Abstract
The fluorescence quenching of fluorescein by 1,4-benzoquinone (BQ) in five solvents – methanol, ethanol, phosphate buffer saline (PBS, pH 7.4), N,N'-dimethylformamide (DMF) and dimethylsulphoxide (DMSO) is hereby investigated. Fluorescein’s fluorescence was effectively quenched by BQ, and the quenching was dynamic (purely collisional) within the BQ’s concentration range (0.001 to 0.004 M) used in this work. Accordingly, the quenching data were in conformity with the Stern-Volmer’s model. Stern-Volmer’s constant (KSV) values range between 17.4 in DMSO and 43.4 in methanol. KSV values, together with the calculated bimolecular rate constants (kD) in the respective solvents, were used to semi-empirically estimate the fluorescence lifetimes (tF) of fluorescein in the individual solvents. Just as for KSV values, tF values are solvent-viscosity dependent, with the lowest values being obtained in methanol and the highest in DMSO, which are the least and most viscous solvents respectively. tF values obtained in this work are 3.55, 3.71, 3.78, 4.13 and 4.51 ns (in methanol, PBS 7.4, ethanol, DMF and DMSO, respectively).  Â
Highlights
IntroductionFluorescein, a yellowish-green emitting dye, possesses many attractive photophysicochemical properties (e.g., high molar absorptivity, high fluorescence quantum yield, and high photostability); in addition, it is water-soluble, biocompatible (Ha et al 2009, Veres et al 2017) and cheap
Fluorescein, a yellowish-green emitting dye, possesses many attractive photophysicochemical properties; in addition, it is water-soluble, biocompatible (Ha et al 2009, Veres et al 2017) and cheap
A relatively unfamiliar but cheaper and simpler method of fluorescence lifetime determination is hereby presented; this method is based on the diffusion-controlled collisional interaction between the fluorophore and quencher molecules, and data treatment via the Stern-Volmer model (Lakowicz 1999)
Summary
Fluorescein, a yellowish-green emitting dye, possesses many attractive photophysicochemical properties (e.g., high molar absorptivity, high fluorescence quantum yield, and high photostability); in addition, it is water-soluble, biocompatible (Ha et al 2009, Veres et al 2017) and cheap. These attributes bestow on it considerable versatility, and make it a compound of choice for many industrial applications and in academia. Fluorescence lifetime is an intrinsic property of a fluorophore, and can be measured in either the frequency domain or the time domain. 1, 4-benzoquinone is used as a quencher for the quenching of fluorescein’s fluorescence; the data treatment leads to the estimation of the fluorescence lifetimes of fluorescein (Fig. 1) in different solvents
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