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 (lambda = 724 nm)-to-blue (lambda = 462 nm) upconversion with a large anti-Stokes shift of 0.97 eV.