Dynamics of a polymer matrix probed by the ring closure of merocyanine

Decolouration kinetics of the merocyanine-spiropyran transformation in a PBMA matrix near T_g are followed for both thermal and photoinduced reaction. The barrier of steric hindrance to the intramolecular rotation of the chromophore is approximated to be 22 kJ/mol with significant inhomogeneous fluctuation (±3 kJ/mol) giving rise to the dispersive nature of the decay. The thermal course of the deviation from exponential behavior indicates a temperature dependent rate at which local configurations reorganize. A quantitative description of these matrix dynamics is given, extending the static model to temperatures where the steric hindrance due to the polymer matrix can no longer be expected to be static on the timescale of the reaction. Experimental findings are quantitatively mapped by the model without the need of discontinuities near T_g.