Characterization of the hemithioindigo photoswitch and its derivatives with x-ray photoabsorption and photoemission spectroscopies

In this study, we investigate the electronic structure of hemithioindigo–hemistilbene (HTI) photoswitches and their functionalized derivatives, HTI-OMe and HTI-SMe, using x-ray photoemission spectroscopy (XPS) and near-edge x-ray absorption fine structure (NEXAFS) spectroscopy. HTI compounds are known for their high quantum yield, thermal bistability, and rapid photoisomerization, making them promising candidates for applications in molecular motors, optical materials, and photocatalysis. Our analysis, supported by first-principles simulations, reveals how the conjugation of heteroatoms within the π-system affects the core-level chemical shifts and ionization intensities in XPS, while NEXAFS probes the influence of substituents on virtual molecular orbitals and energy transitions. In particular, the comparison between different functionalized HTIs allowed us to evaluate the effect of electronic relaxation following core-level photoionization and photo-excitation. These results provide a detailed understanding of the influence of functionalization on the electron distribution of HTI compounds, providing a robust foundation for the study and control of ultrafast charge transfer and photoswitching mechanisms in these molecular systems.