Photo switchable activation of sigma-hole

Project Information

HALO

Grant agreement ID: 101146294

DOI

10.3030/101146294

Project closed

EC signature date 18 March 2024

Start date 1 July 2024

End date 30 June 2026

Funded under

• Marie Skłodowska-Curie Actions (MSCA)

Total cost

No data

EU contribution

€ 188 590,08

Coordinated by

POLITECNICO DI MILANO
Italy

Periodic Reporting for period 1 - HALO (Photo switchable activation of sigma-hole)

Reporting period: 2024-07-01 to 2026-06-30

Summary of the context and overall objectives of the project

The ability to dynamically control molecular interactions is a fundamental requirement for the development of advanced functional materials, responsive molecular systems and next-generation technologies. In biological systems, molecular recognition and regulation are often achieved through reversible changes in electronic structure, enabling precise control of interactions without requiring large structural rearrangements. Translating such principles into synthetic molecular systems remains a significant challenge, particularly for controlling weak non-covalent interactions that govern processes such as molecular recognition, self-assembly, sensing and transport.
The HALO project addressed this challenge by developing light-responsive molecular platforms capable of electronically regulating halogen-based non-covalent interactions. The project explored the use of photo-switchable molecular frameworks to control the electronic properties of halogen-containing interaction sites, providing a new strategy for externally triggered modulation of supramolecular behaviour. Light was selected as an attractive stimulus because it enables remote, non-invasive and highly selective control under mild conditions.
The overall objective was to establish fundamental design principles linking photoinduced electronic changes with modulation of molecular interactions. By combining synthetic chemistry, photophysical analysis, structural characterization, solution-state studies and computational approaches, the project aimed to create a deeper understanding of how molecular electronic states can be translated into controllable intermolecular interactions. The expected long-term impact is the development of new concepts for responsive molecular materials, with potential applications in areas including molecular recognition, sensing, catalysis, transport systems and adaptive functional materials.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The project involved the design, synthesis and investigation of a family of photoresponsive molecular systems incorporating electronically tunable halogen-containing interaction sites. A systematic molecular library was prepared by varying both the position and nature of the halogen substituents and by modifying the photoswitch framework to optimize photochemical performance. The photophysical behaviour of the developed systems was investigated using UV–visible spectroscopy to establish their photo-switching capability, reversibility and thermal relaxation characteristics. Structural modifications were identified that significantly improved the lifetime of the photo-generated state while maintaining efficient reversible photo-conversion.
The influence of photoinduced electronic changes on molecular interactions was subsequently investigated through complementary experimental approaches. Single-crystal X-ray diffraction provided direct structural information on interaction geometries in the activated molecular state, while solution-state spectroscopic studies established that the electronic changes associated with photo-switching were maintained in solution.
These results were supported by electronic structure calculations, which provided insight into the relationship between molecular polarization, electronic redistribution and interaction strength. Together, these studies established a complete experimental framework connecting molecular photo-switching with tunable non-covalent interactions. The project demonstrated that photoinduced electronic changes can be translated into measurable modifications of molecular recognition properties, providing a foundation for the future development of light-controlled supramolecular systems.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The HALO project advances the state of the art in molecular photoswitching and supramolecular chemistry by introducing a strategy in which light controls non-covalent interactions through electronic modulation rather than solely through large-scale structural rearrangement. Existing approaches for controlling molecular recognition commonly rely on conformational changes, chemical modification or external electrochemical stimuli. The project demonstrates an alternative concept based on direct coupling between photoinduced electronic redistribution and interaction strength. The developed molecular systems provide fundamental insight into how changes in molecular polarization can influence directional non-covalent interactions. Beyond the specific molecular platform investigated, the design principles established in this project may be extended to other responsive molecular architectures and interaction motifs. The outcomes create opportunities for future development of adaptive materials, molecular sensors, responsive assemblies and functional systems where external control of molecular interactions is required. Further research will focus on expanding the range of responsive systems, improving operational performance under practical conditions and exploring applications where light-controlled molecular recognition can provide functional advantages.