Synthesis and characterization of photoconducting non-linear optical polymers containing indole-benzoxazole moiety

2-[3-(6-Nitro-benzoxazol-2-yl)-indol-1-yl]-ethanol (5) was synthesized as a photoconducting non-linear optical (NLO) chromophore with thermal and photochemical stabilities and broad transparency at the visible region. The peak wavelength of optical absorption was ca. 100 nm blue-shifted compared to those of conventional NLO chromophores, DANS or DR1. Methacrylate and acrylate ester of 5 were synthesized and subsequently copolymerized with methyl methacrylate and methyl acrylate, respectively, to give photoconducting NLO polymers. To further enhance the photoconductive sensitivity, hydrazone-containing methacrylate monomer was also copolymerized with 5. Alternatively photoconducting plasticizer N′-[9-(2-ethyl-hexyl)-9H-carbazol-3-ylmethylene]-N,N-diphenyl-hydrazone (EHCzHy) was mixed with simple copolymer (PIDBAc13) to give polymer composites with enhanced photoconductivity and reduced glass transition temperature (Tg). Photorefractivity was demonstrated for the 70:30 composite of PIDBAc13/EHCzHy doped with 0.2% thiapyrilium salt (Tg∼61°C) through the two-beam coupling and four-wave mixing.