cycloreversion of DAE under light irradiation produces many exciting functional effects, such as changes in photophysical and photochemical properties, [12] changes in the shape or mechanical properties of the solid, [13] electrical conductivity, [7b,14] and the generation of reactive oxygen species (ROS). [15] This type of photochromic compound can be considered a stilbene derivative. At this time, the most widely known and systematically studied DAE derivative structure contains two aryl groups and a benzene ring (usually two identical or different thiophene units with low aromatic stabilization energy [16] ) and a five-membered ring of perfluorocyclopentene and cyclopentene units [17] where the ethene bridge is located, which significantly improve photochromism. [18] In essence, the DAE photoisomerization process is a reversible electrocyclic reaction of the central 6π-electron systems. [2] Under light irradiation, DAE can rapidly and reversibly transform between its open and closed forms, and that transformation is accompanied by a color change caused by a change in the π-conjugation distribution. [2] The important thing is that the colorless opened-and colored closed-ring isomers are both thermally stable; that is, cyclization and cycloreversion do not proceed spontaneously in the dark; they need to be driven by external light irradiation at specific wavelengths. [2,19] Compared with classic lightresponsive molecules such as azobenzene, [20] the light intensity required to drive the isomerization of DAE is relatively low. Moreover, even after multiple cycles, the photochromic performance does not show significant fatigue in either the solution or solid state. [2,18b,21] DAE research to this point can be roughly divided into three stages in chronological order: early exploration of DAE's molecular structure and theory, nearly two decades of purpose-oriented molecular structure modification research, and about ten years of research into practical applications of DAE in assembly systems. Research before about 2000 focused mainly on developing more abundant DAE-derivative structures and advancing the systematic understanding of DAE's physical and chemical properties and switching performance. To regulate its switching performance and give it new functionality, many strategies for modifying the ethene bridge and aryl groups of DAE have been proposed. [22] In the first two research stages, the mechanisms and structural modification of DAE isomerization were thoroughly and systematically explored, and countless important Diarylethene (DAE) photoswitch is a new and promising family of photochromic molecules and has shown superior performance as a smart trigger in stimulus-responsive materials. During the past few decades, the DAE family has achieved a leap from simple molecules to functional molecules and developed toward validity as a universal switching building block. In recent years, the introduction of DAE into an assembly system has been an attractive strategy that enables the photochromic behavior of the b...
