The synthesis of a novel 3,3'-difl uoro-4,4'-dihexadecyl-2,2'-bithiophene monomer and its copolymerization with thieno[3,2-b]thiophene to afford the fluorinated analogue of the well-known poly(2,5-bis(3-alkylthiophen-2-yl) thieno[3,2-b]-thiophene) (PBTTT) polymer is reported. Fluorination is found to have a significant influence on the physical properties of the polymer, enhancing aggregation in solution and increasing melting point by over 100 degrees C compared to nonfluorinated polymer. On the basis of DFT calculations these observations are attributed to inter and intramolecular S.F interactions. As a consequence, the fluorinated polymer PFBTTT exhibits a fourfold increase in charge carrier mobility compared to the nonfluorinated polymer and excellent ambient stability for a nonencapsulated transistor device.