Synthesis and Properties of Novel 1,3,4-Oxadiazole Derivatives

Preparation of high-efficiency carrier transport material is a key to fabricate more efficient and high performance organic and polymeric light-emitting devices. A series of rod-coil 1,3,4-oxadiazole derivatives with lateral carboxyls, 1,4-bis[5-(4-alkoxyphenyl)-1,3,4-oxadiazol-2-yl]-2,5-di(carboxy)benzenes (7; alkoxy = OCnH2n+1; n = 8, 12 and 16) were synthesized by condensation of terephthaloyl chloride (5) with benzohydrazides containing alkoxy chains with different lengths (2). The results show that introduction of two carboxyls whose electron-accepting ability is stronger reduces the electron density of the conjugated segment of 7, and thus leads to the absorption maximum bathochromic-shift compared to 8 (without carboxyl group). Calculation on the representative compound by the Dmol(3) package of MS Modeling 3.0 revealed that the decrease of energy levels in 7 was due to the change of the frontier molecular orbital distribution in the central benzene ring because of introduction of two carboxyls. The HOMO and LUMO energy levels of the compounds studied are in the range of -3.62 similar to-3.58 eV and -6.94 similar to-6.90 eV, which showed that they functioned well as electron-transporting materials.