selectivity toward benzylamine oxidation with a high yield of H2O2 (9.2 mmol ⋅ gcat −1 ⋅ h−1) under 455 nm LED lamp in air.
The simultaneous production of imine and hydrogen peroxide (H2O2) via photocatalytic aerobic amine oxidation is a bright way to obtain value added products, however, rapid recombination of photogenerated charge leads to low conversion efficiency and selectivity. Herein, a metal-free amino acid modified hyper-cross-linked polymer (H3LP-HCPs) photocatalyst was synthesized for photocatalytic amines oxidation by regulating the ratio of L-phenylalanine (L-Phe) and hexaphenylbenzene (Hex). The results showed that the H3LP-HCPs photocatalyst with 1 : 3 molar ratio of L-Phe and Hex achieves close to 100 % conversion efficiency and 100 % selectivity toward benzylamine oxidation under 455 nm blue LED lamp irradiation. Furthermore, a high yield of H2O2 (9.2 mmol ⋅ gcat −1 ⋅ h−1) was synchronously obtained in benzylamine oxidation. Experiments and time-dependent density functional theory calculation results revealed that the N-functional groups in H3LP-HCPs photocatalyst not only remarkably broadens light-response range, but also facilitates electrons transfer from L-Phe to the Hex, thus accelerating photogenerated charge separation efficiency and the formation of reactive oxygen species (ROS).