Borstelmann Jan, Schneider Lars, Rominger Frank, Deschler Felix, Kivala Milan
Organisch-Chemisches Institut, Universität Heidelberg, Im Neuenheimer Feld 270, 69120, Heidelberg, Germany.
Physikalisch-Chemisches Institut, Universität Heidelberg, Im Neuenheimer Feld 253, 69120, Heidelberg, Germany.
Angew Chem Int Ed Engl. 2024 Jul 15;63(29):e202405570. doi: 10.1002/anie.202405570. Epub 2024 Jun 14.
We report a synthetic approach to π-expanded [6]helicenes incorporating tropone and azocine units in combination with a 5-membered ring, which exhibit intriguing structural, electronic, and chiroptical properties. The regioselective Beckmann rearrangement allows the isolation of helical scaffolds containing 8-membered lactam, azocine, and amine units. As shown by X-ray crystallographic analysis, the incorporation of tropone or azocine units leads to highly distorted [6]helicene moieties, with distinct packing motifs in the solid state. The compounds exhibit promising optoelectronic properties with considerable photoluminescence quantum yields and tunable emission wavelengths depending on the relative position of the nitrogen center within the polycyclic framework. Separation of the enantiomers by chiral high-performance liquid chromatography (HPLC) allowed characterization of their chiroptical properties by circular dichroism (CD) and circularly polarized luminescence (CPL) spectroscopy. The azocine compounds feature manifold redox chemistry, allowing for the characterization of the corresponding radical anions and cations as well as the dications and dianions, with near-infrared (NIR) absorption bands extending beyond 3000 nm. Detailed theoretical studies provided insights into the aromaticity evolution upon reduction and oxidation, suggesting that the steric strain prevents the azocine unit from undergoing aromatization, while the indene moiety dominates the observed redox chemistry.
我们报道了一种合成方法，用于制备包含卓酮和氮杂环辛四烯单元并结合五元环的π-扩展[6]螺旋烯，这些化合物展现出有趣的结构、电子和手性光学性质。区域选择性贝克曼重排使得能够分离出含有八元内酰胺、氮杂环辛四烯和胺单元的螺旋骨架。如X射线晶体学分析所示，卓酮或氮杂环辛四烯单元的引入导致[6]螺旋烯部分高度扭曲，在固态中具有独特的堆积模式。这些化合物表现出有前景的光电性质，具有相当高的光致发光量子产率，并且发射波长可根据多环骨架中氮中心的相对位置进行调节。通过手性高效液相色谱（HPLC）分离对映体，使得能够通过圆二色性（CD）和圆偏振发光（CPL）光谱对其手性光学性质进行表征。氮杂环辛四烯化合物具有多种氧化还原化学性质，能够表征相应的自由基阴离子和阳离子以及二价阳离子和二价阴离子，其近红外（NIR）吸收带延伸超过3000 nm。详细的理论研究为还原和氧化过程中的芳香性演变提供了见解，表明空间应变阻止了氮杂环辛四烯单元发生芳构化，而茚部分主导了观察到的氧化还原化学性质。
