Modulated excited state geometry and Electron-Phonon coupling of lutein by temperature and solvent polarizability

Resonance Raman spectroscopy is one of the spectroscopic methods often chosen for studying linear polyene molecules because the Raman intensities of their υ₁ (C = C) and υ₂ (C-C) stretching vibrations are sensitive to electron-phonon coupling and the π-electron energy gap. Here, the resonance Raman and absorption spectra of lutein were studied as a function of solvent polarizabilities and of temperature in the CS₂ solvent. For lutein in CS₂, as the temperature decreased and CS solidified, the Raman scattering cross-section (RSCS) and the electron-phonon coupling constant had opposite dependence trends on temperature. The wavenumber of the lutein 0-0 electronic transition showed a marked shift to lower wavenumbers when the polarizability of the solvents decreased, and the Huang-Rhys (HR) factors and electron-phonon coupling also decreased. This work helps explore the influence of the external environment (e.g., temperature and solvent) on the excited state geometry of linear polyene molecules.