Coumarin phosphorescence observed with N⁁NPt(ii) bisacetylide complex and its applications for luminescent oxygen sensing and triplet–triplet-annihilation based upconversion

Abstract

A dbbpy platinum(II) bis(coumarin acetylide) complex (Pt-1, dbbpy = 4,4′-di-tert-butyl-2,2′-bipyridine) was prepared. Pt-1 shows intense absorption in the visible region (λ_abs = 412 nm, ε = 3.23 × 10⁴ M⁻¹ cm⁻¹) compared to the model complex dbbpy Pt(II) bis(phenylacetylide) (Pt-2, λ_abs = 424 nm, ε = 8.8 × 10³ M⁻¹ cm⁻¹). Room temperature phosphorescence was observed for Pt-1 (³IL, τ_P = 2.52 μs, λ_em = 624 nm, Φ_P = 2.6%) and the emissive triplet excited state was assigned as mainly intraligand triplet excited state (³IL), proved by 77 K steady state emission, nanosecond time-resolved transient absorption spectroscopy and DFT calculations. Complex Pt-1 was used for phosphorescent oxygen sensing and the sensitivity (Stern–Volmer quenching constant K_SV = 0.012 Torr⁻¹) is 12-fold of the model complex Pt-2 (K_SV = 0.001 Torr⁻¹). Pt-1 was also used as triplet sensitizer for triplet–triplet-annihilation based upconversion, upconversion quantum yield Φ_UC up to 14.1% was observed, vs. 8.9% for the model complex Pt-2.