1. School of Materials Science and Engineering, Nanjing Institute of Technology, Nanjing 211167, China 2. Jiangsu Key Laboratory of Advanced Structural Materials and Application Technology, Nanjing 211167, China
The incorporation of mechanophores, motifs that transform mechanical stimulus into chemical reaction or optical variation, allows creating materials with stress-responsive properties. The most widely used mechanophore generally features a weak bond, but its cleavage is typical an irreversible process. Here, we showed that this problem can be solved by folding–unfolding of a molecular tweezer. We systematically studied the mechanochromic properties of polyurethanes with cyano-substituted oligo(p-phenylene) vinylene (COP) tweezer (DPU). As a control experiment, a class of polyurethanes containing only a single COP moiety (MPU) was also prepared. The DPU showed prominent mechanochromic properties, due to the intramolecular folding–unfolding of COP tweezer under mechanical stimulus. The process was efficient, reversible and optical detectable. However, due to the disability to form either intramolecular folding or intermolecular aggregation, the MPU sample was mechanical inert.
H, Hu Z Y, Ma X R Jia . Reaction cascades in polymer mechanochemistry.Materials Chemistry Frontiers, 2020, 4(11): 3115–3129 https://doi.org/10.1039/D0QM00435A
2
N, Deneke M L, Rencheck C S Davis . An engineer’s introduction to mechanophores.Soft Matter, 2020, 16(27): 6230–6252 https://doi.org/10.1039/D0SM00465K
3
F, Ciardelli G, Ruggeri A Pucci . Dye-containing polymers: methods for preparation of mechanochromic materials.Chemical Society Reviews, 2013, 42(3): 857–870 https://doi.org/10.1039/C2CS35414D
4
K M, Wiggins J N, Brantley C W Bielawski . Methods for activating and characterizing mechanically responsive polymers.Chemical Society Reviews, 2013, 42(17): 7130–7147 https://doi.org/10.1039/c3cs35493h
5
J, Li C, Nagamani J S Moore . Polymer mechanochemistry: from destructive to productive.Accounts of Chemical Research, 2015, 48(8): 2181–2190 https://doi.org/10.1021/acs.accounts.5b00184
6
H, Zeng J S, Leng J P, Gu et al.. A thermoviscoelastic model incorporated with uncoupled structural and stress relaxation mechanisms for amorphous shape memory polymers.Mechanics of Materials, 2018, 124: 18–25 https://doi.org/10.1016/j.mechmat.2018.05.010
7
H, Zeng J S, Leng J P, Gu et al.. Modeling the strain rate-, hold time-, and temperature-dependent cyclic behaviors of amorphous shape memory polymers.Smart Materials and Structures, 2018, 27(7): 075050 https://doi.org/10.1088/1361-665X/aaca50
8
J P, Gu H Y, Sun C Q Fang . A finite deformation constitutive model for thermally activated amorphous shape memory polymers.Journal of Intelligent Material Systems and Structures, 2015, 26(12): 1530–1538 https://doi.org/10.1177/1045389X14544147
9
H, Cai X, Li K, Yin et al.. A comparative study on the degradation properties of Mg wire/poly(lactic acid) composite rods: influence of rod diameter.Journal of Materials Engineering and Performance, 2022, 31(11): 9019–9028 https://doi.org/10.1007/s11665-022-06962-7
10
M, Karman E, Verde-Sesto C Weder . Mechanochemical activation of polymer-embedded photoluminescent benzoxazole moieties.ACS Macro Letters, 2018, 7(8): 1028–1033 https://doi.org/10.1021/acsmacrolett.8b00520
11
M E, McFadden M J Robb . Force-dependent multicolor mechanochromism from a single mechanophore.Journal of the American Chemical Society, 2019, 141(29): 11388–11392 https://doi.org/10.1021/jacs.9b05280
12
H, Chen F Y, Yang Q, Chen et al.. A novel design of multi-mechanoresponsive and mechanically strong hydrogels.Advanced Materials, 2017, 29(21): 1606900 https://doi.org/10.1002/adma.201606900
13
Y, Jia S, Wang W J, Wang et al.. Design and synthesis of a well-controlled mechanoluminescent polymer system based on fluorescence resonance energy transfer with spiropyran as a force-activated acceptor and nitrobenzoxadiazole as a fluorescent donor.Macromolecules, 2019, 52(20): 7920–7928 https://doi.org/10.1021/acs.macromol.9b01556
14
Y J, Lin M H, Barbee C C, Chang et al.. Regiochemical effects on mechanophore activation in bulk materials.Journal of the American Chemical Society, 2018, 140(46): 15969–15975 https://doi.org/10.1021/jacs.8b10376
15
A R, Sulkanen J, Sung M J, Robb et al.. Spatially selective and density-controlled activation of interfacial mechanophores.Journal of the American Chemical Society, 2019, 141(9): 4080–4085 https://doi.org/10.1021/jacs.8b10257
16
T S, Wang N, Zhang J W, Dai et al.. Novel reversible mechanochromic elastomer with high sensitivity: bond scission and bending-induced multicolor switching.ACS Applied Materials & Interfaces, 2017, 9(13): 11874–11881 https://doi.org/10.1021/acsami.7b00176
17
T S, Wang H X, Wang L, Shen et al.. Force-induced strengthening of a mechanochromic polymer based on a naphthalene-fused cyclobutane mechanophore.Chemical Communications, 2021, 57(94): 12675–12678 https://doi.org/10.1039/D1CC05305A
18
P Cawley . Structural health monitoring: closing the gap between research and industrial deployment.Structural Health Monitoring, 2018, 17(5): 1225–1244 https://doi.org/10.1177/1475921717750047
19
M, Raisch D, Genovese N, Zaccheroni et al.. Highly sensitive, anisotropic, and reversible stress/strain sensors from mechanochromic nanofiber composites.Advanced Materials, 2018, 30(39): 1802813 https://doi.org/10.1002/adma.201802813
20
M, Karman E, Verde-Sesto C, Weder et al.. Mechanochemical fluorescence switching in polymers containing dithiomaleimide moieties.ACS Macro Letters, 2018, 7(9): 1099–1104 https://doi.org/10.1021/acsmacrolett.8b00591
21
N, Willis-Fox E, Rognin T A, Aljohani et al.. Polymer mechanochemistry: manufacturing is now a force to be reckoned with.Chem, 2018, 4(11): 2499–2537 https://doi.org/10.1016/j.chempr.2018.08.001
22
Y, Vidavsky S J, Yang B A, Abel et al.. Enabling room-temperature mechanochromic activation in a glassy polymer: synthesis and characterization of spiropyran polycarbonate.Journal of the American Chemical Society, 2019, 141(25): 10060–10067 https://doi.org/10.1021/jacs.9b04229
23
C P, Kabb C S, Obryan C D, Morley et al.. Anthracene-based mechanophores for compression-activated fluorescence in polymeric networks.Chemical Science, 2019, 10(33): 7702–7708 https://doi.org/10.1039/C9SC02487E
T A, Kim C, Lamuta H, Kim et al.. Interfacial force-focusing effect in mechanophore-linked nanocomposites.Advancement of Science, 2020, 7: 1903464
26
K, Seshimo H, Sakai T, Watabe et al.. Segmented polyurethane elastomers with mechanochromic and self-strengthening functions.Angewandte Chemie, 2021, 133(15): 8487–8490 https://doi.org/10.1002/ange.202015196
27
Y F, Pan H, Zhang P X, Xu et al.. A mechanochemical reaction cascade for controlling load-strengthening of a mechanochromic polymer.Angewandte Chemie International Edition, 2020, 59(49): 21980–21985 https://doi.org/10.1002/anie.202010043
28
R C, Rohde A, Basu L B, Okello et al.. Mechanochromic composite elastomers for additive manufacturing and low strain mechanophore activation.Polymer Chemistry, 2019, 10(44): 5985–5991 https://doi.org/10.1039/C9PY01053J
29
M J, Wu Z, Guo W Y, He et al.. Empowering self-reporting polymer blends with orthogonal optical properties responsive in a broader force range.Chemical Science, 2021, 12(4): 1245–1250 https://doi.org/10.1039/D0SC06140A
30
Y J, Chen C J, Yeh Q, Guo et al.. Fast reversible isomerization of merocyanine as a tool to quantify stress history in elastomers.Chemical Science, 2021, 12(5): 1693–1701 https://doi.org/10.1039/D0SC06157C
31
J H, Yang M, Horst S H, Werby et al.. Bicyclohexene-peri-naphthalenes: scalable synthesis, diverse functionalization, efficient polymerization, and facile mechanoactivation of their polymers.Journal of the American Chemical Society, 2020, 142(34): 14619–14626 https://doi.org/10.1021/jacs.0c06454
32
K, Imato R, Yamanaka H, Nakajima et al.. Fluorescent supramolecular mechanophores based on charge-transfer interactions.Chemical Communications, 2020, 56(57): 7937–7940 https://doi.org/10.1039/D0CC03126G
33
Y X, Zhang B P, Ren F Y, Yang et al.. Micellar-incorporated hydrogels with highly tough, mechanoresponsive, and self-recovery properties for strain-induced color sensors.Journal of Materials Chemistry C: Materials for Optical and Electronic Devices, 2018, 6(43): 11536–11551 https://doi.org/10.1039/C8TC03914C
34
B A, Versaw M E, Mcfadden C C, Husic et al.. Designing naphthopyran mechanophores with tunable mechanochromic behavior.Chemical Science, 2020, 11(17): 4525–4530 https://doi.org/10.1039/D0SC01359E
35
T A, Kim M J, Robb J S, Moore et al.. Mechanical reactivity of two different spiropyran mechanophores in polydimethylsiloxane.Macromolecules, 2018, 51(22): 9177–9183 https://doi.org/10.1021/acs.macromol.8b01919
36
W L, Qiu P A, Gurr G G Qiao . Regulating color activation energy of mechanophore-linked multinetwork elastomers.Macromolecules, 2020, 53(10): 4090–4098 https://doi.org/10.1021/acs.macromol.0c00477
37
J P, Lee H, Hwang S, Chae et al.. A reversibly mechanochromic conjugated polymer.Chemical Communications, 2019, 55(63): 9395–9398 https://doi.org/10.1039/C9CC03951A
38
C, Calvino A, Guha C, Weder et al.. Self-calibrating mechanochromic fluorescent polymers based on encapsulated excimer-forming dyes.Advanced Materials, 2018, 30(19): 1704603 https://doi.org/10.1002/adma.201704603
39
C, Calvino Y, Sagara V, Buclin et al.. Mechanoresponsive, luminescent polymer blends based on an excimer-forming telechelic macromolecule.Macromolecular Rapid Communications, 2019, 40(1): 1800705 https://doi.org/10.1002/marc.201800705
40
A, Pucci Cuia F, Di F, Signori et al.. Bis(benzoxazolyl)stilbene excimers as temperature and deformation sensors for biodegradable poly(1,4-butylene succinate) films.Journal of Materials Chemistry, 2007, 17(8): 783–790 https://doi.org/10.1039/B612033D
41
B R, Crenshaw C Weder . Self-assessing photoluminescent polyurethanes.Macromolecules, 2006, 39(26): 9581–9589 https://doi.org/10.1021/ma061685b
42
Y, Sagara M, Karman E, Verde-Sesto et al.. Rotaxanes as mechanochromic fluorescent force transducers in polymers.Journal of the American Chemical Society, 2018, 140(5): 1584–1587 https://doi.org/10.1021/jacs.7b12405
43
Y, Sagara M, Karman A, Seki et al.. Rotaxane-based mechanophores enable polymers with mechanically switchable white photoluminescence.ACS Central Science, 2019, 5(5): 874–881 https://doi.org/10.1021/acscentsci.9b00173
44
T, Muramatsu Y, Sagara H, Traeger et al.. Mechanoresponsive behavior of a polymer-embedded red-light emitting rotaxane mechanophore.ACS Applied Materials & Interfaces, 2019, 11(27): 24571–24576 https://doi.org/10.1021/acsami.9b06302
45
Y, Sagara H, Traeger J, Li et al.. Mechanically responsive luminescent polymers based on supramolecular cyclophane mechanophores.Journal of the American Chemical Society, 2021, 143(14): 5519–5525 https://doi.org/10.1021/jacs.1c01328
46
J, Chen A W, Ziegler B M, Zhao et al.. Chemomechanical-force-induced folding–unfolding directly controls distinct fluorescence dual-color switching.Chemical Communications, 2017, 53(36): 4993–4996 https://doi.org/10.1039/C7CC01643C
47
H, Traeger Y, Sagara D J, Kiebala et al.. Folded perylene diimide loops as mechanoresponsive motifs.Angewandte Chemie International Edition, 2021, 60(29): 16191–16199 https://doi.org/10.1002/anie.202105219
