Modular Electrochromics – Designs for Facile Color-Mixing

Neutral states are quite lucrative in electrochromic design due to their versatile applications in different forms of shading and displays. Color neutrality is typically achieved as a result of subtractive color mixing, using a combination of chromophores having complementary absorption spectra to cover the entirety of the visible region. Several aspects of design should be considered when combining chromophores, including redox potentials, absorption spectra, migration effects during operation, and ease of synthesis or blending. Herein, we present a new system for achieving color neutrality in electrochromic devices by combining a set of complementary chromophores that can either be blended or co-reacted to form a new compound for polymerization that represents its component chromophores. As an example, we highlight a novel multichromophoric electrochromic polymer containing a conjugated 3,4-propylene dioxythiophene (ProDOT) backbone and a reversible redox active small molecule electrochrome tethered to the conjugated chain. The resulting electrochromic device exhibited a 55.7% photopic contrast with bleached and dark state transmittances of 70.4% and 14.7%, respectively. Furthermore, we briefly discuss approaches to develop melt-processable electrochromic polyesters as modular electrochromics.