Introducing ferrocene between polymer segments can endow the polymer with intriguing mechanoresponsive properties. The principle primarily relies on the dissociation process of ferrocene under external force, which involves two mechanisms:

One is the shear process, where the cyclopentadienyl rings above and below the $\mathrm{Fe^{2+}}$ ion displace in opposite directions parallel to the ring plane;

The other is the peeling process, which increases the dihedral angle between the two cyclopentadienyl rings.  

There are two ways to incorporate ferrocene into polymer segments, referred to as $\mathbf{A}$ and $\mathbf{B}$, as shown below.  

<MultiModal>![This is a schematic structural diagram without a title. The image displays two sets of molecular structures, labeled with uppercase letters "$\mathbf{A}$" and "$\mathbf{B}$" below the left and right structures, respectively. Structure A consists of an iron atom marked as $\mathrm{Fe}$ at the center, flanked by two identical five-membered rings above and below. These rings are horizontally arranged and anti-parallel (non-superimposable), each containing an inscribed solid circle near the center. The left vertex of the upper ring extends a straight line ending in a wavy line perpendicular to it, while the right vertex of the lower ring similarly extends a straight line ending in a perpendicular wavy line. Structure B also features a central $\mathrm{Fe}$ atom with two five-membered rings, but the left vertices of the rings are connected by two distinctly bent lines, with $\mathrm{_n(H_2C)}$ labeled at the midpoint (where "$\mathrm{_n}$" precedes the parentheses containing "$\mathrm{H_2C}$"). The right vertices of both rings extend straight lines ending in perpendicular wavy lines. The image contains no other text, axes, units, scales, curves, legends, color indicators, or arrows. No title or numerical data is present, and all chemical elements or structural symbols are as described above.](/media/uploads/c82ceffc-99e4-447d-b23b-096541227fde.png)</MultiModal>  

Select the correct option from the following choices.
在聚合物链段间引入二茂铁，可以使聚合物体现出有趣的力相应性质。其原理主要依赖于外力作用下二茂铁的解离过程，该解离过程存在两种机制：

其中一种为剪切过程, 即$\mathrm{Fe^{2+}}$上下的茂环向平行于茂环平面相反的方向位移; 

另一种为剥离过程, 即增大两个茂环平面的二面角。

存在两种引入二茂铁聚合物片段结构，分别称为$\mathbf{A}$和$\mathbf{B}$,如下图所示。

<MultiModal>![该图像为一个结构示意图，图像中无标题。图像中展示了两组分该图像为一个结构示意图，图像中无标题。图像中展示了两组分子结构，左边的结构和右边的结构下方分别用大写字母“$\mathbf{A}$”和“$\mathbf{B}$”进行标识。A结构由一个中央标记为$\mathrm{Fe}$的铁原子和上下两个相同结构的五元环组成，这两个五元环在$\mathrm{Fe}$原子的两侧，均呈水平放置且互相反平行（不能重合），五元环中心有一个几乎内切的实线圆，在上方五元环的左侧顶点有一根直线延伸出去，末端为垂直于直线的波浪线，下方五元环的右侧顶点有一根直线延伸出去，末端为垂直于直线的波浪线。$\mathbf{B}$结构同样包含中央$\mathrm{Fe}$原子和上下两个五元环，但五元环左侧顶点之间通过两条有明显转折的直线连接，中间连线处标有$\mathrm{_n(H_2C)}$，其中“$\mathrm{_n}$”在括号前，括号内为“$\mathrm{H_2C}$”。两个五元环的右侧顶点各有一根直线延伸出去，末端为垂直于直线的波浪线。无其他文字、坐标轴、单位、范围、曲线、图例、颜色说明或箭头，图片中没有标题，也没有数值信息，所有化学元素或结构符号如上所述全部展现。](/media/uploads/c82ceffc-99e4-447d-b23b-096541227fde.png)</MultiModal>

在下列选项中选择正确的选项。
The structure $\mathbf{A}$ primarily dissociates via a peeling mechanism, but can also undergo shear dissociation simultaneously.
The dissociation mechanism of structure $\mathbf{B}$ is independent of the value of $\mathrm{n}$.
In the above-mentioned polymer chain segments, doping with phenanthroline produces a mechanochromic polymer. When external force is applied, the polymer appears light yellow, and when the force is removed, it turns red.
If $\mathbf{A}$ and $\mathbf{B}$ are both fabricated into the mechanochromic polymers described in option C, the force response of $\mathbf{A}$ exhibits a deeper red color, indicating that the dissociation energy of the ferrocene structure in $\mathbf{A}$ is greater.
Generally, polymers formed from bifunctional monomers cannot undergo crosslinking. However, the polymer formed by structure $\mathbf{B}$ can form a covalent crosslinked network in a protonic solution under external force. The formation of the crosslinked network is primarily due to the D-A reaction between ferrocene units.
To prevent cross-linking, molecules $\mathbf{X}$ or $\mathbf{Y}$ can be added to the solution. The structure of $\mathbf{X}$ is O=C(N1C)C=CC1=O, and the structure of $\mathbf{Y}$ is O=C1C=CCN1C. Then, the effect of $\mathbf{X}$ in preventing cross-linking is weaker than that of $\mathbf{Y}$.
None of the above options is correct
结构$\mathbf{A}$主要采用剥离机制解离，但同时也可以发生剪切解离。
结构$\mathbf{B}$的解离机制与$\mathrm{n}$的值无关。
在上述聚合物链段中，掺杂邻二氮菲，制得一种机械力诱导变色高分子，施加外力时聚合物为浅黄色，撤去外力时，聚合物变为红色。
若$\mathbf{A}$和$\mathbf{B}$分别制成选项C中所述的机械力诱导变色高分子，$\mathbf{A}$的力响应显示的红色更深，说明$\mathbf{A}$的二茂铁结构解离能更大。
通常双官能度的单体形成的聚合物不能发生交联，但结构$\mathbf{B}$形成的聚合物在质子溶液中，在外力作用下可以形成共价交联网络。交联网络的形成主要是由于二茂铁之间的D-A反应。
若想要阻止交联，可以在溶液中加入$\mathbf{X}$或$\mathbf{Y}$两种分子，$\mathbf{X}$的结构为O=C(N1C)C=CC1=O，$\mathbf{Y}$的结构为O=C1C=CCN1C。则$\mathbf{X}$阻止交联的效果弱于$\mathbf{Y}$。
以上选项均不正确
Since the polymer chains of $\mathbf{A}$ are located on opposite sides of the two ferrocenes, it is easier to apply forces in opposite directions along the plane of the ferrocenes, making the shear mechanism dissociation more likely to occur. Therefore, option A is incorrect.  

<Checkpoint>[The polymer chains of $\mathbf{A}$ are located on opposite sides of the two ferrocenes, making the shear mechanism dissociation more likely to occur.](1)</Checkpoint>  

Similarly, due to the presence of the alkyl chain bridging the two ferrocenes in $\mathbf{A}$, when the alkyl chain is of a specific length, parallel relative displacement between the ferrocenes is less likely to occur. Instead, changes in dihedral angles can take place, and the primary dissociation mechanism is the peeling mechanism. However, when the alkyl chain is long and highly flexible, the probability of the shear mechanism increases significantly. In summary, the value of $\mathrm{n}$ is strongly related to the dissociation mechanism, so option B is incorrect.  

<Checkpoint>[The value of $\mathrm{n}$ is strongly related to the dissociation mechanism.](1)</Checkpoint>  

The color of ferrocene is orange-yellow or pale yellow, while the color of the iron(II)-phenanthroline complex is orange-red or red. Therefore, when an external force is applied, ferrocene dissociates, and the free iron(II) ions bind with phenanthroline, causing the color to change from pale yellow to red. Thus, option C is incorrect.  

<Checkpoint>[When an external force is applied, ferrocene dissociates, and the free iron(II) ions bind with phenanthroline, causing the color to change from pale yellow to red.](1)</Checkpoint>  

The color reflects the content of the iron(II)-phenanthroline complex. A higher content of the iron(II)-phenanthroline complex results in a deeper red color, indicating easier dissociation and a smaller dissociation energy. Therefore, the dissociation energy of $\mathbf{A}$ should be smaller than that of $\mathbf{B}$. Option D is incorrect.  

<Checkpoint>[The color reflects the content of the iron(II)-phenanthroline complex. A higher content results in a deeper red color, indicating easier dissociation and a smaller dissociation energy.](1)</Checkpoint>  

Ferrocene dissociates under external force. In protic solvents, the uncoordinated cyclopentadienyl ligands combine with protons to form cyclopentadiene, which further undergoes a Diels-Alder (D-A) reaction. Other possible mechanisms include $\pi$-$\pi$ interactions and ligand exchange. The former is ruled out due to the weak $\pi$-$\pi$ interactions of the cyclopentadienyl groups, while the latter is unlikely because coordination bonds should break under external force. Therefore, option E is correct.  

<Checkpoint>[In protic solvents, the uncoordinated cyclopentadienyl ligands combine with protons to form cyclopentadiene, which further undergoes a Diels-Alder (D-A) reaction.](1)</Checkpoint>  

The principle of preventing cross-linking is to introduce a better electrophilic acceptor for the D-A reaction, competitively reacting with cyclopentadiene to act as a "capping" agent. The double bond of $\mathbf{X}$ is flanked by two carbonyl groups, giving it a lower LUMO and making it a better electrophilic acceptor for the D-A reaction. Compared to $\mathbf{Y}$, which has only one carbonyl group, $\mathbf{X}$ is more effective in preventing cross-linking. Therefore, option F is incorrect.  

<Checkpoint>[The principle of preventing cross-linking is to introduce a better electrophilic acceptor for the D-A reaction, competitively reacting with cyclopentadiene.](1)</Checkpoint>  

<Checkpoint>[The double bond of $\mathbf{X}$ is flanked by two carbonyl groups, giving it a lower LUMO.](1)</Checkpoint>  

In conclusion, the correct option for this question is E.
由于$\mathbf{A}$的聚合物链分别位于两个二茂铁的两侧，所以更容易施加沿二茂铁平面、方向相反的力，更容易发生剪切机制解离，选项A错误。

<Checkpoint>[$\mathbf{A}$的聚合物链分别位于两个二茂铁的两侧，更容易发生剪切机制解离。](1)</Checkpoint>

类似地，由于$\mathbf{A}$桥接两二茂铁的烷基链的存在。当烷基链处于特定长度时，二茂铁间不容易发生平行的相对位移，而可以发生二面角的改变，此时主要解离机制为剥离机制。但当烷基链很长具有较强柔性时，剪切机制发生的概率将明显增加。综上，$\mathrm{n}$的值与解离机制有很强的联系，故选项B错误。

<Checkpoint>[$\mathrm{n}$的值与解离机制有很强的联系](1)</Checkpoint>

二茂铁的颜色为橙黄色或淡黄色；邻二氮菲亚铁配合物的颜色为橙红色或红色。所以施加外力时，二茂铁发生解离，游离的亚铁离子与邻二氮菲结合，颜色由浅黄色转变为红色。故C选项错误。

<Checkpoint>[施加外力时，二茂铁发生解离，游离的亚铁离子与邻二氮菲结合，颜色由浅黄色转变为红色。](1)</Checkpoint>

颜色反映了邻二氮菲亚铁配合物的含量，邻二氮菲亚铁配合物的含量越高，红色就越深，说明更容易解离，解离能更小。所以$\mathbf{A}$的解离能应该小于$\mathbf{B}$的解离能。D选项错误。

<Checkpoint>[颜色反映了邻二氮菲亚铁配合物的含量，邻二氮菲亚铁配合物的含量越高，红色就越深，说明更容易解离，解离能更小。](1)</Checkpoint>

二茂铁在外力作用下发生解离。质子溶剂中，未配位的茂基配体与质子结合形成环戊二烯，进一步发生D-A反应。其他可能的机理有$\pi$-$\pi$相互作用、配体交换作用等，前者由于茂基的$\pi$-$\pi$相互作用较弱而被排除，后者由于在外力下配位键应当被破坏也并不可能。故选项E正确。

<Checkpoint>[质子溶剂中，未配位的茂基配体与质子结合形成环戊二烯，进一步发生D-A反应。](1)</Checkpoint>

阻止交联的原理是加入一个更好的D-A反应亲电受体，竞争性地与环戊二烯发生D-A反应，起到类似于“封端”的作用。$\mathbf{X}$的双键两侧具有两个羰基，具有更低的LUMO，是更好的D-A反应亲电受体，相对于$\mathbf{Y}$只有单侧具有羰基，阻止交联的效果更强。故选项F错误。

<Checkpoint>[阻止交联的原理是加入一个更好的D-A反应亲电受体，竞争性地与环戊二烯发生D-A反应。](1)</Checkpoint>

<Checkpoint>[$\mathbf{X}$的双键两侧具有两个羰基，具有更低的LUMO](1)</Checkpoint>

综上所述，本题的正确选项为E。