Long-lived emissive intra-ligand triplet excited states (3IL): next generation luminescent oxygen sensing scheme and a case study with red phosphorescent diimine Pt(II) bis(acetylide) complexes containing ethynylated naphthalimide or pyrene subunits

The long-lived room temperature (RT) intra-ligand phosphorescence ((IL)-I-3) of dbbpy Pt(II) bis(acetylide) (dbbpy - 4,4'-di-tert-butyl-2,2'-bipyridine) complexes Pt-1 (lambda(em) - 629 nm, tau - 118 mu s, quantum yield phi - 17.5%) and Pt-3 (lambda(em) = 658 nm, tau = 73.6 mu s, phi = 2.1%) (dbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine), containing naphthalimide (NI) and pyrene subunits, respectively, were used for enhanced luminescent oxygen sensing, compared to the model complex dbbpyPt (bisphenylacetylide) (Pt-2, lambda(em) = 559 nm, tau = 0.7 mu s, phi = 49.6%) with the normal (MLCT)-M-3 excited state (metal-to-ligand-charge-transfer). The luminescent lifetimes of Pt-1 and Pt-3 are greatly extended by 168-fold and 105-fold, respectively, when compared to that of Pt-2. The 3IL features of the photoluminescence of Pt-1 and Pt-3 are supported by DFT/TDDFT calculations, which indicated a NI localized triplet excited state but a normal (MLCT)-M-3/(LLCT)-L-3 excited state for Pt-2. The luminescent oxygen sensing properties of the complexes in solution as well as in polymer films were studied. In polymer films, the O-2 sensitivity of Pt-1 (quenching constant K-SV = 0.085 Torr(-1)) and Pt-3 (K-SV = 0.062 Torr(-1)) is 70-fold and 50-fold of Pt-2 (K-SV = 0.0012 Torr(-1)), respectively.