Unified analysis of optical absorption spectra of carotenoids based on a stochastic model.

The chemical structures of the carotenoid molecules are very simple and one might think that their electronic features are easily predicted. However, there is still has so much unknown information excepting the correlation between the electronic energy state and the length of effective conjugation chain of carotenoids. To investigate the electronic feature of the carotenoids, the most essential method is measuring the optical absorption spectra, but simulations based on the resonance Raman spectra are also an effective approach. For this reason, we studied the optical absorption spectra as well as resonance Raman spectra of 15 different carotenoid molecules each possessing a cyclic end-group, recorded in tetrahydrofuran (THF) solutions at room temperature. The whole band shapes of the absorption spectra of all these carotenoid molecules were successfully simulated using a stochastic model and Brownian oscillators. The parameters obtained from the simulation make it possible to discuss the intermolecular interaction between carotenoids and solvent THF molecules quantitatively.