Electrochromic devices offer many technological applications, including flexible displays, dimmable mirrors, and energy-efficient windows. Additionally, adsorbing electrochromic molecular assemblies onto mesoporous metal-oxide surfaces facilitates commercial and manufacturing potential (i.e., screen-printing and/or roll-to-roll processing). These systems also demonstrate synthetic versatility, thus making a wide array of colors accessible. In this work, using Time-Dependent Density Functional Theory (TD-DFT), we investigated ten different bi-aryl type molecules of 3,4-ethylendioxythiophene (EDOT) conjugated to various phenyl derivatives as potential anodically coloring electrochromes (ACEs). The non-substituted phenylene, hexylthiol-EDOT-phenyl-phosphonic acid, PA1, was synthesized and characterized as a means of model validity. PA1 absorbs in the UV region in its neutral state and upon oxidation absorbs within the visible, hence showcasing its potential as an ACE chromophore. The properties of PA1 inspired the designs of the other nine structural derivatives where the number and position of methoxy groups on the phenylene were varied. Using our DFT treatment, we assessed the impact of these modifications on the electronic structures, geometries, and excited-state properties. In particular, we examined stabilization intermolecular interactions (S–O and O–H) as they aid in molecule planarization, thus facilitating charge transport properties in devices. Additionally, destabilizing O–O forces were observed, thereby making some chromophores less desirable. A detailed excited state analysis was performed, which linked the simulated UV-Vis spectra to the dominant excited state transitions and their corresponding molecular orbitals. Based on these results, the nine chromophores were ranked ergo providing an ordered list of synthetic targets.

Subtle structural changes in monomeric building blocks can have an immense effect, whether positive or detrimental, on the resulting properties of conjugated polymers. With this in mind, it is paramount to understand structure–property relationships that serve as the guiding principles for manipulating optical and electrochemical characteristics. Herein, a family of dialkylthiophene-co-propylenedioxythiophene copolymers are synthesized via direct arylation polymerizations, with a key design motif being minimal changes in the structural composition of the propylenedioxythiophene comonomer. Variation in the substitution pattern on the propylene bridge provides insights into the role of stereo- and compositional isomers on the resulting polymer properties. Specifically, time-dependent density functional theory calculations reveal changes in the number and placement of comonomers with varying composition and stereocenters, impacting the calculated absorbance spectra, as evident from calculated absorbance maxima spanning 75 nm, which ultimately manifests in differences in the calculated color. Experimentally, UV–vis absorbance spectroscopy and colorimetry reveal a dependence on the stereo- and regiospecificity, while electrochromic properties, such as contrast and switching times, are not drastically affected by the substitution patterns. Independent of position and functionality, each polymer exhibited a transmittance change greater than 65% at the maximum absorbance wavelength while maintaining the ability to rapidly switch between colored and transmissive states in organic electrolytes. This work highlights how subtle structural changes can manipulate and optimize optical features without sacrificing electrochromic properties such as kinetic switching time and optical contrast. In addition to fundamental insights into monomeric design of propylenedioxythiophene building blocks and their optical and redox characteristics, the results provide an additional structural handle for fine-tuning the observed color of electrochromic polymers.

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The second-order rate constants are reported for reduction of 11 cobalt(III) complexes by viologen radicals, derived from diquaternary salts of 4,4'-bipyridine and 2,2'-bipyridine. Rate constants vary from 1.5 X 102 to 6.0 X 108 M-1 s-1, and an excellent correlation with the Marcus expression for 14 redox reactions is observed. These data conform, on the basis of a unity transmission coefficient, to a self-exchange rate constant for the viologens (X2+/+ couple) of 1.5 X 106 M"1 s'1. It is suggested however that this value is about 102 too low.