Visible-Light-Driven Sensitization of Naphthalene Triplets Using Quantum-Confined CsPbBr₃ Nanocrystals

Recent years have seen the revived interests in the triplet states of polycyclic aromatic hydrocarbons (PAHs) due to their potential applications ranging from photon upconversion to photoredox catalysis. Because of their "dark" nature, these triplets have to be generated via triplet energy transfer (TET) from sensitizers. Traditional sensitization schemes introduce a sizable energy loss (ca. ≥ 0.5 eV) resulting from intersystem crossing (ISC) in sensitizers. Consequently, triplets of naphthalene (Nap), the most energetic PAH triplets (∼2.6 eV), have remained relatively underexplored because ultraviolet (UV) photons and wide-energy-gap sensitizers would be required for the sensitization. Here we show that Nap triplets can be efficiently generated using TET from quantum-confined CsPbBr₃ perovskite nanocrystals (NCs). Quantum confinement is essential to meet the energetics and electronic coupling requirements in TET. Because of the vanishingly small bright-dark states energy splitting in NCs, this sensitization process can take place at the limit of energy conservation, driven by visible photons.