Redox-Modulations of Photophysical and Single-molecule Magnet Properties in Ytterbium Complexes Involving Extended-TTF Triads

Abstract

The reaction between the 2,2’-benzene-1,4-diylbis(6-hydroxy-4,7-di-tert-butyl-1,3-benzodithiol-2-ylium-5-olate triad (H2SQ) and the metallo-precursor [Yb(hfac)3]⋅2H2O led to the formation of a dinuclear coordination complex of formula [Yb2(hfac)6(H2SQ)]⋅0.5CH2Cl2 (H2SQ-Yb). After chemical oxidation of H2SQ in 2,2’-cyclohexa-2,5-diene-1,4-diylidenebis(4,7-di-tert-butyl-1,3-benzodithiole-5,6-dione (Q), the latter triad reacted with the [Yb(hfac)3]⋅2H2O precursor to give the dinuclear complex of formula [Yb2(hfac)6(Q)] (Q-Yb). Both dinuclear compounds have been characterized by X-ray diffraction, DFT optimized structure and electronic absorption spectra. They behaved as field-induced Single-Molecule Magnets (SMMs) nevertheless the chemical oxidation of the semiquinone to quinone moieties accelerated by a factor of five the relaxation time of the magnetization of Q-Yb compared to the one for H2SQ-Yb. The H2SQ triad efficiently sensitized the YbIII luminescence while the chemical oxidation of H2SQ into Q induced strong modification of the absorption properties and thus a quenching of the YbIII luminescence for Q-Yb. In other words, both magnetic modulation and luminescence quenching are reached by the oxidation of the protonated semiquinone into quinone.

Remote Control of Near Infrared Emission with Lanthanide Complexes

“…Beside the above examples, F. Pointillart et al . recently published a new original Yb(III) based NIR switch that can be operated by chemical oxidation [57] . Their strategy was based on an extended tetrathiafulvalene (TTF) ligand, widely known to undergo reversible redox processes, and two semiquinone moieties to coordinate two Yb(III) ions (Figure 19).…”

“… (top left) Chemical structure, (top right) emission spectrum evolution upon oxidation at room temperature in CH 2 Cl 2 (C=4 × 10 −5 M, λ ex =600 nm). (bottom) Proposed sensitization and quenching mechanism in the neutral and oxidized form, respectively (ET: energy transfer, S: SOMO, L: LUMO, H: HOMO, BET: back energy transfer) [57] . Reproduced with permission.…”

Annulation of a 1,3-dithiole ring to a sterically hindered o-quinone core. Novel ditopic redox-active ligands

“…o-Dioxolene redox-active species bearing additional functions are regarded as promising ligands for the synthesis of metallocomplexes exhibiting unusual magnetic, photovoltaic or luminescent properties. Thus, previously reported binuclear rare-earth metal complexes with redox-active triads such as o-quinonetetrathiafulvalene-o-quinone and o-quinone-(p-phenylene extended tetrathiafulvalene)-o-quinone were found to display switching SMM [4][5][6][7] or unique luminescent properties [8].…”

Field-Induced Single-Molecule Magnets of Dysprosium Involving Quinone Derivatives

“…Organic radical semiquinone form is often associated to transition metal to design complexes displaying chemical and physical properties, such as valence tautomerism [4], photo-and thermo-mechanical effects [5]. o-Quinone-like dioxolenes in quinone, semiquinone [6][7][8][9] or catecholate [10][11][12] oxidation states have been associated with lanthanide ions to generate luminescence [13] and single-molecule magnet (SMM) behavior [14][15][16], as well as magnetic or optical switching [17][18][19][20]. It is worth mentioning that SMM behavior is associated to the observation of slow magnetic relaxation at the molecular scale, leading to the opening of a hysteresis loop at low temperature.…”