Speaker
Description
Gels can be defined as composite materials resulting from the combination of a solid (gelator) capable of generating a three-dimensional network that retains the flow of a much larger quantity of fluid due to surface tension. In particular “supramolecular gels” are an increasingly important class of new materials, defined by the ability of the molecular components to self-assemble through non-covalent or supramolecular interactions, generating a three-dimensional network that yields to gels. Importantly, these gels can be tailored to present optical and chiroptical activities,[1] to obtain composite or hybrid materials,[2,3] and to be biocompatible or have therapeutic activity.[4] Due to the fact that the nature of the interactions maintaining the network is dynamic and non-covalent the gelation is reversible in most of the cases. Hence, one of the most pursued characteristics when rationally designing these systems is the responsiveness to external factors such as temperature, mechanical stress, light, chemical agents, enzymes, and pH.[5] Of all of these, the use of light to induce transformations in gels is particularly interesting because it is non-invasive, can be remotely applied, and, if the alteration is reversible, does not change the chemical composition. But, when rationally designing a supramolecular building block for these new materials, it is crucial to rationally design the self-assembly interactions to foster gelation over crystallization because there is a delicate balance for a low-weight molecule to behave as a gelator or as a crystal building block. A balance that could be tuned by changing the experimental conditions during system decomposition and phase formation.[6]
We propose a dual‑beamline, multimodal approach using XALOC and NCD‑SWEET on the same samples to study self‑assembly across multiple length scales, with the aim of elucidating the physicochemical mechanisms that govern this balance. For that, we studied a model system capable of developing reversible trans-to-cis and cis-to-trans transitions upon irradiation with light sources of different energy (365 nm and 520 nm, respectively). Remarkably, as this molecule developed crystalline gels under specific conditions, this photoresponsive feature allowed for the study of simultaneous single-crystal-to-liquid crystal and gel-to-sol transitions, and vice versa. To have a clear insight into the structure-property relationship, we performed high quality single crystal X-ray diffraction studies, which successfully led to the determination of the molecular structure of the systems of interest. Even more, we also conducted SAXS and WAXS experiments to depict a clearer panorama of all the structural changes that are taking place while irradiating with different light sources. The necessity of performing fast data-acquisition during short periods of time to correctly follow the self-assembly process while introducing external irradiation sources into the sample cabinet to account for the stimuli-responses studies made the use of cutting-edge facilities as the BL11 - NCD-SWEET and BL13 - XALOC beamlines mandatory. We believe that this example reflects the synergic nature of these two beamlines working together to tackle novel challenges in crystallography and new materials.