Efficient green-blue-light-emitting cationic iridium complex for light-emitting electrochemical cells.

A highly luminescent novel cationic iridium complex [iridium bis(2-phenylpyridine)(4,4'-(dimethylamino)-2,2'-bipyridine)]PF6 was synthesized and characterized using NMR, UV-visible absorption, and emission spectroscopy and electrochemical methods. This complex displays intense photoluminescence maxima in the green-blue region of the visible spectrum and exhibits unprecedented phosphorescence quantum yields, 80 +/- 10% with an excited-state lifetime of 2.2 mus in a dichloromethane solution at 298 K. Single-layer light-emitting electrochemical cells with the charged complex as conducting and electroluminescent material sandwiched between indium-tin oxide and Ag electrodes were fabricated, which emit green-blue light with an onset voltage as low as 2.5 V. Density functional theory calculations were performed to provide insight into the electronic structure of the [iridium bis(2-phenylpyridine)(4,4'-(dimethylamino)-2,2'-bipyridine)]PF6 complex, comparing these results with those obtained for [iridium bis(2-phenylpyridine)(4,4'-tert-butyl-2,2'-bipyridine)]PF6.

Density functional study of tetraphenolate and calix[4]arene complexes of early transition metals.

Density functional calculations have been performed on some calix[4]arenes complexes of early transition metals. Particular emphasis has been placed on the comparison of the main properties of these metal complexes with the analogous metal complexes based on four monodentate phenolate ligands to study the effect of the geometrical constraints imposed by the calixarenes framework on the electronic structure. The results show that the most stable geometry of titanium and molybdenum tetraphenolates is pseudotetrahedral (slightly flattened for molybdenum) and that the distortion to a square planar coordination requires, respectively, 52.0 and 21.5 kcal x mol(-1). However, a significant energy decrease is found when the four phenolate groups are bent in the same hemisphere, reproducing the calix[4]arene geometry. Such a coordination determines the energy decrease of the unoccupied metal d orbitals of sigma and pi symmetry, which leads to an increase of the electron-accepting properties of these metal fragments.