Controlled spatial distribution of tris(2,2′-bipyridine)ruthenium cation ([Ru(bpy)₃]²⁺) in aluminum containing mesoporous silicas

The adsorption of tris(2,2′-bipyridine)ruthenium(II) ([Ru(bpy) ₃]²⁺) onto aluminum containing mesoporous silicas (BJH pore size of 2.2 and 3.0 nm and Si/Al ratio of ca. 26) was conducted and the photoluminescence of the products was examined as a function of the loaded [Ru(bpy)₃]²⁺ amounts. The loading amount of the complex was controlled below ca. 0.1 mol L^-1 based on the pore volume by changing the initial concentration of the [Ru(bpy)₃]²⁺ ethanol solutions used for the adsorption, resulted from the strong host-guest interactions as evidenced by the H type adsorption isotherm. The concentration dependence of the luminescence intensity was discussed to show the self-quenching process of the complex in the mesopore. The Quasi Stern-Volmer plots showed a linear relationship, suggesting that the spatial distribution of [Ru(bpy)₃]²⁺ was successfully varied in the mesopore by the loading amount of [Ru(bpy)₃]²⁺, even at the high concentration of the complex in the mesopore (ca. 0.1 mol L^-1 based on the pore volume). The difference of the self-quenching efficiencies (coefficients of self-quenching, K_sv values) of [Ru(bpy) ₃]²⁺ adsorbed on aluminum containing mesoporous silicas from that on the mesoporous silica modified with phenethylsulfonic group [M. Sohmiya, Y. Sugahara, M. Ogawa, J. Phys. Chem. B 111 (2007) 8836-8841] suggests that the pore size and the interactions between [Ru(bpy)₃] ²⁺ and the pore surface affects the efficiency; the larger pore size and the weaker interactions between [Ru(bpy)₃]²⁺ and the pore surface results in the higher self-quenching efficiency.