Intrinsic Dynamic and Static Nature of π···π Interactions in Fused Benzene-Type Helicenes and Dimers, Elucidated with QTAIM Dual Functional Analysis.

The intrinsic dynamic and static nature of the π···π interactions between the phenyl groups in proximity of helicenes - are elucidated with the quantum theory of atoms-in-molecules dual functional analysis (QTAIM-DFA). The π···π interactions appear in C-∗-C, H-∗-H, and C-∗-H, with the asterisks indicating the existence of bond critical points (BCPs) on the interactions. The interactions of - are all predicted to have a -CS/vdW nature (vdW nature of the pure closed-shell interaction), except for C-∗-C of , which has a -CS/-HB nature (typical-HBs with no covalency). (See the text for definition of the numbers of C and the bay and cape areas). The natures of the interactions are similarly elucidated between the components of helicene dimers : and : with QTAIM-DFA, which have a -CS/vdW nature. The characteristic electronic structures of helicenes are clarified through the natures predicted with QTAIM-DFA. Some bond paths (BPs) in helicenes appeared or disappeared, depending on the calculation methods. The static nature of C-∗-C is very similar to that of C-∗-C in -, whereas the dynamic nature of C-∗-C appears to be very different from that of C-∗-C. The results will be a guide to design the helicene-containing materials of high functionality.