The first registration of a green liquid-phase chemiluminescence of the divalent Eu²⁺* ion in interaction of β-diketonate complexes Eu(acac)₃·H₂O, Eu(dpm)₃, Eu(fod)₃ and Eu(CH₃COO)₃·6H₂O with Buⁱ₂AlH in THF with the participation of oxygen

Abstract

The first liquid-phase green chemiluminescence (CL) of the divalent europium Eu 2+ * at the study of interactions in the systems EuL3•(Н2О)x-THF-Bu i 2AlH-O2 (L = acac, dpm, fod, and CH3COO; x = 0, 1, 6; Bu i = iso-C4H9) was discovered. The attack of Bu i 2AlH on the water of crystallization of complexes EuL3•(Н2О)x affords aluminoxane (Bu i 2Al)2O, hydrogen, and isobutane. The reaction of Bu i 2AlH and EuL3-moiety of the initial Eu 3+ complexes leads to the previously no synthesized divalent europium complexes EuL2•(THF)2, which were isolated and characterized by elemental and spectral analysis in the present work. In the reaction solutions, these complexes are associated in a bulky complexes with an excess of diisobutylaluminum hydride EuL2•(THF)2-Bu i 2AlH. The measured spectra of CL and photoluminescence (PL) of yellow-green reaction solutions in both cases consist of one broad band with λmax = 555±10 nm due to the emission of the electronexcited state of the Eu 2+ * ion (4f 6 5d 1 →4f 7 transition), a part of the bulky complex EuL2•(THF)2-Bu i 2AlH. The lifetime of the excited states, PL, and CL quantum yields of the Eu 2+* ion in the EuL2•(THF)2-Bu i 2AlH complexes were determined. A mechanism ("indirect CL") is proposed to explain the generation of the green CL. The primary emitter triplet-excited isobutyric aldehyde 3 Rշ C(H)=O* (Rշ = iso-C3H7) is formed in the disproportionation reaction of peroxyl radicalsintermediates of Bu i 2AlH oxidation by oxygen. The exited 3 Rշ C(H)=O* molecules transfer energy to Eu 2+ ion converting it into the eleсtronically exited state Eu 2+ *, which is then deactivated by emitting quanta of green light due to the 4f 6 5d 1 →4f 7 transition. It was found that for a divalent Eu 2+ unlike to trivalent Ln 3+ ions, replacement of the inorganic anion-ligand Cl -(complex EuCl2•(THF)2-Bu i 2AlH) with organic one L (complex EuL2•(THF)2-Bu i 2AlH) decreases the CL and PL intensity and leads to the green-shift of the luminescence maximum of Eu 2+* from the blue (λmax = 465 nm) to the green (λmax = 555 nm) region. The high brightness and duration of the CL, visible to the naked eye in the system Eu(fod)3-THF-Bu i 2AlH-O2, make it promising as a chemical source of green light.

The first example of fluorescence of the solid individual compounds of Eu2+ ion: EuCl2, EuI2, EuBr2

“…Eu 2+ FL could also be usefull to control the valence state of multimodal, oxidation‐responsive contrast agents for magnetic resonance imaging and photoacoustic imaging using differences in the properties between Eu 2+ and Eu 3+ oxidation states . Finally, electronically excited Eu 2+ ions emitting bright blue or green FL have recently been detected as emitters or enhancers in chemiluminescent systems during oxidation of organoaluminum compounds. Most studies on Eu 2+ FL have focused mainly on different Eu 2+ ‐doped solid matrices, containing from 0.01% to several per cent Eu (for example references and references therein).…”

Systematic Tuning of the Optical Properties of Discrete Complexes of EuII in Solution Using Counterions and Solvents

“…For example, optical imaging applications benefit from red-shifted light, and photoredox catalysis can be potentially tuned to access specific functional group reactivity with different wavelengths. There have been some studies of the optical behavior of Eu II in solution with luminescence across the visible-light spectrum: violet-blue, − green, − yellow, , and red. − These studies give some indication of how ligands can shift the emission of Eu II in solution. Similar trends between the ligand and emission are observed with other lanthanides. − However, there is a relative dearth of information about the luminescence properties of ternary discrete complexes in solution, which is important because many Eu II -containing complexes will be in equilibrium with counterions and solvents.…”