It was used as the signal transduction unit in this study
while the diphenyl selenide unit performed as a modulator
to respond to the amount of HOCl. HCSe displays weak
fluorescence with a quantum yield of Φ = 0.005, because
photoinduced electron transfer (PET) from the diphenyl
selenide group to the BODIPY moiety takes place. How-
ever, the strong fluorescence of BODIPY is restored after
the oxidation of selenium by HOCl. This new probe
exhibits high selectivity and sensitivity toward HOCl over
other ROS and reactive nitrogen species (RNS) in aqueous
solution. Most importantly, HCSe shows good cell-
membrane permeability and can be successfully applied
to image endogenous HOCl in living cells.
phosphate-buffered saline (PBS) solution. It was found
that the strong green fluorescence emission only occurred
for the addition of HOCl to the HCSe solution; other ROS
and RNS produced no change in fluorescence (Figure 1).
The quantitative fluorescence spectra of HCSe were re-
corded in the presence of several ROS and RNS, but HOCl
was the only reactive species to cause an obvious fluores-
cence enhancement (Figure 1).
Scheme 1. Synthesis of the Probe HCSe
Figure 1. Fluorescence changes of HCSe (10 μM) in response to
NaOCl (10 μM) and various ROS/RNS (100 μM) in a
H2OÀCH3CN (v/v = 99/1, 0.1 M PBS, pH 7.4) solution. The
excitation wavelength was 510 nm.
The synthesis procedure for the probe HCSe is outlined
in Scheme 1. 2-(Phenylselenyl)benzaldehyde was obtained
from the reaction of diphenyl diselenide with o-bromoben-
zaldehyde in the presence of dithiothreitol (DTT). Treat-
ment of 2-(phenylselenyl)benzaldehyde with excess pyrrole
in the presence of trifluoroacetic acid (TFA) under N2
yielded the corresponding dipyrromethane. In the next step,
the compound 2-(phenylselenyl)phenyldipyrromethane was
oxidized with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone
(DDQ) to yield the corresponding dipyrromethene, which
was transformed into the BODIPY skeleton in the presence
of BF3 under N2. The structure of HCSe was confirmed
using 1H NMR, 13C NMR, 77Se NMR, and MS spectra.
The sensing ability of the probe HCSe was tested toward
various ROS and RNS, including HOCl, bOH, H2O2, 1O2,
NO2À, NO3À, NO, ONOOÀ, O2À, and t-BuOOH, in a
The reaction of HCSe with HOCl was fast; addition of
NaOCl(aq) to the solution of the probe HCSe caused an
immediate, strong change in fluorescence intensity (see
Figure S11 in Supporting Information). During HOCl
titration with HCSe, a new band centered at 526 nm
formed (Figure 2). The emission intensity reached its max-
imum after the addition of 1 equiv of HOCl. The quantum
yield of the oxidized form HCSeO was Φ = 0.690, which is
138-fold higher than that of HCSe, at Φ = 0.005. The
structure of the oxidized form HCSeO was also confirmed
by 77Se NMR and MS spectra. Notably, there was a good
linear correlation between the fluorescence intensity and the
concentration of NaOCl (0À9 μM). Furthermore, it was
found that HCSe has a detection limit of 7.98 nM (see
Figure S12 in Supporting Information), which makes it
sufficiently sensitive for application in living systems.
Density functional theory (DFT) calculation was ap-
plied to determine the detecting mechanism of HCSe for
HOCl. As shown in Scheme 2, the highest occupied
molecular orbital(HOMO) of thediphenylselenide moiety
(electron donor) matches that of the fluorophore BODIPY
(electron acceptor); the HOMO energy level (À5.75 eV) of
the diphenyl selenide moiety is higher than that of the
fluorophore BODIPY (À5.98 eV). Consequently, when
the BODIPY moiety is photoexcited, the intramolecular
electron transfer from the diphenyl selenide moiety to the
BODIPY moiety is energetically favorable. Hence, the
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