Conjugated polyelectrolyte with a backbone integrated by benzene and fluorene for mimicking neural synapses and associative learning†

Conjugated polyelectrolytes featuring both a hydrophobic π-conjugated polymer backbone and hydrophilic side chains exhibit many outstanding properties such as enhanced ionic conductivity, strong electrostatic interactions that can stabilize charge carriers, and facile self-assembly into aggregates, supramolecules or hydrogels. A novel poly[(1,4-bis-6-(3-methyl-1-imidazolium-hexyl)oxy)benzene-alt-(9,9-dihexyl-9H-fluorene)] (POF-NMI⁺Br⁻) was synthesized. The as-fabricated Al/POF-NMI⁺Br⁻/ITO device exhibited an analog-type memristive effect, with eight distinguishable conductance states within a small sweep voltage range of ±1 V, as well as bistable switching and non-volatile rewritable memory performance within a sweep voltage range of ±3 V, with a switch-on voltage of −1.32 V, a switch-off voltage of 2.12 V, and an ON/OFF current ratio of 3 × 10². The effect of the film thickness on the device performance was also explored. In contrast to POF-NMI⁺Br⁻, poly[1,4-bis(hexyloxy)benzene-alt-9,9-dihexyl-9H-fluorene] (POF) without ionic functionalities in the side chains did not show any memristive effects under the same experimental conditions. Associated with an outstanding memristive performance, the as-fabricated Al/POF-NMI⁺Br⁻/ITO device was used to successfully emulate the function of neural synapses and reproduce the associative learning capacity presented in Pavlov's famous experiment with dogs. This work is expected to provide insights into the development of novel conjugated polyelectrolytes for high performance memristors.