Syntheses, structures, spectroscopic properties, and pi-dimeric interactions of [n.n]quinquethiophenophanes.
Syntheses, structures, spectroscopic properties, and pi-dimeric interactions of [n.n]quinquethiophenophanes.
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DOI：
10.1021/ja050783u
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发表时间：
2005-05
影响因子：
15
通讯作者：
T. Sakai;Teizi Satou;T. Kaikawa;K. Takimiya;T. Otsubo;Y. Aso
中科院分区：
文献类型：
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作者：
T. Sakai;Teizi Satou;T. Kaikawa;K. Takimiya;T. Otsubo;Y. Aso
合成了一种桥链连续变化在2 ~ 6个亚甲基之间的环烷型五萜烯，并将其作为理想的pi-二聚体模型进行了研究。这些化合物的双层结构通过内部噻吩的质子核磁共振信号的前场位移得到验证，与单体二甲基五硫代噻吩相比(3)。两个重叠的五硫代烯之间的激子-激子耦合通过空间π电子相互作用干扰了4a-e的电子吸收和发射光谱，这种相互作用以桥接的烷基链缩短为标志。在二氯甲烷中，4a-e与FeCl(3)的单电子氧化导致在电子吸收光谱的近红外区域出现特定的极化带，这是由于在其中一个五硫代烯上产生了一个自由基阳离子（极化子），它与剩余的中性物质电子相互作用。4a-e的双电子氧化引入了光谱变化，揭示了由此产生的两个五硫代烯自由基阳离子很容易形成分子内的pi-二聚体，这要归功于它们的紧密堆叠，而3很难形成分子间的pi-二聚体。4b-e的pi-二聚体光谱由两个强吸收带组成，类似于3的吸收带，其低能带由于有效的pi-二聚体相互作用而红移，这取决于桥接烷基链的长度。完全不同的是，4a的光谱具有pi-二聚体固有的三个吸收带，可能是因为4a的两个短桥链迫使pi-二聚体采取受约束的强相互作用结构。
A cyclophane-type of dimeric quinquethiophenes (4a-e) with the bridge chains consecutively varying from two to six methylenes has been synthesized and studied as ideal pi-dimer models. The double-decker structures of these compounds are verified by upfield shifts for the proton NMR signals of the inside thiophenes, as compared to those of monomeric dimethylquinquethiophene (3). The electronic absorption and emission spectra of 4a-e are perturbed by through-space pi-electronic interactions involving exciton-exciton coupling between the two overlapped quinquethiophenes, which become marked with shortening of the bridged alkylene chains. One-electron oxidation of 4a-e with FeCl(3) in dichloromethane results in the appearance of specific polaronic bands in the near-infrared region of the electronic absorption spectra, due to the generation of a radical cation species (polaron) on one of the quinquethiophenes, which electronically interacts with the remaining neutral species. Two-electron oxidation of 4a-e introduces spectral changes, revealing that the resulting two quinquethiophene radical cations readily form an intramolecular pi-dimer, thanks to their close stacking, in contrast to the difficult formation of an intermolecular pi-dimer from 3. The pi-dimeric spectra of 4b-e are comprised of two strong absorption bands, similar to that of 3, the low-energy band of which is considerably red-shifted by an effective pi-dimeric interaction depending on the lengths of the bridged alkylene chains. Quite different is the spectrum of 4a with three absorption bands inherent in pi-dimer, presumably because the two short bridging chains of 4a force the pi-dimer to take a constrained, strongly interactive structure.