Mechanophores can be used to produce strain-dependent covalent chemical responses in polymeric materials, including stress strengthening, stress sensing and network remodelling. In general, it is desirable for mechanophores to be inert in the absence of force but highly reactive under applied tension. Metallocenes possess potentially useful combinations of force-free stability and force-coupled reactivity, but the mechanistic basis of this reactivity remains largely unexplored. Here, we have used single-molecule force spectroscopy to show that the mechanical reactivities of a series of ferrocenophanes are not correlated with ring strain in the reactants, but with the extent of rotational alignment of their two cyclopentadienyl ligands. Distal attachments can be used to restrict the mechanism of ferrocene dissociation to proceed through ligand ‘peeling’, as opposed to the more conventional ’shearing’ mechanism of the parent ferrocene, leading the dissociation rate constant to increase by several orders of magnitude at forces of ~1 nN. It also leads to improved macroscopic, multi-responsive behaviour, including mechanochromism and force-induced cross-linking in ferrocenophane-containing polymers.
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Akbulatov, S. & Boulatov, R. Experimental polymer mechanochemistry and its interpretational frameworks. ChemPhysChem 18, 1422–1450 (2017).
Willis-Fox, N., Rognin, E., Aljohani, T. A. & Daly, R. Polymer mechanochemistry: manufacturing is now a force to be reckoned with. Chem 4, 2499–2537 (2018).
Izak-Nau, E., Campagna, D., Baumann, C. & Göstl, R. Polymer mechanochemistry-enabled pericyclic reactions. Polym. Chem. 11, 2274–2299 (2020).
Jung, S. & Yoon, H. J. Mechanical force induces ylide‐free cycloaddition of nonscissible aziridines. Angew. Chem. Int. Ed. 59, 4883–4887 (2020).
Hickenboth, C. R. et al. Biasing reaction pathways with mechanical force. Nature 446, 423–427 (2007).
Sagara, Y. et al. Rotaxanes as mechanochromic fluorescent force transducers in polymers. J. Am. Chem. Soc. 140, 1584–1587 (2018).
Kim, T. A., Robb, M. J., Moore, J. S., White, S. R. & Sottos, N. R. Mechanical reactivity of two different spiropyran mechanophores in polydimethylsiloxane. Macromolecules 51, 9177–9183 (2018).
Lin, Y., Barbee, M. H., Chang, C.-C. & Craig, S. L. Regiochemical effects on mechanophore activation in bulk materials. J. Am. Chem. Soc. 140, 15969–15975 (2018).
Yildiz, D. et al. Anti‐Stokes stress sensing: mechanochemical activation of triplet–triplet annihilation photon upconversion. Angew. Chem. Int. Ed. 58, 12919–12923 (2019).
Kosuge, T. et al. Multicolor mechanochromism of a polymer/silica composite with dual distinct mechanophores. J. Am. Chem. Soc. 141, 1898–1902 (2019).
Wang, J., Piskun, I. & Craig, S. L. Mechanochemical strengthening of a multi-mechanophore benzocyclobutene polymer. ACS Macro Lett. 4, 834–837 (2015).
Matsuda, T., Kawakami, R., Namba, R., Nakajima, T. & Gong, J. P. Mechanoresponsive self-growing hydrogels inspired by muscle training. Science 363, 504–508 (2019).
Huang, W. et al. Maleimide–thiol adducts stabilized through stretching. Nat. Chem. 11, 310–319 (2019).
Chen, Z. et al. Mechanochemical unzipping of insulating polyladderene to semiconducting polyacetylene. Science 357, 475–479 (2017).
Sha, Y. et al. Quantitative and mechanistic mechanochemistry in ferrocene dissociation. ACS Macro Lett. 7, 1174–1179 (2018).
Di Giannantonio, M. et al. Triggered metal ion release and oxidation: ferrocene as a mechanophore in polymers. Angew. Chem. Int. Ed. 57, 11445–11450 (2018).
Sha, Y. et al. Generalizing metallocene mechanochemistry to ruthenocene mechanophores. Chem. Sci. 10, 4959–4965 (2019).
Wang, J. et al. Inducing and quantifying forbidden reactivity with single-molecule polymer mechanochemistry. Nat. Chem. 7, 323–327 (2015).
Grandbois, M., Beyer, M., Rief, M., Clausen-Schaumann, H. & Gaub, H. E. How strong is a covalent bond? Science 283, 1727–1730 (1999).
Kouznetsova, T. B., Wang, J. & Craig, S. L. Combined constant-force and constant-velocity single-molecule force spectroscopy of the conrotatory ring opening reaction of benzocyclobutene. ChemPhysChem 18, 1486–1489 (2017).
Pill, M. F. et al. Mechanochemical cycloreversion of cyclobutane observed at the single molecule level. Chem. Eur. J. 22, 12034–12039 (2016).
Schlierf, M., Li, H. & Fernandez, J. M. The unfolding kinetics of ubiquitin captured with single-molecule force-clamp techniques. Proc. Natl Acad. Sci. USA 101, 7299–7304 (2004).
Gossweiler, G. R., Kouznetsova, T. B. & Craig, S. L. Force-rate characterization of two spiropyran-based molecular force probes. J. Am. Chem. Soc. 137, 6148–6151 (2015).
Beyer, M. K. The mechanical strength of a covalent bond calculated by density functional theory. J. Chem. Phys. 112, 7307–7312 (2000).
Lin, Y., Kouznetsova, T. B., Chang, C.-C. & Craig, S. L. Enhanced polymer mechanical degradation through mechanochemically unveiled lactonization. Nat. Commun. 11, 4987 (2020).
Lenhardt, J. M. et al. Mechanistic insights into the sonochemical activation of multimechanophore cyclopropanated polybutadiene polymers. Macromolecules 48, 6396–6403 (2015).
Albrecht, C. et al. DNA: a programmable force sensor. Science 301, 367–370 (2003).
Brockwell, D. J. et al. Pulling geometry defines the mechanical resistance of a β-sheet protein. Nat. Struct. Mol. Biol. 10, 731–737 (2003).
Bailey, A. & Mosey, N. J. Prediction of reaction barriers and force-induced instabilities under mechanochemical conditions with an approximate model: a case study of the ring opening of 1,3-cyclohexadiene. J. Chem. Phys. 136, 01B613 (2012).
Kryger, M. J., Munaretto, A. M. & Moore, J. S. Structure–mechanochemical activity relationships for cyclobutane mechanophores. J. Am. Chem. Soc. 133, 18992–18998 (2011).
Konda, S. S. M. et al. Molecular catch bonds and the anti-Hammond effect in polymer mechanochemistry. J. Am. Chem. Soc. 135, 12722–12729 (2013).
Jacobs, M. J., Schneider, G. & Blank, K. G. Mechanical reversibility of strain‐promoted azide–alkyne cycloaddition reactions. Angew. Chem. Int. Ed. 55, 2899–2902 (2016).
Anslyn, E. V. & Dougherty, D. A. Modern Physical Organic Chemistry (Univ. Science Books, 2006).
Bell, G. I. Models for the specific adhesion of cells to cells. Science 200, 618–627 (1978).
Kauzmann, W. & Eyring, H. The viscous flow of large molecules. J. Am. Chem. Soc. 62, 3113–3125 (1940).
Dudko, O. K., Hummer, G. & Szabo, A. Intrinsic rates and activation free energies from single-molecule pulling experiments. Phys. Rev. Lett. 96, 108101 (2006).
Hummer, G. & Szabo, A. Kinetics from nonequilibrium single-molecule pulling experiments. Biophys. J. 85, 5–15 (2003).
Hummer, G. & Szabo, A. Free energy profiles from single-molecule pulling experiments. Proc. Natl Acad. Sci. USA 107, 21441–21446 (2010).
Gossweiler, G. R. et al. Mechanochemical activation of covalent bonds in polymers with full and repeatable macroscopic shape recovery. ACS Macro Lett. 3, 216–219 (2014).
Robb, M. J. et al. Regioisomer-specific mechanochromism of naphthopyran in polymeric materials. J. Am. Chem. Soc. 138, 12328–12331 (2016).
Fortune, W. & Mellon, M. Determination of iron with o-phenanthroline: a spectrophotometric study. Ind. Eng. Chem. Anal. Ed. 10, 60–64 (1938).
Ramirez, A. L. B. et al. Mechanochemical strengthening of a synthetic polymer in response to typically destructive shear forces. Nat. Chem. 5, 757–761 (2013).
Zhang, H. et al. Mechanochromism and mechanical‐force‐triggered cross‐linking from a single reactive moiety incorporated into polymer chains. Angew. Chem. 128, 3092–3096 (2016).
Davis, D. A. et al. Force-induced activation of covalent bonds in mechanoresponsive polymeric materials. Nature 459, 68–72 (2009).
Wang, Z. et al. A novel mechanochromic and photochromic polymer film: when rhodamine joins polyurethane. Adv. Mater. 27, 6469–6474 (2015).
Chen, Y. et al. Mechanically induced chemiluminescence from polymers incorporating a 1,2-dioxetane unit in the main chain. Nat. Chem. 4, 559–562 (2012).
Clough, J. M., Balan, A., van Daal, T. L. & Sijbesma, R. P. Probing force with mechanobase‐induced chemiluminescence. Angew. Chem. Int. Ed. 55, 1445–1449 (2016).
Hillman, M., Matyevich, L., Fujita, E., Jagwani, U. & McGowan, J. Bridged ferrocenes. 9. Lithiation and subsequent reactions of 1,1’-trimethyleneferrocene. Organometallics 1, 1226–1229 (1982).
Wu, D., Lenhardt, J. M., Black, A. L., Akhremitchev, B. B. & Craig, S. L. Molecular stress relief through a force-induced irreversible extension in polymer contour length. J. Am. Chem. Soc. 132, 15936–15938 (2010).
Klukovich, H. M., Kouznetsova, T. B., Kean, Z. S., Lenhardt, J. M. & Craig, S. L. A backbone lever-arm effect enhances polymer mechanochemistry. Nat. Chem. 5, 110–114 (2013).
Serpe, M. J. et al. A simple and practical spreadsheet-based method to extract single-molecule dissociation kinetics from variable loading-rate force spectroscopy data. J. Phys. Chem. C 112, 19163–19167 (2008).
The polymer synthesis, SMFS studies and mechanistic analysis formed a part of work supported by the National Science Foundation under grant no. CHE-1904016 to C.T. and S.L.C. The bulk mechanochromism and cross-linking studies formed a part of work supported by the US Army Research Laboratory and the Army Research Office under grant W911NF-15-0143 to S.L.C. In addition, C.T. acknowledges partial support from the National Science Foundation EPSCoR Program under grant no. OIA-1655740. The authors thank P. Zhang for help with the DFT calculations.
The authors declare no competing interests.
Peer review information Nature Chemistry thanks the anonymous reviewers for their contribution to the peer review of this work.
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Zhang, Y., Wang, Z., Kouznetsova, T.B. et al. Distal conformational locks on ferrocene mechanophores guide reaction pathways for increased mechanochemical reactivity. Nat. Chem. 13, 56–62 (2021). https://doi.org/10.1038/s41557-020-00600-2
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