Supra-dendron gelator based on Azobenzene-cyclodextrin Host-Guest interaction: Photoswitched Optical and Chiroptical reversibility.

A novel amphiphilic dendron (AZOC(8)GAc) with three l-glutamic acid units and an azobenzene moiety covalently linked by an alkyl spacer has been designed. The compound formed hydrogels with water at very low concentration and self-assembled into chiral-twist structures. The gel showed a reversible macroscopic volume phase transition in response to pH variations and photo-irradiation. During the photo-triggered changes, although the gel showed complete reversibility in its optical absorptions, only an incomplete chiroptical property change was achieved. On the other hand, the dendron could form a 1: 1 inclusion complex through a host-guest interaction with alpha-cyclodextrin (alpha-CD), designated as supra-dendron gelator AZOC(8)GAc/alpha-CD. The supra-dendron showed similar gelation behavior to that of AZOC(8)GAc, but with enhanced photoisomerization-transition efficiency and chiroptical switching capacity, which was completely reversible in terms of both optical and chiroptical performances. The self-assembly of the supra-dendron is a hierarchical or multi-supramolecular self-assembling process. This work has clearly illustrated that the hierarchical and multi-supramolecular self-assembling system endows the supramolecular nanostructures or materials with superior reversible optical and chiroptical switching.