Photomodulation of Supramolecular Systems Containing Bioactive Small Molecules and Biopolymers

Molecular photoswitches can change their conformation upon irradiation with light and convert this molecular movement into macroscopic changes of sophisticated materials. By combining state-of-the-art azobenzenes with supramolecular low-molecular-weight gelators, based on cyclic dipeptides, photomodulation of hydrogels was achieved. Photochromic amino acids with structures related to the natural L-phenylalanine were an essential element. The supramolecular hydrogels are multi-responsive towards pH, ions, temperature, and, in particular, light. Hereby the gelator F₂-PAP-DKP-Lys can be turned into a sol upon irradiation with green light and within this transition a drug, for example an antibiotic, was released. The further improved supergelator Cl₄-PAP-DKP-Lys₂ is reversibly switchable with red and violet light in the range of 0.2-0.5% in an isotonic Ringer's solution. At a concentration of 1%, the hydrogel consisting of Cl₄-PAP-DKP-Lys₂ remains stable in a boiling water bath. Thus, we envision that the enhanced stability of the supramolecular assembly of Cl₄-PAP-DKP-Lys₂ and orthogonal biocompatibility of F₂-PAP-DKP-Lys, could enable further applications, spanning from regenerative medicine to electronic devices, besides our future vision towards photopharmacology.