Unlike the molecular axle of the first generation of pumps (Nat. Nano. 2015), the axles developed in the first period of the LEAPS project can be functionalized while maintaining their photoinduced pumping functionality (Angew. Chem. 2019, 2020; Chem. Eur. J. 2021; JACS 2021). Building on these results, the construction of autonomous light driven rotary motors based on catenanes was achieved. Moreover, it was shown that macrocyclic rings can be transferred and stored in a molecular reservoir under light irradiation to yield a non-equilibrium structure. This result is highly significant because it unveils a new and unconventional route to convert the energy of light (potentially, sunlight) into chemical energy and store it as such in a nanoscale device (publication in preparation).
A key scientific result of the project is a detailed investigation of the mechanism by which the molecular pumps utilize the energy of light to move directionally in a dissipative non-equilibrium regime. The efficiency of the system was measured, and guidelines to optimize the performance in terms of energy conversion and storage were identified (Nat. Nano. 2022). These experiments represent an important step forward towards understanding the non-equilibrium operation of dynamic molecular-based systems that are at the base of life. The new molecular pumps were modified for incorporation in membranes and in polymers. In the latter case, in particular, polymer gels with photoswitchable properties - and in particular the ability to convert and store light energy into potential energy of the material – were prepared and investigated.
Another remarkable result of the project is the demonstration that the ring shuttling motion in rotaxanes can lead to new and potentially useful functions, such as the transfer of chemical information between two distant sites (PNAS 2018), the control of mechanical chirality and chiral anion recognition (JACS 2019), frustrated ring-axle systems (JACS 2021), coupled rotary-translational motion (Chem 2021), and autonomous shuttling based on photocatalytic mechanisms (JACS 2022). Possibilities emerge not only for the rational design of species with tailor-made functional and structural properties, but also for the development of model systems to understand some of Nature’s most effective regulatory mechanisms, namely, allostery, proton-coupled electron transfer and enantioselective molecular recognition.
Significant progress on photoswitchable molecules and materials (Angew. Chem. 2018, JACS 2018, 2020) and on rotaxane chemistry (EJOC 2019, Chem. Sci. 2021) was also reported, and review/perspective articles on influential journals were published (AOP 2019, Chem. Rev. 2020, ACS Energy&Fuels 2021, JACS Au 2023).