Translational motion and isomerization reaction near a solid-liquid interface studied by the interface sensitive transient grating method

Translational diffusion and cis-trans isomerization reaction of a liquid crystal molecule (N-(4-methoxybenzylidene)-4-n-butylaniline (MBBA)) at a solid-liquid interface were studied by the interface sensitive transient grating (TG) technique. The interface sensitivity was achieved by the total internal reflection for the probe light. In all solvents we used, the fringe length dependence of the decay rate constants of the species grating signal reveals that the diffusion constant at the interface region (49 nm) is similar to that in the bulk liquid. In some solvents, faster decays at interface than those in the bulk phase were observed, and they are mainly attributed to the enhanced cis-trans isomerization of MBBA at the interface. The enhancement is not sensitive to the solid surface conditions and depends on the solvents. These facts suggest that the enhancement originates from different solvent structures near the interface from those in the bulk phase. The isomerization rate measured in a porous glass was also increased from that in the bulk phase, which may support this suggestion. The interface sensitive TG signal of another photochromic molecule (spiropyran) was also detected. (C) 1999 Elsevier Science S.A. All rights reserved.