Cyclometalated Platinum(II) Complexes of Lepidine-Based Ligands as Highly Efficient Electrophosphors

Abstract

A new series of lepidine-containing-ligand-based cyclometalated platinum(II) complexes 1-7 with general formula [Pt(L)acac] (L = lepidine-based ligand, acac = acetylacetonate) have been synthesized. The complexes have been characterized using spectral and electrochemical techniques. The single-crystal X-ray structures of complexes 2 and 5 have been successfully determined. The effects of substituents on the electronic features and redox potentials of the cyclometalated phenyl ring of the complexes are discussed. Complexes 1-7 are highly phosphorescent in fluid as well as in solid state, covering a rather broad spectral range from yellow to saturated red. These complexes were successfully used as a dopant material to fabricate the electroluminescent device, ITO/NPB (40 nm)/ CBP-doped Pt complex (5 wt %) (20 nm)/BCP (10 nm)/Alq 3 (20 nm)/LiF (1 nm)/Al (150 nm), which exhibits very promising performance. The device doped with 5 wt % 3 produced a maximum external quantum efficiency of 15.2% with a maximum brightness of 26847 cd m -2 and corresponds to a luminance efficiency of 29.83 cd A -1 .

Phosphorescent Pt(II) Emitters for OLEDs: From Triarylboron‐Functionalized Bidentate Complexes to Compounds with Macrocyclic Chelating Ligands

“…Acetylacetonate (acac) was selected as the ancillary ligand owing to its high triplet energy, excellent solubility as demonstrated previously in the literature. [19][20][21] The HOMO and LUMO diagrams of the model compound, (ppy)Pt(acac), are shown in Figure 8. The HOMO consists of orbitals from phenyl, acac and Pt center while the LUMO is settled on the ppy ligand, suggesting that the lowest electronic transition of (ppy)Pt(acac) can be considered as an admixture of LC (ph!ppy), LLCT (acac!ppy) and MLCT (Pt!ppy) transitions.…”

“…seem to hamper the luminescence from the Pt(II) complexes, as indicated by the low quantum yields of compound 8 – 10 , we decided to replace them with a bidentate ligand. Acetylacetonate (acac) was selected as the ancillary ligand owing to its high triplet energy, excellent solubility as demonstrated previously in the literature . The HOMO and LUMO diagrams of the model compound, (ppy)Pt(acac), are shown in Figure .…”

Heat‐Resistant Properties in the Phosphorescence of trans‐Bis[β‐(iminomethyl)aryloxy]platinum(II) Complexes: Effect of Aromaticity on d–π Conjugation Platforms

“…However, despite marked progress in the chemistry of phosphorescent materials, to date, aromaticity has not been discussed from the viewpoint of the emission properties of d–π conjugation platforms, probably owing to a lack of suitable phosphorescent materials whose emissions are drastically altered in a controllable fashion by varying their aromaticity. Pt 3 and Ir 4 complexes bearing rigid ligands, including N‐heterocyclic carbene,,, C ^ N ‐,,,,, and N ^ N ‐–,,,‐–,–,, metalated nitrogen heteroaromatics, porphyrinoids, and salen exhibit significant variations in emission wavelength and emission efficiency upon changing the number,–‐ and position–,,,,,, of extended benzene rings on the coordination platforms. Emission color changes on the π‐extended platforms have been rationalized based on stabilization/destabilization of the frontier orbitals using simple molecular orbital theory .…”

8‐Hydroxy Quinoline Derivatives as Auxiliary Ligands for Red‐Emitting Cyclic‐Platinum Phosphorescent Complexes: Synthesis and Properties

“…Since the end of last century, many reports have focused on organometallic complexes with heavy metal centers because of their high internal phosphorescence quantum efficiency based on the heavy atom effect which induces strong spin‐orbit coupling making the previously forbidden S 1 → T transition possible. The heavy metal ions include iridium(III), ruthenium, osmium(II), rhenium(I), gold(III), and platinum(II) …”