Orientational properties of 1,3,4-oxadiazoles in liquid-crystalline materials determined by electronic absorption and fluorescence measurements

The electronic absorption and fluorescence spectra of two 4-donor/4 '-acceptor substituted 2,5-diphenyl-1,3,4-oxadiazole derivatives in isotropic solvents (methanol, toluene), in a commercial mixture of low molecular mass liquid crystals - ZLI 1695 (MERCK, Darmstadt), and in a liquid-crystalline polysiloxane with 4-methoxy-4 '-pentoxy-phenylbenzoate side-groups are presented and discussed. The orientational order parameters of the 1,3.4-oxadiazoles, dissolved in the liquid-crystalline films with uniform planar orientation of the mesogenic molecules and in aligned films of the polysiloxane, are determined. The possibility of application in OLEDs of the 1,3,4-oxadiazoles dissolved in homogenous, oriented liquid-crystal line polymers is suggested.