Synthesis and photophysical properties of zeolite-entrapped bisterpyridine ruthenium(II). Dramatic consequences of ligand-field-state destabilization

A bisterpyridine complex of ruthenium(II) (RU(tpy)(2)(2+)) has been prepared in zeolite Y supercages and investigated by electronic absorption, electronic emission, and resonance Raman spectroscopy. In free solution this complex is practically nonluminescent, having a very short excited-state lifetime (250 ps) at room temperature. However, entrapment within the zeolite supercage results in dramatic increases in emission intensity and excited-state lifetime (140 ns) at room temperature. 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 (MLCT)-M-3 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 ruthenium(II) polypyridine complexes.