Characterization of diarylethene-based photoswitches with core and valence photoabsorption and photoemission spectroscopies

We investigate the electronic structure of two dithienylethene (DTE) molecular photoswitches, BTF6 and PTF6, in the gas phase by combining valence photoelectron spectroscopy (PES), x-ray photoelectron spectroscopy, and the near-edge x-ray absorption fine structure. DTEs have attracted significant attention due to their high photoisomerization quantum yield, fatigue resistance, and thermal irreversibility, which underpin applications ranging from molecular machines to photoswitchable biomolecules. Supported by first-principles simulations, our analysis elucidates how the different extent of π-conjugation, arising from the distinct thiophene/benzothiophene subunits, manifests across the various spectroscopic observables. By comparing the calculated signatures of the open- and closed-ring isomers, we further assess the sensitivity of each probe to the structural changes associated with photoinduced cyclization. Overall, these results deliver a detailed picture of the intrinsic electronic properties of DTEs in the gas phase and provide a robust basis for future time-resolved studies of their ultrafast photoisomerization dynamics.