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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. 

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. 

Electro- and photocatalytic reduction of N 2 to NH 3 —the nitrogen reduction reaction (NRR)—is an environmentally- and energy-friendly alternative to the Haber-Bosch process for ammonia production. There is a great demand for the development of novel semiconductor-based electrocatalysts with high efficiency and stability for the direct conversion of inert substrates—including N 2 to ammonia—using visible light irradiation under ambient conditions. Herein we report electro-, and photocatalytic NRR with transition metal dichalcogenides (TMDCs), viz MoS 2 and WS 2 . Improved acid treatment of bulk TMDCs yields exfoliated TMDCs (exTMDCs) only a few layers thick with ∼10% S vacancies. Linear scan voltammograms on exMoS 2 and exWS 2 electrodes reveal significant NRR activity for exTMDC-modified electrodes, which is greatly enhanced by visible light illumination. Spectral measurements confirm ammonia as the main reaction product of electrocatalytic and photocatalytic NRR, and the absence of hydrazine byproduct. Femtosecond-resolved transient absorption studies provide direct evidence of interaction between photo-generated excitons/trions with N 2 adsorbed at S vacancies. DFT calculations corroborate N 2 binding to exMoS 2 at S-vacancies, with substantial π -backbonding to activate dinitrogen. Our findings suggest that chemically functionalized exTMDC materials could fulfill the need for highly-desired, inexpensive catalysts for the sustainable production of NH 3 using Sunlight under neutral pH conditions without appreciable competing production of H 2 . 

The significance of perylenediimide (PDI) in promoting excited charge transfer in push–pull systems carrying TCBD–TPA and DCNQ–TPA, is demonstrated using femtosecond transient absorption and other pertinent methods. 

The importance of diameter-sorted single-wall carbon nanotubes (SWCNTs) non-covalently bound to a donor-acceptor molecular cleft, 1, in prolonging the lifetime of charge-separated states is successfully demonstrated. For this, using a multi-step synthetic procedure, a wide-band capturing, multi-modular, C60-bisstyrylBODIPY-(zinc porphyrin)2, molecular cleft 1, was newly synthesized and shown to bind diameter sorted SWCNTs. The molecular cleft and its supramolecular assemblies were characterized by a suite of physico-chemical techniques. Free-energy calculations suggested that both the (6,5) and (7,6) SWCNTs bound to 1 act as hole acceptors during the photo-induced sequential electron transfer events. Consequently, selective excitation of 1 in 1:SWCNT hybrids revealed a two-step electron transfer leading to the formation of charge-separated states. Due to the distal separation of the cation and anion radical species within the supramolecules, improved lifetimes of the charge-separated states could be achieved. The present supramolecular strategy of improving charge separation involving SWCNTs and donor-acceptor molecular cleft highlights the potential application of these hybrid materials for various light energy harvesting and optoelectronic applications.