Synthesis and characterization of a novel indoline based nonlinear optical chromophore with excellent electro-optic activity and high thermal stability by modifying the π-conjugated bridges

Abstract

Two novel second order nonlinear optical (NLO) chromophores based on indoline donors and tricyanofuran (TCF) acceptors linked together via modified polyene π-conjugation bridges have been synthesized in good overall yields and systematically characterized. Thermal stability, optical property and electro-optic property were measured to investigate the effects of the introduced rigid benzene derivative steric hindrance group on the bridge. Besides, density functional theory (DFT) was used to calculate the HOMO–LUMO energy gaps and first-order hyperpolarizability (β) of these chromophores. After introducing the benzene derivative steric hindrance group into the bridge, chromophore CLH-2 showed very good thermal stability with a decomposition temperature of 250 °C, which was 83 °C higher than chromophore CLH-1 without the isolation group on the bridge. In electro-optic activity, the introduction of rigid steric hindrance groups can effectively reduce dipole–dipole interactions to translate the relatively small β values into bulk high EO activities. By doping chromophores CLH-1 and CLH-2 with a high loading of 45 wt% in APC, EO coefficients (r₃₃) of up to 63 and 102 pm V⁻¹ at 1310 nm can be achieved, respectively. The r₃₃ value of the new chromophore CLH-2 was about 1.6 times that of chromophore CLH-1. The high r₃₃ value, good thermal stability and high yield suggest the promising applications of the new chromophore in nonlinear optical areas.