ИСТИНА

Single crystals of thiophene-phenylene co-oligomers (TPCO) have demonstrated high potential for organic light-emitting transistors (OLETs) due to a unique combination of decent charge-carrier mobility and excellent photoluminescence (PL) efficiency . The attractive feature of organic single crystals is the perfect alignment of the molecules and their transition dipole moments, which might cause electroluminescence (EL) and PL to be strongly polarized. Usually, for OLETs, organic semiconductor crystals with vertical or nearly vertical orientations of molecular transition dipole moments are used, which results in a strong waveguiding effect so that light outcoupling normally to OLET’s plane is ineffective. The effects of EL anisotropy in organic semiconductor single crystals almost have not been studied, and for such studies the in-plane orientation of transition dipole moments is highly desired. In this work, we study EL polarization anisotropy in single crystals of 1,4-bis{5-[4-(trimethylsilyl)phenyl]thiophen-2-yl}benzene (AC5-TMS), whose PL has essential in-plane orientation . For this purpose, OLETs with interpenetrating source and drain electrodes were fabricated. As Fig.1d shows, the EL intensity is minimal when the polarizer is collinear with the longest crystal edge, corresponding to the crystal a-axis. From X-ray diffraction data it is known that molecules are oriented almost perpendicular to a-axisii. Therefore, we conclude that EL is strongly polarized along the molecular backbone; this is in accordance with data on PL polarization anisotropyii. This work was supported by RFBR (project № 18-12-00499-П).