  Liquid crystal based technologies have found considerably diversified uses
and areas of application over the last few decades, proving to be excellent
materials for tunable optical elements from visible to near-infrared
frequencies. Currently, much effort is devoted to demonstrating their
applicability in the far-infrared or THz spectral frequency (1 - 10 THz), where
tremendous advances have been achieved in terms of broadband and intense
sources. Yet a detailed understanding of the dynamics triggered by THz light in
liquid crystals is far from complete. In this work, we perform broadband THz
Time Domain Spectroscopy on the low-frequency modes of 4-cyano-4'-alkylbiphenyl
(nCB) and 5-phenylcyclohexanes (PCH5) across different mesophases. DFT
calculations on isolated molecules capture the majority of the measured
response above 3 THz. In particular, the pronounced modes around 4.5 and 5.5
THz mainly originate from in-plane and out-of-plane bending of the cyano group.
In contrast, the broad response below 3 THz, linked to modes of the alkyl
chain, disagrees with the single molecule calculation. Here, we identify a
clear intermolecular character of the response, supported by dimer and trimer
calculations.

Chemical Physics;Soft Condensed Matter