Abstract
Iridium(III) complexes with N‐heterocyclic (NHC) ligands including fac‐Ir(pmb)~3~ (1), mer‐Ir(pmb)~3~ (2), (pmb)~2~Ir(acac) (3), mer‐Ir(pypi)~3~ (4), and fac‐Ir(pypi)~3~ (5) [pmb = 1‐phenyl‐3__H__‐benzimidazolin‐2‐ylidene, acac = acetoylacetonate, pypi = 1‐phenyl‐5__H__‐benzimidazolin‐2‐ylidene; fac = facial, mer = meridional] were investigated theoretically. The geometry structures of 1–5 in the ground and excited state were optimized with restricted and unrestricted DFT (density functional theory) methods, respectively (LANL2DZ for Ir atom and 6‐31G for other atoms). The HOMOs (highest occupied molecular orbitals) of 1–3 are composed of d(Ir) and π(phenyl), while those of 4 and 5 are contributed by d(Ir) and π(carbene). The LUMOs (lowest unoccupied molecular orbitals) of 1, 2, 4, and 5 are localized on carbene, but that of 3 is localized on acac. The calculated lowest‐lying absorptions with TD‐DFT method based on Perdew‐Burke‐Erzenrhof (PBE) functional of 1 (310 nm), 2 (332 nm), and 3 (347 nm) have ML~carbene~CT/IL~phenyl→carbene~CT (MLCT = metal‐to‐ligand charge transfer; ILCT = intraligand charge transfer) transition characters, whereas those of 4 (385 nm) and 5 (389 nm) are assigned to ML~carbene~CT/IL~carbene→carbene~CT transitions. The phosphorescences calculated by TD‐DFT method with PBE0 functional of 1 (386 nm) and 2 (388 nm) originate from ^3^ML~carbene~CT/^3^IL~phenyl→carbene~CT excited states, but those of 4 (575 nm) and 5 (578 nm) come from ^3^ML~carbene~CT/^3^IL~carbene→carbene~CT excited states. The calculated results showed that the carbene and phenyl groups act as two independent chromophores in transition processes. Compared with 1 and 2, the absorptions of 4 and 5 are red‐shifted by increasing the effective π‐conjugation groups near the C~carbene~ atom. We predicated that (pmb)~2~Ir(acac) is nonemissive, because the LUMO of 3 is contributed by the nonemissive acac ligand. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010