Application of three-coordinate copper(i) complexes with halide ligands in organic light-emitting diodes that exhibit delayed fluorescence

Abstract

A series of three-coordinate copper(I) complexes (L(Me))CuX [X = Cl (1), Br (2), I (3)], (L(Et))CuBr (4), and (L(iPr))CuBr (5) [L(Me) = 1,2-bis[bis(2-methylphenyl)phosphino]benzene, L(Et) = 1,2-bis[bis(2-ethylphenyl)phosphino]benzene, and L(iPr) = 1,2-bis[bis(2-isopropylphenyl)phosphino]benzene] exhibit efficient blue-green emission in the solid state at ambient temperature with peak wavelengths between 473 and 517 nm. The emission quantum yields were 0.38-0.95. The emission lifetimes were measured in the temperature range of 77-295 K using a nanosecond laser technique. The temperature dependence of the emission lifetimes was explained using a model with two excited states: a singlet and a triplet state. The small energy gaps (<830 cm(-1)) between the two states suggest that efficient emission from 1-5 was thermally activated delayed fluorescence (TADF). Alkyl substituents at ortho positions of peripheral phenyl groups were found to have little effect on the electronic excited states. Because the origin of the emission of complexes 2, 4, and 5 was thought to be a (σ + Br)→π* transition, photoluminescence characteristics of these complexes were dominated by the diphosphine ligands. Complexes 2, 4, and 5 had similar emission properties. Complexes 1-5 had efficient green TADF in amorphous films at 293 K with maximum emission wavelengths of 508-520 nm and quantum yields of 0.61-0.71. Organic light-emitting devices that contained complexes 1-5 and exhibited TADF exhibit bright green luminescence with current efficiencies of 55.6-69.4 cd A(-1) and maximum external quantum efficiencies of 18.6-22.5%.

TADF Material Design: Photophysical Background and Case Studies Focusing on CuIand AgIComplexes

“…Such a small ZFS value is a consequence of weak SOC of the T 1 substates with higher lying states. Furthermore, the emission decay time of τ (T 1 )=1200 μs (at 30 K) is extremely long if compared to Cu(dmp)(phanephos) + 21 (Section 3) and many other Cu I complexes . Again, this is a consequence of the weak SOC with respect to the lowest triplet state.…”

Four highly efficient cuprous complexes and their applications in solution-processed organic light-emitting diodes

“…35,36 The HOMOs of these complexes were lowered down by the electron decient POP. [48][49][50][51][52] Cationic emissive Cu(I) complexes are more stable and their emission would be easily adjusted. 37,38 Although neutral Cu(I) complexes without small counterions achieve higher device performance than those with counterions, 39-44 these complexes containing N À -ligands and halogen counterions have much lower stability [45][46][47] or are more difficult to adjust the emission spanning the whole visible region.…”

Blue Luminescent Copper(I) Complexes Bearing a Diphosphine Dioxide Ligand and Enhancement of Emission in the Solid State under Argon

“…The luminescence properties of various metal complexes such as iridium(III) species have been actively studied for light‐emitting devices . Copper(I) complexes have been of interest because of their abundance and their rich long‐lived luminescence, and those bearing nitrogen and phosphorus donor atoms show intense emission with microsecond lifetimes , . We recently found oxygen‐responsive emission for some copper(I) complexes and also reported the emission properties of copper(I) complexes bearing a phosphine sulfide ligand …”