Effect Of Temperature On Electron-Phonon Coupling Of Carotenoids

Carotenoids,the most prevalent light-absorbing pigments in nature,are linear polyene molecules containing conjugated double bonds with π electrons and necessary photovoltaic materials.Therefore,they have an enormous potential for development in directions such as photovoltaic research and continue to spark the research interest of researchers.The most common carotenoids are β-carotene,lycopene,and several hundred other isomers.We closely related their optoelectronic properties to their degree of structural ordering,i.e.,the degree of π-electron delocalization.In this paper,the changes in electron-phonon coupling coefficients of β-carotene and lycopene at different temperatures were discussed in detail through resonance Raman spectroscopy,visible absorption spectra,quantum chemistry calculation,and molecular spectrum theory.We found evidence of different intermolecular interactions between β-carotene and lycopene in the solvent.This master’s degree thesis is mainly divided into the following two parts:1.To explore the characteristics and influencing factors of β-carotene in different solvents.We discussed the experimental results by resonance Raman scattering spectroscopy and molecular calculation method.The results of various solvent tests show that the value of Raman scattering cross section(RSCS)increases with polarizability.The results show no significant correlation between these limiting factors and solvent polarity.Therefore,when discussing the electron-phonon interaction,the polarizability parameter of the solution is the first factor we have to consider,and the dielectric constant can be used as one of the reference factors.2.Using resonance Raman spectra,we found the differences of the characteristic peak position and relative intensity of carotenoid molecules in different temperature solvents,thus revealing why carotenoid molecules have excellent spectra and functions.Combined with UV-vis absorption spectra,we found both the cyclic group at the end of the conjugated chain of β-carotene and the open-chain structure of lycopene were in it.Compared with β-carotene,lycopene has longer conjugated length and different open-chain structure,which makes lycopene more sensitive to temperature change.The results of two-dimensional correlation resonance Raman spectroscopy(2DCRRS)show that the electron-phonon coupling is related to the temperature change.The more complex mode evolution of lycopene organic solution makes the molecules more sensitive to temperature.Finally,we use density flooding theory(DFT)results to study the temperature dependence of electron coupling in π-conjugated molecules.To sum up,this paper studies the variation of electron-phonon coupling parameters with temperature by changing the ambient temperature grasps the phenomenon’s mechanism,and deeply understands the molecular structure and intramolecular and intermolecular interactions.Identifying various electro-acoustic coupling characteristics and spectroscopic mechanisms of linear polyene molecules can not only enrich the content of polyene molecular spectroscopy but also provide strong support and reference for applying high-performance luminescent materials.