Luminescence of Nd3+ complexes with some asymmetric ligands in organic solutions

A novel Nd3+ complex, Nd(POA-D)(3), with asymmetric ligands (POA: perfluorooctanoylacetic acid), was synthesized in order to enhance the transition probability in its f-f transition by reducing symmetry of the ligand field around Nd3+ This complex gives the 2.5 times higher oscillator strength of the hypersensitive transition in methanol-d(4) than the corresponding symmetrical complex, Nd(POM-D)(3) (POM: bisperfluorooctanoylmethane). The Stark splitting of the emitting level of Nd(POA-D)(3) was observed and the Judd-Ofelt analysis gave a large Ohm(2) value, clearly showing the asymmetric environment around Nd3+. C-13 NMR analysis, molecular orbital and molecular mechanics calculations and EXAFS analysis suggest that the asymmetric environment achieved in Nd(POA-D)(3) is ascribed mainly to the asymmetric distribution of electrons on the coordinating O atoms. The higher absorption coefficient of Nd(POA-D)(3) leads to 1.86 times stronger emission than Nd(POM-D)(3) when measured at the common concentration and conditions. It is stressed that introduction of asymmetric ligands is a promising way for promoting emission of Nd3+ in solutions when coupled with replacement of C-H bonds with C-D and C-F in the ligands. (C) 1998 Elsevier Science B.V. All rights reserved.