SYNTHESIS AND HIGH-RESOLUTION OPTICAL SPECTROSCOPY OF BIS(2-(2-THIENYL)PYRIDINATO-C3,N') (2,2'-BIPYRIDINE)IRIDIUM(III)

The synthesis and high-resolution absorption and luminescence spectra at cryogenic temperatures of [Ir(thpy)2bpy]+ (thpyH = 2-(2-thienyl)pyridine, bpy = 2,2'-bipyridine) are reported. In the crystalline host lattices [Rh(ppy)2bpy]PF6 and [Ir(ppy)2bpy]PF6 (ppyH = 2-phenylpyridine) the lowest excited states around 18 900 cm-1 correspond to spin-forbidden 3pi-pi* transitions on the thpy-, whereas the next higher excited state is assigned to an Ir --> bpy charge-transfer transition at 21 700 cm-1. This metal to ligand charge-transfer (3MLCT) state is found to be strongly dependent on the surroundings. In liquid environments it can shift below the 3pi-pi* state, which remains at about the same energy. Evidence for a mixing of charge-transfer character into the 3pi-pi* excited states is provided by the measured oscillator strengths, the luminescence lifetimes, and the vibronic structure and by a comparison with the properties of analogous cyclometalated Rh3+ complexes.