CONCENTRATION-DEPENDENCE OF FADING OF THE OPEN FORM OF 6'-NITROINDOLINOSPIROPYRAN IN A POLYMER MATRIX

The concentration dependence of the fading process of the open form of 6'-nitroindolinospiropyran (BIPS) in PMMA has been studied by fluorescence lifetime measurements at 77 K. At sufficiently high concentrations, the fluorescence decay becomes bi-exponential which indicates that energy transfer occurs to molecules absorbing at longer wavelengths. This leads to a blue-shift of the absorption maximum during the fading process. The retardation of the decolouration of BIPS with increasing concentration is attributed to the interaction between the permanent dipoles of BIPS. Numerical calculations of the concentration dependence of the decolouration rate, which include the dispersive character of the decay rate due to the polymer matrix, are given.