Endohedral and exohedral complexes of substituted benzenes with carbon nanotubes and graphene

Non-covalent complexes of cyclohexane and a series of substituted benzenes with short carbon nanotube (CNT) models are investigated primarily at the B97-D3∕TZV(2d,2p) level of theory. Understanding non-covalent interactions of arenes with CNTs is vital for the development of next-generation organic electronic materials and for harnessing CNTs as nano-reactors and vehicles for drug delivery. The interaction of benzene and cyclohexane with the interior and exterior of CNTs depends on the nanotube diameter, particularly for endohedral complexes. Both benzene and cyclohexane interact more strongly with the interior of CNTs than the outside, with benzene exhibiting stronger interactions than cyclohexane for CNTs larger than (8,8). Studies of two benzenes inside of CNTs predict the formation of one-dimensional sandwich and parallel-displaced stacks of benzenes within certain sized CNTs, which could have interesting optoelectronic properties. Concerning the impact of substituents on the interaction of benzene with CNTs, we find that electrostatic interactions do not control substituent effects. That is, the electron-donating or -withdrawing character of the substituents is not correlated with the predicted interaction energies. Moreover, substituent effects are the same for both endohedral and exohedral complexes, despite the different electronic character of the interior and exterior CNT walls. Ultimately, substituent effects in π-stacking interactions with CNTs and graphene are explained by differences in dispersion interactions between the substituents and CNT walls or graphene surface.