"Russian doll" complexes of [n]cycloparaphenylenes: a theoretical study.

The formation of "Russian doll" complexes consisting of [n]cycloparaphenylenes was predicted using quantum chemistry tools. The electronic structures of multiple inclusion complexes containing up to four macrocycles were explored at the M06-2X/6-31G* level of theory. The binding energy between the macrocycles increases from the center to the periphery of the complex and can be >60 kcal mol(-1) for macrocycles containing 14 and 19 repeating units. It has been demonstrated that additional electrostatic interactions originating from the asymmetric electron density distribution observed when comparing the concave and convex macrocycle sides are responsible for the high binding energies in these Russian doll complexes. Oxidation or reduction of the Russian doll complexes creates polarons that are delocalized across the complexes. In the case of polaron cations, most of the polarons are localized at the macrocycle with the smallest ionization potential; for polaron anions, the negative charge is localized across the outer rings of the complex. Because anion polarons are more delocalized than cation polarons, the relaxation energies of the polaron anions were found to be smaller than those of the polaron cations.