Green to red-emitting neutral iridium complexes with phenyl-indazole type cyclometalating ligand: Synthesis, photophysical properties and DFT calculations

• A series of phenyl-indazole-based iridium(III) complexes have been synthesized and characterized. • The photophysical properties were studied by spectroscopic methods and were rationalized by TD-DFT caculations. • All the complexes show green to red phosphorescence in CH 2 Cl 2 solution. A series of new heteroleptic iridium(III) complexes of the form Ir(C^N) 2 (N^O), Ir(2-hpiz) 2 (pic) ( Ir1 ), Ir(2-hpiz) 2 (pyzc) ( Ir2 ), Ir(2-hpiz) 2 (bop) ( Ir3 ), Ir(2-hpiz) 2 (btp) ( Ir4 ), Ir(4-fpiz) 2 (pic)( Ir5 ), Ir(4-fpiz) 2 (pyzc) ( Ir6 ), Ir(4-fpiz) 2 (bop)( Ir7 ), Ir(4-fpiz) 2 (btp) ( Ir8 ), Ir(2-bipiz) 2 (pic) ( Ir9 ), Ir(2-bipiz) 2 (pyzc) ( Ir10 ), Ir(2-bipiz) 2 (bop) ( Ir11 ) and Ir(2-bipiz) 2 (btp) ( Ir12 ) (2-hpiz = 2-phenyl-2H-indazole, 4-fpiz = 2-(4-fluorophenyl)–2H-indazole, 2-bipiz = 2-([1,1′-biphenyl]-4-yl)–2H-indazole, Hpic = 2-picolinic acid, Hpyzc = 2-pyrazinecarboxylic acid, Hbop = 2-(benzo[ d ]oxazol-2-yl)phenol, Hbtp = 2-(benzo[ d ]thiazol-2-yl)phenol)), have been synthesized and fully characterized. The crystal structures of Ir1 , Ir5 and Ir8 have been determined by X-ray analysis and been confirmed to have intermolecular π − π interactions and intermolecular/intramolecular C H⋯π interactions in the crystal packings. All complexes are green–red emissive with absolute quantum yields of 0.5–2.9 % and lifetimes of 0.21–0.62 μs in solution at room temperature. The relationship between the structures and photophysical properties of complexes Ir1 - Ir12 are considered, and the DFT calculations have been used to further support the deduction. Theoretical calculations reveal that the emission of these complexes can arise from either Ir-C^N → C^N or Ir-C^N N^O → C^N charge transfer, depending on the local environment of these complexes.