Exceptionally fast radiative decay of a dinuclear platinum complex through thermally activated delayed fluorescence

Pander, Piotr, Daniels, Ruth, Zaytsev, Andrey, Horn, Ashleigh, Amit, Sil, Penfold, Thomas J., Williams, J.A. Gareth, Kozhevnikov, Valery and Dias, Fernando B. (2021) Exceptionally fast radiative decay of a dinuclear platinum complex through thermally activated delayed fluorescence. Chemical Science, 12 (17). pp. 6172-6180. ISSN 2041-6520

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Abstract

A novel dinuclear platinum(II) complex featuring a ditopic, bis-tetradentate ligand has been prepared. The ligand offers each metal ion a planar O^N^C^N coordination environment, with the two metal ions bound to the nitrogen atoms of a bridging pyrimidine unit. The complex is brightly luminescent in the red region of the spectrum with a photoluminescence quantum yield of 83% in deoxygenated methylcyclohexane solution at ambient temperature, and shows a remarkably short excited state lifetime of 2.1 μs. These properties are the result of an unusually high radiative rate constant of around 4 × 105 s−1, a value which is comparable to that of the very best performing Ir(III) complexes. This unusual behaviour is the result of efficient thermally activated reverse intersystem crossing, promoted by a small singlet–triplet energy difference of only 69 ± 3 meV. The complex was incorporated into solution-processed OLEDs achieving EQEmax = 7.4%. We believe this to be the first fully evidenced report of a Pt(II) complex showing thermally activated delayed fluorescence (TADF) at room temperature, and indeed of a Pt(II)-based delayed fluorescence emitter to be incorporated into an OLED.

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