Photoswitchable Fluorescent Liquid Crystal Nanoparticles and Their Inkjet‐Printed Patterns for Information Encrypting and Anti‐Counterfeiting

Abstract

Liquid crystal nanoparticles (LCNPs) with desirable multifunctionality are catching increasing attention due to their promising applications in various fields. However, reversible photoswitchable fluorescent LCNPs are not reported until now. Here, the first example of water‐dispersible, reversibly phototunable fluorescent LCNPs prepared through a miniemulsion polymerization technique is presented. The LCNPs mainly consist of an aggregation‐induced emission enhancement (AIEE)‐active dicyanodistyrylbenzene‐based monomer, a LC cross‐linking monomer, and a dithienylethene (DAE) derivative as a photochromic molecular switch. The fluorescence of the resultant LCNPs can be switched reversibly between bright (ON) and dark (OFF) states with a high contrast and excellent repeatability upon alternating irradiation of 365 nm UV light and visible light (λ > 450 nm). This observation could be attributed to ring‐opening/ring‐closing photoisomerization of the DAE structure on the basis of an intraparticle fluorescence resonance energy transfer process between the AIEE‐active monomer and DAE derivative. More importantly, the potential for aqueous dispersion of the photoswitchable fluorescent LCNPs as a security ink for information encryption and anti‐counterfeiting is further demonstrated. The results demonstrate that the reversible photoswitchable fluorescent LCNPs as multifunctional nanomaterials exhibit promising applications in photonic fields.

Circularly polarized luminescent self‐organized helical superstructures: From materials and stimulus‐responsiveness to applications

“…Polymerization of fluorescent monomers with polymerizable functional groups is an effective means of obtaining luminescent LC (LLC) polymers. [70][71][72] On the other hand, the helical structure of small-molecule CLCs can serve as a polymeric template for one-handed LC polymers. Akagi et al developed a complex but ingenious design to form helical network polymers using chiral LCs as asymmetric polymerization solvents (Figure 3C).…”

Multidimensional Information Encryption and Storage: When the Input Is Light

“…For improving the security level of encrypted and stored information, sometimes it is essential to keep its original state invisible under natural light [ 85 ]. The dynamic fluorescent QR code composed of DAE derivatives and AIE molecules showed information invisible under two situations (under natural light before UV light irradiation and under UV light after UV light irradiation), while showing information visible under other two situations ( Figure 3(j) ) [ 80 ]. As a result, it is feasible to control how much information is displayed or concealed by the designed precision synthesis.…”

“…(j) The dual decryption process of the dynamic fluorescent anticounterfeiting QR code printed with liquid crystal nanoparticle-based ink. Reproduced with permissions: (a) from [ 74 ], Copyright 2016, Wiley-VCH; (d, e) from [ 73 ], Copyright 2012, The Royal Society of Chemistry; (f, g) from [ 28 ], Copyright 2017, Wiley-VCH; (i) from [ 79 ], Copyright 2017, American Chemical Society; (j) from [ 80 ], Copyright 2019, Wiley-VCH.…”

Liquid‐Crystalline Polymer Particles Prepared by Classical Polymerization Techniques

“…The electrostatic stabilization of the surfactant was critical in preventing coalescence upon drying, while steric stabilizers such as polyvinyl alcohol failed to provide stabilization, and the particles aggregated. With this surfactant, tuning both the stiffness and morphology of the LC polymer particles have been explored, [41] and the LC polymer particles have been suggested as drug delivery materials,[ 42 , 43 , 44 , 45 , 46 , 47 ] hosts for adjustable fluorescent dyes,[ 48 , 49 ] and photo‐actuators. [50] For instance, fluorescent LC polymer particles were prepared with LC monomer 9 and a fluorescent dye 10 , of which the fluorescent emission redshifts upon aggregation into dimers, trimers, etc.…”