Temperature dependent Raman study of SB → SC transition in liquid crystalline compound N-(4-n-pentyloxybenzylidene)-4′-heptylaniline (5O.7)

Temperature dependent Raman study of C–H in-plane bending mode (∼1163 cm−1 and ∼1190 cm−1) and C–C stretching mode of phenyl ring (∼1571 cm−1 and ∼1594 cm−1) of N-(4-n-pentyloxybenzylidene)-4′-heptylaniline (5O.7) has been done. Vibrational assignment and potential energy distribution (PED) of individual modes have been calculated employing density functional theory (DFT) for the first time. The SB → SC transition is nicely depicted in the variation of the linewidth of the ∼1163 cm−1 band and the peak position of ∼1594 cm−1 band with temperature. Because of a small amount of charge density transfer from the core part to the alkyl chain region, the ∼1163 cm−1 band shifts towards lower wavenumber side whereas the ∼1190 cm−1 band towards higher wavenumber side at SB → SC transition. The ∼1571 cm−1 and ∼1594 cm−1 bands are assigned as 8a and 8b modes, whose relative intensity variation with temperature gives the evidence of increased possibility of C–H bending motion of the linking group and the C–C stretching of the alkyl chain in SC phase.