Axially Chiral Bis-Cycloplatinated Binaphthalenes and Octahydro-Binaphthalenes for Efficient Circularly Polarized Phosphorescence in Solution-Processed Organic Light-Emitting Diodes

Abstract

A new series of axially chiral binuclear Pt­(II) complexes with bridging ligands of binaphthalenes and octahydro-binaphthalenes and auxiliary ligands of β-diketones were designed and prepared. These complexes, identified by spectral and electrochemical methods and single-crystal X-ray diffraction, emit an orange-red phosphorescence with a quantum yield up to 21% and 70% in solution and solid, respectively, due to the effect of steric hindrance from bridging ligands and the 2,3-position extension of chiral axis planes. They can be used as emitters in solution-processed organic light-emitting diodes to achieve luminance efficiency, asymmetry factor, and external quantum efficiency up to 5.4 cd A–1, 3.0 × 10–3, and 3.1%, respectively. Moreover, the essential relationships between their chemical structures and luminescence quantum efficiency and asymmetry factor are discussed, which affords explicit insights for designing circularly polarized luminescent materials and devices.

Highly Phosphorescent Planar Chirality by Bridging Two Square-Planar Platinum(II) Complexes: Chirality Induction and Circularly Polarized Luminescence

“…At first, we used the 5-phenyl-OXT ligand to prepare binuclear Pt­(II) complexes, but we failed due to the very poor solubility. Then Cy-OXT and BINA-OXT ligands were adopted because of their good solubility. ,, A 1 mL portion of CH 2 Cl 2 could dissolve at least 60, 20, 100 and 90 mg of Race-Cy-A , Race-Cy-B , ( R , R , R )-BINA-A and ( R , R , R )-BINA-B , respectively,. The single crystals of Race-Cy-A (CCDC: 2117798) and ( R , R , R )-BINA-A (CCDC: 2117799) were obtained by a slow diffusion and evaporation of CH 3 CN/CH 2 Cl 2 solutions.…”

“…( R )-Cy-A and ( S )-Cy-A molecules can pack closely to form a lamellar arrangement with a short interplanar distance of 3.235 Å but weak intermolecular face-to-face π–π interactions (overlaps in π-conjugated systems) . Since the intermolecular Pt–Pt distances are over 7.859 Å, there are no intermolecular Pt–Pt interactions in Race-Cy-A . In contrast, there are many strong intermolecular noncovalent bonding H–H interactions between Cy and Cy groups (2.341 Å) and between Cy and quinoline groups (2.386 Å), which would help to eliminate the dynamic intramolecular rotations of Cy groups.…”

“…When the problems of solubility and synthesis are considered, it is difficult to improve the asymmetry factor through this method. The third method is to take advantage of self-assembled supramolecular technology, ,, which might be not as efficient for CP-OLEDs, because each layer of OLEDs usually is amorphous and self-assembled crystalline materials would be harmful to device performances . With a comprehensive consideration of EL efficiency and asymmetry factor, this work has the best performance among Pt­(II) complex-based CP-OLEDs.…”

“…Ir­(ppy) 3 , ppy = 2-phenylpyridine) that have an intrinsic metal-induced Λ/Δ chirality, − the chirality of square-planar d 8 Pt­(II) complexes is mainly introduced by chiral ligands. − There are limited examples of chiral Pt­(II) complexes with achiral ligands. − However, their CPL has seldom been reported before, mainly due to not only the weak chirality but also the low emission quantum yield (Φ) (Figure S1) of the distorted-square-planar coordination configuration of the Pt­(II) ion. For the same reason, they have not been applied in circularly polarized OLEDs (CP-OLEDs) before, even though CP-OLEDs can emit CPL directly and have extensive applications in 3D displays, optical data storage, and optical spintronics. − Up to now, just a few Pt­(II) complexes with chiral ligands have been used for applications in CP-OLEDs. ,− For example, Jiang et al used chiral binaphthalene (BINA)-based mononuclear Pt­(II) complexes to fabricate solution-processed CP-OLEDs, which have an external quantum efficiency (EQE) and an asymmetry factor ( g EL ) of up to 2.15% and 1.1 × 10 –3 , respectively. Recently, we also demonstrated that the EQE and g EL can be further improved to 3.1% and 3.0 × 10 –3 , respectively, by chiral BINA-bridging binuclear Pt­(II) complexes .…”

Circularly Polarized Phosphorescence from Cocrystallization of Atomic Precise Silver Nanoclusters with Tartaric Acid

“…[2] As the delicate electronic transition mode on which phosphorescence relies and the chiral structure [3] required for CPL are hard to be achieved simultaneously, the preparation of materials with CPP remains a big challenge. Besides a few examples where pure organic molecules [4] and carbon dots [5] act as luminophores, the majority of the materials with CPP are noble metal complexes containing platinum, [6][7][8][9][10][11][12] iridium, [13,14] or rhenium. [15] through the center of all three Ag 3 trigons.…”