While the details of the fitting of the STM images are discussed in the Supporting Information section 9.1, this procedure allowed us to directly sequence the polymer backbones, as shown in Figure . In particular, we measured the frequencies of cisand trans-PCT isomers within the polymers, obtaining a 1:1.26 ratio over a total of 822 isomers. This is statistically significantly different from the 1:1.06 ratio measured by NMR for the isolated dibrominated monomers, indicating that the trans monomers are incorporated in the polymer sequences with higher probability. The two regioisomers are, however, distributed independently along the backbone, as demonstrated by a statistical test of significance (see Supporting Information ). This suggests that its high solubility is not due to a highly kinked polymer structure that would impede intermolecular packing and aggregation.