Sulfonyl-Substituted Heteroleptic Cyclometalated Iridium(III) Complexes as Blue Emitters for Solution-Processable Phosphorescent Organic Light-Emitting Diodes

Abstract

The synthesis is reported of a series of blue-emitting heteroleptic iridium complexes with phenylpyridine (ppy) ligands substituted with sulfonyl, fluorine, and/or methoxy substituents on the phenyl ring and a picolinate (pic) ancillary ligand. Some derivatives are additionally substituted with a mesityl substituent on the pyridyl ring of ppy to increase solubility. Analogues with two ppy and one 2-(2′-oxyphenyl)pyridyl (oppy) ancillary ligand were obtained by an unusual in situ nucleophilic displacement of a fluorine substituent on one of the ppy ligands by water followed by N^O chelation to iridium. The X-ray crystal structures of seven of the complexes are reported. The photophysical and electrochemical properties of the complexes are supported by density functional theory (DFT) and time-dependent DFT calculations. Efficient blue phosphorescent organic light-emitting devices (PhOLEDs) were fabricated using a selection of the complexes in a simple device architecture using a solution-processed single-emitting layer in the configuration ITO/ PEDOT:PSS/PVK:OXD-7(35%):Ir complex(15%)/TPBi/LiF/Al. The addition of a sulfonyl substituent blue-shifts the electroluminescence by ca. 12 nm to λ max EL 463 nm with CIE x,y coordinates (0.19, 0.29), compared to the benchmark complex FIrpic (λ max EL 475 nm, 0.19, 0.38) in directly comparable devices, confirming the potential of the new complexes to serve as effective blue dopants in PhOLEDs. Replacing a fluorine by a methoxy group in these complexes red shifts the PL and EL λ max by ca. 4−6 nm. The efficiency of the blue PhOLEDs of the sulfonyl-substituted complexes is, in most cases, significantly enhanced by the presence of a mesityl substituent on the pyridyl ring of the ppy ligands.

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

“…This is due to the comparable decreases in the values of k nr for the complexes (by 2-3 orders of magnitude) rather than increases in the values of k r , which are on the order of 10 5 s -1 for 15 and 16 in both DCM and PMMA (comparable to Ir(ppy) 3 k r = 2.1 × 10 5 s -1 ). 13 As the cyclometalating ligands in 15 and 16 have been previously incorporated into complexes that are highly emissive in solution 13,66 it can be concluded that the bridging ligands play a significant role in the photophysical properties of the complexes in the present study (in agreement with the DFT and electrochemistry data above) and are most likely responsible for their matrixdependent behavior. In room temperature DCM solutions the highly flexible bridges facilitate non-radiative decay via intramolecular motion which quenches the emission.…”

“…, 2-(2-fluoro-4-methoxyphenyl)pyridine (10) 66 and N,N'-bis(4-tertbutylphenylbenzoyl)hydrazide (11) 72 were all synthesized according to literature procedures. All solvents used were of analytical reagent grade or higher.…”

Pyridylpyrazole N^N ligands combined with sulfonyl-functionalised cyclometalating ligands for blue-emitting iridium(iii) complexes and solution-processable PhOLEDs

“…carbenes, to increase the crystal field splitting, thereby widening the HOMO-LUMO gap and shifting non-emissive d-d* metal-centred (MC) states to higher energies. 19 The present study combines a pyridylpyrazole-based N^N ligand with sulfonyl-containing cyclometalating ligands 29 to obtain the new heteroleptic complexes 12-15 with emission blue-shifted compared to the archetypal blue emitter, FIrpic, 16 and the analogous picolinate-complexes 1 and 2 29 (Fig. 1).…”

Bright green PhOLEDs using cyclometalated diiridium(iii) complexes with bridging oxamidato ligands as phosphorescent dopants

“…Ligand 3 and the derived complexes 4-6 incorporate a mesityl substituent at C4 of each of the ppy ligands as there is precedent that a mesityl group at this position significantly improves the solubility of iridium complexes in organic solvents thereby facilitating device fabrication by solution processing, while having minimal effect on the emission colour. [38][39][40][41][42][43] The m-dichloro-bridged species 4 43 was obtained in 66% yield using the standard procedure 44 by reacting 3 with IrCl 3 Á3H 2 O in 2-ethoxyethanol. Reaction of 4 with oxamide or with N,N 0 -di-tbutylphenyloxamide in the presence of sodium methoxide gave the target oxamido-bridged complexes 5 and 6 as yellow-orange solids in ca.…”