Acidity constants of β-carbolines in the ground and excited singlet states

The ground state ionization constants p K a(S 0) of β-carboline and three of its derivatives (harmane, harmine and 2-methylharmine) were measured spectrophotometrically in aqueous solutions. The corresponding p K a(S 1) of the first excited singlet state was calculated by means of the Förster cycle...

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Bibliographic Details
Published in:Journal of photochemistry 1983-01, Vol.23 (4), p.355-368
Main Authors: Vert, F.Tomas, Sanchez, I.Zabala, Torrent, A.Olba
Format: Article
Language:English
Subjects:
Atomic and molecular physics
Exact sciences and technology
Fluorescence and phosphorescence
radiationless transitions, quenching (intersystem crossing, internal conversion)
Molecular properties and interactions with photons
Physics
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Summary:The ground state ionization constants p K a(S 0) of β-carboline and three of its derivatives (harmane, harmine and 2-methylharmine) were measured spectrophotometrically in aqueous solutions. The corresponding p K a(S 1) of the first excited singlet state was calculated by means of the Förster cycle from the absorption and emission spectra. It was also established that protonated β-carboline cations are responsible for photoabsorption and fluorescence in acidic solutions. However, in alkaline solutions excitation of the neutral species leads to formation of the protonated β-carboline cations by rapid proton transfer from the solvent. A zwitterion species is produced by diffusion-controlled quenching of the excited state cation by OH − ions.
ISSN:0047-2670
DOI:10.1016/0047-2670(83)87109-3