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 pi center dot center dot center dot pi interactions between the phenyl groups in proximity of helicenes 3-12 are elucidated with the quantum theory of atoms-in-molecules dual functional analysis (QTAIM-DFA). The pi center dot center dot center dot pi 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 3-12 are all predicted to have a p-CS/vdW nature (vdW nature of the pure closed-shell interaction), except for C-2(bay)-*-C-7(bay) of 10, which has a p-CS/t-HBnc 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 6:6 and 7:7 with QTAIM-DFA, which have a p-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-cape-*-C-cape is very similar to that of C-bay-*-C-bay in 9-12, whereas the dynamic nature of C-cape-*-C-cape appears to be very different from that of C-bay-*-C-bay. The results will be a guide to design the helicene-containing materials of high functionality.

Automated summary

This study elucidates the intrinsic dynamic and static nature of the pi center dot center dot center dot pi interactions between the phenyl groups in helicenes using the quantum theory of atoms-in-molecules dual functional analysis (QTAIM-DFA). The results provide insights into the characteristics of helicenes and guide the design of functional helicene-containing materials.