Thermal redistribution of energy from an excited 3ππ∗ term to a nearby chemically reactive 3dd level in [Rh(III)(NN)3](PF6)3 complexes

Below ∼ 150 K [Rh(NN)3](PF6)3 complexes display 3gpπ∗ phosphorescences characteristic of the NN diimine ligand [NN = 1,10-phenanthroline (phen) or 2,2′-bipyridine (bpy)]. Above ∼ 150 K and below the melting point of glycerol, a temperature-dependent first-order photoreaction occurs. Temperature dependencies of these photochemical reactions conform to the Arrhenius equation with activation energies in the 2–3 × 103 cm−1 range. These results are interpreted in terms of thermal redistribution from an excited 3ππ∗ term to a nearby chemcially reactive 3dd manifold. The relationship of the Arrhenius activation energies to the electronic states of the parent complexes and the paths of intramolecular energy migration are discussed.