M. Colombo, H. Guedel
Jul 1, 1993
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Inorganic Chemistry
Abstract
The synthesis and high-resolution absorption and luminescence spectra at cryogenic temperatures of [Ir(thpy)[sub 2]bpy][sup +](thpyH = 2-(2-thienyl)pyridine, bpy = 2, 2'-bipyridine) are reported. In the crystalline host lattices [Rh(ppy)[sub 2]bpy]-PF[sub 6] and [Ir(ppy)[sub 2]bpy]PF[sub 6](ppyH = 2-phenylpyridine) the lowest excited states around 18,900 cm[sup [minus]1] correspond to spin-forbidden [sup 3][pi]-[pi]* transitions on the thpy[minus], whereas the next higher excited state is assigned to an Ir [yields] bpy charge-transfer transition at 21,700 cm[sup [minus]1]. This metal to ligand charge-transfer ([sup 3]MLCT) state is found to be strongly dependent on the surroundings. In liquid environments it can shift below the [sup 3][pi]-[pi]* state, which remains at about the same energy. Evidence for a mixing of charge-transfer character into the [sup 3][pi]-[pi]* excited states is provided by the measured oscillator strengths, the luminescence lifetimes, the vibronic structure, and by a comparison with the properties of analogous cyclometalated Rh[sup 3+] complexes.