In this review, the chirality and stereoselectivity in photochromic reactions are broadly discussed.

Stereoselectivity is categorized into the two main areas of enantioselectivity and diastereoselectivity.

Enantioselective photochromism was discussed according to the methods of generating chirality, that is: (1) optical resolution of chiral and racemic compounds, (2) spontaneous separation of racemic compounds during crystallization, (3) chiral template-assisted photochromic reactions to preferentially generate an enantiomer or cause chirality-based events, and (4) the generation of a non-racemic mixture of the photoisomers by irradiation of circularly polarized light to the racemic starting photoisomer.

Diastereoselective photochromism was discussed for each family of photochromic reactions, namely, (1) fulgides, (2) diarylethenes, (3) spiro-compounds, (4) azobenzenes, and (5) organometallic complexes.

Chirality-related reactions in overcrowded alkenes are discussed in a separate chapter. These include: (1) the discovery of the light-driven molecular motor, (2) the first generation of light-driven molecular motors with unidirectional rotation, which have two chiral carbon atoms in a molecule, (3) the second generation of light-driven molecular motors with unidirectional rotation, which have a single chiral carbon atom in a molecule.

Finally, two distinctive novel photochromic systems are introduced in which the reactions proceed stereoselectively, although their enantio- or diastereoselectivity during photochromic reactions have yet to be examined.

在这篇综述中，对光致变色反应中的手性和立体选择性进行了广泛的讨论。

立体选择性分为对映选择性和非对映选择性两个主要领域。

根据产生手性的方法讨论了对映选择性光致变色，即：（1）手性和外消旋化合物的光学拆分，（2）结晶过程中外消旋化合物的自发分离，（3）手性模板辅助的光致变色反应优先产生对映异构体或引起基于手性的事件，以及（4）通过将圆偏振光照射到外消旋的起始光异构体上，生成光异构体的非外消旋混合物。

讨论了对每个光致变色反应家族的非对映选择性光致变色，即，（1）萤光粉，（2）二芳烃，（3）螺化合物，（4）偶氮苯和（5）有机金属配合物。

在单独的章节中讨论了在过度拥挤的烯烃中与手性有关的反应。其中包括：（1）光驱动分子马达的发现；（2）第一代具有单向旋转的光驱动分子马达，它们在一个分子中具有两个手性碳原子；（3）第二代光单向旋转的分子驱动的分子电动机。

最后，引入了两个独特的新型光致变色系统，其中的反应是立体选择性进行的，尽管在光致变色反应过程中它们的对映体或非对映体选择性尚待研究。