Controlling the local arrangements of π-stacked polycyclic aromatic hydrocarbons through substituent effects

Abstract

PAHs such as coronene and hexa-peri-hexabenzocoronene (HBC, a nanographene) are commonly used in discotic liquid crystals, for which achieving long-range columnular order is vital for the development of materials with maximized charge-transfer rates. We demonstrate that simple substituents can have a dramatic impact on the local orientation of π-stacked polycyclic aromatic hydrocarbons (PAHs), even in the absence of steric or other non-covalent interactions (e.g.: hydrogen bonds). The strong dependence of these π-stacking interactions on the relative position of substituents is a result of the direct, through-space interactions of aryl substituents. B97-D/TZV(2d,2p) interaction energies are presented for stacked dimers of substituted benzenes, coronenes, and HBC, which display diverse orientation potentials depending on the nature of the substituents. The results show that the position of the global energy minimum for stacked PAHs depends on the nature of the aryl substituents. The preferred arrangement of stacked coronenes, for example, can be shifted from a fully staggered arrangement to a fully eclipsed arrangement through the introduction of complementary pairs of substituents.