Spectrokinetic study of 2,2-diphenyl-5,6-benzo(2H)chromene: a thermoreversible and photoreversible photochromic system

In this paper the photochromic reaction of the 2,2-diphenyl-5,6-benzo (2H)chromene is investigated by spectrophotometric methods using monochromatic irradiation wavelengths in the UV and visible ranges. Two coloured species are produced upon irradiation, one is thermoreversible, the other is photoreversible. The colour-forming kinetics were followed under steady irradiation using W light (357 nm). The kinetic parameters (rate coefficient and activation energy) of the thermal ring-closure reaction were determined. The photochemical bleaching was induced by exciting with visible light (422 nm). To determine reaction quantum yields and molar absorption coefficients of the metastable species, both photostationary and photokinetic methods were employed. Based on the results obtained, a plausible reaction mechanism is proposed (C) 1998 Elsevier Science S.A. All rights reserved.