Enhanced the electro-optic activity of optical chromophores via rigid isolation groups modification

We engineered a conjugated organic chromophore, BHC-1, for second-order nonlinear optics, integrating a julolidine donor, a CF3-Ph-TCF acceptor, and a diene bridge. To systematically study steric effects, the diene bridge was further modified with two types of distinct benzene derivative isolation groups, leading to the synthesis of chromophores BHC-2 and BHC-3. In this paper, the synthesized chromophores demonstrated robust thermal stability, as evidenced by decomposition temperatures above 230°C. Notably, UV-Vis analysis revealed that the chromophores BHC-2 and BHC-3 showed a stronger solvent effect, and they were more easily polarized than the chromophore BHC-1. By doping the three chromophores in amorphous polycarbonate (APC) at a significant weight fraction (35 wt%), the highest electro-optic (EO) coefficients (r33) at 1310 nm can reach 70, 121, and 132 pm/V-1. The results showed that polymers doped with chromophores bearing rigid sterically hindered groups exhibit higher EO activity. It suggests that the benzene derivative isolation groups are critical for mitigating dipole-dipole interactions through steric hindrance and enhancing the poling efficiency. The high EO coefficients and the good thermal stability validate its application in the field of nonlinear optics.