Unprecedented linear oligoisoindole derivatives including diisoindole, triisoindole, tetraisoindole, and hexaisoindole species, representing the new family rather than the traditional cyclic oligoisoindole ones, have been synthesized and spectroscopically characterized for the first time. Variable temperature NMR experiments in combination with DFT calculations reveal the tautomerization of the N–H protons between the outer and inner isoindole units in triisoindole, tetraisoindole, and hexaisoindole species at room temperature. The conjugated electronic structure nature of these oligoisoindole compounds has been clearly clarified on the basis of their single crystal molecular structure, electronic absorption, fluorescence, and electrochemical properties together with theoretical calculations. Moreover, the π Mayer bond order calculation suggests that these oligoisoindole compounds have two types of strong conjugated regions including the delocalized conjugated line across the whole skeleton and the localized conjugated circles at the benzene moieties, which are united together into a whole conjugated system by weak π linking bonds. In particular, the π bonds that pervade over all the linear conjugated oligoisoindole skeletons are comparable to those in the traditional cyclic oligoisoindole skeletons. This, in combination with the existence of the well-defined coordination moiety/moieties for these linear oligoisoindoles, suggests their promising application potential in diverse fields including sensors and electronic devices as their cyclic counterparts.

中文翻译：

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具有共轭电子结构的新型线性低聚异吲哚化合物

前所未有的线性低聚异吲哚衍生物，包括二异吲哚，三异吲哚，四异吲哚和六异吲哚类，代表了新的家族，而不是传统的环状低聚异吲哚衍生物，并首次进行了光谱表征。可变温度NMR实验与DFT计算相结合，揭示了室温下三异吲哚，四异吲哚和六异吲哚物种中内，外异吲哚单元之间NH质子的互变异构。基于它们的单晶分子结构，电子吸收，荧光和电化学性质以及理论计算，已经清楚地阐明了这些低聚异吲哚化合物的共轭电子结构性质。而且，πMayer键序计算表明，这些低聚异吲哚化合物具有两种类型的强共轭区域，包括整个骨架上的离域共轭线和苯部分的局域共轭圆，它们通过弱π连接而结合在一起成为一个整体共轭体系债券。特别地，遍及所有线性共轭低聚异吲哚骨架的π键与传统的环状低聚异吲哚骨架中的π键相当。这与这些线性低聚异吲哚的明确定义的配位基团/部分的存在相结合，表明它们在包括传感器和电子设备在内的各种领域中具有广阔的应用前景。