The single-crystal-to-single-crystal (SCSC) transformation is a fascinating and valuable outcome of topochemical reactions. Not like the solution-state reactions, the movement and transformation of the molecule in single-crystal state is such a mysterious and attractive research topic. The molecular packing of the monomers prior to the reaction could provide many possibilities for the formation of complicated topological structures. The further reaction or polymerization in the single crystal state could realize the preparation of covalent complicated topological structures. In this review, we summarized six different types of organic reactions that could realize the SCSC conversion, namely [2 + 2], [4 + 4], and [4 + 2] photo-cycloaddition, dienes polymerization, diacetylenes polymerization and topochemical azide-alkyne cycloaddition. The crystalline packing phases offer the possibility of significant advances in the crystal structure design. Some examples of 1D or 2D polymer single crystals realized by SCSC transformation were summarized subsequently.

中文翻译：

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从单晶到单晶的转变，用于制备小分子，一维和二维聚合物单晶

单晶到单晶（SCSC）的转换是拓扑化学反应的一个有趣而有价值的结果。与溶液状态反应不同，单晶状态下分子的移动和转化是一个如此神秘而诱人的研究课题。反应之前单体的分子堆积可以为形成复杂的拓扑结构提供许多可能性。单晶状态下的进一步反应或聚合可以实现共价复杂拓扑结构的制备。在这篇综述中，我们总结了可以实现SCSC转化的六种不同类型的有机反应，即[2 + 2]，[4 + 4]和[4 + 2]光环加成，二烯聚合，二乙炔聚合和拓扑化学叠氮化物-炔烃环加成。晶体堆积相提供了晶体结构设计的重大进步的可能性。随后总结了通过SCSC转换实现的1D或2D聚合物单晶的一些示例。