Far-infrared and Raman spectra of the solid phases of CBOOA

Abstract

The far-infrared and the Raman spectra of crystalline CBOOA (N-p-cyanobenzilidene-p-n- octyloxyaniline) have been studied above 30 cm-1. The temperature dependence of the far- infrared spectrum reveals the existence of a solid-solid transition at 65 degree C. The two solid modifi- cations can be obtained, respectively, from solvent crystallization (Phase 11) and solidification from the mesophase (Phase I). Differential scanning calorimetric results confirm that an endo- thermic change from Phase II to Phase I occurs at 65 degree C with an associated heat of transition of 2030 cal/mole. X-ray powder diffraction patterns establish that the structures of the two phases are different. Tentative vibrational assignments are made for the far-infrared and the Raman lines observed in the internal mode region. At frequencies below 120 cm-1, both the far-infrared and the Raman spectra of Phase II exhibit distinct modes whereas, Phase I exhibits nearly quasicontinuous spectra. The possible implications of this result for the structure of Phase I and the formation of the mesophase are discussed.