  Designing molecular organic semiconductors with distinct frontier orbitals is
key for the development of devices with desirable properties. Generating
defined organic nanostructures with atomic precision can be accomplished by
on-surface synthesis. We use this dry chemistry to introduce topological
variations in a conjugated poly-para-phenylene chain in the form of
meta-junctions. As evidenced by STM and LEED, we produce a macroscopically
ordered, monolayer thin zigzag chain film on a vicinal silver crystal. These
cross-conjugated nanostructures are expected to display altered electronic
properties, which are now unravelled by highly complementary experimental
techniques (ARPES and STS) and theoretical calculations (DFT and EPWE). We find
that meta-junctions dominate the weakly dispersive band structure, while the
bandgap is tunable by altering the linear segment's length. These periodic
topology effects induce significant loss of the electronic coupling between
neighboring linear segments leading to partial electron confinement in the form
of weakly coupled Quantum Dots. Such periodic quantum interference effects
determine the overall semiconducting character and functionality of the chains.
