Unveiling The Effects Of Substituents On The Packing Motif And The Carrier Transport Of Dinaphtho-Thieno-Thiophene (Dntt)-Based Materials

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 pi-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.