Concentration dependence of fading of the open form of 6 ’-nitroindolinospiropyran i 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 sutliciently high concentrations, the fluorescence decay becomes hi-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 ofBIPS 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 dispenive character of the decay rate due to the polymer matrix, arc given. 1. LntrodlK!tion The photochromic reaction of C-nitroindolino-spiropyran (BIPS, 1) has been extensively studied in the liquid and solid phases and has been employed to study the dynamics of polymer matrices [1,2]. In-terest in the phenomenon of photochromism stems from the numerous applications that are foreseen for this effect, for instance, in the field of optical data storage and, on a more mundane level, for use in su