  Nanosize pores can turn semimetallic graphene into a semiconductor and from
being impermeable into the most efficient molecular sieve membrane. However,
scaling the pores down to the nanometer, while fulfilling the tight structural
constraints imposed by applications, represents an enormous challenge for
present top-down strategies. Here we report a bottom-up method to synthesize
nanoporous graphene comprising an ordered array of pores separated by ribbons,
which can be tuned down to the one nanometer range. The size, density,
morphology and chemical composition of the pores are defined with atomic
precision by the design of the molecular precursors. Our measurements further
reveal a highly anisotropic electronic structure, where orthogonal
one-dimensional electronic bands with an energy gap of ~1 eV coexist with
confined pore states, making the nanoporous graphene a highly versatile
semiconductor for simultaneous sieving and electrical sensing of molecular
species.
