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.

Organic electronics requires materials with high charge mobility. Despite decades of intensive research, charge transport in high-mobility organic semiconductors has not been well understood. In this Letter, we address the physical mechanism underlying the exceptionally high band-like electron mobility in F-TCNQ (2,5-difluoro-7,7,8,8-tetracyanoquinodimethane) single crystals among a crystal family of similar compounds F-TCNQ (n = 0, 2, 4) using a combined experimental and theoretical approach. While electron transfer integrals and reorganization energies did not show outstanding features for F-TCNQ, Raman spectroscopy and solid-state DFT indicated that the frequency of the lowest vibrational mode is nearly twice higher in the F-TCNQ crystal than in TCNQ and F-TCNQ. This phenomenon is explained by the specific packing motif of F-TCNQ with only one molecule per primitive cell so that electron-phonon interaction decreases and the electron mobility increases. We anticipate that our findings will encourage investigators for the search and design of organic semiconductors with one molecule per primitive cell and/or the poor low-frequency vibrational spectrum.

Recent theoretical studies have shown that charge transport in high-mobility organic semiconductors is limited by low-frequency vibrations because of strong non-local electron-phonon interaction. Here we investigate two high-electron-mobility organic semiconductors with similar molecular structures but considerably different crystal packings, TCNQ and F2-TCNQ, and reveal the relationship between the experimental low-frequency Raman spectra and the calculated contributions of various vibrational modes to the electron-phonon interaction. We suggest that the combination of Raman spectroscopy with solid-state DFT is a powerful tool for probing electron-phonon interaction and focused search for high-mobility organic semiconductors.

We suggest and show computationally that operation of the ribosome could be precisely synchronized by charge transport along the RNA, localization of the charges at certain sites and successive conformational relaxation.

The modeling of organic solar cells (OSCs) can provide a roadmap for their further improvement. Many OSC models have been proposed in recent years; however, the impact of the key intermediates from photons to electricity-hot charge-transfer (CT) states-on the OSC efficiency is highly ambiguous. In this study, we suggest an analytical kinetic model for OSC that considers a two-step charge generation via hot CT states. This hot kinetic model allowed us to evaluate the impact of different material parameters on the OSC performance: the driving force for charge separation, optical bandgap, charge mobility, geminate recombination rate, thermalization rate, average electron-hole separation distance in the CT state, dielectric permittivity, reorganization energy and charge delocalization. In contrast to a widespread trend of lowering the material bandgap, the model predicts that this approach is only efficient along with improvement of the other material properties. The most promising ways to increase the OSC performance are decreasing the reorganization energy, i.e., an energy change accompanying CT from the donor molecule to the acceptor, increasing the dielectric permittivity and charge delocalization. The model suggests that there are no fundamental limitations that can prevent achieving the OSC efficiency above 20%.

Theoretical understanding of charge transport in organic semiconductors is exclusively important for organic electronics, but still remains a subject of debate. The recently discovered record-high band-like electron mobility in single crystals of 2,5-difluoro-7,7,8,8-tetracyanoquinodimethane (F-TCNQ) is challenging from the theoretical viewpoint. First, the very small size of the F-TCNQ molecule implies high reorganization energy that seems incompatible with efficient charge transport. Second, it is not clear why the crystals of a similar compound, 7,7,8,8-tetracyanoquinodimethane (TCNQ), show an inefficient hopping electron transport mechanism. To address these issues, we apply DFT and QM/MM calculations to the F-TCNQ (n = 0,2,4) crystal series. We show that multidimensional intermolecular charge delocalization is of key importance for efficient charge transport in materials consisting of small-sized molecules, and commonly used guidelines for the search for high-mobility organic semiconductors are to be corrected.