Solvent- and Temperature-Dependent Conformational Changes between Huckel Antiaromatic and Mobius Aromatic Species in meso-Trifluoromethyl Substituted [28] Hexaphyrins
Solvent- and Temperature-Dependent Conformational Changes between Huckel Antiaromatic and Mobius Aromatic Species in meso-Trifluoromethyl Substituted [28] Hexaphyrins
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内消旋三氟甲基取代的 [28] 六菲林中 Huckel 反芳香族化合物和莫比乌斯芳香族化合物之间的溶剂和温度依赖性构象变化
DOI：
10.1021/jp207731k
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发表时间：
2011
期刊：
影响因子：
--
通讯作者：
Dongho Kim
中科院分区：
文献类型：
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作者：
Min-Chul Yoon;Pyosang Kim;Hyejin Yoo;Soji Shimizu;Taro Koide;Sumito Tokuji;Shohei Saito;Atsuhiro Osuka;Dongho Kim
我们用稳态光谱和时间分辨光谱结合理论计算研究了分别命名为TFM26HandTFM28H的figure-eight-likemeso-hexakis(trifluoromethyl)[26]-和[28]六氢呋喃(1.1.1.1.1.1)的光物理性质，探讨了它们的电子和磁性与分子芳香性的关系。TFM26H表现出良好的吸收特性和强烈的荧光，这两者都不依赖于溶剂和温度。这些光学性质与其在典型的芳香族卟啉类化合物中观察到的HüCKel的[4N+2]芳香性是一致的。TFM26H溶液中∼50ps的S1态寿命比平面芳香族六氢呋喃(>；100ps)短，这可能是由于TFM26H的非平面八字形构型所致。然而，TFM28H的溶剂依赖和温度依赖的吸收光谱以及激发态寿命发生了显著的变化，表明两种构象物种之间发生了动态平衡。通过量子力学几何优化和垂直激发能计算，我们发现在固态和单面扭曲状态下观察到的八字形双面构象可能是两种构象的最佳候选者，根据它们的光学性质、分子轨道结构和激发态寿命，它们应该分别是HüCKel反芳香族和MöBius芳香族物种。用不同溶剂中随温度变化的~1H核磁共振谱详细研究了TFM28H的两种构象之间的构象动力学，结果表明，TFM28H的构象平衡对溶剂非常敏感，即使在173K也发生了比核磁共振时间尺度更快的构象变化。
We investigated the photophysical properties of figure-eight-likemeso-hexakis(trifluoromethyl) [26]- and [28]hexaphyrins(1.1.1.1.1.1) denoted asTFM26HandTFM28H, respectively, using steady-state and time-resolved spectroscopy along with theoretical calculations to explore their electronic and magnetic natures depending on their molecular aromaticity.TFM26Hexhibited a well-resolved absorption feature and intense fluorescence, both of which were neither solvent- nor temperature-dependent. These optical properties were in agreement with its Hückel’s [4n+ 2] aromaticity as observed in typical aromatic porphyrinoids. The S1-state lifetime of ∼50 ps forTFM26Hin solution was shorter than those in planar aromatic hexaphyrins (>100 ps) presumably due to nonplanar figure-eight geometry ofTFM26H. However,TFM28Hexhibited remarkable changes in solvent- and temperature-dependent absorption spectra as well as excited-state lifetimes indicating that a dynamic equilibrium occurs between the two conformational species. With the help of quantum mechanical geometry optimization and vertical excitation energy calculations, we found that the figure-eight double-sided conformer observed in the solid-state and single-sided distorted one could be the best candidates for the two conformers, which should be Hückel antiaromatic and Möbius aromatic species, respectively, based on their optical characteristics, molecular orbital structures, and excited-state lifetimes. Conformational dynamics between these two conformers ofTFM28Hwas scrutinized in detail by temperature-dependent1H NMR spectra in various solvents, which showed that the conformational equilibrium was quite sensitive to solvents and that a conformational change faster than the NMR time-scale occurs even at 173 K.