  We predict an optical effect associated with systems which exhibit
topologically protected states separated by a finite distance. We develop a
tight-binding model to calculate the optical selection rules in linear chains
of atoms of different lengths, and show the crucial importance of edge states.
For long enough molecules the interband transitions involving these edge states
are in the highly sought-after THz frequency range. Although we have
specifically considered finite carbon chains terminated by gold nanoparticles,
the main results of our work can be generalized to various systems which
exhibit topologically protected states separated by a finite distance.
