There is disclosed a method of coordinating ligands, such as nitrogen-containing ligands to metal centers of metal-containing macrocyclic compounds, such as Magnesium Tetraphenyl Porphyrin (MgTPP) or Zinc Tetraphenyl Porphyrin (ZnTPP). The disclosed method comprises (a) forming an organic film comprising the disclosed metal-containing, macrocyclic compound; and (b) exposing the organic film to a vapor comprising at least one ligand for a time sufficient to coordinate the ligand to metal centers in the metal-containing, macrocyclic compound. There is also disclosed a method for preparing an organic photovoltaic device, such as a solar cell, comprising an ordered crystalline organic film made by the disclosed chemical annealing process.