Kinetics of photobleaching of Aberchrome 540 in various solvents: solvent effects

Abstract

The fulgide known as Aberchrome 540, E-form ((E) α-(2,5-dimethyl-3-furylethylidene) (isopropylidene) succinic anhydride), is a photochromic dye which undergoes conrotatory ring closure when irradiated with UV light at λ > 300 nm to give a red dye, C-form (7,7a-dihydro-2,4,7,7,7a-pentamethylbenzo[b]furan-5,6-dicarboxylic anhydride). The C-form is bleached with white light to revert back to the E-form. The photobleaching reaction was conducted in a number of solvents of various polarities over the temperature range 303–333 K. The extent of bleaching was monitored spectrophotometrically by measuring the absorbance of the C-form at λ max = 493 nm. The reaction is pseudo-first-order allowing for the extraction of the apparent rate constants and the apparent activation energies. The solvent polarity affects the rate of the photoinduced reaction and, in addition, other factors, such as the solvent viscosity and hydrogen bonding, are important.