COLORED MEROCYANINE AGGREGATES - LONG-LIVED CRYSTALS OF LARGE-SIZE (10-100-MU-M) AND DEAGGREGATION OF SMALL AGGREGATES IN SOLUTIONS

Prolonged (>30 min) UV irradiation of 6- and ',3'-trimethylspiro[2H-1- benzopyran-2,2'-indoline] in some nonpolar solvents precipitated large -sized merocyanine crystals. The sizes of crystals (10-100 mum) were m uch larger than those of quasicrystals reported by Krongauz et al. Col ored merocyanine was long-lived (more than days) in these crystals. Ra man spectra indicate a structure in which transoid merocyanine conform ers are coupled to each other via the NO group in the aci-nitro struct ure. In the very initial stage of aggregate formation, anomalous nonex ponential absorption decay at the merocyanine monomer band was observe d. The anomaly was more pronounced for higher initial dye (spiropyran) concentration, for lower temperature, and for longer UV irradiation t ime. The anomalous absorption decay indicated partial deaggregation of small merocyanine aggregates in these solutions.