Efficient Triplet-Triplet Annihilation Upconversion with Platinum(II) Bis(arylacetylide) Complexes That Show Long-Lived Triplet Excited States

NNPtIIbis(acetylide) complexes [NN = 4,4'-bis(tert-butyl-2,2'-bipyridine) (dbbpy)] with ethynylpyrene (Pt-2) or 4-ethynyl-1,8-naphthalimide ligands (Pt-3) that show long-lived 3IL triplet excited states (tT = 118.0 mu s) were used as new triplet sensitizers for triplettriplet annihilation (TTA) based upconversion (UC). UC quantum yields of up to 18.1?% were observed. We found that the triplettriplet energy-transfer (TTET) processes, which are crucial for the TTA UC, were improved by up to 150-fold and 250-fold with Pt-2 (SternVolmer quenching constant KSV = 5.70?X?105 M1) and Pt-3 (KSV = 9.64?X?105 M1), respectively, relative to the model complex dbbpyPtIIbis(phenylacetylide) (Pt-1) (KSV = 3.80?X?103 M1). The efficient upconversion is attributed to the long-lived triplet excited states as well as the high T1-state energy level of the sensitizers Pt-2 and Pt-3.