  We investigate the functionalization of functional groups to graphene
nanoribbons with zigzag and armchair edges using first principles calculations.
We find that the formation energy for the configuration of the functional
groups functionalized to the zigzag edge is ~0.2 eV per functional group lower
than that to the armchair edge. The formation energy difference arises from a
structural deformation on the armchair edge by the functionalization whereas
there is no structural deformation on the zigzag edge. Selective
functionalization on the zigzag edge takes place at a condition of the
temperature and the pressure of ~25 oC and 10-5 atm. Our findings show that the
selective functionalization can offer the opportunity for an approach to the
separation of zigzag graphene nanoribbons with their solubility change.
