Optical switching of 2-(2′-hydroxyphenyl) benzoxazole in different solvents

All-optical switching and beam deflection of 2-(2'-hydroxyphenyl) benzoxazole (HBO) in three species of solvent (cyclohexane, ethanol and dimethyl sulfoxide) have been investigated by using third-harmonic generation (355 nm) of a mode-locked Nd:YAG laser as a pump beam and a continuous-wave He-Ne laser (632.8 nm) as a probe beam. The nonlinear refractive indices of HBO in different solvents are determined by using the Z-scan technique. The optical switching and beam-deflection effects are due to the change of the refractive index of HBO under the pump beam. Through the study of the absorption spectra and the fluorescence spectra of HBO in different solvents, we conclude that the principal reason for the change of the refractive index of HBO is not the thermal effect because of absorption of the pump beam, but the excited-state intramolecular proton-transfer (ESIPT) effect of HBO under the pump beam. As the ESIPT process is very fast, HBO might be an excellent material for high-speed optical switching.