Bridged diiridium complexes for electrophosphorescent OLEDs: synthesis, X-ray crystal structures, photophysics, and devices

Abstract

Results are presented which challenge the accepted view that dinuclear transition metal-ligand complexes are unsuitable for organic light-emitting device (OLED) applications due to their low luminescence quantum efficiencies. We establish for the first time that halo-and pseudo-halobridged diiridium(III) species are viable electrophosphorescent dopants in OLEDs. New cyclometalated chloro-and isocyanate-bridged diiridium(III) complexes, viz. ) 2 NCO] 2 (complex 4) were obtained in high yield from the 9,9-dihexyl-2-(pyridin-2-yl)fluorene (flpyH) ligand 1. The X-ray crystal structures are described for 3 and the monomeric complex Ir(flpy) 2 NCO(DMSO) (5) which was obtained from 4. The solution-state photophysical properties of complexes 3 and 4 are characterised by emission from mixed 3 p-p*/ 3 MLCT states at y545-550 nm. Complex 4 displays a solution-state photoluminescence quantum yield which is five times that of the dichloro-bridged analogue 3. This is ascribed to an increase in the ligand-LUMO/metal e g gap which reduces the probability of non-radiative decay processes. Spin-coated organic light emitting devices (OLEDs) made from the host polymer poly(9,9-bis-2ethylhexylfluorene-2,7-diyl) (PF2/6) end-capped with bis-(4-methylphenyl)phenylamine (PF2/6am4) doped with 12.5 wt% of the complexes 3 and 4 show good stability: turn-on voltages are low (,4 V) with maximum EL intensities of y1300 and 13 000 cd m 22 , and peak external quantum efficiencies (EQE) of 0.1 and 0.8%, at ca. 400 and 60 mA cm 22 , respectively.

Synthesis, Diastereomer Separation, and Optoelectronic and Structural Properties of Dinuclear Cyclometalated Iridium(III) Complexes with Bridging Diarylhydrazide Ligands

“…5 Å. 23,26,27,32,34,40,47 (It is noteworthy that with [Ir(ppy) 2 µ-Cl] 2 -type complexes where the Ir-Ir distances are <4 Å only the less sterically congested rac ΔΔ/ɅɅ diastereomers have been reported to date [15][16][17][18]39,[48][49][50][51][52][53][54][55] ). For 13-16 the diastereomers were separated by fractional crystallization, silica column chromatography, or a combination of the two techniques.…”

“…11 Such complexes have found widespread use as precursors to cyclometalated heteroleptic and homoleptic monoiridium complexes. 12,13 However, μ-dichloro-bridged dimers are generally poorly emissive 14,15 (apart from a few recent exceptions 16,17 ), a feature common to many diiridium systems, e.g. 1, 2 and 3 ( Figure 1).…”

“…39 An interesting design feature of these bridges is that they provide a short conjugative pathway between the two Ir centers. We now present a series of new diiridium complexes (13)(14)(15)(16) featuring different cyclometalated ligands. In all cases the diastereomers have been separated and characterized by their single-crystal X-ray structures.…”

Synthesis, structure and properties of a novel iridium(III) pyrimidine complex

“…Generally, the crude products of dimers are directly used for subsequent preparation of heteroleptic complexes. Thus, there are very limited reports on the crystal structures of Cl-bridged dimers to this day [8][9][10][11][12].…”

Solvothermal synthesis, structure and photoluminescent properties of europium complex based on fluorene derivatives

“…For example, how to affect energy levels of the materials from diverse chromophore groups or conjugate units [10]. According to the spin conservation principle of quantum chemistry, the luminescent efficiency would be enhanced through the spin-orbit coupling effect between metal ions and organic ligands by the introduction of some metal ions into the luminescent materials [11][12][13]. A key step for construction of the conjugated organic ligands and metal ion (d-π, or f-π) resultants is to design suitable bridging connectors that can promote the energy transfer from the π-block antenna chromophores to the centers [14,15].…”