Low-energy vibrational modes in phenylene oligomers studied by THz time-domain spectroscopy

Low-energy vibrational modes have been investigated in polycrystalline biphenyl, para-terphenyl, para-quaterphenyl and para-sexiphenyl using THz time-domain spectroscopy (THz-TDS). Anumber of both internal and external infrared-active modes were observed for wavenumbers ranging between 20 and 80 cm � 1 . The temperature dependence of these modes is consistent with structural phase transitions occurring in the molecular crystal, indicating that THz-TDS is a sensitive probe of the conformation of conjugated molecular systems.

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