π‐Extended Hexapyrrolylbenzenes: Exploring Charge‐Transfer Phenomena in Donor–Acceptor Propellers

A family of propeller‐shaped donor–acceptor hexapyrrolylbenzenes (HPBs) were designed and synthesized by sequential nucleophilic substitution of hexafluorobenzene with π‐extended pyrroles. In particular, four hybrids were obtained, containing various combinations of electron‐rich and electron‐poor acenaphthylene‐fused pyrroles. Additionally, to probe the efficiency of ortho transfer interactions, a system was designed containing unique donor and acceptor subunits spatially separated with four unfunctionalized pyrroles. DFT calculations showed propeller‐shaped geometries of all HPB molecules and separation of frontier molecular orbitals between donor and acceptor subunits. Steady‐state and time‐resolved photophysical measurements revealed charge‐transfer (CT) character of the emission with strong positive dependence on solvent polarity. The principal CT pathway involves ortho‐positioned pairs of donors and acceptors and requires bending of the acceptor in the excited state