1D Anionic Dysprosium(III) Coordination Polymers with Photoactive Protonated 4-Styrylpyridinium Counter-Ions: Photoinduced Modulation of Magnetic Behavior via Synergistic Dual Photoresponses

Abstract

Molecular nanomagnets with dynamically tunable properties are pivotal for the development of advanced, multi-stimuli-responsive magnetic materials. Here, we report a strategy for photoinduced modulation of single-molecule magnet (SMM) behavior by engineering the synergy between two distinct photoresponses. A series of isomorphic rare earth(III) complexes, (H-R-4-spy)[RE(H₂-HEDP)₂] (R = Me, H, Cl, RE = Dy, Y, Gd, 4-spy = 4-styrylpyridine, HEDP = hydroxyethylidene diphosphonate), were designed with the 4-spy ligand serving as a dual photoreactive module. We demonstrate that the electronic nature of the substituent R functions as a molecular dial, concurrently governing the efficiency of photoinduced radical generation and the progression of a [2+2] photocycloaddition. While the electron-donating methyl group permits only cycloaddition, insufficient to activate SMM properties, the H- and Cl-substituted analogues undergo both processes upon irradiation, leading to the emergence of slow magnetic relaxation. Notably, the electron-deficient Cl substituent enhances the efficiency of photoinduced electron transfer and is associated with a substantially increased effective energy barrier for magnetization reversal. This work establishes substituent engineering as a predictive tool for coordinating multiple photoresponses, providing a design blueprint for creating programmable multi-state photomagnetic materials.