Backbone‐Controlled Ion‐Side Chain Accessibility in Conjugated Polymers for Organic Electrochemical Synaptic Transistors

Achieving stable and nonvolatile synaptic plasticity remains a central challenge for organic neuromorphic devices. While previous efforts have independently focused on backbone or side chain modifications, the fundamental role of conjugated backbone design in directing side chain–ion interaction has remained elusive. Here, we demonstrate that modulation of thiophene units in the backbone governs the spatial arrangement and ionic accessibility of glycol side chains, thereby enabling strong anion adsorption and long‐term retention. Electrolyte‐gated organic synaptic transistors (EGOSTs) with extended backbones exhibit pronounced structural reorganization, suppressed ion back‐diffusion, and stable nonvolatile characteristics. As artificial synapses, the devices realize robust neuromorphic functions, including paired‐pulse facilitation, long‐term potentiation/depression, and achieves 89.34% accuracy in convolutional neural network simulations. This work establishes conjugated backbone regulation as a straightforward strategy for controlling side‐chain‐electrolyte contiguity, thereby proposing a novel design principle for nonvolatile synaptic devices and advancing the development of reliable organic neuromorphic computing.