Photochromism of phenoxynaphthacenequinones: diabatic or adiabatic phenyl group transfer?
|Year of publication||2007|
|Type||Article in Periodical|
|Magazine / Source||PHOTOCHEMICAL & PHOTOBIOLOGICAL SCIENCES|
|MU Faculty or unit|
|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.|