Gelation enabled charge separation following visible light excitation using self-assembled perylene bisimides

Perylene bisimides (PBIs) can be functionalised to enable controlled aggregation into complex supramolecular structures and are promising materials for photovoltaic and solar fuel applications. Amino acid appended PBIs such as PBI-alanine (PBI-A) have been found to form photoconductive films containing worm-like structures that enable charge transport. However, despite being strong chromophores in the visible region, when PBI-A films are prepared by drying down solutions, activity only occurs under UV illumination. This limits potential applications. The requirement for UV illumination has previously been suggested to be due to the large ion-pair energy in the low dielectric environment of the dried samples. Hydrogel films, rehydrated xerogels and dry xerogels of PBI-A can also be prepared offering an ideal sample set to examine the influence of hydration on charge-separation. Using transient absorption (TA) spectroscopy, we demonstrate a correlation between water content and efficiency of generation of long-lived charge separated states within the PBI-A materials, highlighting their potential, particularly for light-driven water splitting

Using the hydrolysis of anhydrides to control gel properties and homogeneity in pH-triggered gelation

The pH of an aqueous solution of a low molecular weight gelator can be adjusted through the hydrolysis of a number of anhydrides to the corresponding acids. The rate of hydrolysis and hence of pH change can be used to control the rate of gel formation. This rate does not affect the primary assembly of the low molecular weight gelator, but does affect the mechanical properties of the resulting gels, as well as the homogeneity and reproducibility of the gels. The mechanical properties are compared by both rheology and dynamic nanoindentation