Highly Efficient Phosphorescent Furo[3,2-c]pyridine Based Iridium Complexes with Tunable Emission Colors over the Whole Visible Range

Efficient narrowband yellow organic light-emitting diodes based on iridium(III) complexes with the rigid indolo[3,2,1-jk]carbazole unit

Phosphorescent material with narrowband emission is crucial for advancing wide-color-gamut organic light-emitting diodes (OLEDs). In this work, two iridium(III) complexes, (PhthzICz)2Ir(tmd) and (thzICz)2Ir(tmd), using rigid 2-(benzothiazole-2-yl)indolo[3,2,1-jk]carbazole (PhthzICz) and 2-(thiazole-2-yl)indolo[3,2,1-jk]carbazole (thzICz) as cyclometalated ligands and 2,2,6,6-tetramethyl-3,5-heptanedione (tmd) as ancillary ligands, were synthesized. When these complexes were doped into the host material 3,3'-di(9H-carbazol-9-yl)-1,1'-biphenyl, the doped films exhibited yellow photoluminescence (PL) peaking at 537 and 531 nm, full width at half maximum (FWHM) bands of 35 and 60 nm, and PL quantum yields of 89.9% and 85.9%, respectively. OLEDs based on these two emitters display moderate performance characteristics with maximum external quantum efficiencies of 25.2% and 22.7%. Notably, the device based on (PhthzICz)2Ir(tmd) exhibits a narrow FWHM of 31 nm. Overall, the study highlights the practicality of incorporating rigid groups into the cyclometalated ligands of Ir(III) complexes as a viable strategy for achieving efficient Ir(III) complexes for OLEDs with narrow emission and high efficiency.

A novel furo[3,2-c]pyridine-based AIE photosensitizer for specific imaging and photodynamic ablation of Gram-positive bacteria

An Rh-catalyzed tandem reaction was performed to construct an AIE-active furo[2,3-c]pyridine-based photosensitizer, named LIQ-TF. LIQ-TF showed near-infrared emission with high quantum yield, and high ¹O₂ and ˙OH generation efficiency, and could be used for specific imaging and photodynamic ablation of Gram-positive bacteria in vitro and in vivo, showing great potential for combating multiple drug-resistant bacteria.

Ultrafast excited state relaxation dynamics in a heteroleptic Ir(iii) complex, fac-Ir(ppy)2(ppz), revealed by femtosecond X-ray transient absorption spectroscopy

The experimental and calculation results demonstrate that the ³ML_ppzCT state generated by the spin-forbidden transition rapidly relaxes to ³ML_ppyCT through internal conversion process with a time constant of ∼450 fs.

Unsymmetric Heteroleptic Ir(III) Complexes with 2-Phenylquinoline and Coumarin-Based Ligand Isomers for Tuning Character of Triplet Excited States and Achieving High Electroluminescent Efficiencies

2-Phenylquinoline (PQ) and four coumarin-based ligand isomers with ease of synthesis have been selected to construct the unsymmetric heteroleptic [Ir(C₁^∧N)(C₂^∧N)(acac)]-type complex phosphors for organic light-emitting diodes (OLEDs). Six unsymmetric heteroleptic Ir(III) complexes have been obtained by employing four coumarin-based ligand isomers (L-C5/L-C6/L-C7/L-C8) in the [Ir(PQ)(C^∧N)(acac)] structure due to two different coordinating carbon atoms in ligands L-C6 and L-C7 to form C-Ir bond. Through adopting unsymmetric heteroleptic [Ir(C₁^∧N)(C₂^∧N)(acac)] structure, these Ir(III) complexes can not only achieve impressive absolute quantum yield Φ_p (ca. 0.5-1.0), higher than that of complex [Ir(PQ)₂(acac)] (ca. 0.4), but also realize a dual modulation of both emission color from orange (AIrC6out, λ = 578 nm) to red (AIrC5, λ = 622 nm) and the character of the lowest triplet excited states (T₁), showing both ³MLCT character and ³ILCT (intraligand charge transfer) character in their T₁ states. AIrC5, AIrC7out, and AIrC7in show MLCT character from Ir(III) center to ligand L-C5 or L-C7 and ILCT character in ligand L-C5 or L-C7 in their T₁ states, while AIrC6out, AIrC6in, and AIrC8 show MLCT character from Ir(III) center to ligand PQ and ILCT character in ligand PQ in their T₁ states. Moreover, the color-tuning mechanism and the lowest triplet state characters are investigated in detail. AIrC6in and AIrC8 were selected as emitters to evaluate the electroluminescent (EL) performance due to their high Φ_P of nearly up to unity. Optimal orange-emitting device B2 based on AIrC8 can give a maximum external quantum efficiency (η_ext) of 23.9%, a maximum current efficiency (η_L) of 70.9 cd A^-1, and a maximum power efficiency (η_P) of 60.7 lm W^-1. All these impressive results can definitely demonstrate the effectiveness of our simple approach for tuning character of the triplet excited states and achieving high-performance Ir-based phosphors in OLEDs.

High stability and luminance efficiency thieno[2,3-d]pyridazine-based iridium complexes and their applications in high-performance yellow OLEDs

An OLED based on complex 1 shows promising efficiencies of 18.2%, 58.5 cd A⁻¹ and 45.9 lm W⁻¹ which are 40% higher than those of PO-01.

Four-membered red iridium(iii) complexes with Ir-S-P-S structures: rapid room-temperature synthesis and application in OLEDs

In this work, with sulfur-containing ancillary ligands of triethylamine salts of bis(4-methoxyphenyl)-phosphinodithioic acid (omess) and bis(3,5-di-tert-butyl-4-methoxyphenyl)phosphinodithioic acid (tbuss), two four-membered red iridium(iii) complexes (tfmpqz)₂Ir(omess) and (tfmpqz)₂Ir(tbuss) with Ir-S-P-S structures were synthesized rapidly at room temperature within 5 min, in which 4-(4-(trifluoromethyl)phenyl)quinazoline (tfmpqz) was used as the main ligand. The calculated Gibbs free energy changes of the complex formation reactions prove that they are exothermic and thermodynamically beneficial processes. Both Ir(iii) complexes show almost the same PL emissions at 624 and 623 nm with high phosphorescence quantum yields of 0.60 and 0.72, respectively. Using the two complexes as emitters, both organic light-emitting devices (OLEDs) with the structure of ITO/HATCN (hexaazatriphenylenehexacabonitrile, 5 nm)/TAPC ((bis(4-(N,N-ditolylamino)phenyl)cyclohexane, 30 nm)/(tfmpqz)₂Ir(omess) or (tfmpqz)₂Ir(tbuss):26DCzppy (2,6-bis-(3-(carbazol-9-yl)phenyl)pyridine) (12 wt%, 10 nm)/TmPyPB (1,3,5-tri((3-pyridyl)-phen-3-yl)benzene, 30 nm)/LiF (1 nm)/Al (100 nm) achieve good performances. Particularly, due to the introduction of tert-butyl groups into the (tfmpqz)₂Ir(tbuss) complex, its device exhibits better device properties with a maximum luminance of 26 184 cd m^-2, maximum current efficiency of 30.24 cd A^-1, maximum power efficiency of 22.61 lm W^-1 and maximum external quantum efficiency of 21.50% with CIE coordinates at (0.65, 0.34).

Enhancing Molecular Aggregations by Intermolecular Hydrogen Bonds to Develop Phosphorescent Emitters for High-Performance Near-Infrared OLEDs

Phosphorescent near-infrared (NIR) organic light-emitting devices (OLEDs) have drawn increasing attention for their promising applications in the fields such as photodynamic therapy and night-vision readable displays. Here, three simple phosphorescent Pt(II) complexes are synthesized, and their intermolecular interactions are investigated in crystals and neat films by X-ray single crystal diffraction and grazing-incidence wide-angle X-ray scattering, respectively. The photophysical properties, molecular aggregation (including Pt-Pt interaction), molecular packing orientation, and electron transport ability are all influenced by the strong intermolecular hydrogen bonds. Consequently, the nondoped OLEDs based on tBu-Pt and F-Pt show electroluminescent emissions in NIR region with the highest external quantum efficiencies of 13.9% and 16.7%, respectively.

Achieving Deep-Blue Thermally Activated Delayed Fluorescence in Nondoped Organic Light-Emitting Diodes through a Spiro-Blocking Strategy

A deep-blue thermally activated delayed fluorescence (TADF) emitter TXADO-spiro-DMACF has been reported for nondoped organic light-emitting diodes (OLEDs) by integrating an appropriate blocking unit with the donor (D)-acceptor (A)-donor (D)-type TADF emitter via a spiro linkage. Benefiting from the characteristic perpendicular arrangement, the intermolecular interactions are expected to be weakened to some degree. As a result, TXADO-spiro-DMACF shows a very small bathochromic shift of 8 nm associated with a narrowed full width at half maximum of 54 nm on going from solution to the film. The corresponding nondoped device successfully achieves a bright deep-blue emission, revealing Commission Internationale de l'Eclairage coordinates of (0.16, 0.09) and a peak external quantum efficiency of 5.3% (5.3 cd/A, 5.9 lm/W). The results clearly indicate that spiro-blocking is a promising strategy to develop deep-blue TADF emitters capable of nondoped OLEDs.

Sulfur atom containing ligands induced rapid room temperature synthesis of red iridium(iii) complexes with Ir–S–P–S structures for OLEDs

Two red iridium(iii) complexes containing a four-membered ring Ir–S–P–S backbone were synthesized at room temperature in 5 min, and their OLEDs exhibit an EQE_max of 19.90%.

Recent Progress in Sublimable Cationic Iridium(III) Complexes for Organic Light-Emitting Diodes

Sublimable cationic iridium(III) complexes consisting of light-emitting coordinated iridium(III) cations and nonluminous negative counter-ions, show excellent photophysical properties, superior electrochemical behaviors and high thermal stabilities, therefore have emerged as a new library of phosphorescent materials for various organic optoelectronic devices. Here we summarize and highlight the recent progress in sublimable cationic iridium(III) complexes, regarding the material design strategies, synthetic routes, photoluminescent characteristics in both solutions and neat films, together with the current utilization in organic light-emitting diodes based on the emissive material layers fabricated by vacuum evaporation deposition. Finally, we present a brief outlook thereon, indicating the great promise and brilliant application prospect of sublimable cationic iridium(III) complexes in future flat-panel display and solid-state lighting technology.

Controlling Ion Distribution for High-Performance Organic Light-Emitting Diodes Based on Sublimable Cationic Iridium(III) Complexes

Sublimable charged iridium(III) complexes are becoming an attractive family of new phosphors and making their way into vacuum-evaporated-deposited organic light-emitting diodes, while it remains challenging to achieve high device performance. Here, we demonstrate a substantial mitigation of exciton quenching not only by reducing the dopant concentration, but also by controlling the ion distribution in the emissive material layers. We, therefore, achieved green luminescence with high brightness, superior efficiencies, and low driving voltages. Following this strategy, we further developed another six sublimable charged iridium(III) complexes and attained blue-green, yellow, and red-emitting devices with record-high performance. This study represents an important advance in the construction of bright electroluminescence from ionic transition metal complexes and shows their great promise in various optoelectronic applications.