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

Abstract 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-d4 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 Ω2 value, clearly showing the asymmetric environment around Nd3+. 13C 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.

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