Cyclometalated iridium complexes synthesized by C-H activation enhances the emission intensity of the complexes (eg. complexes derived from iridium(2-phenylpyridine) precursor, but the same complex ( i.e. chelating ligands are same) prepared with pentamethylcyclopentadienyl iridium precursor shows very low or no fluorogenic property. What is the reason behind it?
possess a large ligand-field stabilization of iridium: high oxidation state, presence of 5d orbitals. and most importantly, a high ligand-field splitting energy due to the presence of two C-N ligands. Characterized by long-lived triplet excited state (τ ~μs) and strong spin orbit coupling (ζIr = 3909 cm-1)
A carbanion increases the the ligand field strength around the metal. This might raise the deactivating d-d state which in turn gives rise to a luminescent state.
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