Journal
JOURNAL OF PHYSICAL CHEMISTRY LETTERS
Volume 12, Issue 3, Pages 1025-1031Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.jpclett.0c03459
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Funding
- German Research Foundation (DFG) [ME 1600/13-3]
- China Scholarship Council (CSC)
- Spanish Science Ministry (MINECO-FEDER) [CTQ2017-87054, SEV-2016-0686]
- Campus of International Excellence (CEI) UAM+CSIC
- European Commission
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Tautomerization is a fundamental chemical reaction involving proton relocation, presenting a challenge in studying the optical properties of tautomeric species. Single-molecule experiments reveal the reorientation of the transition dipole moment during tautomerization in molecules such as hypericin. By combining image pattern flipping observations with time-dependent density functional theory calculations, this study identifies four tautomers and their conversion path in hypericin molecules.
Tautomerization is a fundamental chemical reaction which involves the relocation of a proton in the reactants. Studying the optical properties of tautomeric species is challenging because of ensemble averaging. Many molecules, such as porphines, porphycenes, or phenanthroperylene quinones, exhibit a reorientation of the transition dipole moment (TDM) during tautomerization, which can be directly observed in single-molecule experiments. Here, we study single hypericin molecules, which is a prominent phenanthroperylene quinone showing antiviral, antidepressive, and photodynamical properties. Observing abrupt flipping of the image pattern combined with time-dependent density functional theory calculations allows drawing conclusions about the coexistence of four tautomers and their conversion path. This approach allows the unambiguous assignment of a TDM orientation to a specific tautomer and enables the determination of the chemical structure in situ. Our approach can be applied to other molecules showing TDM reorientation during tautomerization, helping to gain a deeper understanding of this important process.
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