Reversible Photochromic Photonic Crystal Device with Dual Structural Colors

An ultrawide-range photochromic molecular fluorescence emitter

Photocontrollable luminescent molecular switches capable of changing emitting color have been regarded as the ideal integration between intelligent and luminescent materials. A remaining challenge is to combine good luminescence properties with wide range of wavelength transformation, especially when confined in a single molecular system that forms well-defined nanostructures. Here, we report a π-expanded photochromic molecular photoswitch, which allows for the comprehensive achievements including wide emission wavelength variation (240 nm wide, 400-640 nm), high photoisomerization extent (95%), and pure emission color (<100 nm of full width at half maximum). We take the advantageous mechanism of modulating self-assembly and intramolecular charge transfer in the synthesis and construction, and further realize the full color emission by simple photocontrol. Based on this, both photoactivated anti-counterfeiting function and self-erasing photowriting films are achieved of fluorescence. This work will provide insight into the design of intelligent optical materials.

Rewritable Photoluminescence and Structural Color Display for Dual-Responsive Optical Encryption

Optical encryption using coloration and photoluminescent (PL) materials can provide highly secure data protection with direct and intuitive identification of encrypted information. Encryption capable of independently controlling wavelength-tunable coloration as well as variable light intensity PL is not adequately demonstrated yet. Herein, a rewritable PL and structural color (SC) display suitable for dual-responsive optical encryption developed with a stimuli-responsive SC of a block copolymer (BCP) photonic crystal (PC) with alternating in-plane lamellae, of which a variety of 3D and 2D perovskite nanocrystals is preferentially self-assembled with characteristic PL, is presented. The SC of a BCP PC is controlled in the visible range with different perovskite precursor doping times. The perovskite nanocrystals developed in the BCP PC are highly luminescent, with a PL quantum yield of ≈33.7%, yielding environmentally stable SC and PL dual-mode displays. The independently programmed SC and PL information is erasable and rewritable. Dual-responsive optical encryption is demonstrated, in which true Morse code information is deciphered only when the information encoded by SCs is properly combined with PL information. Numerous combinations of SC and PL realize high security level of data anticounterfeiting. This dual-mode encryption display offers novel optical encryption with high information security and anti-counterfeiting.

Brochosome-inspired binary metastructures for pixel-by-pixel thermal signature control

Microscale thermal signature control using incoherent heat sources remains challenging, despite recent advancements in plasmonic materials and phase-change materials. Inspired by leafhopper-generated brochosomes, we design binary metastructures functioning as pixel twins to achieve pixelated thermal signature control at the microscale. In the infrared range, the pixel twins exhibit distinct emissivities, creating thermal counterparts of "0-1" binary states for storing and displaying information. In the visible range, the engineered surface morphology of the pixel twins ensures similar scattering behaviors. This renders them visually indistinguishable, thereby concealing the stored information. The brochosome-like pixel twins are self-emitting when thermally excited. Their structure-enabled functions do not rely on the permittivities of specific materials, which distinguishes them from the conventional laser-illuminated plasmonic holographic metasurfaces. The unique combination of visible camouflage and infrared display offers a systemic solution to microscale spatial control of thermal signatures and has substantial implications for optical security, anticounterfeiting, and data encryption.

Permanent irreversible structural color based on core-shell chemically bonded SiO2@P(St-BA) particles

Novel core-shell chemically bonded SiO₂@P(St-BA) particles were designed and self-assembled to prepare photonic crystals. Due to the irreversible collapse of polymer shells during hot-pressing, SiO₂@P(St-BA) particles could provide new ideas for high-stability and bright red-shifted structural color patterns.

Portable Comestible-Liquid Quality Test Enabled by Stretchable and Reusable Ion-Detection Photonic Papers

Currently, there have been widespread investigation conducted into responsive photonic crystal hydrogels (RPCHs) characterized by high selectivity and sensitivity for colorimetric indicators and physical/chemical sensors. In spite of this, it remains challenging to use RPCHs for sensing due to their limited mechanical property and molding capability. In the present study, a double-network structure is proposed to design highly stretchable, sensitive, and reusable ion-detection photonic papers (IDPPs) for assessing the quality of visual and portable comestible liquids (e.g., soy sauce). It is constructed by integrating polyacrylamide and poly-methacryloxyethyl trimethyl ammonium chloride with highly ordered polystyrene microspheres. The double-network structure improves the mechanical properties of IDPPs with their elongation at break increasing from 110 to 1600%. Meanwhile, the optical properties of photonic crystals are retained. The IDPPs achieve a fast ion response by applying control on the swelling behavior of the hydration radius of the counter ions through ion exchange. Given a certain concentration range (0.01-0.10 M), chloride ions can be detected fast (3-30 s) by exchanging ions with a small hydration radius through an IDPP, which is clearly observable. Due to the improvement of mechanical properties and the reversible exchange of ions derived from IDPPs, their reusability is significantly enhanced (>30 times). Characterized by a simple operation, high durability, and excellent sustainability, these IDPPs are promising for practical application in food security and human health assessment.

Programming Thermochromic Liquid Crystal Hetero-Oligomers for Near-Infrared Reflectors: Unequal Incorporation of Similar Reactive Mesogens in Thiol-ene Oligomers

Cholesteric liquid crystal oligomers are widely researched for their interesting thermochromic properties. However, structure-property relationships to program the thermochromic properties of these oligomers have been rarely reported. In this work, we use the versatile thiol-ene click reaction to synthesize a series of hetero-oligomers and study the impact of different compositions on the thermochromic behavior of the resulting material. Characterization of the oligomers shows significantly different rates of reaction for the monomers despite their very similar structures, which leads to oligomer compositions that do not match the original reaction feed. The oligomers are then used to produce thin near-infrared reflecting coatings. The best-performing thermochromic reflector has a room-temperature reflection band that shifts a total of 510 nanometers upon heating to 120 °C. The shift is repeatable for up to 10 times with no appreciable degradation. The room temperature reflection of the coatings is shown to be tunable not only by adjusting the chiral dopant concentration but also by the ratio of the monomers. Finally, we show that the oligomers can be chemically modified by making their reactive end groups undergo a reaction with monothiol compounds. These modifications allow for further fine-tuning of liquid crystal oligomers for heat-regulating window films, for example.