Display technology is entering a new era, driven by electrochemical reaction-based materials that enable dynamic color and light modulation at low voltage. A research team from Chiba University, Japan, has developed a novel dual-mode electrochemical device that combines luminescence and coloration within a layered clay matrix. By embedding luminescent europium(III) complexes and color-changing viologen derivatives in smectite clay, the device achieves simultaneous control of emission and color with minimal energy consumption. This advancement has the potential to transform display technology, smart windows, and adaptable sensors.
Electrochemical stimuli-responsive materials are gaining significant attention for their ability to change optical properties based on external voltage. Unlike traditional displays, which rely on backlighting or liquid crystals, these materials undergo electrochemical reactions that induce color changes and fluorescence quenching. By integrating the functional molecules onto the electrode surface rather than dispersing them in solution, the research team has enhanced efficiency, stability, and response speed in electrochemical display devices.
The study introduces a novel approach to dual-mode display technology by merging luminescence and coloration into a single electrochemical system. The researchers utilized smectite, a layered clay compound known for its high ion exchange capacity and strong adsorption properties, to stabilize and enhance the performance of the electrochromic and luminescent materials. The clay matrix supports two key components: europium(III) complex (Eu(hfa)₃(TPPO)₂), which provides bright red luminescence, and heptyl viologen (HV²⁺) derivatives, which enable striking electrochromic color changes. These materials, when integrated into the smectite matrix, create a hybrid solution that enables synchronized electrochemical control of both emission and coloration.
To construct the device, the researchers combined Eu(III), hexafluoroacetylacetone (hfa-H₂), and triphenylphosphine oxide (TPPO) to create a europium complex. Hybrid films containing smectite, HV²⁺, and Eu(hfa)₃(TPPO)₂ were then applied onto indium tin oxide (ITO) electrodes. These modified electrodes exhibited dynamic optical properties upon the application of voltage. Under open circuit conditions, the device appeared colorless and emitted red luminescence from the Eu(III) complex. When a voltage of −2.0V was applied for 150 seconds, the HV²⁺ molecules underwent an electrochemical reaction, turning deep cyan while quenching the Eu(III) luminescence. This simultaneous modulation of color and light represents a significant advancement in display engineering, with potential applications in reflective and emissive screens.
Beyond its scientific significance, this development also supports sustainability in electronic devices. The use of naturally abundant clay compounds as a stabilizing matrix reduces reliance on synthetic materials, while the device’s low-voltage operation significantly cuts energy consumption. The technology bridges the gap between energy-efficient reflective displays and high-visibility emissive screens. Its adaptability to different lighting conditions makes it an ideal solution for digital signage, smart windows, and portable devices. Laboratory results confirmed the device’s operation under various environmental conditions, with key insights into how the clay matrix enhances the interaction between luminescent and electrochromic molecules. The interlayer spacing in the clay facilitated electron movement, improving the efficiency of electrochemical reactions.
The observed changes in color and luminescence result from two key mechanisms. The first is fluorescence resonance energy transfer (FRET), where the reduced viologen derivative (HV⁺) absorbs light at a wavelength overlapping with the emission from Eu(III), leading to a quenching effect that reduces red luminescence. The second is the inner filter effect, where the electrochemically generated cyan HV⁺ species reabsorbs Eu(III) luminescence, further suppressing emission. By leveraging these mechanisms, the device achieves precise electrochemical control over light and color without requiring additional energy-consuming components.
The researchers believe their dual-mode display offers a promising alternative to existing technologies, with potential applications in reflective e-paper displays, digital signage, smart windows, and wearable electronics. Looking ahead, the research team aims to expand the device’s functionality by integrating additional luminescent materials, improving its versatility for commercial applications. Their ultimate goal is to design display technologies that are not only more sustainable but also more versatile.
Reference
Cao, R., Kobayashi, N., Nakamura, K., & Kobayashi, N. (2025). Electrochemically controllable emission and coloration using a modified electrode with a layered clay compound containing viologen derivative and europium(III) complex. Journal of Materials Chemistry C, 13(4), 1628-1636. https://doi.org/10.1039/D4TC04026K
