Temperature effects on molecular alignments at the surface of ultrathin films studied by SHG and fluorescence techniques

Poly(methyl methacrylate) (PMMA) thin films incorporating amphiphilic dyes, ruthenium tris(2,2-bipyridine)-type complexes, were prepared by water casting. Films fabricated in this manner are peculiar with their well lined-up molecular orientations at the surface and thus are highly nonlinear effective. Unfortunately, like most other nonlinear materials, the surface orders of the dye molecules tend to collapse once exposed to heat. This work presents our recent studies on heat-induced molecular reorientation by probing SHG and fluorescence spectra. It shows that, in the course of heating between 20 °C and 80°C, the secondary glass transition of PMMA molecules is responsible for both the randomization of the surface alignments of the Ru complex molecules and the migration of these molecules into the body of the PMMA layer.