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

Abstract

New bis-pyrazole complexes [Pt(C^C*)(RpzH) ]X, containing a cyclometalated N-heterocyclic carbene ligand (HC^C*=1-(4-(ethoxycarbonyl)phenyl)-3-methyl-1H-imidazol-2-ylidene) were prepared as chloride (X=Cl , RpzH: 3,5-Me pzH 1 a, 4-MepzH 2 a, pzH 3 a), perchlorate (X=ClO , 1 b-3 b), or hexafluorophosphate (X=PF , RpzH: 3,5-Me pzH 1 c) salts. The X-ray structure of 1 a showed that the Cl anion is trapped by the cation through two N-H⋅⋅⋅Cl bonds. In solution of methanol, acetone and THF at RT, 1 a-3 a coexist in equilibrium with the corresponding [PtCl(C^C*)(RpzH)] (B) and RpzH species. In CH Cl , this equilibrium takes place just for 2 a and 3 a, but it is completely shifted to the left at 243 and 223 K for 2 a and 3 a, respectively. The low-lying absorption and emission bands were assigned to intraligand (ILCT) charge transfer on the NHC group. Quantum yield measurements in PMMA films revealed that 1 b, 2 b and 1 c are amongst the most efficient blue-light emitters, with values up to 100 %. Proton abstraction from the coordinated 3,5-Me pzH in 1 b by NEt and replacement by Ag afforded a neutral [Pt Ag ] cluster containing Pt→Ag dative bonds.

A Cyclometalated N‐Heterocyclic Carbene: The Wings of the First Pt2(II,II) Butterfly Oxidized by CHI3

“…In the molecule, each Pt center lies in a distorted square planar coordination environment as a consequence of the small bite angle of the EtO 2 C‐C^C* cyclometalated ligand ca 80°. These angles and the Pt−C Ar and Pt−C* distances are similar to those found in other compounds containing five‐membered cycloplatinated N‐heterocyclic carbenes . The Pt−N bond lengths are also similar to those found in dinuclear bis‐pyrazolate‐bridge complexes containing ligands with high trans influence …”

“…In the molecule, each Pt center lies in ad istorted square planar coordination environmenta saconsequence of the small bite angle of the EtO 2 C-C^C*c yclometalated ligand ca 808.T hese angles and the PtÀC Ar and PtÀC* distances are similar to those found in other compounds containing fivemembered cycloplatinated N-heterocyclic carbenes. [16][17][18] The PtÀNb ond lengths are also similart ot hose found in dinuclear bis-pyrazolate-bridge complexes containing ligands with high trans influence. [9a, 15, 19] The reaction of 1 (syn/anti mixture) with an excess of CHI 3 (molar ratio 1:4, see Scheme 1p ath c) in the air and in sunlight renderedP t 2 (III,III)I 2 as the major species, with complex [{Pt(C^C*)(m-pz)I)} 2 ]( 2), with an anti arrangement of the C^C* groups,b eing precipitated and separated from the mixture in a4 1% yield.…”

“…Compound 1 was prepared by two paths, from [{Pt(C^C*)(μ‐Cl)} 2 ] or [Pt(C^C*)(pzH) 2 ]ClO 4 as a mixture of syn / anti isomers with respect to the relative orientation of the two cyclometalating C^C* ligands (see Scheme paths a, b). The composition of 1 , with the anti isomer being the major one ( 1 H and 195 Pt{ 1 H} NMR spectra in Figures S1 and S2 in Supporting Information), is in agreement with the DFT ground‐state (S 0 ) calculations, which showed the anti isomer to be 3.1 kcal mol −1 lower in energy than the syn one (See Figure S3 in Supporting Information) .…”

“…Information describing Instrumental methods used for characterization, details concerning DFT calculations and X‐ray structure determination are provided in the Supporting Information. The starting materials [{Pt(μ‐Cl)(EtO 2 C‐C^C*)} 2 ] ( A ) and [Pt(EtO 2 C‐C^C*)(pzH) 2 ]ClO 4 ( B ) were prepared following the literature procedure. pzH was purchased from MERCK.…”

Highly Efficient Deep Blue Phosphorescent OLEDs Based on Tetradentate Pt(II) Complexes Containing Adamantyl Spacer Groups

“…[ 4–11 ] Recently, square‐planar Pt(II) complexes have been studied for their unique optical properties, which include high photoluminescence quantum yields (PLQYs) and unique emission colors. [ 12–23 ] Tetradentate ligand‐based Pt(II) complexes offer narrow emission spectra originating from their rigid structures. [ 24–34 ] However, one critical issue with Pt(II) complexes is undesirable spectral changes when doped in a solid film.…”