Complexes of carboxyl-containing polymer and monosubstituted bipyridinium salts

•Monosubstituted 4,4′-bipyridinium halides form two energetically stable structures.•We calculated the partial charge transfer system to be energetically more favorable.•Coulomb interactions stabilize complexes between BpyR(Hal) and COOH group.•Water molecules play an important role in complex formation.•The complex formation leads to change from partial charge transfer to ion pair.