<MultiModal>![The image contains 8 organic structural formulas, numbered **1-8** respectively. **1** is C12=CC=CC=C1C=CCO2; **2** is C1(/N=N/C2=CC=CC=C2)=CC=CC=C1; **3** is CC1(C)C2(OC(C=CC([N+]([O-])=O)=C3)=C3N=C2)N(C)C4=CC=CC=C41; **4** is CC1(C)C2(OC(C=CC3=C4C=CC=C3)=C4N=C2)N(C)C5=CC=CC=C51; **5** is FC1(F)C(F)(F)C(F)(F)C(C2=C(C)SC3=C2C=CC=C3)=C1C4=C(C)SC5=C4C=CC=C5; **6** is O=C(C(/C1=C(C)/C)=C/C2=C(C)OC=C2)OC1=O; **7** is OC1=CC=CC=C1/C=N/C2=CC=CC=C2; **8** is OC(/C=C(C(OC(C)(C)O1)=O)\C1=O)=C\C=C\N(CC)CC.](/media/uploads/0506600d-1b65-4921-91b8-f3bc0e0d1f5d.png)</MultiModal>

The above image displays 8 photochromic compounds, which are characterized by changes in molecular structure upon exposure to light, leading to alterations in their absorption spectra.

These compounds exhibit three classifications of photochromic mechanisms, and each compound belongs to only one photochromic mechanism type. It is known that type **A** is the most common mechanism among these compounds after classification. Classify the photochromic mechanisms of these compounds and identify which of the following options is correct.
<MultiModal>![该图片包含8种有机结构式，分别编号**1-8**。**1**为C12=CC=CC=C1C=CCO2；**2**为C1(/N=N/C2=CC=CC=C2)=CC=CC=C1，**3**为CC1(C)C2(OC(C=CC([N+]([O-])=O)=C3)=C3N=C2)N(C)C4=CC=CC=C41；**4**为CC1(C)C2(OC(C=CC3=C4C=CC=C3)=C4N=C2)N(C)C5=CC=CC=C51；**5**为FC1(F)C(F)(F)C(F)(F)C(C2=C(C)SC3=C2C=CC=C3)=C1C4=C(C)SC5=C4C=CC=C5；**6**为O=C(C(/C1=C(C)/C)=C/C2=C(C)OC=C2)OC1=O；**7**为OC1=CC=CC=C1/C=N/C2=CC=CC=C2；**8**为OC(/C=C(C(OC(C)(C)O1)=O)\C1=O)=C\C=C\N(CC)CC。](/media/uploads/0506600d-1b65-4921-91b8-f3bc0e0d1f5d.png)</MultiModal>

上图展示了8种可以发生光致变色的化合物在未见光时的结构，这种化合物的特点是见光后分子结构会发生变化，从而导致吸收光谱的变化。

这些化合物的光致变色机理共有3种分类，且每一种化合物只有一种光致变色机理类型，已知类型**A**为这些化合物按照光致变色机理分类之后所含的化合物最多的一种类型。

请归类这些化合物的光致变色机理，并指出下列选项中哪一项是正确的。
The molecular structure of compound **1** exhibits aromaticity upon exposure to light.
The photoisomerization mechanism type of compound **2** belongs to category **A**.
Compound **3** exhibits a molecular structure without formal charges upon exposure to light.
The molecular structure of compound **6** exhibits aromaticity upon exposure to light.
The class of photochromic mechanism to which compound **7** belongs contains a total of two compounds.
The molecular structure of compound **8** after exposure to light only contains a six-membered ring.
Type **A** consists of 5 compounds in total.
None of the above options is correct.
化合物**1**见光后的分子结构具有芳香性。
化合物**2**的光致异构机理类型属于**A**类型。
化合物**3**见光后的分子结构不带形式电荷。
化合物**6**见光后的分子结构具有芳香性。
化合物**7**的光致发光机理类型包含**7**在内的两种化合物。
化合物**8**见光后的分子结构只具有六元环。
类型**A**共有5种化合物。
以上选项均不正确。
Photochemical reaction mechanisms can generally be divided into cis-trans isomerization type, ring-opening/closing type, and tautomerization type.

<Checkpoint>[光致变色机理一般可分为顺反异构类型，开关环类型和互变异构类型。](1)</Checkpoint>

Analyzing each compound individually:

1.  Upon exposure to light, the substrate undergoes a [3,3]σ sigmatropic rearrangement to generate a conjugated structure that exhibits color, O=C1C=CC=C/C1=C/C=C, with the pyran ring opening. The photochromic mechanism is of the ring-opening/closing type. In this structure, the benzene ring is disrupted and lacks aromaticity; therefore, option A is incorrect.

<Checkpoint>[**1**的见光结构为O=C1C=CC=C/C1=C/C=C，为开关环类型](1)</Checkpoint>

<Checkpoint>[**1**的见光结构苯环被破坏不具有芳香性](1)</Checkpoint>

2.  The substrate is trans-azobenzene. Upon irradiation, it undergoes cis-trans isomerization to yield cis-azobenzene, which exhibits color, C1(/N=N\C2=CC=CC=C2)=CC=CC=C1. The photochromic mechanism is of the cis-trans isomerization type.

<Checkpoint>[反式偶氮苯光照下发生顺反异构得到顺式偶氮苯C1(/N=N\C2=CC=CC=C2)=CC=CC=C1显色](1)</Checkpoint>

<Checkpoint>[反式偶氮苯光致发光机理类型为顺反异构类型](1)</Checkpoint>

3/4. These two are the same type of photochromic molecule. Upon exposure to light, these compounds can generate an imine cation, causing the spiro ring to open, resulting in a large conjugated system that exhibits color. Subsequently, the generated hydroxide anion can also perform nucleophilic attack on the imine cation, restoring the original form. Therefore, the light-induced structures of **3** and **4** are CC1(C)C(/C=C/C2=CC([N+]([O-])=O)=CC=C2[O-])=[N+](C)C3=CC=CC=C31, CC1(C)C(/C=C/C2=C(C=CC=C3)C3=CC=C2[O-])=[N+](C)C4=CC=CC=C41, respectively. The photochromic mechanisms of these two compounds are both of the ring-opening/closing type. According to the structure, option C is incorrect.

<Checkpoint>[**3，4**见光可生成亚胺正离子使得螺环开环](1)</Checkpoint>

<Checkpoint>[**3，4**见光结构分别为CC1(C)C(/C=C/C2=CC([N+]([O-])=O)=CC=C2[O-])=[N+](C)C3=CC=CC=C31,CC1(C)C(/C=C/C2=C(C=CC=C3)C3=CC=C2[O-])=[N+](C)C4=CC=CC=C41](1)</Checkpoint>

<Checkpoint>[**3，4**为开关环类型](1)</Checkpoint>

5/6. These two substrates are also the same type of photochromic molecule. Their substrates both have a six-membered ring electrocyclization structure. Upon exposure to light, they undergo an electrocyclization reaction to form a ring, forming a conjugated system that emits light. The light-induced structures are FC1(F)C(F)(F)C(F)(F)C2=C3C(C(C4=C21)(C)SC5=C4C=CC=C5)(C)SC6=C3C=CC=C6, O=C(C1=C2C(C3(C)C(C=CO3)=C1)(C)C)OC2=O, respectively; both are also of the ring-opening/closing type.

<Checkpoint>[**5，6**底物均具有六元环电环化结构，光照下发生电环化反应](1)</Checkpoint>

<Checkpoint>[**5，6**见光结构分别为FC1(F)C(F)(F)C(F)(F)C2=C3C(C(C4=C21)(C)SC5=C4C=CC=C5)(C)SC6=C3C=CC=C6，O=C(C1=C2C(C3(C)C(C=CO3)=C1)(C)C)OC2=O](1)</Checkpoint>

<Checkpoint>[**5，6**为开关环类型](1)</Checkpoint>

In the light-induced structure of **6**, the furan ring is disrupted and lacks aromaticity; therefore, option D is incorrect.

7. This is a well-known Schiff base type compound. Its phenolic hydroxyl group can tautomerize to a keto carbonyl group, thereby changing the conjugated structure and causing a change in the absorption wavelength. The light-induced structure is O=C1C=CC=C/C1=C/NC2=CC=CC=C2, and the photochromic type is tautomerization.

<Checkpoint>[**7**酚羟基可互变异构为酮羰基从而改变共轭结构](1)</Checkpoint>

<Checkpoint>[**7**发光结构为O=C1C=CC=C/C1=C/NC2=CC=CC=C2，为互变异构型](1)</Checkpoint>

8. This is a DASA-type compound. The nitrogen atom of the tertiary amine is nucleophilic and can intramolecularly attack the keto carbonyl group of the enol tautomer, forming a five-membered ring and disrupting the conjugated structure, thereby changing the color. Therefore, the structure of the photochromic is CC(O1)(C)OC([O-])=C(C2C(C=CC2[N+](CC)([H])CC)=O)C1=O, which is also of the ring-opening/closing type. From the structure, option F is incorrect.

<Checkpoint>[**8**中三级胺的氮原子可以分子内进攻烯醇互变异构的酮羰基形成五元环破坏共轭结构](1)</Checkpoint>

<Checkpoint>[**8**光致变色的结构CC(O1)(C)OC([O-])=C(C2C(C=CC2[N+](CC)([H])CC)=O)C1=O，为开关环类型](1)</Checkpoint>

In summary, the ring-opening/closing type compounds are the most numerous, with 6. Therefore, type **A** is the ring-opening/closing type, and option G is incorrect.

<Checkpoint>[类型**A**即为开关环类型，有6个化合物](1)</Checkpoint>

The photochromic mechanism type of compound **7** is tautomerization, and only **7** itself belongs to this type, so option E is incorrect. (If azobenzene is also classified into this category, the requirement of 3 types of mechanisms in the question will not be met.)

The mechanism type of compound **2** is cis-trans isomerization, which does not belong to type **A**, the ring-opening/closing type, so option B is incorrect.

In summary, options A-G are all incorrect, and option H is correct.

<MultiModal>![本图展示了从**1-8**化合物的见光后的结构，SMILES分别为O=C1C=CC=C/C1=C/C=C，C1(/N=N\C2=CC=CC=C2)=CC=CC=C1，CC1(C)C(/C=C/C2=CC([N+]([O-])=O)=CC=C2[O-])=[N+](C)C3=CC=CC=C31,CC1(C)C(/C=C/C2=C(C=CC=C3)C3=CC=C2[O-])=[N+](C)C4=CC=CC=C41，FC1(F)C(F)(F)C(F)(F)C2=C3C(C(C4=C21)(C)SC5=C4C=CC=C5)(C)SC6=C3C=CC=C6，O=C(C1=C2C(C3(C)C(C=CO3)=C1)(C)C)OC2=O，O=C1C=CC=C/C1=C/NC2=CC=CC=C2，CC(O1)(C)OC([O-])=C(C2C(C=CC2[N+](CC)([H])CC)=O)C1=O。](/media/uploads/05b66a76-1ddf-407c-9969-33badbb986ea.png)</MultiModal>
光致变色机理一般可分为顺反异构类型，开关环类型和互变异构类型。

<Checkpoint>[光致变色机理一般可分为顺反异构类型，开关环类型和互变异构类型。](1)</Checkpoint>

逐个对化合物进行分析：

1.底物见光可发生[3,3]σ迁移重排生成共轭结构显色O=C1C=CC=C/C1=C/C=C，吡喃环开环，光致发光机理为开关环类型。该结构中苯环被破坏不具有芳香性，选项A错误。

<Checkpoint>[**1**的见光结构为O=C1C=CC=C/C1=C/C=C，为开关环类型](1)</Checkpoint>

<Checkpoint>[**1**的见光结构苯环被破坏不具有芳香性](1)</Checkpoint>

2.底物为反式偶氮苯，光照下发生顺反异构得到顺式偶氮苯显色，C1(/N=N\C2=CC=CC=C2)=CC=CC=C1，光致发光机理为顺反异构类型。

<Checkpoint>[反式偶氮苯光照下发生顺反异构得到顺式偶氮苯C1(/N=N\C2=CC=CC=C2)=CC=CC=C1显色](1)</Checkpoint>

<Checkpoint>[反式偶氮苯光致发光机理类型为顺反异构类型](1)</Checkpoint>

3/4. 这两种为同类型的光致变色分子，该类化合物见光可生成亚胺正离子使得螺环开环产生大共轭体系显色，之后产生的羟基负离子还可对亚胺正离子进行亲核从而恢复原本的形式；因此**3**，**4**的发光结构分别为CC1(C)C(/C=C/C2=CC([N+]([O-])=O)=CC=C2[O-])=[N+](C)C3=CC=CC=C31,CC1(C)C(/C=C/C2=C(C=CC=C3)C3=CC=C2[O-])=[N+](C)C4=CC=CC=C41。这两种化合物光致发光机理均为开关环类型。根据结构可知选项C错误。

<Checkpoint>[**3，4**见光可生成亚胺正离子使得螺环开环](1)</Checkpoint>

<Checkpoint>[**3，4**见光结构分别为CC1(C)C(/C=C/C2=CC([N+]([O-])=O)=CC=C2[O-])=[N+](C)C3=CC=CC=C31,CC1(C)C(/C=C/C2=C(C=CC=C3)C3=CC=C2[O-])=[N+](C)C4=CC=CC=C41](1)</Checkpoint>

<Checkpoint>[**3，4**为开关环类型](1)</Checkpoint>

5/6. 这两种底物也是同类型的光致变色分子，其底物均具有六元环电环化结构，光照下发生电环化反应成环形成共轭体系发光，发光结构分别为FC1(F)C(F)(F)C(F)(F)C2=C3C(C(C4=C21)(C)SC5=C4C=CC=C5)(C)SC6=C3C=CC=C6，O=C(C1=C2C(C3(C)C(C=CO3)=C1)(C)C)OC2=O；同样均为开关环类型。

<Checkpoint>[**5，6**底物均具有六元环电环化结构，光照下发生电环化反应](1)</Checkpoint>

<Checkpoint>[**5，6**见光结构分别为FC1(F)C(F)(F)C(F)(F)C2=C3C(C(C4=C21)(C)SC5=C4C=CC=C5)(C)SC6=C3C=CC=C6，O=C(C1=C2C(C3(C)C(C=CO3)=C1)(C)C)OC2=O](1)</Checkpoint>

<Checkpoint>[**5，6**为开关环类型](1)</Checkpoint>

**6**的见光结构中呋喃环被破坏，不具有芳香性，选项D错误。

7.这是著名的Schiff碱类型化合物，其酚羟基可互变异构为酮羰基从而改变共轭结构，发生吸收波长的变化；发光结构为O=C1C=CC=C/C1=C/NC2=CC=CC=C2，光致变色类型为互变异构类型。

<Checkpoint>[**7**酚羟基可互变异构为酮羰基从而改变共轭结构](1)</Checkpoint>

<Checkpoint>[**7**发光结构为O=C1C=CC=C/C1=C/NC2=CC=CC=C2，为互变异构型](1)</Checkpoint>

8.这是DASA类化合物，三级胺的氮原子具有亲核性，可以分子内进攻烯醇互变异构的酮羰基形成五元环破坏共轭结构从而改变颜色，故光致变色的结构为CC(O1)(C)OC([O-])=C(C2C(C=CC2[N+](CC)([H])CC)=O)C1=O，同样为开关环类型。从结构可知选项F错误。

<Checkpoint>[**8**中三级胺的氮原子可以分子内进攻烯醇互变异构的酮羰基形成五元环破坏共轭结构](1)</Checkpoint>

<Checkpoint>[**8**光致变色的结构CC(O1)(C)OC([O-])=C(C2C(C=CC2[N+](CC)([H])CC)=O)C1=O，为开关环类型](1)</Checkpoint>

综上，开关环类型的化合物最多，有6个；从而类型**A**即为开关环类型，选项G错误。

<Checkpoint>[类型**A**即为开关环类型，有6个化合物](1)</Checkpoint>

化合物**7**的光致发光机理类型为互变异构类型，只有**7**自身，选项E错误。（若将偶氮苯也归于此类，则达不到3类机理的题设要求）

化合物**2**的机理类型为顺反异构型，不属于**A**开关环类型，选项B错误。

综上，选项A-G均错误，选项H正确。

<MultiModal>![本图展示了从**1-8**化合物的见光后的结构，SMILES分别为O=C1C=CC=C/C1=C/C=C，C1(/N=N\C2=CC=CC=C2)=CC=CC=C1，CC1(C)C(/C=C/C2=CC([N+]([O-])=O)=CC=C2[O-])=[N+](C)C3=CC=CC=C31,CC1(C)C(/C=C/C2=C(C=CC=C3)C3=CC=C2[O-])=[N+](C)C4=CC=CC=C41，FC1(F)C(F)(F)C(F)(F)C2=C3C(C(C4=C21)(C)SC5=C4C=CC=C5)(C)SC6=C3C=CC=C6，O=C(C1=C2C(C3(C)C(C=CO3)=C1)(C)C)OC2=O，O=C1C=CC=C/C1=C/NC2=CC=CC=C2，CC(O1)(C)OC([O-])=C(C2C(C=CC2[N+](CC)([H])CC)=O)C1=O。](/media/uploads/05b66a76-1ddf-407c-9969-33badbb986ea.png)</MultiModal>