A 10(-5) M solution of 7-azaindole in an inert solvent such as 2-methylbutane at a low temperature (77 K) consists of a dimer of C-2h symmetry of the compound. Electronic excitation of such a dimer causes a rapid double proton transfer via a concerted mechanism and produces fluorescent emission with an onset at 413 nm and a maximum at 480 nm, but the resulting tautomeric C-2h dimer does not emit phosphorescence. In this Letter, the phosphorescence of the tautomeric C-2h structure is reported for the first time, which is induced by the intramolecular heavy atom effect present in 3-bromo-7-azaindole dimer. (c) 2006 Elsevier B.V. All rights reserved.