Laser flash photolysis (337.1 nm) combined with kinetic absorption-emission spectrophotometry has been used to study the photoreduction of tris(2,2'-bipyridine)ruthenium(II) by phenols and the effects of solvent, temperature, and ionic strength on electron transfer kinetics and yields. The excited-state quenching rate constants (k/sub q/) are in the range 1 x 10/sup 6/-5 x 10/sup 9/ M/sup -1/s/sup -1/ for substituted phenolate ions (pH 12.7) and correlate well with Hammett sigma/sup +/ values and with oxidation potentials. The plot of RT in k'/sub q/ against E/sub ArO./ArO/sup -// has a slope of -0.56, k'/sub q/ being the quenching rate constant corrected for the initial diffusional process. Arrhenius plots for k/sub q/ in the cases of p-CH/sub 3/O-C/sub 6/H/sub 4/O/sup -/, C/sub 6/H/sub 5/O/sup -/, and p-COO/sup -/-C/sub 6/H/sub 4/O/sup -/ as quenchers in aqueous solutions are linear from 0 to 80/sup 0/C. With p-methoxyphenolate ion and p-methoxy-N,N-dimethylaniline as quenchers, k/sub q/ increases on changing solvent from water to 95% ethanol or 95% acetone; k/sub q/ goes through a minimum at intermediate solvent compositions. Electron transfer yields (eta) are 0.3 to 1.0 for various phenolate ions in aqueous solutions (pH 12.7). For p-methoxyphenolate ion and p-methoxy-N,N-dimethylaniline, eta exhibits an increasing trend at elevatedmore » temperatures, in aqueous solvent systems richer in the nonaqueous component (acetone or ethanol), and at lower ionic strengths. The excited-state absorption spectrum (triplet-triplet) or tris(2,2'-bipyridine)ruthenium(II) in aqueous solution (230 to 800 nm) shows small absorption at (500 to 800 nm) and prominent three-band feature at 240 to 400 nm.« less