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Sign Reversal of a Large Circularly Polarized Luminescence Signal by the Twisting Motion of a Bidentate Ligand

Sign Reversal of a Large Circularly Polarized Luminescence Signal by the Twisting Motion of a Bidentate Ligand

Junpei Yuasa, Hiroshi Ueno, Tsuyoshi Kawai

Chemistry. 2014 Jul 7;20(28):8621-7.

PMID: 24958164

Abstract:

This work demonstrates sign reversal of large circularly polarized luminescence (CPL) signal based on the hinge-like twisting motion of a bidentate ligand, 3,3-bis(diphenylphosphoryl)-2,2-bipyridine (BIPYPO), in a cis-trans isomerization of chiral europium(III) complexes. X-ray diffraction analysis revealed that twisting motion of BIPYPO provides s-cis and s-trans geometries of a chiral Eu(III) complex containing either tris[3-(trifluoromethylhydroxymethylene)-(+)-camphorate] (D-1) or tris[3-(heptafluoropropylhydroxymethylene)-(+)-camphorate] (D-2). The s-cis Eu(III) complexes show eight-coordinate geometry around the Eu(III) ion, in which the chelate between the phosphoryl oxygen and the Eu(III) ion forces the s-cis geometry of BIPYPO. In contrast, the phosphorus-nitrogen interaction provides a conformational lock for the s-trans geometry of the BIPYPO ligand, inducing a quasi-seven-coordinate Eu(III) complex. The difference in coordination geometry causes the sign change of the CPL signals between the s-cis and s-trans isomers, whereby the s-cis and s-trans isomers of Eu(III) complexes exhibit the positive and negative CPL signals, respectively, for the (5) D0 →(7) F1 transition. The proportion of the s-trans-D-1 against s-cis-D-1 increases upon changing the solvent from [D3 ]acetonitrile to [D6 ]acetone, inducing a sign change of the CPL signals. The complexes D-1 and D-2 show a biexponential decay with two different lifetimes, suggesting two emitting species, that is, the s-cis and s-trans isomers of Eu(III) complexes. In both cases, the proportions of the longer lifetime components (τ1 ) decrease and instead the shorter lifetime components (τ2 ) increase upon changing the solvent from [D3 ]acetonitrile to [D6 ]acetone.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
IAR42710	Europium tris[3-(heptafluoropropylhydroxymethylene)-(−)-camphorate]			Price

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