Electronic Spectra of Jet-Cooled 3-Methyl-7-azaindole Dimer. Symmetry of the Lowest Excited Electronic State and Double-Proton Transfer

Abstract

The fluorescence excitation spectra are recorded for jet-cooled dual hydrogen-bonded 3-methyl-7-azaindole dimer (3MAI)2-hh and deuterated dimers (3MAI)2-hd and (3MAI)2-dd near the electronic origin region of the S1−S0 transition, where hd and dd indicate the deuteration of an imino hydrogen and two imino hydrogens, respectively. A single origin is detected in the spectra of (3MAI)2-hh and (3MAI)2-dd, whereas two electronic origins separated by 13 cm-1 are detected in the spectrum of (3MAI)2-hd. The excited-state double-proton transfer (ESDPT) occurs in (3MAI)2-hh, while (3MAI)2-hd and (3MAI)2-dd undergo excited-state proton/deuteron transfer and excited-state double deuteron transfer, respectively. In (3MAI)2-hd, the excitation is localized on either the 3MAI-h or 3MAI-d moiety. The localization of the excitation is explained by a weak coupling of the excitonic states of (3MAI)2-hh and (3MAI)2-dd. The effective symmetry of the lowest excited state of (3MAI)2-hh and (3MAI)2-dd belongs to the C2h point grou...