Intelligent Textile System Research Center, Department of Chemistry, College of Natural Sciences, Seoul National University, Seoul 151-747, Korea.
Inorg Chem. 2010 Aug 16;49(16):7340-52. doi: 10.1021/ic100325c.
Three ruthenium(II) complexes with N-heterocyclic carbene (NHC) or NHC/2,2':6',2''-terpyridine (tpy) hybrid ligands, bis[2,6-bis(3-methylimidazol-3-ium-1-yl)pyridine-4-carboxylic acid]ruthenium(II) (BCN), 2,6-bis(3-methylimidazolium-1-yl)pyridine-4-carboxylic acidruthenium(II) (TCN), and [2,6-bis(3-methylimidazol-3-ium-1-yl)pyridine](2,2';6'2''-terpyridine-4'-carboxylic acid)ruthenium(II) (CTN), have been synthesized and characterized by (1)H and (13)C NMR, high-resolution mass spectrometry, and elemental analysis. The molecular geometry of the TCN complex was determined by X-ray crystallography. Electronic absorption spectra of these complexes exhibit typical pi-pi* and metal-to-ligand charge transfer bands in the UV and visible regions, respectively. The lowest energy absorption maxima were 430, 448, and 463 nm with molar extinction coefficients of 28,100, 15,400, and 7400 M(-1)cm(-1) for BCN, TCN, and CTN, respectively. Voltammetric data suggest that energy levels of the highest occupied molecular orbitals (HOMOs) of the three complexes reside within a 10 meV window despite the varying degrees of electronic effect of the constituent ligands. The electronic structures of these complexes calculated via density functional theory (DFT) indicate that the three HOMOs and the three lowest unoccupied MOs (LUMOs) are metal and ligand centered in character, for the former and the latter, respectively. Time-dependent DFT (TD-DFT) calculation predicts that the lowest energy absorption bands of each complex are comprised of multiple one-electron excitations. TD-DFT calculation also suggests that the background of spectral red shift stems most likely from the stabilization of unoccupied MOs rather than the destabilization of occupied MOs. The overall efficiencies of the dye-sensitized solar cell systems of these complexes were found to be 0.48, 0.14, and 0.10% for BCN, TCN, and CTN, respectively, while that of a commercial bis(4,4'-dicarboxylato-2,2'-bipyridine)-bis(isothiocyanoto)ruthenium(II) (N719) system was 6.34%.
三种钌（II）配合物具有 N-杂环卡宾（NHC）或 NHC/2,2':6',2''-三联吡啶（tpy）混合配体，二[2,6-双（3-甲基咪唑-3-基）吡啶-4-羧酸]钌（II）（BCN），[2,6-双（3-甲基咪唑啉-1-基）吡啶-4-羧酸]（2,2':6'2''-三联吡啶）钌（II）（TCN），和[2,6-双（3-甲基咪唑啉-1-基）吡啶]（2,2':6'2''-三联吡啶-4'-羧酸）钌（II）（CTN），已通过（1）H 和（13）C NMR、高分辨率质谱和元素分析进行了合成和表征。TCN 配合物的分子几何形状通过 X 射线晶体学确定。这些配合物的电子吸收光谱在紫外和可见区域分别显示出典型的 pi-pi* 和金属-配体电荷转移带。最低能量吸收最大值分别为 430、448 和 463nm，摩尔消光系数分别为 28100、15400 和 7400M(-1)cm(-1)，对于 BCN、TCN 和 CTN。伏安数据表明，尽管组成配体的电子效应程度不同，但三个配合物的最高占据分子轨道（HOMO）的能级位于 10meV 窗口内。通过密度泛函理论（DFT）计算的这些配合物的电子结构表明，三个 HOMO 和三个最低未占据 MO（LUMO）分别为金属和配体中心性质。时变密度泛函理论（TD-DFT）计算预测，每个配合物的最低能量吸收带由多个单电子激发组成。TD-DFT 计算还表明，光谱红移的背景很可能源于未占据 MO 的稳定化，而不是占据 MO 的去稳定化。这些配合物的染料敏化太阳能电池系统的整体效率分别为 0.48%、0.14%和 0.10%，用于 BCN、TCN 和 CTN，而商业双（4,4'-二羧基-2,2'-联吡啶）-双（异硫氰酸根）钌（II）（N719）系统的效率为 6.34%。
