Thiophene or Pyridine-Substituted Quinoline Derivatives: Synthesis, Properties, and Electropolymerization for Energy Storage

Abstract

Designing novel electropolymerizable monomers is essential in developing electron donor-electron acceptor (D-A) type conjugated polymers for applications in sensing, catalysis, and energy storage. Thiophene and pyridine-substituted quinoline-based molecules (Th-Q, DTh-Q, and Py-Q) are synthesized in this work, and their crystal structures, optical properties, and electrochemical properties are investigated. The potentiostatic electropolymerization of these molecules are successfully carried out on carbon cloth substrate, with the thiophene and quinoline as the possible electropolymerizable units. The PTh-Q shows the best charge storage performance ( $1.12\times {10}^{-3}$  C at 0.02 mA cm-2 in the potential range of 0-1 V) in 0.1 M Na2SO4, and maintains 77% of the initial capacity after 3000 charge-discharge cycles at 0.02 mA cm-2. The morphology and structure of the PTh-Q does not alter significantly after the repetitive charge-discharge cycling. The superior charge storage performance of the PTh-Q than PDTh-Q and PPy-Q is originated from the exposed highest amount of electrochemically active sites and the participation of redox processes of both hydroxyl/ketone structures on quinoline and thiophene groups.