Gaps of ladder-like PThs

Ladder topology allows delocalization over more than one strand in the polymer, potentially leading to broad energy bands and a small bandgap. It is clear from the last two columns of Table 7.1 that this is not automatically the case very different electronic structures can arise from seemingly similar ladder polymers and their gaps can be fairly large. In this section, we discuss three thiophene-based 

The bond alternation may be different and must be determined first. 

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