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

• Published in: Chemistry : a European journal 2018-07, Vol.24 (37), p.9377-9384
• Main Authors: Arnal, Lorenzo, Fuertes, Sara, Martín, Antonio, Sicilia, Violeta
• Format: Article
• Language: English
• Subjects: Acetone; Charge transfer; Chemistry; Dichloromethane; Emitters; luminescence; metal–metal interactions; N-heterocyclic carbenes; Perchlorate; Perchloric acid; Platinum; Polymethyl methacrylate; Polymethylmethacrylate; Pyrazole; Pyrazoles; Salts; Silver
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201800646

New bis‐pyrazole complexes [Pt(C^C*)(RpzH)2]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‐Me2pzH 1 a, 4‐MepzH 2 a, pzH 3 a), perchlorate (X=ClO4−, 1 b–3 b), or hexafluorophosphate (X=PF6−, RpzH: 3,5‐Me2pzH 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 CH2Cl2, 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 ion from the coordinated 3,5‐Me2pzH in 1 b by NEt3 and replacement by Ag+ afforded a neutral [Pt2Ag2] cluster containing Pt→Ag dative bonds. A winning mix for PtII: Pyrazoles combined with N‐heterocyclic carbenes cyclometallated to a PtII center have been shown to produce fully efficient blue‐light emitters with QY of 100 %.