Orbitally Matched Edge-Doping in Graphene Nanoribbons

A series
of trigonal planar N-, O-, and S-dopant atoms incorporated
along the convex protrusion lining the edges of bottom-up synthesized
chevron graphene nanoribbons (cGNRs) induce a characteristic shift
in the energy of conduction and valence band edge states along with
a significant reduction of the band gap of up to 0.3 eV per dopant
atom per monomer. A combination of scanning probe spectroscopy and
density functional theory calculations reveals that the direction
and the magnitude of charge transfer between the dopant atoms and
the cGNR backbone are dominated by inductive effects and follow the
expected trend in electronegativity. The introduction of heteroatom
dopants with trigonal planar geometry ensures an efficient overlap
of a p-orbital lone-pair centered on the dopant atom with the extended
π-system of the cGNR backbone effectively extending the conjugation
length. Our work demonstrates a widely tunable method for band gap
engineering of graphene nanostructures for advanced electronic applications.