A europium complex with enhanced long-wavelength sensitized luminescent properties

Abstract

We report a new complex Eu(tta)₃·bpt (tta = thenoyltrifluoroacetonate; bpt = 2-(N,N-di-ethylanilin-4-yl)-4,6-bis(pyrazol-1-yl)-1,3,5-triazine) with excellent long-wavelength sensitized luminescent properties, in which four hydrogen atoms replace the methyl groups at the 3,3′- and 5,5′-positions of the pyrazolyl rings in a previously reported complex Eu(tta)₃·dpbt. Upon visible-light excitation (λ_ex = 410 nm) at 295 K, the quantum yield (Φ^Ln_L) of Eu³⁺ luminescence of Eu(tta)₃·bpt is higher by 23% than that of Eu(tta)₃·dpbt. Different from the case of Eu(tta)₃·dpbt, Φ^Ln_L of Eu(tta)₃·bpt increases linearly with the decrease in temperature. Because of the different coordination environments around Eu³⁺ ion, the fine structure of the hypersensitive ⁵D₀ → ⁷F₂ emission band of Eu(tta)₃·bpt is quite different from that of Eu(tta)₃·dpbt, with the strongest emission line locating at 620 nm rather than 613 nm where the strongest emission line of Eu(tta)₃·dpbt appears. The excitation window of Eu(tta)₃·bpt is much broader than that of Eu(tta)₃·dpbt with a red edge extending up to 450 nm in a dilute toluene soluton (1.0 × 10⁻⁵ M) and 500 nm in a toluene solution (1.0 × 10⁻² M). Eu(tta)₃·bpt also exhibits excellent two-photon-excitation luminescent properties.