Azobenzene is a well-known derivative of stimulus-responsive molecular switches and has shown superior performance as a potential guest for many synthesized macrocycles such as cyclodextrins (CDs), calixarenes (CXs) and cucurbiturils (CBs). Incorporating stimuli-responsive building blocks in cucurbiturils constitutes the most efficient strategy to endow these supramolecular assemblies with dynamic functions and improved photochromic and solvatochromic properties.<br/>The intermolecular interactions of a variety of N, N-dimethylamino substituted azobenzene dyes with Cucurbituril[7] (CB[7]) were studied. The protonated azonium state of these azobenzenes has a larger affinity for CB[7] and greatly influences the binding mode of the complex. The protonated N, N-dimethylamino azobenzenes are found to be stabilized by hydrogen bonding at the CB[7] portal and hydrophobic and dispersion interactions in the cavity, making them deeply inserted into the cavity. The complexation with CB[7] increases dye solubility in aqueous solutions. We employed this phenomenon to promote complexation-induced protonation, de-aggregation, and enhanced water solubility for a family of azobenzene-conjugated near-infrared heptamthine cyanine guests that can find applications in several fields such as imaging and drug delivery (attached image).<br/>CB7 complexation of azobenzene compounds is emerging as a structurally rich topic with the complexes adopting a range of subtly different co-conformations. Many azobenzene compounds are potential drug candidates or theranostic agents, but they are often not water soluble. However, it should be possible to formulate many of them as CB7 inclusion complexes with improved solubility, stability, and pharmaceutical profile. One of the goals of future studies is to develop systems with enhanced kinetic and thermodynamic stability in buffer solutions.

Complexation of azobenzene dyes inside cucurbituril[7]

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