Recent Advances in the Z/E Isomers of Tetraphenylethene Derivatives: Stereoselective Synthesis, AIE Mechanism, Photophysical Properties, and Application as Chemical Probes.

Focused research on the Z/E isomers of tetraphenylethene (TPE) derivatives is scarce in comparison with the thousands of luminogens with AIE properties (AIEgens) that have been synthesized based on the TPE moiety. The similar chemical and physical properties of the Z/E isomers make them difficult to separate by using conventional chromatographic techniques. However, they can be isolated by introducing polar groups and the pure isomers exhibit very different photophysical properties, mechanochromism, and host-guest coordination, as well as assisting in deciphering the AIE mechanism. In this Minireview, we present an overview of the disagreement regarding the AIE mechanism between the restriction of intramolecular vibration and photoinduced Z/E isomerization. Then, we discuss the development of (Z)-/(E)-TPE derivatives, their use in host-guest detection, and their mechanoluminescence properties, with a focus on their photophysical characteristics. Finally, we explore the stereoselective synthesis of pure (Z)-/(E)-TPE derivatives.