Phosphorescence Color Tuning of Cyclometalated Iridium Complexes by o?Carborane Substitution

摘要

Heteroleptic (C∧N)2Ir(acac) (C∧N = 4-CBppyn(1); 5-CBppy (2), 4-fppy (4) CB = ortho-methylcarborane; ppyn= 2-phenylpyridinato-C2,N, 4-f ppy = 2-(4-fluorophenyl)-npyridinato-C2,N, acac = acetylacetonate) complexes werenprepared and characterized. While 1 exhibits a phosphorescencenband centered at 531 nm, which is red-shiftedncompared to that of unsubstituted (ppy)2Ir(acac) (3) (λem =n516 nm), the emission spectrum of 2 shows a blue-shiftednband at 503 nm. Comparison with the emission band for the 4-nfluoro-substituted 4 (λem = 493 nm) indicates a substantialnbathochromic shift in 1. Electrochemical and theoreticalnstudies suggest that while carborane substitution on the 4-nposition of the phenyl ring lowers the 3MLCT energy by anlarge contribution to lowest unoccupied molecular orbital (LUMO) delocalization, which in turn assigns the lowest triplet statenof 1 as [dπ(Ir)→π*(C∧N)] 3MLCT in character, the substitution on the 5-position raises the 3MLCT energy by the effectivenstabilization of the highest occupied molecular orbital (HOMO) level because of the strong inductive effect of carborane. Annelectroluminescent device incorporating 1 as an emitter displayed overall good performance in terms of external quantumnefficiency (6.6%) and power efficiency (10.7 lm/W) with green phosphorescence.