Solid-state photochemistry: Energy-transfer and electron-transfer of ³CT in crystals of [Os_xRu_1-x(bpy)₃]X₂ (x = 0-0.23)

Time-correlated single-photon counting method and time-resolved absorption-spectroscopy were applied to bimolecular reactions of energy-transfer and electron-transfer in the crystals of [Os_xRu_1-x(bpy)₃]X₂ (bpy = 2,2′-bipyridine). Migration of the triplet excited charge-transfer state (³CT) of [Ru(bpy)₃](PF₆)₂ gave rise to either energy-transfer to a small amount of [Os(bpy₎3]²⁺ or bimolecular annihilation with the ³CT. The rate of hopping in the migration of ³CT ((2-24) × 10⁸ s^-1) was determined from the bimolecular rate-constants of the energy-transfer and ³CT-³CT annihilation in the single crystal of [Ru(bpy)₃]X₂ (X = Cl^-, ClO₄ ^- and PF₆ ^-) or the transparent crystal of [Ru(bpy)₃]X₂ ground together with KCl. Rate of the energy-transfer from ³CT(Ru) to an Os(II) without energy-migration was determined to be 1.7 × 10¹¹ s^-1 for the crystal heavily doped with Os²⁺ . Time-resolved absorption spectroscopy revealed that the annihilation of the ³CT in the transparent crystal of [Ru(bpy)₃]X₂ ground together with KCl formed the one-electron-transferred products in 40 ps.