Photochemistry of Transient Tautomer of 7-Azaindole H-Bonded Dimer Studied by Two-Step Laser Excitation Fluorescence Measurements

Article abstract of DOI:10.1021/ja00239a010

Formation of the monomeric tautomer (7H-pyrrolo<2,3-b>pyridine) in the photodissociation of the transient groun-state dimeric tautomer, generated via excited-state double proton transfer of 7-azaindole H-bonded dimer in 3-methylpentane (MP), was confirmled by transient absorption and two-step laser excitation (TSLE) fluorescence spectroscopies.The intense XeCl laser pulse (308-nm) excitation of the H-bonded dimer in MP at room temperature produced short- (17 μs) and a long-lived (47 μs) transients.The former and latter were ascribed to the dimeric and monomeric tautomers in the ground state, respectively.It is suggested that the second pulse excitation of the short-lived dimeric tautomer induces efficient dissociation to form a monomeric tautomer in the xcited state together with that in the ground state.One-color (308-nm) biphotonic processes within the XeCl laser pulse are therefore responsible for the long-lived monomeric tautomer in the ground state.The decay of the monomeric tautomer in the dark is attributable to the H-transfer reaction to yield 7-azaindole.Significant deuterium isotope effects were found for H-transfer of the monomeric tautomer as well as for photodissociation of the dimeric tautomer.