MID-FREQUENCY AND LOW-FREQUENCY RAMAN-SPECTRA OF STABLE AND METASTABLE CRYSTALLINE STATES OF THE 4-N-ALKYL-4'-CYANOBIPHENYL (N=9, 11, 12) LIQUID-CRYSTALS

Metastable crystalline states of each of the title compounds were reproducibly generated by rapid low-temperature quenching of the corresponding liquids, as judged by the phonon-like appearance of their low-frequency Raman spectra (5-200 cm-1) and by a splitting of the mid-Raman (ca. 2220 cm-1) CN stretch. Their observed aspects of peak frequencies, peak multiplicities and band widths differ markedly from those of the corresponding spectra of the stable crystals. We propose that the solid metastable configurations consist of packings or stacks of immobilized smectic-like structures with significant long-range positional order within each, but with disordered director orientations between them.