The Use of Cyclometalated NHCs and Pyrazoles for the Development of Fully Efficient Blue Pt II 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
• 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‐1 H ‐imidazol‐2‐ylidene) were prepared as chloride (X=Cl − , RpzH: 3,5‐Me 2 pzH 1 a , 4‐MepzH 2 a , pzH 3 a ), perchlorate (X=ClO 4 − , 1 b – 3 b ), or hexafluorophosphate (X=PF 6 − , RpzH: 3,5‐Me 2 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 2 Cl 2 , 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 2 pzH in 1 b by NEt 3 and replacement by Ag + afforded a neutral [Pt 2 Ag 2 ] cluster containing Pt→Ag dative bonds.