title: Differences between the Interactions of Linear and Tetrahedron-like Ditopic Guests with Cucurbit[8]uril: Steric Hindrance and Molecular Structure Play Dominant Roles.
abstract: A tetrahedron-like guest molecule (THV) with four ditopic arms, consisting of viologen (V) and hexylene moieties, was synthesized, and its interaction with cucurbit[8]uril (CB[8]) was investigated. As a reference, the interaction between CB[8] and an analogue of the arm of the linear ditopic guest (LHV) was first explored by1H NMR and UV/Vis spectroscopy. In this case, CB[8] was located on the hexylene moiety and resulted in the formation of a binary complex. However, when THV interacted with CB[8], despite having four arms with four hexylene moieties, only two CB[8] molecules were identified as located on the hexylene moieties; the other two CB[8] molecules resided on the V moieties. Great steric hindrance among the arms played a dominant role in the interaction between THV and CB[8]. Regardless of whether the guest molecule was THV or LHV, CB[8] moved to its V moiety (electron-deficient part) to form the charge-transfer complex upon the addition of a stopper containing a naphthol residue (electron-rich part). Guests LHV and THV were reduced to LHV+(+.)and THV+4(+.)upon the addition of sodium dithionite. Dimerization of LHV+(+.)was enhanced when CB[8] was present in less than 0.5 equivalents. In contrast, dimerization was suppressed when CB[8] was present in more than 0.5 equivalents. However, the V+.units of THV+4(+.)stacked intramolecularly because of the tetrahedron-like molecular structure of THV. The influence of CB[8] on the dimerization of THV+4(+.)was weaker than that on LHV+(+.).
authors.affiliation: School of Chemistry and Chemical Engineering, Shandong University, Jinan, 250100, P.R. China.|Key Laboratory of Special Functional Aggregated Materials, Shandong University, Jinan, 250100, P.R. China.
authors.forename: Shengzhen
authors.initials: S
authors.lastname: Hou
authors.affiliation: School of Chemistry and Chemical Engineering, Shandong University, Jinan, 250100, P.R. China.|Key Laboratory of Special Functional Aggregated Materials, Shandong University, Jinan, 250100, P.R. China.
authors.forename: Hao
authors.initials: H
authors.lastname: Chen
authors.affiliation: School of Chemistry and Chemical Engineering, Shandong University, Jinan, 250100, P.R. China.|Key Laboratory of Special Functional Aggregated Materials, Shandong University, Jinan, 250100, P.R. China.
authors.forename: Haili
authors.initials: H
authors.lastname: Ma
authors.affiliation: School of Chemistry and Chemical Engineering, Shandong University, Jinan, 250100, P.R. China.|Key Laboratory of Special Functional Aggregated Materials, Shandong University, Jinan, 250100, P.R. China.
authors.forename: Yebang
authors.initials: Y
authors.lastname: Tan
keywords: cucurbit[8]uril; host-guest systems; molecular recognition; noncovalent interactions; steric hindrance