  Graphyne (GY) and graphdiyne (GDY)-based materials represent an intriguing
class of two-dimensional (2D) carbon-rich networks with tunable structures and
properties surpassing those of graphene. However, the challenge of fabricating
atomically well-defined crystalline GY/GDY-based systems largely hinders
detailed electronic structure characterizations. Here, we report the emergence
of an unconventional band structure in mesoscopically regular (~1 {\mu}m)
metallated GDY sheets featuring a honeycomb lattice on Ag(111) substrates.
Employing complementary scanning tunnelling and angle-resolved photoemission
spectroscopies, electronic band formation with a gap of 2.5 eV is rigorously
determined in agreement with real-space electronic characteristics. Extensive
density functional theory calculations corroborate our observations as well as
recent theoretical predictions that doubly degenerate frontier molecular
orbitals on a honeycomb lattice give rise to flat, Dirac and Kagome bands close
to Fermi level. These results illustrate the tremendous potential of
engineering novel band structures via molecular orbital and lattice symmetries
in atomically precise 2D carbon scaffolds.
