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The precise value of linewidths obtained after correcting for the slitwidth effect for five Raman bands associated with the core of a liquid crystalline compound, terepthal-bis-decyl aniline (TBDA), have been studied in the temperature range of 12-472 K. The variation of the linewidth with temperature confirms two already reported phase transitions at 346 and 427 K. However, the phase transition at 427 K is not purely first order as reported earlier, but of mixed order in nature. From the measured linewidths of the ν φ−N and ν C=N modes below room temperature, the estimated activation energy for rotation along the φ-N bond closely matches with the S IS C phase transition temperature suggesting that the rotation about the φ-N bond is closely linked with this transition.

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The basic structural di erences between three thermotropic liquid crystals TB4A, TB7A and TB10A have been interpreted by analysing their Raman spectra. Three spectral regions, 925± 1025, 1275± 1475 and 1525± 1650 cmÕ 1 , have been chosen in this context to incorporate their structural dissimilarity. The induced planarity of the backbone, as an e ect of increasing chain length, has been studied by observing the changes in the respective Raman spectra of the three compounds. A tentative assignment of all the modes observed in the region 400± 1700 cmÕ 1 is made in this context. The molecular conformations of the three compounds have been predicted in their solution states, and are compared with the molecular environment that exists in their liquid crystalline states. Structural disorder at the solid± SmG transition is discussed and the changes are incorporated systematically.

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