title: OFF-ON-OFF Dual Emission at Visible and UV Wavelengths from Carbazole Functionalized β-Diketonate Europium(III) Complex.
abstract: This work demonstrates dual emission "OFF-ON-OFF" switching at visible and UV wavelengths of a carbazole functionalized β-diketone (LH) by a simple change of a europium(III) ion (Eu(3+)) concentration in the submicromolar concentration range. In the presence of 0.25 equiv of Eu(3+) (5 μM), LH forms a luminescent 4:1 complex ([Eu(3+)(L(-))4](-)) exhibiting dual emission at 357 and 613 nm resulting from the local excitation of the carbazole ring and ligand-sensitized luminescence from the Eu(3+)-β-diketonate unit, respectively. The 4:1 complex begins to convert into a 2:1 complex ([Eu(3+)(L(-))2](+)) via a 3:1 complex [Eu(3+)(L(-))3] above a molar ratio ([Eu(3+)]/[LH]) of 0.25, which provides the opportunity for binding of solvent methanol molecules to the vacant site of the Eu(3+) ion in the complex ([Eu(3+)(L(-))2(MeOH)n](+)). The OH oscillators of coordinated methanol molecules facilitate the nonradiative pathway of the Eu(3+) emission; hence the emission at 613 nm almost disappears above the 0.50 equivalent of Eu(3+) (11 μM), while the UV emission at 357 nm remains mostly constant over the whole concentration range.
authors.affiliation: Graduate School of Materials Science, Nara Institute of Science and Technology , 8916-5 Takayama, Ikoma, Nara 630-0192, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Imai
authors.affiliation: Graduate School of Materials Science, Nara Institute of Science and Technology , 8916-5 Takayama, Ikoma, Nara 630-0192, Japan.
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Kawai
authors.affiliation: Graduate School of Materials Science, Nara Institute of Science and Technology , 8916-5 Takayama, Ikoma, Nara 630-0192, Japan.|Precursory Research for Embryonic Science and Technology (PRESTO), Science and Technology Agency (JST), 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan.
authors.forename: Junpei
authors.initials: J
authors.lastname: Yuasa