Long-lived emissive intra-ligand triplet excited states (IL): 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) of dbbpy Pt(ii) bis(acetylide) (dbbpy = 4,4′-di-tert- butyl-2,2′-bipyridine) complexes Pt-1 (λ = 629 nm, τ = 118 μs, quantum yield = 17.5%) and Pt-3 (λ = 658 nm, τ = 73.6 μs, = 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, λ = 559 nm, τ = 0.7 μs, = 49.6%) with the normal MLCT 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 IL 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/LLCT 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 sensitivity of Pt-1 (quenching constant K = 0.085 Torr) and Pt-3 (K = 0.062 Torr) is 70-fold and 50-fold of Pt-2 (K = 0.0012 Torr), respectively. © 2010 The Royal Society of Chemistry.