Validation of an Accurate and Expedient Initial Rates Method for Characterizing Mechanophore Reactivity

McFadden, Molly E.; Overholts, Anna C.; Osler, Skylar K.; Robb, Maxwell J.

doi:10.1021/acsmacrolett.3c00054

Cited by 10 publications

(6 citation statements)

References 38 publications

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“…The product distributions for 5,6-BCH and 1,6-BCH were not varied by using polymers with different molecular masses. Both scission cycle and initial rate analysis revealed the same relative mechanochemical reactivity for the three isomers, 1,4-BCH > 1,6-BCH > 5,6-BCH, with rate constants determined by the initial rate method as 0.020, 0.018, and 0.008 min –1 , respectively, in polymers with a molecular mass around 40 kDa (Figure S71).…”

Section: Resultsmentioning

confidence: 99%

Bicyclo[2.2.0]hexene: A Multicyclic Mechanophore with Reactivity Diversified by External Forces

Ding,

Wang,

Germann

et al. 2024

J. Am. Chem. Soc.

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Polymer mechanochemistry has been established as an enabling tool in accessing chemical reactivity and reaction pathways that are distinctive from their thermal counterparts. However, eliciting diversified reaction pathways by activating different constituent chemical bonds from the same mechanophore structure remains challenging. Here, we report the design of a bicyclo[2.2.0]hexene (BCH) mechanophore to leverage its structural simplicity and relatively low molecular symmetry to demonstrate this idea of multimodal activation. Upon changing the attachment points of pendant polymer chains, three different C−C bonds in bicyclo[2.2.0]hexene are specifically activated via externally applied force by sonication. Experimental characterization confirms that in different scenarios of polymer attachment, the regioisomers of BCH undergo different activation reactions, entailing retro-[2+2] cycloreversion, 1,3-allylic migration, and retro-4π ring-opening reactions, respectively. Control experiments with small-molecule analogues reveal that the observed diversified reactivity of BCH regioisomers is possible only with mechanical force. Theoretical studies further elucidate that the differences in the positions of substitution between regioisomers have a minimal impact on the potential energy surface of the parent BCH scaffold. The mechanochemical selectivity between different C−C bonds in each constitutional isomer is a result of selective and effective coupling of force to the aligned C−C bond in each case.

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Section: Resultsmentioning

confidence: 99%

Bicyclo[2.2.0]hexene: A Multicyclic Mechanophore with Reactivity Diversified by External Forces

Ding,

Wang,

Germann

et al. 2024

J. Am. Chem. Soc.

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“…Recent work by Robb and coworkers have demonstrates the initial rates method is an useful technique for rapid characterization of rate constants of which avoids complications associated with non-specific chain scission events. [21] The polymer degradation rate constant of PMA-1 is 1.59×10 À 5 min À 1 and the degradation rate constant of PMA-2 is 1.40×10 À 5 min À 1 (for further details, refer to Figure S16-S25 and Table S2-S11 in the SI). For mechanophore-free PMA synthesized from ethyl 2-bromo-2-methylpropionate, the degradation rate is determined to be 9.78×10 À 6 min À 1 , which is much lower than PMA-1 and PMA-2.…”

Section: Resultsmentioning

confidence: 99%

Mechanochemical Reactivity of a 1,2,4‐Triazoline‐3,5‐dione‐Anthracene Diels‐Alder Adduct

Chang,

Liang,

Luc

et al. 2023

Chemistry An Asian Journal

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Force‐responsive molecules that produce fluorescent moieties under stress provide a means for stress‐sensing and material damage assessment. In this work, we report a mechanophore based on Diels‐Alder adduct TAD‐An of 4,4′‐(4,4′‐diphenylmethylene)‐bis‐(1,2,4‐triazoline‐3,5‐dione) and initiator‐substituted anthracene that can undergo retro‐Diels‐Alder (rDA) reaction by pulsed ultrasonication and compressive activation in bulk materials. The influence of having C−N versus C−C bonds at the sites of bond scission is elucidated by comparing the relative mechanical strength of TAD‐An to another Diels‐Alder adduct MAL‐An obtained from maleimide and anthracene. The susceptibility to undergo rDa reaction correlates well with bond energy, such that C−N bond containing TAD‐An degrades faster C−C bond containing MAL‐An because C−N bond is weaker than C−C bond. Specifically, the results from polymer degradation kinetics under pulsed ultrasonication shows that polymer containing TAD‐An has a rate constant of 1.59×10−5 min−1, while MAL‐An (C−C bond) has a rate constant of 1.40×10−5 min−1. Incorporation of TAD‐An in a crosslinked polymer network demonstrates the feasibility to utilize TAD‐An as an alternative force‐responsive probe to visualize mechanical damage where fluorescence can be “turned‐on” due to force‐accelerated retro‐Diels‐Alder reaction.

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“…Subsequently, mechanochemical activation of the TTA UC process was carried out by ultrasonication − of a solution of linear PMA chains containing the BTD mechanophore embedded within their center (BTD-PMA) in toluene for 6 h. Before sonication, BTD-PMA showed M n = 60 kDa and Đ M = 1.46 determined by gel permeation chromatography (GPC) in THF. By contrast, this changed to M n = 22 kDa and Đ M = 1.36 after sonication indicating mechanochemical bond scission of the PMA backbone (Figure a).…”

Section: Upconversion Experimentsmentioning

confidence: 99%

Mechanochemical Activation of Red-Light-Excited Triplet–Triplet Annihilation Photon Upconversion

Broschinski,

Majer,

et al. 2024

ACS Appl. Opt. Mater.

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Optical force probes (OFPs) are mechanochemically latent sensors that visualize stress and strain at the molecular level by changing their optical properties upon force-induced bond scission. Yet, the incorporation of mechanochemical responsivity into established fluorophore motifs is difficult, which is why redand near-infrared (NIR)-excited OFPs are rarely reported. Here, an approach to solve this issue is presented, relying on triplet− triplet annihilation photon upconversion (TTA UC). OFPs based on Diels−Alder adducts of anthracene and maleimide are used as latent annihilators, and a phthalocyanine derivative is used as the triplet sensitizer. By incorporation of the annihilator motif in the center of linear polymer chains and subsequent ultrasonication, the latent annihilator is mechanochemically activated. In combination with the sensitizer and red excitation, TTA UC leads to yellow emission only after mechanochemical bond scission but not in its pristine form. Thereby, mechanochemically activated TTA UC is demonstrated with excitation energies as low as that of NIR light.

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Validation of an Accurate and Expedient Initial Rates Method for Characterizing Mechanophore Reactivity

Cited by 10 publications

References 38 publications

Bicyclo[2.2.0]hexene: A Multicyclic Mechanophore with Reactivity Diversified by External Forces

Bicyclo[2.2.0]hexene: A Multicyclic Mechanophore with Reactivity Diversified by External Forces

Mechanochemical Reactivity of a 1,2,4‐Triazoline‐3,5‐dione‐Anthracene Diels‐Alder Adduct

Mechanochemical Activation of Red-Light-Excited Triplet–Triplet Annihilation Photon Upconversion

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