Photoinduced charge separation across the solid-liquid interface of porous sol-gel glasses: Catalyzed hydrogen generation from water

Photoinduced electron transfer between [Ir(bpy)₂(C³,N′)bpy]³⁺, Ir(III), trapped in a porous silica glass generated by the sol-gel process, and 1,4-dimethoxybenzene (DMB) dissolved in a water phase in the pores of the glass, was observed. The kinetics of the redox reactions associated with the Ir(II) + DMB⁺ radical ion pair were studied at different pH and ionic strength values. A retardation of 4 orders of magnitude of the back-electron-transfer process, with respect to homogeneous solutions, was observed at neutral pH for ∼25% of the generated Ir(II). The effect is attributed to the immobilization of Ir(II) by trapping in the glass matrix and of DMB⁺ by adsorption on the pores' surface. At acidic pH, retardation of the back-reaction leads to catalyzed hydrogen generation from water.