Oligothiophene catenanes and knots: a theoretical study

Oligothiophene 2]catenanes and knots containing up to 28 thiophene units have been studied at the BHandHLYP/3-21G level of theory. Small knots (less than 22 thiophene units) and 2]catenanes (less than 18 thiophene units) are strained molecules. Larger knots and 2]catenanes are almost strain-free. 2]Catenanes and knots having less than 18 and 24 units, respectively, show transversal electronic coupling destroying one-dimensionality of molecules reflecting in smaller band gaps compared to larger knots and catenanes. Ionization potentials of knots and catenanes are always higher compared to that of lineal oligomers due to less effective conjugation. Polaron formation in catenanes is delocalized only over one ring, leaving another intact. In the case of a knot containing 22 thiophene units, estimated polaron delocalization is 8 to 9 repeating units.