Fluorinated perylene diimides: Synthesis, electrochemical-photophysical properties, and cellular imaging

Article abstract of DOI:10.1016/j.tetlet.2014.12.112

We report the synthesis and properties of perylene diimides with fluorinated substituents on the bay (BFPDIs). These BFPDIs exhibit good water solubility, high extinction coefficients, and high fluorescence quantum yields. Furthermore, these BFPDIs are us

Full text of DOI:10.1016/j.tetlet.2014.12.112

Tetrahedron Letters 56 (2015) 824–827
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Fluorinated perylene diimides: synthesis, electrochemical–
photophysical properties, and cellular imaging
Jia Wang a, Shilong Zhong a, Wenfeng Duan a, Baoxiang Gao a,b,
⇑
a College of Chemistry and Environmental Science, Hebei University, Baoding 071002, PR China
b Key Laboratory of Medicinal Chemistry and Molecular Diagnosis, Ministry of Education, Baoding 071002, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
We report the synthesis and properties of perylene diimides with fluorinated substituents on the bay
(BFPDIs). These BFPDIs exhibit good water solubility, high extinction coefficients, and high fluorescence
quantum yields. Furthermore, these BFPDIs are used as probes in cellular imaging.
Ó 2014 Elsevier Ltd. All rights reserved.
Received 3 October 2014
Revised 11 December 2014
Accepted 19 December 2014
Available online 31 December 2014
Keywords:
Perylene diimides
Fluorination
Electrochemical properties
Photophysical properties
Cellular imaging
Introduction
tions than its non-fluorinated counterpart.13 These successful
applications point to the potential of fluorinated chromophores
Perylene diimides (PDIs) represent a class of organic chromoph-
ores with photochemical stabilities, high extinction coefficients,
and high quantum yields.1,2 PDIs are key chromophores for
high-tech applications, such as organic photovoltaics,3 organic
field-effect transistors,4 biolabeling,5 sensors,6 single molecular
spectroscopy,7 and supramolecular assemblies.8 Stability, chemical
robustness, and ease of preparation are among a few of the neces-
sary characteristics for organic chromophores used in these fields.9
Currently available synthetic methods allow the preparation of
stable chromophores with increasingly negative reduction
potentials.10
Fluorine is the strongest element with electron affinity and a
small atom that can be introduced onto molecules with minimal
effect on steric hindrance. Highly fluorinated materials display a
variety of interesting properties, such as thermal and chemical
stability, low surface energy, and high resistance to oxidation.11
Swager and co-workers have recently reported two highly fluori-
nated poly(p-phenylene ethynelene)s with outstanding fluores-
cence quantum yields in solution and in thin films.12
Furthermore, fluorous polymers are also biocompatible. Zhang
et al. reported a highly fluorescent fluorinated semiconducting
polymer dot that is eight times brighter in cell-labeling applica-
in biological applications.
Our group aims to develop photochemically stable and biocom-
patible perylene dyes with high fluorescence in aqueous solutions
for bioimaging.14 In this study, we report the synthesis of perylene
diimides with fluorinated substituents on the bay (BFPDIs), as well
as their electrochemical–photophysical properties and applica-
tions for cellular imaging.
Results and discussion
Chart 1 shows the chemical structures of BPPDI and BFPDIs,
which were efficiently synthesized by the stepwise synthetic pro-
tocol illustrated in Scheme S1. BPPDI without fluorinated substit-
uents on the bay was used as a reference compound to study the
mechanisms by which fluorinated substituents affect the proper-
ties of PDIs. Dibromo-perylene tetracarboxylic dianhydride15 and
2,5,8,12,15,18-hexaoxa-10-nonadecanamine16 were prepared
according to the literature procedures. The reaction of
2,5,8,12,15,18-hexaoxa-10-nonadecanamine 1 with Cbz-protected
L-aspartic acid yielded compound 2. The Cbz group was removed
by catalytic hydrogenation with Pd/C to obtain compound 3. Com-
pound 5 was obtained via a coupling reaction between dibromo-
perylene tetracarboxylic dianhydride and compound 3. BPPDI
and BFPDIs compounds were prepared by Suzuki coupling with
compound 5 and the corresponding phenylboronic acid, followed
⇑
Corresponding author. Tel.: +86 312 3382004; fax: +86 312 5079317.
E-mail address: bxgao@hbu.edu.cn (B. Gao).
http://dx.doi.org/10.1016/j.tetlet.2014.12.112
0040-4039/Ó 2014 Elsevier Ltd. All rights reserved.

J. Wang et al. / Tetrahedron Letters 56 (2015) 824–827
825
R
laser desorption/ionization mass spectrometry (MALDI-TOF-MS).
Details of the synthetic route and all spectroscopies are provided
in the Supporting information.
O
O
O
O
O
N
O
O
N
O
O
O
O
O
O
O
O
O
CONH
HNOC
HNOC
O
O
O
O
O
O
O
O
O
O
O
O
CONH
The electrochemical properties of BPPDI and BFPDIs in dichloro-
methane were studied in a three-electrode electrochemical cell
using Bu4NPF6 (0.1 M) and Ag/AgCl as the electrolyte and the refer-
ence electrode, respectively. The CV curves are shown in Figure 1.
BPPDI revealed one irreversible oxidation potential at 1.69 V versus
Ag/AgCl and one reversible reduction potential at À0.55 V versus
Ag/AgCl. After installing the fluorinated substituents on the bay of
PDIs, the first reduction potentials of BFPDIs (À0.40 V for BFPDI-
1, À0.38 V for BFPDI-2) were shifted by approximately 150 mV
toward more positive potentials compared with that of BPPDI.
These BFPDIs showed an increase in the first reduction potential,
indicating that the electron-accepting power increased in strength.
By contrast, the CV scan for the BFPDIs with anodic scanning from 0
to 2 V showed no peaks, suggesting that the electron-donating prop-
erty of the BFPDIs became weak. The lowest unoccupied molecular
orbital (LUMO) levels were estimated from the onset of the first
reduction potentials.17 LUMO levels of the three compounds were
calculated as À3.85 eV, À4.00 eV, and À4.02 eV, respectively. The
decreased LUMO levels are ascribed to the electron-deficient fluori-
nated substituents on the bay of perylene diimides.
R
F
F
F
F
F
R=
F
BFPDI-1
BPPDI
BFPDI-2
F
F
F
Chart 1. Chemical structures of BPPDI and BFPDIs.
BPPDI
1 uA
BFPDI-1
BFPDI-2
The optical properties of BPPDI and BFPDIs in water were stud-
ied and compared with those in toluene. In the hydrophobic tolu-
ene solvent, the absorption maximum of BPPDI appeared at
551 nm, along with higher vibronic transitions located at 518 nm
(Fig. 2A). With fluorinated benzene on the bay, the maximum
absorption of the BFPDIs was blue-shifted to 542 nm for BFPDI-1
and 539 nm for BFPDI-2. Interestingly, the extinction coefficients
of these fluorinated PDIs were higher than that of the non-fluori-
nated counterpart. The photoluminescence (PL) peak of BPPDI in
toluene solution appeared at 606 nm. With fluorinated substitu-
-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0
Potential vs Ag/AgCl (V)
Figure 1. Cyclic voltammograms of compounds BPPDI and BFPDIs in dichloro-
methane at a scan rate of 0.1 V/s.
by purification through column chromatography on silica gel.
These new perylene diimides were fully characterized by 1H
NMR spectroscopy, 13C NMR spectroscopy and matrix-assisted
6
1.2
BPPDI
A
BPPDI
B
BFPDI-1
BFPDI-2
5
4
3
2
1
0
BFPDI-1
BFPDI-2
0.9
0.6
0.3
0.0
300
400
500
600
700
500
550
600
650
700
750
800
wavelength(nm)
wavelength(nm)
1.2
0.9
0.6
0.3
0.0
6
5
4
3
2
1
0
BPPDI
BPPDI
D
C
BFPDI-1
BFPDI-2
BFPDI-1
BFPDI-2
500
550
600
650
700
750
800
300
400
500
600
700
wavelength(nm)
wavelength(nm)
Figure 2. UV–vis absorption at 1.0 Â 10À4 M and PL spectroscopy at 1.0 Â 10À5 M of PDIs in toluene solution (A, B) and aqueous solution (C, D).

826
J. Wang et al. / Tetrahedron Letters 56 (2015) 824–827
The cytocompatibility or cytotoxicity of BPPDI and BFPDIs
must be assessed to demonstrate their potential utility in cellular
imaging. The biocompatibility of BPPDI and BFPDIs was evaluated
in HeLa cells using the MTT cell-viability assay. Figure 3 summa-
rizes the viability of HeLa cells after being cultured with BPPDI
and BFPDIs solutions at a concentration of 2.5 Â 10À5 mol LÀ1 for
24 and 48 h. These compounds showed very low cytotoxicity (over
90% viability) after 48 h of incubation. This result indicates that the
introduction of fluorine has almost no effect on the biocompatibil-
ity of BFPDIs. This bodes well for the utility of this fluorinated fluo-
rescent probe, particularly in live cell imaging applications and the
research of the biological active substances.
Live cell imaging based on these PDIs was investigated using
confocal laser scanning microscopy (CLSM). After being incubated
with these PDI solutions (1.0 Â 10À5 mol LÀ1) for 45 min, the cells
were washed three times with PBS buffer. The excitation wave-
length was fixed at 488 nm, and fluorescent signals were collected
from 535 nm to 635 nm for BFPDI-1 and 560–660 nm for BPPDI
and BFPDI-2. Figure 4D shows the confocal microcopy images of
HeLa cells incubated with BPPDI, where weak fluorescence was
detected. The low brightness of images is attributed to the low
fluorescence quantum yield of BPPDI. However, the fluorescence
from the cells stained by BFPDI-1 was enhanced (Fig. 4E). Figure 4F
shows strong fluorescence from the cells stained by BFPDI-2. This
finding reveals that these BFPDIs can efficiently accumulate in live
cells and perform cellular imaging. Changes in the fluorescence
images of HeLa cells stained by BPPDI and BFPDIs under continu-
ous 488 nm laser (10% of laser intensity) irradiation were moni-
tored to evaluate the photostability of BPPDI and BFPDIs in cells.
After irradiation for 1 min, the intensity of the fluorescence images
remained almost unchanged (Fig. S1 in the Supporting informa-
tion). These results prove the relatively high photostability of
BPPDI and BFPDIs in harsh physiological environment. Thus, these
Figure 3. In vitro viability of HeLa cells treated with BPPDI and BFPDIs solutions at
2.5 Â 10À5 mol LÀ1 for 24 and 48 h, respectively.
ents, the PL peaks of these PDIs also were blue-shifted to 593 nm
for BFPDI-1 and 583 nm for BFPDI-2. Furthermore, these PDIs
showed similar quantum yields of 65–74%. The relatively high
quantum yields suggest the minimal aggregation of the PDIs in tol-
uene solution.18
These PDIs are highly soluble in water. In aqueous solution, the
absorption maximum of these PDIs was red-shifted to 557 nm for
BPPDI, 550 nm for BFPDI-1, and 548 nm for BFPDI-2, compared
with those in toluene solution. The PL peaks of these PDIs appeared
at 637 nm for BPPDI, 613 nm for BFPDI-1, and 603 nm for BFPDI-
2. BPPDI revealed a low fluorescence quantum yield of 15% in
aqueous solution. With fluorinated substituents on the bay, the
fluorescence quantum yields of these PDIs were improved to 28%
for BFPDI-1 and 36% for BFPDI-2. The continuously enhanced
quantum yields may be attributed to the strong hydrophobic prop-
erties of F atoms together with F-F and/or F-H interactions, which
minimized the aggregation-induced quenching.13
Figure 4. The bright-field images of Hela cells stained by BPPDI (A), BFPDI-1 (B), and BFPDI-2 (C) and the confocal fluorescence images of Hela cells stained by BPPDI (D),
BFPDI-1 (E), and BFPDI-2 (F).

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Conclusions
Fluorinated perylene diimides were synthesized by installing
fluorinated substituents on the bay of perylene diimides. With
fluorinated substituents, these perylene diimides showed
increased first reduction potential, low cytotoxicity, good water
solubility and photostability, and high extinction coefficients and
fluorescence quantum yields in aqueous solution. Furthermore,
these fluorinated perylene diimides can efficiently accumulate in
live cells and perform cellular imaging.
Acknowledgements
This work was supported by the Program for Distinguished
Young Scholar of Hebei Province China (B2012201031), the
National Natural Science Foundation China (21274036), the Pro-
gram for New Century Excellent Talents in University China
(NCET-12-0684), the Program for Training Innovative Research
Team and Leading talent in Hebei Province University China
(LJRC024), the Program for Innovative talent in Hebei Province Uni-
versity China (GCC2014054).
Supplementary data
Supplementary data (detailed synthetic procedures and charac-
terization, general procedures, and supporting spectroscopic) asso-
ciated with this article can be found, in the online version, at
http://dx.doi.org/10.1016/j.tetlet.2014.12.112.
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