Phenylacetylide ligand mediated tuning of visible-light absorption, room temperature phosphorescence lifetime and triplet–triplet annihilation based up-conversion of a diimine Pt(II) bisacetylide complex

• The impact of linked coumarin ligands on the photophysics of diimine Pt(II) bisacetylide complexes were investigated.
• A room temperature long-lived phosphorescence of the coumarin was observed.
• A general strategy of direct metalation of the organic chromophore is proposed.
• The Pt(II) complexes were efficient as triplet sensitizers for triplet–triplet annihilation upconversion.

We addressed the impact of coumarin ligands linkage on the photophysics of a series of diimine Pt(II) bisacetylide complexes. The long-lived room temperature phosphorescence of the coumarin unit was observed (λem = 636 nm, ΦP = 0.2%, τT = 20.15 μs) within the complex Pt(dbbpy)(CC-phenylene-coumarin)2, where dbbpy stands for 4,4′-di(tert-butyl)-2,2′-bipyridine and CC-phenylene-coumarin is 6-(4′-ethynylphenyl)-coumarin. Comparison with the alternative complex Pt(dbbpy)(CC-coumarin)2 which has ɛ = 32,300 M−1 cm−1 at 404 nm, where CC-coumarin stands for 6-ethynylcoumarin, revealed that Pt(dbbpy)(CC-phenylene-coumarin)2 also showed strong absorption in the visible range (ɛ = 71,900 M−1 cm−1 at 407 nm). The emissive triplet excited state of Pt(dbbpy)(CC-phenylene-coumarin)2 was characterized as 3IL and the extension of the π-conjugation system inside the coumarin ligand was found account for elongation of the lifetime of triplet excited states. Inspired by its unusual phosphorescence behavior, Pt(dbbpy)(CC-phenylene-coumarin)2 was used as the sensitizer for the triplet–triplet annihilation based upconversion and the observed upconversion quantum yield was up to 19.7%.

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