Structural design of nonlinear optical chromophores for high-performance photorefractive polymers

Photorefractive response rate in a polymer composite of poly(N-vinylcarbazole)/2,4,7-trinitro-9-fluorenone, doped with 2,5-dimethyl-4-(4′-nitrophenylazo)anisole (DMNPAA) is improved by modifying the structure of DMNPAA. We found that four kinds of modified DMNPAA with alkyl substituents have fast orientational response to an external electric field and keep large anisotropy in polarizability. Among them, 4-butoxy-3-propyl-1-(4′-nitorophenylazo)benzene has the shortest reorientation time constant of 19 ms (E = 54 V/μm) and photorefractive time constant of 80 ms (I = 2 W/cm2, E = 54 V/μm) that are 2,300 times and 63 times faster than those of the DMNPAA composite. The mechanism of the fast reorientation in new polymer composites is investigated. The fast reorientational response is achieved by the improvement of the dispersivity in the polymer composites and the decrease of the glass transition temperature.