Controlled photoisomerization in acrylic copolymer nanoparticles based on spironaphthoxazine for reduced thermal reversion

Scalable, Green, Flexible Photochromic Bacterial Cellulose for Multicolor Switching, Photo-patterning, and Daily Sunlight UV Monitoring

Sustainable, durable, and diverse photochromic smart textiles based on bacterial cellulose (BC) have emerged as attractive candidates in UV-sensing applications due to the green and easy functionalization of BC. However, existing BC-based photochromic textiles lack photochromic efficiency and combining fastness. In this study, a green strategy for in situ fermentation is developed to achieve the directional distribution of functional particles and remarkable photochromism in photochromic bacterial cellulose (PBC). The unique functional design obtained by regulating the photochromic dye distribution in 3D nanonetworks of PBCs during in situ growth affords a more uniform distribution and high fastness. Benefiting from the uniform distribution of photochromic dyes and adequate utilization of the 3D network structure, more surface area is provided to receive and utilize the photon energy from the UV rays, making the photochromic process more effective. The as-prepared PBCs exhibited rapid (within 1 min) and stable (30 cycles) discoloration and multicolor selectivity. Their simple preparation process and exceptional wearability, e.g., their flexibility, lightweight, and air permeability, make them suitable for various applications, including tunable color switching systems, photopatterning, and daily sunlight UV monitoring. This study provides empirical value for the biofabrication of photochromic textiles and wearable flexible UV sensors.

Spectral and kinetic manifestations of chain flexibility and polarity in the reversible photoisomerization of spironaphthoxazine-based acrylic copolymers

Future advances in photoresponsive materials essentially depend on our knowledge about how the substrates, and typically their T_g and polarity, affect their photochromic properties.

Photoluminescent and Chromic Nanomaterials for Anticounterfeiting Technologies: Recent Advances and Future Challenges

Counterfeiting and inverse engineering of security and confidential documents, such as banknotes, passports, national cards, certificates, and valuable products, has significantly been increased, which is a major challenge for governments, companies, and customers. From recent global reports published in 2017, the counterfeiting market was evaluated to be $107.26 billion in 2016 and forecasted to reach $206.57 billion by 2021 at a compound annual growth rate of 14.0%. Development of anticounterfeiting and authentication technologies with multilevel securities is a powerful solution to overcome this challenge. Stimuli-chromic (photochromic, hydrochromic, and thermochromic) and photoluminescent (fluorescent and phosphorescent) compounds are the most significant and applicable materials for development of complex anticounterfeiting inks with a high-security level and fast authentication. Highly efficient anticounterfeiting and authentication technologies have been developed to reach high security and efficiency. Applicable materials for anticounterfeiting applications are generally based on photochromic and photoluminescent compounds, for which hydrochromic and thermochromic materials have extensively been used in recent decades. A wide range of materials, such as organic and inorganic metal complexes, polymer nanoparticles, quantum dots, polymer dots, carbon dots, upconverting nanoparticles, and supramolecular structures, could display all of these phenomena depending on their physical and chemical characteristics. The polymeric anticounterfeiting inks have recently received significant attention because of their high stability for printing on confidential documents. In addition, the printing technologies including hand-writing, stamping, inkjet printing, screen printing, and anticounterfeiting labels are discussed for introduction of the most efficient methods for application of different anticounterfeiting inks. This review would help scientists to design and develop the most applicable encryption, authentication, and anticounterfeiting technologies with high security, fast detection, and potential applications in security marking and information encryption on various substrates.

Preparation and analysis of photochromic behavior of carboxymethyl chitin derivatives containing spiropyran moieties

1ʹ-(2-Acryloxyethyl)-3,3ʹ-dimethyl-6-nitrospiro[2 H-1-benzopyran-2,2ʹ-indoline] (SPA) was synthesized and grafted onto a water-soluble carboxymethyl chitin (CMCH) macromolecule to prepare a photochromic copolymer (CMCH-g-SPA). The structure of CMCH-g-SPA was characterized by Fourier-transform infrared (FT-IR) spectroscopy, thermogravimetric (TG) analysis, X-ray diffraction (XRD) analysis, water-solubility evaluation, and UV-vis spectroscopy. XRD patterns of CMCH-g-SPA revealed that grafting copolymerization disrupts the CMCH semicrystalline structure, thus improving water solubility. UV-vis spectroscopy results supported the negative photochromic behavior of the merocyanine (MC) form of CMCH-g-SPA (CMCH-g-MCA) present in a water solution of the target copolymer. In addition to high solvent polarity, the intermolecular and intramolecular electrostatic attraction between the indolenine cation and the COO⁻ anion were found to be influencing factors, which stabilize these MC form of spiropyran groups grafted onto CMCH. In a water solution, visible light bleaching was completed over a short period (8 minutes) under artificial visible light irradiation and the thermal coloration reaction, whose rate constant at 25 °C was 4.64 × 10⁻⁴ s⁻¹, which fit the first-order reaction equation. After ten photochromic cycles in water solution, the relative absorption intensity of CMCH-g-MCA decreased by 7.92%.

Preparation and Photochromic Performance of Homogeneous Phase Nitrocellulose Membrane Grafting Spirooxazine Moieties

The synthesis of 1,3,3-trimethyl-9′-acryloxyspiro[indoline-2,3′(3H)naphtho[2,1-b][l,4]-oxazine] (AISO) was carried out by catalytic esterification of 1,3,3-trimethyl-9′-hydroxyspiro-[indoline-2,3′(3H)naphtho[2,1-b][l,4]oxazine] (SO–OH) and acrylic acid in the presence of 1,3-dicyclohexylcarbodiimide (DCC) and N-dimethylaminopyridine (DMAP). Then, the synthesis of the target copolymer (NC-g-AISO) was was carried out by benzoyl peroxide (BPO)-induced graft copolymerization of the AISO monomer onto nitrocellulose (NC) in a homogeneous methyl isobutyl ketone medium. The structure of NC-g-AISO was characterized by Fourier transform infrared (IR) spectroscopy, 13C Nuclear Magnetic Resonance (NMR) spectra and thermogravimetric (TG) analysis. The photochromic properties of NC-g-AISO were investigated by examining UV–Vis spectra in ethyl acetate solution and solid membrane. Compared with the AISO monomer in ethyl acetate solution, the thermal color decay stability of the colored form of NC-g-AISO in ethyl acetate solution and in solid membrane improved significantly. The thermal color decay reaction rate constants in ethyl acetate solution and membrane at 25 °C were 1.77 × 10–2 and 1.36 × 10–3 s–1, respectively, fitted using the first-order reaction equation. After ten photochromic cycles, the relative absorption intensity of the colored form of NC-g-AISO decreased by 0.85%, indicating that the NC-g-AISO membrane has good reversible photochromic behavior.