Red luminescence control of Eu(iii) complexes by utilizing the multi-colored electrochromism of viologen derivatives

The electroresponsive switching of red photoluminescence based on the electrochemical coloration of cyan-magenta-green (CMG) viologen components was achieved by combining a luminescent Eu³⁺ chelate and viologen derivatives, resulting in CMG coloration in a single cell. The cell coloration was controlled by an electrochromic (EC) reaction, which also modulated the photoluminescence of the Eu³⁺ chelate with high contrast, by transferring energy from the excited state of the Eu³⁺ ion to the colored states of EC molecules. Cyclic voltammograms, photoluminescence spectra, absorption spectra, luminescence quantum yields, and luminescence lifetimes were measured to clarify the differences between the luminescence quenching and energy transfer efficiencies for each C, M, and G coloration associated with the electrochromism. Thus, the spectral overlap between the luminescence band of the Eu³⁺ chelate and the absorption band of the colored EC molecules was proven to affect the efficiency of luminescence modulation.