Photochromic heteroarylethenes with fast thermal isomerization kinetics

Stilbenes (diphenylethenes) are fully examined organic chromophores for very diverse applications. However, these molecules might show poor stability under irradiation because several simultaneous reactions (oxidative photocyclization and dimerization) can take place during the photochemical isomerization of their C--C bond. In this context, heteroarylethenes emerge as powerful counterparts thanks to their improved stability. In addition, the chosen heterocycles and their functionalization allows to fine tune and increase the speed at which the thermal back reaction occurs, broadening the scope of application of the resulting chromophores. Here we report on the thermal Z-to -E isomerization kinetics of a series of rationally designed heteroarylethenes and how the chemical architecture of the chromophore modulates the speed of the process. Specifically, the metastable Z isomers display relaxation times covering a wide time window, from a few hours to hundreds of microseconds. In fact, one of the studied dyes is the fastest photochromic switch based on heteroarylethenes. It should be also noticed that the described heteroarylethenes exhibit great photochemical stability, it being possible to switch them back and forth many times without degradation.

Automated summary

Stilbenes (diphenylethenes) are widely used organic chromophores, but their stability under irradiation is a concern. Heteroarylethenes, on the other hand, offer improved stability and increased speed of thermal back reaction. In this study, we investigate the isomerization kinetics of rationally designed heteroarylethenes and their chemical architecture's impact on the speed of the process.