Synthesis and spectral properties of 2-pyridyl N-methyl-2-imidazolyl ketone complexes of iridium(III)

Abstract

Complexes of iridium(III) with 2-pyridyl N-methyl-2-imidazolyl ketone (pik), K[Ir(pik)Cl 4] ( 1) and [Ir(pik)(phen)Cl 2] + ( 2), have been successfully prepared and characterized. Both complexes show high intensity bands in the UV region, and these are assigned to spin-allowed π–π* transitions. The medium-intensity absorption band profile in the lower energy region can be explained by spin-allowed CT and, perhaps, convoluted with the weaker n–π* transitions. At low temperature (77 K), complex 2 in EtOH/MeOH (4:1, v/v) shows a structural emission with a single vibrational progression of 1090 cm −1. The luminescence lifetime measured at 474 nm ( ν max, 0–0′ band) emission is 9.7 μs and the emission energy becomes smaller while the polarity of solvent increases. Electrochemical data have also been obtained for complex 2 in MeCN. There were two reduction peaks observed for the complex and both are one-electron charge transfer process. Through examination of influence on reduction potential in the presence of phenol, the redox orbital involved in each of the reduction processes is assigned to be the π* orbital localized at the carbonyl fragment of pik. On the basis of analysis of the luminescence and electrochemical data, the emission of complex 2 is assigned as 3MLCT, with a charge transfer to the accepting pik π* orbital.