  A kinetic framework for the ultrafast photophysics of
tris(2,2-bipyridine)ruthenium(II) phosphonated and methyl-phosphonated
derivatives is used as a basis for modeling charge injection by ruthenium dyes
into a semiconductor substrate. By including the effects of light scattering,
dye diffusion and adsorption kinetics during sample preparation, and the
optical response of oxidized dyes, quantitative agreement with multiple
transient absorption datasets is achieved on timescales spanning femtoseconds
to nanoseconds. In particular, quantitative agreement with important
spectroscopic handles, decay of an excited state absorption signal component
associated with charge injection in the UV region of the spectrum and the
dynamical redshift of an approximately 500 nm isosbestic point, validates our
kinetic model. Pseudo-first-order rate coefficients for charge injection are
estimated in this work, with an order of magnitude ranging 1011 s-1 to 1012
s-1. The model makes the minimalist assumption that all excited states of a
particular dye have the same charge injection coefficient, an assumption that
would benefit from additional theoretical and experimental exploration. We have
adapted this kinetic model to predict charge injection under continuous solar
irradiation, and find that as many as 68 electron transfer events per dye per
second take place, significantly more than prior estimates in the literature.
