Ladder-Type Conjugated Polymers: Synthesis and Their Application in Organic Electrochemical Transistors/Artificial Neurons

Organic electrochemical transistors (OECTs) are a rapidly advancing technology that plays a crucial role in the development of next-generation bioelectronic devices. Recent advances in p-type/n-type organic mixed ionic-electronic conductors (OMIECs) have enabled power-efficient complementary OECT technologies for various applications, such as chemical/biological sensing, large-scale logic gates, and neuromorphic computing. However, ensuring both high performance and long-term operational stability remains a significant challenge that hinders their widespread adoption. Ladder-type conjugated polymers, with their rigid backbone structure composed of double-strand chains linked by condensed π-conjugated units, can sustain high electrochemical doping levels without any conformational disorder, which leads to exceptional operational stability, high charge carrier mobility, and large volumetric capacitance. In this report, we demonstrate our recent development on ladder-type conjugated polymers, with p-type/n-type high mixed ionic-electronic conducting performance and high stability in long-term OECT operation. Reasonable molecular design and improvement of synthesis methods have enabled the synthesis of high-performance p-type/n-type ladder polymers with mobility increased by more than 10 times. Their unique ladder-type structure enables them to have long-term stability within &gt;90% current remain after 6 hours continues operation, and enables them to accommodate more carrier injections with of up to two charges per repeat unit. Density of states filling and opening of a hard Coulomb gap around the Fermi energy at high electrochemical doping levels enable the ion-tunable antiambipolarity in these ladder polymers. The development of ladder-based polymer ink formulations has also enabled printed electronics. With these ladder-type polymers, we developed complementary inverters with a record-high DC gain of 194 V/V and excellent stability. We report the first organic electrochemical neurons (OECNs) with ion-modulated spiking, based on all-printed complementary organic electrochemical transistors. We demonstrate facile bio-integration of OECNs with Venus Flytrap (Dionaea muscipula) to induce lobe closure upon input stimuli. We report a biorealistic conductance-based organic electrochemical neuron (c-OECN) using a mixed ion–electron conducting ladder-type polymer with stable ion-tunable antiambipolarity. The latter is used to emulate the activation/inactivation of sodium channels and delayed activation of potassium channels of biological neurons. These c-OECNs can spike at bioplausible frequencies nearing 100 Hz, emulate most critical biological neural features, demonstrate stochastic spiking and enable neurotransmitter-/amino acid-/ion-based spiking modulation, which is then used to stimulate biological nerves in vivo.[1-5]<br/><br/>References:<br/>1. Adv. Mater. 2018, 30, 1704916.<br/>2. Adv. Funct. Mater. 2022, 32, 2112276.<br/>3. Adv. Electron. Mater. 2022, 8, 2100907.<br/>4. Adv. Mater. 2022, 34, 2106235.<br/>5. Nat. Commun. 2022, 13, 901.<br/>6. Nat. Mater. 2023, 22, 242–248.