Extended Benzene‐Fused Oligo‐BODIPYs: In Three Steps to a Series of Large, Arc‐Shaped, Near‐Infrared Dyes

We present a straightforward, three‐step synthesis engaging an oligomerization and subsequent one‐pot oxidation step to form fully conjugated, benzene‐fused oligo‐BODIPYs from simple BODIPY precursors. FeCl3 serves as an efficient, bifunctional oxidant for a (multiple) cyclization/desaturation process, applied to ethylene‐bridged dimeric, trimeric and oligomeric species to transform linking ethano units into stiff benzene fusions between unsubstituted β‐positions of each BODIPY unit. The structural integrity was verified by X‐ray crystallography, and all target compounds were studied in detail by photophysical, electrochemical and computational means. The main S1 excited state gradually converges to a structure‐specific excitation limit, displaying a strong shift of the absorption event from about 500 nm (BODIPY monomer) to 955 nm (octamer) with attenuation coefficients up to ca. 500 000 M−1 cm−1. Simple ethylene‐bridged oligo‐BODIPY precursors of various sizes serve as ideal substrates to undergo a one‐pot, multistep oxidation sequence with FeCl3 to furnish benzene‐fused counterparts as fully conjugated, semicircular, near‐infrared dyes with interesting reduction behavior and high air stability.