DRAMATIC INCREASE OF (3)MLCT STATE LIFETIME OF A RUTHENIUM(II) POLYPYRIDINE COMPLEX UPON ENTRAPMENT WITHIN Y-ZEOLITE SUPERCAGES

A bis-heteroleptic, tris-ligated polypyridine complex of ruthenium(II) (Ru(bpy)(2)(daf)(2+)) has been prepared in zeolite Y supercages and i nvestigated by electronic absorption, electronic emission, and resonan ce 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 dramat ic increases in emission intensity and lifetime (302 ns at room temper ature), providing access to practically important potential photoredox reactivity; of the complex. The observed temperature dependence of th e excited-state lifetime has been modeled by a kinetic equation with t wo thermal terms corresponding to the so-called fourth (3)MLCT state a nd ligand field state (LF), respectively. It is shown that the increas ed lifetime of the entrapped complex results from zeolite-induced dest abilization of the LF state, a conclusion which is in agreement with r esults obtained for a number of other zeolite-entrapped Ru(II) polypyr idine complexes.