Photochromism and Photomagnetism in 1,4-bis(4,5-diphenyl-imidazolyl)benzene Chromophores: Water-Assisted π-Stacks for the Generation of Stable Free Radicals in the Solid State

Abstract

Photochromism and photomagnetism are two important properties for the generation of smart materials that are useful for optical switches and memory devices. Very few materials, mostly containing metal ions, are known to date to exhibit both properties at room temperature. Herein, we report a class of bis-imidazole-based organic molecules that show reversible photochromism and photomagnetism at room temperature due to the generation of free radicals in the solid state. 1,4-Bis(4,5-diphenyl-1H-imidazol-2-yl)benzene (BDPI) was found to act as an organic photomagnet without the use of any traditional photochromic couplers or radical containing moieties. Solvent molecules (e.g., water and DMSO) form hydrogen bonds with the imidazole rings that act as a binding glue in the stacking of 1,4-bis(imidazolyl)benzene moieties via π•••π interactions. These interactions were found to play a significant role in promoting strong spin−spin interaction in the solid state that can be inferred from the appearance of a broad EPR signal, whereas a sharp signal appeared only after irradiation. The sharp signal indicates the formation of paramagnetic free radicals that influence antiferromagnetic exchange interactions with significant weakening of the magnetic susceptibility. This work provides a unique direction in the generation of metal-free photochromic and photomagnetic materials, where a simple 1,4-bis(imidazolyl)benzene system changes its color, radical activity, and magnetic behavior with photoirradiation.

Halogen and Hydrogen Bonding Interplay Triggered Reversible Phase Transformations through Water Release/Uptake: X-ray Powder Diffraction Studies on Halogen-Substituted 1,4-Bis(4,5-diphenyl-imidazolyl)benzene

“…Recently, we have shown that the as-synthesized 1,4-bis­(4,5-diphenyl-1 H -imidazol-2-yl)­benzene (BDPI) exists as a tetrahydrate for which the single crystals cannot be obtained . However, the crystal structure was determined by its powder diffraction.…”

A persistent radical anion naphthalenediimide-based hybrid material for near-infrared photothermal conversion and photocatalytic oxidative organic transformations

“…1–7 Conventional radical-doped organic materials may not only require complicated synthesis procedures, but also suffer from ready decomposition and photobleaching during practical application. 8–10 These shortcomings lead to increased costs and the risk of performance degradation. Therefore, it is necessary to design radical-doped materials with a stable structure and performance.…”