Novel Benzothiadiazole‐based Donor‐Acceptor Systems: Synthesis, Ultrafast Charge Transfer and Separation Dynamics

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 donor‐ability. 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 strong intramolecular CT and subsequent charge separation (CS) processes in these D‐A constructs. The spectral and temporal responses of different photoproducts are obtained from transient studies. 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. These findings are likely to expand the horizons of BTD‐based multimodular CT systems to revolutionize the realm of solar energy conversion and associated photonic applications.