Electron-Deficient Polycyclic π‑System Fused with Multiple B←N Coordinate Bonds

An extensive polycyclic π-system
with 23 fused rings is synthesized
via a highly efficient borylation reaction, in which four B–N
covalent bonds and four B←N coordinate bonds are formed in
one pot. B←N coordinate bonds not only lock the backbone into
a near-coplanar conformation but also decrease the LUMO energy level
to around −3.82 eV, demonstrating the dual utility of this
strategy for the synthesis of extensive rigid polycyclic molecules
and the development of n-type conjugated materials
for organic electronics and organic photovoltaics.