Intrinsically Electrochromic and Luminescent [MnCl ₄ ] ²⁻ ‐based Ionic Liquid for Liquid Electrochromic Devices, UVC Sensing, and Anticounterfeiting

The attractive luminescence emission features of complexes incorporating tetrahedrally coordinated Mn(II) have garnered increasing attention for displays and lighting technologies. This work focuses on the ionic liquid (IL) N‐butylpyridinium tetrachloromanganate(II) ([C 4 Py] 2 [MnCl 4 ]), which offers unique dual electrochromic and photoluminescent behaviour. Electrochemical studies confirm the reversibility of the redox processes of the [MnCl 4 ] 2− ions, enabling visible color switching from pale yellow to bright green, emphasizing the potential of this IL for liquid electrochromic devices. Aiming to explore applications in UVC sensing and anti‐counterfeiting, new materials composed of poly(oxyethylene) (POE) and a range of concentrations of [C 4 Py] 2 [MnCl 4 ], with the notation POE n [C 4 Py] 2 [MnCl 4 ] (n = ∞, 71, 35, 21, and 11, is the molar ratio of oxyethylene units per Mn 2+ ion) is explored. Their structural, morphological, thermal, and optical properties are characterized. The quantum yield (QY) of [C 4 Py] 2 [MnCl 4 ] (0.68±0.07) is significantly higher than those of other reported tetrachloromanganate(II) complexes. The QY of the POE n [C 4 Py] 2 [MnCl 4 ] materials range from 0.07±0.01 (n = 71) to 0.19±0.02 (n = 21). The potential of the latter sample for UVC (100−280 nm) sensing and anti‐counterfeiting is highlighted. This work opens new avenues for the development of low‐cost, eco‐friendly, and easily processable polymer films of Mn(II) halide hybrids with bright green luminescence.