Chiroptical, linear, and second-order nonlinear optical properties of tetrathiafulvalenylallene: a multifunctional molecular material

Abstract

Time-dependent density functional theory (TDDFT) calculations have been used to investigate chiroptical, linear, and second-order nonlinear optical (NLO) properties of the novel tetrathiafulvalenylallene in both neutral and two cationic states for the first time. The calculated UV-Vis/ECD spectra of the studied compound are in good agreement with the experimental ones, which can be used to assign its absolute configuration (AC) with high confidence. From neutral state to the two cationic states, the studied compound exhibits pronounced different chiroptical effects and second-order NLO response values. For example, the calculated β₀ value of 1²⁺ is 10.36 times as large as that of 1, while the β₀ value of 1⁴⁺ is 46.51 times as large as that of 1. These effects mainly result from the structural modifications of TTF units in the redox process. It is found that charge transfer between the tetrathiafulvalene (TTF) unit and the allene framework plays a key role in determining the chiroptical properties and electronic transition properties. It is interesting to find that the two benzene rings have vanishingly small effects on the chiroptical properties. The studied compound could act as both a chiroptical switch and NLO switch material from the standpoint of different chiroptical and NLO responses, reversible redox processes, and high stability. The effects of different functionals and basis sets, including solvent effects on the UV-Vis/ECD spectra were also considered.