Photoproperties of favipiravir and its 6-substituted analogues: fluorescence controlled through halogen substitution and tautomerism.
Org Biomol Chem
; 22(19): 3910-3925, 2024 May 15.
Article
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| MEDLINE
| ID: mdl-38656328
ABSTRACT
Herein, we have showed the photophysical properties of favipiravir and its 6-substituted analogues. Also, we interpreted the origin of fluorescence of favipiravir and its 6-substituted analogues as a function of tautomerism modulation in ground and excited states. Favipiravir, the 6-fluorine derivative, showed the best photophysical profile, exhibiting a dominant emission wavelength of 430 nm, a high quantum yield (Q.Y.) of 1.0 and a long-lived state (10 ns). Its analogues also showed a maximum emission at 430 nm, but their Q.Y. values were 5-fold lower than that found for favipiravir, decreasing as a function of 6-substitution as follows F > Cl > Br > I > H. Pyrazines bearing the least electronegative 6-substituent (X = Br, I, H) showed an extra lifetime, which was shorter (0.2-0.3 ns) and less abundant (>15%) than the main lifetime (10 ns, 85%). Further 2D excitation-emission matrix and solvent studies supported that these 3-hydroxy-2-pyrazinecarboxamides present two emissive states. The first of them (λem = 430 nm), which was the most abundant, most fluorescent and long-lived state, was characterized as "locally excited" (LE). Its fluorescence was favored with an increase of the hydrogen-donor nature of the solvent and for pyrazines having a high enolic characteristic. Thus, the high LE-fluorescence of these types of pyrazines depends on the keto-tautomerization of the ground state using a protic solvent and its feasible enol-tautomerization upon excitation. Finally, the second excited state (λem = 536 nm) was suggested as an excited-state intramolecular proton-transfer (ESIPT), and it was observed only, although discretely, for pyrazines bearing the least electronegative 6-substituent.
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Colección:
01-internacional
Base de datos:
MEDLINE
Idioma:
En
Revista:
Org Biomol Chem
Asunto de la revista:
BIOQUIMICA
/
QUIMICA
Año:
2024
Tipo del documento:
Article
País de afiliación:
Uruguay
Pais de publicación:
Reino Unido