At the University of Amsterdam, Michiel Hilbers and Wybren Jan Buma of the Molecular Photonics group (Van ’t Hoff Institute for Molecular Sciences) contributed to the research of which the synthetic and reaction characterization part was conducted in the laboratories of Wiktor Szymanski and Nobel laureate Ben Feringa at the University of Groningen.

Photoclick chemistry is a light-activated variety of click chemistry (Nobel Prize in Chemistry 2022), a set of elegant and efficient chemical reaction methods that couple dedicated molecular units to yield desired products. Photoclick chemistry has unique advantages over conventional click chemistry as it allows for a high degree of both spatial and temporal control  over the reaction. It has a broad range of applications, including 3D printing, protein labelling, and bioimaging.

A boost for the PQ-ERA photoclick reaction

A specific photoclick reaction is the so-called PQ-ERA reaction - the light-induced photocycloaddition of 9,10-phenanthrenequinone (PQ) with electron-rich alkenes (ERA). It has drawn much attention because of its excellent kinetics and biocompatibility. However, the conventionally used PQ compounds show limited reactivity, which hinders its overall efficiency.

In the study now presented in Chemical Science, the international research team presents a simple strategy to change that. They describe how a thiophene substitution at the 3-position of the PQ scaffold significantly boosts the reactivity of the PQ triplet state to enhance the efficiency of the PQ-ERA reaction. Nanosecond time-resolved spectroscopic studies and quantum chemical studies in the Amsterdam Molecular Photonics group combined with femtosecond time-resolved spectroscopic studies performed in Florence provided a fundamental understanding of this specific photoclick chemistry. The investigations show that the substitution significantly increases the population of the reactive triplet state (³ππ*) during excitation of 3-thiophene PQs. This results in a superb photoreaction quantum yield (FP, up to 98%), high second order rate constants (k₂, up to 1974 M⁻¹ s₋₁), and notable oxygen tolerance for the PQ-ERA reaction system.

These results now pave the way for a further improvement of the reaction, offering excellent prospects for fast and efficient photoclick transformations.

Paper details

Youxin Fu, Georgios Alachouzos, Nadja A. Simeth, Mariangela Di Donato, Michiel F. Hilbers, Wybren Jan Buma, Wiktor Szymanski and  Ben L. Feringa: Establishing PQ-ERA photoclick reactions with unprecedented efficiency by engineering of the nature of the phenanthraquinone triplet state. Chem. Sci., 2023, 14, 7465. DOI: 10.1039/d3sc01760e

See also

• 2023 Chemical Science HOT Article collection
• 2023 Chemical Science Pick of the Week collection
• Research group Molecular Photonics (UvA)
• Szymanski Lab (RUG)
• Ben Feringa Research Group (RUG)