Conjugated coupler curvature enhances magnetic spin coupling in π-diradicals

Abstract

Buckybowls have been drawing considerable attention because of their unique electronic structures and physical properties. However, few studies have investigated their magnetic properties. In the present investigation on organic molecular magnets, flatly conjugated structures are generally used as couplers. However, there are few reports on the use of curvature couplers for constructing molecular magnets. In this study, a series of dual nitroxide diradical molecular magnets are designed with triphenylene and its edge-modified derivatives (by the –CH₂–, –NH–, or –O– edge-bridging groups) as the couplers, and their magnetic coupling properties are studied at the density functional theory level. It is interesting to note that all the designed diradicals exhibit antiferromagnetic (AFM) properties and the curvature of the coupler can considerably enhance their magnetic coupling strength. The curvature of the coupler can reduce its aromaticity and increase the spin polarization of nitroxide groups, thereby enhancing the AFM. The electronic properties of the bridging groups (such as –NH–, –O–) can further enhance the AFM coupling strength of the diradicals by manipulating the π electron distribution on the coupler, especially with the assistance of intramolecular H-bonds for the –NH– edge-bridge. This study provides insights into the magnetic modulation of molecular magnets through the curvature of couplers and also offers valuable information on constructing curved molecular magnets.