Understanding the Mechanochemistry of Ladder-Type Cyclobutane Mechanophores by Single Molecule Force Spectroscopy
Understanding the Mechanochemistry of Ladder-Type Cyclobutane Mechanophores by Single Molecule Force Spectroscopy
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DOI：
10.1021/jacs.1c05857
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发表时间：
2021-07-26
影响因子：
15
通讯作者：
Xia, Yan
中科院分区：
文献类型：
--
作者：
Horst, Matias;Yang, Jinghui;Xia, Yan
我们最近报道了一系列阶梯型环丁烷机械载体，其聚合物可以从非共轭结构转变为共轭结构并一次改变许多性质。这些多环机械载体，即外环烷/烯、内苯并二烯和外环环己烯-环萘，与第一环丁烷融合的环结构不同，开环时的自由能变化显著不同，立体化学性质也不同。为了更好地了解它们的机械化学性质，我们使用单分子力谱（SMFS）来表征它们的力扩展行为并测量阈值力。阈值力与第一键的活化能相关，但与聚合物主链远端的熔合环的应变无关，这表明这些阶梯型机械载体的激活发生在类似的早期过渡态，这得到了力修正势能表面计算的支持。我们进一步确定了机械生成的二烯的立体化学性质，并通过实验和计算观察到这些机械团的显著和可变的轮廓长度伸长。对梯子型机械团的基本理解将有助于未来设计具有放大力响应的多环机械团及其作为机械响应材料的应用。
We have recently reported a series of ladder-type cyclobutane mechanophores, polymers of which can transform from nonconjugated structures to conjugated structures and change many properties at once. These multicyclic mechanophores, namely, exo-ladderane/ene, endo-benzoladderene, and exo-bicyclohexene-perinaphthalene, have different ring structures fused to the first cyclobutane, significantly different free energy changes for ring-opening, and different stereochemistry. To better understand their mechanochemistry, we used single molecule force spectroscopy (SMFS) to characterize their force-extension behavior and measure the threshold forces. The threshold forces correlate with the activation energy of the first bond, but not with the strain of the fused rings distal to the polymer main chain, suggesting that the activation of these ladder-type mechanophores occurs with similar early transition states, which is supported by force-modified potential energy surface calculations. We further determined the stereochemistry of the mechanically generated dienes and observed significant and variable contour length elongation for these mechanophores both experimentally and computationally. The fundamental understanding of ladder-type mechanophores will facilitate future design of multicyclic mechanophores with amplified force-response and their applications as mechanically responsive materials.