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Nona-Coordinated Chiral Eu(III) Complexes with Stereoselective Ligand–Ligand Noncovalent Interactions for Enhanced Circularly Polarized Luminescence

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journal contribution
posted on 18.06.2012, 00:00 by Takashi Harada, Hiroyuki Tsumatori, Katsura Nishiyama, Junpei Yuasa, Yasuchika Hasegawa, Tsuyoshi Kawai
Circularly polarized luminescence (CPL) of chiral Eu­(III) complexes with nona- and octa-coordinated structures, [Eu­(R/S-iPr-Pybox)­(D-facam)3] (1-R/1-S; R/S-iPr-Pybox, 2,6-bis­(4R/4S-isopropyl-2-oxazolin-2-yl)­pyridine; D-facam, 3-trifluoroacetyl-d-camphor), [Eu­(S,S-Me-Ph-Pybox)­(D-facam)3] (2-SS; S,S-Me-Ph-Pybox, 2,6-bis­(4S-methyl-5S-phenyl-2-oxazolin-2-yl)­pyridine), and [Eu­(Phen)­(D-facam)3] (3; Phen, 1,10-phenanthroline) are reported, and their structural features are discussed on the basis of X-ray crystallographic analyses. These chiral Eu­(III) complexes showed relatively intense photoluminescence due to their 5D07F1 (magnetic-dipole) and 5D07F2 (electric-dipole) transition. The dissymmetry factors of CPL (gCPL) at the former band of 1-R and 1-S were as large as −1.0 and −0.8, respectively, while the gCPL of 3 at the 5D07F1 transition was relatively small (gCPL = −0.46). X-ray crystallographic data indicated specific ligand–ligand hydrogen bonding in these compounds which was expected to stabilize their chiral structures even in solution phase. CPL properties of 1-R and 1-S were discussed in terms of transition nature of lanthanide luminescence.