Unveiling the effects of substituents on the packing motif and the carrier transport of dinaphtho-thieno-thiophene (DNTT)-based materials

Abstract

Molecular modification plays an important role in tuning the packing motif and charge transport in organic semiconductor materials. In particular, electron-withdrawing substituents and functional heteroatoms have seen a recent surge of interest. Here, we modeled four crystal structures of dinaphtho-thieno-thiophene (DNTT) derivatives with the trifluoromethyl (–CF₃) group and heteroatoms (O- and N-atoms), and elaborately delineated the impact of intermolecular interactions to establish the relationship between microscopic molecular structures and macroscopic solid-state packing. The effects of –CF₃, O-, and N-atom positions on the charge transport properties were systematically investigated via multi-scale theoretical simulations. The results show that the reorganization energy and frontier molecular orbital energy levels are more sensitive to the positions of O- and N-atoms than the –CF₃ position. Significantly, the substitution of heteroatoms on the terminal benzene ring can lead to ambipolar materials after introducing –CF₃. The cooperative effect of –CF₃, O-, and N-atom substitution can transform the molecular packing from herringbone-stacking to π-stacking. The simultaneous introduction of –CF₃ in the trans-position and O-, and N-atoms in the terminal benzene ring can bring the most compact packing and more hydrogen bonds. Besides, the transfer integral fluctuation caused by the position of –CF₃ is more intense than that of O- and N-atoms, which originated from the long- and short-axis sliding motions that act as “killer” phonon modes. Our work shows that suitable substituent engineering on p-channel materials might simultaneously realize changes in molecular packing and carrier transport, paving the way toward designing higher-performance specific ambipolar transport materials.