A theoretical study of the structure and binding energies of dimers of Zn(II)-Porphyrin derivatives

Zinc complexed porphyrin and chlorophyll derivatives form functional aggregates with remarkable photophysical and optoelectronic properties. Understanding the type and strength of intermolecular interactions between these molecules is essential for designing new materials with desired morphology and functionality. The dimer interactions of a molecular set comprised of porphyrin derivatives obtained by substitutional changes starting from free-base porphyrin is studied. It is found that B97M-rV/def2-TZVP level of theory provides a good compromise between the accuracy and cost to get the dimer geometries and interaction energies. The neglect of the relaxation energy due to the change in the monomer configurations upon complex formation, causes a more significant error than the basis set superposition error. The metal complexation increases the binding energy by about -6 to -8 kcal/mol, and the introduction of keto and hydroxy groups further stabilizes the dimers by -10 to -15 kcal/mol. Although the saturation of one of the pyrrol double bonds does not change the interaction energy, the addition of R groups increases it.