We synthesized a two-dimensional (2D) crystalline covalent organic framework (sp2c-COF) that was designed to be fully π-conjugated and constructed from all sp2 carbons by C=C condensation reactions of tetrakis(4-formylphenyl)pyrene and 1,4-phenylenediacetonitrile. The C=C linkages topologically connect pyrene knots at regular intervals into a 2D lattice with π conjugations extended along both x and y directions and develop an eclipsed layer framework rather than the more conventionally obtained disordered structures. The sp2c-COF is a semiconductor with a discrete band gap of 1.9 electron volts and can be chemically oxidized to enhance conductivity by 12 orders of magnitude. The generated radicals are confined on the pyrene knots, enabling the formation of a paramagnetic carbon structure with high spin density. The sp2 carbon framework induces ferromagnetic phase transition to develop spin-spin coherence and align spins unidirectionally across the material.
Bibliographical noteFunding Information:
E.J. acknowledges Chinese Scholarship Concert for financial support for his study in Japan. S.D. is now an international research fellow of the Japan Society for the Promotion of Science. M.A.B. acknowledges the Advanced Light Source, which is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under contract DE-AC02-05CH11231. T.H. and M.A. acknowledge supercomputer time at ZIH Dresden and financial support by the European Research Council (grant ERC-StG 256962 C3ENV) and the VolkswagenStiftung. D.J. acknowledges a Grant-in-Aid for Scientific Research (A) (17H01218) from the Ministry of Education, Culture, Sports, Science and Technology, Japan, and support from the ENEOS Hydrogen Trust Fund and the Ogasawara Foundation for the Promotion of Science and Engineering. D.J. conceived and designed the project. E.J., Q.X., S.D., H.X., and Q.C. conducted the experiments. M.A.A. and T.H. conducted DFTB calculations and structure simulations. M.A. and T.N. conducted ESR and SQUID measurements. M.A.B. conducted WAXS measurements. D.J., E.J., Q.C., and S.D. wrote the manuscript and discussed the results with all authors. All data are reported in the main text and supplementary materials.
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