The singular coincidence of fluorescence spectra of the anionic and cationic species formed by the respective deprotonated and protonated pyrido-pyrrolo bases
Jc. Del Valle et al., The singular coincidence of fluorescence spectra of the anionic and cationic species formed by the respective deprotonated and protonated pyrido-pyrrolo bases, INT J QUANT, 77(1), 2000, pp. 118-127
Study of the chemically produced anionic and cationic species of the hetero
cyclics 7-azaindole (7-AI) and 1-H-pyrrolo[3,2-h]quinoline (1-HPQ) in 298 K
solution spectroscopy displays a striking coincidence of the anion/cation
spectra for each. A hybrid density functional calculation revealed that, in
spite of a very large electrostatic skeletal perturbation for the respecti
ve anion and cation pair, the lowest S-0 --> S-1 transition energy was larg
ely unperturbed. Generalization to other anion/cation pairs suggests the fo
llowing theorem: In a diheterocyclic aromatic molecule with proton-acceptor
and proton-donor heteroatom sites, a coincidence or near coincidence of th
e coa corresponding cation and anion fluorescence bands will be manifested
as a result of(+) and (-) electrostatic skeletal perturbations on the intac
t pi-electron system. An analysis of the detailed electronic mechanistic st
eps involved in the sequential laser pulse (1) excitation and (2) photoioni
zation steps indicate that an observed (7-AI)(H+) mass-119 cation observed
in femtosecond time-of-flight mass spectrometry is produced in the invasive
photoionization step and is not a likely intermediate in the biprotonic ph
ototransfer in the 7-AI H-bonded dimer. (C) 2000 John Wiley & Sons, Inc.