RELATIONSHIP BETWEEN REORIENTATIONAL MOTIONS OF A PHOTOCHROMIC DOPANTAND LOCAL RELAXATION PROCESSES OF A GLASSY POLYMER MATRIX

The reorientational relaxation process of the photochromic molecule ro xymethyl-10-[(naphthylmethoxy)-methyl]anthracene (HNMA) was observed i n glassy poly(methyl methacrylate) (PMMA). For this purpose, the intra molecular photodimerization of HNMA incorporated in a PMMA matrix was selectively induced by irradiation with linearly polarized light. The optical anisotropy created in this way in the sample was allowed to re lax to equilibrium by annealing at different temperatures. The reorien tational relaxation of HNMA associated with this thermal treatment was subsequently observed by monitoring the time dependence of the two di chroic absorbance components of the anthracene moieties of HNMA. It wa s found that this relaxation process is well described by the sum of a n exponential function of annealing time and a baseline which strongly depends on temperature. This fact implies that HNMA was not completel y randomized in the glassy state of PMMA upon annealing. Furthermore, within the range of experimental temperatures, the activation energy o f the reorientational relaxation rates of HNMA is close to that of the gamma-process of the PMMA matrix, suggesting that the relaxation of t he anthracene moieties is affected by the rotational motions of the al pha-methyl groups on the PMMA chain backbone. These preliminary result s might provide some helpful guiding principles for controlling the st ability of host/guest polymer materials using non-linear optical dyes.