We use a combination of computational and
experimental techniques to study the self-assembly and gelation of
water-soluble perylene bisimides derivatised at the imide position with an
amino acid. Specifically, we study the likely structure of self-assembled
aggregates of the alanine-functionalised perylene bisimide (PBI-A) and the
thermodynamics of their formation using density functional theory and predict
the UV-vis spectra of such aggregates using time-dependent density functional
theory. We compare these predictions to experiments in which we study the
evolution of the UV-Vis and NMR spectra and rheology of alkaline PBI-A
solutions when gradually decreasing the pH. Based on the combined computational
and experimental results, we show that PBI-A self-assembles at all pH values
but that aggregates grow in size upon protonation. Gelation is driven not by
aggregate growth but reduction of the aggregation surface-charge and a decrease
in the colloidal stability of the aggregation with respect to agglomeration.
Liquid crystals of hard rectangles on flat and cylindrical manifolds
