Excited state interactions in electropolymerized thin films of Ru-II, Os-II, and Zn-II polypyridyl complexes

Emission from thin films of poly[Ru(vbpy)(3)](PF6)(2) (vbpy = 4-methyl-4'-vinyl-2,2'-bipyridine) prepared by reductive electropolymerization on ITO (Sn:In2O3) is dominated by time-dependent effects and dramatically reduced excited state Lifetimes compared to related monomers. The origins of these effects have been investigated by photophysical measurements on a series of copolymeric films containing mixtures of the Zn-II, Ru-II, and Os-II forms of poly[M(vbpy)(3)](PF6)(2). In copolymeric Ru-II and Os-II films, facile energy transfer occurs from Ru-II to Os-II. Dilution of Ru-II by Zn-II in copoly-(chi)[Ru(vbpy)(3)](PF6)(2),(1-(chi))[Zn(vbpy)(3)](PF6)(2)(chi = mole fraction of Ru-II) mixtures is accompanied by an increase in emission energy and average excited state lifetime. These results point to a quenching mechanism in poly[Ru(vbpy)(3)](PF6)(2) arising from facile energy transfer to low-energy, short-lived ''trap sites''. The trap sites may be created by electronic coupling between special pairs of adjacent complexes present in small amounts. The decrease in excited state lifetime at the trap sites is predicted qualitatively by the energy gap law for nonradiative decay.