Photoswitchable Azobenzene/Cyclodextrin Host-Guest Complexes: From UV- to Visible/Near-IR-Light-Responsive Systems

UV-light-responsive azobenzene (Azo)/cyclodextrin (CD) host-guest complexes are attractive for designing smart stimuli-responsive materials, and have been extensively investigated over the past three decades. However, when applied in biomedical fields, as a result of the harmfulness and poor penetrability of UV light to human tissue, Azo/CD host-guest complexes responsive to light of longer wavelengths is required. In this Minireview, we reviewed the traditional UV-light-responsive Azo/CD host-guest systems and developments to red-shift the switching light to the visible or even to the near-infrared (NIR) light region. Indirect methods, including upconversion and two-photon processes, and direct methods to chemically modify Azo molecules for red-shifting the inducing light were summarized and compared. In addition to biomedical applications, we provide an overview of the potential of visible/NIR-light-responsive Azo/CD host-guest complexes in the design of intelligent multifunctional supramolecular materials that function through orthogonal light control.