Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309, USA.
Inorg Chem. 2009 Dec 7;48(23):11161-75. doi: 10.1021/ic901637b.
Computational studies using density functional theory (DFT) are reported for a series of donor-acceptor (DA) transition metal complexes and related excited-state and electron transfer (ET) photoproduct models. Three hybrid Hartree-Fock/DFT (HF/DFT) functionals, B3LYP, B3PW91, and PBE1PBE, are employed to characterize structural features implicated in the dynamical control of productive forward and energy wasting back ET events. Energies and optimized geometries are reported for the lowest energy singlet state in Ru(dmb)(2)(bpy-phi-MV) (DA1), Ru(dmb)(2)(bpy-o-tolyl-MV) (DA2), Ru(dmb)(2)(bpy-2,6-Me(2)-phi-MV) (DA3), and Ru(tmb)(2)(bpy-2,6-Me(2)-phi-MV) (DA3'), where dmb is 4,4'-dimethyl-2,2'-bipyridine, tmb is 4,4',5,5'-tetramethyl-2,2'-bipyridine, MV is methyl viologen, and phi is a phenylene spacer. These indicate that the dihedral angle theta(1) between the aryl substituent and the bipyridine fragment to which it is bound, systematically increases with the addition of steric bulk. Energies, optimized geometries, and unpaired electron spin densities are also reported for the lowest energy triplet state of Ru(dmb)(2)(4-p-tolyl-2,2'-bipyridine) (D1*), Ru(dmb)(2)(4-(2,6-dimethylphenyl)-2,2'-bipyridine) (D2*), Ru(dmb)(2)(4-mesityl-2,2'-bipyridine) (D3*), and Ru(tmb)(2)(4-mesityl-2,2'-bipyridine) (D3'*). Each of these serves as a model of a reactant excited state in the forward electron-transfer photochemistry allowing us to qualify and quantify the role of excited-state intraligand electron delocalization in driving substantial geometry changes (especially with respect to theta(1)) relative to its respective DA counterpart. Next, energies, optimized geometries, and spin densities are reported for the lowest energy triplet of each DA species: (3)DA1, (3)DA2, (3)DA3, and (3)DA3'. These are used to model the ET photoproduct and they indicate that theta(1) increases following ET, thus, verifying switch-like properties. Finally, we report data for geometry optimized DA1 and (3)DA1 in a continuum model of room temperature acetonitrile. This study shows a complete recovery of theta(1) to its ground state value which has implications in efforts to trap electrons in charge-separated states.
本文报道了一系列给体-受体（DA）过渡金属配合物及相关激发态和电子转移（ET）光产物模型的基于密度泛函理论（DFT）的计算研究。采用三种混合 Hartree-Fock/DFT（HF/DFT）泛函（B3LYP、B3PW91 和 PBE1PBE）来描述与动力学控制相关的结构特征，这些特征涉及到有生产性的正向 ET 反应和能量浪费的反向 ET 反应。本文报道了Ru(dmb)(2)(bpy-phi-MV)（DA1）、Ru(dmb)(2)(bpy-o-tolyl-MV)（DA2）、Ru(dmb)(2)(bpy-2,6-Me(2)-phi-MV)（DA3）和Ru(tmb)(2)(bpy-2,6-Me(2)-phi-MV)（DA3'）中最低能量单重态的能量和优化几何形状，其中 dmb 是 4,4'-二甲基-2,2'-联吡啶，tmb 是 4,4',5,5'-四甲基-2,2'-联吡啶，MV 是甲基紫精，phi 是亚苯基间隔基。这些结果表明，芳基取代基与联吡啶片段之间的二面角 theta(1)随着空间位阻的增加而系统地增加。本文还报道了Ru(dmb)(2)(4-p-tolyl-2,2'-bipyridine)（D1*）、Ru(dmb)(2)(4-(2,6-dimethylphenyl)-2,2'-bipyridine)（D2*）、Ru(dmb)(2)(4-mesityl-2,2'-bipyridine)（D3*）和Ru(tmb)(2)(4-mesityl-2,2'-bipyridine)（D3'*）中最低能量三重态的能量、优化几何形状和未配对电子自旋密度。这些都作为正向 ET 光化学反应中反应物激发态的模型，使我们能够定性和定量地确定激发态内配位电子离域在驱动结构发生显著变化（尤其是相对于 theta(1)）方面的作用，相对于其各自的 DA 对应物。接下来，报道了每个 DA 物种的最低能量三重态（3）DA1、（3）DA2、（3）DA3 和（3）DA3'的能量、优化几何形状和自旋密度。这些被用来模拟 ET 光产物，并表明 theta(1)在 ET 之后增加，因此验证了开关样的特性。最后，报道了在室温乙腈连续模型中优化的 DA1 和（3）DA1 的几何形状数据。该研究表明 theta(1)完全恢复到其基态值，这对在电荷分离态中捕获电子的努力具有重要意义。
