1997
DOI: 10.1021/ja962476h
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Excited-State Photophysics of Hypericin and Its Hexamethoxy Analog:  Intramolecular Proton Transfer as a Nonradiative Process in Hypericin

Abstract: The excited-state photophysics of the light induced antiviral agent, hypericin, are compared with those of its methylated analog, hexamethoxyhypericin. This comparison is instructive in understanding both the groundand the excited-state properties of hypericin. That the hexamethoxy analog has no labile protons that can be transferred, that it cannot protonate its own carbonyl groups, that it has a reduced fluorescence quantum yield and lifetime with respect to hypericin, and that it exhibits no stimulated emis… Show more

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Cited by 93 publications
(89 citation statements)
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“…7,8 This seemed to be reasonable, especially given the breadth of the visible absorption spectrum; there are no "gaps" of zero absorbance anywhere between the ultraviolet and ∼600 nm. This suggestion also seemed to be supported by the observation that the transient absorbance 9,10 and upconversion 11 kinetics of hypericin differ with excitation wavelength and probe wavelength, respectively. For hypericin, however, evidence is emerging that the groundstate is much less heterogeneous than we had believed.…”
Section: The Current Picture That We Have Formed Of the Excited-statementioning
confidence: 83%
“…7,8 This seemed to be reasonable, especially given the breadth of the visible absorption spectrum; there are no "gaps" of zero absorbance anywhere between the ultraviolet and ∼600 nm. This suggestion also seemed to be supported by the observation that the transient absorbance 9,10 and upconversion 11 kinetics of hypericin differ with excitation wavelength and probe wavelength, respectively. For hypericin, however, evidence is emerging that the groundstate is much less heterogeneous than we had believed.…”
Section: The Current Picture That We Have Formed Of the Excited-statementioning
confidence: 83%
“…40 As noted in the Introduction, we have invoked a ground-state equilibrium between tautomeric or isomeric forms of hypericin, and its analogue hypocrellin, to rationalize the mirror-image symmetry between their absorption and emission spectra and the differences between their respective excited-state kinetics. The existence of such heterogeneity is supported by the observation of dependence of the excited-state kinetics of hypericin with respect to excitation or emission wavelength, 16,17,19,20 as well as that of its continuous absorption spectrum from the ultraviolet to the visible.…”
Section: Discussionmentioning
confidence: 95%
“…Our current knowledge of the excited-state transfer process is not detailed enough to specify whether the process is a proton or an atom transfer.) This argument has consistently been borne out by the study of tetra-and hexamethoxy analogues of hypericin 16,17,19 and by the observation of a deuterium isotope effect in the hypericin analogue, hypocrellin. 18 Of special relevance to the role of labile protons for the lightinduced biological activity of hypericin is the observation that hypericin acidifies its surroundings upon light absorption.…”
mentioning
confidence: 94%
“…[1][2][3][4][5] We have argued that they also present a fascinating system with which to study excited-state intramolecular H-atom transfer. [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Hypericin executes an intramolecular excited-state H-atom transfer in ∼10 ps. 20 This reaction is independent of solvent.…”
Section: Introductionmentioning
confidence: 99%