Enlarging the π System of Phosphorescent (C^C*) Cyclometalated Platinum(II) NHC Complexes

Abstract

Cyclometalated (C^C*) platinum(II) N-heterocyclic carbene (NHC) complexes are emerging as a new class of phosphorescent emitters for the application in organic light-emitting devices (OLEDs). We present the synthesis of six new complexes of this class to investigate the influence of extended π systems. Therefore, six different NHC ligands with a varying number of additional phenyl substituents were used in combination with the monoanionic acetylacetonate (acac) ligand to obtain complexes of the general formula [(NHC)Pt(II)(acac)]. The complexes were fully characterized by standard techniques and advanced spectroscopic methods ((195)Pt NMR). For all complexes the solid-state structure determination revealed a square-planar coordination of the platinum atom. Absorption and emission spectra were measured in thin amorphous poly(methyl methacrylate) films at room temperature. Four compounds emit in the blue-green region of the visible spectrum with quantum yields of up to 81%.

Concise Stereoselective Synthesis of Oxaspirocycles with 1‐Tosyl‐1,2,3‐triazoles: Application to the Total Syntheses of (±)‐Tuberostemospiroline and (±)‐Stemona‐lactam R

“…Replacing the acac ligand with a more bulky congener, namely, the dimesitoylmethanato (mesacac) ligand, led to increased solubility, reduced aggregation behavior, and an improvement of the photoluminescence properties to 91 %, 466 nm, and 18.9 μs (Scheme ) 7c. Furthermore, we recently showed that an extension of the π‐system in the rigid NHC backbone could increase the quantum yield 7e. In the present study we combine these earlier results in one system and investigate the influence of different ways of attaching the DBF fragment to the heterocyclic system and thus the metal center with the goal to reduce the decay lifetime, which remains a very critical aspect in overall device stability.…”

Sky‐Blue Triplet Emitters with Cyclometalated Imidazopyrazine‐Based NHC‐Ligands and Aromatic Bulky Acetylacetonates

“…Also, the electronic properties of both the cyclometalated and the carbene fragments can be fine‐tuned. For example, modifying the π‐conjugation on the C^C* ligand, the phosphorescent decay time can be changed between 8 and 400 μs . Recently we also reported that the introduction of a heteroatom in the backbone of the N ‐heterocyclic carbene changes the photophysical properties of the C^C* platinum(II) complexes.…”

The Chameleonic Nature of Platinum(II) Imidazopyridine Complexes

“…The formation of the carbene complex was verified by the disappearance of the characteristic NCHN protons ignal of the imidazolium salt in the 1 HNMR experiment and the appearance of the characteristic ipso carbon signal of the carbene at 163-164 ppm in the 13 CNMR experiment. Thermal stability of all complexes was analyzed by determining their melting point, which are in the range of 234 8C (11)t om ore than 350 8C (12). Thermal stability of all complexes was analyzed by determining their melting point, which are in the range of 234 8C (11)t om ore than 350 8C (12).…”

“…This assignment is confirmed by concentration dependent measurements at 77 Ki naglassy 2Me-THF matrix (Figure S7). [10c] Strikingly,t his phenomenon is not observed in the case of the analogous benzimidazole platinum(II) complex [12] (Figure S13 and Table S3). However,t he emission at lower energies maintains an unstructured profile.…”

“…The introduction of bulkier substituents in the acetylacetonate fragment (complexes [10][11][12]o ri nt he NHC moiety (complexes 13-14)e fficiently prevents the aggregation process. The introduction of bulkier substituents in the acetylacetonate fragment (complexes [10][11][12]o ri nt he NHC moiety (complexes 13-14)e fficiently prevents the aggregation process.…”