Two main factors governing the effect of terminal substituents on the properties of thiophene–phenylene co-oligomers are revealed.

Efficient operation of organic electronic devices requires high charge‐carrier mobilities in their active layers, but only several organic semiconductors show confirmed charge‐carrier mobilities exceeding that of amorphous silicon (≈1 cm2 V−1 s−1). Charge transport in high‐mobility organic semiconductor crystals is considerably hindered by non‐local electron‐phonon interaction (NLEPI) transforming dynamic disorder induced by low‐frequency (LF) vibrations into fluctuations of charge transfer integrals. In this work, using two crystals of naphthalene diimide derivatives as an example, LF vibrational modes that strongly modulate the charge transfer integrals are computationally revealed. The importance of the discussed LF modes for limiting the charge‐carrier mobility is justified by analyzing the effect of the dynamic disorder on the charge‐carrier dynamics, estimating the charge‐carrier mobility in the two crystals, and observing quite a good agreement of the latter with the experimental values. Finally, it is shown that the contribution of various modes to the NLEPI correlates with their experimental Raman intensities. As a result, it is suggested that LF Raman spectroscopy can be used for experimental study of NLEPI, which can help with screening organic semiconductors showing high charge‐carrier mobility and promote rational design of such materials.

Organic optoelectronics requires materials combining bright luminescence and efficient ambipolar charge transport. Thiophene-phenylene co-oligomers (TPCOs) are promising highly emissive materials with decent charge-carrier mobility; however, they typically show poor electron injection in devices, which is usually assigned to high energies of their lowest unoccupied molecular orbitals (LUMOs). A widely used approach to lower the frontier orbitals energy levels of a conjugated molecule is its fluorination. In this study, we synthesized three new fluorinated derivatives of one of the most popular TPCOs, 2,2′-(1,4-phenylene)­bis­[5-phenylthiophene] (PTPTP) and studied them by cyclic voltammetry, absorption, photoluminescence, and Raman spectroscopies. The obtained data reveal a positive effect of fluorination on the optoelectronic properties of PTPTP: LUMO levels are finely tuned, and photoluminescence quantum yield and absorbance are increased. We then grew crystals from fluorinated PTPTPs, resolved their structures, and showed that fluorination dramatically affects the packing motif and facilitates π-stacking. Finally, we fabricated thin-film organic field-effect transistors (OFETs) and demonstrated a strong impact of fluorination on charge injection/transport for both types of charge carriers, namely, electrons and holes. Specifically, balanced ambipolar charge transport and electroluminescence were observed only in the OFET active channel based on the partially fluorinated PTPTP. The obtained results can be extended to other families of conjugated oligomers and highlight the efficiency of fluorination for rational design of organic semiconductors for optoelectronic devices.