Oligothiophene catenanes and knots. Part II. Mono and dications. A theoretical study.
Mono- and dications of catenanes and knots containing 16, 22, and 28 thiophene units have been studied at the BHandHLYP/3-21G* level of theory. The polaron localization and relaxation energies of monoionized molecules increase with dihedral angle between thiophene fragments, being higher for catenanes and knots compared to linear oligomers. Monoionization of catenanes results in the polaron localization at one macrocycle leaving another one intact. In all diionized oligomers, polaron pairs were found to be more stable than corresponding bipolarons. The energy difference between bipolaron and polaron pairs increases with the number of repeating units in oligomers for all studied molecular architectures. Singlet polaron pairs are more stable than triplet ones. The energy difference between triplet and singlet states does not exceed 7-8 kcal/mol and decreases with the number of thiophene units in oligomers. Two different singlet minima were found for diionized catenanes. In the first one (the most stable), each macrocycle loses one electron, and in the other one, the polaron pairs are located at one macrocycle, leaving another intact. The energy difference between two minima decreases with the number of repeating units in catenanes.
Fomine
Serguei
S
Instituto de Investigaciones en Materiales, Universidad Nacional Autónoma de México, Apartado Postal 70-360, CU, Coyoacán, México DF 04510, México.
Guadarrama
Patricia
P
Flores
Paola
P