How to (not) Evaluate a Photoswitch Performance; Benchmarking of Methods Used for Processing Kinetic Data on an Example of Arylazopyrazole Z‐Isomer Half‐Life

Photoswitchable molecular systems are nowadays very popular and promising for development of molecular electronics in the future. Their physico‐chemical properties, such as activation wavelength, quantum yields, or stability of metastable forms are usually compared with the already published data, with the aim to demonstrate their improvement. An investigation of chemical kinetics is not always straightforward and requests careful data analysis and their processing. Importantly, stability of metastable forms is quantified by half‐life values τ 1/2 , which can be determined in several ways, leading to incomparable results. In this comparative study, it is demonstrated that processing the same data set by different approaches used in literature leads to a wide range of the half‐life values. As model compounds, we prepared azopyrazole derivatives 1 and 2 with the most stable Z isomers published ( τ 1/2 46 years and 1000 days at room temperature, respectively). Depending on the processing method the half‐life values of 1 in a range of 41.9–57.4 years were determined, with 16% of deviation. And for 2 in a range of 492–826 days (25% deviation). The results let us recommend a comprehensive methodology of how to process and evaluate the kinetic data with the aim of producing comparable results among laboratories all over the world.