Aggregation-induced emission on benzothiadiazole dyads with large third-order optical nonlinearity

Abstract

Two kinds of D–A molecular of (4-(4-(9H-carbazol-9-yl)phenyl))-7-nitrobenzothiadiazole (BSC) and 4-((4-(9H-carbazol-9-yl)phenyl)ethynyl)-7-nitrobenzothiadiazole (BEC) containing carbazole moieties as the donor were synthesized. X-ray crystal data elucidated the multiple intermolecular interactions. They exhibit distinctly different self-assembly behaviours. The nonlinear optical properties were studied using the top-hat Z-scan technique at 532 nm with a 21 ps pulse. The results indicate that they exhibit large third-order nonlinear absorption effects. The nonlinear absorption coefficients α₂ fitting the experimental data are 6.3 × 10⁻¹² m W⁻¹ for BSC and 3.6 × 10⁻¹¹ m W⁻¹ for BEC. The time-resolved pump–probe results show that both nonlinear absorption and nonlinear refraction of BEC in CH₂Cl₂ solution have rapid optical responses, which indicate the nonlinear absorption and nonlinear refraction mechanism are excited-state nonlinear. Moreover, both of these two compounds are observed to be aggregation-induced emission (AIE) active. The aggregates of the well-formed one-dimensional microrods of BEC and BSC endow the material with potential applications in the field of optical devices.