Synthesis and characterisation of diketopyrrolopyrrole-based hydrogels.

Diketopyrrolopyrrole (DPP) based materials can be easily tuned by functionalising with groups that extend the conjugation and thus alter the electronic properties. When attaching thiophenes to give dithiophene-diketopyrrolopyrroles (DTDPPs), a donor-acceptor-donor system is created that is suitable for charge-transfer applications. This core also promotes π-stacking and hydrophobic interactions. Here, we describe a number of DTDPPs functionalised with amino acids that undergo pH-trigerred gelation. We show that the optical properties of our DTDPPs are affected by whether the amino acids have aromatic or aliphatic side chains. We also describe the effect of solvent polarity. We have successfully produced hydrogels via a pH trigger with examples containing phenylalanine (F), valine (V), leucine (L) and alanine (A) amino acids. Viscosity and small angle X-ray scattering measurements show the presence of micellar structures in solution in water at pH 10.5, with gelation starting at a pH less than 7 due to the formation of a fibrous network.