The synthesis of a new series of mixed phenylene-thiophene oligomers is reported; 2,5-bis(4-n-hexylphenyl)thiophene (dH-PTP, 1), 5,5'-bis(4-n-hexylphenyl)-2,2'-bithiophene (dH-PTTP, 2), 5,5' '-bis(4-n-hexylphenyl)-2,2':5',2' '-terthiophene (dH-PT(3)P, 3), 5,5' "-bis(4-n-hexylphenyl)-2,2':5',2' ':5' ',2' "-quaterthiophene (dH-PT(4)P, 4), 1,4-bis[5-(4-n-hexylphenyl)-2-thienyl]benzene (dH-PTPTP, 5), and 2,5-bis[4(4'-n-hexylphenyl)phenyl]thiophene (dH-PPTPP, 6) were characterized by (1)H NMR, elemental analysis, UV-visible spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. Vacuum-evaporated and solution-cast films were characterized by X-ray diffraction and scanning electron microscopy. All compounds display high p-type carrier mobilities as evaporated (up to 0.09 cm(2)/Vs) and as solution-cast (up to 0.03 cm(2)/Vs) films on both Si/SiO(2) and ITO/GR (glass resin) substrates. The straightforwardly synthesized dH-PTTP (2) displays an unprecedented combination of mobility, on/off ratio, stability, and processability. Both dH-PTTP (2) and dH-PPTPP (6) display a reversible, tunable, and stable memory effect even as solution-cast devices, with turn-on characteristics shifting from accumulation mode to zero or depletion mode after a writing voltage V(w) is applied. The charge storage is distributed over the gate dielectric structure and is concentrated near the dielectric-semiconductor interface, as evidenced by the response of "floating gate" configuration devices. Simple nonvolatile elements have been fabricated by solution-only techniques on ITO substrates using spin-coated glass resin, solution-cast oligomeric semiconductors, and painted graphite paste electrodes.

The solid-state properties and FET electrical behavior of several series of alpha,omega- and beta,beta'-fluorocarbon- and alkyl-substituted and unsubstituted oligothiophenes nTs (n = 2-6) are compared and contrasted. The thin films were grown by slow vacuum deposition over a range of substrate temperatures and/or by casting from solution and were investigated by X-ray diffraction and scanning electron microscopy. Our results indicate that vacuum deposition at 60-80 degrees C affords films with remarkably similar microstructures despite the extensive H --> F substitution. Trends in observed d spacing versus molecular core extension provide quantitative information on molecular orientation. Field-effect transistor measurements performed for all systems and having the same device structure, components, and fabrication conditions demonstrate that all nTs functionalized with fluorocarbon chains at the thiophene termini are n-type semiconductors, in contrast to the p-type activity of the remaining systems. One of these systems, alpha,omega-diperfluorohexyl-4T, exhibits a mobility of 0.22 cm2/(V s) and an Ion:Ioff ratio of 10(6), one of the highest so far reported for an n-type organic semiconductor. The effect of substitution regiochemistry on FET majority charge carrier was additionally studied, in the case of a 6T core, by shifting the fluorocarbon substituents from the terminal to the central thiophene units. Finally, we propose a simple theoretical model for electrode/organic interfacial carrier injection. The results suggest why modest substituent-induced changes in the injection barrier can produce working n-type materials.

A substantial enhancement of thermal stability, volatility, and electron affinity, switching the semiconducting behavior from p‐ to n‐type, is achieved by fluoroalkyl substitution of thiophene oligomers (see Figure). When this novel series is compared with the fluorine‐free analogues, trends in molecular packing, optical absorption, HOMO–LUMO gap, and π–π interactions are found to be strikingly similar.

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 3 P, 3), 5,5′′′-bis(4-nperfluorooctylphenyl)-2,2′:5′,2′′:5′′,2′′′-quaterthiophene (DFO-PT 4 P, 4), and 1,4-bis[5-(4-nperfluorooctylphenyl)-2-thienyl]benzene (DH-PTPTP, 5). These systems have been characterized by 1 H and 19 F NMR, elemental analysis or HRMS, optical absorption and emission spectroscopies, differential scanning calorimetry, and thermogravimetric analysis. Vacuumdeposited 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 cm 2 V -1 s -1 , depending on the substrate deposition temperature. Furthermore, these films exhibit very large current I on :I off ratios (up to ∼10 7 ) 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.

The grain structure is compared for films of the organic semiconductor 6PTTP6 prepared in the open air and in a closed, static atmosphere saturated with xylene vapor. The effect of surface functional groups affixed to the dielectric substrate on the grain appearance and film mobility is probed, to determine optimal fabrication conditions for films with usable mobility, high on/off ratio, and good uniformity. A single-crystal device, also obtained from solution deposition under a particular set of conditions, is characterized and displays an expected higher mobility, >0.1 cm2/Vs. Mesophases are identified in the presence and absence of the xylene and tentatively identified through polarized optical microscopy (POM). Finally, a preliminary observation of the film evolution using an in situ X-ray diffraction (XRD) technique is reported, and lattice spacings are assigned.