Enhancing charge mobilities in selectively fluorinated oligophenyl organic semiconductors: a design approach based on experimental and computational perspectives

Fluorination can be used to tune optoelectronic properties at the molecular level. A series of oligophenyls with various difluorinations of the phenyl rings has been synthesized, crystalized, structurally resolved and computationally analyzed for charge mobility. We find that difluorination of the phenyl rings at para positions leads to oligophenyls that are stacked in symmetrical overlap with significantly enhanced hole mobility as well as the highest electron mobility of the molecules considered. Other difluorinations lead to relatively shifted molecular units in the pi-stacked crystal and therefore to lower mobilities. The selectively fluorinated oligophenyls were synthesized using the Suzuki-Miyaura cross coupling reaction. The structures of the products were characterized by X-ray diffraction (XRD), H-1, C-13, F-19 NMR spectroscopy and gas chromatography (GC)/mass spectroscopy (MS) measurements. Computational analysis of the materials based on state-of-the-art tools are used to predict their charge transport properties in the crystal phase. In short, we establish a molecular design approach based on fluorination of oligophenyls to achieve enhanced hole mobilities and relatively high electron mobilities.