Beyond State of Charge: Electrochemical States and Trajectory Design in Organic Mixed Conductors

Organic mixed ionic-electronic conductors (OMIECs) couple electronic redox, ion transport, solvation, structural reorganization, and mechanics, enabling diverse electrochemical functions but making their internal states poorly represented by scalar descriptors such as voltage, charge, conductivity, or nominal doping level. This Review establishes a state-centered framework that treats electrochemical operation as the writing, observation, reconstruction, and design of multidimensional, history-dependent state trajectories. A problem-specific minimal sufficient state basis is introduced to distinguish essential from redundant coordinates, while waveform history and spatial heterogeneity define when lumped descriptions remain valid. Optical, electrical, ion-specific, gravimetric, structural, mechanical, and temporal readouts are analyzed as selective projections whose complementarity determines state observability and hidden-state reconstruction. Within this framework, congruence, kinetic ordering, decoupling, observational degeneracy, and mapping drift become experimentally testable relationships rather than isolated phenomena. Electrochromics, organic electrochemical transistors (OECTs), electrochemical memories, actuators, reconfigurable systems, and energy-storage and conversion devices are then recast as technologies that select different trajectories through a shared electrochemical-state landscape. The framework ultimately connects molecular structure, electrolyte, morphology, device architecture, and driving protocol to the inverse design of observable, controllable, reversible, and durable electrochemical trajectories.