Synthesis and characterization of carbazole-based nonlinear optical polymers possessing chromophores in the main or side chains

Abstract

We synthesized novel carbazole-based push–pull type nonlinear optical (NLO) polymers, P(Cz-CN), P(Cz-DR 19), and P(Cz-TCN). The structure of P(Cz-CN) was designed to contain di-acceptor-chromophores in the main chain and to have a two-dimensional (2D) charge transfer (CT) configuration. P(Cz-DR 19) and P(Cz-TCN) were designed to have NLO chromophores in the side chain. All the polymers synthesized were thermally stable approximately up to 250 °C. The glass transition temperatures ( T g) of P(Cz-DR 19) and P(Cz-TCN) appeared at 117 °C and 104 °C, respectively. The ratio of the second harmonic coefficients ( d 33/ d 31) was 1.5 in P(Cz-CN) and 3.3 in P(Cz-DR 19) and P(Cz-TCN). P(Cz-CN) showed enhanced off-diagonal tensor components due to 2D CT effects. The d 33 values of P(Cz-DR 19) and P(Cz-TCN) were 61.6 pm/V and 41.7 pm/V, respectively. The electro-optic coefficients ( r 33) of P(Cz-DR 19) and P(Cz-TCN) were 40.5 pm/V and 17.8 pm/V at 632.8 nm, respectively. P(Cz-DR 19) showed higher second-order optical nonlinearity than that of P(Cz-TCN) due to higher β-values of DR 19 moiety in the side chain. P(Cz-DR 19) and P(Cz-TCN) showed stable NLO coefficient up to 98 °C and 75 °C, respectively. The intensity of SHG of P(Cz-DR 19) was stable up to 20 days at room temperatures.