Impact of π-π Interaction Mode and Vinylene Bond Geometry on Helical Wrapping of Carbon Nanotubes

Recent experimental work demonstrates that the parallel displaced (P) and the Y-shaped conformations of the benzene dimer are favorable over the previously assumed lowest energy configuration. Here we report on a systematical study on various conformations of the benzene dimer in excellent agreement with experimental observations. The study also demonstrates the important role of dispersion forces on the structural and electronic stability of parallel displaced and Y-shaped conformations. Our results provide important insight into the nature of π-π interactions. The corresponding conformational effects of π-conjugated polymers on the helical wrapping of single-walled carbon nanotubes are studied using dispersion-corrected density-functional calculations. The effective dispersion of nanotubes depends on the helical pitch length associated with the conformations of linkages as well as π-π stacking configurations. Our electronic structure calculation results reveal that long-range dispersive forces play a significant role in determining the relative stability of T-shaped, Y-shaped, and parallel-displaced P configurations. The implications of dispersion mechanism and future nanotube separations are discussed.