Low temperature Raman study of a liquid crystalline system 4-Decyloxy benzoic acid (4DBA)

• Low structural modification in a liquid crystal below room temperature observed.
• Peak shift and relative intensity change of marker bands gives signatures.
• Peak shift explained by anharmonic coupling with low wavenumber modes.

The Raman spectra of a liquid crystalline system, 4-Decyloxy benzoic acid (4DBA) have been recorded at different temperatures within the interval 300–78 K in order to identify the structural changes in crystalline state of a nematogen and to understand the molecular alignment therein. The earlier predicted dimer structure of 4DBA was optimized with DFT method and the theoretical Raman spectra of dimer as well as monomer have been calculated for comparison with the experimental spectra. The mode specific quartic coupling coefficient; Ai,ω and phonon frequency; ωi have been calculated using temperature dependent anharmonic perturbation theory. The precise band shape analysis of Raman bands at ∼807, ∼881, ∼1255, ∼1282, ∼1436, ∼1576, ∼1604, ∼2881 and ∼3081 cm−1 gives signature of temperature induced slow crystal modification. The structural changes leading to crystal modification have been discussed.

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