Solid Materials with Near‐Infrared‐Induced Fluorescence Modulation

Solid molecular materials modulating their luminescent properties upon irradiation are typically based on photochromic dyes. Despite these are potentially interesting for applications such as anticounterfeiting, bioimaging, optical data storage, and writable/erasable devices, key features are preventing their use in marketable products: the lack of straightforward strategies to obtain near infrared (NIR) radiation‐responding photochromic dyes and the dramatic response modification these molecules suffer in solids. Herein a photochrome‐free approach is reported to achieve solid materials whose luminescence modulation is induced by NIR radiation. This strategy is based on the capacity of phase change materials (PCMs) to modify the emission properties of fluorescent dyes upon photothermally induced interconversion between their solid and liquid states. The preparation of several NIR‐responsive thermofluorochromic materials of high fatigue resistance and nondestructive readout is illustrated and this approach is extended to different commercially available dyes, taking advantage of distinct fluorescence modulation mechanisms, providing, thus, color tunability. The modulation response is straightforwardly tuned by simply varying the irradiation power density, the gold nanoshell concentration, and/or the PCM type. This tunability allows to accomplish NIR‐activated multistate thermofluorochromic materials and fast/slow/irreversible responses in NIR‐writings/drawings of good spatial resolution, which can be of interest for barcodings, anticounterfeiting technologies and (re)writable devices. Herein is reported a new, straightforward, and photochrome‐free strategy to obtain luminescent materials whose fluorescence can be modulated by near infrared (NIR) radiation. This approach allows obtaining solid cellulose‐based papers for which, self‐erasing upon low‐intense NIR irradiation or permanent drawings (e.g., barcodes) in very good resolution are easily obtained.