Extending the Legible Time of Light-Responsive Rewritable Papers with a Tunable Photochromic Diarylethene Molecule

Stimuli-Chromic Oxazolidine Latex Nanoparticles for Dual-Responsive pH-Sensors and Rewritable Halochromic Papers: A Physicochemical Study on Colorimetric and Fluorimetric Signals

Oxazolidine is a new category of stimuli-chromic compounds that has unique intelligent behaviors such as halochromism, hydrochromism, solvatochromism, and ionochromism, all of which have potential applications for designing and constructing chemosensors by using functionalized-polymer nanocarriers. Here, the poly(MMA-co-HEMA) based nanoparticles were synthesized by emulsion copolymerizing methyl methacrylate (MMA) and 2-hydroxyethyl methacrylate (HEMA) in different copolymer compositions. The poly(MMA-co-HEMA) based nanoparticles were modified physically with tertiary amine-functionalized oxazolidine (as an intelligent pH-responsive organic dye) to prepare halochromic latex nanoparticles. Investigation of optical properties including absorbance and emission by spectroscopic methods indicates that the halochromic behavior of the oxazolidine in nanoparticles is influenced significantly by the particle size, morphology, and concentration of hydroxyl groups. To develop optical chemosensors for the detection of pH, the pH-responsivity of halochromic latex nanoparticles in aqueous solutions with different pHs in the wide range of 1-14 were studied by UV-vis and fluorescence spectroscopies, and these results confirmed the successful photodetection of pH in a fast and facile manner. The investigation of the solid-state optical properties and pH-responsivity of halochromic nanoparticles by impregnation of latex-coated cellulosic papers with solutions having different pHs indicates the halochromic nanoparticles maintained their optical properties after incorporation to cellulose matrix and displayed notable colorimetric and fluorimetric pH-responsivity. Hence, the paper-based pH-sensors were prepared from halochromic papers and the investigation of their pH-responsivities showed the halochromic papers constructed from halochromic nanoparticles with HEMA concentration above 20 wt % have the best pH-responsivity with high resolution, high contrast, and high-intensity color change and fluorescence emission change. In addition, the halochromic papers were used as rewritable hydrochromic papers for hand-writing and stamp-printing by using acid and base solutions as inks, in which papers based on halochromic nanoparticles with a HEMA concentration above 20 wt % have maximum printability, resolution, and intensity. This study proposed the significant effects of polarity and concentration of functional groups on the halochromic properties of oxazolidine molecules and the unique role of functionalized polymer nanoparticles as a carrier of oxazolidine for its protection toward environmental degradations. These parameters should be considered in future studies on the development of halochromic papers for intelligent pH-sensor and rewritable papers.

Multi-Colored Aqueous Ink for Rewritable Paper

As sustainable and eco-friendly replacements to conventional paper, rewritable paper is a very attractive alternative for communication, information circulation, and storage. Development is made for rewritable paper using chromogenic materials that change its color in presence of external stimuli. However, the new techniques have faced several major challenges including feasible operational method, eco-friendly approach. Herein, a simple, convenient, and eco-friendly strategy is described for the preparation of rewritable paper substrate, and multi colored ink for efficient use in writing, painting or printing purpose. In addition, writing with "invisible ink" on the rewritable paper can be realized for potential anti-counterfeiting application. The written, painted, or printed information on the paper substrate can be easily erased using an aqueous solution. Thus, the original paper can be retrieved and the paper substrate can be reused multiple times. Besides, the written or printed information can be retained for a prolonged time at ambient conditions. Overall, this approach shows the rewritable paper as a prototype of multicolor writing/painting application, offering a sustainable solution for reducing paper waste and promoting environmental stewardship.

Large-Area Rewritable Paper Based on Polyurethane Inverse Photonic Glass with Durable High-Resolution Information Storage and Structural Stability

To alleviate the negative effects of resource waste and environmental pollution caused by the excessive use of paper, technologies for rewritable paper have received widespread attention and in-depth research. Despite the growing interest in rewritable paper, meeting the requirements of large-scale preparation, long-lasting information storage time, high reversibility, and good environmental stability remains a huge challenge for this technology. This study developed a solvent-responsive copolymerized polyurethane-based rewritable paper with an inverse photonic glass structure (co-PUIPG paper). Comprehensive writing modes, including handwriting, spraying, and printing, were realized by using the swelling effect of different solvents and the local force field formed by capillary force to control the deformation degree of the inverse photonic glass structure. Co-PUIPG paper can persistently store high-resolution information and has a green and environmentally friendly "write-erase" method. Meanwhile, it exhibits good rewritability, as well as high mechanical strength and exceptional resistance to environmental factors, such as friction, high temperature, and sunlight. Because the spraying method can prepare templates quickly and extensively and polyurethane materials are economical, co-PUIPG rewritable paper possesses great potential as a substitute for commercial fiber paper and its industrialization is full of great possibilities.

A series of naphthalenediimide-based metal-organic frameworks: synthesis, photochromism and inkless and erasable printing

Three new three-dimensional metal-organic frameworks were synthesized based on a naphthalenediimide derivative ligand, all of which exhibit photochromic behaviour due to the presence of the naphthalenediimide core. Interestingly, two of them possess significant colour changes under light, excellent stability, and appropriate photochromic lifetimes, thus showing potential for application in inkless and erasable printing media.

Cold crystallization and photo-induced thermal behavior of alkyl-derivatized diarylethene molecules

The thermal behavior of alkylated diarylethene molecules (2,3-bis(2,4,5-trimethyl-3-thienyl)-N-alkylmaleimides; DAE-Cn) was investigated. DAE-C1 and DAE-C2 exhibited cold crystallization, which is a heat-storage phenomenon. In addition, DAE-Cn showed photoisomerization; the open-ring isomer O-DAE-Cn was formed by visible light irradiation and transformed to the closed-ring isomer C-DAE-Cn by UV light irradiation. X-ray diffraction and optical microscopy analyses revealed that O-DAE-Cn exhibited cold crystallization and C-DAE-Cn showed poor crystallinity. UV irradiation (365 nm) inhibited cold crystallization, and visible light irradiation (525 nm) triggered cold crystallization, suggesting that heat storage by the cold crystallization of DAE-Cn can be photo-controlled.

The alkylated diarylethene molecules exhibited cold crystallization, and their thermal behavior can be photo-controlled.