Excited-State Dynamics in Charge Transfer Systems

Excited-state dynamics govern how materials and molecules respond to light at the electronic level, with particular relevance for systems exhibiting charge transfer between distinct regions or moieties. Upon absorption of a photon, electrons may relocate from donor to acceptor units, generating transient states whose evolution depends on the coupling between electronic and nuclear motions. This coupling can direct energy along radiative or non-radiative channels, influence conversion efficiencies in optoelectronic devices and determine rates of processes such as intersystem crossing and internal conversion. In molecular aggregates, delocalised excitations known as Frenkel excitons can migrate through lattices or supramolecular assemblies, while in push–pull compounds, intramolecular charge transfer produces characteristic spectral shifts and dynamic pathways. Understanding these processes requires elucidating the role of molecular geometry changes, solvent interactions and conformational dynamics, and exploiting points of near-degeneracy between electronic states, often mediated by conical intersections. Insights into excited-state pathways underpin advances in solar energy conversion, light-emitting diodes, photodetectors and bioimaging, where precise control of charge separation and recombination holds the key to performance and sustainability.

Research from Nature Portfolio

One recent study examined how specific hydrogen bonds to the electron-accepting group in a prototypical push–pull stilbene adsorbed on a glass surface influence its primary charge transfer absorption band. By modelling diverse adsorption motifs and their interaction energies, researchers demonstrated that O–H⋯O bonding to the nitro group induces a marked redshift and enhanced intensity of the first bright state, whereas O–H⋯N interactions with the donor unit produce a blueshift, thereby offering a route to tune optical responses in surface-bound photoswitches. In another investigation, the interplay between solvent properties and photoinduced charge transfer in solution was systematically probed through a multivariate analysis of implicit solvent parameters. This work revealed that factors such as hydrogen bond basicity and surface tension can be adjusted to regulate charge separation extent and migration length, ultimately proposing solvent engineering as a strategy to control excited-state charge dynamics in polar environments.

Excited-State Dynamics in Charge Transfer Systems publication trend

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

Technical terms

Excited state: An electronic configuration attained after photon absorption, in which one or more electrons occupy higher-energy molecular orbitals.

Charge transfer: Movement of electron density from a donor region to an acceptor region within or between molecules upon excitation.

Nonadiabatic dynamics: The interplay of electronic and nuclear motions that enables transitions between electronic states during excited-state evolution.

Conical intersection: A point of degeneracy between two electronic potential energy surfaces that facilitates rapid nonradiative transitions.

Frenkel exciton: A bound electron–hole pair localised on one molecule or delocalised across adjacent units within a molecular assembly.

Push–pull chromophore: A molecule with electron-donating and electron-accepting groups linked by a π-conjugated bridge, promoting intramolecular charge transfer on excitation.

References

1. Modeling Excited States of Molecular Organic Aggregates for Optoelectronics. Annual Review of Physical Chemistry (2023).
2. Hydrogen bonding to the electron accepting group controls the absorption spectrum of a push–pull stilbene adsorbed on amorphous silica. Communications Physics (2024).
3. The Dependence of Implicit Solvent Model Parameters and Electronic Absorption Spectra and Photoinduced Charge Transfer. Scientific Reports (2020).
4. Surface Hopping Dynamics with the Frenkel Exciton Model in a Semiempirical Framework. Journal of Chemical Theory and Computation (2021).
5. Linear and Nonlinear Photon-Induced Cross Bridge/Space Charge Transfer in STC Molecular Crystals. Nanomaterials (2022).