Solvent-dependent luminescence of eight-coordinated Eu(III) complexes with bidentate phosphine oxide

Solvent-dependent luminescence of Eu(III) complexes composed of oxo-linked bidentate phosphine oxide ligands, 4,5-bis(diphenylphosphoryl)-9,9-dimethylxanthene (xantpo), 4,5-bis(di-tert-butylphosphoryl)-9,9-dimethylxanthene (tBu-xantpo) and low-vibrational frequency hexafluoroacetylacetonato (hfa) ligands is reported. The Eu(III) complexes, Eu(hfa)2(xantpo)2 and Eu(hfa)3(tBu-xantpo), exhibit eight-coordinated square antiprism and trigonal dodecahedron structure, respectively. Their emission quantum yield, emission lifetime, and radiative and non-radiative rate constant are characterized using acetone, acetone-d6, toluene, chloroform, and DMF. The relationship between photophysical properties and coordination structures of eight-coordinated Eu(III) complexes is discussed for the first time.