Processable circularly polarized luminescence material enables flexible stereoscopic 3D imaging

Abstract

Endowing three-dimensional (3D) displays with flexibility drives innovation in the next-generation wearable and smart electronic technology. Printing circularly polarized luminescence (CPL) materials on stretchable panels gives the chance to build desired flexible stereoscopic displays: CPL provides unusual optical rotation characteristics to achieve the considerable contrast ratio and wide viewing angle. However, the lack of printable, intense circularly polarized optical materials suitable for flexible processing hinders the implementation of flexible 3D devices. Here, we report a controllable and macroscopic production of printable CPL-active photonic paints using a designed confining helical co-assembly strategy, achieving a maximum luminescence dissymmetry factor (g_lum) value of 1.6. We print customized graphics and meter-long luminous coatings with these paints on a range of substates such as polypropylene, cotton fabric, and polyester fabric. We then demonstrate a flexible textile 3D display panel with two printed sets of pixel arrays based on the orthogonal CPL emission, which lays an efficient framework for future intelligent displays and clothing.

Fig. 1.. Large-scale synthesis of CPL-PPs.

(A) Flow chart showing the process to prepare CPL-PPs. (B) RGB CPL-PPs. (C) Schematic summarizing the preparation of chiral core-shell microspheres: The CPL precursors composed of E7 liquid crystals, R/S5011 chiral dopants, and dyes were emulsified successively with acacia solution and gelation solution. Then the coacervation reaction occurred when reducing the pH of the system, and the microspheres precipitated. Cooling promotes the phase transition of CLC, and gelatin molecules are crosslinked into a network structure to firm the shell. (D) Schematic illustration of materials and the left- or right-handed CPL emitted from as-prepared microspheres upon ultraviolet (UV) irradiation.

Fig. 2.. Characterization of CPL-PPs.

(A) Photographs of prepared CPL-PPs. Bottle volume, 1000 ml. Scale bar, 4 cm. (B) Photographs showing right- and left-handed RGB-emissive CPL-PPs. Scale bar, 4 cm. (C) Bright-field optical microscopy image of the typical CPL-PPs sample in transmission mode. Scale bar, 100 μm. (D) Bright-field optical microscopy images in reflection mode (the top row) and corresponding POM images of microspheres (the bottom row), from left to right are left-handed red emissive, right-handed red emissive, left-handed green emissive, right-handed green emissive, left-handed blue emissive, and right-handed blue emissive, respectively. Scale bars, 3 μm. (E) Corresponding PL spectra of the CPL-PPs in (B). a.u., arbitrary units. (F to I) Cyan-emissive (F), pink-emissive (G), yellow-emissive (H), and white-emissive (I) CPL-PPs obtained by mixing two or three kinds of CPL-PPs (B + G, B + R, G + R, and B + G + R, respectively). Insets showing their photographs under 365 nm UV irradiation. Scale bars, 1 cm. (J) CIE 1931 chromaticity coordinates of different emissions of CPL-PPs, which are (0.16, 0.05) for blue emission, (0.18, 0.62) for green emission, (0.52, 0.46) for red emission, and (0.33, 0.33) for white emission, respectively. (K) FTIR spectra of the CLC core, polymer shell, and CPL-PPs. (L) Thermogravimetry–differential scanning calorimetry (TG-DSC) curves of the CPL-PPs between 30° and 800°C in a nitrogen atmosphere. (M) DSC curves of heating-cooling cycles of the CPL-PPs between 0° and 100°C in a nitrogen atmosphere.

Fig. 3.. CPL performance.

(A to C) Emission intensity of blue-emissive (A), green-emissive (B), and red-emissive (C) CPL-PPs as a function of polarization angle, where θ represents the transmission angle and r refers to the transmittance. (D) CPL spectra of red-, green-, and blue-emissive CPL-PPs. The solid (dashed) curves correspond to right (left)-handed materials. (E) Calculated g_lum values corresponding to (D). (F) g_lum evolution of blue-emissive CPL-PPs under ambient atmosphere for 80 days. Error bars correspond to the SD of three measurements. (G to I) Photoluminescence spectra of the right-handed blue-emissive (G), green-emissive (H), and red-emissive (I) CPL-PPs measured through left-handed (solid line) and right-handed (dashed line) circular polarization filters, respectively.

Fig. 4.. Printing CPL-PPs to form circularly polarized luminous patterns.

(A) Dispenser for direct pattern writing with a moving nozzle. (B to D) “CPL” patterns on different substrates: from the rigid polypropylene plate (B) to flexible cotton fabric (C) and flexible PET fabric (D). Scale bars, 1 cm. (E and F) Spray printing of CPL-PPs on PET substrates observed under natural light (E) and upon 365-nm UV irradiation (F). Scale bars, 1 cm. (G and H) Emission intensity of left-handed (left column) and right-handed (right column) red-emissive luminous fabrics as a function of polarization angle, where θ is the transmission angle and r is the transmittance (G). The results evidencing the circular polarization characteristic of luminescence is maintained after spray printing (H). (I) Photograph of a 1.5-m-long luminous textile printed by CPL-PPs. (J) Photographs of the luminous fabrics after exposure in the acid solution, pure water, basic solution, and n-hexane solution for 7 days, respectively. Scale bar, 5 mm.

Fig. 5.. Flexible 3D display based on printed orthogonal CPL matrix.

(A) Fabrication strategy of the flexible 3D display. Left- and right-handed polarization images can be achieved from flexible array panels with printed CPL-active orthogonal matrix. Through a polarization glass, the two images enter the left and right eyes, respectively, and the brain can fuse the two images into 3D sensation. (B) Schematic diagram of a flexible array panel, containing pixelated CPL arrays obtained by printing CPL-PPs on the flexible substrates. (C to H) Photographs of “USTC 1958” patterns obtained by alternately printing left- and right-handed CPL-PPs with RGB emissions on PET fabrics. Observed under natural light [(C), (E), and (G)] and under UV irradiation [(D), (F), and (H)]. Scale bars, 1 cm. (I) Photograph of the bent flexible 3D display panel based on the orthogonal CPL matrix while a pattern was displayed on it. Scale bar, 1 cm. (J) Photograph of a wearable watch-like flexible 3D display wearing on the wrist. Scale bar, 1 cm. Inset photograph showing the display panel. Scale bar, 5 mm. (K) Conceptual image of a wearable 3D display device, demonstrating the stereoscopic navigation information that is displayed on the smart wear.