Department of Chemistry, R. K. Mission Residential College, Narendrapur, Kolkata, 103, India.
Dalton Trans. 2011 Jul 28;40(28):7375-84. doi: 10.1039/c1dt10270b. Epub 2011 Jun 17.
Three types of atropisomeric unsymmetrical diimine complexes, tetrahedral (L(R)(Φ))MX(2) (M = Zn, Cd; X = Cl, Br; R = Me, CMe(3), OH, OMe, Cl; 1a-k, type-I), tetrahedral (L(Me2)(Φ))ZnBr(2) (2, type-II) and square planar (L(OH)(ϕ))PdCl(2) (3, type-III) with different photoluminescence properties, have been reported (L(R)(Φ) = (E)-4-R-N-(pyridine-2-ylmethylene)aniline; Φ = dihedral angle between the diimine unit including the pyridine ring and the phenyl ring planes). In crystals, Φ = 0° for type-I, 90° for type-II and 63° for type-III atropisomers have been confirmed by single crystal X-ray structure determinations of 1c, 1e, 2 and 3·H(2)O isomers. Optimizations of geometries in methanol have established Φ = 28-32° for type-I, 90.83° for type-II and 43.44° for type-III isomers. In solids, type-I atropisomers with Φ = 0, behave as conjugated 14πe systems facilitating π-π stacking and are brightly luminescent at room temperature while type-II and type-III isomers in solid and type-I isomers in solutions are more like non-conjugated 8πe + 6πe systems and non-emissive. Frozen glasses of acetonitrile, methanol and dichloromethane-toluene mixture at 77 K of type-I isomers are emissive and display structured excitation and emission spectra for R = Me, CMe(3), OMe species. Excitation and emission maxima of frozen glasses (λ(ex) = 320-380 nm; λ(em) = 440-485 nm) are red shifted in the solid (λ(ex) = 390-455 nm; λ(em) = 470-550 nm). TD-DFT calculations on 1b, 1d, 1f and stacked (1b)(2) isomers and luminescence lifetime measurements have elucidated that an excited (1)ILCT state has been the origin of emission of the type-I isomers and delocalizations of the photoactive π(diimine) and π(diimine)(*) orbitals of the L(R)(Φ) over the stacked layers shift the λ(ext) and λ(em) of solids to lower energies than those in frozen glasses. The trends of diimine ligand based electron transfer events of the complexes in DMF have been investigated by cyclic voltammetry at 298 K.
三种类型的手性非对称二亚胺配合物，四面体（L(R)(Φ))MX(2)（M = Zn，Cd；X = Cl，Br；R = Me，CMe(3)，OH，OMe，Cl；1a-k，I 型）、四面体（L(Me2)(Φ))ZnBr(2)（2，II 型）和平面四方（L(OH)(ϕ))PdCl(2)（3，III 型）具有不同的光致发光性质，已经被报道（L(R)(Φ) = (E)-4-R-N-(吡啶-2-基亚甲基)苯胺；Φ = 二亚胺单元包括吡啶环和苯环平面之间的二面角）。在晶体中，通过单晶 X 射线结构测定 1c、1e、2 和 3·H(2)O 异构体，已经证实 I 型异构体的 Φ = 0°，II 型异构体的 Φ = 90°，III 型异构体的 Φ = 63°。在甲醇中的几何优化确定 I 型异构体的 Φ = 28-32°，II 型异构体的 Φ = 90.83°，III 型异构体的 Φ = 43.44°。在固体中，具有 Φ = 0 的 I 型异构体表现为共轭 14πe 体系，有利于π-π堆积，在室温下具有明亮的发光性，而 II 型和 III 型异构体在固体中和 I 型异构体在溶液中更类似于非共轭 8πe + 6πe 体系，不发光。在 77 K 下，I 型异构体的乙腈、甲醇和二氯甲烷-甲苯混合物的冷冻玻璃是发光的，并显示出 R = Me、CMe(3)、OMe 物种的结构化激发和发射光谱。冷冻玻璃的激发和发射最大值（λ(ex) = 320-380nm；λ(em) = 440-485nm）在固体中发生红移（λ(ex) = 390-455nm；λ(em) = 470-550nm）。对 1b、1d、1f 和堆积（1b)(2)异构体的 TD-DFT 计算和荧光寿命测量表明，激发态（1）ILCT 态是 I 型异构体发光的起源，并且光活性的 π(diimine)和 π(diimine)(*)轨道在堆积层上的离域将固体的 λ(ext)和 λ(em)移向比冷冻玻璃更低的能量。通过在 298 K 下的循环伏安法研究了配合物在 DMF 中基于二亚胺配体的电子转移事件的趋势。
