Photon Upconversion by Triplet-Triplet Annihilation in Ru(bpy)3- and DPA-Functionalized Polymers

Two photophysically active polymers, each containing one absorbing Ru(bpy)(3) triplet sensitizing core and multiple 9,10-diphenylanthracene (DPA) triplet energy acceptors, are shown to exhibit noncoherent photon upconversion by triplet triplet annihilation (TTA) in both fluid solution and in thin solid films. An analysis of the kinetics and absorbed power dependencies of the upconverted fluorescence demonstrates that, in fluid solution, TTA is occurring in the low-power, pseudo-first order limit, and that the energy transfer mechanism involves fast, efficient intramolecular triplet energy transfer from the excited Ru(bpy)(3) core to the DPA acceptors in the macromolecule's pendant arms, followed by intermolecular TTA. Intermolecular triplet energy transfer, diffusion coefficient, and quantum yield measurements using Ru(bpy)(3) and DPA controls suggest that, although a minority of the intermolecular encounters result in TTA in this one absorbing core system, efficient intramolecular TTA could be realized in a polymer with multiple absorbing centers.