ИСТИНА

Thiophene-phenylene co-oligomers (TPCO) are promising optoelectronic materials for light-emitting devices and lasers as they combine efficient charge carrier transport and high luminescence1,2. These organic materials exhibit mostly p-type charge transport; whereas the n-type transport is not easy to realize. Fluorination is a well-known approach to alter the electronic properties of p-type semiconductors. For example, common p-conductive organic semiconductors such as pentacene, copper phthalocyanine, diethynyl naphthalene and oligophenylenevinylenes can be converted to the n-conductive ones via fluoro-substituents3,4. Here, we study the impact of fluorination of the methyl terminal group on the structural and electronic properties of single- and polycrystals of TPCO with the phenylene-thiophene-thiophene-phenylene (PTTP) conjugated core using x-ray diffraction, DFT and dipole moment calculations, total current spectroscopy (TCS) and field-effect transistor (FET) measurements. Our experimental data show that fluorination of the methyl terminal group in CH3-TPCO results in an insignificant impact on the crystal habit and on the molecular orientation vs their basal plane but switches the conductivity from the p-type to the n-type (Fig. 1a). We suggest that the terminal groups control the charge injection type into the FET active layer. This work was partially supported by RFBR (project № 18-03-00020), by RSF (project № 18-12-00499) for material synthesis and device fabrication and studies, and by the Foundation for the advancement of theoretical physics and mathematics «BASIS».