Light upconversion by triplet–triplet annihilation in diphenylanthracene-based copolymers†
Low-power light upconversion by triplet–triplet annihilation (TTA-UC) was only recently achieved in glassy materials. Here, a new strategy based on covalent tethering of diphenylanthracene (DPA) emitters to a polymeric backbone is reported. The design aims to optimize the efficiency of this photophysical process in glassy polymeric materials by increasing the emitter content. To that end, DPA molecules were covalently attached to a methacrylate-type monomer and further copolymerized with methylmethacrylate (MMA). Green-to-blue (543 to 440 nm) upconversion was observed at power densities as low as 32 mW cm−2 in films prepared by solution casting and compression molding (co)polymers containing 8–72 wt% of DPA and palladium octaethyl porphyrin (PdOEP) as a sensitizer (0.03–0.7 wt%). The upconversion intensity was studied as a function of DPA and PdOEP contents and the results suggest that upconversion is optimal for DPA and PdOEP weight fractions of 34 and 0.05 wt% respectively.