Raman investigation of the low-temperature phase transition in a liquid crystalline system: terephthalidine-bis-heptylaniline (TB7A)

• Published in: Journal of Raman spectroscopy 2002-09, Vol.33 (9), p.720-725
• Main Authors: Singh, Ranjan K., Schluecker, S., Asthana, B. P., Kiefer, W.
• Format: Article
• Language: English
• ISSN: 0377-0486; 1097-4555
• DOI: 10.1002/jrs.906

Raman spectra of terephthalidine‐bis‐heptylaniline (TB7A) were recorded in the region 1125–1225 cm−1 from room temperature to 10 K at 18 different temperatures. The splitting of the ∼1165 cm−1 band, and the variation of the ratio of integrated intensities of the original band at ∼1165 cm−1 to the new component at 1170/1171 cm−1 reveals a solid modification. The analysis of the temperature dependence of the linewidth was made using Rakov's relation. A logarithmic plot as a function of 1/T gives two straight lines with an abrupt discontinuity, which clearly exhibits a phase transition at about 210 K. The temperature dependence of the linewidth of the ∼1165 cm−1 band was used to characterize this transition. A relatively large variation (∼3 cm−1) of the linewidth on going from 250 to 10 K in TB7A having an odd (n = 7) number of carbon atoms in the alkyl tail compared with those observed (∼1 cm−1) in other homologues having an even (n = 2 or 10) number of carbon atoms in the alkyl tail is a clear demonstration of the even–odd effect. Copyright © 2002 John Wiley & Sons, Ltd.