Regioregularity and Single Polythiophene Chain Conformation

The regioregularity of a conjugated polymer can greatly affect bulk film morphologies and properties. However, it remains unclear how regioregularity affects the conformation of isolated individual chains where interchain interactions are absent. Here, the effect of the regioregularity on the conformations adopted by regioregular (rr-) and regiorandom (rra-) poly(3-hexylthiophene) (P3HT) chains was studied using single molecule fluorescence excitation polarization spectroscopy. While every rr-P3HT chain within an ensemble was found to fold into a highly ordered conformation, single rra-P3HT chains adopted a wide variety of conformations, ranging from highly ordered to isotropic. This distribution is likely due to variations in the positions of nonhead-to-tail linkages of the side-chains along the backbone of the different polymer chains. Molecular dynamics simulation on atomistic models of rr- and rra-P3HT chains supports the effect of regioregularity on the collapsed conformations. These results demonstrate that side-chains govern the morphology of P3HT, even at the single chain level.