An observation of back energy transfer in complex Tb(III) with 2-naphthoate in methanol

Abstract

Nanosecond transient absorption measurements have been conducted on lanthanide complexes (Ln 3+=Eu, Gd, Tb) with 2-naphthoate (2-NA) in methanol. The excitation was carried out in the ligand centered (LC) band at 300 nm ( 1ππ→ 1ππ* of 2-NA) and the transient absorption spectra of 2-NA in the region of 390–460 nm (T 1→T n ) were obtained. The transient state decays in 7.5 and 9.1 μs for Gd and Tb, respectively, and faster than ns time scale for Eu. Only the luminescence of Tb(2-NA) 3 from 5D 4→ 7F 6−0 of Tb 3+ was quenched by O 2. Because of the intrinsically long life time of the 5D 4 excited state and the small energy gap (∼300 cm −1) between the 5D 4 level of Tb 3+ and the 3ππ* of 2-NA, back energy transfer is activated. Thus, O 2 quenching of Tb 3+ luminescence in Tb(2-NA) 3, exhibits a rapid 3ππ* ↔ 5D 4 pre-equilibrium, and does not take place by the interaction of O 2 with the excited Tb 3+ ions, but reflects the O 2 quenching of the 3ππ* of 2-NA bound to the lanthanide ion.