Optical and magnetic properties of the exact PPP states of biphenyl
Optical and magnetic properties of the exact PPP states of biphenyl
复制标题
联苯精确 PPP 状态的光学和磁性
DOI：
10.1080/00268979100100411
复制
发表时间：
1991
影响因子：
1.7
通讯作者：
B. Sinha
中科院分区：
文献类型：
--
作者：
S. Ramasesha;I. D. L. Albert;B. Sinha
用图解价键法在PPP模型中精确地得到了联苯的低洼单重态和三重态。单重态流形内的能隙以及最低的单重态-三重态能隙与实验结果吻合较好。实验报告的4.1和4.2 eV之间的两个弱吸收归因于位于光学间隙下方的两个态在电子-空穴和反转对称性被打破时变得弱允许。观测到的光谱线的蓝移，归因于二面角的变化，从晶体到溶液再到气相，也在PPP模型中得到了很好的再现。键序表明，基态单线态为苯态，而偶极激发态和最低三重态为醌态和平面态。与实验自旋密度和三重态精细结构常数D和E的比较表明，它们的相关性比PPP模型假设的要弱一些。
The low-lying singlets and triplets of biphenyl are obtained exactly within the PPP model using the diagrammatic valence bond method. The energy gaps within the singlet manifold as well as the lowest singlet-triplet gap are found to be in good agreement with experimental results. The two weak absorptions between 4·1 and 4·2 eV reported experimentally are attributed to the two states lying below the optical gap that become weakly allowed on breaking electron-hole and inversion symmetries. The observed blue shift of the spectral lines, attributed to a change in dihedral angle, on going from crystalline to solution to vapour phase is also well reproduced within the PPP model. The bond orders show that the ground singlet state is benzenoidal while the dipole excited state as well as the lowest triplet state are quinonoidal and planar. Comparison with the experimental spin densities and the fine structure constants D and E in the triplet state point to slightly weaker correlations than assumed by the PPP model...