New NHC cycloplatinated compounds. Significance of the cyclometalated group on the electronic and emitting properties of bis-cyanide compounds

Abstract

Compounds NBu4[Pt(CˆC*A/B/C)(CN)2] (HCˆC*A = 1-(4-(ethoxycarbonyl)phenyl)-3-methyl-1H-imidazol-2-ylidene 1, HCˆC*B = 1-(4-cyanophenyl)-3-methyl-1H-imidazol-2-ylidene 2, HCˆC*C = 1-(3,5-dichlorophenyl)-3-methyl-1H-imidazol-2-ylidene 3) and NBu4 [Pt(CˆC*A/B/C)(13CN)2] (1′-3′) were synthesized by addition of KCN (or K13CN) to freshly prepared species [Pt(CˆC*A/B/C)(NCCH3)2]ClO4, in a 2:1 M ratio. Single crystal X-ray structures of 1–3 showed the absence of intermolecular π-π and Pt-Pt interactions. The 195Pt{1H} NMR data of 1–3 were obtained and compared with those of the related compounds NBu4[Pt(CˆN)(CN)2] (CˆN = benzoquinolate, bzq; phenylpyridinate, ppy). They indicate that the electronic density on the Pt center is larger for NBu4[Pt(CˆC*A/B/C)(CN)2](1–3) than for NBu4[Pt(CˆN)(CN)2], which has been proved through NBO charge distribution analysis. Compounds 1 and 2 resulted to be rather good blue-emitters with their emissions arising mainly from 3IL [π(NHC) → π*(NHC)] excited states with little 3MLCT [5d(Pt) → π*(NHC)] character. The emission of 2 in PMMA film render PLQY (Ф) of 70% and Commission Internationale de L'Eclairage (CIE) coordinates (0.15, 0.19) highly close to the optimal ones for blue emitters (0.15, 0.15).