Determining the absorption spectra and photostationary state distributions of molecular photoswitches

We describe how to determine the photostationary state (PSS) distributions of photoswitch isomers in a tutorial-like presentation. The key requirements for measurements are described, as are the assumptions employed in a range of analysis techniques. We frame the problem of determining the metastable isomer's spectrum as a non-negative matrix factorization. We present a Python notebook for solving this problem and outputting the spectrum of the metastable state, and the isomer ratio at each PSS. Our method also evaluates the uniqueness of the solution. Where multiple different metastable spectra are consistent with the experimental data, it presents a range of solutions, allowing users to appreciate the uncertainty in the analysis. Our method is general and can be used to determine the spectrum of the metastable isomer and the PSS distributions for common photoswitches.