Picosecond Time-Resolved Fluorescence Spectroscopy of the Photochromic Reaction of Spiropyran in Langmuir-Blodgett Films

Article abstract of DOI:10.1021/j100163a020

The photochromic reaction of spiropyran <-> merocyanine has been studied with 1'-octadecyl-3',3'-dimethyl-6-nitrospiro<2H-1-benzopyran-2,2'-indoline> (SSP) incorporated in Langmuir- Blodgett (LB) films prepared in a mixed film with stearic acid, arachidic acid, and tripalmitine.Time-resolved fluorescence spectra and decay curves of SSP and its photoisomer, merocyanine (SMC), were measured with a picosecond time-correlated, single-photon-counting apparatus.When SSP in LB films was excited at 360 nm, two fluorescence bands were observed: one has a maximum at 660 nm, and the other has a relatively weak band at 530 nm.We assigned them respectively to the fluorescence band of SMC and an intermediate X as a precursor of SMC.The rigidity of the medium surrounding photochromic molecules is an important factor in determining the rate of reversible photoconversion of SSP <-> SMC.