Spectroscopic study on the structural isomers of 7-azaindole(ethanol)n (n=1–3) and multiple-proton transfer reactions in the gas phase

Abstract

The resonance-enhanced two-photon ionization (RE2PI) and laser-induced fluorescence excitation spectra were recorded for the S(1)-S(0)(pipi( *)) region of the 7-azaindole(ethanol)(n) (n=1-3) [7AI(EtOH)(n) (n=1-3)] clusters in the gas phase to investigate the geometrical structures and the multiple-proton/hydrogen atom transfer reaction dynamics. Four and two structural isomers were identified for 7AI(EtOH)(2) and 7AI(EtOH)(3), respectively. Density functional theory calculations at the B3LYP/6-31++G( * *)/6-31G( *) level predicted four different conformations of the ethyl group for 7AI(EtOH)(2), in good agreement with the observation of the four structural isomers in the RE2PI spectra. Visible fluorescence from the tautomeric forms was observed in the S(1) states for all isomers of 7AI(EtOH)(2), but no sign of double-proton/hydrogen atom transfer and quadruple-proton/hydrogen atom transfer has been obtained in the electronic spectra of 7AI(EtOH)(1) and 7AI(EtOH)(3), respectively. These results suggest that the multiple-proton transfer reaction is cluster-size selective, and the triple-proton/hydrogen atom transfer potential is dominated by the cyclic hydrogen-bonded network in 7AI(EtOH)(2). The excitation of the in-phase intermolecular stretching vibration prominently enhances the excited-state triple-proton/hydrogen atom transfer reaction.

Fast excited state dynamics in the isolated 7-azaindole-phenol H-bonded complex

“…In the gas phase, it has been shown that when both nitrogen atoms are connected by a H-bonded molecular wire of two H 2 O, 34,35 CH 3 OH, 36, 37 CH 3 CH 2 OH 38 molecules or in the case of the Hbonded (7AI) 2 dimer 39 and other substituted 7AI dimers, 40 the increased basicity and acidity of the two sites trigger the excited state tautomerization of 7AI. Vibrational mode selective tautomerization dynamics was experimentally observed from frequency-resolved, 34,37,38 and picosecond pump and probe experiments. 35 Excited state ab initio calculations suggest that the vibrational mode selective tautomerization mechanism in all the above mentioned complexes is due to a concerted double or triple proton transfer, while the electron remains in the π * orbital of the chromophore.…”

Polymorphism, Hydrogen Bond Properties, and Vibrational Structure of 1H-Pyrrolo[3,2-h]Quinoline Dimers

“…A well-known example is 7-azaindole (7AI, Figure 1), which forms doubly hydrogen bonded dimers in solution [2], while the X-ray data reveal a tetrameric structure in the crystalline state [3]. Different stoichiometries and structures are possible for the complexes of 7AI with methanol and water: 1 : 1, 1 : 2, and 1 : 3 species have been detected [4][5][6][7][8][9].…”

The Cyclic Hydrogen‐Bonded 6‐Azaindole Trimer and its Prominent Excited‐State Triple‐Proton‐Transfer Reaction

“…These results provide,for the first time,method for probing the fundamental of symmetric triple proton transfer using aH-bonded trimer in the excited state.Itisconceivable that such ac yclic H-bonded trimer should exist in the gas phase-particularly in the cold gas generated from am olecular beam-such that the fundamental of ESTPT can be probed with high resolution spectroscopy free from external environmental perturbation. [25] These findings illuminate the processes that underlie formation of multiple Hbonds and the associated multiple proton transfers that occur in the excited state.…”