The recombination reaction between nanocrystalline anatase TiO2 and a series of symmetrically substituted triphenylamine (TPA) redox mediators that possessed electron donating or withdrawing groups at the para-position of the phenyl rings was quantified on nanosecond and longer time scales. The groups utilized afforded an ~0.5 V change in TPA+/0 reduction potential. The nanocrystalline TiO2 thin films were sensitized by a ruthenium polypyridyl complex bearing either a carboxylic or a phosphonic acid functional group for surface anchoring. Pulsed light excitation of the film resulted in excited-state injection to yield TiO2(e-)|S+. Sensitizer regeneration and the subsequent charge recombination reaction TiO2(e-) + TPA+ → TiO2 + TPA were then monitored spectroscopically. Concentration dependent data revealed that recombination could be described by a distribution of first-order rate constants that became strictly first-order when the driving force was larger. The reaction rate increased with more positive TPA+/0 reduction potentials, consistent with electron transfer in the Marcus normal region. The recombination reaction was monitored as a function of temperature, and an Arrhenius analysis provided activation energies. Interestingly, the same activation barrier was abstracted for all the TPA derivatives, suggesting that a common rate limiting step exists for all these reactions. A model for recombination consistent with both the thermodynamics and activational parameters will be presented.