Quantum chemical calculations are presented for several dye-sensitized TiO₂ nanocrystalline systems with the aim to elucidate fundamental electron transfer properties in photoelectrochemical devices such as dye-sensitized solar cells. The calculations have been performed using model TiO₂ nanocrystals, and both organic and ruthenium dyes have been investigated. Effective electronic coupling strengths have been extracted from the calculated densities of states, and are used to predict femtosecond photo-induced electron injection rates across the molecule-metal oxide interface. Direct comparisons with femtosecond spectroscopy experiments show that the calculations predict injection rates of the right order of magnitude, and correctly reproduce experimental trends with regards to the variations in injection rates for different anchor-cum-spacer groups. This shows the central role played by the interfacial electronic coupling for ultrafast surface electron transfer processes in molecular photovoltaics.