Heteroleptic Ir(iii) complexes containing both azolate chromophoric chelate and diphenylphosphinoaryl cyclometalates; Reactivities, electronic properties and applications

Abstract

The synthesis of a new family of octahedral Ir(III) complexes with dual cyclometalating phosphine chelates, namely: 1-(diphenylphosphino)naphthalene (dpnaH) and isoquinoline (dppiH), is reported. Two series of intermediate complexes, [Ir(dpna)(tht)₂Cl₂] (1), [Ir(dpna)₂(OAc)] (2), [Ir(dppiH)(dppi)Cl₂] (3) and [Ir(dppi)₂(OAc)] (4), which can be classified by the coexistence of either a pair of cis-chlorides or a single acetate chelate, were obtained from treatment of phosphine with [IrCl₃(tht)₃] (tht = tetrahydrothiophene). The in situ generated acetate complexes 2 and 4 could react with azolate chelates, namely: 5-(2-pyridyl)-3-trifluoromethyl pyrazole (fppzH) and 5-(1-isoquinolyl)-3-tert-butyl- 1,2,4-triazole (iqbtzH), to afford a new series of luminescent complexes [Ir(dpna)₂(fppz)] (5a and 5b), [Ir(dpna)₂(iqbtz)] (6a and 6b), [Ir(dppi)₂(fppz)] (7a) and [Ir(dppi)₂(iqbtz)] (8a). The phosphorescence lifetime (τ_obs) fell in the range of a few tens of μs, showing possession of excessive ligand-centered ππ* mixed in part with MLCT character. A density functional theory (DFT) study was also conducted in order to shed light on the origin of the transitions in the absorption and emission spectra and to predict emission energies for these complexes. Organic light emitting diodes (OLEDs) displaying bright orange emission and with maximum η_ext up to 17.1% were fabricated employing complexes 6a and 8a as the phosphorescent dopants.