Abstract
The measurement of the electronic spectra of jet-cooled 4-chloro-7-azaindole dimer (4CAI₂) revealed that the Cl substitution substantially suppresses the excited-state double-proton transfer (ESDPT). Quantum chemistry calculation at the CIS level suggested that the change in the intermolecular stretching mode, which promotes ESDPT, is important for the suppression of ESDPT.