Photoinduced Long-Distance Hydrogen-Atom Transfer in Molecules with a 7-Hydroxyquinoline Frame and a Carbaldehyde or Aldoxime Group as the Intramolecular Hydrogen Transporting Crane

The photochemical properties of monomeric 7-hydroxyquinoline substituted at position 8 with carbaldehyde or aldoxime groups were studied for the molecules isolated in solid Ar low-temperature matrices (at 10 K). It was experimentally demonstrated that upon UV excitation, both carbaldehyde and aldoxime groups act as intramolecular cranes transmitting hydrogen atoms from the hydroxyl group to the remote nitrogen atom of the quinoline ring. Furthermore, in the case of 7-hydroxyquinoline-8-aldoxime (and its derivatives), the second photochemical channel was activated upon UV (lambda > 360 nm) excitation. This process involves syn-anti isomerization around the double C=N bond in the aldoxime group. The structures of the reactant hydroxy tautomeric form and the photoproduced isomers of the studied molecules were unequivocally determined by means of IR spectroscopy combined with theoretical predictions of the IR spectra of the candidate structures.