Electron delocalization in cross-conjugated p-phenylenevinylidene oligomers.
Electron delocalization in cross-conjugated p-phenylenevinylidene oligomers.
复制标题
交叉共轭对亚苯基亚乙烯基低聚物中的电子离域。
DOI：
10.1002/chem.200204671
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发表时间：
2003
期刊：
影响因子：
--
通讯作者：
C. V. van Walree
中科院分区：
文献类型：
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作者：
M. Klokkenburg;M. Lutz;A. Spek;J. H. van der Maas;C. V. van Walree
报道了一系列具有1 ~ 4个双键的交叉共轭对苯乙烯低聚物的合成、结构和电子性质。具有两个双键的化合物的x射线晶体结构显示出C（苯基）-C（偏乙基）和C（苯基）-C（偏乙基）形式单键的扭角分别为39.5(2)度和30.5(2)度的非平面构象。在基态中观察到类醌性质的混合。红外和拉曼光谱并不能清楚地反映出该系列中电子离域的程度，因为C=C的拉伸模式不能充分反映C=C键的顺序，具有局域性。相反，电子光谱和电化学数据以及AM1和PPP/SCF计算表明，交叉共轭化合物基本上表现为线性共轭体系，即分子轨道在整个结构上离域并且能量系统地变化。然而，重复单元之间的电子相互作用不是很强，这导致分子轨道的空间扩展不会导致最高占据分子轨道-最低未占据分子轨道（HOMO-LUMO）电子跃迁的红移。这与HOMO-LUMO间隙随链长而适度缩小的特征有关，伴随着相对较大的电子斥力降低。这一发现表明，在使用电子光谱评价共轭现象时应小心谨慎。
The synthesis, structure, and electronic properties of a series of cross-conjugated p-phenylenevinylidene oligomers with one to four double bonds are reported. The X-ray crystal structure of the compound with two double bonds reveals a nonplanar conformation with torsion angles about the C(phenylene)-C(vinylidene) and C(phenyl)-C(vinylidene) formal single bonds of 39.5(2) degrees and 30.5(2) degrees, respectively. Admixture of quinoid character in the ground state is observed. Infrared and Raman spectroscopy do not provide a clear picture of the degree of electron delocalization in the series, since the C=C stretching mode does not adequately reflect the C=C bond order and has a local nature. In contrast, electronic spectra and electrochemical data, as well as AM1 and PPP/SCF calculations, reveal that the cross-conjugated compounds basically behave as linearly pi-conjugated systems in the sense that molecular orbitals are delocalized over the entire structure and systematically change in energy. The electronic interaction between the repeating units is, however, not very strong, which has the consequence that spatial extension of the molecular orbitals does not lead to a red shift of the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) electronic transition. This is related to the feature that the modest narrowing of the HOMO-LUMO gap with the chain length is accompanied by a relatively large reduction of electron repulsion. This finding implies that care should be taken in the use of electronic spectra for the evaluation of conjugation phenomena.
DOI：
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发表时间：
1986
期刊：
--
影响因子：
--
作者：
T. Skotheim;R. Elsenbaumer;J. Reynolds
通讯作者：
T. Skotheim;R. Elsenbaumer;J. Reynolds