Supramolecular Self-Assembly of Cucurbit[8]uril with 2,2′-(Heptane-1,7-dily) Dibenzimidazolium Chloride

The interaction and corresponding supramolecular self-assembly of cucurbit[8]uril (Q[8]) with 2,2'-(heptane-1,7-dily) dibenzimidazolium chloride (SBHt) in solutions were investigated by means of H-1 NMR spectroscopy, dynamic light scattering (DLS), ultraviolet absorption spectroscopy, fluorescence spectroscopy in details. The pKa shift of guest in the presence of Q[8] was first investigated in order to decide the pH of medium condition for investigation of interaction and corresponding supramolecular self-assembly of related host and guest. H-1 NMR analysis revealed that the proton resonances of the aromatic ring move upfield of the unbound SBHt proton resonances, while the proton resonances of the alkyl chain move downfield of the unbound SBHt proton resonances, suggesting that interaction of Q[8] with SBHt could result in the formation of supramolecular polymer, and this suggestion was further confirmed by dynamic light scattering (DLS), ultraviolet absorption spectroscopy, fluorescence spectroscopy technologies. The average radius of the aggregates in the aqueous solution of Q[8]-SBHt is revealed to be over 100 nm. This gives an unambiguous evidence for the formation of a supramolecular architecture among Q[8] and SBHt. Moreover, the observed stability constants of Q[8]/SBHt host-guest complex were obtained by ultraviolet absorption spectroscopy, fluorescence spectroscopy technologies, they were 2.79x10(5) L/mol and 2.48x10(5) L/mol respectively. While the crystals structure analysis showed a simple 1 : 2 host-guest complex, which was different from that formed in solution. The competition of the outer-surface interaction of Q[n]s and the host-guest inclusion interaction could be the reason resulting in the formation of different self-assemblies of Q[8]/SBHt in solution and in solid state. In this particular case, the outer-surface interactions of Q[n] s include: 1) the C-H center dot center dot center dot pi interaction between the waist methine groups or the bridged methylene groups on the outer surface of Q[8] molecule and the aromatic moiety in SBHt; 2) pi center dot center dot center dot pi stacking between portal carbonyl and the aromatic moiety in SBHt; moreover, 3) the unusual hydrogen bonding between the portal carbonyl oxygen of a Q[8] molecule and the waist methine groups or the bridged methylene groups from neighboring Q[8] molecule.