Photochemically controlled supramolecular curdlan/single-walled carbon nanotube composite gel: Preparation of molecular distaff by cyclodextrin modified curdlan and phase transition control

We propose a single-walled carbon nanotube (SWNT) composite with a molecular recognition property, which is prepared by mixing α- cyclodextrin-modified curdlan (CD-CUR) with SWNTs in water. The visible/near-infrared (Vis/NIR) spectrum of the CD-CUR/SWNT composite exhibits characteristic absorption bands corresponding to the band-gap transitions for van Hove singularities of metallic and semiconductor carbon nanotubes. The structure of the CD-CUR/SWNT composites was characterized by transmission electron microscopy (TEM) and atomic force microscopy (AFM). The TEM and AFM images show that the CD-CUR/SWNT composite exhibits dispersed fibers with a narrow fiber diameter distribution, which suggests that CD-CUR helically wraps around SWNTs to form one-dimensional superstructural composites. Because we hypothesized that the CD-CUR/SWNT composite possesses a molecular recognition property, we attempted to create supramolecular hydrogels containing SWNTs by using a CD-CUR/SWNT composite and a guest polymer (pAC₁₂Azo) with an azobenzene guest pendant. The CD-CUR/SWNT composite selectively forms supramolecular hydrogels with pAC₁₂Azo. UV irradiation (λ= 365 nm) of the supramolecular hydrogel decreases the viscosity upon isomerization of the trans-azo group to give the sol. In contrast, irradiation with visible light at λ= 430 nm (or heating) of the sol state recovers the viscosity to restore the hydrogel within 2 min, indicating that irradiation affects the association and dissociation between the α-CD unit and the azobenzene unit during phase transition. In summary, we demonstrate the formation of a CD-CUR/SWNT composite and a photoresponsive sol-gel supramolecular SWNT hydrogel.