Low bandgap ladder polymers

Unique new ladder polymers consisting of condensed succession of six and five membered conjugated carbon rings have been made recently by Scherf and Müllen. Seven topological isomers of these polyindenoindenes are considered theoretically. The results are analyzed in terms of topological bandgaps and geometry relaxation. Three isomers are expected to have a bandgap smaller than 0.2 eV, although the possibility of a ferrimagnetic ground state for these can not be ruled out.