Three ruthenium(II) sensitizers, [Ru(L)₂(dcb)]²⁺, were anchored to mesoporous TiO₂ thin films where the ligand L = 4,4′-(CH₃)₂-bpy (dmb), 4,4′-(C(CH₃)₃)₂-bpy (dtb), and 4,4′-(CF₃)₂-bpy (bpyCF₃) controls the thermodynamics and electronic coupling for self-exchange intermolecular Ru^III/II “hole hopping”. Apparent electron difussion coefficients, D_app, were reported to increase in the order bpyCF₃ ≪ dtb < dmb. Nanosecond transient absorption measurements made over an 80° temperature range were conducted to abstract average charge recombination rate constants, k_cr, under conditions of sub-percolation and saturated sensitizer surface coverages. For sensitizers [Ru(dmb)₂(dcb)]²⁺ and [Ru(dtb)₂(dcb)]²⁺, the k_cr values at saturation coverages were significantly larger than those at low coverages, by a degree that followed the trend in D_app. The inability of [Ru(bpyCF₃)₂(dcb)]²⁺ to introduce hole transport was afirmed by recombination kinetic data that were insensitive to the sensitizer surface converage. An Arrhenius analysis indicated that lateral Ru^III/II hole hopping decreased the barrier for electron transfer that ultimately led to faster recombination rates.

中文翻译：

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电子从TiO ₂转移到氧化染料的活化能：与横向空穴跳跃相关的表面覆盖率依赖性

将三种钌（II）敏化剂[Ru（L）₂（dcb）] ²⁺固定在介孔TiO ₂薄膜上，其中配体L = 4,4'-（CH ₃）₂ -bpy（dmb），4 ，4'-（C（CH ₃）₃）₂ -bpy（dtb）和4,4'-（CF ₃）₂ -bpy（bpyCF ₃）控制自交换分子间Ru ^{III /}的热力学和电子耦合^II “跳孔”。据报道表观电子扩散系数D _app按bpyCF ₃的顺序增加。≪ dtb <dmb。在超渗滤和饱和敏化剂表面覆盖的条件下，进行了在80°温度范围内进行的纳秒瞬态吸收测量，以提取平均电荷复合速率常数k _cr。对于敏化剂的[Ru（DMB）₂（DCB）] ²⁺和[茹（DTB）₂（DCB）] ²⁺，所述ķ _CR饱和覆盖度值比在低覆盖率显著越大，由程度随后进行的D _app的趋势。[Ru（bpyCF ₃）₂（dcb ）] ²⁺的无能对致敏剂表面均不敏感的重组动力学数据证实了引入空穴传输。Arrhenius分析表明，Ru ^{III / II}侧向空穴跳跃降低了电子转移的障碍，最终导致更快的重组速率。