Facile Construction of a Supramolecular Organic Framework Using Naphthyl Viologen Guests and CB[8] Host via Charge-Transfer Complexation.

Abstract

Herein, we report the synthesis of guest–host systems comprising naphthyl–viologen–naphthyl (Np–Vio–Np) and viologen–naphthyl–viologen (Vio–Np–Vio) guest molecules and their subsequent supramolecular polymerization in the presence of a CB[8] host in water. In addition, the guest complexation of ethyl-terminated trimeric viologen (ETV) with Np–Vio–Np and CB[8] was investigated. As a result of supramolecular interactions, 2D supramolecular organic frameworks with high internal periodicity were constructed. 1H NMR studies clearly demonstrated the formation of a host-stabilized charge-transfer complex via folding back (Np–Vio–Np and Vio–Np–Vio) in the presence of CB[8]. In the case of ETV + Np–Vio–Np + CB[8], a large polymeric network was formed as indicated by the NMR titrations. UV–vis and fluorescence studies clearly confirm the formation of an inter/intra molecular CT complex upon complexation with cucurbit[8]uril. The size obtained using the dynamic light scattering (DLS) method pinpoints the formation of larger supramolecular aggregates in the order of μm through host–guest assembly, which is further complemented by FESEM and TEM. SAXS measurements indicate the formation of a 2D supramolecular polymer/polymer aggregate with long-range order.