Stimuli-responsive porous frameworks

The search for new sophisticated functions integrated in porous solids prompted us to engineer switches and motors in metal-organic and covalent architectures for the construction of working nanodevices. 3D Porous Aromatic Frameworks were built with photo-active monomer units, and could be switched on command between two permanent states, entailing structure breathing and gas sorption switching. A fast molecular rotor in the solid state whose rotation speed approaches that of unhindered rotations in organic moieties even at very low temperatures (10 GHz below 2 K) was realized generating continuous, unidirectional hyperfast rotation with an energy barrier of 6.2 cal/mol. The energy transfer effect with radiation up-grading was also realized in Porous Emitting Frameworks (PEFs): porphyrin (red absorber) and diphenyl-antracene (blue emitter) were integrated in a 3D network showing very effective convertion of low energy light into photons of higher energy. With a similar concept, motors were inserted into metal-organic frameworks (MOFS), wherein two linkers with complementary absorption-emission properties were integrated in the same materials. The linkers were put in action by the visible light up-grading to UV-radiation, for fuelling the motors. MOF nanocrystals comprising high-Z linking nodes interacting with the ionizing radiation, arranged in an orderly fashion at a nanometric distance from ligand emitters showed ultrafast sensitization of the ligand fluorescence, thus supporting the development of new engineered scintillators. A. Comotti, B. L. Feringa et al Nature Chem. 2020, 12, 595; A. Comotti, P. Sozzani et al Nature Chem. 2020, 12, 845; P. Sozzani, A. Comotti, A. Monguzzi et al Adv. Mater. 2019, 31, 1903309; A. Comotti, B. L. Feringa et al J. Am. Chem. Soc. 2020, 142, 9048; A. Comotti, A. Monguzzi et al Nature Photonics 2021, doi 10.1038/s41566-021-00769-z.