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Flear EJ, Horst M, Yang J, Xia Y. Force Transduction Through Distant Force-Bearing Regioisomeric Linkages Affects the Mechanochemical Reactivity of Cyclobutane. Angew Chem Int Ed Engl 2024:e202406103. [PMID: 38818671 DOI: 10.1002/anie.202406103] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2024] [Revised: 05/24/2024] [Accepted: 05/29/2024] [Indexed: 06/01/2024]
Abstract
Fundamental understanding of mechanochemical reactivity is important for designing new mechanophores. Besides the core structure of mechanophores, substituents on a mechanophore can affect its mechanochemical reactivity through electronic stabilization of the intermediate or effectiveness of force transduction from the polymer backbone to the mechanophore. The latter factor represents a unique mechanical effect in considering polymer mechanochemistry. Here, we show that regioisomeric linkage that is not directly adjacent to the first cleaving bond in cyclobutane can still significantly affect the mechanochemical reactivity of the mechanophore. We synthesized three non-scissile 1,2-diphenyl cyclobutanes, varying their linkage to the polymer backbone via the o, m, or p-position of the diphenyl substituents. Even though the regioisomers share the same substituted cyclobutane core structure and similar electronic stabilization of the diradical intermediate from cleaving the first C-C bond, the p isomer exhibited significantly higher mechanochemical reactivity than the o and m isomers. The observed difference in reactivity can be rationalized as the much more effective force transduction to the scissile bond through the p-position than the other two substitution positions. These findings point to the importance of considering force-bearing linkages that are more distant from the bond to be cleaved when incorporating mechanophores into polymer backbones.
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Affiliation(s)
- Erica J Flear
- Department of Chemistry, Stanford University Stanford, California, 94305, United States
| | - Matías Horst
- Department of Chemistry, Stanford University Stanford, California, 94305, United States
| | - Jinghui Yang
- Department of Chemistry, Stanford University Stanford, California, 94305, United States
| | - Yan Xia
- Department of Chemistry, Stanford University Stanford, California, 94305, United States
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2
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Tabirja DS, Kostjukov VV. Intramolecular excimers of open forms of 2 H-benzopyran, 2 H- and 3 H-naphthopyrans in solution: TD-DFT/DFT analysis. Phys Chem Chem Phys 2024; 26:4412-4421. [PMID: 38240023 DOI: 10.1039/d3cp05755k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2024]
Abstract
We hypothesized that in the open forms of diphenyl-substituted photochromic compounds, immediately after the photoinduced cleavage of the C-O bond, one of the phenyl rings forms a stack with an aromatic system at the other end of the alkyl linker. The formation of these intramolecular stacking excimers is made possible by a known increase in the rotational mobility of the linker double bonds in the excited state. The flexibilities of linkers are analyzed in terms of changes in their dihedral angles. After internal conversion, stacking is partially broken but it still prevents the recovery of the C-O bond. This explains the significantly greater stability of the open forms of diphenyl-substituted benzopyran and naphthopyran compared to dimethyl-substituted ones. Open structures with residual stacking are intermediate and by thermal motion, they transform into stable trans-trans and cis-trans forms. However, in our opinion, they significantly affect the equilibrium of closed and open isomers in solution. In particular, the calculated stacking energy of 2H-naphthopyran turned out to be higher than that of 3H-naphthopyran, which partly explains the significantly greater stability of the open form of the former. For the DFT/TD-DFT calculations performed in this work, the following functionals were selected to provide reliable stacking for the open forms of all three studied compounds: APFD, M052X, M06HF, as well as B3LYP with D3(BJ) Grimme dispersion correction. The 6-311++G(d,p) basis set and cyclohexane solvent modeled using IEFPCM were also used.
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Affiliation(s)
- Daiana S Tabirja
- Sevastopol State University, Universitetskaya str., 33, Sevastopol 299053, Crimea, Ukraine.
| | - Victor V Kostjukov
- Sevastopol State University, Universitetskaya str., 33, Sevastopol 299053, Crimea, Ukraine.
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3
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He X, Tian Y, O’Neill RT, Xu Y, Lin Y, Weng W, Boulatov R. Coumarin Dimer Is an Effective Photomechanochemical AND Gate for Small-Molecule Release. J Am Chem Soc 2023; 145:23214-23226. [PMID: 37821455 PMCID: PMC10603814 DOI: 10.1021/jacs.3c07883] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2023] [Indexed: 10/13/2023]
Abstract
Stimulus-responsive gating of chemical reactions is of considerable practical and conceptual interest. For example, photocleavable protective groups and gating mechanophores allow the kinetics of purely thermally activated reactions to be controlled optically or by mechanical load by inducing the release of small-molecule reactants. Such release only in response to a sequential application of both stimuli (photomechanochemical gating) has not been demonstrated despite its unique expected benefits. Here, we describe computational and experimental evidence that coumarin dimers are highly promising moieties for realizing photomechanochemical control of small-molecule release. Such dimers are transparent and photochemically inert at wavelengths >300 nm but can be made to dissociate rapidly under tensile force. The resulting coumarins are mechanochemically and thermally stable, but rapidly release their payload upon irradiation. Our DFT calculations reveal that both strain-free and mechanochemical kinetics of dimer dissociation are highly tunable over an unusually broad range of rates by simple substitution. In head-to-head dimers, the phenyl groups act as molecular levers to allow systematic and predictable variation in the force sensitivity of the dissociation barriers by choice of the pulling axis. As a proof-of-concept, we synthesized and characterized the reactivity of one such dimer for photomechanochemically controlled release of aniline and its application for controlling bulk gelation.
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Affiliation(s)
- Xiaojun He
- Department
of Chemistry, College of Chemistry and Engineering, Xiamen University, Xiamen, Fujian 361005, China
| | - Yancong Tian
- Department
of Chemistry, University of Liverpool, Crown Street, Liverpool L69 7ZD, U.K.
| | - Robert T. O’Neill
- Department
of Chemistry, University of Liverpool, Crown Street, Liverpool L69 7ZD, U.K.
| | - Yuanze Xu
- Department
of Chemistry, College of Chemistry and Engineering, Xiamen University, Xiamen, Fujian 361005, China
| | - Yangju Lin
- Department
of Chemistry, College of Chemistry and Engineering, Xiamen University, Xiamen, Fujian 361005, China
| | - Wengui Weng
- Department
of Chemistry, College of Chemistry and Engineering, Xiamen University, Xiamen, Fujian 361005, China
| | - Roman Boulatov
- Department
of Chemistry, University of Liverpool, Crown Street, Liverpool L69 7ZD, U.K.
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4
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Sun Y, McFadden ME, Osler SK, Barber RW, Robb MJ. Anomalous photochromism and mechanochromism of a linear naphthopyran enabled by a polarizing dialkylamine substituent. Chem Sci 2023; 14:10494-10499. [PMID: 37800007 PMCID: PMC10548511 DOI: 10.1039/d3sc03790h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2023] [Accepted: 09/01/2023] [Indexed: 10/07/2023] Open
Abstract
In contrast to common angular naphthopyrans that exhibit strong photochromic and mechanochromic behavior, constitutionally isomeric linear naphthopyrans are typically not photochromic, due to the putative instability of the completely dearomatized merocyanine product. The photochemistry of linear naphthopyrans is thus relatively understudied compared to angular naphthopyrans, while the mechanochromism of linear naphthopyrans remains completely unexplored. Here we demonstrate that the incorporation of a polarizing dialkylamine substituent enables photochromic and mechanochromic behavior from polymers containing a novel linear naphthopyran motif. In solution phase experiments, a Lewis acid trap was necessary to observe accumulation of the merocyanine product upon photochemical and ultrasound-induced mechanochemical activation. However, the same linear naphthopyran molecule incorporated as a crosslinker in polydimethylsiloxane elastomers renders the materials photochromic and mechanochromic without the addition of any trapping agent. This study provides insights into the photochromic and mechanochromic reactivity of linear naphthopyrans that have conventionally been considered functionally inert, adding a new class of naphthopyran molecular switches to the repertoire of stimuli-responsive polymers.
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Affiliation(s)
- Yan Sun
- Division of Chemistry and Chemical Engineering, California Institute of Technology Pasadena California 91125 USA
| | - Molly E McFadden
- Division of Chemistry and Chemical Engineering, California Institute of Technology Pasadena California 91125 USA
| | - Skylar K Osler
- Division of Chemistry and Chemical Engineering, California Institute of Technology Pasadena California 91125 USA
| | - Ross W Barber
- Division of Chemistry and Chemical Engineering, California Institute of Technology Pasadena California 91125 USA
| | - Maxwell J Robb
- Division of Chemistry and Chemical Engineering, California Institute of Technology Pasadena California 91125 USA
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McFadden ME, Barber RW, Overholts AC, Robb MJ. Naphthopyran molecular switches and their emergent mechanochemical reactivity. Chem Sci 2023; 14:10041-10067. [PMID: 37772118 PMCID: PMC10530568 DOI: 10.1039/d3sc03729k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2023] [Accepted: 08/23/2023] [Indexed: 09/30/2023] Open
Abstract
Naphthopyran molecular switches undergo a ring-opening reaction upon external stimulation to generate intensely colored merocyanine dyes. Their unique modularity and synthetic accessibility afford exceptional control over their properties and stimuli-responsive behavior. Commercial applications of naphthopyrans as photoswitches in photochromic ophthalmic lenses have spurred an extensive body of work exploring naphthopyran-merocyanine structure-property relationships. The recently discovered mechanochromic behavior of naphthopyrans has led to their emergent application in the field of polymer mechanochemistry, enabling advances in the design of force-responsive materials as well as fundamental insights into mechanochemical reactivity. The structure-property relationships established in the photochemical literature serve as a convenient blueprint for the design of naphthopyran molecular force probes with precisely tuned properties. On the other hand, the mechanochemical reactivity of naphthopyran diverges in many cases from the conventional photochemical pathways, resulting in unexpected properties and opportunities for deeper understanding and innovation in polymer mechanochemistry. Here, we highlight the features of the naphthopyran scaffold that render it a powerful platform for the design of mechanochromic materials and review recent advances in naphthopyran mechanochemistry.
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Affiliation(s)
- Molly E McFadden
- Division of Chemistry and Chemical Engineering, California Institute of Technology Pasadena California 91125 USA
| | - Ross W Barber
- Division of Chemistry and Chemical Engineering, California Institute of Technology Pasadena California 91125 USA
| | - Anna C Overholts
- Division of Chemistry and Chemical Engineering, California Institute of Technology Pasadena California 91125 USA
| | - Maxwell J Robb
- Division of Chemistry and Chemical Engineering, California Institute of Technology Pasadena California 91125 USA
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6
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Ditzler RAJ, King AJ, Towell SE, Ratushnyy M, Zhukhovitskiy AV. Editing of polymer backbones. Nat Rev Chem 2023; 7:600-615. [PMID: 37542179 DOI: 10.1038/s41570-023-00514-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/12/2023] [Indexed: 08/06/2023]
Abstract
Polymers are at the epicentre of modern technological progress and the associated environmental pollution. Considerations of both polymer functionality and lifecycle are crucial in these contexts, and the polymer backbone - the core of a polymer - is at the root of these considerations. Just as the meaning of a sentence can be altered by editing its words, the function and sustainability of a polymer can also be transformed via the chemical modification of its backbone. Yet, polymer modification has primarily been focused on the polymer periphery. In this Review, we focus on the transformations of the polymer backbone by defining some concepts fundamental to this topic (for example, 'polymer backbone' and 'backbone editing') and by collecting and categorizing examples of backbone editing scattered throughout a century's worth of chemical literature, and outline critical directions for further research. In so doing, we lay the foundation for the field of polymer backbone editing and hope to accelerate its development.
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Affiliation(s)
- Rachael A J Ditzler
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Andrew J King
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Sydney E Towell
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Maxim Ratushnyy
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
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7
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He W, Yuan Y, Wu M, Li X, Shen Y, Qu Z, Chen Y. Multicolor Chromism from a Single Chromophore through Synergistic Coupling of Mechanochromic and Photochromic Subunits. Angew Chem Int Ed Engl 2023; 62:e202218785. [PMID: 36642693 DOI: 10.1002/anie.202218785] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2022] [Revised: 01/13/2023] [Accepted: 01/13/2023] [Indexed: 01/17/2023]
Abstract
We report a versatile mechanophore exhibiting a vividly detectable, light-regulable multicolor mechanochromism. Such optical features rely on the synergistic coupling of mechanochromic bis-rhodamine (Rh) and photochromic bisthienylethene (BTE). Poly(methyl acrylate)s incorporating this bis-mechanophore can be mechanically activated under sonication. The relative distribution of the two distinctly colored and fluorescent Rh ring-opening products is altered with different magnitudes of applied force. Orthogonal use of the photochromic reaction of the BTE core can strengthen the mechanochromism and gate the mechanofluorescence in polymers. Due to increased conjugation offered by the BTE linker, both force- and light-induced optical signals display high contrast. Combined DFT simulated and experimental results reveal that the three subunits (two Rhs and one BTE) in this chromophore are activated sequentially, thus generating switchable three-colored forms and gradient optical responses.
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Affiliation(s)
- Weiye He
- Department of Chemistry, Tianjin Key Laboratory of Molecular Optoelectronic Science, Tianjin University, Tianjin, 300354, P. R. China
| | - Yuan Yuan
- Department of Chemistry, Tianjin Key Laboratory of Molecular Optoelectronic Science, Tianjin University, Tianjin, 300354, P. R. China
| | - Mengjiao Wu
- State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Changchun, 130012, P. R. China
| | - Xinxin Li
- Department of Chemistry, Tianjin Key Laboratory of Molecular Optoelectronic Science, Tianjin University, Tianjin, 300354, P. R. China
| | - Yanbing Shen
- Department of Chemistry, Tianjin Key Laboratory of Molecular Optoelectronic Science, Tianjin University, Tianjin, 300354, P. R. China
| | - Zhiyu Qu
- College of Chemistry and Molecular Engineering, Peking University, Beijing, 100871, P. R. China
| | - Yulan Chen
- Department of Chemistry, Tianjin Key Laboratory of Molecular Optoelectronic Science, Tianjin University, Tianjin, 300354, P. R. China.,State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Changchun, 130012, P. R. China
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8
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Willis-Fox N, Watchorn-Rokutan E, Rognin E, Daly R. Technology pull: scale-up of polymeric mechanochemical force sensors. TRENDS IN CHEMISTRY 2023. [DOI: 10.1016/j.trechm.2023.02.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/08/2023]
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9
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McFadden ME, Osler SK, Sun Y, Robb MJ. Mechanical Force Enables an Anomalous Dual Ring-Opening Reaction of Naphthodipyran. J Am Chem Soc 2022; 144:22391-22396. [PMID: 36459076 DOI: 10.1021/jacs.2c08817] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
Abstract
Multimodal mechanophores that exhibit complex mechanochromic behavior beyond the typical binary response are capable of distinguishing between multiple stress states through discrete changes in color. Naphthodipyran photoswitches contain two pyran rings fused to a central naphthalene core and represent a potentially promising framework for multimodal reactivity. However, the concurrent ring opening of both pyran moieties has previously proven inaccessible via photochemical activation. Here, we demonstrate that mechanical force supplied to naphthodipyran through covalently linked polymer chains generates the elusive dual ring-opened dimerocyanine product with unique near-infrared absorption properties. Trapping with boron trifluoride renders the merocyanine dyes thermally persistent and reveals apparent sequential ring-opening behavior that departs from the reactivity of previously studied mechanophores under the high strain rates imposed by ultrasound-induced solvodynamic chain extension.
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Affiliation(s)
- Molly E McFadden
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
| | - Skylar K Osler
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
| | - Yan Sun
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
| | - Maxwell J Robb
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
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Luo SM, Barber RW, Overholts AC, Robb MJ. Competitive Activation Experiments Reveal Significantly Different Mechanochemical Reactivity of Furan–Maleimide and Anthracene–Maleimide Mechanophores. ACS POLYMERS AU 2022; 3:202-208. [PMID: 37065719 PMCID: PMC10103189 DOI: 10.1021/acspolymersau.2c00047] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/29/2022] [Revised: 11/01/2022] [Accepted: 11/01/2022] [Indexed: 11/23/2022]
Abstract
During the past two decades, our understanding of mechanochemical reactivity has advanced considerably. Nevertheless, an incomplete knowledge of structure-activity relationships and the principles that govern mechanochemical transformations limits molecular design. The experimental development of mechanophores has thus benefited from simple computational tools like CoGEF, from which quantitative metrics like rupture force can be extracted to estimate reactivity. Furan-maleimide (FM) and anthracene-maleimide (AM) Diels-Alder adducts are widely studied mechanophores that undergo retro-Diels-Alder reactions upon mechanical activation in polymers. Despite possessing significantly different thermal stability, similar rupture forces predicted by CoGEF calculations suggest that these compounds exhibit similar mechanochemical reactivity. Here, we directly probe the relative mechanochemical reactivity of FM and AM adducts through competitive activation experiments. Ultrasound-induced mechanochemical activation of bis-adduct mechanophores comprising covalently tethered FM and AM subunits reveals pronounced selectivity-as high as ∼13:1-for reaction of the FM adduct compared to the AM adduct. Computational models provide insight into the greater reactivity of the FM mechanophore, indicating a more efficient mechanochemical coupling for the FM adduct compared to the AM adduct. The methodology employed here to directly interrogate the relative reactivity of two different mechanophores using a tethered bis-adduct configuration may be useful for other systems where more common sonication-based approaches are limited by poor sensitivity.
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Affiliation(s)
- Stella M. Luo
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
| | - Ross W. Barber
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
| | - Anna C. Overholts
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
| | - Maxwell J. Robb
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
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11
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Gao W, Xiang S, Bai M, Ruan Y, Zheng J, Cao X, Xu Y, Chen Y, Weng W. Carbon dot crosslinking towards mechanochemically and photochemically induced fluorescence resonance energy transfer. POLYMER 2022. [DOI: 10.1016/j.polymer.2022.125278] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/14/2022]
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