Domagalska BW, Wilk KA, Szymusiak H, Zielinski R
Institute of Organic and Polymer Technology, Wroclaw University of Technology, Poland.
Comput Chem. 2000 May;24(3-4):359-67. doi: 10.1016/s0097-8485(00)00062-0.
In this work we report the results of our study on electronic and spectral properties of conjugated polyenes with electron-accepting 1,3-dialkyl-2-thiobarbituric acid moiety. In model calculations, we examine the effect of the conjugated polyene length on infrared (IR) and Raman spectra of the polyenes by means of ab initio HF/3-21G*. Nonlinear properties were also studied by AM1 method in frames of the sum-over-states (SOS) and finite-field formalism. It was concluded that in well-resolved IR and Raman spectra the frequencies and band intensities can provide valuable information relating to C=C bond lengths in polyene chain and relative polarizabilities. Near-linear correlation between polarizability and integral IR band intensity, corresponding to all C=C stretching modes, and the rather nonlinear relationship of polarizability with integral Raman activity, was found. In our calculation we predict that polarizability and the first hyperpolarizability increases with elongation of polyene chain while the second hyperpolarizability increases smoothly in a quadratic way. In contrast to the linear relationship between polarizability and polyene chain length the dipole moment versus chain length is predicted to be nonlinear. A good agreement was found between experimental and calculated Raman spectra of one newly synthesized compound studied.
在本研究中，我们报告了对带有吸电子1,3 - 二烷基 - 2 - 硫代巴比妥酸部分的共轭多烯的电子和光谱性质的研究结果。在模型计算中，我们通过从头算HF/3 - 21G*方法研究了共轭多烯长度对多烯红外（IR）光谱和拉曼光谱的影响。还采用AM1方法在态叠加（SOS）和有限场形式框架下研究了非线性性质。结果表明，在分辨率良好的IR和拉曼光谱中，频率和谱带强度能够提供与多烯链中C = C键长度以及相对极化率相关的有价值信息。发现极化率与对应所有C = C伸缩模式的积分IR谱带强度之间存在近线性关系，而极化率与积分拉曼活性之间的关系则较为非线性。在我们的计算中预测，极化率和第一超极化率随多烯链的伸长而增加，而第二超极化率以二次方的方式平滑增加。与极化率和多烯链长度之间的线性关系不同，偶极矩与链长度的关系预计是非线性的。在所研究的一种新合成化合物的实验拉曼光谱和计算拉曼光谱之间发现了良好的一致性。
