The potential energy surfaces associated with the triplet electronic state of the Ir(ppz)3 and Ir(ppy)3 cyclometalated complexes, respectively, are calculated using density functional theory [where ppz = 1-phenylpyrazolyl-N,C2′, ppy = 2-phenylpyridyl]. Both surfaces present a metal-to-ligand charge-transfer energy minimum and a ligand-field energy minimum, connected by a chemical path involving only the rotation of one pyrazolyl or pyridyl group. Unlike Ir(ppy)3, the lowest energy minimum of Ir(ppz)3 is the ligand-field state.
Substitution effects on the photoluminescence and electrochemical properties and the photochemical stability of tris-(phenylbenzimidazolinato)Ir III complexes were investigated. Facial and meridional isomers of a series of complexes having the general structure of Ir(C C) 3 , where (C C) is (4-Rphenyl)benzimidazolinato (R = H, CF 3 , CN, OCH 3 ), were prepared. They are abbreviated to Ir(pmb) 3 (1), Ir-(CF 3 pmb) 3 (2), Ir(CNpmb) 3 (3), and Ir(Opmb) 3 (4), respectively. Electron-donating or -withdrawing groups on the phenyl ring lead to both higher emission quantum yields and longer emission lifetimes compared to those of 1 in each mer and fac series. Particularly, the emission quantum yields were high in the cases of 2a, 3a, 3b, and 4a. No photochemical isomerization was observed in both fac-(a) and mer (b)
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