RESUMO
The UV/Vis absorption and fluorescence properties of dibenzofluorescein (DBFL) in organic solvents were measured and used to shed light on the possible presence of its tautomers or various prototropic forms. DBFL in aprotic solvents mainly exists in two tautomeric forms, viz. quinoid and lactone, but neither are efficiently fluorescent. In protic solvents, such as methanol and ethanol, both the monoanion and neutral quinoid are present and showed the highest fluorescence quantum yield. In contrast, DBFL is fully dissociated to the monoanion and dianion in deionized water.
Assuntos
Acetona/química , Acetonitrilas/química , Álcoois/química , Dimetil Sulfóxido/química , Éter/química , Fluoresceínas/química , Corantes Fluorescentes/química , Fluoresceínas/isolamento & purificação , Fluoresceínas/efeitos da radiação , Fluorescência , Corantes Fluorescentes/isolamento & purificação , Corantes Fluorescentes/efeitos da radiação , Ligação de Hidrogênio , Conformação Molecular , Fotoquímica , Sensibilidade e Especificidade , Solventes/química , Espectrometria de Fluorescência/métodos , Espectrofotometria Ultravioleta/métodos , Estereoisomerismo , Raios UltravioletaRESUMO
The deprotonation of dibenzofluorescein (DBFL), a long wavelength fluorescence probe, results in the simultaneous occurrence of neutral form, monoanion and dianion under physiological conditions. The fluorescence properties of the former two cannot be measured directly because they are always coexistent with some other species. By measuring the fluorescence under various pHs we computed the fluorescence parameters for each species involved in the prototropic equilibria of DBFL, including each species' emission spectrum, excitation spectrum, emission and excitation maximum, fluorescence quantum yield and lifetime. It was found that the monoanion is the most fluorescent chromospheres (Phif=0.66, compared to Phif=0.25 for dianion, 0.18 for cation and 0.0 for the neutral form). Together with the computed pKas, we are able to suggest that the monoanion plays a major role under physiological conditions when DBFL is used as a fluorescence probe, contrary to the assumption in literature.
