Excited-State Dynamics in Supramolecular Systems

Supramolecular systems—assemblies of molecules held together by non-covalent interactions—exhibit complex pathways for the flow of electronic energy following photoexcitation. These processes govern applications such as light harvesting, photocatalysis and optoelectronic switching. Upon absorption of a photon, chromophoric units within a host framework undergo transitions to excited electronic states; the subsequent redistribution of energy involves interchromophoric couplings, charge‐ and energy‐transfer events, proton transfers and intersystem crossings. The dynamics unfold on femtosecond to nanosecond timescales and are mediated by the landscape of conical intersections and the strength of intermolecular interactions such as π–π stacking and hydrogen bonding. Advances in ultrafast spectroscopy and nonadiabatic molecular‐dynamics simulations have revealed how structural organisation and environment modulate the efficiency of processes such as singlet fission, exciton migration and excited-state proton transfer. A deeper mechanistic understanding of these pathways is crucial for the rational design of supramolecular assemblies that convert, transport or store photonic energy with high efficiency and selectivity.

Research from Nature Portfolio

Recent studies have explored singlet fission within π-stacked chromophore arrays, demonstrating that precisely tuned stacking energies and near-degenerate singlet and triplet excitations enable efficient generation of triplet pairs. Computational analyses of photosensitiser dimers revealed that moderate π–π interactions—slightly exceeding solvation energies—favour rapid formation and eventual separation of triplet–triplet states, while slow intersystem crossing pathways can be modulated through molecular design. Complementary time-resolved spectroscopic investigations on anthraquinone derivatives have illustrated how spatial separation of donor and acceptor moieties within a supramolecular scaffold influences photoredox reactivity. These studies show that increasing the distance between electron-donating and accepting sites leads to a two-step charge-transfer pathway with reduced overall quantum yield, emphasising the delicate balance between electronic coupling and structural architecture in controlling excited-state fate.

Research from all publishers

Investigations of hydrogen-bonded acid dimers in solution have elucidated how bond strength dictates early excited-state relaxation. Time-resolved infrared absorption measurements and ab initio calculations revealed that strong hydrogen bonding stabilises the excited state against dissociation, steering relaxation through a ring-buckling motion around the bridge that funnels the system back to the ground state via conical intersections on a few-picosecond timescale. In contrast, weaker bonding leads to transient separation of monomers before solvent-cage effects mediate recombination over tens of picoseconds. Meanwhile, nonadiabatic molecular-dynamics simulations of photoisomerisation in fulgide-based assemblies have applied pattern-recognition algorithms to automate trajectory analysis. These simulations confirm that bulky substituents can enhance photocyclisation quantum yields without substantially altering ring-closing timescales, offering a blueprint for designing supramolecular photoswitches with predictable dynamic behaviour.

Excited-State Dynamics in Supramolecular Systems publication trend

The graph below shows the total number of articles in excited-state dynamics in supramolecular systems across all publications each year (not limited to Nature Index journals).

Technical terms

Supramolecular assembly: An organised structure of discrete molecules held together by non-covalent interactions such as hydrogen bonds, π–π stacking or metal coordination.

Excited state: A higher electronic energy level populated when a molecule absorbs a photon, from which relaxation processes such as fluorescence, intersystem crossing or energy transfer can occur.

Singlet fission: A process in which one photoexcited singlet state splits into two triplet states, potentially doubling the number of excitons available for photochemical conversion.

Nonadiabatic molecular dynamics: A simulation technique that accounts for coupled electronic and nuclear motions, allowing transitions between electronic states at conical intersections.

Conical intersection: A point of degeneracy between two electronic states that provides an ultrafast pathway for nonradiative relaxation.

Charge transfer: The movement of electron density from donor to acceptor units within or between molecules in the excited state.

References

1. Singlet fission initiating organic photosensitizations. Scientific Reports (2024).
2. Time-Resolved Spectroscopic Study on the Photoredox Reaction of 2-(p-Hydroxymethyl)phenylAnthraquinone. Scientific Reports (2017).
3. Structural dynamics around a hydrogen bond: Investigating the effect of hydrogen bond strengths on the excited state dynamics of carboxylic acid dimers. The Journal of Chemical Physics (2024).
4. Nonadiabatic molecular dynamics simulations shed light on the timescale of furylfulgide photocyclisation. New Journal of Chemistry (2024).