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A Butterfly-Shaped Pyrene Derivative of Cholesterol and Its Uses as a Fluorescent Probe
A butterfly-shaped pyrene derivative
of cholesterol, namely, <i>N</i>,<i>N</i>′-(ethane-1,2-diyl)-bisÂ(<i>N</i>-(2-(chol-amino)Âethyl)Âpyrene-1-sulfonamide) (ECPS), has
been designed and synthesized. Solvent effect studies revealed that
in good solvents such as <i>n</i>-hexane, benzene, and 1,4-dioxane,
the profile of the fluorescence emission of the compound is characterized
by pyrene monomer emission, but in poor solvent such as water, the
emission is dominated by pyrene excimer emission. Quantitatively speaking,
the ratio of the excimer emission to monomer emission changes from
50 to 0 when ECPS is dissolved in water and <i>n</i>-hexane,
respectively. In contrast, for a commonly used polarity probe pyrene,
the ratio of I<sub>3</sub>/I<sub>1</sub> varies only from ∼0.6
to ∼1.7, where I<sub>3</sub> and I<sub>1</sub> stand for the
intensities of the fluorescence emission at peak 3 and peak 1, respectively.
This value suggests that a more powerful discriminating ability of
the new compound in polarity sensing. Furthermore, unlike the main
components of the compound, pyrene and cholesterol, its main chain
is composed of multiple hydrophilic structures, and it is this structure
that makes the emission of the compound in organic solvents sensitive
to the presence of water. Accordingly, the applicability of the compound
in determination of the trace amount of water in some organic solvents
was evaluated. As expected, the detection limit of the compound toward
water in acetonitrile reaches 7 ppm, a result never reached before.
Furthermore, the fluorescence emission of the compound is also sensitive
to viscosity variation. Therefore, it is assumed that ECPS may be
used both as a polarity probe and a viscosity probe. On the bases
of a series of steady-state and time-resolved fluorescence, as well
as dynamic light scattering studies, a structural model was proposed
to rationalize the fluorescence behavior of the compound in different
solvents and its polarity and viscosity probing performances