Electrochromism of alkylene-linked discrete chromophore polymers with broad radical cation light absorption

Abstract

This study focuses on examining the design principles of creating multi-heterocycle chromophores with a discrete conjugation length, which absorb ultraviolet light in the neutral state and upon oxidation absorb throughout a broad spectral range in the visible region. In this analysis, three discrete-length chromophore polymers with alkylene linkers were examined via time dependent DFT, which were synthesized via direct heteroarylation polymerization, and the electrochromic properties of their thin films were characterized. Using a feedback loop of theoretical calculations with design and synthesis, we elucidate how steric interactions can be used to control the absorption of the neutral and oxidized states of these discrete chromophore polymers. We show that systems with high inter-ring strain can be used to increase the molar absorptivity of the charged state by forming multiple radical cation states on a single discrete chromophore. We also demonstrate the challenges of electrochemical redox reversibility in the solid state in these systems, while they maintain their chemical redox reversibility.