Photon upconversion sensitized by a Ru(II)-pyrenyl chromophore

The near-visible-to-blue singlet fluorescence of anthracene sensitized by a ruthenium chromophore with a long-lived triplet-excited state, [Ru(5-pyrenyl-1,10-phenanthroline)(3)](PF(6))(2), in acetonitrile was investigated. Low intensity non-coherent green light was used to selectively excite the sensitizer in the presence of micromolar concentrations of anthracene generating anti-Stokes, singlet fluorescence in the latter, even with incident power densities below 500 μW cm(-2). The resultant data are consistent with photon upconversion proceeding from sensitized triplet-triplet annihilation (TTA) of the anthracene acceptor molecules, confirmed through transient absorption spectroscopy as well as static and dynamic photoluminescence experiments. Additionally, quadratic-to-linear incident power regimes for the upconversion process were identified for this composition under monochromatic 488 nm excitation, consistent with a sensitized TTA mechanism ultimately producing the anti-Stokes emission characteristic of anthracene singlet fluorescence.