The S-1 <- S-0 fluorescence excitation spectra have been measured for the dual hydrogen-bonded (3-methyl-7-azaindole)-(7-azaindole) hetero-dimer and its isotopomers in a supersonic free jet-expansion. The excited-state double-proton transfer (ESDPT) reaction occurs in the locally excited S, state of the undeuterated (3-methyl-7-azaindole)*-(7-azaindole) dimer. It has been found that the removal of the exciton resonance interaction provides little effect on the ESDPT reaction. (c) 2005 Elsevier B.V. All rights reserved.