Solid State Photon Up-Conversion Emission from Chromophore-Tethered PPV Films

Solid state triplet–triplet annihilation (TTA) upconversion (UC) systems may find application as elements in a wide range of practical photon energy conversion technologies. One strategy to produce highly efficient UC emission in the solid state is to create systems that can efficiently transport generated triplets to distances significantly longer than afforded by the Dexter mechanism under restriction of molecular movement. In this work, we present a new solid state UC system through integration of conjugated poly­(p-phenylene vinylene) (PPV) derivatives, with tethered and/or blended chromophores of (9,10-bisphenylethynylanthracene (BPEA) as an emitter and palladium­(II) meso-tetraphenyltetrabenzoporphyrine (TBP)) as a sensitizer. Photoluminescence spectroscopy reveals that the introduction of a small ratio (ca. 3%) of covalently bound BPEA onto the PPV backbone enhances UC emission around an order of magnitude compared to the homo-PPV when mixed with 2 wt % TBP. On the other hand, time-resolved measurements find more rapid consumption of the generated sensitizer triplets with BPEA increased concentrations (up to 50 mol %), suggesting that these BPEA units provide accelerated triplet energy transfer (TET) compared to in homo-PPV, however there exists a significant loss channel via energy back transfer in PPV-BPEA with higher contents of the BPEA unit. Moreover, microsecond time scale decay behavior, where a small population of triplets exist, show that triplets were mainly transmitted through the conjugated polymer phase.