Heteroleptic Cycloplatinated N-Heterocyclic Carbene Complexes: A New Approach to Highly Efficient Blue-Light Emitters

Abstract

New heteroleptic compounds of platinum(II)-containing cyclometalated N-heterocyclic carbenes, [PtCl(R-C^C*)(PPh)] [R-CH^C*-κC* = 3-methyl-1-(naphthalen-2-yl)-1H-imidazol-2-ylidene (R-C = Naph; 1A), 1-[4-(ethoxycarbonyl)phenyl]-3-methyl-1H-imidazol-2-ylidene (R = COEt; 1B), and [Pt(R-C^C*)(py)(PPh)]PF (py = pyridine; R-C = Naph, 2A; R = COEt, 2B], have been prepared and fully characterized. All of them were obtained as the trans-(C*,PPh) isomer in high yields. The selectivity of their synthesis has been explained in terms of the degree of transphobia (T) of pairs of ligands in trans positions. X-ray diffraction studies on both 2A and 2B revealed that only in 2A, containing a C^C* with a more extended π system, do the molecules assemble themselves into head-to-tail pairs through intermolecular π···π contacts. The photophysical properties of 2A and 2B and those of the related compounds [Pt(NC-C^C*)(PPh)L]PF [NC-CH^C*-κC* = 1-(4-cyanophenyl)-3-methyl-1H-imidazol-2-ylidene; L = pyridine (py; 2C), 2,6-dimethylphenylisocyanide (CNXyl; 3C), and 2-mercapto-1-methylimidazole (MMI; 4C)] have been examined to analyze the influence of the R substituent on R-C^C* (R-C = Naph; R = COEt, CN) and that of the ancillary ligands (L) on them. Experimental data and time-dependent density functional theory calculations showed the similarity of the electronic features associated with R-C^C* (R = CN, COEt) and their difference with respect to R-C^C* (R-C = Naph). All of the compounds are very efficient blue emitters in poly(methyl methacrylate) films under an argon atmosphere, with QY values ranging from 68% (2B) to 93% (2C). In the solid state, the color of the emission changes to yellowish-orange for compounds 2A (λ = 600 nm) and 3C (λ = 590 nm) because of the formation of aggregates through intermolecular π···π interactions. 2C and 3C were chosen to fabricate fully solution-processed electroluminescent devices with blue-light (2C), yellow-orange-light (3C), and white-light (mixtures of 2C and 3C) emission from neat films of the compounds as emitting layers.

The Use of Cyclometalated NHCs and Pyrazoles for the Development of Fully Efficient Blue PtII Emitters and Pt/Ag Clusters

“…1450 cm −1 ] corresponding to the C=C/C=N stretches of the cyclometalated NHC ligands (see Figure for 1 b Figure S29 and Table ) with long emission lifetime decays (14–22 μs), typical of phosphorescent Pt II systems. The emission energies are neither affected by the nature of the RpzH ligand nor the anion and are very similar to those of related compounds containing the same “(C^C*)Pt” fragment ,…”

Highly efficient platinum-based emitters for warm white light emitting diodes

“…2 and ESI † part 4), as previously stated. 26,27 On the other hand, the low energy bands of the dppm derivatives (1A and 1B) appear red shifted with respect to the corresponding dppe and dppbz ones (2A, 2B and 3A, 3B), indicating that both R-C^C* and P^P ligands are involved in the lowest energy spin-allowed transition. These absorptions obey Beer's law in the range 10 À3 -10 À6 M in CH 2 Cl 2 , in agreement with the absence of significant aggregation in this concentration range.…”

“…[19][20][21][22][23][24] The work presented here represents the research of technological alternatives that could improve solid state lighting (SSL) technology in terms of light quality and cost; light quality because we report on systems capable of generating white light with high CRI and low CCT values, and cost because all the compounds reported in this work are 100% rare-earth-free emitting phosphors. Therefore, keeping with our mastered organometallic approach of using cyclometalated N-heterocyclic carbenes (NHC) as highly efficient emitters to prepare lighting devices, [25][26][27] herein we report the synthesis and complete structural and photophysical studies of cycloplatinated NHC compounds with diphosphines (P^P) as auxiliary ligands, [Pt(R-C^C*)(P^P)]PF 6 (R-C = Naph, P^P = dppm 1A, dppe 2A, dppbz 3A; R = CO 2 Et, P^P = dppm 1B, dppe 2B, dppbz 3B). Taking into account their emitting features, we used a selection of them as blue (1B, 3B), and orange (1A) emitters for SSL applications: WOLEDs and remote pcWLEDs.…”

Strong red emissions induced by Pt–Pt interactions in binuclear cycloplatinated(II) complexes containing bridging diphosphines

“…The luminescence properties of the cyclometalated platinum(II) complexes make them appropriate candidates for investigation by many research groups . Regarding these properties, cycloplatinated(II) complexes have various applications such as in light‐emitting devices, dye‐sensitized solar cells, photoswitches, photocatalysts and chemical or biochemical sensors .…”