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Abstract Unraveling the intriguing aspects of the intramolecular charge transfer (ICT) phenomenon of multi‐modular donor‐acceptor‐based push–pull systems are of paramount importance considering their promising applications, particularly in solar energy harvesting and light‐emitting devices. Herein, a series of symmetrical and unsymmetrical donor‐acceptor chromophores1–6, are designed and synthesized by the Corey‐Fuchs reaction via Evano's condition followed by [2+2] cycloaddition retroelectrocyclic ring‐opening reaction with strong electron acceptors TCNE and TCNQ in good yields (~60–85 %). The photophysical, electrochemical, and computational studies are investigated to explore the effect of incorporation of strong electron acceptors 1,1,4,4‐tetracyanobuta‐1,3‐diene (TCBD) and dicyanoquinodimethane (DCNQ) with phenothiazine (PTZ) donor. An additional low‐lying broad absorption band extended towards the near‐infrared (NIR) region suggests charge polarization after the introduction of the electron acceptors in both symmetrical and asymmetrical systems, leading to such strong ICT bands. The electrochemical properties reveal that reduction potentials of3and6are lower than those of2and5, suggesting DCNQ imparts more on the electronic properties and hence largely contributes to the stabilization of LUMO energy levels than TCBD, in line with theoretical observations. Relative positions of the frontier orbitals on geometry‐optimized structures further support accessing donor‐acceptor sites responsible for the ICT transitions. Eventually, ultrafast carrier dynamics of the photoinduced species are investigated by femtosecond transient absorption studies to identify their spectral characteristics and target analysis further provides information about different excited states photophysical events including ICT and their associated time profiles. The key findings obtained here related to excited state dynamical processes of these newly synthesized systems are believed to be significant in advancing their prospect of utilization in solar energy conversion and related photonic applications. 

Abstract Near‐infrared (NIR) absorbing electron donor‐acceptor (D−A) chromophores have been at the forefront of current energy research owing to their facile charge transfer (CT) characteristics, which are primitive for photovoltaic applications. Herein, we have designed and developed a new set of benzothiadiazole (BTD)‐based tetracyanobutadiene (TCBD)/dicyanoquinodimethane (DCNQ)‐embedded multimodular D−A systems (BTD1‐BTD6) and investigated their inherent photo‐electro‐chemical responses for the first time having identical and mixed terminal donors of variable donicity. Apart from poor luminescence, the appearance of broad low‐lying optical transitions extendable even in the NIR region (>1000 nm), particularly in the presence of the auxiliary acceptors, are indicative of underlying nonradiative excited state processes leading to robust intramolecular CT and subsequent charge separation (CS) processes in these D−A constructs. While electrochemical studies identify the moieties involved in these photo‐events, orbital delocalization and consequent evidence for the low‐energy CT transitions have been achieved from theoretical calculations. Finally, the spectral and temporal responses of different photoproducts are obtained from femtosecond transient absorption studies, which, coupled with spectroelectrochemical data, identify broad NIR signals as CS states of the compounds. All the systems are found to be susceptible to ultrafast (~ps) CT and CS before carrier recombination to the ground state, which is, however, significantly facilitated after incorporation of the secondary TCBD/DCNQ acceptors, leading to faster and thus efficient CT processes, particularly in polar solvents. These findings, including facile CT/CS and broad and intense panchromatic absorption over a wide window of the electromagnetic spectrum, are likely to expand the horizons of BTD‐based multimodular CT systems to revolutionize the realm of solar energy conversion and associated photonic applications. 

The electrocatalytic nitrogen reduction reaction (NRR) is of significant interest as an environmentally friendly method for NH 3 production for agricultural and clean energy applications. Selectivity of NRR vis-à-vis the hydrogen evolution reaction (HER), however, is thought to adversely impact many potential catalysts, including Earth-abundant transition metal oxynitrides. Relative HER/NRR selectivities are therefore directly compared for two transition metal oxynitrides with different metal oxophilicities—Co and V. Electrocatalytic current–potential measurements, operando fluorescence, absorption, and GC measurements of H 2 and NH 3 production, ex situ X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations are combined to directly compare NRR and HER activities under identical reaction conditions. Results show that cobalt oxynitrides – with Co primarily in the Co( ii ) oxidation state – are NRR active at pH 10, with electrochemical reduction of both lattice nitrogen and dissolved N 2 , the latter occurring without N incorporation into the lattice. Removal of lattice N then yields Co( ii ) oxide, which is still NRR active. These results are complemented by calculations showing that N 2 binding at Co( ii ) sites is energetically favored over binding at Co( iii ) sites. GC analysis demonstrates that H 2 production occurs in concert with ammonia production but at a far greater rate. In contrast, vanadium oxynitride films are HER inactive under the same (pH 10) conditions, as well as at pH 7, but are NRR active at pH 7. DFT calculations indicate that a major difference in the two materials is hindered O–H dissociation of H 2 O adsorbed at O-ligated Co vs. V cation centers. The combined studies indicate significant variation in HER vs. NRR selectivity as a function of employed transition metal oxynitrides, as well as different HER mechanisms in V and Co oxynitrides. 

Abstract Using the popular metal‐ligand axial coordination self‐assembly approach, donor‐acceptor conjugates have been constructed using zinc tetrapyrroles (porphyrin (ZnP), phthalocyanine (ZnPc), and naphthalocyanine (ZnNc)) as electron donors and imidazole functionalized tetracyanobutadiene (Im‐TCBD) and cyclohexa‐2,5‐diene‐1,4‐diylidene‐expanded‐tetracyanobutadiene (Im‐DCNQ) as electron acceptors. The newly formed donor‐acceptor conjugates were fully characterized by a suite of physicochemical methods, including absorption and emission, electrochemistry, and computational methods. The measured binding constants for the 1 : 1 complexes were in the order of 10⁴–10⁵ M⁻¹in o‐dichlorobenzene. Free‐energy calculations and the energy level diagrams revealed the high exergonicity for the excited state electron transfer reactions. However, in the case of the ZnNc:Im‐DCNQ complex, owing to the facile oxidation of ZnNc and facile reduction of Im‐DCNQ, slow electron transfer was witnessed in the dark without the aid of light. Systematic transient pump‐probe studies were performed to secure evidence of excited state charge separation and gather their kinetic parameters. The rate of charge separation was as high as 10¹¹ s⁻¹suggesting efficient processes. These findings show that the present self‐assembly approach could be utilized to build donor‐acceptor constructs with powerful electron acceptors, TCBD and DCNQ, to witness ground and excited state charge transfer, fundamental events required in energy harvesting, and building optoelectronic devices. 

Abstract A far‐red absorbing sensitizer, BF₂‐chelated azadipyrromethane (azaBODIPY) has been employed as an electron acceptor to synthesize a series of push‐pull systems linked with different nitrogenous electron donors, viz.,N,N‐dimethylaniline (NND), triphenylamine (TPA), and phenothiazine (PTZ) via an acetylene linker. The structural integrity of the newly synthesized push‐pull systems was established by spectroscopic, electrochemical, spectroelectrochemical, and DFT computational methods. Cyclic and differential pulse voltammetry studies revealed different redox states and helped in the estimation of the energies of the charge‐separated states. Further, spectroelectrochemical studies performed in a thin‐layer optical cell revealed diagnostic peaks of azaBODIPY⋅⁻in the visible and near‐IR regions. Free‐energy calculations revealed the charge separation from one of the covalently linked donors to the¹azaBODIPY* to yield Donor⋅⁺‐azaBODIPY⋅⁻to be energetically favorable in a polar solvent, benzonitrile, and the frontier orbitals generated on the optimized structures helped in assessing such a conclusion. Consequently, the steady‐state emission studies revealed quenching of the azaBODIPY fluorescence in all of the investigated push‐pull systems in benzonitrile and to a lesser extent in mildly polar dichlorobenzene, and nonpolar toluene. The femtosecond pump‐probe studies revealed the occurrence of excited charge transfer (CT) in nonpolar toluene while a complete charge separation (CS) for all three push‐pull systems in polar benzonitrile. The CT/CS products populated the low‐lying³azaBODIPY* prior to returning to the ground state. Global target (GloTarAn) analysis of the transient data revealed the lifetime of the final charge‐separated states (CSS) to be 195 ps for NND‐derived, 50 ps for TPA‐derived, and 85 ps for PTZ‐derived push‐pull systems in benzonitrile. 

Abstract Copper and silver tritolylcorroles (TTC) are symmetrically functionalized to carry two tetracyanobutadiene (TCBD) entities via [2+2] cycloaddition‐retroeletrocyclization reaction involving ethynyl functionalized corroles with an electron acceptor, tetracyanoethylene (TCNE) in excellent yields, as the first examples of corrole‐TCBD push‐pull systems. The strong push‐pull effect resulted in charge polarization in the ground state resulting in a considerable hypsochromic shift of the spectrum extending it into the near‐IR region. Electrochemical studies coupled with computational studies revealed considerable interactions between the two TCBD entities via the corrole π‐system and the degree of such interactions was found to depend on the metal ion present in the corrole cavity. Energy considerations suggested charge transfer (CT) from the S₂or vibrationally hot S₁state but not the relaxed S₁state in the case of CuTTC(TCBD)₂while CT to occur from all these states in the case of AgTTC(TCBD)₂. Additionally, the high‐energy CT states populate the low‐lying triplet states. Systematic femtosecond pump‐probe studies provided the ultimate proof for the occurrence of excited CT as a function of excitation wavelength followed by the efficient population of the triplet states. The present study brings out the significance of charge transfer in efficiently populating the triplet states in rather unusual copper and silver corroles carrying two TCBD entities.