Synthesis, X-ray crystal structure and optical properties of novel 2,5-diaryl-1,3,4-oxadiazole derivatives containing substituted pyrazolo[1,5-a]pyridine units

A series of pyrazolo[1,5-a]pyridine-containing 2,5-diaryl-1,3,4-oxadiazole derivatives were synthesized and their structures were characterized by IR, 1H NMR and HRMS spectra. The crystal structure of 3a was determined using single crystal X-ray crystallography. Its spatial structure was found to be monoclinic, and all aromatic rings were approximately coplanar, which allowed conjugation. The absorption results showed that compounds 1a–f presented their absorption peaks ranging from 264 nm to 290 nm, while compounds 3a–f with a larger conjugation system exhibited red-shifted absorption character (absorption maxima between 283 nm and 303 nm) compared to the corresponding absorption of 1a–f. Fluorescence spectra revealed that these compounds exhibited blue fluorescence (421–444 nm) in dilute solutions and showed quantum yields of fluorescence between 0.32 and 0.83 in dichloromethane.

► The first optical properties report of pyrazolo[1,5-a]pyridine compounds.
► The target heterocyclic compounds showing high quantum yields of fluorescence.
► First report on synthesis of 1,3,4-oxadiazole-containing pyrazolo[1,5-a]pyridines.