Real time optical monitoring of cascade mechanochemical reactions and capture of ultra-unstable intermediates under hydrostatic pressure

Abstract

Mechanochemistry plays an indispensable role in industrial production and daily life. However, as an intricate process accompanied by miscellaneous physical and chemical changes, it is difficult for researchers to clarify the unabridged process of mechanochemistry. In this article, optical monitoring as well as diamond anvil cell (DAC) techniques are used for in-depth research into the mechanochemistry of tetraphenylethene and pyrene modified cyano spiropyrans (TPE-Sp-CN and Py-Sp-CN), which can reversibly switch into different structures with distinct optical signals. Not only the physical process of pressure induced emission enhancement (PIEE) properties but also the multi-step cascade reactions are disclosed with these two fluorophores. Moreover, cis/trans tautomerization of spiropyran under hydrostatic pressure is observed and investigated in detail, and ultra-unstable intermediates of merocyanine form are monitored by optical characterization, which confirms the mechanochemical kinetics of isomerization for spiropyran. The progress paves the way toward the dynamic research on cleavage of covalent bonds in mechanochemistry, most of which can only be deduced from the initial and terminated substances previously. Thus, this article exhibits a more intuitive optical method for the research on physical and chemical evolution processes of organic materials under pressure.