Regioregularity effect on conformation and opto-electronic properties in single polythiophene chains

Abstract

We have previously shown that regioregularity (i.e., the percentage of head-to-tail linkages between monomer units in the polymer backbone) is a critical factor which determines the morphology of poly(3- hexylthiophene) (P3HT) even at the single chain level. Here, we examined the excitation wavelength dependence on the fluorescence polarization anisotropy of single regioregular ( rr- ) and regiorandom ( rra- ) P3HT. For both rr- and rra- P3HT chains, the observed anisotropy is higher as the longer wavelength is used to excite single polymer chains. This indicates that chromophores with longer conjugation length are predominantly located in more highly ordered regions of the chain. However, at any excitation wavelength, the difference between rr- and rra- P3HT is observed. Single rr- P3HT chains fold into highly ordered conformation while rra- P3HT chains assume a wide variety of conformations from isotropic to anisotropic. These new results further support that regioregularity is important for P3HT even at the single chain level and give deeper insights of polymer morphology and its effect on optical property.