Effects of the structural order of canthaxanthin on the Raman scattering cross section in various solvents: A study by Raman spectroscopy and ab initio calculation

In this work, we measure the Raman scattering cross sections (RSCSs) of the carbon-carbon (CC) stretching vibrational modes of canthaxanthin in benzene, acetone, n-heptane, cyclohexane, and m-xylene. It is found that the absolute RSCS of CC stretching mode of canthaxanthin reaches a value of 10^-24 cm²·molecule^-1·sr^-1 at 8×10^-5 M, which is 6 orders of magnitude larger than general RSCS (10^-30 cm²·molecule^-1·sr^-1), and the RSCSs of canthaxanthin in various solvents are very different due to the hydrogen bond. A theoretical interpretation of the magnetic experimental results is given, which is introduced in a qualitative nonlinear model of coherent weakly damped electron-lattice vibration in the structural order of polyene chains. In addition, the optimal structure and the bond length alternation (BLA) parameter of canthaxanthin are calculated using quantum chemistry calculation (at the b3lyp/6-31g (d, p) level of theory). The theoretical calculations are in good agreement with the experimental results. Furthermore, the combination of Raman spectroscopy and the quantum chemistry calculation study would be a quite suitable method of studying the structures and the properties of the π -conjugated systems.