Influence of Phenyl Perfluorination on Charge Transport Properties of Distyryl-Oligothiophenes in Organic Field-Effect Transistors

In this study, solution and solid-state properties, as well as the organic thin film transistor (OTFT) behavior, of two perfluoroarene-containing analogues of distyryl-oligothiophenes (DFSnT, n = 2, 4) are presented. High-vacuum evaporated thin films were implemented as semiconducting layers into organic thin film transistors (OTFTs). The results aim at understanding the influence of perfluorination on the arene moieties on the distyryl-oligothiophene skeleton (DSnT). Surprisingly, OTFT measurements performed in air and under moderate vacuum for DFSnT films show that these compounds behave as p-type semiconductors. Furthermore, detailed shelf-life tests of hole mobility (μ) and threshold voltage (Vt) under atmospheric conditions (air, temperature) of OTFTs based on DFS4T are shown to underscore the air-operating performance of p-type DFSnT compounds. A theoretical study using density functional theory (DFT) and spin density distribution provides a better understanding of the effects of perfluorination on the arene moieties occurring in the intramolecular electronic properties. The combined analyses, theory and experimental, stress that modifications of p-type distyryl-oligothiophene cores with electronegative substituents lower the lowest unoccupied molecular orbital (LUMO) energy but not sufficiently, as compared to literature compounds, to facilitating electron injection and switch from p- to n-charge transport in OTFT devices.