High-Spin Diradical Dication of Chiral π-Conjugated Double Helical Molecule
High-Spin Diradical Dication of Chiral π-Conjugated Double Helical Molecule
复制标题
DOI：
10.1021/jacs.9b08711
复制
发表时间：
2019-10-30
影响因子：
15
通讯作者：
Rajca, Andrzej
中科院分区：
文献类型：
--
作者：
Shu, Chan;Zhang, Hui;Rajca, Andrzej
我们报告了手性D-2对称联体双[5]二氮杂螺旋烯的空气稳定双自由基双标，具有前所未有的高自旋（三重态）基态、单重态三重态能隙、Delta E-ST = 0.3 kcal mol(-1)。双自由基双自由基具有 16 个π电子周长的闭壳层 (Kekule) 共振形式。双自由基双阳离子在低温下在邻苯二甲酸二丁酯 (DBP) 基质中呈单体形式，在环境条件下、存在过量氧化剂的情况下，其半衰期超过 2 周。通过实验确定了中性联体双[5]二氮杂螺旋烯中构型反转的能垒约为35 kcal mol(-1)，而通过DFT计算预测其自由基阳离子和双自由基双键的反转能垒在中性物质的几kcal mol(-1)以内。手性 HPLC 拆分提供了手性 D-2-对称联体双[5]二氮杂螺旋烯，富含 (P,P)- 或 (M,M)-对映体。对映体富集的三重态双自由基双自由基在室温下构型稳定48小时，从而提供了构型反转势垒的下限为27 kcal mol(-1)。联体双[5]二氮杂螺旋烯及其双自由基双键显示出与[6]螺旋烯或碳-硫[7]螺旋烯相当的强手性光学性质，由各向异性因子确定，垂直条g垂直条=垂直条Δε垂直条/ε=0.007在348nm（中性）和垂直条g垂直条=0.005在348nm（中性）和垂直条g垂直条=0.005 385 nm（双自由基指示）。自由基阳离子的 DFT 计算表明 SOMO 和 HOMO 能级接近简并。
We report an air-stable diradical dication of chiral D-2-symmetric conjoined bis[5]diazahelicene with an unprecedented high-spin (triplet) ground state, singlet triplet energy gap, Delta E-ST = 0.3 kcal mol(-1). The diradical dication possesses closed-shell (Kekule) resonance forms with 16 pi-electron perimeters. The diradical dication is monomeric in dibutyl phthalate (DBP) matrix at low temperatures, and it has a half-life of more than 2 weeks at ambient conditions in the presence of excess oxidant. A barrier of similar to 35 kcal mol(-1) has been experimentally determined for inversion of configuration in the neutral conjoined bis[5]diazahelicene, while the inversion barriers in its radical cation and diradical dication were predicted by the DFT computations to be within a few kcal mol(-1) of that in the neutral species. Chiral HPLC resolution provides the chiral D-2-symmetric conjoined bis[5]diazahelicene, enriched in (P,P)- or (M,M)-enantiomers. The enantiomerically enriched triplet diradical dication is configurationally stable for 48 h at room temperature, thus providing the lower limit for inversion barrier of configuration of 27 kcal mol(-1). The enantiomers of conjoined bis[5]diazahelicene and its diradical dication show strong chirooptical properties that are comparable to [6]helicene or carbon-sulfur [7]helicene, as determined by the anisotropy factors, vertical bar g vertical bar = vertical bar Delta epsilon vertical bar/epsilon = 0.007 at 348 nm (neutral) and vertical bar g vertical bar = 0.005 at 385 nm (diradical dication). DFT computations of the radical cation suggest that SOMO and HOMO energy levels are near-degenerate.