Photoresponsive Magnetic Relaxation Behavior of a Highly Stable π···π Interaction-Stacked Framework Based on a DyIII Single-Ion Magnet

Abstract

Endowing lanthanide single-ion magnets (Ln-SIMs) with high stability and stimulus responsiveness is of significance for the practical applications of these novel magnetic materials, but still of challenge at present. Herein, we report on a highly stable and photoresponsive Ln-SIM system achieved by designing and synthesizing a π···π interaction-stacked framework based on DyIII-SIM (πOF-1). Its molecular formula is [Dy(thqa)] (H3thqa = tris[(8-hydroxyquinoline-2-yl)methylene]amino). Each of its C3-symmetric molecules consists of a thqa3– ligand and a DyIII ion, and it is linked to three neighbors by intermolecular π···π interactions, forming a supermolecular two-dimensional (2D) honeycombed topology. Such unique structure endows πOF-1 with not only air and thermal stability but also excellent chemical stability in different solvents, even in alkali solutions, including a 20 M NaOH aqueous solution. Dual magnetic relaxation behavior was observed in πOF-1. Magnetic dilution revealed that it is related to π···π-mediated intermolecular magnetic interactions. More significantly, both the static magnetic susceptibility and the dual-relaxation behavior of πOF-1 show response to photoirradiation, which could be ascribed to the photo-triggered intermolecular π → π* charge transfer (CT). So far as we know, πOF-1 could be the first Ln-SIM system possessing both a high stability and photoresponsiveness, and also the first photoresponsive Ln-SIM supermolecular system that does not rely on the single-crystal to single-crystal (SCSC) structural transformation. Its successful design and synthesis suggests that the introduction of π···π interactions can be a new strategy to fabricate stable and/or photoresponsive Ln-SIMs.