The spectra and photochemistry of the different isomers of some anils of salicylaldehyde and hydroxynaphthaldehyde were investigated over a range of solvents and temperatures. By running flash experiments in fluid solutions it was shown that both intramolecularly Hhyphen;bonded enol (E) andcishyphen;keto (QA) tautomers yield thetranshyphen;keto isomer (QC) as a common photoproduct. In a rigid paraffin glass only the Erarr;QC, but not the QArarr;QC, photoisomerization can be induced. Two previous suggestions for the mechanism of anils photochromism (i.e., the Erarr;QCconversion) were rehyphen;examined in terms of the experimental data. It is concluded that neither is applicable in its original form. The dark QCrarr;E relaxation in lowhyphen;polarity systems was investigated and was shown to proceed via dimer intermediates. The flash photolysis of a keto dimer (QB) was also studied. Excitation of QBleads to dissociation to enol monomers. An additional path is the formation of a shorthyphen;lived transient, presumably an excited triplet of the pair.
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