Stable Expanded Porphycene-Based Diradicaloid and Tetraradicaloid

Article abstract of DOI:10.1002/anie.201807411

The synthesis of a bithiophene-bridged 34π conjugated aromatic expanded porphycene 1 and a cyclopentabithiophene bridged 32π conjugated anti-aromatic expanded porphycene 2 by a McMurry coupling strategy is presented. Magnetic measurements and theoretical calculations reveal that both 1 and 2 exhibit an open-shell singlet ground state with significant radical character (y₀=0.63 for 1; y₀=0.68, y₁=0.18 for 2; y₀: diradical character, y₁: tetraradical character) and a small singlet–triplet energy gap (ΔE_S-T=?3.25 kcal mol^?1 for 1 and ΔE_S-T=?0.92 kcal mol^?1 for 2). Despite the open-shell radical character, both compounds display exceptional stability under ambient air and light conditions owing to effective delocalization of unpaired electrons in the extended cyclic π-conjugation pathway.