A Study of the Degree of Fluorination in Regioregular Poly(3-hexylthiophene)

Abstract

We systematically varied the degree of fluorination along the backbone of a series of highly regioregular 3-hexylthiophene-based polymers, P3HT-50F, P3HT-33F, and P3HT-25F, in which 50%, 33%, and 25% of the thiophene units within the polymer chain contain fluorine atoms in the available 4-position, respectively. These materials were homopolymerized using the Kumada catalyst transfer polycondensation method from a set of mono-fluorinated bi-, ter-, and quarterthiophenes to ensure high polymer regioregularity and evenly spaced fluorine atoms along the conjugated thiophene backbone. The monomers were obtained from a synthetic route consisting of iterative Migita–Stille couplings of fluorinated and non-fluorinated 3-hexylthiophenes. The effect of the fluorine atoms on both polymer structure and properties is presented, with supporting quantum mechanical calculations that rationalize the intrinsic conformation preferences of the three P3HT derivatives. P3HT-50F (M̅n = 34 kg/mol, 98.5% rr), P3HT-33F (M̅n = 46 kg/mol, 98% rr), and P3HT-25F (M̅n = 53 kg/mol, 95% rr) displayed HOMO levels of −5.34, −5.26, and −5.24 eV, bandgaps of 1.98, 1.98, and 1.97 eV, and average field-effect transistor hole mobilities of 4.5 × 10–3, 2.7 × 10–2, and 1.2 × 10–2 cm2 V–1 s–1, respectively.