Rhodium-catalyzed annulation of pyrrole substituted BODIPYs with alkynes to access π-extended polycyclic heteroaromatic molecules and NIR absorption

Abstract

A series of π-extended BODIPY derivatives fused with an indolizine scaffold were prepared smoothly via rhodium-catalyzed C–H functionalization/annulation with excellent chemoselectivity and regioselectivity, where the pyrrole moiety serves as a directing group. The resulting BODIPY dimer was selectively constructed by FeCl₃-mediated intermolecular oxidative aromatic coupling of its precursor at the α-position of the pyrrole unit, exhibiting the maximum absorption wavelength at 947 nm. The structures of two representative BODIPY monomers and the BODIPY dimer were unambiguously confirmed by X-ray crystallographic analysis. These fluorophores show significantly red-shifted absorption compared with their corresponding precursors and reported BODIPY analogues, reaching the near infrared (NIR) spectral region. Meanwhile, these diindolizine-fused BODIPYs display large Stokes shifts. Electrochemical properties were determined and DFT calculations were also performed to deepen our understanding of the electronic structures and spectral properties of these new BODIPYs.