Herein, we report the synthesis and guest‐host complexation between isomeric xylylene interconnected ethyl terminated bis‐viologens (EDV) with p‐sulfonatocalix[4]arene (SC4 A). Guest‐host interactions between EDV and SC4 A were monitored by CV (cyclic voltammetry), 1H and DOSY (Diffusion Ordered Spectroscopy) NMR titrations. CV titrations showed a partial inclusion complex formation between EDV and SC4 A which is further confirmed by 1H NMR and DOSY titrations. It is evident from 1H NMR titrations that all the three isomers of EDV forms a stable inclusion complex with SC4 A where SC4 A caps the terminal. o‐ and m‐ isomers of EDV interacts differently than their corresponding p‐isomer. 1H NMR titration reveals that o‐ and m‐xylylene units are incorporated into the SC4 A cavity whereas p‐xylylene unit is only partially included into the cavity during the interaction. Further, it is observed that the ethyl terminated viologen adopts axial orientation in concordance with previous reports. DOSY measurements further confirmed the formation of inclusion complex between the bis‐viologen and SC4 A and indicated the formation of aggregates at higher concentrations of SC4 A. Results clearly indicate that the bis‐viologens possess multiple binding sites for the multivalent SC4 A host and based on the concentration of SC4 A, several types of interactions exists between the two predicting a complex binding model.
The inclusion of thioflavin T (ThT) with p‐sulfonatocalix[4]arene (p‐SC4) is briefly discussed in solution as well as solid state. The restricted rotation of C−C single bond between indole and benzene ring system is the reason for emission property of ThT. The encapsulation of ThT using a flexible charged host molecule exploit the correlation between the C−C single bond rotation and emission enhancement. The binding of ThT with p‐SC4 in solution state is studied using absorption, emission, electrochemical, 1H NMR and rotating frame nuclear overhauser effect spectroscopy (ROESY) techniques. A stable water insoluble supramolecular complex is synthesized from water soluble ThT and p‐SC4. The structural features of the prepared solid complex is established from infrared (FT‐IR), powder X‐ray diffraction (XRD), Mass, 1H NMR and nuclear overhauser effect spectroscopy (NOESY) analyses.
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