Near infrared-to-blue photon upconversion by exploiting direct S–T absorption of a molecular sensitizer

Triplet–triplet annihilation-based photon upconversion (TTA-UC) from NIR to blue light remains a great challenge. Here, we employ a direct singlet-to-triplet (S–T) excitation to circumvent an energy loss associated with the intersystem crossing (ISC) of triplet sensitizers. The TTA-UC based on the S–T absorption (STUC) allowed an efficient NIR (λ = 724 nm)-to-blue (λ = 462 nm) upconversion with a large anti-Stokes shift of 0.97 eV.