Mixed-Valence Chemistry and Electron Transfer Dynamics

Mixed-valence chemistry concerns molecules or materials featuring two or more sites of differing oxidation states linked by covalent or supramolecular bridges. Electron transfer dynamics describe how an electron migrates between redox centres, governed by factors including electronic coupling, reorganisation energy and nuclear modes. In mixed-valence systems these transfers manifest as hopping between localised centres or as delocalised charge distribution, often probing the boundary between quantum coherence and classical kinetics. The Robin–Day classification partitions mixed-valence species into three classes: class I (localised charge without interaction), class II (partial electronic coupling with observable intervalence charge-transfer bands) and class III (full delocalisation and strong coupling). Advances in spectroscopy, electrochemistry and theoretical modelling now permit real-time characterisation of intramolecular electron-transfer rates, activation parameters and coupling strengths, enabling tailored design of molecular wires, catalysts and spintronic components. Practical applications extend from artificial photosynthetic centres and redox flow batteries to single-molecule electronics and nanoreactors since control over charge mobility and localisation underpins energy conversion, sensing and information processing technologies.

Research from Nature Portfolio

Studies of oligoacene-linked diarylamine systems have elucidated how π-conjugation length modulates electron transfer. A series of bis(diarylamino) dimers bridged by benzene to pentacene revealed an exponential attenuation of electronic coupling with an attenuation constant around 0.14 Å⁻¹. The radical cations displayed intervalence charge-transfer bands consistent with Robin–Day class II behaviour, while density functional theory offered insight into the nature of super-exchange pathways. In a separate investigation, a ruthenium-amine dyad bridged by para-oligophenylene wires demonstrated long-range electronic communication over distances exceeding 27 Å. Spectroelectrochemical measurements identified intervalence charge-transfer transitions and an exponential decay of coupling with distance, corroborated by DFT calculations and providing a blueprint for designing molecular-scale redox interconnects.

Mixed-Valence Chemistry and Electron Transfer Dynamics publication trend

The graph below shows the total number of articles in mixed-valence chemistry and electron transfer dynamics across all publications each year (not limited to Nature Index journals).

Technical terms

Mixed-valence compound: A molecule containing two or more metal or redox-active centres in different formal oxidation states.

Robin–Day classification: A scheme dividing mixed-valence systems into class I (localised), class II (intermediate coupling) and class III (fully delocalised).

Electronic coupling (H_ab): A measure of the interaction strength between redox centres that governs the rate of electron transfer.

Intervalence charge-transfer (IVCT): An optical absorption band associated with electron transfer between mixed-valent sites.

Reorganisation energy (λ): The energy required to reorganise nuclear positions and solvent environment during electron transfer.

Electron transfer rate: The frequency at which an electron tunnels or hops between redox centres, often described by non-adiabatic Marcus theory.

References

1. Charge and Spin Transfer Dynamics in a Weakly Coupled Porphyrin Dimer. Journal of the American Chemical Society (2024).
2. Elaborately Tuning Intramolecular Electron Transfer Through Varying Oligoacene Linkers in the Bis(diarylamino) Systems. Scientific Reports (2016).
3. Long-Range Ruthenium-Amine Electronic Communication through the para-Oligophenylene Wire. Scientific Reports (2015).
4. Light-driven electron transfer in a lipid bilayer with mixed valence molecular wires. Sustainable Energy & Fuels (2025).
5. Electronic Coupling in Triferrocenylpnictogens. ACS Organic & Inorganic Au (2024).