PHOTOISOMERIZATION OF SPIROBENZOPYRAN IN POLYSTYRENE FILM

The photoisomerization mechanism of 1,3,3-trimethylindolino-6'-nitrospirobenzopyran in a polystyrene film was studied by means of a transient absorption measurement system with a pulsed laser and a streak camera. The results in polystyrene were compared with those in toluene. The excited triplet state of the cisoid open form (3X) was found in polystyrene at 440 nm. The slow isomerization process via 3X* was also found in polystyrene in addition to the fast process via excited singlet state 'X*. These were similar to the case of degassed toluene. Microviscosity environments produced a different effect in the process having a conformational change from the cisoid open form to a colored merocyanine form. The rise time of the transient absorbance of the merocyanine species was 1.2 ns, 10 times as long as that in toluene. © 1990, American Chemical Society. All rights reserved.