Spectral-luminescent and solvatochromic properties of 2-(3′-coumarinyl)-5-(2′-(R-amino)-phenyl)-1,3,4-oxadiazoles

Spectral-luminescent properties of the newly synthesized 2-(3′-coumarinyl)-5-(2′-(R-amino)-phenyl)-1,3,4-oxadiazoles has been investigated in solvents of various polarity and hydrogen-bonding ability. It has been found that for all the studied compounds no excited state intramolecular proton transfer occurs despite the presence of coumarinyl fragment – electron acceptor effect of the coumarinyl fragment is not sufficient to increase the excited state acidity of the amino group. It has been found that the absorption spectra of the studied compounds shift to higher energy with increase in solvent polarity, whereas corresponding fluorescence spectra shift to lower energy with solvent polarity increase. It has been suggested that long-wavelength shifts of the fluorescence spectra of the studied compounds with increase in solvent polarity is caused by the solvent relaxation. The observed solvent relaxation effect allow us to propose some of the studied compounds as potential probes to monitor changes in solvent relaxation in low-polar media and as potential probes for rigidochromic effect.

► Spectral properties of coumarinyl-oxadiazoles were investigated in different solvents.
► No excited state intramolecular proton transfer occurs.
► Solvent relaxation causes red shifts of fluorescence spectra in polar solvents.
► Potential probes to monitor changes in solvent relaxation in low-polar media.