Light-Induced Antiferromagnetic\nto Ferromagnetic Transition\nin Halogen Substituted 1,4-Bis(imidazolyl)benzene Systems: An Effect\nof Spin–Orbit Coupling and π‑Stacking in Enhanced\nPhotomagnetism

Employing the spin–orbit coupling effect by introducing\nhalogen substituents is an excellent strategy to tune the magnetic\nbehavior of organic or metal–organic materials. Light is an\nalternative tool to modulate the magnetic behavior of a material through\na photoinduced electron transfer process, without changing its chemical\nidentity. In this work, three halogen containing 1,4-bis(4,5-diphenyl-1<i>H</i>-imidazol-2-yl)benzene (F-BDPI, Cl-BDPI and Br-BDPI) systems\nhave been chosen to exploit the role of halogen substituents on solid-state\nphotoinduced phenomena. Through a comprehensive analysis involving\nvarious characterization techniques, including UV/vis diffuse reflectance,\nsolid-state photoluminescence, and EPR measurements, it was found\nthat the as-synthesized forms Cl-BDPI-IA and Br-BDPI-IA (IA denotes\nthe hexahydrate form of Cl/Br-BDPI) exhibited fast photochromic response\nthrough the generation of photoinduced free radicals in the solid\nstate. Moreover, the SQUID analysis revealed an antiferromagnetic\nto ferromagnetic transition in Cl-BDPI-IA through photoirradiation,\nwhich led to an increase in the magnetic moment value up to 38% at\nroom temperature. This signifies the first occurrence of such a significant\nlevel of magnetization amplitude compared with previously reported\nmetal–organic photomagnets. This investigation underscores\nthe significance of halogen substitution in tailoring the magnetic\nproperties of organic photomagnets, where strong halogen−π\nand π–π interactions facilitate the spin–orbit\ncoupling effect in the solid state.