Molecular Switches and Photoresponsive Systems

Molecular switches are discrete entities capable of undergoing reversible structural or electronic changes in response to external stimuli, with light standing out as a particularly versatile trigger. Photoresponsive systems exploit the photochromic properties of certain chromophores—such as azobenzenes, diarylethenes and donor–acceptor Stenhouse adducts—to achieve precise, non-invasive control over molecular configuration, polarity or binding affinity. Mechanically interlocked architectures, notably rotaxanes and catenanes, integrate photoswitchable units into defined topologies, enabling functions ranging from directional motion to logic operations. Advances in synthetic design have led to electrically driven motors, wavelength-selective control of multiple switches in a single solution and supramolecular assemblies with reversible luminescence. These developments underpin applications in smart materials, data storage, anticounterfeiting, nanorobotics and photopharmacology. By translating nanoscale photoinduced events into macroscopic responses—through hierarchical assembly into interfaces, liquid crystals or polymer networks—researchers aim to create adaptive devices capable of reconfiguring in real time. The global significance of these systems lies in their ability to merge molecular precision with on-demand functionality, promising breakthroughs in sustainable energy conversion, responsive surfaces and remote-controlled therapeutics.

Research from Nature Portfolio

Recent work has demonstrated an electrically driven molecular motor based on a [3]catenane scaffold in which two interlocked rings undergo unidirectional circumrotation under an oscillating voltage. This system achieves continuous directional motion without chemical waste and represents a step towards integrating molecular motors into solid‐state devices. Parallel efforts have realised orthogonal photocontrol of two distinct photoswitches—one a donor–acceptor Stenhouse adduct and the other an azobenzene—within a single medium. By exploiting three different irradiation wavelengths and thermal relaxation, each switch operates independently, opening routes to multiplexed photonic logic. In another advance, a photoresponsive supramolecular coordination polyelectrolyte has been constructed from lanthanide ions, bis-ligands and a diarylethene unit. Upon alternating UV and visible light, the material toggles between luminescent on and off states, enabling multilevel anticounterfeiting patterns in security inks.

Molecular Switches and Photoresponsive Systems publication trend

The graph below shows the total number of articles in molecular switches and photoresponsive systems across all publications each year (not limited to Nature Index journals).

Technical terms

Molecular switch: A molecule that adopts two or more stable states in response to an external stimulus.

Photoresponsive system: An assembly that changes its physical or chemical properties upon exposure to light.

Mechanically interlocked molecule (MIM): A structure such as a rotaxane or catenane in which components are linked by topology rather than covalent bonds.

Photochromism: The reversible transformation between two molecular forms with distinct absorption spectra under light irradiation.

Photoisomerisation: The light-induced conversion of a molecule from one isomeric form to another.

Orthogonal photoswitching: Independent control of multiple photoswitchable units using different wavelengths of light.

References

1. An electric molecular motor. Nature (2023).
2. Collective Molecular Machines: Multidimensionality and Reconfigurability. Nano-Micro Letters (2024).
3. Enlightening Materials with Photoswitches. Advanced Materials (2020).
4. Orthogonal photoswitching in a multifunctional molecular system. Nature Communications (2016).
5. Photoresponsive supramolecular coordination polyelectrolyte as smart anticounterfeiting inks. Nature Communications (2021).
6. Molecular photoswitches in aqueous environments. Chemical Society Reviews (2021).