Temperature-dependent raman spectroscopic study of the nematic liquid crystal 4-n-pentyl-4′-cyanobiphenyl

The spectral behaviors of 4-n-pentyl-4′-cyanobiphenyl (5CB) have been studied by means of temperature-dependent Raman spectroscopy in the range between -70 and 70°C. The v(C≡N) bands in the Raman spectra were found splitting below the transition temperature from the solid to the nematic liquid crystalline phase at ∼24°C, suggesting the existence of solid crystalline polymorphism. The interfacial structures of 5CB on metal plate surfaces have been reexamined by surface-enhanced Raman scattering (SERS) at different temperatures. On Ag and Au, the asymmetric shapes of the v(C≡N) bands suggest that there should exist different binding schemes for 5CB on metal surfaces. These asymmetric bands in the v(C≡N) stretching region were found to vary in changing temperature.