Reactivity and selectivity modulation within a molecular assembly: recent examples from photochemistry

In recent years, photochemical reactions have emerged as powerful transformations which significantly expand the repertoire of organic synthesis. However, a certain lack of selectivity can hamper their application and limit their scope. In this context, a major research effort continues to focus on an improved control over stereo- and chemoselectivity that can be achieved in molecular assemblies between photosubstrates and an appropriate host molecule. In this tutorial review, some recent, representative examples of photochemical reactions have been collected whose unique outcome is dictated by the formation of a molecular assembly driven by non-covalent weak interactions. Graphical Abstract

Exploring Electron-Sink Behaviors of Molecular Assemblies

Metal carbonyl clusters, such as the [Ni32C6(CO)36]6- anion, have been documented to display electron-sink phenomena. However, such large clusters suffer from inefficient yields due to their demanding and unreliable synthesis routes. To approach this obstacle, we investigated the electrochemical properties of Fe2(μ-PPh2)2(CO)6, an organometallic complex known to experience a reversible two-electron transfer process. In this work, we report a modular synthetic strategy for expanding the electron-sink capacity of molecular assemblies by installing Fe2(μ-PPh2)2(CO)6 redox mediators to arylisocyanide ligands. Specifically, the coordination of three Fe2(μ-PPh2)2(CO)6 subunits to a trifunctional arylisocyanide ligand produces an electron-sink ensemble that can accommodate six electrons, exceeding the precedent benchmark [Ni32C6(CO)36]6- anion. The redox mediators store electrons within quantized unoccupied frontier orbitals and act as individual quantum capacitors. Ultimately, we propose to modify the electrode surfaces with these redox mediators to examine the relationship between the electrode’s mesoscopic structure and its macroscopic capacitance.