Sensitizer design for efficient triplet-triplet annihilation upconversion: annihilator-appended tris-cyclometalated Ir(III) complexes.

Enhanced triplet-triplet annihilation upconversion efficiency is achieved with two tris-cyclometalated iridium sensitizers covalently tethered with a pyrene annihilator. The improved sensitizing ability and very long phosphorescence lifetimes (1-2 ms) of these bichromophore molecules are both attributed to the intramolecular energy transfer between the iridium complex and appended pyrene group.