Electrospun UV-responsive supramolecular nanofibers from a cyclodextrin–azobenzene inclusion complex

Abstract

A combination of the unique hosting properties of cyclodextrins (CDs) and the peculiar UV-responsive trans–cis isomerization of the guest molecule azobenzene has endowed light-responsibility of the inclusion complex (IC). The IC of 4-aminoazobenzene (AAB) and hydroxypropyl-β-cyclodextrin (HPβCD), with its inherent viscosity from hydrogen bondings between CDs and π–π stacking between AABs, was electrospun into nanofibers from water without using any carrier polymer matrix. The integrity of electrospun ICs was proven by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), together with Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The homogeneous distribution of HPβCD–AAB-IC was confirmed by surface chemistry mapping using time-of-flight secondary ion mass spectrometry (ToF-SIMS). The UV response of ICs prior to, during and post electrospinning was investigated. UV irradiation prior to electrospinning caused precipitation of AAB from the aqueous IC solution. UV irradiation during electrospinning flight demonstrated the interruption of ICs and consequently broader diameter distributions were obtained. Post-spinning UV irradiation induced topography and adhesion force changes on the electrospun nanofiber surfaces, demonstrated by in situ atomic force microspectroscopy (AFM) quantitative nanomechanical mapping. The present study is the first case where the supramolecule with stimuli response was electrospun into nanofibers with retained activity.