ИСТИНА

Organic light-emitting field-effect transistors (OLETs) allow creating bright and flexible displays that can be more efficient and convenient than modern OLED displays. Single crystals of thiophene-phenelyne co-oligomers (TPCOs) are appropriate candidates for OLETs owing to their high luminescence and effective charge transport. However, in TPCO single crystals the correlation of the molecular order with charge transport and light emission properties is practically unexplored. In this work, we study crystal structure, low- (LF) and high-frequency (HF) vibrations of TPCO 5,5 -bis[4-(trifluoromethyl)phenyl-1-yl]- -bithiophene2 (CF3-PTTP-CF3). According to the X-ray diffraction analysis, its crystals have only 2 molecules per unit cell that simplifies the analysis of the crystal structure role in charge transport and thus in OLET performance. We have recorded HF and LF Raman spectra of solution, powder and single crystals and explored anisotropic properties of scattering. Optical characteristics and intramolecular vibrations were calculated using density functional theory (DFT). The DFT results correlate well with the experimental data. LF Raman spectra are of particular interest as this part of the vibrational spectrum (~10-200 cm-1) enables us to study collective vibrations of the crystal lattice. By studying the temperature dependence of the LF Raman spectra, we correlate the vibrational force constants with the crystal structure parameters extracted from the X-ray diffraction data recorded at different temperatures. The interrelation between intermolecular packing, vibrations and semiconducting properties of the studied crystals are discussed.