Understanding the mechanisms of electrochemically driven molecular switches capable of multielectron processes

The PhD work will focus on electrochemical characterizations and mechanistic elucidation of novel organic electrophores, with two main objectives:

• Electrochemical characterization. Systematically investigate the behavior of synthesized organic electron carriers by varying key parameters such as the scan rate (cyclic voltammetry), nature and concentration of counter-ions, solvent type, substituent effects (electron-donating or -withdrawing groups), and temperature.
• Mechanistic modelling. Formulate and validate mechanistic models explaining the experimental electrochemical behavior. Mechanisms will be supported by electrochemical theories and refined through numerical simulation of cyclic voltammograms using DigiElch or COMSOL Multiphysics.

A key frontier at the interface between molecular chemistry and energy storage is the design of advanced molecular electron carriers, so called super-electrophores, that can reversibly load and release multiple electrons in an apparently single electrochemical step. Achieving such multielectron exchanges at the molecular level would open new directions for molecular actuators memory devices, electrochromic systems, catalytic processes, and energy storage technologies.^[1-6]

To enable multi-electron transfer at a single potential, the molecular carriers must overcome electrostatic repulsion that arises during charge accumulation. This can occur through potential inversion between successive redox events, often mediated by structural rearrangements. Yet, only a limited number of organic systems have been shown to exhibit this inversion,^[11] and molecular-scale accumulation of four or more electrons remains a formidable challenge.^[12]

In this context, the group of P. Lainé (ITODYS) has proposed to use redox-active pyridinium-based architectures as building blocks. Depending on their design, these systems can follow different molecular redox paradigms:^[7]

(i) Expanded Bi-Pyridinium (EBP): electrochemically reversible accumulation of multiple electrons facilitated by large structural reorganizations of expanded bipyridinium frameworks.^[8]

(ii) Structronic (STR): chemically reversible but electrochemically slow two-electron storage involving supramolecular orbitals (supra-MOs), which describe intramolecular orbital synergies that accommodate extra electrons.^{[4, 9]}

(iii) Extended Viologen (EV): multielectron processes driven by through-space (TSI) and through-bond interactions (TBI) in ortho/para-disubstituted benzene cores bearing bulky 4-(N-methylpyridinium) groups. These effects may act either competitively or cooperatively, strongly shaping the redox and electronic properties of the system.^[10]

Regardless of the paradigm (EBP, STR, or EV), the relative spatial arrangement of pyridinium units dictates whether charge accumulation is electrochemically reversible or electrochemically irreversible but chemically reversible. This distinction can be experimentally recognized by the presence or absence of electrochemical hysteresis in cyclic voltammetry.^[7]

[1]           Baroncini, M.; Silvi, S.; Credi, A. Photo- and Redox-Driven Artificial Molecular Motors. Chem. Rev. 2020, 120 (1), 200−268.

[2]           Suzuki, T.; Ohta, E.; Kawai, H.; Fujiwara, K.; Fukushima, T. Dynamic redox systems as electrochromic materials: Bistability and advanced response. Synlett 2007, 2007 (06), 0851−0869.

[3]           Suzuki, T.; Tamaoki, H.; Nishida, J.; Higuchi, H.; Iwai, T.; Ishigaki, Y.; Hanada, K.; Katoono, R.; Kawai, H.; Fujiwara, K.; Fukushima, T. Redox-Mediated Reversible σ-Bond Formation/Cleavage. In Organic Redox Systems: Synthesis, Properties, and Applications; Wiley, 2016; pp 13−37.

[4]           Gosset, A.; Wilbraham, L.; Nováková Lachmanová, Š.; Sokolová, R.; Dupeyre, G.; Tuyèras, F.; Ochsenbein, P.; Perruchot, C.; de Rouville, H.-P. J.; Randriamahazaka, H.; Pospíšil, L.; Ciofini, I.; Hromadová, M.; Lainé, P. P. Electron Storage System Based on a Two-Way Inversion of Redox Potentials. J. Am. Chem. Soc. 2020, 142(11), 5162−5176.

[5]   Liu, Y.; Flood, A. H.; Bonvallet, P. A.; Vignon, S. A.; Northrop, B. H.; Tseng, H.-R.; Jeppesen, J. O.; Huang, T. J.; Brough, B.; Baller, M.; et al. Linear artificial molecular muscles. J. Am. Chem. Soc. 2005, 127 (27), 9745−9759.

[6]   H. Li, M. Wen, W. Dong, Y. Duan, F. Hu, J. Yang, Z. Jiang, H. Fan, B. Hu, R. Mahalingam, J. Song. Viologen Derivatives in Aqueous Organic Redox Flow Batteries: Progress and Perspectives. Adv. Mater. 2025, e14004

[7]           (a) M. Hromadová, P. P. Lainé. Recent advances in electrochemistry of pyridinium-based electrophores: A structronic approach. Curr. Opin. Electrochem., 2022, 34, 100996. (b) É. Brémond, M. Hromadová, P. P. Lainé. The Structronic Concept: Harnessing Carbon–Carbon Chemical Bonding for Electron Storage and Related Applications. ChemElectroChem 2025, DOI: 10.1002/celc.202500037.

[8]           (a) J. Fortage, C. Peltier, F. Nastasi, F. Puntoriero, F. Tuyèras, S. Griveau, F. Bedioui, C. Adamo, I. Ciofini, S. Campagna, P. P. Lainé. Designing Multifunctional Expanded Pyridiniums: Properties of Branched and Fused Head-to-Tail Bipyridiniums. J. Am. Chem. Soc., 2010, 132, 16700–16713. (b) Š. Lachmanová, G. Dupeyre, J. Tarábek, P. Ochsenbein, C. Perruchot, I. Ciofini, M. Hromadová, L. Pospíšil, P. P. Lainé. Kinetics of Multielectron Transfers and Redox-Induced Structural Changes in N-Aryl-Expanded Pyridiniums: Establishing Their Unusual, Versatile Electrophoric Activity. J. Am. Chem. Soc., 2015, 137, 11349–11364. (c) J. Fortage, C. Peltier, C. Perruchot, Y. Takemoto, Y. Teki, F. Bedioui, V. Marvaud, G. Dupeyre, L. Pospísil, C. Adamo, M. Hromadová, I. Ciofini, P. P. Lainé. Single-Step versus Stepwise Two-electron Reduction of Polyarylpyridiniums: Insights from the Steric Switching of Redox Potential Compression. J. Am. Chem. Soc., 2012, 134, 2691–2705.

[9]   (a) A. Gosset, Š. Nováková Lachmanová, S. Cherraben, G. Bertho, J. Forté, C. Perruchot, H.-P. Jacquot de Rouville, L. Pospíšil, M. Hromadová, É. Brémond, P. P. Lainé. On the Supra-LUMO Interaction: Case Study of a Sudden Change of Electronic Structure as a Functional Emergence. Chem. Eur. J., 2021, 27, 17889–17899. (b) E. Vaněčková, M. Dahmane, J. Forté, S. Cherraben, X.-Q. Pham, R. Sokolová, É. Brémond, M. Hromadová, P. P. Lainé. Are Redox-active Centers Bridged by Saturated Flexible Linkers Systematically Electrochemically Independent? Angew. Chem. Int. Ed., 2024, 63, e202406299.

[10]        S. Hünig, H. Berneth. "Two Step Reversible Redox Systems of the Weitz Type." Top. Curr. Chem., 1980, 92, 1–44.

[11]        D. H. Evans. One-Electron and Two-Electron Transfers in Electrochemistry and Homogeneous Solution Reactions. Chem. Rev., 2008, 108, 2113–2144.

[12] P. W. Antoni, C. Golz, M. M. Hansmann. Organic Four-Electron Redox Systems Based on Bipyridine and Phenanthroline Carbene Architectures. Angew. Chem. Int. Ed. 2022, 61, e202203064.

The PhD will be hosted within the TERE team (Electron Transfer and Electrochemical Reactivity) of the ITODYS laboratory, well recognized for its expertise in molecular and materials electrochemistry.

This PhD research is part of the ANR project MultE, coordinated by P. Lainé and funded by the French National Research Agency (ANR). The consortium brings together four teams from ITODYS, combining expertise in chemical synthesis, electrochemical characterization, mechanistic analysis, and theoretical molecular modelling.

We seek a highly motivated candidate with a solid background in electrochemistry and molecular chemistry. Experience in molecular electrochemistry, reaction mechanisms, or redox-active organic systems will be considered an advantage. The candidate should be eager to explore fundamental questions bridging molecular reactivity, molecular actuators, and energy storage.