Electronic Spectra of Hydrogen-Bonded Indazole in a Supersonic Free Jet

Fluorescence properties of indazole complexes with various protic molecules in supersonic jets are investigated. Indazole forms hydrogen-bonded complexes with acetic acid, formic acid, water and ethanol in jets and the 0-0 bands are shifted by 256, 243, 274 and 201 cm\u27 to the red of the 0-0 band of free indazole, respectively. The dispersed fluorescence spectra of these complexes are all similar indicating similar complex structures. Different from the cases of indazole-acid complexes in solution, no spectroscopic evidence was obtained in jets for excited state tautomerization or protonation. On the basis of the analysis of the fluorescence excitation and emission spectra, it is suggested that indazole-acid complexes in jets are bonded by a single hydrogen bond