LAUSR

A series of charge-neutral bis-tridentate Ir(III) complexes (1, 3 and 4) were prepared via employing three distinctive tridentate pro-chelates, i.e., (pzptBphFO)H2, [(phpyim)H2·(PF6)] and [(pimb)H3·(PF6)2], which possess one dianionic, tridentate pzptBphFO, together with a second monoanionic chelate, namely: (pzptBphFO)H, phpyim, and pimb, while complex 2 with monoanionic chelate (pzptBphFO)Me was obtained by methylation of (pzptBphFO)H of 1 in basic media. Moreover, the closely related cationic complexes 5 - 7 were obtained by further methylation of remaining pyrazolate unit of neutral complexes 2 - 4, followed by anion metatheses. All of these Ir(III) metal complexes showed broadened emission profile with an onset at ∽450 nm, a result of enlarged ligand-centered ππ* transition gap, but with distinct efficiencies ranging from 0.8% to nearly unitary in CH2Cl2 solution at RT. Comprehensive spectroscopic as well as computational approaches were executed, providing a correlation for the emission efficiencies versus energy gaps between the metal-to-ligand charge transfer (MLCT)/ππ* emitting excited state and upper lying metal-centered dd quenching state. Furthermore, Ir(III) complexes 3 and 4 were selected as dopant emitters in fabrication of sky-blue phosphorescent OLEDs, affording max. external quantum efficiencies of 16.7% and 14.6% and with CIEx,y coordinates of (0.214, 0.454) and (0.191, 0.404) at current density of 102 cd/m2, respectively. Hence, this research highlights an inherent character of bis-tridentate Ir(III) complexes in achieving high phosphorescence quantum yield at molecular level.