Which Flavor of 9,10-Bis(phenylethynyl)anthracene is Best for Perovskite-Sensitized Triplet-Triplet Annihilation?

The lack of viable solid-state annihilators is the greatest hurdle in perovskite-sensitized triplet-triplet annihilation upconversion (UC). Unfavorable singlet and triplet energy surfaces in the solid state have limited successful the implementation of many conventional solution-based annihilators. To date, rubrene is still the best performing annihilator; however, this comes at the cost of a small apparent anti-Stokes shift. To this point, anthracene derivatives are promising candidates to increase the apparent anti-Stokes shift. The well-known green glowstick dye 9,10-(bisphenylethynyl) anthracene (BPEA) and its chlorinated derivatives have already shown great promise in solution-based UC applications. Due to favorable band alignment of the perovskite and triplet energy levels of BPEA, it is conceivable that a wide variety of BPEA derivatives could be compatible with the perovskite-based UC system. Here, we investigate the properties of the parent molecule BPEA and its derivatives 1-chloro-9,10-(bisphenylethynyl)anthracene and 2-chloro-9,10-(bisphenylethynyl) anthracene. Despite similar optical properties in solution, the different molecules exhibit vastly different properties in thin films. UC studies in lead halide perovskite/BPEA bilayer devices demonstrate the importance of intermolecular coupling on the resulting properties of the upconverted emission.