π-Stacks of radical-anionic naphthalenediimides in a metal-organic framework

Bongkyeom Kim; Juhyung Lee; Ying-Pin Chen; Xue-Qian Wu; Joongoo Kang; Hwakyeung Jeong; Sang-Eun Bae; Jian-Rong Li; Jooyoung Sung; Jinhee Park

doi:10.1126/sciadv.ade1383

π-Stacks of radical-anionic naphthalenediimides in a metal-organic framework

Sci Adv. 2022 Dec 23;8(51):eade1383. doi: 10.1126/sciadv.ade1383. Epub 2022 Dec 23.

Authors

Affiliations

¹ Department of Physics and Chemistry, Daegu Gyeongbuk Institute of Science and Technology (DGIST), 333 Techno Jungang-daero, Dalseong-gun, Daegu 42988, Republic of Korea.
² NSF's ChemMatCARs, The University of Chicago Argonne, Chicago, IL 60439, USA.
³ Faculty of Environment and Life, Beijing University of Technology, Beijing 100124, P.R. China.
⁴ Nuclear Chemistry Research Team, Korea Atomic Energy Research Institute, Daejeon 34057, Republic of Korea.
⁵ Beijing Key Laboratory for Green Catalysis and Separation, Department of Chemistry and Chemical Engineering, College of Environmental and Energy Engineering, Beijing University of Technology, Beijing 100124, P.R. China.

Abstract

Radical-ionic metal-organic frameworks (MOFs) have unique optical, magnetic, and electronic properties. These radical ions, forcibly formed by external stimulus-induced redox processes, are structurally unstable and have short radical lifetimes. Here, we report two naphthalenediimide-based (NDI-based) Ca-MOFs: DGIST-6 and DGIST-7. Neutral DGIST-6, which is generated first during solvothermal synthesis, decomposes and is converted into radical-anionic DGIST-7. Cofacial (NDI)₂^•- and (NDI)₂^2- dimers are effectively stabilized in DGIST-7 by electron delocalization and spin-pairing as well as dimethylammonium counter cations in their pores. Single-crystal x-ray diffractometry was used to visualize redox-associated structural transformations, such as changes in centroid-to-centroid distance. Moreover, the unusual rapid reduction of oxidized DGIST-7 into the radical anion upon infrared irradiation results in effective and reproducible photothermal conversion. This study successfully illustrated the strategic use of in situ prepared cofacial ligand dimers in MOFs that facilitate the stabilization of radical ions.