Homochiral Dy2 single-molecule magnets with strong magneto-optical Faraday effects and strong third-harmonic generation

Abstract

Four pairs of homochiral Dy₂ complexes were directionally prepared using homochiral β-diketone ligands {D-Htfc/L-Htfc = (+)/(−)-3-trifluoroacetyl camphor, D-Hpfc/L-Hpfc = 3-(perfluorobutyryl)-(+)/(−)-camphor} and hydrazone Schiff base bridging ligands {H₂L1 = (E)-N’-(2-hydroxy-3-methoxybenzylidene)pyrazine-2-carbohydrazide, H₂L2 = (E)-N’-(2-hydroxy-3-methoxybenzylidene)nicotinohydrazide} at room temperature: [Dy₂(D-tfc/L-tfc)₂(L1)₂(H₂O)₂]·2DMF (D-1/L-1), [Dy₂(D-tfc/L-tfc)₂(L2)₂(H₂O)₂]·2DMF (D-2/L-2), [Dy₂(D-pfc/L-pfc)₂(L1)₂(DMF)₂] (D-3/L-3), and [Dy₂(D-pfc/L-pfc)₂(L2)₂(H₂O)₂]·2DMF (D-4/L-4). These enantiomers show intramolecular ferromagnetic interactions between Dy³⁺ ions and exhibit good single-molecule magnet (SMM) properties at a zero dc field, with U_eff/k values of 47.6 K, 152.2 K, 173.8 K and 116.2 K for D-1, D-2, D-3 and D-4, respectively. These magnetic properties were explained with ab initio calculations. The magnetic circular dichroism (MCD) investigation revealed that these four pairs of enantiomers have strong magneto-optical Faraday effects. Besides the second harmonic generation (SHG), they exhibit surprisingly strong third harmonic generation (THG). Notably, the magnetic properties, magneto-optical properties and nonlinear optical properties of such homochiral SMMs can be adjusted by the functional groups on the ligands. Among them, D-1/L-1 has the potential for applications in magneto-optical and/or nonlinear optical materials or devices due to its strongest THG intensity (661.8 × α-SiO₂) and strongest magneto-optical Faraday effect.