title: Photochromism of phenoxynaphthacenequinones: diabatic or adiabatic phenyl group transfer?
abstract: The photochromic reactions of 6-phenyloxy-5,12-naphthacenequinone (1) and of the 6,11-diphenyloxy derivative 2 were investigated by subpicosecond pump-probe, photoacoustic, and emission spectroscopies, and by nanosecond laser flash photolysis (LFP). The transformation of the trans-quinones 1 and 2 to their ana-isomers proceeds via short-lived triplet states of 1 and 2 (tau ca. 2 ns) and spiro-bridged biradical intermediates (ca. 6 ns). The long-lived (micros) ana-triplets that are observed by LFP of 1 and 2 are formed (predominantly) by reexcitation of the biradicals and ana-quinones, which appear during the laser pulse. The reverse reaction, ana-->trans, proceeds exclusively from the lowest pi,pi* singlet state of the ana-quinones.
authors.affiliation: Departement Chemie der Universität Basel, Klingelbergstrasse 80, 4056, Basel, Switzerland.
authors.forename: Reto
authors.initials: R
authors.lastname: Born
authors.forename: Walter
authors.initials: W
authors.lastname: Fischer
authors.forename: Dominik
authors.initials: D
authors.lastname: Heger
authors.forename: Bogdan
authors.initials: B
authors.lastname: Tokarczyk
authors.forename: Jakob
authors.initials: J
authors.lastname: Wirz