She Chunxing, Guo Jianchang, Irle Stephan, Morokuma Keiji, Mohler Debra L, Zabri Herve, Odobel Fabrice, Youm Kyoung-Tae, Liu Fang, Hupp Joseph T, Lian Tianquan
Department of Chemistry, Emory University, Atlanta, Georgia 30322, USA.
J Phys Chem A. 2007 Jul 26;111(29):6832-42. doi: 10.1021/jp0709003. Epub 2007 May 23.
The effects of anchoring groups on electron injection from adsorbate to nanocrystalline thin films were investigated by comparing injection kinetics through carboxylate versus phosphonate groups to TiO2 and SnO2. In the first pair of molecules, Re(LA)(CO)3Cl (ReC1A) and Re(Lp)(CO)3Cl (ReC1P), [LA=2,2'-bipyridine-4,4'-bis-CH2-COOH, Lp=2,2'-bipyridine-4,4'-bis-CH2-PO3H2], the anchoring groups were insulated from the bipyridine ligand by a CH2 group. In the second pair of molecules, Ru(dcbpyH2)2(NCS)2 (RuN3) and Ru(bpbpyH2)2(NCS)2 (RuN3P), [dcbpy=2,2'-bipyridine-4,4'-biscarboxylic acid, bpbpy=2,2'-bipyridine-4,4'-bisphosphonic acid], the anchoring groups were directly connected to the bipyridine ligands. The injection kinetics, as measured by subpicosecond IR absorption spectroscopy, showed that electron injection rates from ReC1P to both TiO2 and SnO2 were faster than those from ReC1A. The injection rates from RuN3 and RuN3P to SnO2 films were similar. On TiO2, the injection kinetics from RuN3 and RuN3P were biphasic: carboxylate group enhances the rate of the <100 fs component, but reduces the rate of the slower components. To provide insight into the effect of the anchoring groups, the electronic structures of Re-bipyridyl-Ti model clusters containing carboxylate and phosphonate anchoring groups and with and without a CH2 spacer were computed using density functional theory. With the CH2 spacer, the phosphonate group led to a stronger electronic coupling between bpy and Ti center than the carboxylate group, which accounted for the faster injection from ReC1P than ReC1A. When the anchoring groups were directly connected to the bpy ligand without the CH2 spacer, such as in RuN3 and RuN3P, their effects were 2-fold: the carboxylate group enhanced the electronic coupling of bpy pi* with TiO2 and lowered the energy of the bpy orbital. How these competing factors led to different effects on TiO2 and SnO2 and on different components of the biphasic injection kinetics were discussed.
通过比较羧酸盐基团和膦酸盐基团与TiO₂和SnO₂之间的注入动力学，研究了锚定基团对从吸附物到纳米晶薄膜电子注入的影响。在第一对分子Re(LA)(CO)₃Cl（ReC1A）和Re(Lp)(CO)₃Cl（ReC1P）中，[LA = 2,2'-联吡啶-4,4'-双-CH₂-COOH，Lp = 2,2'-联吡啶-4,4'-双-CH₂-PO₃H₂]，锚定基团通过-CH₂基团与联吡啶配体隔离。在第二对分子Ru(dcbpyH₂)₂(NCS)₂（RuN3）和Ru(bpbpyH₂)₂(NCS)₂（RuN3P）中，[dcbpy = 2,2'-联吡啶-4,4'-二羧酸，bpbpy = 2,2'-联吡啶-4,4'-二膦酸]，锚定基团直接与联吡啶配体相连。通过亚皮秒红外吸收光谱测量的注入动力学表明，从ReC1P到TiO₂和SnO₂的电子注入速率比从ReC1A的快。从RuN3和RuN3P到SnO₂薄膜的注入速率相似。在TiO₂上，从RuN3和RuN3P的注入动力学是双相的：羧酸盐基团提高了<100 fs成分的速率，但降低了较慢成分的速率。为了深入了解锚定基团的影响，使用密度泛函理论计算了含有羧酸盐和膦酸盐锚定基团且有和没有-CH₂间隔基的Re-联吡啶-Ti模型簇的电子结构。有-CH₂间隔基时，膦酸盐基团导致bpy和Ti中心之间的电子耦合比羧酸盐基团更强，这解释了从ReC1P比ReC1A更快的注入。当锚定基团直接与没有-CH₂间隔基的bpy配体相连时，如在RuN3和RuN3P中，它们的影响有两方面：羧酸盐基团增强了bpy π*与TiO₂ 的电子耦合并降低了bpy轨道的能量。讨论了这些相互竞争的因素如何对TiO₂和SnO₂以及对双相注入动力学的不同成分产生不同影响。
