Theoretical study on photophysical properties of twisted D-A interaction TPA-BSM derivatives

Luminogens with aggregation-induced emission (AIE) properties have received considerable attention as excellent candidates for optoelectronics, chemical/biosensors, and bioimaging. Recently, molecule TPA-BSM with the twisted intramolecular charge transfer, with a twist angle of 40.96 degrees between the donor TPA and acceptor BSM units, has exhibited unique photophysical properties, especially the AIE properties in the aggregate and solid state. However, the relationship between their structure and performance has not been fully explored, which will further expand their application areas. Herein, based on the reported TPA-BSM, four new derivatives are designed. Their electronic structure, electron absorption, hole reorganization energy and second-order NLO response have been systematically studied using DFT and TD-DFT theories. It is found that they are all narrow bandgap derivatives. The introduction of donor units can reduce the energy gap, red-shift the first absorption peak, increase the dipole moment and the static first hyperpolarizability, while the introduction of acceptor units is just the opposite. However, the introduction of donor or acceptor units cannot further enhance the hole transport performance, but except for molecule TB-N(CH3)(2), the other four derivatives are potential hole transport materials. Due to have large first hyperpolarizabilities of the investigated derivatives, they are promising candidates for excellent second-order NLO materials.