Low-power NIR-to-vis upconversion (UC) of incoherent excitation mediated by triplet-triplet annihilation (TTA) has a variety of promising applications, i.e. in photovoltaics, however these are strongly hampered by low UC efficiency...

Rubrene is the most widely used triplet-triplet annihilation (TTA) emitter for NIR-to-vis photon upconversion (UC), however, strong singlet fission (SF) in the solid films quenches its emission and hampers practical...

Solar energy harvesting is among the best solutions for a global transition toward carbon-neutral energy technologies. The existing solar energy harvesting technologies like photovoltaics (PV) and emerging molecular concepts such...

Singlet fission is detrimental to NIR-to-vis photon upconversion in the solid rubrene (Rub) films, as it diminishes photoluminescence efficiency. Previous studies have shown that thermally activated triplet energy transport drives singlet fission with nearly 100% efficiency in closely packed Rub crystals. Here, we examine triplet separation and recombination as a function of intermolecular distance in the crystalline films of Rub and the t -butyl substituted rubrene ( t BRub) derivative. The increased intermolecular distance and altered molecular packing in t BRub films cause suppressed singlet dissociation into free triplets due to slower triplet energy transport. It was found that the formation of correlated triplet pairs 1 (TT) and partial triplet separation 1 (T···T) occurs in both Rub and t BRub films despite differences in intermolecular coupling. Under weak intermolecular coupling as in t BRub, geminate triplet annihilation of 1 (T···T) outcompetes dissociation into free triplets, resulting in emission from the 1 (TT) state. Essentially, increasing intermolecular distance up to a certain point (a sweet spot) is a good strategy for suppressing singlet fission and retaining triplet–triplet annihilation properties.

Triplet-triplet annihilation (TTA) mediated NIR-to-vis photon upconversion (UC) operating under incoherent and low power excitation is increasingly attractive for various applications including photovoltaics. Unfortunately, efficient TTA emitters/annihilators for this spectral...

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