Jean-Claude Bunzli - Influence of charge-transfer states on the Eu(III) luminescence in mononuclear triple helical complexes with tridentate aromatic ligands

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  Petoud,S., Bunzli,J.C.G., Glanzman,T., Piguet,C., Xiang,Q.,   Thummel,R.P. Journal of Luminescence  1999 82 (1) 69-79

  Abstract: The photophysical properties of a   series of mononuclear Eu-containing 1 : 1 nitrate complexes and 1   : 3 triple-helical complexes with terpyridine, [EU(tpy)(3)](3+),   and 2,6-bis(1'-methylbenzimidazol-2'-yl)pyridine   [EU(L-1)(3)](3+), are investigated with the aim of unravelling   the respective influence of the ligand-to-metal charge-transfer   state (LMCT) and of pi-pi interactions between the ligand strands   in the large quenching of the metal-centred luminescence   sustained by the [Eu(L-1)(3)](3+) complexes, as compared to the   nitrate complexes with the same ligand. Both metal-centred and   ligand-centred luminescence quantum yield and lifetimes are   investigated. The energy of the LMCT state is estimated from the   difference measured by cyclic voltammetry between the half-peak   potentials of the oxidation of the ligand and of the reduction of   Eu-III. It is found that the energy of the LMCT state drops   considerably in the 1 : 3 complexes with respect to the 1 : 1   compounds, as a result of the cage-like arrangement of the three   ligand strands, and that it is the main factor responsible for   the luminescence quenching in [EU(L-1)(3)](3+). Other factors,   such as pi-pi interactions play a minor role only. (C) 1999   Elsevier Science B.V. All rights reserved

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