She Chunxing, Anderson Neil A, Guo Jianchang, Liu Fang, Goh Wan-Hee, Chen Dai-Tao, Mohler Debra L, Tian Zhong-Qun, Hupp Joseph T, Lian Tianquan
Department of Chemistry, Emory University, Atlanta, Georgia 30322, USA.
J Phys Chem B. 2005 Oct 20;109(41):19345-55. doi: 10.1021/jp053948u.
Photoinduced interfacial electron transfer (ET) from molecular adsorbates to semiconductor nanoparticles has been a subject of intense recent interest. Unlike intramolecular ET, the existence of a quasicontinuum of electronic states in the solid leads to a dependence of ET rate on the density of accepting states in the semiconductor, which varies with the position of the adsorbate excited-state oxidation potential relative to the conduction band edge. For metal oxide semiconductors, their conduction band edge position varies with the pH of the solution, leading to pH-dependent interfacial ET rates in these materials. In this work we examine this dependence in Re(L(P))(CO)3Cl (or ReC1P) [L(P) = 2,2'-bipyridine-4,4'-bis-CH2PO(OH)2] and Re(L(A))(CO)3Cl (or ReC1A) [L(A) = 2,2'-bipyridine-4,4'-bis-CH2COOH] sensitized TiO2 and ReC1P sensitized SnO2 nanocrystalline thin films using femtosecond transient IR spectroscopy. ET rates are measured as a function of pH by monitoring the CO stretching modes of the adsorbates and mid-IR absorption of the injected electrons. The injection rate to TiO2 was found to decrease by 1000-fold from pH 0-9, while it reduced by only a factor of a few to SnO2 over a similar pH range. Comparison with the theoretical predictions based on Marcus' theory of nonadiabatic interfacial ET suggests that the observed pH-dependent ET rate can be qualitatively accounted for by considering the change of density of electron-accepting states caused by the pH-dependent conduction band edge position.
光诱导分子吸附物与半导体纳米颗粒之间的界面电子转移（ET）一直是近期研究的热点。与分子内电子转移不同，固体中准连续电子态的存在导致电子转移速率依赖于半导体中接受态的密度，而接受态密度会随着吸附物激发态氧化电位相对于导带边缘的位置而变化。对于金属氧化物半导体，其导带边缘位置随溶液pH值变化，导致这些材料中界面电子转移速率与pH值相关。在这项工作中，我们使用飞秒瞬态红外光谱研究了Re(L(P))(CO)3Cl（或ReC1P）[L(P)=2,2'-联吡啶-4,4'-双-CH2PO(OH)2]和Re(L(A))(CO)3Cl（或ReC1A）[L(A)=2,2'-联吡啶-4,4'-双-CH2COOH]敏化的TiO2以及ReC1P敏化的SnO2纳米晶薄膜中的这种相关性。通过监测吸附物的CO伸缩模式和注入电子的中红外吸收来测量电子转移速率随pH值的变化。发现注入TiO2的速率在pH值从0到9时降低了1000倍，而在类似的pH范围内注入SnO2的速率仅降低了几倍。与基于马库斯非绝热界面电子转移理论的理论预测进行比较表明，通过考虑pH值依赖的导带边缘位置引起的电子接受态密度变化，可以定性地解释观察到的pH值依赖的电子转移速率。
