Synthesis and Charge Transport Properties of Conjugated Polymers Incorporating Difluorothiophene as a Building Block

A series of conjugated copolymers, PDPPFT and PNDIFT, were developed using difluoroterthiophene and DPP or NDI as the cobuilding block. We obtained two different molecular weight polymers for each polymer type by changing the conditions for the Stille coupling reaction and studied their optoelectrochemical properties and charge-transport behavior in organic field-effect transistors (OFETs). Both the lower molecular weight polymers, PDPPFT­(L) and PNDIFT­(L), showed better long-range ordered structures in films, whereas the polymers with higher molecular weights were less long-range ordered and showed a more preferential face-on orientation. By virtue of their favorable polymer packing structures, PDPPFT­(L) and PNDIFT­(L) exhibited much higher hole mobilities compared with their higher molecular weight counterparts, PDPPFT­(H) and PNDIFT­(H). By contrast, both PDPPFT and PNDIFT maintained good n-channel properties independent of their molecular weights, thus their long-range ordering in a film. The strong electron-withdrawing fluorine groups are favorable for stabilizing electrons on the polymer chain and would enable the polymer to transport electrons efficiently even in the case of a less-ordered packing structure with an unfavorable face-on orientation