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Updated: Jun 7, 2025

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The Dual-Role of Benzothiadiazole Fluorophores for Enabling Electrofluorochromic and Electrochromic Devices
Mohan Raj Anthony Raj1, Chengzhang Yao1, Gokul Balakrishnan Muthuperumal1
1Department of Chemistry, Université de Montréal, Montreal, QC, Canada, H3C 3J7.
Abstract:
Three unsymmetric fluorophores differing in their flanking electron acceptor (-NO2, -CN, -CHO) were investigated for their electrofluorochromism and electrochromism. The emission yield of the -NO2 substituted fluorophore in the solid state was ca. 9-fold less than its -CN and -CHO counterparts. Visible color changes of the fluorophores were observed with an applied potential. The intensity of the near-infrared absorption at ca. 1500 nm formed upon electrochemical oxidation was contingent on the electron-withdrawing group: 2-fold more intense with the -CN substitution than its -H counterpart. The coloration efficiency was upwards of 655 cm2 C-1 and the bleaching kinetics (tb; 22 s) of the NIR band decreased according to -NO2>-CN>- CHO ≈ -H. The electrochemically generated states could be reversibly formed during 120 min of switching the applied potential. The contrast ratio of the radical cation and the NIR absorption was near unity and 60-82 %, respectively. The photoemission intensity of the fluorophores could also be modulated with applied potentials. The collective electrochemically mediated color switching and emission intensity modulation along with their solid-state emission demonstrate that benzothiadiazole fluorophores can play a dual role in chromic devices both as the color switching and photoemission intensity modulating material.
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Colors and Magnetism
When atoms or molecules absorb light at the proper frequency, their electrons are excited to higher-energy orbitals. For many main group atoms and molecules, the absorbed photons are in the ultraviolet range of the electromagnetic spectrum, which cannot be detected by the human eye. For coordination compounds, the energy difference between the d orbitals often allows photons in the visible range to be absorbed and emitted, which is seen as colors by the human...