Direct Observation of Structural Heterogeneity and Tautomerization of Single Hypericin Molecules

Tautomerization is a fundamental chemical reaction which involves the relocation of proton in reactants. Studying optical properties tautomeric species challenging because ensemble averaging. Many molecules, such as porphines, porphycenes, or phenanthroperylene quinones, exhibit reorientation transition dipole moment (TDM) during tautomerization, can be directly observed single-molecule experiments. Here, we study single hypericin prominent quinone showing antiviral, antidepressive, and photodynamical properties. Observing abrupt flipping image pattern combined with time-dependent density functional theory calculations allows drawing conclusions about coexistence four tautomers their conversion path. This approach unambiguous assignment TDM orientation to specific tautomer enables determination structure situ. Our applied other molecules helping gain deeper understanding this important process.