Electrogenerated chemiluminescence from newly synthesized α-diimine-ligated heteroleptic iridium(III) complexes

Abstract A series of α-diimine ligands including alkyl-, bromo-, silyl- or silylethynyl-substituted 2,2′-bipyridines (bpy) for auxiliary neutral ligands on iridium(III) complexes were prepared. Using those ligands, α-diimine-ligated heteroleptic iridium(III) complexes with 2,4-difluorophenylpyridine as the primary cyclometalating ligand were synthesized by a conventional two-step synthesis followed by the anion exchange reaction using NH 4 PF 6 . The physical features such as spectroscopic, electrochemical and electrogenerated chemiluminescence (ECL) properties for the newly prepared complexes were characterized and compared to that of well-known tris(2,2′-bipyridine)rutheniun(II), [Ru(bpy) 3 ](PF 6 ) 2 , and previously reported (2,2′-bipyridine)bis[2-(2,4-difluorophenyl)pyridine]iridium(III), [Ir(dfppy) 2 (bpy)](PF 6 ) ( 2 ), complex as the reference. All the iridium(III) complexes synthesized showed strong green emission and higher ECL intensities compared to the well-known Ru(bpy) 3 2 + . The iridium(III) complexes containing α-diimine ligands with electron donating dimethyl, trimethylsilyl, and triphenylsilyl groups on bpy showed the increased ECL intensities compared to that of the reference ( 2 ). Among those iridium(III) complexes, the complex ligated with 5-(trimethylsilyl)-2,2′-bipyridine and 2,4-difluorophenylpyridine showed the most intense ECL responses and exhibited ECL intensities as high as 7.6 times greater than that of the reference ( 2 ). However, the iridium(III) complexes containing α-diimine ligands containing more conjugated carbon-carbon triple bond showed the decreased ECL intensities compared to that of the complexes with no triple bond conjugation.