School of Chemistry Colloquium: Dr Larissa von Krbek Stimuli responsiveness in molecules, cages, and dynamic libraries

Photoswitchable molecules can reversibly interconvert between two different isomers. With new applications for photoswitches constantly emerging, the necessity arises to continue to develop photoswitches with different properties than the already established ones. We have developed a versatile synthesis for macrocyclic azobenzenes, which allows for facile modification of these photoswitches. One example shows high chemical stability, long half-life of its Z-isomer, quantitative Z→E conversion under white light, and excellent separation of the excitation bands to address either the E or Z- state selectively. Almost quantitative Z→E conversion, even under white light, is a unique feature with an important impact on applications, in which the configuration under ambient light needs to be close to 100%.

Spin-crossover (SCO) metal-organic cages are capable of switching between high-spin and low-spin states, which enables these molecular containers to be used as magnetic sensors and switches. A SCO tetrahedral Fe(II) cage is capable of encapsulating various guests, which stabilize different cage spin states depending on guest size. Conversely, the SCO tetrahedron exhibits different affinities for the guests in different spin states, which is inferred to result from the subtle structural differences of the cavity caused by the change in metal centre spin state.

A dynamic library of metallo-supramolecular assemblies formed from a bis-urea-functionalized subcomponent reconfigured in response to the addition of monosaccharide derivatives, which served as guests for specific library members. The (P) enantiomer of the [Fe(II)2]L3 helical structure bound β-D-glucose selectively over α-D-glucose. As a consequence, the library collapsed into the (P)-[Fe(II)]2L3 helicate following glucose addition.