The wavelength- and solvent-dependent photochemistry of 1,1-dicyano-2-methyl-4-phenylbut-1-ene; reaction from two excited states1

Abstract

1,1-Dicyano-2-methyl-4-phenylbut-1-ene (4), on u.v. irradiation in solution, yields two products, 3,3-dicyano-2-methyl-4-phenylbut-1-ene (5) and 1-dicyanomethyl-1-methylindane (6). The photoreaction is dependent both on solvent polarity and on the excitation wavelength. A long-wavelength band in the absorption spectrum of (4), not present in the spectra of its isolated chromophores, is attributed to an intramolecular charge-transfer interaction. The unusual dependence on solvent and wavelength is explained in terms of a reaction mechanism in which (5) is formed from a delocalised excited state, with a staggered conformation, and (6) from a charge-transfer excited state, with an eclipsed conformation.