Shifting emission of oxadiazoles via inter- or intramolecular hydrogen bonding

Abstract

Light-emissive compounds able to transfer protons, either intra- or intermolecularly in the excited state, have increasingly attracted attention, especially by structural diversification of recognized fluorophores. We report herein synthesis and structural characterization of novel 1,3,4-oxadiazole-based compounds functionalised by salicylaldehyde or o-vanillin moieties. Solution absorption and emission spectroscopy performed on the resulted compounds indicated the essential influence of the established (intra and/or intermolecular) hydrogen bonds onto the optical properties. Theoretical calculations positively contributed to the effort of understanding the emissive behaviour of the compounds and the calculated data correlated very well to experiments. Occurrence of hydrogen bond interactions has been also observed in solid state and we discuss their molecular structures and the effects on the luminescent behaviour. The phenol groups in close proximity of the oxadiazole core were further exploited in cocrystallization experiments with pyridine-based co-partners. Hydrogen bonding were also found responsible for the supramolecular recognition between the two components. One type of the resulted co-crystals preserved the luminescence of the starting compound.