Vibrational spectra and molecular dynamics of alkoxycyanobiphenyls

The IR and Raman spectra of 3-alkoxy-4'-cyanobiphenyls (nOCB, when n = 3-8 is the number of carbon atom in the alkyl chain) were measured in the 30-3200 cm(-1) spectral region at 77-400 K. With the DSC and DTA methods, the temperatures and enthalpies of the state transitions were determined for the substances under study in the 100-400 K temperature range. The changes of the spectral parameters of several vibrational bands at phase transitions were interpreted as being caused by conformational changes of the nOCB molecules. The mechanism of intradimer energy transfer which explains the Q(C drop N) band broadening in the liquid crystal and isotropic liquid phases is discussed. (C) 1999 Elsevier Science B.V. All rights reserved.