Effect Of Solvent Polarity On The Electron-phonon Coupling Of β-carotene

Carotenoid is a kind of natural pigment, which widely exists in nature, betacarotene has been a great concern for researchers. This is mainly because it has a widerange of applications in medicine and food engineering. beta carotene can be used asfood additives, colorants；effectively increase the resistance of the body to preventcancer, cataracts, cardiovascular disease. β-carotene is a short straight-chain moleculewith conjugated double bond structure, which is an ideal experimental study samplefor studying polyene molecules. In summary, β-carotene are very good researchwhether from the theoretical value or prospects. Our group conducted years ofresearch on it, and has made some achievements.β-carotene is a straight-chain molecule, its nature and molecular structure has avery close relationship. We study the molecular structure and properties by changingthe external field condition (temperature, solvent, pressure, etc.). When the molecularstate (liquid, gas, solution) change, energy levels and spectra of molecules will alsochange because its energy levels the will be affected by surrounding environment.Solvent effect will change the electronic spectra of molecules; vibrational spectra linewidth, intensity, and frequency. It has a very important value and significance forunderstanding the internal structure and the molecular interaction, through studyingthe spectral changes summarizing its variation.1. Solvent effect plays an important role in determining electron-phononcoupling constant, however, the physical properties of solvent effects and therelationship between them still need to be investigated. We measure the UV-visibleabsorption and Raman spectra of β-carotene in10typical solvents. The results showthat polarizability and dielectric constant of solvent have a significant effect on theelectron-phonon coupling constant of β-carotene. With the increase of polarizability,no matter whether the solvent is of polarity, Huang-Ryes factor and the electron- phonon coupling of β-carotene decrease and the Raman scattering cross sectionincreases. As to nonpolar solvent, Huang-Ryes factor and the electron-phononcoupling constant of β-carotene decrease with increasing the dielectric constant of thesolvent. For polar solvent, no good regularity is obtained. In this paper, the regularityof solvent effect on the electron-phonon coupling constant is presented, which canprovide a reference for how to choose the solvent in studying the electron-phononcoupling constant.2. We have measured the UV-visible absorption and Raman spectra of β-carotene which in polar1,2-dichloroethane and nonpolar cyclohexane at thetemperature range from20℃-60℃.The results showed that the Raman scatteringcross-section for CC bond of β-carotene in polar solvent1,2-dichloroethane is small,Huang-Ryes factor and electron-phonon coupling constants is larger than in nonpolarsolvent.