Putting the “P” back in Delayed Fluorescence – Silylethynyl Substitution Generates Efficient Pyrene Annihilators for Red-to-Blue Photon Upconversion

Triplet-triplet annihilation photon upconversion (TTA-UC) converts low-energy photons to higher-energy ones under low-intensity incoherent excitation, thus enabling applications in fields ranging from medicine to solar energy conversion. Silylethynyl mono- and di-substitution of acenes, offers an attractive route to creating new annihilators that operate with minimal energy loss. Here, we demonstrate this approach can be extended to pyrene, yielding annihilators that display efficient red-to-blue upconversion. While pyrene is the namesake of P-type delayed fluorescence, the original name for triplet-triplet annihilation, it is known to be a poor annihilator due to its propensity for forming excimers. By tetra-substituting pyrene with silylethynyl groups, we substantially hinder excimer formation while simultaneously minimizing the energy gap between the singlet and triplet pair states that participate in TTA-UC, yielding outstanding annihilators for red-to-blue upconversion that operate with quantum yields of upwards of 19% (30% when corrected for inner filter effects). Further, we find reducing the bulkiness of the silyl substituents is key to achieving high TTA-UC quantum yields, which highlights the importance of annihilator side group selection when optimizing photon upconversion.