Teacups, a Python Package for the Simulation of Time-Resolved EPR Spectra of Spin-Polarized Multi-Spin Systems

Spin-polarized magnetic systems, generated by the interaction of photoactive molecules with light, play a key role in a wide range of scientific applications. Representative examples are OLEDs, organic photovoltaics, and singlet fission. Further, they are important intermediates in certain biological processes including photosynthesis and, possibly, avian magnetoreception. Transient continuous-wave electron paramagnetic resonance (trEPR) spectroscopy is a powerful tool to reveal the temporal evolution of nonequilibrium spin states, which contains valuable information on any photoinduced dynamic processes occurring in these systems. For the analysis of the recorded trEPR data, simulations are essential. While the simulation of static trEPR spectra is supported well by tools like EasySpin, the simulation of time-resolved trEPR data is less developed. Here, we introduce teacups, a new freely available and well-documented Python-based routine for the simulation of the temporal evolution of trEPR spectra. The internal dynamics of different spin-polarized systems can be analyzed, thereby enhancing our mechanistic understanding. In this manuscript, we explain the theoretical background and provide a description of the features and setup of teacups. Further, a step-by-step example for data analysis is provided.