Electron‐Deficient Bipyrrole Boomerangs. Bright Fluorophores Obtained via Double C−H Bond Activation

Żyła-Karwowska, M.; Moshniaha, L.; Hong, Y.; Zhylitskaya, H.; Cybińska, J.; Chmielewski, P. J.; Lis, T.; Kim, D.; Stępień, M.
Chem. Eur. J. 2018, 24, 7525-7530 | view at publisher's site

PdII‐mediated annulative double C−H activation is shown to efficiently convert 1,n‐dipyrrolylalkanes into extensively π‐conjugated bipyrroles not accessible via conventional oxidative coupling protocols. This approach is applicable to both electron‐rich and electron‐deficient systems, and has been further developed into tandem processes involving further cyclization of substituents or oxygenation of pyrrolic α‐positions. The new bipyrrole intermediates show enhanced fluorescence, and tunable optical properties controlled by the alignment of chromophore subunits. Photophysical data, including femtosecond transient absorption, reveal solvent‐induced intramolecular charge transfer in excited states, de‐pendent on the polarity of the medium.