Reversible Light-Induced Dimerization of Secondary Face Azobenzene-Functionalized β-Cyclodextrin Derivatives

Abstract

β-cyclodextrin (βCyD) derivatives equipped with aromatic appendages at the secondary face exhibit tailorable self-assembling capabilities. The aromatic modules can participate in inclusion phenomena and/or aromatic–aromatic interactions. Supramolecular species can thus form that, at their turn, can engage in further co-assembling with third components in a highly regulated manner; the design of nonviral gene delivery systems is an illustrative example. Endowing such systems with stimuli responsiveness while keeping diastereomeric purity and a low synthetic effort is a highly wanted advancement. Here, we show that an azobenzene moiety can be “clicked” to a single secondary O-2 position of βCyD affording 1,2,3-triazole-linked βCyD-azobenzene derivatives that undergo reversible light-controlled self-organization into dimers where the monomer components face their secondary rims. Their photoswitching and supramolecular properties have been thoroughly characterized by UV–vis absorption, induced circular dichroism, nuclear magnetic resonance, and computational techniques. As model processes, the formation of inclusion complexes between a water-soluble triazolylazobenzene derivative and βCyD as well as the assembly of native βCyD/βCyD-azobenzene derivative heterodimers have been investigated in parallel. The stability of the host–guest supramolecules has been challenged against the competitor guest adamantylamine and the decrease of the medium polarity using methanol–water mixtures. The collective data support that the E-configured βCyD-azobenzene derivatives, in aqueous solution, form dimers stabilized by the interplay of aromatic–aromatic and aromatic-βCyD cavity interactions after partial reciprocal inclusion. Photoswitching to the Z-isomer disrupts the dimers into monomeric species, offering opportunity for the spatiotemporal control of the organizational status by light.