Development of Novel Photo-responsive Hybrid Polyoxometalates as Potential Molecular Machines

The field of artificial molecular machines, a branch of supramolecular chemistry, focuses on designing molecules capable of controlled motion at the molecular scale. These molecular machines hold great promise for applications in catalysis, materials science, and medicine. Within this context, polyoxometalates (POMs) exhibit remarkable catalytic and redox properties, which could introduce new functionalities when integrated into molecular machine architectures. This thesis explores the development of novel hybrid polyoxometalates (HPOMs) as potential scaffolds for photoswitchable molecular machines. To this end, azobenzene, a photoswitchable molecule, was first grafted onto a Lindqvist-type hexavanadate system to create the first building block of a photoresponsive rotaxane. The successful synthesis of the bis-functionalized hexavanadate (V6Azo) was confirmed using various spectroscopic techniques, including 1H NMR, 51V NMR, ESI-MS, IR, and SC-XRD, which provided structural validation. Subsequently, the end-capping of the resulting molecule with two Anderson–Evans polyoxomolybdates was tested, and the success of the reaction was confirmed by spectroscopic analyses. The formation of pseudorotaxanes was investigated in deuterated water by combining the HPOM compound with α-cyclodextrin (αCD). The establishment of intermolecular interactions between V6Azo HPOM and αCD was monitored via 1H NMR, and the encapsulation of the azobenzene moiety was confirmed by 2D NMR spectroscopy. Finally, the photoswitching behavior and photoactivity of V6Azo were examined using NMR and UV-Vis spectroscopy, both in the absence and presence of CDs. Despite the promising outcome, the assembly showed limited stability, thus hampering a thorough investigation. To avoid decomposition phenomena and enhance the photoactive behavior, a preliminary study was performed on an HPOM featuring an azobenzene molecule functionalized at both ends with two Anderson–Evans polyoxomolybdates ((TrisNH2 AlMo6)2Azo). The synthesis and photoresponsive behavior were confirmed via 1H NMR, showing promising stability for this compound.