Comparison of second-order nonlinear optical chromophores with D–π–A, D–A–π–A and D–D–π–A architectures: diverse NLO effects and interesting optical behavior

Abstract

Four second-order nonlinear optical chromophores with D–π–A, D–A–π–A and D–D–π–A architectures have been synthesized and systematically characterized. Chromophores A and C have been synthesized with an additional acceptor (–CN) or donor group (thiophene) on the π bridge, termed the D–A–π–A and D–D–π–A configurations. D–π–A structural chromophores B and D were chosen as reference compounds for comparison. The results show that incorporation of the –CN group could increase poling efficiency possibly due to reduced intermolecular dipole–dipole interactions which results in comparable r₃₃ values (48 pm V⁻¹). An r₃₃ value of 45 pm V⁻¹ was obtained for the film C/APC suggesting significant site isolation. Compared with the D–π–A structural chromophores B and D, chromophores A and C demonstrated similar or enhanced NLO effects and better optical transparency.