Wavelength-selective duotone single-component photochromic gallophosphate-oxalate with multidirectional UVB/UVC/NIR photoswitch electron transfer

Abstract

Prolonged exposure to UVB and UVC can cause serious health problems such as skin and eye cancer. It is therefore crucial but challenging to explore portable and rapidly recyclable wavelength-selective UV-responsive materials that can visually distinguish between indoor UVC and outdoor UVB irradiation. In this work, we present a multidirectional photoswitchable single-component photochromic inorganic–organic gallophosphate-oxalate |C₁₀N₂H₁₀|₂[Ga₂(HPO₄)₂(C₂O₄)₃] (denoted as IL-GaPO) synthesized through an ionothermal decomposition-reassembly strategy. IL-GaPO is insensitive to visible light and UVA light but exhibits wavelength-selective duotone photochromic behavior to visually distinguish between UVB and UVC with a significant color change from light ivory to blue under UVB irradiation and from light ivory to violet under UVC irradiation. UVB and UVC detection procedures using portable test tablets indicate that colorimetric detection using IL-GaPO exhibits a linear response to both UVB and UVC doses, making it highly promising for portable and efficient visual detection of UV light indoors and outdoors. In addition, IL-GaPO exhibits a modulated NIR photothermal conversion phenomenon under low constant NIR laser density (808 nm, 0.23–2.25 W cm⁻²) because of the tunable H₂bpy˙⁺ π-aggregate radicals generated via a UV-induced PIET process and high-speed photoswitching behavior triggered by high constant NIR laser density (13 s, 808 nm, 9.75 W cm⁻²) due to the fast thermal quenching of radicals. This multidirectional photoswitchable photochromic material can be rapidly colored under outdoor and indoor UV light (10 s) and quickly decolored under NIR light (13 s), which paves the way for the development of wavelength-selective duotone photochromic materials to visually distinguish between outdoor and indoor UV light and sheds light on the multidirectional all-optical switching process in PIET photochromic materials.