Thermally Induced Defluorination during a mer to fac Transformation of a Blue-Green Phosphorescent Cyclometalated Iridium(III) Complex

The new homoleptic tris-cyclometalated [Ir­(C∧N)3] complexes mer-8, fac-8, and fac-9 incorporating γ-carboline ligands are reported. Reaction of 3-(2,4-difluorophenyl)-5-(2-ethylhexyl)-pyrido­[4,3-b]­indole 6 with iridium­(III) chloride under standard cyclometalating conditions gave the homoleptic complex mer-8 in 63% yield. The X-ray crystal structure of mer-8 is described. The Ir–C and Ir–N bonds show the expected bond length alternations for the differing trans influence of phenyl and pyridyl ligands. mer-8 quantitatively isomerized to fac-8 upon irradiation with UV light. However, heating mer-8 at 290 °C in glycerol led to an unusual regioselective loss of one fluorine atom from each of the ligands, yielding fac-9 in 58% yield. fac-8 is thermally very stable: no decomposition was observed when fac-8 was heated in glycerol at 290 °C for 48 h. The γ-carboline system of fac-8 enhances thermal stability compared to the pyridyl analogue fac-Ir­(46dfppy)3 10, which decomposes extensively upon being heated in glycerol at 290 °C for 2 h. Complexes mer-8, fac-8, and fac-9 are emitters of blue-green light (λmaxem = 477, 476, and 494 nm, respectively). The triplet lifetimes for fac-8 and fac-9 are ∼4.5 μs at room temperature; solution ΦPL values are 0.31 and 0.22, respectively.