Non-symmetrical 1,3,4-oxadiazole derivatives: Synthesis, characterization, and computational study of their optical properties

Applications in electronics and photonics have spurred research on new electronic and optical materials, including organic chromophores. In this work, we synthesized and characterized five compounds (4 of which novel) containing the 1,3,4-oxadiazole group. Four of the molecules contain one oxadiazole moiety connected on one side to a phenylene bridge and an aliphatic tail, while the other side terminates with either a thiophene or a pyridine group. The fifth molecule features an additional phenylene and oxadiazole group separating the core from its thiophene terminus. DFT calculations were used to investigate the photophysical properties of the molecules. The calculated excitation energy reflected well the trend observed in the UV-Vis spectra. The calculated first hyperpolarizability (beta(0)) increased as the pyridine groups replaced the thiophenes. Extending the pi-conjugated bridge did increase beta in comparison to the shorter analog (both with the 2-thiophenyl end group), probably due to decreasing bandgap and excitation energy. Still, the highest beta(0) found was for the compound containing the 4-pyridyl end group (Oxa-4-Py, 24.0 x 10-30 e.s.u.), suggesting that the appropriate end group might overcome the effect of extending pi-conjugation.

Automated summary

In this study, five compounds containing the 1,3,4-oxadiazole group were synthesized and characterized. DFT calculations were used to investigate the photophysical properties of the molecules. The results showed that the presence of pyridine groups increased the first hyperpolarizability, and extending the π-conjugated bridge also increased the value, with the compound containing the 4-pyridyl end group showing the highest value.