Synthesis and characterization of diperfluorooctyl-substituted phenylene-thiophene oligomers as n-type semiconductors. Molecular structure-film microstructure-mobility relationships, organic field-effect transistors, and transistor nonvolatile memory elements

A new series of mixed phenylene-thiophene oligomers with terminal n-perfluorooctyl groups has been synthesized. These compounds are 2,5-bis(4-n-perfluorooctylphenyl)-thiophene (DFO-PTP, 1), 5,5′-bis(4-n- perfluorooctylphenyl)-2,2′-bithiophene (DFO-PTTP, 2), 5,5″-bis(4-n- perfluorooctylphenyl)-2,2′:5′,2″-terthiophene (DFO-PT ₃P, 3), 5,5‴-bis(4-n-perfluorooctylphenyl)-2,2′: 5′,2″:5″,2‴-quaterthiophene (DFO-PT₄P, 4), and 1,4-bis[5-(4-n-perfluorooctylphenyl)-2-thienyl]benzene (DH-PTPTP, 5). These systems have been characterized by ¹H and ¹⁹F NMR, elemental analysis or HRMS, optical absorption and emission spectroscopies, differential scanning calorimetry, and thermogravimetric analysis. Vacuum-deposited films were characterized by optical absorption and emission spectroscopy, X-ray diffraction, scanning electron microscopy, and field effect transistor measurements. As thin films, all of the fluorinated compounds are n-type semiconductors with carrier mobilities ranging from ∼ 10^-6 to ∼ 0.1 cm² V^-1 s^-1, depending on the substrate deposition temperature. Furthermore, these films exhibit very large current I_on:I_off ratios (up to ∼ 10⁷) due to substantially suppressed off-currents. Particularly interesting is straightforwardly synthesized DFO-PTTP (2), which displays a combination of high mobility, high current I_on:I_off ratio, and reversible, tunable, and stable memory effects.