The photochemistry of azo-dyes. The wavelength-dependent photo-reduction of 4-diethylamino-4′-nitroazobenzene

Abstract

4-Diethylamino-4′-nitroazobenzene (I) is photoreduced upon irradiation at 254 nm, and in alcohols, also at 313 nm, while visible light is inactive. The products are the corresponding hydrazo-derivative (II) or the amines (III) and (IV). Triplet sensitizers of sufficiently high energy are effective, while the lowest triplet is not reduced. The reaction is inhibited by nitroxyl radicals. A mechanism implying hydrogen-abstraction on the part of some high lying triplet states of trans-(I) is proposed. Other than by energy transfer, these states can be reached by intersystem crossing from high lying singlet states.