A 1,5‐Naphthyridine‐Fused Porphyrin Dimer: Intense NIR Absorption and Facile Redox Interconversion with Its Reduced Congener

Pt II ‐catalyzed cyclization of β‐to‐β ethynylene‐bridged meso ‐amino Ni II porphyrin dimer 4 followed by oxidation with PbO 2 afforded 1,5‐naphthyridine‐fused porphyrin dimer 5 in good yield. This dimer possesses a redox‐active 1,4‐diazabutadiene linkage that is interconvertible with its reduced 1,2‐diaminoethene linkage upon treatments with NaBH 4 or PbO 2 . The dimer 5 exhibits an intense NIR absorption and a narrow HOMO–LUMO gap with a remarkably low reduction potential mainly due to effective bonding interactions in the LUMO through the 1,4‐diazabutadiene linkage. In contrast, the reduced dimer 7 is fairly electron‐rich with high HOMO energy and shows a relatively large HOMO–LUMO gap compared to that of 5 .