Effect Of Environment On Electron-phonon Coupling Of Lutein

In recent years,?-conjugated organic molecules have attracted extensive attention of researchers due to their great potential for applications in displays,photovoltaics,and wearable devices.Linear polyene molecule is a typical?-conjugated molecular system,which has the characteristics of large nonlinear coefficient and fast photoelectric response.As a typical linear polyene molecule,carotenoids have the advantages of wide distribution and sensitivity to environmental changes in addition to the above advantages.They are ideal molecules for studying the intermolecular interactions of ?-conjugated organic systems.In this paper,taking lutein in carotenoids as the research object,the effects of environmental changes on the molecular vibration of lutein solution were studied by means of resonance Raman spectroscopy,ultraviolet-visible absorption spectroscopy and variable temperature measurement.The dependence of lutein spectrum on solution temperature,solvent phase transition and solvent polarizability was obtained,and the corresponding Raman scattering cross-section changes and electron-phonon coupling coefficients were calculated.This study is helpful to obtain information such as vibrational transition,electronic energy gap,energy surface shift between excited state and ground state,and effective conjugation length of lutein molecule,which is of great value for studying the optoelectronic properties of carotenoid molecules.The research content is divided into the following two parts:1.By studying the resonance Raman spectra and UV-Vis absorption spectra of lutein solution in solid phase,phase change and liquid phase,the variation of Raman scattering cross section and electron-phonon coupling coefficient during lutein cooling process in these three states were obtained.In the temperature range of293K-123 K,except for the phase transformation region,the Raman characteristic peak and absorption characteristic peak of lutein molecule both appear red shift with the decrease of temperature.When the temperature drops to 183K-163 K region,the slope of fundamental frequency changes,and the lutein solution enters the phase transformation state.According to the characteristic peak frequency shift-temperature curve,the change process can be divided into three phases: solid phase,phase transition and liquid phase.According to Dudik formula and R Tubino calculation method,the Raman scattering cross section and electron phonon coupling coefficient in the cooling process of lutein are calculated respectively.It is found that the Raman cross section of lutein increases and the electron-phonon coupling decreases with the decrease of temperature when the solution is in solid phase,and the trend of liquid and solid phase is similar.However,in the phase transition region,the variation of Raman cross section and electron phonon coupling is opposite to that of solid state.2.Using UV-Vis absorption spectroscopy and resonance Raman scattering spectroscopy,the Raman scattering cross section and electron-phonon coupling coefficient of lutein molecule were studied under the change of solvent polarizability.The study found that with the increase of the polarizability of the solvent,the Raman peak position did not change significantly,but the wavelength of the 0-0 absorption peak of the UV-Vis absorption spectrum decreased linearly with the increase of the polarizability.This phenomenon is mainly due to as the polarizability of the solvent increases,the energy level spacing decreases,so that the energy required for the transition decreases,resulting in the decrease of the Huang-Rhys factor with the increase of the polarizability.Moreover,with the increase of solvent polarizability,the Raman scattering cross section of lutein molecule increases and the electron-phonon coupling coefficient decreases,indicating that solvent polarizability can affect the geometric distortion and recombination energy of lutein from ground state to excited state.