Construction of Photoresponsive 3D Structures Based on Triphenylethylene Photochromic Building Blocks

Abstract

Photoresponsive materials have been widely used in sensing, bioimaging, molecular switches, information storage, and encryption nowadays. Although a large amount of photoresponsive materials have been reported, the construction of these smart materials into precisely prescribed complex 3D geometries is rarely studied. Here we designed a novel photoresponsive material methyl methacrylate containing triphenylethylene (TrPEF₂-MA) that can be directly used for digital light processing (DLP) 3D printing. Based on TrPEF₂-MA, a series of photoresponsive 3D structures with reversible color switching under ultraviolet/visible light irradiations were fabricated. These complex photoresponsive 3D structures show high resolutions (50 μm), excellent repeatability (25 cycles without fatigue), and tunable saturate color degrees. Multicomponent DLP 3D printing processes were also carried out to demonstrate their great properties in information hiding and information-carrying properties. This design strategy for constructing photoresponsive 3D structures is attractive in the area of adaptive camouflage, information hiding, information storage, and flexible electronics.

Figure 1

Comprehensive feature of 3D-printable photoresponsive materials.

Figure 2

(a) Illustration of the photoresponsive material using the DLP 3D printing technology. (b) Time-dependent UV-Vis absorption spectra of TrPEF₂-MA in degassed THF solution (1.0 × 10⁻¹ M) during the irradiation process. (c) Time-dependent UV-Vis absorption spectra of TrPEF₂-MA in degassed THF solution (1.0 × 10⁻¹ M) during the bleaching process. (d) Recycling of the photochromic processes for TrPEF₂-MA in solution state as a function of exposure to UV light (365 nm) and visible light for 5 minutes and 30 minutes, respectively. (e) The transmittance of the TrPEF₂-MA polymer films with the thickness of ca. 2 mm before and after UV irradiation. (f) Different preparation processes of TrPEF₂-MA containing doped and copolymerized films. (g) Comparison of photochromic properties between doped and grafted materials before and after swelling. SEM images of TrPEF₂-MA containing doped (h) and copolymerized (i) films.

Figure 3

Constructions and the investigation of photoresponsive 3D structures. (a) Schematic of digital light processing-based 3D printing process. (b) Chemical structures of photopolymer inks (including monomer, cross-linker, and initiator) and formed cross-linked structure via photopolymerization and the general schemes of dynamic-based photochromic covalent bonds before and after UV/Vis irradiation. (c) Images of 3D-printed photoresponsive flower. (d) Schematic diagram of photochromic mechanism of triphenylethylene group. (e) Photochromic process of the 3D-printed tree based on TrPEF₂-MA containing resin. (f) SEM images of the printed photoresponsive 3D structures.

Figure 4

Photochromic properties of the printed 3D structures. (a) Photoresponsive pictures of the printed hollow 3D structures containing different mass fractions of TrPEF₂-MA. (b) Time-dependent UV-Vis absorption spectra of the printed hollow 3D structures with resin B during the photochromic bleaching process. (c) Time-dependent UV-Vis absorption spectra of the printed hollow 3D structures with resin C during the photochromic bleaching process. (d) Time-dependent UV-Vis absorption spectra of the printed hollow 3D structures with resin D during the photochromic bleaching process. (e and f) Recycling of the photochromic process of 3D-printed Eiffel Tower as a function of exposure to UV light (365 nm) and visible light.

Figure 5

3D-printed multicomponent photoresponsive structures. (a) Schematic of 3D-printed multicomponent QR code with liquid resin A and resin D. (b) A printed photochromic four-tier pyramid with resins A-D. (c) Schematic of the 3D-printed multicomponent framework for information carrying and encryption.