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Deep blue emitting Cu(I) tripod complexes. Design of high quantum yield materials showing TADF-assisted phosphorescence

Abstract

In a previous investigation, it was shown that [Cu(tpym)(PPh3)]PF6 1 with tpym = tris(2-pyridyl)methane represents a deep blue emitter (λmax = 466 nm) though with a low emission quantum yield ΦPL if doped in a polymer (7 %) or dissolved in a fluid solvent (≪ 1%). In this study, we present new tripod compounds with sterically demanding ligands: [Cu(tpym)(P(o-tol)3)]PF6 2 and [Cu(tpym)(P(o-butyl-ph)3)]PF6 3 with P(o-tol)3 = tris(ortho-tolyl)phosphine and P(o-butyl-ph)3 = tris(ortho-n-butylphenyl)phosphine. These compounds show high emission quantum yields even in a fluid solution (dichloromethane) reaching a benchmark value for 3 of ΦPL = 76 %. This becomes possible due to the specific design of rigidifying the complexes. Importantly, the deep blue emission color is maintained or even further blue shifted to λmax = 452 nm (compound 3 powder). Compound 2 is characterized photophysically in detail. In particular, it is shown that the lowest excited triplet state T1 experiences very efficient spin-orbit coupling (SOC). Accordingly, the phosphorescence decay rate is as large as 5·104 s-1 (20 μs) belonging to the fastest T1→S0 values (shortest decay times) reported so far. Investigations down to T = 1.5 K reveal large total zero-field splitting (ZFS) of 7 cm-1 (0.9 meV). Although thermally activated delayed fluorescence (TADF) grows in for T ≥ 160 K, phosphorescence of 2 still dominates (60 %) over TADF (40 %) at ambient temperature. Thus, the compound represents a singlet harvesting-plus-triplet harvesting material, if applied in an OLED.

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Publication details

The article was accepted on 29 Oct 2018 and first published on 30 Oct 2018


Article type: Paper
DOI: 10.1039/C8DT04093A
Citation: Dalton Trans., 2018, Accepted Manuscript
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    Deep blue emitting Cu(I) tripod complexes. Design of high quantum yield materials showing TADF-assisted phosphorescence

    A. Schinabeck, N. Rau, M. Klein, J. Sundermeyer and H. Yersin, Dalton Trans., 2018, Accepted Manuscript , DOI: 10.1039/C8DT04093A

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