She Chunxing, Guo Jianchang, Lian Tianquan
Department of Chemistry, Emory University, Atlanta, Georgia 30322, USA.
J Phys Chem B. 2007 Jun 21;111(24):6903-12. doi: 10.1021/jp070561d. Epub 2007 May 23.
Factors that control photoinduced interfacial electron transfer (ET) between molecular adsorbates and semiconductor nanoparticles have been intensely investigated in recent years. In this work, the solvent dependence of interfacial ET was studied by comparing ET rates in dye sensitized TiO2 nanocrystalline films in different solvent environments. Photoinduced ET rates from Re(LA)(CO)3Cl [LA=dcbpy=4,4'-dicarboxy-2,2'-bipyridine] (ReC1A) to TiO2 nanocrystalline thin films in air, pH buffer, MeOH, EtOH, and DMF were measured by femtosecond transient IR spectroscopy. The ET rates in these solvent environments were noticeably different. However, differences between the rates in pH buffer and nonaqueous solvents (MeOH, EtOH, and DMF) were much smaller than the values expected from much more negative TiO2 conduction band-edge positions in the latter solvents under anhydrous conditions. It was suggested that the presence of adsorbed water, which was evident in FTIR spectra, lowered the band edge of TiO2 in these solvents and reduced the rate differences. The important effect of adsorbed water was verified by comparing two samples of Re(LP)(CO)3Cl [LP=2,2'-bipyridine-4,4'-bis-CH2PO(OH)2] sensitized TiO2 in DMF, in which the presence of a trace amount of water was found to significantly increase the injection rate.
近年来，人们对控制分子吸附物与半导体纳米颗粒之间光致界面电子转移（ET）的因素进行了深入研究。在这项工作中，通过比较不同溶剂环境下染料敏化TiO₂纳米晶薄膜中的ET速率，研究了界面ET对溶剂的依赖性。利用飞秒瞬态红外光谱法测量了Re(LA)(CO)₃Cl [LA = dcbpy = 4,4'-二羧基-2,2'-联吡啶]（ReC1A）在空气、pH缓冲液、甲醇、乙醇和N,N-二甲基甲酰胺（DMF）中向TiO₂纳米晶薄膜的光致ET速率。这些溶剂环境中的ET速率明显不同。然而，pH缓冲液和非水溶剂（甲醇、乙醇和DMF）中的速率差异远小于在无水条件下后一种溶剂中TiO₂导带边缘位置更负得多时预期的值。研究表明，傅里叶变换红外光谱（FTIR）中明显存在的吸附水降低了这些溶剂中TiO₂的带边，并减小了速率差异。通过比较在DMF中用Re(LP)(CO)₃Cl [LP = 2,2'-联吡啶-4,4'-双-CH₂PO(OH)₂]敏化的TiO₂的两个样品，验证了吸附水的重要作用，发现痕量水的存在显著提高了注入速率。
