Molecular Design and Synthesis of Hetero-trichromophore for Enhanced Nonlinear Optical Activity

A new hetero-trichromophore (HT-1) was designed and synthesized by linking neutral-ground-state (NGS) chromophore 1 with zwitterionic (ZWI) chromophore 2, and their molecular structures were confirmed by elemental analysis, UV−vis absorption spectra, 1H NMR, etc. Theoretical calculations show that there is a decrease of molecular dipole moments in gas phase when chromophores 1 and 2 are linked together. The polymer films were fabricated by doping trichromophore HT-1, NGS chromophore 1, and ZWI chromophore 2 into poly(4-vinylphenol) (PVPh). The second harmonic generation coefficients (d 33) of the films and the thermal stability of optical nonlinearities were measured by in situ second harmonic generation (SHG) measurement. The results show that almost a 5-fold enhancement in second harmonic coefficients (d 33) is realized as the combination of NGS chromophore and ZWI chromophore. The results indicate that NGS and ZWI chromophore combined hetero-trichromophores can efficiently improve the macroscopic optical nonlinearities in poled polymer materials.