Xuesong
Yang
a,
Marieh B.
Al-Handawi
b,
Liang
Li
bc,
Panče
Naumov
*bdef and
Hongyu
Zhang
*a
aState Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Changchun 130012, P. R. China. E-mail: hongyuzhang@jlu.edu.cn
bSmart Materials Lab, New York University Abu Dhabi, PO Box 129188, Abu Dhabi, UAE. E-mail: pance.naumov@nyu.edu
cDepartment of Sciences and Engineering, Sorbonne University Abu Dhabi, PO Box 38044, Abu Dhabi, UAE
dCenter for Smart Engineering Materials, New York University Abu Dhabi, PO Box 129188, Abu Dhabi, UAE
eResearch Center for Environment and Materials, Macedonian Academy of Sciences and Arts, Bul. Krste Misirkov 2, MK-1000 Skopje, Macedonia
fMolecular Design Institute, Department of Chemistry, New York University, 100 Washington Square East, New York, NY 10003, USA
First published on 8th January 2024
Organic molecular crystals have historically been viewed as delicate and fragile materials. However, recent studies have revealed that many organic crystals, especially those with high aspect ratios, can display significant flexibility, elasticity, and shape adaptability. The discovery of mechanical compliance in organic crystals has recently enabled their integration with responsive polymers and other components to create novel hybrid and composite materials. These hybrids exhibit unique structure–property relationships and synergistic effects that not only combine, but occasionally also enhance the advantages of the constituent crystals and polymers. Such organic crystal composites rapidly emerge as a promising new class of materials for diverse applications in optics, electronics, sensing, soft robotics, and beyond. While specific, mostly practical challenges remain regarding scalability and manufacturability, being endowed with both structurally ordered and disordered components, the crystal–polymer composite materials set a hitherto unexplored yet very promising platform for the next-generation adaptive devices. This Perspective provides an in-depth analysis of the state-of-the-art in design strategies, dynamic properties and applications of hybrid and composite materials centered on organic crystals. It addresses the current challenges and provides a future outlook on this emerging class of multifunctional, stimuli-responsive, and mechanically robust class of materials.
Fig. 1 Time-line and milestones in the research on the mechanical properties and effects of molecular crystals, and evolution of the crystal adaptronics. Reproduced with permission from ref. 12, Copyright 2022 Spring Nature. Reproduced with permission from ref. 13, Copyright 2022 Wiley-VCH. Reproduced with permission from ref. 14, Copyright 2022 Wiley-VCH. Reproduced with permission from ref. 46, Copyright 2012 Wiley-VCH. Reproduced with permission from ref. 47, Copyright 2013 Royal Society of Chemistry. Reproduced with permission from ref. 48, Copyright 2014 American Chemical Society. Reproduced with permission from ref. 49, Copyright 2015 Spring Nature. Reproduced with permission from ref. 50, Copyright 2016 Wiley-VCH. Reproduced with permission from ref. 51, Copyright 2017 Spring Nature. Reproduced with permission from ref. 52, Copyright 2018 American Chemical Society. Reproduced with permission from ref. 53, Copyright 2019 Royal Society of Chemistry. Reproduced with permission from ref. 54, Copyright 2020 Wiley-VCH. Reproduced with permission from ref. 55, Copyright 2021 American Chemical Society. Reproduced with permission from ref. 56, Copyright 2023 American Chemical Society. Reproduced with permission from ref. 57, Copyright 2023 Wiley-VCH. |
Fig. 2 Research on flexible organic crystals. (a) Illustration of the crystal arrangement in an elastically bendable cocrystal. (a) Reproduced with permission from ref. 46, Copyright 2012 Wiley-VCH. (b) Images under both daylight and UV light, showing a single crystal of 1,4-bis[2-(4-methylthienyl)]-2,3,5,6-tetrafluorobenzene, notable for its remarkable elasticity. (b) Reproduced with permission from ref. 50, Copyright 2016 Wiley-VCH. (c) Depicts the chemical structure of [Cu(acac)2], an image of a sharply bent crystal, and its crystal structure. (c) Reproduced with permission from ref. 51, Copyright 2017 Spring Nature. (d) Diagram and optical micrographs showing 3,3′-dimethylazobenzene crystals moving vertically when exposed to ultraviolet (UV) light (365 nm) and visible light (VIS) (465 nm). Dashed lines mark the crystals' initial positions. (d) Reproduced with permission from ref. 49, Copyright 2015 Spring Nature. (e) Photoreactive behaviour of azobenzene crystals, which exert force on PDMS pillars during bending, for force measurement. (e) Reproduced with permission from ref. 68 under the terms of the CC-BY license. (f) Schematic and optical microscopic views of five micromechanical processes conducted using an atomic force microscopy (AFM) tip on a flexible crystal. (f) Reproduced with permission from ref. 72, Copyright 2020 Wiley-VCH. (g) Image of flexible optical waveguides made from organic crystals. (g) Reproduced with permission from ref. 78, Copyright 2018 Wiley-VCH. (h) Image of flexible organic crystals bent at −196 °C. (h) Reproduced with permission from ref. 79, Copyright 2020 Wiley-VCH. (i) Flexible organic single crystal having a polarization-rotation functionality. (i) Reproduced with permission from ref. 80, Copyright 2019 Wiley-VCH. (j) Doping for the creation of diverse fluorescent whispering-gallery-mode (WGM) hetero-microrings. (j) Reproduced with permission from ref. 81, Copyright 2023 Wiley-VCH. (k) WGB Lasers utilizing self-assembled organic single-crystalline microrings. (k) Reproduced with permission from ref. 82, Copyright 2019 American Chemical Society. (l) Development and production of a wafer-scale organic printed photonic chip. (l) Reproduced with permission from ref. 83 under the terms of the CC-BY license. |
Fig. 3 Preparation process, deposition method, classification, functionality, and other details pertinent to the hybrid organic–polymer materials. |
Fig. 4 Preparation of hybrid organic crystals. (a) Diagram showing the process for creating organic/polymer hybrids that are sensitive to low temperatures. (a) Reproduced with permission from ref. 91, Copyright 2022 American Chemical Society. (b) Illustration of the construction process and structure of solvent-resistant hybrid organic crystals. (b) Reproduced with permission from ref. 92, Copyright 2021 Wiley-VCH. (c) The technique for preparation of humidity-responsive hybrid crystals, with the lower-row SEM images highlighting the crystals in orange, the polymer coating in purple, and the moisture-reactive polymer (PVA) in green. (c) Reproduced with permission from ref. 13, Copyright 2022 Wiley-VCH. (d) Procedure for fabrication of hybrid crystals that react to magnetic field. (d) Reproduced with permission from ref. 12, Copyright 2022 Spring Nature. (e) Method for developing photoresponsive arrays using hybrid organic crystals. (e) Reproduced with permission from ref. 26, Copyright 2023 Spring Nature. |
Fig. 5 Response of hybrid organic crystals. (a) Optical images displaying the shape transformation of temperature-sensitive hybrid crystals at 20 °C, −120 °C, and when submerged in liquid nitrogen. (a) Reproduced with permission from ref. 14, Copyright 2022 Wiley-VCH. (b) Optical images of humidity-sensitive hybrid organic crystals bending in response to humidity under UV light. (b) Reproduced with permission from ref. 13, Copyright 2022 Wiley-VCH. (c) Images showing hybrid organic crystals bending when exposed to infrared light. (c) Reproduced with permission from ref. 26, Copyright 2023 Spring Nature. (d) Images of Ti3C2Tx-coated enol-1 crystal rapidly bending upon exposure to near-infrared LED light. (d) Reproduced with permission from ref. 93, Copyright 2023 Wiley-VCH. (e) Images of magnetically responsive hybrid organic crystals bending when a magnet is applied. (e) Reproduced with permission from ref. 12, Copyright 2022 Spring Nature. |
Fig. 6 Applications of hybrid organic crystals. (a) Illustrative diagram and photographs showing a soft robot designed to mimic spider-like movements. (b) Diagram and images of a soft gripper constructed from hybrid organic crystal. (c) Schematic and photographs depicting the ‘walking’ movement of organic polymer–crystal hybrid materials on a surface. (a–c) Reproduced with permission from ref. 27, Copyright 2023 Spring Nature. |
Fig. 7 Applications of hybrid organic crystals. (a) A worm-like movement of hybrid crystal–polymer materials at high and low temperatures, with the central diagram illustrating the initial and final states of motion. (b) Shows a soft robot made from hybrid organic crystals, demonstrating its ability to grab objects at low temperatures. (a and b) Reproduced with permission from ref. 14, Copyright 2022 Wiley-VCH. (c) Illustrates a dual-function optical/electrical signal transmission circuit using a hybrid organic crystal. A bulb serves as an indicator, activated by a 355 nm laser. The waveguide output's position indicates the ambient temperature (marked with a white dashed line), with a white arrow showing output change upon cooling. The crystals are outlined with red rectangles. (c) Reproduced with permission from ref. 25, Copyright 2022 Spring Nature. (d) Depicts the spatial control of light output influenced by humidity. A crystal fixed at one end is shown bending with increased humidity (indicated by a white arrow), altering the light output's position. This bending is marked by a yellow broken line, with red arrows showing the light's path in both straight and bent states. (d) Reproduced with permission from ref. 13, Copyright 2022 Wiley-VCH. (e) A hybrid crystal functioning as a magnetically controlled optical waveguide. One end is fixed, with the other controlled by a magnet's movement. The crystal, excited by a 355 nm laser (blue arrow), directs light (yellow arrow) influenced by the magnet's movement (white arrow). The red dot marks the light output. (e) Reproduced with permission from ref. 12, Copyright 2022 Spring Nature. |
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