POLARIZATION-SELECTIVE PHOTOCHROMIC REACTION OF CYCLOPHANE IN GLASSY POLY(METHYL METHACRYLATE) MATRIX

Intramolecular photodimerization of the photochromic molecule tetraeth yl -(9,10)-anthracenophane-2,2,15,15-tetracarboxylate (abbreviated her eafter as cyclophane) was induced by irradiation with linearly polariz ed Light in the glassy state of,poly(methyl: methacrylate) (PMMA). Com pared to its homolog, roxymethyl)-10-[(naphthylmethoxy)methyl]anthrace ne (HNMA), which is known to undergo intramolecular photodimerization via conformational rearrangements, the reaction of cyclophane is more selective. These results were attributed to the specific cagelike stru cture of the cyclophane. The time evolution of the induction efficienc y eta(t) obtained from the two dichroic I absorbance components of cyc lophane shows a rise-and-decay behavior, indicating that irradiation i nterferes with the selectivity of the reaction. In order to separate t his effect from the reorientational; relaxation process of cyclophane in the polymer matrix; the optical anisotropy created by linear polari zed light was allowed to relax to the equilibrium state by annealing t he irradiated samples over different: time intervals. The decay of eta (t) can be well expressed by the sum of exponential functions of annea ling time. From the curve-fitting process, it was found that the tempe rature dependence of the reorientational relaxation rates of cyclophan e follows the Arrhenius type with the activation energy comparable to the beta-process of the PMMA matrix. The activation energy of HNMA obt ained under the same conditions is, on the other hand, similar to the gamma-relaxation process of PMMA, These results imply that the reorien tational relaxation of molecular dopants might be affected by the loca l-relaxation processes of the matrix, and dopants with different sizes reflect the rotational motions of different segments of polymer chain s. The experimental method described in this work not only provides an intriguing means to design polymer materials with controllable refrac tive index distribution but also gives a molecular basis for the under standing of the destabilization mechanism of dyes/polymer systems. use d in optoelectronic applications.