Iridium(III) Sensitisers and Energy Upconversion: The Influence of Ligand Structure upon TTA‐UC Performance

Six substituted ligands based upon 2-(naphthalen-1-yl)quinoline-4-carboxylate and 2-(naphthalen-2-yl)quinoline-4-carboxylate have been synthesised in two steps from a range of commercially available isatin derivatives. These species are shown to be effective cyclometallating for IrIII, yielding complexes the form [Ir(C^N)2(bipy)]PF6 (where C^N=cyclometallating ligand; bipy=2,2′-bipyridine). X-ray crystallographic studies on three examples demonstrate that adopt distorted octahedral geometry wherein cis-C,C trans-N,N coordination mode is observed. Intraligand torsional distortions evident all cases. The IrIII display photoluminescence red part visible region (668–693 nm), which modestly tuneable through ligand structure. triplet lifetimes clearly influenced by precise structure each case. Supporting computational (DFT) suggest differences observed lifetime likely due differing admixtures ligand-centred versus MLCT character instilled facets Triplet–triplet annihilation upconversion (TTA-UC) measurements 1-naphthyl derived viable photosensitisers with quantum efficiencies 1.6–6.7 %.