Dramatic Increase of 3MLCT State Lifetimes of a Ruthenium(II) Polypyridine Complex upon Entrapment within Y-Zeolite Supercages

Abstract

A bis-heteroleptic, tris-ligated polypyridine complex of ruthenium(II) (Ru(bpy){sub 2}(daf){sup 2+}) has been prepared in zeolite Y supercages and investigated by electronic absorption, electronic emission, and resonance Raman spectroscopy. While liquid solutions of this complex exhibit very weak luminescence with excited-state lifetime shorter than 10 ns at room temperature, entrapment in zeolite supercage results in dramatic increases in emission intensity and lifetime (302 ns at room temperature), providing access to practically important potential photoredox reactivity of the complex. The observed temperature dependence of the excited-state lifetime has been modeled by a kinetic equation with two thermal terms corresponding to the so-called fourth {sup 3}MLCT state and ligand field state (LF), respectively. It is shown that the increased lifetime of the entrapped complex results from zeolite-induced destabilization of the LF state, a conclusion which is in agreement with results obtained for a number of other zeolite-entrapped Ru(II) polypyridine complexes.