Kinnibrugh Tiffany L, Salman Seyhan, Getmanenko Yulia A, Coropceanu Veaceslav, Porter William W, Timofeeva Tatiana V, Matzger Adam J, Brédas Jean-Luc, Marder Seth R, Barlow Stephen
Department of Natural Sciences, New Mexico Highlands University, Las Vegas, NM 87701; School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, GA 30332-0400; Department of Chemistry, University of Michigan, Ann Arbor, MI 48109-1055.
Organometallics. 2009;28(5):1350-1357. doi: 10.1021/om800986s.
Crystal structures have been determined for six dipolar polyene chromophores with metallocenyl - ferrocenyl (Fc), octamethylferrocenyl (Fc″), or ruthenocenyl (Rc) - donors and strong heterocyclic acceptors based on 1,3-diethyl-2-thiobarbituric acid or 3-dicyanomethylidene-2,3-dihydrobenzothiophene-1,1-dioxide. In each case, crystals were found to belong to centrosymmetric space groups. For one example, polymer-induced heteronucleation revealed the existence of two additional polymorphs, which were inactive in second-harmonic generation, suggesting that they were also centrosymmetric. The bond-length alternations between the formally double and single bonds of the polyene bridges are reduced compared to simple polyenes, indicating significant contribution from charge-separated resonance structures, although the metallocenes are not significantly distorted towards the (η(6)-fulvene)(η(5)-cyclopentadienyl)metal(II) extreme. DFT geometries are in excellent agreement with those determined crystallographically; while the π-donor strengths of the three metallocenyl groups are insufficiently different to result in detectable differences in the crystallographic bond-length alternations, the DFT geometries, as well as DFT-calculations of partial charges for atoms, suggest that π-donor strength decreases in the order Fc″ ≫ Fc > Rc. NMR, IR and electrochemical evidence also suggests that octamethylferrocenyl is the stronger π-donor, exhibiting similar π-donor strength to a p-(dialkylamino)phenyl group, while ferrocenyl and ruthenocenyl show very similar π-donor strengths to one another in chromophores of this type.
已确定了六种偶极多烯发色团的晶体结构，这些发色团带有金属茂基——二茂铁基（Fc）、八甲基二茂铁基（Fc″）或钌茂基（Rc）——供体以及基于1,3 - 二乙基 - 2 - 硫代巴比妥酸或3 - 二氰基亚甲基 - 2,3 - 二氢苯并噻吩 - 1,1 - 二氧化物的强杂环受体。在每种情况下，发现晶体属于中心对称空间群。例如，聚合物诱导的异相成核揭示了另外两种多晶型物的存在，它们在二次谐波产生中无活性，这表明它们也是中心对称的。与简单多烯相比，多烯桥的形式上的双键和单键之间的键长交替减小，这表明电荷分离共振结构有显著贡献，尽管金属茂没有明显向(η(6)-富烯)(η(5)-环戊二烯基)金属(II)极端变形。密度泛函理论（DFT）几何结构与晶体学测定的结构非常吻合；虽然三个金属茂基的π供体强度差异不足以导致晶体学键长交替出现可检测到的差异，但DFT几何结构以及原子部分电荷的DFT计算表明，π供体强度按Fc″≫Fc>Rc的顺序降低。核磁共振（NMR）、红外（IR）和电化学证据也表明，八甲基二茂铁基是较强的π供体，其π供体强度与对 - （二烷基氨基）苯基相似，而在这类发色团中，二茂铁基和钌茂基彼此显示出非常相似的π供体强度。
