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 excitedstate lifetime of 2.2 mu s 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(2phenylpyridine)(4,4 '-tert-butyl-2,2 '-bipyridine)]PF6.