Effect Of Molecules Polarity On The Resonance Raman Spectrum Of Caroteniod

Research into the linear polyene molecule of containing conjugated double bondhas been a subject of much attention. This type of molecule have achieved innanometer material and optoelectronic devices. Carotenoid is the polyene linearbiological molecules which have a few to a dozen CC conjugated double bond, thespecial structure of molecule determines its own property, which not only have thebiological function of photosynthesis, light degradation, anti-cancer but also have thelong-chain polyene molecules with optical and electrical properties, and has importantapplications in optoelectronic devices, batteries, laser, etc. Therefore, the research forcarotenoids linear polyene molecules has theoretical value and a bright applicationprospect. Material properties and functions are closely related to molecular structure,and temperature, electromagnetic fields, the van der Waals force environment on themolecular structure and the state has an important impact. Our group has carried outresearch that the external field effect the linear polyene molecular structure orderlyand performance and have made some innovative results.In this paper, we have measured non-polar molecules beta-carotene and polarmolecules canthaxanthin in non-polar solvents CS2and a polar solvent1,2dichloroethane at room temperature UV-visible absorption spectra and83K-293K atemperature within the range of resonance Raman spectroscopy. In the liquid regionand solid-state area, different polarity of carotenoids solute molecules in solvents ofdifferent polarity, ordered structure of the optical properties of microscopicintermolecular interactions on carotenoids, mainly achieved the following innovativeresults.1. In the sample liquid and solid areas, the Raman scattering cross section of thetwo carotenoids in solvent of different polarity are increase with decreasing temperatures. Raman scattering cross-section of nonpolar bimolecular moleculesall-trans-β-carotene in nonpolar solvent CS2is the maximum, while Ramanscattering cross-section of the polar molecules canthaxanthin in polar solvent1,2-dicholoroethane is the minimum. The reason is that the non-polar solutes innon-polar solvent does not exist induction force, orientation force and with galvanicmoment the electrostatic interaction and the molecular structure ordered phase of thecarotene is better than solute solvent solution. Thus beta-carotene in nonpolar solventCS2, molecular structure an orderly best increases effective conjugate length, theextension of the pi-electron delocalization generate strong coherent weakly dampedvibration, and so the Raman scattering cross section is the maximum. Canthaxanthinin polar solvent1,2-dichloroethane, the solute and the solvent are polar molecule,the electrostatic interaction existence of between the solute and the solvent moleculesand solute-solvent, and these interaction is ordered molecular structure deteriorationand reduced effective resonant length. In addition, because the Raman half high widthof canthaxanthin in1,2-dichloroethane is widest of all solvent, that the CC bondlength difference components increases, but also reflects the molecular ordering theworst. So p-electron delocalized expansion is blocked coherent weakest the weaklydamped Electronics-lattice vibrations, and thus its Raman scattering cross section isminimum.2. Within a temperature range83K-293K, Raman linewidth of four solutions aredecreases with decreasing temperature. The linewidth of beta-carotene in CS2isnarrowest, while the line width of canthaxanthin in1,2-dichloroethane is widest. Thisis because the non-polar solutes in non-polar solvent, the intermolecular interactionforce and the type of force is decrease and pi-electron delocalization expansion isincreases, increasing the linear polyene molecular structure orderly so that the bondlength of each CC tends to be the same, resulting in the decrease in the vibrationfrequency component, and thus the spectral linewidth of beta-carotene in CS2isnarrowest. Polar solutes in a polar solvent, the intermolecular interaction force and thetype of force is increase, to prevent the extension of the π electron delocalization,weakened the linear polyene molecular structure orderly, such that each CC bond length is inconsistent, resulting in vibration frequency components increases, whichmade the Raman broadening of the spectrum, and line width of canthaxanthin in1,2-dichloroethane is widest.