Light-Induced Antiferromagnetic to Ferromagnetic Transition in Halogen Substituted 1,4-Bis(imidazolyl)benzene Systems: An Effect of Spin–Orbit Coupling and π-Stacking in Enhanced Photomagnetism
Subhajit Saha, Sudipta Khamrui, Kumar Biradha
Abstract
Employing the spin–orbit coupling effect by introducing halogen substituents is an excellent strategy to tune the magnetic behavior of organic or metal–organic materials. Light is an alternative tool to modulate the magnetic behavior of a material through a photoinduced electron transfer process, without changing its chemical identity. In this work, three halogen containing 1,4-bis(4,5-diphenyl-1 H -imidazol-2-yl)benzene (F-BDPI, Cl-BDPI and Br-BDPI) systems have been chosen to exploit the role of halogen substituents on solid-state photoinduced phenomena. Through a comprehensive analysis involving various characterization techniques, including UV/vis diffuse reflectance, solid-state photoluminescence, and EPR measurements, it was found that the as-synthesized forms Cl-BDPI-IA and Br-BDPI-IA (IA denotes the hexahydrate form of Cl/Br-BDPI) exhibited fast photochromic response through the generation of photoinduced free radicals in the solid state. Moreover, the SQUID analysis revealed an antiferromagnetic to ferromagnetic transition in Cl-BDPI-IA through photoirradiation, which led to an increase in the magnetic moment value up to 38% at room temperature. This signifies the first occurrence of such a significant level of magnetization amplitude compared with previously reported metal–organic photomagnets. This investigation underscores the significance of halogen substitution in tailoring the magnetic properties of organic photomagnets, where strong halogen−π and π–π interactions facilitate the spin–orbit coupling effect in the solid state.