Anion-tuning of supramolecular gel properties

The study of supramolecular gels has developed into a well-recognised field of materials science, pertaining to the general area of soft matter. The use of small molecules that aggregate through supramolecular interactions (such as hydrogen bonds, π–π interactions, coordination bonds and van der Waals interactions) has given materials scientists an alternative to polymeric compounds for the development of practical gels. There have been further attempts to functionalize, activate or control the physical properties of such gels by means of the reversibility of the interactions between the component molecules. Tuning of these characteristics has been accomplished by using mechanical, thermal, electrochemical, electromagnetic and chemical stimuli. The use of anions as a chemical stimulus has been a recent development and is the subject of this Perspective. Small anions can be used to modulate the physical properties of supramolecular gels by interacting with the low-molecular-weight gelators from which such materials are composed. A better understanding of this anion-tuning effect will aid in the rational design of responsive gels that may prove useful for a number of practical applications.