Photochromism of phenoxynaphthacenequinones: diabatic or adiabatic phenyl group transfer?

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Authors	BORN R. FISCHER W. HEGER Dominik TOKARCZYK B. WIRZ Jakob
Year of publication	2007
Type	Article in Periodical
Magazine / Source	PHOTOCHEMICAL & PHOTOBIOLOGICAL SCIENCES
MU Faculty or unit	Faculty of Science
Citation
Field	Nuclear and quantum chemistry, photochemistry
Keywords	LASER FLASH-PHOTOLYSIS; CONJUGATED RADICALS; ELECTRON-TRANSFER; PHOTOISOMERIZATION; MECHANISM; DERIVATIVES; SINGLET; STATE; 6-PHENOXY-512-NAPHTHACENEQUINONE; PHOTOCHEMISTRY
Description	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. ash 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 ( mu s) 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.
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