Determination of the charge transport abilities of polymorphs [C6F5Cu]2(4,4′-bipy) with different interactions: a density functional theoretical investigation

Abstract

Due to the different molecular stacking conformations, two kinds of intermolecular interactions, arene–arene π-stacking interaction and Cu–Cu interaction coexist in the polymorphs of [C6F5Cu]2(4,4′-bipy) crystals, 3-α and 3-β. However, the relative magnitude of the two kinds of intermolecular interactions in 3-α and 3-β is different. With the help of first-principle band structure calculations, the relationship between the charge transport abilities and the intermolecular interactions in the two polymorphs was investigated for the first time. The analysis of band structures and Г point wave functions of the band-edge state in the valence band of crystal 3-α shows that the Cu–Cu interaction so-called cuprophilic interaction determines the hole transport ability, although this interaction is weaker than that in crystal 2 of C6F5Cu(py) discussed in our previous work, which is a promising hole transport material. For polymorph crystal 3-β, the wave functions of LUMO are mainly localized on the bipyridine (bpy) groups, which are result from the arene–arene π-stacking interaction between the bpy groups. Such a π–π stacking interaction dominates the electron transport ability in the conduction band of 3-β and makes the electron main carrier for transporting. The results are also supported by the analysis of effective masses and density of states (DOS). Thus, the charge transport properties are dominated by different intermolecular interactions due to the different molecule stacking in the two polymorphs.