Key Laboratory for Ultrafine Materials of Ministry of Education, School of Materials Science and Engineering, East China University of Science and Technology, Shanghai, People's Republic of China.
J Phys Chem A. 2011 Dec 22;115(50):14495-501. doi: 10.1021/jp2066452. Epub 2011 Nov 28.
Studies on the molecular geometries, electronic properties and second-order nonlinearities of a series of mono- and binuclear chromium carbazole complexes: (N-vinylcarbazole)Cr(CO)(3) (M1), (N-vinylcarbazole)Cr(CO)(2)PPh(3) (M2), (CO)(3)Cr(N-vinylcarbazole)Cr(CO)(3) (B1), and (CO)(3)Cr(N-vinylcarbazole)Cr(CO)(2)PPh(3) (B2) were carried out, using the density functional theory (DFT) at the B3LYP//LanL2DZ/6-31G(d) level. The experimental singlet metal-to-ligand charge transfer ((1)MLCT) spectra of these complexes can also be well simulated and discussed by the time-dependent DFT (TDDFT) at the B3LYP//LanL2DZ/6-311+G(d) level associated with the polarizable continuum model (PCM). The computational results show that an unusual characteristic of chromium carbazole structures is explained in terms of interaction between frontier molecular orbitals of the metal and its ligands. The highest occupied molecular orbitals (HOMOs) of these complexes are composed of a set of distorted degenerated Cr 3d orbitals, whereas the lowest unoccupied molecular orbitals (LUMOs) are predominantly the N-vinylcarbazole ligand π* orbitals. The HOMO-LUMO energy gaps decrease in the order NVC > M1 > B1 > M2 > B2. The considerable coupling between the carbazole and (CO)(3) in M1 creates an asymmetric environment about the chromium atom, leading to modest second-order responses. The PPh(3) ligand is acting as a donor which increases the donating strength of the d(π) orbitals in chromium carbazole species, resulting in the large electronic asymmetry in M2. As for the binuclear chromium carbazole chromophores, a wide-range (1)MLCT band and large oscillator strength are found, allowing for the electronic interactions between two metal centers which can be modified by altering the ligand bound to the metals to induce peculiar asymmetry. Essentially, Cr(CO)(3) acceptor and Cr(CO)(2)PPh(3) donor units in B2 make significant contribution to the charge-transfer process or NLO responses via conventional push-pull chromophoric architecture.
对一系列单核和双核铬咔唑配合物的分子几何形状、电子性质和二阶非线性进行了研究：(N-乙烯基咔唑)Cr(CO)3 (M1)、(N-乙烯基咔唑)Cr(CO)2PPh3 (M2)、(CO)3Cr(N-乙烯基咔唑)Cr(CO)3 (B1)和(CO)3Cr(N-乙烯基咔唑)Cr(CO)2PPh3 (B2)，使用密度泛函理论(DFT)在 B3LYP//LanL2DZ/6-31G(d)水平上进行。这些配合物的实验单重金属-配体电荷转移((1)MLCT)光谱也可以通过时间相关密度泛函理论(TDDFT)在 B3LYP//LanL2DZ/6-311+G(d)水平上与极化连续模型(PCM)相关联进行很好的模拟和讨论。计算结果表明，铬咔唑结构的一个不寻常特征可以用金属及其配体的前线分子轨道之间的相互作用来解释。这些配合物的最高占据分子轨道(HOMOs)由一组扭曲简并的 Cr 3d 轨道组成，而最低未占据分子轨道(LUMOs)主要是 N-乙烯基咔唑配体π*轨道。HOMO-LUMO 能隙按 NVC > M1 > B1 > M2 > B2 的顺序减小。M1 中咔唑和(CO)3 之间的相当大的耦合在铬原子周围产生了不对称的环境，导致二阶响应适度。PPh3 配体充当供体，增加了铬咔唑物种中 d(π)轨道的供电子强度，导致 M2 中电子不对称性增大。对于双核铬咔唑发色团，发现了宽范围的(1)MLCT 带和大的振子强度，允许通过改变与金属结合的配体来调节两个金属中心之间的电子相互作用，从而诱导奇特的不对称性。本质上，B2 中的 Cr(CO)3 受体和 Cr(CO)2PPh3 供体单元通过传统的推拉发色团结构对电荷转移过程或 NLO 响应做出重要贡献。
