Phonon self-energies and phase transitions in a prototype discotic liquid crystal

Specific Raman active vibrations in the discotic liquid crystal nematogen hexakis(6-hexyloxy)triphenylene are shown to be sensitive to either the isotropic<-->columnar or the columnar<-->solid phase transitions. Changes in frequency and/or intensity of vibrations with specific symmetries demonstrate that the method can be used not only to monitor the phase transitions themselves with a microscopic and noninvasive optical technique, but also to gain physical information on the origin of the molecular interactions that produce them.