Department of Chemistry and The Institute for Sustainable Energy, Environment and Economy, University of Calgary, 2500 University Drive N.W., Calgary T2N-1N4, Canada.
Inorg Chem. 2011 Jun 20;50(12):5494-508. doi: 10.1021/ic200011m. Epub 2011 May 19.
The syntheses and the electrochemical spectroscopic properties of a suite of asymmetrical bistridentate cyclometalated Ru(II) complexes bearing terminal triphenylamine (TPA) substituents are reported. These complexes, which contain structural design elements common to both inorganic and organic dyes that exhibit superior power conversion efficiencies in the dye-sensitized solar cell (DSSC), are broadly formulated as Ru(II)(L-2,5'-thiophene-TPA-R(1))(L-R(2)) [L = tridentate chelating ligand (e.g., 2,2':6',2''-terpyridine (tpy); deprotonated forms of 1,3-di(pyridin-2-yl)benzene (Hdpb) or 6-phenyl-2,2'-bipyridine (Hpbpy)); R(1) = -H, -Me, -OMe; R(2) = -H, -CO(2)Me, -CO(2)H]. The following structural attributes were systematically modified for the series: (i) electron-donating character of the terminal substituents (e.g., R(1) = -H, -Me, -OMe) placed para to the amine of the "L-2,5'-thiophene-TPA-R(1)" ligand framework; (ii) electron-withdrawing character of the tridentate chelate distal to the TPA-substituted ligand (e.g., R(2) = -H, -CO(2)Me, -CO(2)H); and (iii) position of the organometallic bond about the Ru(II) center. UV-vis spectra reveal intense and broad absorption bands arising from a collection of metal-to-ligand charge-transfer (MLCT) and TPA-based intraligand charge-transfer (ILCT) transitions that, in certain cases, extend beyond 800 nm. Electrochemical data indicate that the oxidative behavior of the TPA and metal chelate units can be independently modulated except in cases where the anionic phenyl ring is in direct conjugation with the TPA unit. In most cases, the anionic character of the cyclometalating ligands renders a metal-based oxidation event prior to the oxidation of the TPA unit. This situation can, however, be reversed with an appropriately positioned Ru-C bond and electron-rich R(1) group. This finding is important in that this arrangement confines the highest occupied molecular orbital (HOMO) to the TPA unit rather than the metal, which is optimal for sensitizing TiO(2); indeed, a remarkably high power conversion efficiency (η) in the DSSC (i.e., 8.02%) is measured for the TPA-substituted pbpy(-) chelate where R(1) = -OMe. These results provide a comprehensive strategy for improving the performance of bistridentate Ru sensitizers devoid of NCS(-) groups for the DSSC.
报告了一系列不对称双齿环金属化 Ru(II)配合物的合成及电化学光谱性质，这些配合物具有终端三苯基胺 (TPA) 取代基，包含无机和有机染料中都有的结构设计元素，在染料敏化太阳能电池 (DSSC) 中表现出更高的功率转换效率。这些配合物广泛地被表述为 Ru(II)(L-2,5'-噻吩-TPA-R(1))(L-R(2)) [L = 三齿螯合配体（例如 2,2':6',2''-三联吡啶 (tpy)；1,3-二（吡啶-2-基）苯 (Hdpb) 或 6-苯基-2,2'-联吡啶 (Hpbpy) 的去质子形式)；R(1) = -H，-Me，-OMe；R(2) = -H，-CO(2)Me，-CO(2)H]。为了形成这一系列，系统性地修改了以下结构属性：(i) 胺基邻位上终端取代基的供电子特性 (例如 R(1) = -H，-Me，-OMe)，这是“L-2,5'-噻吩-TPA-R(1)”配体骨架的一部分；(ii) 与 TPA 取代配体远端的三齿螯合配体的吸电子特性 (例如 R(2) = -H，-CO(2)Me，-CO(2)H)；以及 (iii) Ru(II)中心周围的有机金属键的位置。紫外可见光谱显示出强烈且宽的吸收带，源于一系列金属到配体电荷转移 (MLCT) 和 TPA 基内配体电荷转移 (ILCT) 跃迁，在某些情况下，吸收带延伸至 800nm 以上。电化学数据表明，TPA 和金属螯合单元的氧化行为可以独立调节，除非阴离子苯基与 TPA 单元直接共轭。在大多数情况下，环金属化配体的阴离子特性使得金属基氧化事件先于 TPA 单元的氧化。然而，这种情况可以通过适当定位的 Ru-C 键和富电子 R(1)基团来逆转。这一发现非常重要，因为这种排列将最高占据分子轨道 (HOMO)限制在 TPA 单元而不是金属上，这对敏化 TiO(2)是最佳的；实际上，在 TPA 取代的 pbpy(-)螯合物中，测量到了高达 8.02%的 DSSC 的高功率转换效率 (η)，其中 R(1) = -OMe。这些结果为提高不含 NCS(-)基团的双齿 Ru 敏化剂在 DSSC 中的性能提供了一个全面的策略。
