β-胡萝卜素分子的黄琨因子的温度特性

摘要

A Visible absorption and Raman spectra of all-trans-β-carotene was measured in cyclohexanol solution in the temperature range from 68 ℃ to 26 ℃.The results indicated that the visible absorption spectra are red-shifted,Raman scattering cross section increases,Huang-Ryes factor and electmn-phonon coupling constants of CC bond vibration modes decreases with the temperature decreasing.The changes are interpreted using the theory of "coherent weakly damped electronic-lattice vibration model" and "effective conjugation length model".The red shift of the absorption spectra and intensity of the Rarman active are attributed to the thermal conformational change-induced increase in the effective conjugation length in all-trans-β-camtene chains.All-trans-β-carotene has strong coherent weakly damped CC bonds vibrational properties,which lead to large Raman scattering cross section in the solvent of low temperature.The electron-phonon coupling constants with dimension are used,which can easily establish relation with the Huang-Rhys factor and calculate the electromphonon coupling constants of CC bond vibration modes.Effective conjugation length,the welectron delocalization range and the Raman scattering cross section are described by the electromphonon coupling constants.%β-胡萝卜素具有光采集、光防护功能,又是重要的光电材料,它在外场下的分子结构和性能变化既有理论意义也有应用价值.测量了β-胡萝卜素在环己醇中68～26℃温度范围内的紫外-可见吸收、拉曼光谱.实验结果表明随着温度的降低,黄琨因子和碳碳键每个振动模的电子-声子耦合常数减小,紫外-可见吸收光谱红移,碳碳键拉曼散射截面增加.用线性链状多烯分子的“相干弱阻尼电子-晶格振动模型”、“有效共轭长度模型”等理论给予了解释.随着温度的降低,β-胡萝卜素分子的热无序减小,分子结构有序性增加,π电子离域扩展,有效共轭长度增加,导致紫外-可见吸收光谱红移和强的拉曼活性.相干弱阻尼电子-品格振动增强,使碳碳键拉曼散射截面增加.引用带有量纲的电子-声子相互作用常数,既可以与黄昆因子建立关系式,计算出碳碳键每个振动模的数值,也可以表征分子的有效共轭长度,π电子离域程度及拉曼散射截面的大小等.