PICOSECOND FLUORESCENCE OF MEROCYANINES DERIVED FROM PHOTOCHROMIC SPIRONAPHTHOXAZINES

The emission of the merocyanines derived from the photochromic lspiro[ indoline-2,3'[3H]naphth[2,1-b][1,4]oxazine] 1, the 4,5-dimethyl-substi tuted compound 2 and the 6'-piperidino-substituted derivative 3, in so lution with acetonitrile or ethanol, was studied by means of a time-co rrelated single photon counting system with ca 10 ps time resolution. The signal decays were described by a sum of two or three exponential components with tau(1) = 10-60 ps, tau(2) = 0.5-1 ns, tau(3) = 1-2 ns, corresponding to the contribution of different fluorescing merocyanin e isomers. The most intense emission, the shortest lived one, is chara cterized by extremely low quantum yields (<10(-6)). The effect of the addition of LiClO4 to acetonitrile solutions of 2 is in agreement with the formation of ground-state complexes with particular open isomers.