Electrochemically controllable emission and coloration using a modified electrode with a layered clay compound containing viologen derivative and europium(iii) complex

Abstract

Novel displays based on electrochemical reactions have significant potential for various applications. In this study, a layered clay compound was used to immobilize a luminescent Eu(III) complex and an electrochromic viologen derivative (heptylviologen, HV²⁺) on an electrode to construct a novel dual-mode display device capable of achieving electro-switchable emission and coloration. X-ray powder diffraction, absorption, photoluminescence, cyclic voltammograms, and luminescence lifetimes were recorded to elucidate the structure and photoelectrochemical properties of the hybrid clay material containing the Eu(III) complex and HV²⁺. The electrochromic HV²⁺ and Eu(III) complex were adsorbed on/between the clay layers, and it was found that approximately 80% of HV²⁺ and 20% of Eu(III) complex were adsorbed in cases with a 25%:16.7% vs. cation exchange capacity (CEC) ratio. The insertion of the Eu(III) complex resulted in the expansion of the interlayer spacing, facilitating the movements of the supporting electrolyte between the layers and improving the electrochemical redox reaction of HV²⁺. By constructing a two-electrode device using a hybrid clay-modified electrode, the coloration and emission of the device were electrochemically modulated through the redox reaction of HV²⁺. The dual-mode representation was achieved via excitation energy transfer from the Eu(III) complex to the colored HV˙⁺ and the reabsorption of the luminescence from the Eu(III) complex. This modulation of the electrochemical properties of layered clay compounds holds potential for the development of advanced electrochemical systems and innovative display devices.