Photochromism induced aggregate-monomer interconversion and fluorescence switch of porphyrin with spiropyran

A photo-induced fluorescence switch based on a novel mechanism was provided by physically mixed TPPS (tetra (4-phenylsulfonicacid) porphyrin) and SP (1-(β-carboxyethyl)-3, 3-dimethyl-5′-nitrospiro (indoline-2, 2′ [2H-1] benzopyran)). The ground state dipole moment of the open form (photomerocyanine, MC) is much larger than that of SP, thus it can induce the transformation of aggregated TPPS to its monomer, which is confirmed by UV–Vis absorption spectra, RLS spectra, and fluorescence lifetime. While TPPS aggregate has a fluorescence self-quenching phenomenon, its fluorescence was greatly enhanced after the formation of monomer. When the mixture was exposed to visible light, MC decayed back to SP, and consequently, TPPS monomer aggregated again, which resulted in its fluorescence turn off. Copyright © 2007 John Wiley & Sons, Ltd.