Discrete Donor–Acceptor Conjugated Systems in Neutral and Oxidized States: Implications toward Molecular Design for High Contrast Electrochromics

Abstract

Donor–acceptor systems are ubiquitous redox-active materials in electrochromic devices, making the study of their neutral and charged state characteristics expedient for the design of materials with improved properties. In this paper, we explore the absorption properties of the neutral and oxidized states of two dioxythiophene- and benzothiadiazole-containing penta- and hepta-heterocycles (EPBPE, EPPBPPE) having a monodisperse, well-defined π-conjugated structure, using electrochemistry, optical absorption and electron paramagnetic resonance (EPR) spectroscopy, spectroelectrochemistry, and microscopy. The molecules and their precursors were obtained via a direct (hetero)arylation coupling strategy that exploits stoichiometric control to obtain well-defined ter- and penta-heterocycles from bifunctional heteroarenes. Both molecules show intense and narrow dual-band absorptions in the visible region, reflecting the discrete nature of their π-systems, leading to strongly colored neutral states. The electron-r...