Structure and polarized IR spectra of 4-isothiocyanatophenyl 4-heptylbenzoate (7TPB)

Single crystals of liquid crystalline 4-isothiocyanatophenyl 4-heptylobenzoate (7TPB) were grown and the X-ray crystal and molecular structures were determined. The polarized IR spectra were measured over a wide temperature range, passing from the isotropic liquid to the crystalline state, and compared with calculated spectra. The band assigned to ν(NCS) vibrations, which undergoes a spectacular blue-shift when going from isotropic to ordered states, appeared to be the most characteristic. Calculations show that the about 50 cm−1 shift should be ascribed to the formation of dimeric core-to-core antiparallel species. Analysis of the orientation of the molecules between the KRS-5 windows was performed based on the dichroic ratio in polarized IR radiation for various modes with parallel and perpendicular directions of the transition dipole moment vectors against the long axis of the molecule.