Secret
information recorded by traditional single-encrypted invisible inks
is easily cracked because the inks can switch only between “NONE”
and “TRUTH”. Developing double-encrypted systems makes
the information reversibly switchable between “FALSE”
and “TRUTH”, which is helpful to ensure the safety of
the secret information during transport. Here, we prepared heat-developed
invisible inks by hydrochromic molecules donor–acceptor Stenhouse
adducts (DASAs) and oxazolidines (OXs) and promoted the invisible
inks from single to double encryption. DASAs coordinate with water
molecules and form stable colorless cyclic DASA·xH2O molecules, which lose coordinated water molecules
after heating and switch to colored linear DASAs. In contrast, OXs
are colored with water and are colorless after heating. Single-encrypted
secrecy was realized by DASA invisible inks. The information is invisible
under the encrypted state and becomes bright purple after heating.
Vapor treating re-encrypted the information in ∼5 min. Furthermore,
the single-encryption was promoted to double-encryption by a DASA/OX
invisible inks system. Heating and vapor treating switch the information
between the “FALSE” and “TRUTH” reversibly.
The DASA/OX invisible ink system is applied for secrecy of texts,
graphic images, and quick response (QR) codes.
In this report, we designed surfaces with reversible green-light-switched wettability via donor−acceptor Stenhouse adducts (DASAs). Photoresponsive micro/nanoparticles were prepared by coating the surfaces of silica micro/nanoparticles with polydopamine and then postmodifying with DASA molecules. Then, the particles were immobilized on a glass substrate surfaces either with double-sided adhesive tape or cross-linking poly-(dimethylsiloxane). Silica micro/nanoparticles with various diameters (0.2, 2.5, and 85 μm) were used to fabricate the photoresponsive surface. Green light irradiation switches the hydrophobic linear DASA to a hydrophilic cyclic isomer, which further increases the wettability and contact angle hysteresis on the surface. On the other hand, heating (100 °C) induces the cyclic-to-linear isomerization of DASA molecules and switches the surface back to hydrophobic. The wettability of the DASA-modified surface is reversible under alternate green light irradiation and heating.
Photoswitchable and photoluminescent ternary supramolecular hydrogels were fabricated by host–guest and ionic interactions between polyacrylic acid, azobenzene guanidine and α-cyclodextrin grafted cellulolytic enzyme lignin nanoparticles.
In the present research, novel tri‐block‐copolymers bearing polyethylene glycol (PEG), azobenzene (Azo), and tetra‐ortho‐methoxy‐substituted Azo (mAzo) segments are synthesized and explored. Light‐controlled PEG‐PmAzo‐PAzo self‐assemblies switching between multi‐stationary states is realized. Under controlling of UV, blue, green, and red light, PEG‐PmAzo‐PAzo isomerize between 4 photostationary states. The enrichment of cis isomers of Azo and mAzo induces the self‐assembly of PEG‐PmAzo‐PAzo in toluene. The morphologies and scale of the self‐assemblies can be switched between four stationary states, which are investigated by dynamic light scattering, scanning electron microscopy, and transmission electron microscopy.
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