Farnum Byron H, Morseth Zachary A, Brennaman M Kyle, Papanikolas John M, Meyer Thomas J
Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina 27599-3290, United States.
J Phys Chem B. 2015 Jun 18;119(24):7698-711. doi: 10.1021/jp512624u. Epub 2015 Feb 10.
Degenerately doped In2O3:Sn semiconductor nanoparticles (nanoITO) have been used to study the photoinduced interfacial electron-transfer reactivity of surface-bound Ru(II)(bpy)2(4,4'-(PO3H2)2-bpy) (RuP(2+)) molecules as a function of driving force over a range of 1.8 eV. The metallic properties of the ITO nanoparticles, present within an interconnected mesoporous film, allowed for the driving force to be tuned by controlling their Fermi level with an external bias while their optical transparency allowed for transient absorption spectroscopy to be used to monitor electron-transfer kinetics. Photoinduced electron transfer from excited-state -RuP(2+) molecules to nanoITO was found to be dependent on applied bias and competitive with nonradiative energy transfer to nanoITO. Back electron transfer from nanoITO to oxidized -RuP(3+) was also dependent on the applied bias but without complication from inter- or intraparticle electron diffusion in the oxide nanoparticles. Analysis of the electron injection kinetics as a function of driving force using Marcus-Gerischer theory resulted in an experimental estimate of the reorganization energy for the excited-state -RuP(3+/2+) redox couple of λ* = 0.83 eV and an electronic coupling matrix element, arising from electronic wave function overlap between the donor orbital in the molecule and the acceptor orbital(s) in the nanoITO electrode, of Hab = 20-45 cm(-1). Similar analysis of the back electron-transfer kinetics yielded λ = 0.56 eV for the ground-state -RuP(3+/2+) redox couple and Hab = 2-4 cm(-1). The use of these wide band gap, degenerately doped materials provides a unique experimental approach for investigating single-site electron transfer at the surface of oxide nanoparticles.
简并掺杂的In2O3:Sn半导体纳米颗粒（纳米ITO）已被用于研究表面结合的Ru(II)(bpy)2(4,4'-(PO3H2)2-bpy)（RuP(2+)）分子的光致界面电子转移反应活性，该反应活性是驱动力在1.8 eV范围内的函数。相互连接的介孔膜中存在的ITO纳米颗粒的金属特性，使得通过外部偏压控制其费米能级来调节驱动力成为可能，而其光学透明度则允许使用瞬态吸收光谱法监测电子转移动力学。发现从激发态-RuP(2+)分子到纳米ITO的光致电子转移取决于施加的偏压，并且与向纳米ITO的非辐射能量转移相互竞争。从纳米ITO到氧化态-RuP(3+)的反向电子转移也取决于施加的偏压，但不会因氧化物纳米颗粒中的颗粒间或颗粒内电子扩散而变得复杂。使用Marcus-Gerischer理论分析作为驱动力函数的电子注入动力学，得到激发态-RuP(3+/2+)氧化还原对的重组能的实验估计值λ* = 0.83 eV，以及由于分子中的供体轨道与纳米ITO电极中的受体轨道之间的电子波函数重叠而产生的电子耦合矩阵元Hab = 20 - 45 cm(-1)。对反向电子转移动力学的类似分析得出基态-RuP(3+/2+)氧化还原对的λ = 0.56 eV和Hab = 2 - 4 cm(-1)。这些宽带隙简并掺杂材料的使用为研究氧化物纳米颗粒表面的单中心电子转移提供了一种独特的实验方法。
