Rational Design of Electric Field-Responsive Building Blocks for All-Organic 2D Magnetoelectric Materials

Abstract

Development of technologically promising magnetoelectric materials, where magnetic properties can be controlled by electric fields (E-fields), has focused on inorganic systems. Here, we propose a strategy for modulating magnetic exchange coupling (J) in purely organic systems through experimentally realizable E-fields. Our approach leverages two established concepts: (i) E-field-induced twisting of dipolar organic linkers and (ii) control of J via conformational changes in organic diradicals. Using density functional theory calculations, we investigated the effects of applied E-fields on diradicals with two coplanar spin-carrying trioxotriangulene (TOT) radicals connected by dipolar aryl linkers. We find that E-fields induce significant conformational changes in the linkers (twisting) that alters π-conjugation and, in turn, the magnetic J coupling between TOT radicals. In-plane E-fields twist the linkers toward the plane of the radicals, enhancing π-conjugation and increasing AFM coupling. Out-of-plane E-fields induce more orthogonal linker conformations and decrease the coupling strength. The magnetoelectric response depends on a combination of steric hindrance, π-conjugation, and polarization. Significant and measurable cumulative changes in J of up to 3.9 meV could be achieved by using in-plane and out-of-plane E-fields of up to 0.5 V/Å. In some cases, applied E-fields can also induce switching between paramagnetism and antiferromagnetism. Calculations on a 2D covalent organic framework (COF) based on a network of TOT radicals and dipolar linkers confirm that this approach is also viable for extended systems. Such COFS could also display E-field induced ferroelectric responses. Overall, our proof-of-principle study highlights the interplay between molecular structure, E-fields, and magnetism and establishes an innovative and chemically rational framework for developing all-organic magnetoelectric materials.