reformation of columnar aggregates controlled by the trans–cis isomerization of the
azobenzene moiety are realized by UV irradiation [51].
The gel–sol transition via photoisomerization may change the aggregate and
modulate the interactions between gelator and the surrounding solvent molecules,
which induce swelling or contraction of the gel, as encapsulate bulk liquid depending
on the solvent–gel interface energy. It is worth noting that while light-induced swollen
and deswelling transition is similar with those induced by heating; the microstructural
changes in these processes can be obviously different. Xie and co-workers demonstrated that coassembled gel of the dentron gelator 14 and azobenzene derivative 15
Fig. 2.7 Illustration of the multichannel supramolecular chiroptical switches composed by gelator
12. Reprinted with the permission from Ref. [58]. Copyright 2011 American Chemical Society
Fig. 2.8 Schematic representation showing aggregation of the melamine−azobenzene conjugate
(13) with barbiturate (B1) and cyanurate (C1) derivatives. Reprinted with the permission from Ref.
[51]. Copyright 2005 American Chemical Society
2.2 Light Responsive Gels
19