C−H activation: Rh-phosphine complexes can activate C−H bonds in otherwise unreactive alkanes. Quantum chemical calculations provide mechanistic insights into the generation of the active species which is formed via the light-induced CO dissociation at Rh(I) complexes featuring trimethylphosphine and 1,2-bis(dimethylphosphino)ethane. The calculations align well with experimental photochemical studies on the Rh(I) complexes.

Abstract

The activation step of Vaska-type Rh(I) complexes, such as the photocleavage of the Rh−CO bond, plays an important role in the subsequent C−H activation. To elucidate the details of the photochemistry of Vaska-type Rh(I) complexes, such as trans-Rh(PMe₃)₂(CO)(Cl), we here present a computationally derived picture as obtained at the density functional level of theory in combination with multireference wavefunction-based methods. We have identified that the photocleavage of CO proceeds via the metal-centered excited state (³MC, ), which is populated through intersystem crossing from the dipole-allowed excited state S₁( - ). Moreover, the present study unraveled the reasons for the low C−H activation efficiency when using Rh featuring the bidentate ligand 1,2-bis(dimethylphosphino)ethane (dmpe), namely due to its unfavorable photochemical properties, i. e., the small driving force for light-induced CO loss and the fast deactivation of ³MC state back to the singlet ground state. In this study, we provide theoretical insight into mechanistic details underlying the light-induced CO dissociation process, for Rh complexes featuring PMe₃ and dmpe ligands.

The review has systematically summarized several methods recently developed to increase Stokes shift of fluorophores by structural modification, and highlighted typical applications of fluorophores with large Stokes shift in single-excitation multi-color imaging and ratiometric imaging. The review will provide a theoretical guidance for the design of novel fluorophores with large Stokes shift.

Abstract

Fluorophores and fluorophores-based probes or labels can visualize the structures and content fluctuations of biomolecules, and have made great progress in the broad range of biomedicine fields. However, many commercially available fluorophores suffer from small Stokes shift, which results in insufficient signal-to-noise ratio and self-quenching in advanced imaging techniques. Moreover, the small Stokes shift also hinders the application of fluorophores in some complex imaging, such as single-excitation multicolor imaging. In the past two decades, many effects have been made to enlarge Stokes shift of fluorophores. In this review, we clarified the reasons for the small Stokes shift building on the structural analysis of fluorophores, systematically summarize the methods of structural modification to increase Stokes shift, and present some representative applications of fluorophores with large Stokes shift in imaging and sensing.

In this review, the development of catalyst-free photo-induced reactions involving photoexcited nitroarenes is summarized and a brief outline of future directions in this field is provided.

Abstract

Nitroarenes are usually excited to form photoexcited species in light-induced reactions due to their unique properties, leading to the development of numerous related catalyst-free photo-induced reactions encompassing diverse reaction types and key intermediates. This review aims to summarize the progress in catalyst-free photo-induced reactions involving photoexcited nitroarenes and offers a brief overview of future directions in this field.

Self-assembled Proteophenes. Oligothiophenes with distinct amino acid side-chain functionalities along the conjugated backbone displayed distinct chiroptical and structural properties in acidic or alkaline solutions. The distinct photophysical characteristics, as well as the supramolecular structures of the assemblies were highly influenced by the chemical nature of the amino acid, as well as the positioning of distinct amino acid moieties along the thiophene backbone.

Abstract

Oligothiophenes with specific photophysical properties and molecular organization are of great interest, since this class of materials are used in organic electronics and bioelectronics, as well as biosensing. Herein, 8 different pentameric oligothiophenes, denoted proteophenes, with different amino acid substitution patterns at distinct positions along the thiophene backbone were investigated. Spectroscopic and microscopic studies of the ligands revealed the formation of optically active self-assembled materials under acidic or basic conditions. The distinct photophysical characteristics, including induced circular dichroism, as well as the supramolecular structures of the assemblies deduced from light scattering and transmission electron microscopy, were highly influenced by the positioning of distinct amino acid moieties along the thiophene backbone. Proteophenes functionalized with only glutamate residues or these functionalities in combination with hydrophobic valine moieties formed fibrillar structures with excellent chiroptical properties under acidic conditions. In addition, the amino acid functionality at the β-position of distinct thiophene moieties influenced the induced circular dichroism pattern observed from the proteophenes. Overall, the obtained results demonstrate how changes in the position of various amino acid functionalities, as well as the chemical nature of the amino acid side chain functionality greatly affect the optical properties as well as the architecture of the self-assembled materials.

A pair of chiral TADF-active polymer emitters were designed and synthesized by the spiro donor-chiral acceptor strategy, and intense CPEL signals were detected from the corresponding CP-PLED devices.

Abstract

Circularly polarized electroluminescence (CPEL) from polymers with thermally activated delayed fluorescence (TADF) properties has been rapidly developed in recent years. So far, the designing strategies of such chiral TADF-active polymers are still limited. In this work, a new strategy of D−A* co-polymerization was proposed and two chiral polymers R-pSACODP and S-pSACODP were synthesized. The circularly polarized polymer light-emitting diode (CP-PLED) devices fabricated with R-pSACODP and S-pSACODP achieved comparable performances with maximum external quantum efficiencies (EQEs) of 12.0 % and 11.7 % at the wavelength of 581 nm, respectively. Moreover, mirror-imaged CPEL signals were also detected with electroluminescence dissymmetry factors (g _EL) of −1.1×10⁻³ and +1.3×10⁻³ from the corresponding CP-PLED devices, respectively. The results in this work effectively extend the designing strategies for the achievement of CPEL from chiral TADF-active polymers.

The introduction of the NiFe₂O₄ layer into the hematite results in a reduction in the onset potential, signifying an enhancement in the performance of PEC water splitting. This shift is attributed to the inhibition of electron back transfer from the FTO substrate to the hematite film.

Abstract

We found a new blocking layer (nickel ferrite, NiFe₂O₄), that could be utilized for the suppression of the back recombination, occurring in the hematite (α-Fe₂O₃) photoanode. The photoanode in which the NiFe₂O₄ layer was introduced showed a cathodic shift of the onset potential in the current density versus applied voltage curve. We successfully demonstrated that the NiFe₂O₄ layer effectively inhibited the back recombination in the hematite film through the use of electrochemical and time-resolved spectroscopic methods.

Different advanced oxidation processes (AOPs), such as Fenton, photo-Fenton and heterogeneous photocatalysis have been tested towards the degradation of Diclofenac sodium salt. Toxicity tests performed using Daphnia magna as model species unveiled the type of treatment which allows detoxification of the solution.

Abstract

Diclofenac sodium salt was photodegraded by means of advanced oxidation processes (AOPs), such as Fenton, photo-Fenton and heterogeneous photocatalysis. For the latter different photocatalysts were compared, namely commercial titania P25 and titania metallized with gold (0.1 % Au/P25), silver (1 % Ag/P25) and palladium (0.1 % Pd/P25). Homogeneous treatments demonstrated effective in the degradation of the selected pollutant (>80 % conversion @2 h) when the irradiation occurred within the solution. Also, photo-Fenton process assisted by visible light rather than UV was effective but slower and characterized by a toxicity of the residual solution due to unreacted H₂O₂. The photocatalyzed treatment performed at its best when P25 was used (70 % conversion @2 h), while modified photocatalysts reached the same conversion when H₂O₂ was added to the solution. Overall, in vitro toxicity tests using Daphnia Magna unveiled that the wastewater treated via M/TiO₂ treatment and photo-Fenton under UV in combination with H₂O₂ showed an acute toxicity comparable with the control group (almost 100 % viability @48 h). Conversely, the other processes failed to degrade completely either the pollutant or the hydrogen peroxide, leading to the mortality of 30–80 % of the individuals. An important outcome of the work is the direct comparison of different treatments to optimise the outcome, i. e. rapidity of degradation and non toxicity of the treated solution for living bodies.

The SPR-generated electric field (E-field) intensities around a Ag nanocube (NC) before and after covered by BaTiO3 (BTO) layer (BTO@Ag NC) were calculated. It was observed that the theoretical E-field intensities were reduced on BTO@Ag NC, thus suggesting inferior catalytic activities under visible light illumination. However, BTO@Ag NCs experimentally displayed better photocatalytic performance than that of Ag NCs under illumination at 633 nm, both in ambient argon (Ar) and in ambient air, where PATP molecules were used to probe the conversion. The mechanism can be attributed to the surface polarization of BTO layer trigged by SPR effect of Ag core. The oscillation of free electrons in Ag core aroused appearance of surface polarization charge on ferroelectric (FE) BTO surface, which resulted in the enhanced catalytic properties of BTO@Ag NCs. Therefore, our finding may provide a novel method to enhance visible-light responsive photocatalytic activity of wide bandgap FE materials by depositing them on plasmonic metal nanostructures.

Furanyl-substituted diketopyrrolopyrroles (DPP) with different branching of the alkyl side chains were studied. Both formed two distinct types of π-stacking leading to H-aggregates with considerably different energetics in terms of mixed lowest Frenkel and charge transfer (CT) states. The combined effect of the molecular structure and solid-state arrangement lead to fast and efficient CT mediated singlet fission, with one of the highest efficiencies (160 %) ever reported within the DPP family.

Abstract

Small modifications of the diketopyrrolopyrrole (DPP) molecular structure induced remarkable changes in its spectral and photophysical behavior. Using furan (F) heterosubstitution instead of thiophene (T) substituent resulted in a small blue shift and decreased Huang-Rhys factor of the absorption spectra in solution, irrespectively to N,N'-alkyls. Branching of alkyl side chains by formal 2-ethylation of n-hexyl substituent (C6 to EH) switched the slipped-stack arrangement, irrespectively on the heteroatoms. Consequent changes in steady-state absorption spectra of thin films were interpreted using time dependent density functional theory calculations, carried out on model dimers. Solid-state luminescence is weak and partially dependent on an excitation wavelength. Singlet fission was observed by femtosecond transient absorption spectroscopy, with considerably different yields for variously π-stacked FDPP-EH (30 %) and FDPP-C6 (160 %). The shape of triplet-triplet absorption spectra was also influenced by various π-stacking. The results are discussed in terms of different mixing of both Frenkel and charge transfer states in model dimers and different excitonic and electronic coupling in both types of π-stacks, visualized by natural transition orbitals.

The photoreaction of a styrylpyridine derivative leads to a DNA-binding benzoquinolizinium derivative with selectivity towards abasic site-containing DNA (AP-DNA), as caused by the sterically demanding substituents. Notably, the DNA binding is accomplished by photoinduced in situ formation of the ligand in the presence of AP-DNA.

Abstract

The photocyclization reaction of sterically demanding styrylpyridine derivatives was investigated and shown to depend on the type of substituent. With this method, a 2,2-diphenyl-1,3-benzodioxolo-annelated benzo[c]quinolizinium was synthesized, and its association with regular and abasic site-containing DNA (AP-DNA) was investigated by absorption, fluorescence, circular and linear dichroism spectroscopy. Specifically, this ligand binds preferentially to AP-DNA relative to regular duplex DNA, and the AP-DNA/ligand complex is formed in situ upon irradiation of the styrylpyridine substrate in the presence of the DNA.