Photophysics of 7-azaindole, its doubly-H-bonded base-pair, and corresponding proton-transfer-tautomer dimeric species, via defining experimental andtheoretical results
J. Catalan et M. Kasha, Photophysics of 7-azaindole, its doubly-H-bonded base-pair, and corresponding proton-transfer-tautomer dimeric species, via defining experimental andtheoretical results, J PHYS CH A, 104(46), 2000, pp. 10812-10820
Photophysical research on the experimental and theoretical bases for the bi
protonic transfer in the doubly-H-bonded dimer of 7-azaindole (7AI) is repo
rted. The spectroscopic properties of the 7AI monomer, the normal-tautomer
dimer, and the proton-transfer tautomer dimer are delineated by absorption,
fluorescence and excitation spectra. The monomeric 7AI molecule is shown t
o exist at 10(-6) M in hydrocarbon solution at 298 K, and the pure dimer at
temperatures below 227 K in 10(-4) M solution in 2-methylbutane (2MB). Deu
teration of the pyrrolic sites yields dimers which exhibit only normal-taut
omer fluorescence, whereas the nondeuterated 7AI dimer yields unique proton
-transfer tautomer fluorescence, indicating quantum-mechanical tunneling as
the principal mechanism for the biprotonic transfer. Density functional th
eory (B3LYP/6-31G** framework) calculations on the ground-state potential e
nergy curves conform to the experimental results.