Spectral properties and orientational order of tetrafluoro-pentenyl-perylene dye in uniformly aligned liquid-crystalline films

The spectral properties of 3,4,9,10-tetra-(2,2,3,3,4,4,5,5,5-tetrafluoro-pentenyl)-perylene in low-molar-mass liquid crystals, 4-n-heptyl-4′-cyanobiphenyl, 4-n-octyl-4′-cyanobiphenyl, and trans-4-(4-heptyl-cyclohexyl)-benzonitrile, are investigated using electronic absorption and fluorescence methods. The experiments reveal the presence of the bands in the spectra characteristic of perylene precursor. Subsequently, the orientational order parameters of the fluorescent dye molecules in the calamitic liquid crystals are determined from the absorption and fluorescence anisotropies. The investigations show that the orientational distribution of the dye molecules in the liquid-crystalline films is anisotropic which make such systems technologically applicable in optoelectronics. However, the relatively low order parameters values for the tetrafluoro-pentenyl-perylene are a drawback in utilization of this dye as a fluorescent probe for determination the orientational order parameters of liquid crystal molecules.