Stable Expanded Porphycene-Based Diradicaloid and Tetraradicaloid.

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 (ΔES-T =-3.25 kcal mol-1 for 1 and ΔES-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.