The solvent sensitivity of the spectroscopy, emission lifetime, and photosubstitution quantum yield of the hexaamminechromium(III) ion, [Cr(NH3)(6)](3+), has been investigated in water, dimethylformamide, dimethyl sulfoxide, and hexamethylphosphoramide. The vibronic features in the emission and absorption spectra show solvent-induced trends with the Gutmann donor number scale which are consistent with a specific electron-donor interaction between the solvent and complex. Emission lifetimes are also seen to vary with solvent, and a strong correlation is observed at 315 K between In(k(obs)), where k(obs) is the reciprocal of the observed doublet-state lifetime, and donor number. The corresponding activation energies E(a)(k(obs)) and volumes of activation Delta V double dagger(k(obs)) range from 46.0 +/- 1.3 kJ mol(-1) and +4.3 +/- 0.3 cm(3) mol(-1) in H2O to 51.5 +/- 0.8 kJ mol(-1) and +3.4 +/- 0.2 cm(3) mol(-1) in HMPA, respectively. Quantum yields for photosolvolysis are much less solvent-dependent at 296 K; these are the same in H2O and DMF (0.44 +/- 0.01) and are only slightly decreased in DMSO (0.40 +/- 0.01). The values of Phi(rx) at 298 K in H2O are the same for both quartet and doublet band irradiation (0.43 and 0.44, respectively), as are the associated activation volumes Delta V double dagger(Phi(rx)), which are about -6 cm(3) mol(-1) for irradiation of either band. The differences in solvent and pressure dependencies for the measured photophysical and photosubstitutional parameters give evidence of a dominant decay route proposed to be a nonradiative thermally-activated back-intersystem crossing from the (2)E(g) State to the T-4(2g) state.