N, N ‐heterocyclic Ancillary Ligands for Enhanced Photoluminescence Quantum Yields of Orange/Red‐Emitting 1‐(4‐(Trifluoromethyl)phenyl)isoquinoline‐Based Iridium (III) Complexes

Four new cationic iridium (III) complexes: [(cf 3 piq) 2 Ir(pzpy)] + PF 6 − ( Ir1 ), [(cf 3 piq) 2 Ir(pzpyz)] + PF 6 − ( Ir2 ), [(cf 3 piq) 2 Ir(impy)] + PF 6 − ( Ir3 ), and [(cf 3 piq) 2 Ir(impyz)] + PF 6 − ( Ir4 ) (where cf 3 piq=1‐(4‐(trifluoromethyl)phenyl)isoquinoline, pzpy=2‐(1H‐pyrazol‐3‐yl)pyridine, pzpyz=2‐(1H‐pyrazol‐3‐yl)pyrazine, impy=2‐(1H‐imidazol‐2‐yl)pyridine, and impyz=2‐(1H‐imidazol‐2‐yl)pyrazine) have been synthesized and fully characterized. The single crystal structure of Ir3 has been determined by X‐ray diffraction, and confirmed to have two hydrogen bonds (C14−H14⋅⋅⋅N2 and C57−H57⋅⋅⋅N9) and one intermolecular π‐π stacking interaction. The UV‐vis absorption, photoluminescence, and electrochemistry properties of all complexes have been studied. These complexes emit orange‐red photoluminescence with quantum yields of 28–46 % and excited state lifetimes of 0.48‐0.65 μs in CH 2 Cl 2 solution at room temperature. Based on the DFT calculations, we concluded that their emission originated predominantly from a hybrid 3 MLCT/ 3 ILCT excited state.