Exploring the role of phenothiazine conformations and their interconversion on the electrochemical behaviour of organic electrodes

Abstract

Organic electrode materials are promising candidates for rechargeable batteries due to their environmental friendliness, low-temperature synthesis, and tunable structure. While most studies focus on molecular design, we begin to explore how molecular conformation and aggregation state affect electrochemical performance. Herein, we synthesized three phenothiazine (PTZ) derivatives by connecting two PTZ units with electron-withdrawing pyridine (Py), pyrazine (Pz), and pyridazine (Dz) cores. Single-crystal structure analysis, various electrochemical studies, and DFT calculations have, for the first time, shown that the redox potential of organic electrodes is influenced not only by the electron-withdrawing ability of the acceptor cores Py, Pz, and Dz, but also by the quasi-axial (ax)/quasi-equatorial (eq) conformation of the donor PTZ. Together, these factors determine the HOMO energy levels of the molecules. Additionally, during cycling, the PTZ unit may change from one conformation to another. Small conformational changes contribute to enhanced cycling stability of the electrodes. From the perspective of molecular aggregation, weak intermolecular interactions and loose molecular stacking lead to low molecular crystallinity, which is conducive to its uniform dispersion inside the electrode and the formation of a conductive network, thereby improving the practical capacity and rate performance of the electrode. Overall, this work establishes a new research paradigm for organic electrodes by linking molecular structure, conformation, and aggregation state, providing valuable insights for the future design of organic materials.