Regulation of dipolar rotor dynamics by gas adsorption and photoinduced gas uptake/release

Molecular Rotors, especially when bearing dipoles, are an attractive research field entailing a number of useful phenomena, such as switchable ferroelectricity, and the fabrication of dynamic elements of molecular motors in solids. In turn, porous materials are an innovative playground for supporting switchable molecular rotors.[1,2] We have recently discovered hybrid porous materials with intrinsic dynamics due to the presence of fast molecular rotors in their architectures [3,4]. The highly-organized porous scaffolds supporting organic elements allowed the fabrication of fast molecular rotors (k>108 Hz), such as p-phenylene units and dipolar rotors containing C-F dipoles. Such dipolar rotors face the pores and are entirely exposed to the guest molecules which acted as regulators. In a particular example iodine enters the channels and selectively reacts with the double bonds of the divinyl-fluoro-p-phenylene rotors without disrupting the structure, affecting their motion and the dielectric properties.Moreover, we exploited the photoisomerization of molecular crystals containing star-shaped molecules engineered in such a way that photoisomerizable units are attached to a C-atom node [5]. The starting crystal is porous and shows gas adsorption while the modification of molecular shape induced by the irradiation produces a change in adsorption properties. The phenomenon is reversible by relaxation of the molecules, upon heating and visible light irradiation, to the more stable isomer. A gas can be pumped in and out a photoswitchable material, producing a pressure change in a closed vessel: by this actuator work can produced from radiative energy