  We present a theoretical study on narrow armchair graphene nanoribbons
(AGNRs) with hydroxyl functionalized edges. Although this kind of passivation
strongly affects the structure of the ribbon, a high degree of edge
functionalization proves to be particularly stable. An important consequence of
the geometric deviations is a severe reduction of the band-gap of the
investigated 7-AGNR. This shift follows a linear dependence on the number of
added hydroxyl groups per unit cell and thus offers the prospect of a tunable
band-gap by edge functionalization. We furthermore cover the behavior of
characteristic phonons for the ribbon itself as well as fingerprint modes of
the hydroxyl groups. A large down-shift of prominent Raman active modes allows
the experimental determination of the degree of edge functionalization.
