A new class of charge-neutral, bis-tridentate Ir(III) metal complexes is designed, synthesized and applied as emitters in the fabrication of organic light emitting diodes. Their basic properties are ...discussed vs. their tris-bidentate counterparts.
Display omitted
•Relationship of the terpyridine complexes Ru(tpy)22+ and Ir(tpy)23+ are reviewed.•Dianionic chelates are constructed using pyrazole, pyridine and phenyl fragments.•N^C^N, C^N^C and C^C^C type ancillaries are employed to obtain monoanionic chelates.•Properties of the charge-neutral bis-tridentate Ir(III) complexes are discussed.•Bis-tridentate Ir(III) metal complexes are useful emitters for OLEDs.
This review is an update on current advances in metal complexes with d6-electronic configuration and bearing two tridentate chelates. We first elaborate the basic properties of the famous cationic complexes Ru(tpy)22+ and Ir(tpy)23+, where tpy represents 2,2′:6′,2″-terpyridine. The emphasis is then switched to various charge-neutral, bis-tridentate Ir(III) complexes, with emission spanning the whole visible region from blue, green to red. These Ir(III) metal complexes are capable of exhibiting high luminescence efficiency, reduced radiative lifetime, and adequate volatility and stability, similar to those of their traditional tris-bidentate Ir(III) counterparts, destined to be viable OLED phosphors.
Deep‐red (DR)‐to‐near‐infrared (NIR) phosphorescent organic light‐emitting diodes (OLEDs) have potentials for application in various fields ranging from phototherapy to sensing. Accordingly, herein, ...phenylpyridazine‐based bidentate ligands are synthesized and subsequently utilized for the preparation of dinuclear Pt(II) complexes (1–6). The molecular structures of 1–3 is investigated by single‐crystal X‐ray diffraction, and the results suggest that these complexes have substantially shortened Pt···Pt distances (2.906–2.911 Å). Complexes 1–6 exhibit intense emissions in the NIR region (700–726 nm), high photoluminescence quantum yield (PLQY) (0.11–0.18), and short phosphorescence decay lifetimes (τ = 0.64–0.95 µs) in a CH2Cl2 solution. To examine the effect of N‐substitution on the dinuclear Pt complexes, the phenylpyrimidine‐based Pt(II) emitters 7 and 8 are prepared and discovered to have Pt···Pt distances of 2.933 Å. 7 and 8 demonstrate strong emissions in the 628–650 nm range with high PLQY of 0.52–0.65. Theoretical studies indicate that the functional groups or atoms in the ligands play crucial roles in the formation of emitters with significantly shortened Pt···Pt distances. 3 and 7 are employed as non‐doped emitters to fabricate NIR OLEDs, and the resulting OLEDs exhibit electroluminescence peaks at 754 and 692 nm with maximum external quantum efficiencies of 3.0 and 4.4%, respectively.
Pt⋅⋅⋅Pt interactions play a crucial role in the formation of efficient Pt(II)‐based near‐infrared emitters. The substituents on the molecular framework are making significant changes, for example, shortened Pt···Pt distance, red‐shifted emission, enhanced efficiency (induced MMLCT), and high thermal stability. Non‐doped organic light‐emitting diode using functionalized emitters shows electroluminescence peaks at 754 and 692 nm with enhanced efficiency of 3.0 and 4.4%, respectively.
Pt···Pt Interactions
Pt···Pt interactions are important in dinuclear Pt(II) complexes because they tend to tune the emission wavelength towards the near‐infrared region (NIR) and increase emitter ...efficiency. In article number 2211853, Seunghyup Yoo, Min Hyung Lee, and co‐workers, utilize these molecules effectively for the fabrication of NIR organic light‐emitting diodes by the vacuum deposition method, which has potential applications, e.g., biomedical treatment and photodynamic therapy.
A series of novel diiridium complexes (1–4) bearing both functional 2‐pyrazolyl‐6‐phenyl pyridine chelate and bidentate phenyl imidazolylidene chelate are synthesized, for which the pyrazolate ...fragment of the tridentate 2‐pyrazolyl‐6‐phenyl pyridine also behaves as the bridge to hold two iridium atoms in close vicinity. Their structure is unambiguously confirmed using X‐ray structure determination on the corresponding derivative 2a bearing 1,3‐bis(4‐fluorophenyl)‐1H‐Imidazolyl cyclometalate. Their photophysical and electrochemical properties are studied and further affirmed by the computational approaches. All these Ir(III) metal complexes 1–4 are very stable in both solution and solid film with near unity emission quantum efficiency. As opposed to most of diiridium complexes documented in literature, 1–4 are volatile and suitable for fabrication of organic light emitting diodes (OLEDs) under vacuum evaporation. The corresponding electroluminescent devices exhibit superior performance, among which external quantum efficiency of 27.6% using 2 as dopant stands for the record high of OLEDs using dinuclear Ir(III) complexes. They also offer a low roll‐off at high luminance, demonstrating their potential en route to high performance OLEDs.
Diiridium based metal phosphors (1–4) bearing both functional 2‐pyrazolyl‐6‐phenyl pyridine chelate and bidentate phenyl imidazolylidene ancillary are synthesized, investigated, and applied as emitters for vacuum‐deposited organic light emitting diodes, achieving record‐high external quantum efficiency up to 27.6%.
A semirigid ligand, 1,4-bis(2-nonylbenzimidazol-1-ylmethyl)benzene (Nbenzbix), containing a long alkyl chain substituted stator and a rotating unit was designed and synthesized. Three dinuclear ...metallacycles (Re(CO)3)(μ-L)(μ-Nbenzbix)(Re(CO)3) (1, H2-L = H2-dhnq = 6,11-dihydroxy-5,12-naphthacenedione; 2, H2-L = H2-dhaq = 1,4-dihydroxy-9,10-anthraquinone; and 3, H2-L = H2-CA = 2,5-dichloro-3,6-dihydroxy-p-benzoquinone) were synthesized from Re2(CO)10, Nbenzbix, and H2-L units. Compounds 1–3 and the ligand Nbenzbix were characterized by elemental analysis, FT-IR, and 1H NMR spectroscopy. Compound 1 was further characterized by a single-crystal X-ray diffraction analysis. The dynamic properties of 1–3 in solution were studied using variable-temperature 1H NMR spectroscopy, and the findings indicate that the p-phenylene unit in the metallacycle rotates in solution. To prevent the stator units from undergoing conformational changes due to the syn/anti arrangement of the benzimidazolyl units, a long-chain alkyl group was introduced at the 2-position of the benzimidazolyl unit. Molecular modeling calculations indicate that the energy barrier for the p-phenylene rotating unit in the metallacycle would be very low. Hence, these neutral metallacycles can be regarded as surface-mounted altitudinal rotors in which the bischelating unit is related to the surface, the nonylbenzimidazolyl units are related to the stators, and the p-phenylene is related to the rotating unit.
The meso-salicylaldehyde substituted BODIPY was synthesized over a sequence of steps and characterized by X-ray crystallography, mass, NMR, absorption, fluorescence and electrochemical techniques. ...The crystal structure showed the presence of strong intramolecular hydrogen bonding between hydroxyl and formyl groups, which induces rigidity in the BODIPY core and makes the BODIPY relatively more fluorescent than the meso-phenyl BODIPY. Our studies showed that the meso-salicylaldehyde BODIPY can be used as a specific chemidosimetric sensor for CN(-) ions. The presence of a hydroxyl group adjacent to a formyl group helps in activating the formyl group for a nucleophilic attack. Upon addition of the CN(-) ion to the meso-salicylaldehyde BODIPY, the CN(-) ion attacks the formyl group and converts it to the cyanohydrin group. This irreversible reaction was monitored by following the changes in absorption, fluorescence and electrochemical properties and the results support the view that the meso-salicylaldehyde substituted BODIPY can be used as a specific chemodosimetric sensor for CN(-) ions. To substantiate the role of the hydroxyl group, we also prepared the meso(m-formylphenyl) BODIPY which contains only the formyl group on meso-phenyl, and our studies indicated that the meso(m-formylphenyl) BODIPY cannot be used as a chemodosimetric sensor for CN(-) ions, as verified by absorption and emission studies.
Rigid naphthalene benzimidazole (NBI) based ligands (L1 and L2) are synthesized and utilized to make deep red phosphorescent cyclometalated iridium(III) complexes (Ir(NBI)2(PyPzCF3) (1) and ...Ir(DPANBI)2(PyPzCF3) (2)). Complexes 1 and 2 are prepared from the reaction of L1/L2 with the aid of ancillary ligands (PyPzCF3 , 2-(3-(trifluoromethyl)-1H-pyrazol-5-yl)pyridine) in a two step method. The complexes are characterized by analytical and spectroscopic methods, as well as X-ray diffraction for 1. These complexes show a strong emission in the range of 635–700 nm that extends up to the near-infrared region (800 nm). The introduction of the diphenylamino (DPA) donor group on the naphthalene unit leads to a further red-shift in the emission. The complexes exhibit radiative quantum efficiency (ΦPL) of 0.27–0.29 in poly(methylmethacrylate) film and relatively short phosphorescence decay lifetimes (τ = 1.1–3.5 μs). The structural, electronic, and optical properties are investigated with the support of density functional theory (DFT) and time-dependent-DFT calculations. The calculation results indicate that the lowest-lying triplet (T1) excited state of 1 has a mixed metal-to-ligand charge transfer (3MLCT) and ligand-centered (3LC) character, while 2 shows a dominant 3LC character. Deep red-emitting organic light-emitting diodes fabricated using 1 as a dopant display a maximum external quantum efficiency of 10.9% with the CIE color coordinates of (0.690, 0.294), with an emission centered at 644 and 700 nm. Similarly, the emitter 2 also shows a maximum external quantum efficiency of 6.9% with emissions at 657 and 722 nm.
Thiophene/bithiophene units decorated flexible ditopic benzimidazolyl donors (Ln) were synthesized. Neutral, heteroleptic, dinuclear rhenium(I)-based organometallic supramolecular coordination ...complexes (SCCs) (1–4) were synthesized using Ln, Re2(CO)10 and tetrahydroxy-p-benzoquinone via one-step procedure. All the molecules were characterized by various methods. SCCs 1, 2 and 4 were further analyzed by X-ray analysis. All the ligands and the complexes are emissive at room temperature.
Display omitted
•Flexible ditopic benzimidazolyl donors bearing thiophene/bithiophene functional units were prepared and utilized as structural framework motif.•M2LL′-type neutral, heteroleptic supramolecular coordination complexes (SCCs) decorated with thiophene motifs were prepared.•The SCCs are neutral, air- and moisture stable, and possesses uncoordinated two thiophene/bithiophene units on the SCCs framework.
