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 monoc hromatic irradiation wavelengths in the UV and visible ranges. Two col oured species are produced upon irradiation, one is thermoreversible, the other is photoreversible. The colour-forming kinetics were followe d under steady irradiation using W light (357 nm). The kinetic paramet ers (rate coefficient and activation energy) of the thermal ring-closu re reaction were determined. The photochemical bleaching was induced b y exciting with visible light (422 nm). To determine reaction quantum yields and molar absorption coefficients of the metastable species, bo th photostationary and photokinetic methods were employed. Based on th e results obtained, a plausible reaction mechanism is proposed (C) 199 8 Elsevier Science S.A. All rights reserved.