Zheng Shijun, Barlow Stephen, Risko Chad, Kinnibrugh Tiffany L, Khrustalev Viktor N, Jones Simon C, Antipin Mikhail Yu, Tucker Neil M, Timofeeva Tatiana V, Coropceanu Veaceslav, Brédas Jean-Luc, Marder Seth R
School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, GA 30332-0400, USA.
J Am Chem Soc. 2006 Feb 15;128(6):1812-7. doi: 10.1021/ja0541534.
We report the first structural data for bis(diarylamine) "bipolarons": we have isolated and crystallographically characterized salts of the dications obtained by two-electron oxidation of E-4,4'-bis[di(p-anisyl)amino]stilbene and E,E-2,5-bis{4-[di(p-anisyl)amino]styryl}-3,4-di(n-butoxy)thiophene, 1 and 2 respectively. ESR, NMR, and magnetometry suggest both species have singlet ground states. X-ray structures, together with (1)H NMR coupling constants for 2, indicate geometries in which the bond lengths are shifted toward a quinoidal pattern relative to that in the neutral species, but not to a fully quinoidal extent. In particular, the bond-length alternations across the vinylene bridging groups approach zero. DFT calculations with closed-shell singlet configurations reproduce the observed structures well. Our results indicate that singlet species for which one might expect quinoidal geometries (with differences of ca. 0.1 A between formally single and double bonds) on the basis of a limiting valence-bond representation of the structure can, in fact, show structures with significantly different patterns of bond lengths.
我们报道了双（二芳基胺）“双极子”的首个结构数据：我们已经分离并通过晶体学表征了由E-4,4'-双[二（对甲氧基苯基）氨基]芪和E,E-2,5-双{4-[二（对甲氧基苯基）氨基]苯乙烯基}-3,4-二（正丁氧基）噻吩经双电子氧化得到的双阳离子盐，分别为1和2。电子顺磁共振（ESR）、核磁共振（NMR）和磁学测量表明这两种物质都具有单重基态。X射线结构，连同2的氢核磁共振（1H NMR）耦合常数，表明其几何结构中键长相对于中性物质向醌式模式移动，但未达到完全醌式程度。特别是，亚乙烯基桥连基团上的键长交替接近零。采用闭壳单重态构型的密度泛函理论（DFT）计算很好地再现了观察到的结构。我们的结果表明，基于结构的极限价键表示可能预期具有醌式几何结构（形式上单键和双键之间相差约0.1 Å）的单重态物质，实际上可能呈现出键长模式显著不同的结构。
