Magnetic and Luminescent Dual Responses of Photochromic Hexaazamacrocyclic Lanthanide Complexes

Abstract

Herein, hexaazamacrocyclic ligand LN6 was employed to construct a series of photochromic rare-earth complexes, [Ln(LN6)(NO3)2](BPh4) [1-Ln, Ln = Dy, Tb, Eu, Gd, Y; LN6 = (3E,5E,10E,12E)-3,6,10,13-tetraaza-1,8(2,6)-dipyridinacyclotetradecaphane-3,5,10,12-tetraene]. The behavior of photogenerated radicals of hexaazamacrocyclic ligands was revealed for the first time. Upon 365 nm light irradiation, complexes 1-Ln exhibit photochromic behavior induced by photogenerated radicals according to EPR and UV–vis analyses. Static and dynamic magnetic studies of 1-Dy and irradiated product 1-Dy* indicate weak ferromagnetic interactions among DyIII ions and photogenerated LN6 radicals, as well as slow magnetization relaxation behavior under a 2 kOe applied field. Further fitting analyses show that the magnetization relaxation in 1-Dy* is markedly different from 1-Dy. Time-dependent fluorescence measurements reveal the characteristic luminescence quenching dynamics of lanthanide in the photochromic process. Especially for irradiated product 1-Eu*, the luminescence is almost completely quenched within 5 min with a quenching efficiency of 98.4%. The results reported here provide a prospect for the design of radical-induced photochromic lanthanide single-molecule magnets and will promote the further development of multiresponsive photomagnetic materials.

Lanthanide Complexes with a Potential Docking Spot: Structure and Magnetism

“…Complexes (1) , (3) , (4) , and (5) were all lower than the theoretical saturation value (10, 18, 20, and 18 μ B , respectively), while complex (2) was higher than the theoretical saturation value of the Dy­(III) ion (20 μ B ). The M and H / T curves of complex (1) tend to be saturated at different temperatures, which is consistent with the magnetization of Ising-like Dy­(III) ion with ground-coupled pole m J at high magnetic fields, and these magnetic dynamics may be due to the anisotropy and low excited states, and the existence of SMM properties is also revealed. , However, the M and H / T curves of complexes (2–5) do not overlap at different temperatures, implying the existence of low excited states caused by crystal field splitting and/or magnetic coupling. − …”

Lanthanide–radical single-molecule magnets: current status and future challenges

“…, 2,4,6-tri(4-pyridyl)-1,3,5-triazine and hexaazamacyclic ligands) as guests or chelating ligands is helpful to construct magneto-optical multi-switches with photochromic properties. 80 When employing organic radicals with magnetic bistability ( i.e. , dithiadiazolyl radicals 81 ), we can exploit novel systems that exhibit a hysteretic response to various external stimuli.…”

Multifunctionality of luminescent molecular nanomagnets based on lanthanide complexes

“…A few research groups have addressed this challenge using luminescent Ln-SMMs. 129,[254][255][256][257][258] They mainly explored a strategy that relies on the incorporation of photo-responsive organic components into the system, which, through photo-chemical reactions, causes structural changes that affect both luminescence and magnetic properties. Wang et al reported a family of coordination-chain-based supramolecular compounds, [Ln III 3 (H-HEDP) 3 (H 2 -HEDP) 3 ]Á2(H 3 -TPT)Á(H 4 -HEDP)Á 10H 2 O (Ln = Dy, Gd, Y; HEDP = hydroxyethylidene diphosphonate; TPT = 2,4,6-tri(4-pyridyl)-1,3,5-triazine), that exhibit reversible roomtemperature photochromism (both in absorption and emission) and photomagnetism (Fig.…”