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

TLDR: 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.

Abstract: 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 .