Polymer-Network Toughening and Highly Sensitive Mechanochromism via a Dynamic Covalent Mechanophore and a Multinetwork Strategy

Watabe, Takuma; Aoki, Daisuke; Otsuka, Hideyuki

doi:10.1021/acs.macromol.2c00724

Cited by 32 publications

(37 citation statements)

References 32 publications

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“…[35] The exceptionally high barrier of dissociation that DFSN exhibits encouraged us to develop DFSN-based polymer networks through radical polymerization, which is difficult using DABBF and TASN. [36][37][38][39][40] The dimerization of a fluorene with a phenyl group at the 9-position did not afford bis(phenyl fluorene) (BPF), albeit that it was possible to isolate the corresponding peroxide (BPF peroxide; Figure 1b). [41] This organic peroxide spurred us to develop novel mechanoresponsive materials that release fluorescent small molecules.…”

Section: Introductionmentioning

confidence: 99%

Theoretical and Experimental Investigations of Stable Arylfluorene‐Based Radical‐Type Mechanophores

Sugita

Aoki

et al. 2023

Chemistry A European J

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Radical‐type mechanophores (RMs) can undergo homolytic cleavage of their central C−C bonds upon exposure to mechanical forces, which affords radical species. Understanding the characteristics of these radical species allows bespoke mechanoresponsive materials to be designed and developed. The thermal stability of the central C−C bonds and the oxygen tolerance of the generated radical species are crucial characteristics that determine the functions and applicability of such RM‐containing mechanoresponsive materials. In this paper, we report the synthesis and characterization of two series of arylfluorene‐based RM derivatives, that is, 9,9’‐bis(5‐methyl‐2‐pyridyl)‐9,9’‐bifluorene (BPyF) and 9,9’‐bis(4,6‐diphenyl‐2‐triazyl)‐9,9’‐bifluorene (BTAF). BPyF and BTAF derivatives were synthesized without generating any peroxides initially, albeit that BPyF slowly converted to the corresponding peroxide in solution. DFT calculations revealed the importance of the thermodynamic stability and the values of the α‐SOMO levels of the corresponding radical species for their thermal stability and oxygen tolerance. Furthermore, the mechanochromism of BTAF was demonstrated by ball‐milling a BTAF‐centered polymer, which was synthesized by atom‐transfer radical polymerization (ATRP).

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Section: Introductionmentioning

confidence: 99%

Theoretical and Experimental Investigations of Stable Arylfluorene‐Based Radical‐Type Mechanophores

Sugita

Aoki

et al. 2023

Chemistry A European J

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“…The majority of the reported mechanochromic systems rely on two-state systems that typically switch between two colors. Such binary mechanochromophore systems include retro-Diels-Alder reactions, − homolytic bond scissions ,− or ring-opening reactions of spiro-compounds, and other reactive-ring systems. − One major drawback of binary systems is that a monotonic correlation of the mechanochromic response with force is hardly possible. Along this line, supramolecular mechanochromic systems open up further possibilities in terms of broader variation of the signal output .…”

Section: Introductionmentioning

confidence: 99%

Conformer Ring Flip Enhances Mechanochromic Performance of ansa-Donor–Acceptor–Donor Mechanochromic Torsional Springs

et al. 2022

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Mechanochromophores based on conformational changes of donor−acceptor−donor (DAD) springs allow sensing of forces acting on polymer chains by monotonic changes of absorbance or photoluminescence (PL) wavelength. Here, we identify a series of thiophene (D)-flanked quinoxalines (A) as molecular torsional springs for force sensing in bulk polymers at room temperature. The mode of DAD linkage to the polymer matrix and linker rigidity are key parameters that influence the efficacy of force transduction to the DAD spring and thus mechanochromic response, as probed by in situ PL spectroscopy of bulk films during stress−strain experiments. The largest shift of the PL maximum, and thus the highest sensitivity, is obtained from an ansa-DAD spring exhibiting bridged D units and a stiff A linker. Using detailed spectroscopy and density functional theory calculations, we reveal conformer redistribution in the form of a thiophene ring flip as the major part of the overall mechanochromic response. At forces as low as 27 pN at early stages of deformation, the ring flip precedes mechanically induced planarization of the ansa-DAD spring, the latter process producing a PL shift of 21 nm nN −1 . Within the stress−strain diagram, the thiophene ring flip and DAD planarization are thus two separated processes that also cause irreversible and reversible mechanochromic responses, respectively, upon sample failure. As the thiophene ring flip requires much smaller forces than planarization of the DAD spring, such micromechanical motion gives access to sensing of tiny forces and expands both sensitivity and the force range of conformational mechanochromophores.

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“…For example, Watabe et al incorporated the difluorenylsuccinonitrile (DFSN) mechanophores into a multiple network elastomer to quantitatively reveal the toughening mechanism. [39] However, most of these mechanophores are hydrophobic and the mechanochromic polymeric materials are usually obtained as the elastomers, prepared with hydrophobic chemicals. It is still challenging to make mechanochromic hydrogels, which contain large amounts of water, despite their great potential in the fields of soft robots, [40] biomedical adhesives, [41] artificial cartilages, [42] stretchable electronics, [43] etc.…”

Section: Introductionmentioning

confidence: 99%

Hybrid Phenol‐Rhodamine Dye Based Mechanochromic Double Network Hydrogels with Tunable Stress Sensitivity

Luo

Wang

et al. 2022

Macromol. Rapid Commun.

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Mechanochromic hydrogels, which can switch their color in response to the applied external force, have shown great potential in stress visualization and damage indication. However, the kinds of colors in the reported mechanochromic hydrogels are limited. It is challenging to develop mechanochromic hydrogels with new kinds of color changes. Herein, a kind of mechanochromic double network (DN) hydrogel is reported based on the hybrid phenol-rhodamine mechanophore. The hydrogels turn into orange color with an emission wavelength of around 566/574 nm in response to tensile and compressive stress. The DN hydrogels show great reversibility. The color of DN hydrogels vanishes slowly after releasing the stress. The stress sensitivity can be tailored by the crosslinking density and the mechanophore concentration of the first network. In addition, the influence of the pH on the mechanochromic properties of DN hydrogels is also studied. This study provides an insightful study in tuning the stress sensitivity in the mechanochromic hydrogel, which will be beneficial for the development of mechanochromic materials.

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Polymer-Network Toughening and Highly Sensitive Mechanochromism via a Dynamic Covalent Mechanophore and a Multinetwork Strategy

Cited by 32 publications

References 32 publications

Theoretical and Experimental Investigations of Stable Arylfluorene‐Based Radical‐Type Mechanophores

Theoretical and Experimental Investigations of Stable Arylfluorene‐Based Radical‐Type Mechanophores

Conformer Ring Flip Enhances Mechanochromic Performance of ansa-Donor–Acceptor–Donor Mechanochromic Torsional Springs

Hybrid Phenol‐Rhodamine Dye Based Mechanochromic Double Network Hydrogels with Tunable Stress Sensitivity

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