A structure property relationship study of neutral heteroleptic (1 and 2, [Ir(CAN),((LX)-X-Lambda)]) and homoleptic (3 and 4, fac-[Ir((CN)-N-Lambda)3])" Ir(III) complexes (where (LX)-X-Lambda = anionic 2,2,6,6-tettamethylheptane-3,5-diona-to-kO(3),kO(6) (thd) and 'CAN = a cyclonietalating ligand bearing a-pentafluorosulfanyl (-SF5) electron-withdrawing group (EWG) at the C-4 (HL1) and C-3 (HL2) positions of the phenyl,moiety) is preSented. These. complexes have been fully structurally characterzed, Including by single-crystal X-ray diffraction, and their,electrochemical and optical properties have also been extensively studied. While complexes, 1 ([Ir(L,1)(2)(thd)), 3 (II-(L1)(3)), and 4 (Ir(L2)(3)) exhibit, irreversible first reduction waves based on,the,pentafluorosulfanyl substituent in the range of 1.71 to 1:88 V (vs SCE), omplex 2 ([Ir(L2)(2)(thd)]) exhibits a quasi-reversible pyridineeN,based first reduction wave that is anodically shifted at -138 V. The metal + (CN)-N-Lambda ligand oxidation waves are all quasi-reversible in the range of 1.08-1.54 V (vs SCE). The optical gap, determined from the:lowest energy absorption maxima, decreases from 4 to 2 to 3 to 1 and this trend is consistent with the Hammett behavior =(sigma(m)/sigma(p)-with, respect to the metal carbon bond) of the -SF5 EWG. In degassed aCetonitrile, for complexes 2-4, introduction of the SF5 group produced a blue-shifted emission (lambda(em) 484-506 mu) in comparison to, reference complexes [Ir(ppy)2(aCac)] (R1, where acac = acetylacetonato) (lambda(em) 528 rim in MeCN),[Ir(CF3-ppy) (acac)] (R3, where CF3-ppyH = 2-(4-(trifluoromethyl)phenyl)pyridine) (ilem,52:2 nrn in DCM), and [Ir(CF5-ppy)3] (R8) (lambda(em), i; 507 nm in MeCN). The emission of complex 1, in contrast, was modestly red shifted 1(.1, 534 nm): Complexes 2 and 4, where the -SF5 EWG is substituted para to the Ir-C-C Lambda N bond, are efficient phosphorescent emitters, with high photoluminescence quantum yieldS (Phi(PL) = 58-79% in degassed MeCN solution)-and microsecond emission lifetimes-(tau(epsilon) = 1.35-3.02 mu s). Theoretical and experimental observations point toward excited states that are prineipally ligand centered :((LC)-L-3) in nature, but witha minor metal-to-ligand charge-transfer ((MLCT)-M-3) transition comptment, as a function of the regiOchemistry of the pentafluorosulfanyl group. The (LC)-L-3 character is predominant over the mixed (CT)-C-3 character for complexes 1, 2, and 4, while in complex 3, there is exclusive (LC)-L-3 character as demonstrated by unrestricted density functional theory (DTI') calculations. The short emission lifetimes and reasonable On values in doped thin film (5 wt % in PMMA), particularly for 4, suggest that these neutral complexes would be attractive candidate emitters in organic light-emitting diodes.