Role of the Ancillary Ligand N,N-Dimethylaminoethanol in the Sensitization of Eu^III and Tb^III Luminescence in Dimeric β-Diketonates

Abstract

Two types of dimeric complexes [Ln2(hfa)6(mu2-O(CH2)2NHMe2)2] and [Ln(thd)2(mu2,eta2-O(CH2)2NMe2)]2 (Ln = YIII, EuIII, GdIII, TbIII, TmIII, LuIII; hfa- = hexafluoroacetylacetonato, thd- = dipivaloylmethanato) are obtained by reacting [Ln(hfa)3(H2O)2] and [Ln(thd)3], respectively, with N,N-dimethylaminoethanol in toluene and are fully characterized. X-ray single crystal analysis performed for the TbIII compounds confirms their dimeric structure. The coordination mode of N,N-dimethylaminoethanol depends on the nature of the beta-diketonate. In [Tb2(hfa)6(mu2-O(CH2)2NHMe2)2], eight-coordinate TbIII ions adopt distorted square antiprismatic coordination environments and are O-bridged by two zwitterionic N,N-dimethylaminoethanol ligands with a Tb1...Tb2 separation of 3.684(1) A. In [Tb(thd)2(mu2,eta2-O(CH2)2NMe2)]2, the N,N-dimethylaminoethanol acts as chelating-bridging O,N-donor anion and the TbIII ions are seven-coordinate; the Tb1...Tb1A separation amounts to 3.735(2) A within centrosymmetric dimers. The dimeric complexes are thermally stable up to 180 degrees C, as shown by thermogravimetric analysis, and their volatility is sufficient for quantitative sublimation under reduced pressure. The EuIII and TbIII dimers display metal-centered luminescence, particularly [Eu2(hfa)6(O(CH2)2NHMe2)2] (quantum yield Q(L)Ln = 58%) and [Tb(thd)2(O(CH2)2NMe2)]2 (32%). Consideration of energy migration paths within the dimers, based on the study of both pure and EuIII- or TbIII-doped (0.01-0.1 mol %) LuIII analogues, leads to the conclusion that both the beta-diketone and N,N-dimethylaminoethanol ligands contribute significantly to the sensitization process of the EuIII luminescence. The ancillary ligand increases considerably the luminescence of [Eu2(hfa)6(O(CH2)2NHMe2)2], compared to [Ln(hfa)3(H2O)2], through the formation of intra-ligand states while it is detrimental to TbIII luminescence in both beta-diketonates. Thin films of the most luminescent compound [Eu2(hfa)6(O(CH2)2NHMe2)2] obtained by vacuum sublimation display photophysical properties analogous to those of the solid-state sample, thus opening perspectives for applications in electroluminescent devices.

Brilliant Photoluminescence and Triboluminescence from Ternary Complexes of DyIII and TbIII with 3-Phenyl-4-propanoyl-5-isoxazolonate and a Bidentate Phosphine Oxide Coligand

“…15 The loss in emission quantum yield in the presence of ancillary ligands in Tb III complexes is known, and the reason is explained in our previous reports. 22,36 On the other hand, a slight increase in luminescence lifetime is noted, 795 ± 1 μs for 3 compared to 785 ± 1 μs for [Tb(PPI) 3 (H 2 O) 2 ], and might be due to minimization of concentration quenching. Indeed, the shortest Tb−Tb distance 41 the mechanism of sensitization in luminescent lanthanide complexes consists of three major steps: (i) absorption of ultraviolet/blue light that excites the ligand (antenna) to the excited singlet state ( 1 π−π*), (ii) energy migration via intersystem crossing from the singlet state to a triplet state ( 3 π−π*), and (iii) nonradiative energy transfer from the lowest triplet state to a resonant state of a coordinated Ln III ion, resulting a multiphonon relaxation and emission.…”

Seven‐Coordinate Luminophores: Brilliant Luminescence of Lanthanide Complexes with C3v Geometrical Structures

“…[4] Eliseeva and co-workers have also reported the dinuclear lanthanide complexes with six oxygen atoms and one nitrogen atom. [5] While seven-coordination may influence the orbit splitting of metals, multinuclear complexes have a difficulty for analyzing the physicochemical property in detail. Zuo and co-workers studied on seven-coordinate lanthanide porphyrinate and phthalocyaninate complexes with tripodal phosphine oxide ligand for single-molecule magnet.…”

New hetero-dilanthanide complexes containing Ln1(fod)3 and Ln2(fod)3 fragments (Ln=Pr–Nd; Nd–Sm; Eu–Tb and Ho–Er) linked by bis-diimine bridging ligand

“…The spectrum is complicated possibly due to fluorine atom transfer and easy splitting of CF 3 fragments as observed in the lanthanide complexes containing fluorinated β-diketone ligands [27]. Therefore, various peaks at mass distribution m/z = 923, 1083, 1099 including the most intense peak at m/z = 1241 in the mass spectrum could not be identified.…”