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 (similar to 1163 cm(-1) and similar to 1190 cm(-1)) and C-C stretching mode of phenyl ring (similar to 1571 cm(-1) and similar to 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 S-B -> S-C transition is nicely depicted in the variation of the linewidth of the similar to 1163 cm(-1) band and the peak position of similar to 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 similar to 1163 cm(-1) band shifts towards lower wavenumber side whereas the similar to 1190 cm(-1) band towards higher wavenumber side at S-B -> S-C transition. The similar to 1571 cm(-1) and similar to 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 S-C phase. (C) 2010 Published by Elsevier B.V.