A photophysical Study of 6,7,8,9-tetrahydro-5H-pyrido[2,3-b]indole dissolved in 2-methylbutane at decreasing temperatures from 293 to 93 K revealed the presence of two different fluorescence emissions due to doubly hydrogen-bonded dimers of the monomer species. One of the emissions is assigned to the normal tautomer form of the dimer of C-2 symmetry, and the other is mostly assigned to the most stable dimer, which is nonsymmetric (C-1) and exhibits single-proton transfer upon electronic excitation. As shown here, when the doubly hydrogen-bonded 7-azaindole dimer loses its centrosymmetry, by fusing a six-membered ring to the molecular structure, its first excited electronic state does not undergo I double-proton transfer but rather a single proton transfer, which, ill a fluid medium, causes the dimer to dissociate; if the medium can trap the resulting excited structure, then the compound exhibits fluorescence in the 410 nm region, which is typical of its protonated or deprotonated forms.