Photoinduced long-distance hydrogen-atom transfer in molecules with 7-hydroxyquinoline frame and carbaldehyde, aldoxime or Schiff base groups as intramolecular hydrogen-atom-transporting cranes

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 10K). It was experimentally demonstrated that upon UV excitation both carbaldehyde and aldoxime groups act as intramolecular cranes transmitting hydrogen atom 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 (λ > 360 nm) excitation. This process involves syn-anti isomerization by rotation around the double C=N bond in the aldoxime group. Analogous UV-induced processes (long-range hydrogen-atom transfer and syn-anti isomerization) were theoretically predicted to occur in molecules of 7-hydroxyquinoline substituted at position 8 with a Schiff-base group.