Spacer Conjugation and Surface Support Effects in Monolayer Electrochromic Materials

Electrochromic
(EC) materials that change their color under applied voltage are a
rapidly growing segment of “smart” materials. Recent
and potential applications of EC materials include “smart”
windows, a range of optoelectronic, energy conversion, and indication
devices that require miniaturization, easy integration, and sustainable
development. This can be achieved by forming just a monolayer of EC
molecules on a conductive support with a large surface area (i.e.,
surface-enhanced conductive support). In this study, we have developed
a range of supports by screen printing two commercial indium tin oxide
(ITO-30 and ITO-50) nanoparticles and synthesized fluorine-doped tin
oxide (FTO) nanoparticles on ITO/glass and FTO/glass substrates. We
have discovered the influence of spacer conjugation (single, double,
and triple bond) in the terpyridine-based iron complexes anchored
as EC monolayers, on the properties of EC materials. Resulting materials
demonstrate fast charge transfer kinetics and a significant color
difference that depends on both the nature of the ligand and substrate.
Solid-state EC devices (ECDs) demonstrate a noticeable optical difference
in colored and bleached states (ΔOD), enhanced spectroelectrochemical
stability, and exceptional coloration efficiency. Electron mobility
and EC memory are heavily impacted by the substrate. Moreover, sufficient
values of pseudocapacitance and the ability to power up an LED suggest
potential applications of these materials in dual-function EC supercapacitors.
Density functional theory (DFT) and time-dependent density functional
theory (TDDFT) calculations have been employed to support the experimental
findings in terms of geometries, electronic structure, interpretation
of photospectra, charge distributions, and transfer, revealing significant
variations between the ligands.