A thermochromic macrocyclic material exhibiting slow relaxation of magnetization: support for magnetic response and visualization applications

Abstract

Development of multifunctional single-molecule magnet (SMM) materials presents an exciting challenge. In this study, we introduce the first high-temperature thermochromic material with SMM properties, investigating the relationship between magnetic relaxation dynamics and thermal effects. Using the Schiff base L^N5 ligand (L^N5 = 2,14-dimethyl-3,6,10,13,19-pentaazabicyclo[13.3.1]nonadecal-1(19),2,13,15,17-pentaene), the mononuclear precursor [Dy(L^N5)Cl₂(H₂O)](ClO₄) (1) and the complex [Dy(L^N5)(2,6-dichloro-4-nitro-PhO)₂Cl](H₂O) (2) with a phenolic ligand were synthesized. More interestingly, a peroxo bridge was introduced through solvent-controlled self-assembly to create the dinuclear complex [Dy₂(L^N5)₂(μ-η²:η²-O₂)Cl₂](ClO₄)₂ (3). Both complexes 2 and 3 exhibit slow magnetic relaxation behavior, attributed to strong axial ligand fields and magnetic interactions. Notably, free radicals generated during the heating of complex 3 contribute to the thermochromism and significantly influence its magnetic behavior, resulting in a fourfold faster relaxation time. The remarkable thermal responsive discoloration of complex 3 highlights its potential applications in visualization, information encryption, and anti-counterfeiting.