Excitation and deexcitation processes of Eu(III) benzo-15-crown-5 complex studied on comparing with its first coordination sphere

Abstract

The coordination sphere and the deexcitation mechanism of the Eu(III) benzo-15-crown-5 complex, Eu(B15C5), were studied with references of the Eu(III) complexes with a similar coordination sphere; the dibenzo-18-crown-6 complex, Eu 3(B 218C6) 2, and the cryptand[2.2.1] complex, Eu([2.2.1]). NMR spectroscopy reveals that the Eu(B15C5) complex is quite stable in acetonitrile solution whereas only 40% of the Eu(III) ion forms the complex in the equimolar Eu(NO 3) 3 and B 218C6 acetonitrile solution. The coordination sphere of the Eu(III) complexes in acetonitrile solutions were also discussed by the degenerate 7F 0→ 5D 0 transition energy levels. The Eu(B15C5) have a negative shift compared with the europium(III) nitrate in acetonitrile and it is explained by the coordination of both nitrate ions and the crown ether ligand. Energy transfer from the n–π* excited state located in the catechol structure to the central europium ion was first observed as the sensitized luminescence of 5D 0→ 7F J. The excited state lifetime of the Eu(B15C5) complex was first determined as 201 μs in the present study.