Using Aggregation-Induced Emission to Understand Dipeptide Gels

We describe the formation of structured liquids and gels from a functionalised dipeptide based on tetraphenylethylene. Tetraphenylethylene is well-known to be able to undergo aggregation-induced emission. We use the emission data to understand the behaviour of the dipeptide in water under a variety of conditions. The dipeptide forms viscous solutions at high pH. Gels can be formed by a pH-trigger, but syneresis occurs. Addition of a calcium salt also leads to a gel with slight syneresis. Addition of sodium chloride leads to a self-supporting material, but this is not a true gel from the rheological perspective. From the emission data, we infer that there are limited structural changes on addition of sodium chloride or acid, but there are significant changes in molecular packing when the gel is formed by addition of a calcium salt.