The role of chemisorption for push-pull chromophores on SiO^sub 2^ surfaces in non-electrically poling host-guest NLO polymers

For decades, host-guest nonlinear optical (NLO) polymers have been studied because of their versatilities. NLO polymers do not display second-order nonlinearities in as-prepared conditions because the guest chromophores are randomly oriented in the host polymers and they are centro-symmetric. We report non-electrical poling behaviors of push-pull guest chromophores that consist of a π-conjugated phenylene vinylene bridged by an electron-accepting tricyanofuran moiety and electron-donating phenyl amine derivatives in poly (methyl methacrylate). When the phenyl amine moieties were substituted either by hydroxyl or carboxyl groups, enhanced emissions of second harmonic generations (SHG) were observed after annealing at temperatures above the glass transition point of the host polymers in the absence of external electric fields. The number of hydroxyl or carboxylic groups exerted significant influence on the polar ordering of the chromophores. The orientation behaviors of the chromophores were examined using heterodyne SHG, polarized linear absorption and polarized SHG spectroscopies.