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The solvent sensitivity of the spectroscopy, emission lifetime, and photosubstitution quantum yield of the hexaamminechromium(II1) ion, [Cr(NH3)6I3+, 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 ln(k,b,), where k,bs is the reciprocal of the observed doublet-state lifetime, and donor number. The corresponding activation energies Ea(kobs) and volumes of activation Avf(k0b,) range from 46.0 f 1.3 W mol-' and f4.3 f 0.3 cm3 mol-' in H20 to 51.5 f 0.8 W mol-' and f 3 . 4 f 0.2 cm3 mol-' 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 i 0.01) and are only slightly decreased in DMSO (0.40 f 0.01). The values of QrX at 298 K in H20 are the same for both quartet and doublet band irradiation (0.43 and 0.44, respectively), as are the associated activation volumes Avf(Qrx), which are about -6 cm3 mol-' 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 backintersystem crossing from the 2E, state to the 4T2, state.

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