Light-Written Reversible 3D Fluorescence and Topography Dual-Pattern with Memory and Self-Healing Abilities

Abstract

To achieve the dynamical dual-pattern with multiplex information of complex topography and 3D fluorescence is challenging yet promising for wide applications ranging from visual bioassays, memory, smart devices to smart display. Here, we develop a convenient, reliable, and versatile method to realize the well-ordered dual-pattern with reversible topography and 3D fluorescence via a light direct-writing approach based on the wrinkle mechanism. By introducing the charge transfer (CT) interaction between π-electron-rich anthracene (AN) and π-electron-poor naphthalene diimide (NDI) into the polymer system, both modulus and fluorescence of the polymer films can be spatially regulated through the photodimerization of AN, which is controlled in-plane by photomasks, and becomes gradient in the vertical direction due to the filter effect of light. Therefore, the exposed sample displays a well-ordered complex pattern with the same topography as the applied photomask and 3D gradient change of fluorescence from red to green laterally across the layers simultaneously. The spatial cross-linking and CT interaction of the gradient layer can be controlled independently, which not only provides the reliability and reversibility of the topographical and fluorescence dual-pattern but also endows the possibility for tailoring the pattern with memory and self-healing. These characters of the dual-pattern with reversible topography and 3D fluorescence declare the clear applications in smart multiplex displays, memory, anticounterfeiting, visual detections, and so on.

Scheme 1

Schematic of patterns with 3D topography and 3D fluorescence, including (a) the direct-writing procedure of the dual-pattern on the film, (b) the involved chemical structures and dynamic reaction of the transformation between CT complex and dimers of anthracene, (c) the resulting 3D topography, and (d) the resulting 3D fluorescence images.

Figure 1

Optical microscope images of the patterns direct-written using a series of positive concentric circular annulus photomasks with different sizes: (a) 30 μm; (b) 60 μm; (c) 100 μm; (d) 200 μm; (e) 300 μm; (f) 500 μm. The thickness of polymer blend film is fixed at approximately 200 μm. The intensity and exposure time of 365 nm UV light are approximately 50 mW/cm² and 30 seconds, respectively.

Figure 2

The evolution of the direct-written pattern from positive concentric square photomasks (size width/space: 50/50 μm) with different exposure time observed with LSCM images: (a) 10 S; (b) 60 S; (c) 120 S. (d) The statistical height (h) of the patterns dependent on the exposure time. The thickness of the polymer blend film was ≈200 μm. The intensity of 365 nm UV light is approximately 50 mW/cm².

Figure 3

3D Fluorescence image of the dual-pattern obtained via the light direct-writing method. (a) Fluorescence image on the upside of the pattern; (b) fluorescence image on the downside of the pattern; (c-f) the fluorescence images and corresponding sectional fluorescence images of the dual-patterns at different depths of the film (5 μm, 10 μm, 15 μm, and 20 μm). The pattern was written with positive concentric square photomasks (size width/space: 50/50 μm). The thickness of the polymer blend film was ≈200 μm. The intensity and exposure time of 365 nm UV light were ≈50 mW/cm² and 30 seconds, respectively.

Figure 4

The reversibility, memory behavior, and healing ability of the dual-pattern. (a) The LSCM and fluorescence images showing the cyclic erasable process: writing the patterns, erasing the patterns, and rewriting the patterns: (a, I) topography and fluorescence image of the original sample; (a, II) topography and fluorescence image of the written sample with the patterns of concentric squares (size width/space: 50/50 μm); (a, III) the topography of the written sample without the mask during the exposure; (a, IV) 3D topography and fluorescence of the written sample with the patterns of “SJTU.” The thickness of the polymer blend film was ≈200 μm. The intensity and exposure time of 365 nm UV light were ≈50 mW/cm² and 30 seconds, respectively. (b) LSCM images showing the shape memory process of the 3D well-ordered pattern: (b, I) the original shape of the pattern (concentric squares, size width/space: 50/50 μm); (b, II) temporary state of the pattern; (b, III) the recovery shape of the pattern after heated at about 60°C for 3 minutes. (c) Optical images showing the self-healing process of the 3D pattern: (c, I) the damaged sample (concentric circular annulus (size width/space: 100/100 μm)) with a crack; (c, II) the healed sample after heated at about 80°C for 5 minutes.

Figure 5

Laser scanning confocal microscope (LSCM) images showing the complex patterns obtained via the light direct-writing method. (a) 3D school badge of Shanghai Jiao Tong University. The intensity and exposure time of 365 nm UV light were ≈50 mW/cm² and 30 seconds, respectively. (b) 3D “QR Code” with fluorescence under UV light. The thickness of the polymer blend film was ≈200 μm. The intensity and exposure time of 365 nm UV light were ≈50 mW/cm² and 25 seconds, respectively.