Materials based on biradicals/biradicaloids have potential applications for organic electronics, photonics and spintronics. In this work, we demonstrated that hybridization of porphyrin and polycyclic aromatic hydrocarbon could lead to a new type of stable biradicals/biradicaloids with tunable ground state and physical property. Mono- and bis-phenalenyl fused porphyrins >1 and >2 were synthesized via an intramolecular Friedel–Crafts alkylation-followed-by oxidative dehydrogenation strategy. Our detailed experimental and theoretical studies revealed that >1 has a closed-shell structure with a small biradical character (y = 0.06 by DFT calculation) in the ground state, while >2 exists as a persistent triplet biradical at room temperature under inert atmosphere. Compound >1 underwent hydrogen abstraction from solvent during the crystal growing process while compound >2 was easily oxidized in air to give two dioxo-porphyrin isomers >11a/>11b, which can be correlated to their unique biradical character and spin distribution. The physical properties of >1 and >2, their dihydro/tetrahydro-precursors >7/>10, and the dioxo-compounds >11a/>11b were investigated and compared.
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