Synthesis of Fluorinated Organic and Organometallic Electroluminescent Materials: Tuning Emission in the Blue (original) (raw)
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Synthetic Metals, 2015
Two heteroleptic iridium complexes were synthesized and their photophysical properties studied. The two complexes vary by their ancillary ligand that is respectively acetylacetone (acac) or dibenzoylmethane (dbm). Interestingly, only the acac-based complex proved to be highly emissive and electroluminescent devices were only fabricated with this complex. In order to determine the emissive properties of this new complex, comparison with complexes previously reported in the literature was established.
Inorganic chemistry, 2016
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.
Highly Phosphorescence Iridium Complexes and Their Application in Organic Light-Emitting Devices
Journal of the American Chemical Society, 2003
A new series of iridium(III) mixed ligand complexes TBA[Ir(ppy)2(CN)2] (1), TBA[Ir(ppy)2(NCS)2] (2), TBA[Ir(ppy)2(NCO)2] (3), and [Ir(ppy)2(acac)] (4) (ppy) 2-phenylpyridine; acac) acetoylacetonate, TBA) tetrabutylammonium cation) have been developed and fully characterized by UV-vis, emission, IR, NMR, and cyclic voltammetric studies. The lowest energy MLCT transitions are tuned from 463 to 494 nm by tuning the energy of the HOMO levels. These complexes show emission maxima in the blue, green, and yellow region of the visible spectrum and exhibit unprecedented phosphorescence quantum yields, 97 (3% with an excited-state lifetimes of 1-3 µs in dichloromethane solution at 298 K. The near-unity quantum yields of these complexes are related to an increased energy gap between the triplet emitting state and the deactivating e g level that have been achieved by meticulous selection of ligands having strong ligand field strength. Organic light-emitting devices were fabricated using the complex 4 doped into a purified 4,4′-bis(carbazol-9-yl)biphenyl host exhibiting a maximum of the external quantum efficiencies of 13.2% and a power efficiency of 37 lm/W for the 9 mol % doped system.
Tailoring the Emission of Fluorinated Bipyridine-Chelated Iridium Complexes
ACS Omega, 2018
New functionalized tris(2′,6′-difluoro-2,3′-bipyridinato-N,C4′)iridium(III) ((dfpypy) 3 Irs) complexes, including small molecules and their dendrimer embedded analogoues, were synthesized and characterized. It is demonstrated that both the fac-(dfpypy) 3 Ir-based polyphenylene dendrimers and (triisopropylsilyl)ethynyl (TIPSE)-substituted (dfpypy) 3 Ir complexes induce large bathochromic shifts (∼50 nm) of emission bands compared with fac-(dfpypy) 3 Ir. This is due to the pronounced 3 π−π* character of emissive excited states and the extended conjugation. A further remarkable feature is the small bathochromic shift of the emissions of fac-tris(2-phenylpyridine) iridium (fac-(ppy) 3 Ir)-based polyphenylene dendrimers when compared to those of the iridium (Ir) complex core. Obviously, the triplet metal-to-ligand charge transfer makes emission less sensitive to extended conjugation than the 3 π−π* transition. This finding suggests new concepts for designing blue phosphorescent dendrimer emitters. Both the dendrimers and the TIPSE-substituted (dfpypy) 3 Ir complexes represent new green and the trimethylsilyl-functionalized (dfpypy) 3 Ir new blue phosphorescent emitters. Incorporation of TIPSE moieties into the ligands of iridium complex gives rise to enhanced phosphorescence.
Fluorine-free blue-green emitters for light-emitting electrochemical cells
Journal of Materials Chemistry C, 2014
There is presently a lack of efficient and stable blue emitters for light-emitting electrochemical cells (LEECs), which limits the development of white light emitting systems for lighting. Cyclometalated iridium complexes as blue emitters tend to show low photoluminescence efficiency due to significant ligandcentred character of the radiative transition. The most common strategy to blue-shift the emission is to use fluorine substituents on the cyclometalating ligand, such as 2,4-difluorophenylpyridine, dFppy, which has been shown to decrease the stability of the emitter in operating devices. Herein we report a series of four new charged cyclometalated iridium complexes using methoxy-and methyl-substituted 2,3 0bipyridine as the main ligands. The combination of donor groups and the use of a cyclometalated pyridine has been recently reported for neutral complexes and found electronically equivalent to dFppy.
Bulletin of the Korean Chemical Society, 2014
Blue phosphorescent (dfpypy) 2 Ir(mppy), where dfpypy = 2',6'-difluoro-2,3'-bipyridine and mppy = 5-methyl-2-phenylpyridine, has been synthesized by newly developed effective method and its solid state structure and photoluminescent properties are investigated. The glass-transition and decomposition temperature of the compound appear at 160 o C and 360 o C, respectively. In a crystal packing structure, there are two kinds of intermolecular interactions such as hydrogen bonding (C-H F) and edge-to-face C-H π(py) interaction. This compound emits bright blue phosphorescence with λ max = 472 nm and quantum efficiencies of 0.23 and 0.32 in fluid and the solid state. The emission band of the compound is red-shifted by 40 nm relative to homoleptic congener, Ir(dfpypy) 3. The ancillary ligand in (dfpypy) 2 Ir(mppy) has been found to significantly destabilize HOMO energy, compared to Ir(dfpypy) 3 , (dfpypy) 2 Ir(acac) and (dfpypy) 2 Ir(dpm), without significantly changing LUMO energy.
Materials, 2010
This review is an overview of our previous work on the synthesis and properties of poly(p-phenylenevinylene)s (PPVs) selectively fluorinated in different positions of the conjugated backbone. Both the synthetic challenges and the effects of functionalization with fluorine atoms on the optical behavior are discussed, highlighting the peculiarities and the interest of this class of conjugated polymers. A general polymerization protocol for PPVs, that is based on the Pd-catalyzed Stille cross-coupling reaction of bis-stannylated vinylene monomers with aromatic bis-halides, has been successfully extended to the synthesis of selectively fluorinated poly(p-phenylenevinylene)s. The properties of a series of these PPVs differing in the number and positions of the fluorine atoms on the conjugated backbone have been studied, even in comparison with the non-fluorinated counterparts. The intriguing optical features of the resulting materials are discussed considering not only the role of the electronic and steric effects induced by the fluorine substituents, but also the impact of the fluorination on the solid state organization and intermolecular interactions.
Chemistry - A European Journal, 2014
Reactions of 2-(N-arylimino)pyrroles (HNC 4 H 3 C(H)= N-Ar) with triphenylboron (BPh 3) in boiling toluene afford the respective highly emissive N,N'-boron chelate complexes, [BPh 2 {k 2 N,N'-NC 4 H 3 C(H)=N-Ar}] (Ar = C 6 H 5 (12), 2,6-Me 2-C 6 H 3 (13), 2,6-iPr 2-C 6 H 3 (14), 4-OMe-C 6 H 4 (15), 3,4-Me 2-C 6 H 3 (16), 4-F-C 6 H 4 (17), 4-NO 2-C 6 H 4 (18), 4-CN-C 6 H 4 (19), 3,4,5-F 3-C 6 H 2 (20), and C 6 F 5 (21)) in moderate to high yields. The photophysical properties of these new boron complexes largely depend on the substituents present on the aryl rings of their N-arylimino moieties. The complexes bearing electronwithdrawing aniline substituents 17-20 show more intense (e.g., f f = 0.71 for Ar = 4-CN-C 6 H 4 (19) in THF), higher-energy (blue) fluorescent emission compared to those bearing electron-donating substituents, for which the emission is redshifted at the expense of lower quantum yields (f f = 0.13 and 0.14 for Ar = 4-OMe-C 6 H 4 (15) and 3,4-Me 2-C 6 H 3 (16), respectively, in THF). The presence of substituents bulkier than a hydrogen atom at the 2,6-positions of the aryl groups strongly restricts rotation of this moiety towards coplanarity with the iminopyrrolyl ligand framework, inducing a shift in the emission to the violet region (l max = 410-465 nm) and a significant decrease in quantum yield (f f = 0.005, 0.023, and 0.20 for Ar = 2,6-Me 2-C 6 H 3 (13), 2,6-iPr 2-C 6 H 3 (14), and C 6 F 5 (21), respectively, in THF), even when electron-withdrawing groups are also present. Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations have indicated that the excited singlet state has a planar aryliminopyrrolyl ligand, except when prevented by steric hindrance (ortho substituents). Calculated absorption maxima reproduce the experimental values, but the error is higher for the emission wavelengths. Organic light-emitting diodes (OLEDs) have been fabricated with the new boron complexes, with luminances of the order of 3000 cd m À2 being achieved for a green-emitting device.