We have measured the terahertz (THz) absorption spectra of MBBA (4-Methoxybenzylidene-4'-n-butylaniline) and its
homologues by using THz time-domain and polarized fourier transform far-infrared (FT-IR) spectroscopy, and observed
the absorption peak due to the permanent dipole moments perpendicular to the molecular long axis. In addition, we also
measured the THz absorption spectra of CCN47 (4'-trans-butyl-4-cyano-4-trans-heptyl-1,1'-bicyclohexane) which has a
large permanent moment perpendicular to the long axis, by using polarized far-infrared FT-IR spectroscopy. The relation
between the vibration modes and the absorption in the THz region is discussed.