We exploit a reversible acid–base triggered molecular shuttling process to switch an appropriately designed rotaxane between prochiral and mechanically planar chiral forms. The mechanically planar enantiomers and their interconversion, arising from ring shuttling, have been characterized by NMR spectroscopy. We also show that the supramolecular interaction of the positively charged rotaxane with optically active anions causes an imbalance in the population of the two enantiomeric coconformations. This result represents an unprecedented example of chiral molecular recognition and can disclose innovative approaches to enantioselective sensing and catalysis.

The transport of substrates is one of the main tasks of biomolecular machines in living organisms. We report a synthetic small‐molecule system designed to catch, displace, and release molecular cargo in solution under external control. The system consists of a bistable rotaxane that behaves as an acid–base controlled molecular shuttle, whose ring component bears a tether ending with a nitrile group. The latter can be coordinated to a ruthenium complex that acts as the load, and dissociated upon irradiation with visible light. The cargo loading/unloading and ring transfer/return processes are reversible and can be controlled independently. The robust coordination bond ensures that the cargo remains attached to the device while the transport takes place.

The size‐tunable emission of luminescent quantum dots (QDs) makes them highly interesting for applications that range from bioimaging to optoelectronics. For the same applications, engineering their luminescence lifetime, in particular, making it longer, would be as important; however, no rational approach to reach this goal is available to date. We describe a strategy to prolong the emission lifetime of QDs through electronic energy shuttling to the triplet excited state of a surface‐bound molecular chromophore. To implement this idea, we made CdSe QDs of different sizes and carried out self‐assembly with a pyrene derivative. We observed that the conjugates exhibit delayed luminescence, with emission decays that are prolonged by more than 3 orders of magnitude (lifetimes up to 330 μs) compared to the parent CdSe QDs. The mechanism invokes unprecedented reversible quantum dot to organic chromophore electronic energy transfer.

The size‐tunable emission of luminescent quantum dots (QDs) makes them highly interesting for applications that range from bioimaging to optoelectronics. For the same applications, engineering their luminescence lifetime, in particular, making it longer, would be as important; however, no rational approach to reach this goal is available to date. We describe a strategy to prolong the emission lifetime of QDs through electronic energy shuttling to the triplet excited state of a surface‐bound molecular chromophore. To implement this idea, we made CdSe QDs of different sizes and carried out self‐assembly with a pyrene derivative. We observed that the conjugates exhibit delayed luminescence, with emission decays that are prolonged by more than 3 orders of magnitude (lifetimes up to 330 μs) compared to the parent CdSe QDs. The mechanism invokes unprecedented reversible quantum dot to organic chromophore electronic energy transfer.

Molecular and supramolecular‐based systems and materials that can perform predetermined functions in response to light stimulation have been extensively studied in the past three decades. Their investigation continues to be a highly stimulating topic of chemical research, not only because of the inherent scientific value related to a bottom‐up approach to functional nanostructures, but also for the prospective applications in diverse fields of technology and medicine. Light is an important tool in this context, as it can be conveniently used both for supplying energy to the system and for probing its states and transformations. In this microreview we recall some basic aspects of light‐induced processes in (supra)molecular assemblies, and discuss their exploitation to implement novel functionalities with nanostructured devices, machines and materials. To this aim we illustrate a few examples from our own recent work, which are meant to illustrate the trends of current research in the field.

A high-yielding synthesis of a series of polyimide dendrimers, including decacyclene- and perylene-containing dendrimer D6, in which two types of polyimide dyes are present, is reported. In these constructs, the branching unit is represented by trisphenylamine, and the solubilizing chains by N-9-heptadecanyl-substituted perylene diimides. The photophysical properties of the dendrimers have been studied by absorption, steady-state, and time-resolved emission spectroscopy and pump-probe transient absorption spectroscopy. Photoinduced charge-separated (CS) states are formed on the femtosecond timescale upon visible excitation. In particular, in D6, two different CS states can be formed, involving different subunits that decays independently with different lifetimes (ca. 10-100 ps).

The development of artificial nanoscale motors that can use energy from a source to perform tasks requires systems capable of performing directionally controlled molecular movements and operating away from chemical equilibrium. Here, the design, synthesis and properties of pseudorotaxanes are described, in which a photon input triggers the unidirectional motion of a macrocyclic ring with respect to a non-symmetric molecular axle. The photoinduced energy ratcheting at the basis of the pumping mechanism is validated by measuring the relevant thermodynamic and kinetic parameters. Owing to the photochemical behavior of the azobenzene moiety embedded in the axle, the pump can repeat its operation cycle autonomously under continuous illumination. NMR spectroscopy was used to observe the dissipative non-equilibrium state generated in situ by light irradiation. We also show that fine changes in the axle structure lead to an improvement in the performance of the motor. Such results highlight the modularity and versatility of this minimalist pump design, which provides facile access to dynamic systems that operate under photoinduced nonequilibrium regimes.

Among the plethora of photochromes reported so far, azobenzene has been proven to be the most suitable photoswitch for molecular systems and materials, due to its highly efficient and clean E-Z photoisomerization. Here we report two ammonium-based molecular axles bearing one or two p-cyanoazobenzene units at the extremities, able to form pseudorotaxanes with a crown ether macrocycle. The photochemistry of these compounds was studied in the isolated forms and in the pseudorotaxanes, showing that the functionalization speeds up the threading process without affecting the photochemical properties of the system. These results suggest that the investigated pseudorotaxanes can form the basis of new prototypes of artificial molecular-level pumps.