Raman Spectroscopic Observation of Gradual Polymorphic Transition and Phonon Modes in CuPc Nanorod

A Raman scattering investigation of a single alpha-CuPc nanorod is demonstrated here within the temperature range 300-770 K From the typical thermal dispersion of Raman shift and phonon line width of in-plane Big mode at 1526 cm(-1), the metastable alpha polymorph is observed to undergo unambiguous phase transition to thermally stable beta phase. The phase transition temperature (456 K) is observed to be significantly lower than that reported for bulk samples. Extensive computation of normal modes associated with both alpha- and beta-CuPc reveal that the fingerprint domain across 1300-1600 cm(-1) is particularly sensitive to this = 50 polymorphic transition where a silent Beg mode appears at 1303 cm(-1) in the spectral vicinity of molecular edge vibration sensitive A(g)-B-g Davydov doublet.