PHOTOISOMERIZATION OF 2-(2'-HYDROXYPHENYL)BENZOXAZOLE - FORMATION ANDDECAY OF THE TRANS-KETO TAUTOMER IN DRY AND IN WATER-CONTAINING 3-METHYLPENTANE

2-(2'-Hydroxyphenyl)benzoxazole, like other o-hydroxyphenylbenzazoles, forms after excited-state intramolecular proton transfer the trans-ke to tautomer, K-1(tr). In dry, inert solvents this tautomer is relative ly long-lived and decays in a bimolecular reaction by doubleproton tra nsfer. Traces of water shorten the lifetime of K-1(tr) drastically due to proton-catalyzed re-enolization. In former investigations, the for mation of K-1(tr) has been overlooked by us. The quantum yield of tran s-keto formation is temperature dependent and becomes negligibly small below similar to 160 K.