Carbene Dynamics and Spectroscopy in Molecular Systems

Carbenes are transient, divalent carbon species that play a central role in diverse chemical processes ranging from organic synthesis to atmospheric chemistry and materials science. Their high reactivity arises from the presence of two nonbonded electrons, which can adopt either a paired (singlet) or unpaired (triplet) configuration. Advances in ultrafast spectroscopic techniques have enabled direct observation of carbene formation, interconversion, and decay on femtosecond to nanosecond timescales. Complementary theoretical methods, including hybrid quantum mechanics/molecular mechanics approaches and high‐level electronic structure calculations, have elucidated the energy landscapes that govern spin‐state energetics, insertion pathways and rearrangement mechanisms. In solution, dynamic interactions with solvent molecules, particularly through hydrogen-bond networks, have emerged as critical factors in steering branching between insertion, ylide formation and rearrangement channels. Insights into the interplay between spin states, solvation and reaction dynamics are informing the rational design of carbene‐mediated catalysis, photoactivated processes and functional materials.

Research from Nature Portfolio

Recent studies have employed broadband femtosecond transient absorption spectroscopy combined with quantum mechanics/molecular mechanics simulations to dissect solvent–diphenylcarbene interactions. These experiments reveal that hydrogen-bonded second-shell solvents, rather than immediate neighbours, determine whether the carbene undergoes C–H insertion or forms a hydrogen-bonded ylide intermediate. At ambient temperature, protic solvent complexes transiently stabilise specific reaction channels, extending analogous observations previously restricted to cryogenic matrices. Such work emphasises that collective solvent dynamics, rather than isolated solute–solvent contacts, govern ultrafast carbene photochemistry in solution and open avenues for controlling selectivity through solvent engineering.

Carbene Dynamics and Spectroscopy in Molecular Systems publication trend

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

Technical terms

Carbene: A neutral carbon centre with two nonbonded electrons, existing in singlet or triplet spin configurations and characterised by high reactivity.

Singlet state: Spin configuration in which the two nonbonded electrons of a carbene are paired in the same orbital, often resulting in distinct reactivity and spectroscopic signatures.

Triplet state: Spin configuration with two unpaired electrons in separate orbitals, typically rendering the carbene longer-lived and altering its insertion pathways.

Transient absorption spectroscopy: Ultrafast optical technique that monitors changes in absorption following photoexcitation, allowing direct observation of short-lived intermediates.

QM/MM simulations: Hybrid computational method combining quantum mechanical treatment of the reactive centre with classical molecular mechanics for the surrounding environment.

Ylide: Zwitterionic intermediate formed when a carbene reacts with a nucleophile, characterised by adjacent positively and negatively charged centres.

Hydrogen-bonded complex: Transient association between a polar site of a molecule and a hydrogen-bond donor, which can direct reaction pathways and influence spectroscopic properties.

References

1. Competitive solvent-molecule interactions govern primary processes of diphenylcarbene in solvent mixtures. Nature Communications (2016).
2. Direct Observation of the Dynamics of Ylide Solvation by Hydrogen-bond Donors Using Time-Resolved Infrared Spectroscopy. Journal of the American Chemical Society (2022).
3. Formation of 3‑Oxa- and 3‑Thiacyclohexyne from Ring Expansion of Heterocyclic Alkylidene Carbenes: A Mechanistic Study. Organic Letters (2023).