The Influence of Halogen Anions on the Color/Fluorescence Dual-Switching Behaviors of 1,10-Phenanthroline-Based Viologen Derivatives

Stimuli-responsive color/fluorescence dual-switchable materials have garnered significant attention in displays, sensors, and anti-counterfeiting. However, current material systems are hampered by the single stimulus-response and unregulated fluorescence. Viologen derivatives featuring fluorophore as N-substituent and halogen anions as counteranions not only exhibit responsiveness to both electric and light stimuli but also enable adjustable emission. In this work, we explored the influence of halogen anions on the color/fluorescence dual-switching behaviors of 1,10-phenanthroline-based viologen derivatives. The energy level gaps for phen-Vio[2Cl⁻] (2.93 eV), phen-Vio[2Br⁻] (2.67 eV), and phen-Vio[2I⁻] (2.34 eV) decreased with the decrease of electron affinity of halogen anions (Cl⁻>Br⁻>I⁻), which leads to a sequential improvement in their electrochromic/electrofluorochromic and photochromic/photofluorochromic properties. This work has important guidance for the design and development of smart materials and their optoelectronic devices.