Synthesis and properties of fluorescence dyes: Tetracyclic pyrazolo[3,4- b ]Pyridine-based coumarin chromophores with intramolecular charge transfer character

Article abstract of DOI:10.1021/jo3002722

Two series of new tetracyclic pyrazolo[3,4-b]pyridine-based coumarin chromophores were synthesized through a facile reaction between 3-aldehyde-7-diethylaminocoumarin (5) or 3-acetyl-7-diethylaminocoumarin (6) and 5-aminopyrazole derivatives (7) in a one-pot procedure. Different condensed products were obtained from compounds 5 and 6, and the potential reaction mechanism was studied using the reaction of 5 with 5-amino-1-phenylpyrazole (7a). The molecular structures were characterized by NMR and HRMS and confirmed by X-ray diffraction. The photophysical, electrochemical, and thermal properties of these compounds were investigated by absorption spectroscopy, fluorescence spectroscopy, single photon counting technique, cyclic voltammetry, thermogravimetric analysis, etc. Results show that the compounds exhibited high fluorescence quantum yields and good electrochemical, thermal, and photochemical stabilities. In addition, the application of these highly fluorescent compounds in living cell imaging was also explored by laser scanning confocal microscopy.

Full text of DOI:10.1021/jo3002722

Article
pubs.acs.org/joc
Synthesis and Properties of Fluorescence Dyes: Tetracyclic
Pyrazolo[3,4-b]Pyridine-Based Coumarin Chromophores with
Intramolecular Charge Transfer Character
Jianhong Chen,†,‡,§ Weimin Liu,†,§ Jingjin Ma,†,‡ Haitao Xu,† Jiasheng Wu,† Xianglin Tang,†,‡
Zhiyuan Fan,†,‡ and Pengfei Wang*,†
†Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry, Chinese
Academy of Sciences, Beijing, 100190, China
‡Graduate School of Chinese Academy of Sciences, Beijing, 100049, China
S
* Supporting Information
ABSTRACT: Two series of new tetracyclic pyrazolo[3,4-
b]pyridine-based coumarin chromophores were synthesized
through a facile reaction between 3-aldehyde-7-diethylamino-
coumarin (5) or 3-acetyl-7-diethylaminocoumarin (6) and 5-
aminopyrazole derivatives (7) in a one-pot procedure.
Different condensed products were obtained from compounds
5 and 6, and the potential reaction mechanism was studied
using the reaction of 5 with 5-amino-1-phenylpyrazole (7a).
The molecular structures were characterized by NMR and
HRMS and confirmed by X-ray diffraction. The photophysical,
electrochemical, and thermal properties of these compounds were investigated by absorption spectroscopy, fluorescence
spectroscopy, single photon counting technique, cyclic voltammetry, thermogravimetric analysis, etc. Results show that the
compounds exhibited high fluorescence quantum yields and good electrochemical, thermal, and photochemical stabilities. In
addition, the application of these highly fluorescent compounds in living cell imaging was also explored by laser scanning
confocal microscopy.
properties. In the present work, two series of tetracyclic
pyrazolo[3,4-b]pyridine-based coumarin (PPC) derivatives,
which show distinct photophysical properties because of their
different molecular skeletons, were designed and synthesized.
Interestingly, two types of tetracyclic PPC derivatives can be
derived in a one-pot procedure; this approach is highly
attractive in synthetic chemistry similar to domino reactions.11
The readily available pyrazolo[3,4-b]pyridine and coumarin-
fused scaffold may serve as a new opportunity for the
development of novel pyrazolo[3,4-b]pyridine/coumarin-
based organic functional materials. The properties of these
tetracyclic PPC derivatives were also investigated by X-ray
diffraction, absorption spectroscopy, fluorescence spectroscopy,
single photon counting technique, cyclic voltammetry,
thermogravimetric analysis, and density functional theory
(DFT) calculations. As a straightforward application, tetracyclic
PPC derivatives (1a and 2a) were also used for confocal
fluorescence imaging in living HeLa cells.
INTRODUCTION
■
The design and synthesis of brightly emissive molecules with a
polycyclic aromatic backbone remain key objectives of current
research in view of their potential applications in optoelectronic
devices1 and sensing materials.2 From the perspective of
molecular design for highly fluorescent dyes, an important
approach is to design fused heterocyclic aromatic analogues
with intramolecular charge transfer (ICT) character because of
the following advantages: (i) the suppression of both the
proximity effect caused by the interaction of n−π and π−π
electron configurations and internal conversion decay from the
free rotation of unbridged double bonds; (ii) minimal self-
reabsorption, especially in the solid state; and (iii) relatively
narrow emission bands resulting from reduced vibration.3
Pyrazolo[3,4-b]pyridine derivatives as aza analogues of
indazole have received considerable attention given their
significant biological activities.4 Their fused large conjugated
derivatives are highly fluorescent and used in organic light-
emitting diodes (OLEDs) or as chemosensors, such as
pyrazolo[3,4-b]quinoxaline,3 pyrazoloquinoline,5 and bipyrazo-
lopyridine.6 Coumarin derivatives with ICT character have
been widely investigated and applied in diverse fields, including
biomedicine,7 OLEDs,8 chemosensors,9 and laser dyes.10 It can
be conceived that compounds containing pyrazolo[3,4-b]-
pyridine and coumarin moieties may show extraordinary
RESULTS AND DISCUSSION
■
Synthesis and Mechanism. Compounds 5 and 6 were
synthesized according to previously reported procedures.12
Received: February 7, 2012
Published: March 19, 2012
© 2012 American Chemical Society
3475
dx.doi.org/10.1021/jo3002722 | J. Org. Chem. 2012, 77, 3475−3482

The Journal of Organic Chemistry
Article
Table 1. Synthesis of Tetracyclic PPC Derivatives
entry
R1
R2
Ph
R3
yield
5 + 7a
5 + 7b
5 + 7c
5 + 7d
6 + 7a
6 + 7b
6 + 7c
6 + 7d
H
H
1a (50%)
1b (69%)
1c (75%)
1d (76%)
3a (trace)
3b (trace)
3c (trace)
3d (trace)
2a (23%)
2b (1%)
CH3
Ph
Ph
H
Ph
H
2c (trace)
2d (trace)
4a (19%)
4b (23%)
4c (17%)
4d (22%)
Ph
CH3
Ph
H
H
CH3
CH3
CH3
CH3
CH3
Ph
Ph
Ph
Ph
CH3
Scheme 1. Proposed Reaction Pathways
Tetracyclic PPC derivatives (1a−1d, 2a and 2b, and 4a−4d)
were obtained in a one-pot procedure through the
condensation of 5 or 6 with corresponding 5-aminopyrazole
derivatives (7a−7d) in ethanol without any catalyst (Table 1).
Interestingly, different primary products were obtained from
compounds 5 and 6.
We chose the reaction of compounds 5 and 7a to study the
potential reaction mechanism, as shown in Scheme 1. The
reactions may proceed via two different reaction procedures
including C−C or C−N condensation reaction, intramolecular
Diels−Alder reaction, and aromatization. In path A, the
addition of the 4-C atom of 7a to 5 formed unstable
intermediate 8, which can be converted into main product
1a.13 The existence of intermediate 8 can also be confirmed by
byproduct 9 (yield 8%), which may be obtained through the
addition of another molecular 7a to intermediate 8 and
confirmed by X-ray crystallography (Figure S8 in Supporting
Information). Likewise, in path B, compound 2a was obtained
3476
dx.doi.org/10.1021/jo3002722 | J. Org. Chem. 2012, 77, 3475−3482

The Journal of Organic Chemistry
Article
by the C−N condensation reaction of 5 and 7a, accompanied
by the formation of a key intermediate 10 (yield 5%). Schiff
base 10 was separated, and 2a was also obtained through the
reflux of sole 10 under the same conditions.4a These results are
Table 2. Crystallographic and Theoretical Calculation Data
of 1a, 1b, 2b and 4a−4d
a
b
product
θ (deg)
θ (deg)
1
1a
1b
2b
4a
4b
4c
4d
7.70/2.55
2.83
2.52
2.49
supported by the findings derived from X-ray diffraction, H
NMR, 13C NMR, and HRMS.
18.54
19.14
5.50
The main products obtained from compound 5 are C−C
condensation products (1a−1d); the derivation can be
explained by the theoretical calculations. For example, the
difference in relative energy between 1a and 2a was about −7.6
kcal/mol, with preference for the formation of 1a as the major
thermodynamically favored product.14 Moreover, the yields of
C−N condensation products (2a−2d) for 5 decreased rapidly
in the series hydrogen → methyl → phenyl, in line with the
increasing steric hindrance of the 3-C atom of 5-aminopyrazole
derivatives: 23% for 2a, 1% for 2b, and trace for 2c and 2d
(Table 1). By contrast, the C−N condensation compounds
(4a−4d) were the primary products for compound 6 through a
path similar to path B because the reactivity of carbonyl
decreased rapidly given the steric hindrance of methyl.
Compound 6 is highly difficult to react through a path similar
to path A (trace for 3a−3d).
11.87/0.16
22.04
22.42
26.33
16.78
15.43
25.19
a
b
The torsion angle determined from crystal structure. The torsion
angle determined from theoretical calculation.
conclusions are consistent with the results of the DFT
calculations. Details of the X-ray experimental conditions, cell
data, and refinement data of compounds 1a, 1b, 2b, and 4a−4d
are summarized in Table 3.
Furthermore, because of the anisotropic effects of the phenyl,
Ha and Hb (for atomic labels, see Figure 2) of 4c and 4d
exhibited distinct upfield shifts15 (about 0.78 and 0.82 ppm for
Ha, 1.13 and 1.15 ppm for Hb, respectively) compared with 4a
1
X-ray Structures and NMR Spectra. The molecular
structures of 1a, 1b, 2b, and 4a−4d were elucidated by X-ray
crystallography (Figures 1 and S1−S7), revealing pyrazolo[3,4-
in H NMR, while Hc slightly changed (6.59, 6.53, and 6.48
ppm for 4a, 4c, and 4d, respectively). Moreover, because Hb is
closer to phenyl than Ha, the change in chemical shift of Hb is
greater (1.13 ppm vs 0.78 ppm for 4c).
Photophysics. The absorption and fluorescence spectra of
all of the compounds were investigated in different solvents
(Figures 3, S9, and S10). The C−N condensation products (2a,
2b, and 4a−4d) exhibited a narrow absorption band, whereas
the C−C condensation products (1a−1d) displayed a broad
band with a shoulder peak (an ICT transition16) at lower
energy. Compared with the C−C condensation products, those
of the C−N condensation products exhibited a slight red shift
for absorption peaks because the decrease in π-conjugate
interaction for it elevates the HOMO level, thereby resulting in
a narrow band gap. In cyclohexane, the structured absorption
bands indicate that a narrow distribution of vibrational states is
involved in the electronic transition.17 For all of the
compounds, the maximum absorption band is attributed to
the π→π* transition because of their high molar extinction
coefficients of above 104 M−1 cm−1 in CH2Cl2 (Table 4).18
Although solvent polarity has little effect on the absorption
spectra, significant bathochromic shift of the emission bands
was observed with increasing solvent polarity because of the
ICT character. These results suggest that the excited states
possess more polar character than the ground states.19 Figure 3
shows that the fluorescence for 1b and 2b had two different
origins: a locally excited (LE) state responsible for a π*→π
fluorescence and an ICT state, which produces ICT emission.20
In the polar solvents, the LE emission vanished, and only ICT
emission was observed. The emission spectra of 1b and 2b
became red-shifted and broadened as solvent polarity increased
from cyclohexane to CH3OH, which is typical of ICT excited
states.21 It indicates effective electronic communication
between the diethylamino group and the pyrazolopyridine
core, which is compatible with the result of the DFT
calculations.22 Given the stronger ICT properties, the C−C
condensation products exhibited longer fluorescence lifetimes
and larger Stokes shifts in CH2Cl2 than the C−N condensation
products (Table 4). The magnitude of Stokes shifts for the C−
C condensation products implies a large difference between the
Figure 1. Crystal structures of 1b and 2b with ellipsoids shown at the
50% probability level (hydrogen atoms are omitted for clarity).
b]pyridine and coumarin-fused skeleton (see Supporting
Information for details). They are all racemic mixtures given
the helix structure and the presence of both enantiomers in the
unit cells. The tetracyclic molecular skeletons are twisty because
of steric hindrance. The torsion angles θ of the M isomers for
1a (C(12)−C(13)−N(1)−N(3)), 1b (C(19)−C(20)−N(1)−
N(2)), 2b (C(17)−C(16)−N(2)−N(1)), 4a (C(5)−C(10)−
N(4)−N(3)), 4b (C(20)−C(21)−N(2)−N(1)), 4c (C(5)−
C(6)−N(4)−N(3)), and 4d (C(8)−C(7)−N(1)−N(2)) (for
atomic labels, see Figures 1 and S1−S7) are listed in Table 2.
Two torsion angles were observed in the antiparallel crystal
packing of 1a and 4a; thus, they have more isomers in the unit
cells than the other compounds. Compound 1b showed more
planar and more π-conjugate interaction than compounds 2b
and 4b−4d. The torsion angle of 4b is larger than that of 2b
because of an additional methyl. Because of the steric hindrance
of the substituent on the 3-C atom of pyrazole, the torsion
angles of 4b and 4c are larger than that of 4a. These
3477
dx.doi.org/10.1021/jo3002722 | J. Org. Chem. 2012, 77, 3475−3482

The Journal of Organic Chemistry
Article
Table 3. Selected Crystallographic Data of 1a, 1b, 2b and 4a−4d
1a
1b
2b
4a
4b
4c
4d
formula
C23H20N4O2
384.43
C24H22N4O2
398.46
C24H22N4O2
398.46
C24H22N4O2
398.46
monoclinic
P21/c
C25H24N4O2
412.48
C30H26N4O2
474.55
C25H24N4O2
412.48
formula weight
crystal system
space group
a, Å
triclinic
monoclinic
P21/c
triclinic
triclinic
triclinic
triclinic
P1
P1
̅
P1
̅
P1
̅
P1
̅
̅
9.4170(18)
12.514(3)
16.573(4)
88.219(10)
75.860(10)
80.763(10)
1869.24
4
6.4584(13)
20.649(4)
15.101(3)
90.00
7.486(2)
11.283(3)
12.414(4)
80.3410(18)
76.4090(14)
73.2770(15)
970.41
12.609(4)
15.739(3)
19.556(4)
90.00
9.372(3)
11.126(4)
11.340(4)
105.318(4)
105.023(4)
104.512(2)
1034.84
2
10.157(3)
10.670(3)
11.257(3)
103.417(8)
93.162(6)
90.024(5)
1184.77
2
9.573(4)
9.815(4)
11.061(4)
92.907(7)
95.692(7)
94.927(7)
1028.49
2
b, Å
c, Å
α, deg
β, deg
101.92(3)
90.00
93.380(3)
90.00
γ, deg
V, Å3
1970.44
4
3874.2
8
Z
2
ρ, g/cm3
R factor (%)
number of reflections
Rint
1.366
1.343
1.364
1.366
1.324
1.33
1.332
6.33
7.85
7.61
8.14
6.57
7.56
6.87
21183
17579
7297
28790
13801
13324
7745
0.0819
0.0635
0.0501
0.0807
0.0952
0.1784
0.0466
0.0552
0.0475
0.0917
0.1684
R(F) (all data)
wR(F2) (all data)
0.0873
0.1003
0.0955
0.0772
0.0947
0.1458
0.1435
0.1616
0.1396
0.1475
Figure 3. Absorption (left) and fluorescence spectra (right) of
compounds 1b and 2b in different solvents (c = 1 × 10−5 M): black
(cyclohexane), red (CH2Cl2), green (ethyl acetate, EA), blue
(CH3CN), cyan (DMF), and magenta (CH3OH).
displayed a positive solvent effect and high fluorescence
quantum yields both in less polar solvents and in the solid
state. Compounds 2a and 2b displayed two distinct emission
1
Figure 2. Partial H NMR spectra of compounds 4a, 4c, and 4d.
excited state reached after absorption and that from which the
emission starts.19
Table 4. Photophysical Properties of All Compounds in
CH2Cl2
The fluorescence quantum yields (Φ) of all of the
compounds are given in Table 5. Compounds 1a−1d exhibited
low Φ in polar solvents because of the strong ICT character.23
A general trend is that the C−C condensation products showed
lower Φ compared with the C−N condensation products
(comparison between 1a and 2a, and 1b and 2b). The addition
of a substituent decreased Φ from 0.717 to 0.310, in
comparison with the results obtained for 1a, 1b, and 1c in
cyclohexane. This decrease is presumably due to an increase in
the nonradiative decay pathways caused by C−C bond
vibrations.21 The C−N condensation products (2a, 2b, and
4a−4d) showed intense blue fluorescence even in strong polar
solvents (0.222 to 0.430 in CH3OH). All of the compounds
product
λmax (nm)
λem (nm)
Stokes
ε (M−1 cm−1
)
τ (ns)
1a
1b
1c
1d
2a
2b
4a
4b
4c
4d
379
377
359
350
405
404
403
403
410
408
501
499
509
506
441
445
439
452
461
461
6425
6485
8209
8809
2016
2281
2035
2690
2698
2818
25500
30200
45300
36500
62000
25000
53000
37100
46200
38200
16.85
17.06
17.86
18.91
2.48
3.34
2.72
3.61
3.51
4.28
3478
dx.doi.org/10.1021/jo3002722 | J. Org. Chem. 2012, 77, 3475−3482

The Journal of Organic Chemistry
Article
Table 5. Fluorescence Quantum Yields of All Compounds in Different Solvents and the Solid State
product
Φ (cyclohexane)
Φ (CH2Cl2)
Φ (EA)
Φ (CH3CN)
Φ (DMF)
Φ (CH3OH)
Φ(λf) (solid state)
1a
1b
1c
1d
2a
2b
4a
4b
4c
4d
0.717
0.486
0.310
0.338
0.926
0.694
0.931
0.852
0.635
0.699
0.325
0.312
0.240
0.292
0.916
0.688
0.829
0.827
0.653
0.673
0.233
0.231
0.195
0.202
0.885
0.601
0.685
0.733
0.634
0.627
0.023
0.030
0.018
0.020
0.554
0.445
0.627
0.608
0.51
0.023
0.030
0.013
0.015
0.296
0.370
0.37
0.002
0.002
0.002
0.002
0.222
0.279
0.294
0.428
0.396
0.430
0.42 (479)
0.58 (478)
0.33 (470)
0.62 (486)
0.44 (474, 501)
0.50 (486, 564)
0.48 (456)
0.60 (476)
0.09 (473)
0.44 (470)
0.562
0.51
0.493
0.483
peaks in the solid state, which may be due to the existence of
intermolecular interactions.24 Compounds 1c and 4c exhibited
weak emission in the solid state compared with the other
compounds probably because of well-ordered π stacking that
led to strong intermolecular interactions and fluorescence self-
quenching.25
Electrochemical and Thermal Properties. All of the
compounds displayed a one-electron reversible oxidation wave
(Figure S11). As shown in Table 6, the oxidation processes
restricted B3LYP/6-31 G (d) functions at the DFT level.
The calculated typical torsion angles of compounds 1a, 1b, 2b,
and 4a−4d are listed in Table 2. As expected, the result of
geometry optimizations is consistent with the experimental data
obtained from single-crystal structures. For 1b, the calculated
angle (2.49°) well agrees with the experimental data (2.83°).
Conversely, the calculated angle for 4c (26.33°) slightly
deviates from the corresponding experimental data (16.78°).
The discrepancy between the calculation results and exper-
imental data may have been caused by intermolecular
interactions in the latter. The calculated HOMOs and
LUMOs of all of the compounds are shown in Figures 4,
Table 6. Electrochemical and Thermal Data of the Dyes
a
b
c
d
e
f
g
Eox
product (V)
HOMO
(eV)
LUMO
(eV)
ΔEop
Tg
Tm
Td
(eV)
(°C) (°C)
(°C)
1a
1b
1c
1d
2a
2b
4a
4b
4c
4d
0.69
0.68
0.69
0.68
0.79
0.77
0.77
0.74
0.74
0.73
5.49
5.48
5.49
5.48
5.59
5.57
5.57
5.54
5.54
5.53
2.66
2.62
2.74
2.67
2.72
2.69
2.70
2.66
2.74
2.69
2.83
2.86
2.75
2.81
2.87
2.88
2.87
2.88
2.80
68
69
87
77
60
60
72
58
73
71
198
218
221
217
222
203
235
217
242
218
351
316
358
320
287
314
317
325
310
298
2.84
a
b
Obtained from cyclic voltammograms. Derived from the oxidation
c
potential using EHOMO = 4.8 + Eox. Deduced using the formula ELUMO
d
= EHOMO − ΔEop. Calculated from the optical edge measured in
e
f
CH3CN. Glass transition temperature. Melting point temperature.
g
Decomposition temperature.
occurred at slightly more positive potentials for 2a, 2b, and 4a−
4d (0.73−0.79 V) relative to those of 1a−1d (0.68−0.69 V).
The causes of the anodic shift for 2a, 2b, and 4a−4d may be
their efficient ICT character.26 The HOMOs (5.48−5.59 eV)
and LUMOs (2.62−2.74 eV) of all of the compounds are well
matched with those of the most commonly used hole transport
material α-naphthylphenylbiphenyl diamine (NPB, 5.50 eV)27
and electron transport material 1,3,5-tris(N-phenylbenzimida-
zol-2-yl)benzene (TPBI, 2.7 eV),28 respectively, suggesting
their potential applications as emitters in OLEDs. The thermal
behavior of all of the materials was determined through a
repeated heating−cooling cycle by differential scanning
calorimetry (Table 6). All of the compounds exhibited
moderate glass transition temperatures (Tg) varying from 58
to 87 °C, and thermal decomposition (Td) ranged from 287 to
358 °C.
Figure 4. Spatial distributions of calculated HOMOs and LUMOs of
compounds 1b and 2b.
S12, and S13. The density of all of the compounds in terms of
HOMOs and LUMOs was predominantly localized on the
tetracyclic structure. The C−C condensation products 1a−1d
exhibited stronger ICT character and effective electronic
communication between the diethylamino group and pyrazo-
lopyridine core. This result was previously confirmed by the
photophysical properties.
Photostability and Cell Imaging. To evaluate the
practical utility of the dyes, photostability studies were
performed by continuous irradiation of 1a and 2a (compared
with coumarin 151) using a 500 W high-pressure mercury lamp
Theoretical Basis. To investigate the geometric and
electronic properties of all of the compounds, quantum
calculations using the Gaussian 03 program have been
performed.29 The calculations were optimized using the
3479
dx.doi.org/10.1021/jo3002722 | J. Org. Chem. 2012, 77, 3475−3482

The Journal of Organic Chemistry
Article
as the light source. Photoinduced bleaching was quantified by
monitoring absorption intensity as a function of irradiation time
(Figure 5). Compound 1a exhibited greater photostability than
CONCLUSIONS
■
In this study, we developed a one-pot synthesis approach to the
construction of two different pyrazolo[3,4-b]pyridine-based
coumarin molecular skeleton, which showed high fluorescence
quantum yields in both less polar solvents and the solid state
with ICT character. The relationships between the chemical
structures and properties of these compounds were investigated
by X-ray diffraction, absorption spectroscopy, fluorescence
spectroscopy, single photon counting technique, cyclic
voltammetry, thermogravimetric analysis, and DFT calcula-
tions. This work provides a promising strategy for exploiting
pyrazolo[3,4-b]pyridine-based coumarin derivatives. In addi-
tion, laser scanning confocal microscopy experiments con-
firmed that these compounds can be successfully used in living
HeLa cells. Further development of pyrazolo [3,4-b]pyridine-
based coumarin chromophores in the red part of the spectrum
and their applications in organic electroluminescent devices or
chemosensors are in progress in our laboratory.
Figure 5. Photostability of compounds 1a, 2a, and coumarin 151 in
ethanol. Absorption intensity was measured at 373 nm for 1a, at 403
nm for 2a, and at 381 nm for coumarin 151.
EXPERIMENTAL SECTION
■
Materials and Methods. All commercial chemicals were used
without further purification. Single crystals of compounds 1a, 1b, 2b,
and 4a−4d suitable for X-ray crystallographic analysis were obtained
by slow diffusion of hexane into ethanol solution of the compounds at
ambient temperature. Data collection was done on an MM007-HF
CCD (Saturn 724+) diffractometer with Mo Kα radiation (λ =
0.71073 Å) at 173 K. 1H NMR and 13C NMR spectra were recorded at
400 and 100 MHz, respectively. Absorption and fluorescence spectra
of all compounds were obtained in a Hitachi U-3010 absorption
spectrometer and a Hitachi F-4500 fluorescence spectrometer at 25
°C, respectively. The stock solutions of all compounds were prepared
in CH2Cl2 (1.0 × 10−3 M). All fluorescence spectra were recorded
under 350 nm excitation. Fluorescence quantum yields were measured
using coumarin 151 in hexane as the reference (Φf = 0.19).30 All cyclic
voltammetry (CV) measurements were recorded in CH3CN with 0.1
M tetrabutylammonium hexafluorophosphate as supporting electrolyte
(scan rate 100 mV/s). The experiments were performed at room
temperature with a conventional three-electrode configuration
consisting of a glass carbon working electrode, a platinum wire
counter electrode, and a nonaqueous Ag/AgCl reference electrode.
The working electrode was polished with a 0.05 μm alumina paste and
sonicated for 2 min before use. The electrolyte solution was degassed
by bubbling with argon for 15 min before measurement. HeLa cells
(gifted from the center of cells, Peking Union Medical College) were
cultured in confocal dishes in culture media (Dulbecco’s modified
Eagle medium (DMEM) supplemented with 10% fetal bovine serum
(FBS), 50 unit/mL penicillin, and 50 mg/mL of streptomycin) under
5% carbon dioxide/air at 37 °C in a humidified incubator. After 24 h,
the cells were incubated with dyes 1a (10 μM) and 2a (50 nM) for 20
min. The stock solutions of 1a (1.0 × 10−3 M) and 2a (1.0 × 10−5 M)
were prepared in CH2Cl2. The cells were washed with PBS (phosphate
buffered saline) at least five times, and their fluorescence images were
taken by confocal fluorescence microscopy.
2a and commercial dye coumarin 151. After 2 h of continuous
ultraviolet irradiation, the absorbance of 1a remained stable,
whereas that of 2a dropped by 28.7%, which was comparable to
that of coumarin 151 (28.3%). We tested 1a and 2a for
bioimaging in HeLa cells. As shown in Figure 6, intense
Figure 6. Confocal fluorescence images of living HeLa cells with 1a
(10 μM) and 2a (50 nM).
intracellular blue fluorescence was observed in the cytosol of
HeLa cells after being incubated with dyes 1a (10 μM) and 2a
(50 nM) for 20 min. The high fluorescence quantum yields
were sufficient for highly fluorescent cell staining for only 50
nM for dye 2a. The blue fluorescence of 1a may have
originated from the aggregation of the dye, as evidenced by the
corresponding emission spectra of 1a in aqueous ethanol with
different ethanol/water ratios. Figure S14 illustrates that
increasing water content in ethanol caused the peak of emission
spectra to move from 572 to 480 nm. This result is consistent
with fluorescence in the solid state (479 nm). The above-
mentioned results reveal that the tetracyclic PPC derivatives 1a
and 2a can efficiently penetrate the cell membrane and
specifically label cytosol.
Synthesis of 3-Aldehyde-7-diethylaminocoumarin (5). Com-
pound 5 was synthesized according to our previously reported
work:12a 1H NMR (400 MHz, CDCl3) δ 10.13 (s, 1H), 8.26 (s, 1H),
7.43 (d, 1H), 6.67 (d, 1H), 6.50 (s, 1H), 3.49 (m, 4H), 1.25 (t, 6H).
Synthesis of 3-Acetyl-7-diethylaminocoumarin (6). 4-Dieth-
ylaminosalicylaldehyde (1.12 g, 5.8 mmol), diethylmalonate (1 mL, 7.9
mmol), and morpholine (0.25 mL) were added into anhydrous
ethanol (15 mL). The mixture was refluxed for 2 h, and 6 was obtained
1
by filtration as a yellow solid (1.2 g, 80%): H NMR (400 MHz,
CDCl3) δ 8.42 (s, 1H), 7.40−7.38 (d, 1H), 6.63−6.60 (q, 1H), 6.47−
6.46 (d, 1H), 3.48−3.42 (q, 4H), 2.67 (s, 3H), 1.25−1.22 (t, 6H).
Synthesis of Compounds 1a, 2a, 9, and 10. Compounds 5 (0.5
g, 2.04 mmol) and 7a (0.39 g, 2.45 mmol) were added into anhydrous
ethanol (50 mL). The mixture was refluxed for 8 h. Then the solvent
3480
dx.doi.org/10.1021/jo3002722 | J. Org. Chem. 2012, 77, 3475−3482

The Journal of Organic Chemistry
Article
1
was removed under vacuum, and the products were purified by
column chromatography using v(EA)/v(petroleum ether, PA) = 1:15
as the eluent.
Rf = 0.54 in EA/PA = 1:4; H NMR (400 MHz, CDCl3) δ 9.25 (s,
1H), 8.52−8.49 (d, 2H), 8.41−8.38 (d, 1H), 8.10−8.08 (d, 2H),
7.61−7.54 (m, 4H), 7.52−7.50 (m, 1H), 7.39−7.35 (m, 1H), 6.76−
6.74 (d, 1H), 6.54 (s, 1H), 3.48−3.43 (q, J = 7.08 Hz, 4H), 1.27−1.23
(t, J = 7.04 Hz, 6H); 13C NMR (100 MHz, CDCl3) δ 162.6, 155.0,
153.1, 152.0, 151.3, 146.2, 139.4, 135.2, 131.9, 129.5, 129.2, 129.1,
127.6, 126.5, 126.2, 121.1, 114.7, 111.1, 109.3, 107.4, 97.8, 45.0, 12.7;
9-Diethylamino-2-phenyl-[1]benzopyrano[2,3-e]pyrazolo[3,4-b]-
pyridine-6-one (1a): Yellow solid (0.39 g, 50%); mp 224−225 °C; Rf
= 0.46 in EA/PA = 1:4; 1H NMR (400 MHz, CDCl3) δ 9.01 (s, 1H),
8.44−8.41 (m, 3H), 8.31 (s, 1H), 7.61−7.57 (m, 2H), 7.39−7.36 (m,
1H), 6.77−6.75 (d, 1H), 6.57 (s, 1H), 3.49−3.44 (q, J = 7.04 Hz, 4H),
1.27−1.24 (t, J = 7.04 Hz, 6H); 13C NMR (100 MHz, CDCl3) δ 162.4,
155.0, 152.2, 152.0, 151.3, 139.4, 136.0, 134.8, 129.2, 126.5, 126.3,
121.1, 116.4, 111.2, 109.3, 107.5, 97.9, 45.0, 12.7; SIMS-HRMS m/z
calcd for [C23H20N4O2 + H]+ 385.1659, found 385.1658.
+
SIMS-HRMS m/z calcd for C29H24N4O2 460.1894, found 460.1893.
Synthesis of 9-Diethylamino-2-methyl-4-phenyl-[1]-
benzopyrano[2,3-e]pyrazolo[3,4-b]pyridine-6-one (1d). Com-
pounds 5 (0.22 g, 0.90 mmol) and 7d (0.18 g, 1.04 mmol) were added
into anhydrous ethanol (15 mL). The mixture was refluxed for 8 h,
and 1d was obtained by filtration as a yellow solid (0.27 g, 76%): mp
219−220 °C; Rf = 0.46 in EA/PA = 1:4; 1H NMR (400 MHz, CDCl3)
δ 9.24 (s, 1H), 8.47−8.45 (d, 1H), 8.02−8.00 (d, 2H), 7.55−7.52 (m,
2H), 7.48−7.44 (m, 1H), 6.80 (s, 1H), 6.62 (s, 1H), 4.25 (s, 3H),
3.49−3.44 (q, J = 7.04 Hz, 4H), 1.28−1.24 (t, J = 7.04 Hz, 6H); 13C
NMR (100 MHz, CDCl3) δ 162.9, 154.8, 153.4, 151.6, 151.2, 144.8,
135.3, 132.3, 129.1, 129.0, 127.1, 126.1, 112.8, 110.5, 109.0, 107.3,
97.7, 44.9, 34.0, 12.6; SIMS-HRMS m/z calcd for [C24H22N4O2 + H]+
399.1816, found 399.1809.
Synthesis of 9-Diethylamino-5-methyl-3-phenyl-[1]-
benzopyrano[4,3-d]pyrazolo[3,4-b]pyridine-6-one (4a). Com-
pounds 6 (1.06 g, 4.09 mmol) and 7a (0.64 g, 4.03 mmol) were added
into anhydrous ethanol (50 mL). The mixture was refluxed for 15 h,
and 4a was obtained by filtration as a yellow solid (0.31 g, 19%): mp
240−241 °C; Rf = 0.39 in EA/PA = 1:4; 1H NMR (400 MHz, CDCl3)
δ 8.68 (s, 1H), 8.30−8.28 (m, 2H), 8.23−8.21 (m, 1H), 7.57−7.53 (m,
2H), 7.38−7.35 (m, 1H), 6.81−6.78 (m, 1H), 6.59−6.58 (m, 1H),
3.50−3.45 (q, J = 7.08 Hz, 4H), 3.12 (s, 3H), 1.29−1.25 (t, J = 7.12
Hz, 6H); 13C NMR (100 MHz, CDCl3) δ 164.1, 160.7, 155.6, 151.3,
150.5, 140.8, 139.1, 134.8, 129.1, 128.0, 126.7, 122.0, 109.4, 108.5,
107.6, 105.3, 97.8, 45.0, 28.6, 12.6; SIMS-HRMS m/z calcd for
9-Diethylamino-3-phenyl-[1]benzopyrano[4,3-d]pyrazolo[3,4-b]-
pyridine-6-one (2a): Yellow solid (0.18 g, 23%); mp 201−202 °C; Rf
= 0.29 in EA/PA = 1:4; 1H NMR (400 MHz, CDCl3) δ 9.40 (s, 1H),
8.73 (s, 1H), 8.22−8.20 (m, 3H), 7.59−7.55 (m, 2H), 7.42−7.38 (m,
1H), 6.83−6.80 (m, 1H), 6.63−6.62 (m, 1H), 3.52−3.46 (q, J = 7.12
Hz, 4H), 1.30−1.26 (t, J = 7.12 Hz, 6H); 13C NMR (100 MHz,
CDCl3) δ 161.3, 155.8, 152.4, 152.0, 151.5, 139.1, 138.9, 134.7, 129.2,
127.9, 127.1, 122.4, 109.6, 109.1, 108.5, 104.8, 98.3, 45.1, 12.6; SIMS-
HRMS m/z calcd for [C23H20N4O2 + H]+ 385.1659, found 385.1656.
3-Bis(5-amino-1-phenylpyrazole-4-yl)methyl-7-diethylaminocou-
marin (9): Filemot solid (85 mg, 8%); mp 119−120 °C; Rf = 0.18 in
1
EA/PA = 2:1; H NMR (400 MHz, CDCl3) δ 7.61−7.57 (m, 5H),
7.51−7.47 (m, 6H), 7.38−7.34(m, 2H), 7.28−7.26 (m, 1H), 6.61−
6.59 (m, 1H), 6.52−6.51 (m, 1H), 5.16 (s, 1H), 3.98 (b, 4H), 3.45−
3.39 (q, J = 7.04 Hz, 4H), 1.23−1.19 (t, J = 7.04 Hz, 6H); 13C NMR
(100 MHz, CDCl3) δ 163.6, 155.7, 150.4, 142.3, 140.1, 139.6, 138.8,
129.6, 128.9, 127.5, 124.0, 123.1, 109.1, 108.8, 103.7, 97.3, 44.9, 30.5,
12.5; SIMS-HRMS m/z calcd for [C32H31N7O2 + H]+ 546.2612, found
546.2619.
(Z)-7-Diethylamino-3-(1-phenylpyrazole-5-ylimino)-
methylcoumarin (10): Red solid (40 mg, 5%); mp 206−208 °C; Rf =
1
0.49 in EA/PA = 1:2; H NMR (400 MHz, CDCl3) δ 8.89 (s, 1H),
+
C24H22N4O2 398.1737, found 398.1742.
8.37 (s, 1H), 7.76−7.74 (m, 2H), 7.65−7.64 (m, 1H), 7.55−7.46 (m,
2H), 7.42−7.33 (m, 2H), 6.63−6.60 (m, 1H), 6.51−6.50 (m, 1H),
6.38−6.37 (m, 1H), 3.47−3.43 (q, J = 7.12 Hz, 4H), 1.27−1.23 (t, J =
7.12 Hz, 6H); 13C NMR (100 MHz, CDCl3) δ 162.2, 157.9, 155.3,
152.4, 150.5, 141.7, 140.3, 139.7, 131.3, 128.6, 126.8, 124.5, 114.7
109.9, 108.9, 97.3, 93.9, 45.2, 12.6; SIMS-HRMS m/z calcd for
[C23H22N4O2 + H]+ 387.1816, found 387.1821.
Synthesis of Compounds 1b and 2b. Compounds 5 (0.35 g,
1.43 mmol) and 7b (0.31 g, 1.79 mmol) were added into anhydrous
ethanol (40 mL). The mixture was refluxed for 8 h, and 1b was
obtained by filtration. Then the solvent of filtrate was removed under
vacuum, and 2b was purified by column chromatography using v(EA)/
v(PA) = 1:15 as the eluent.
Synthesis of 9-Diethylamino-1,5-dimethyl-3-phenyl-[1]-
benzopyrano[4,3-d]pyrazolo[3,4-b]pyridine-6-one (4b). Com-
pounds 6 (110.1 mg, 0.43 mmol) and 7b (96.2 mg, 0.56 mmol) were
added into anhydrous ethanol (15 mL). The mixture was refluxed for
15 h, and 4b was obtained by filtration as a yellow solid (40 mg, 23%):
1
mp 219−220 °C; Rf = 0.50 in EA/PA = 1:4; H NMR (400 MHz,
CDCl3) δ 8.26−8.24 (m, 2H), 8.13−8.11 (d, 1H), 7.55−7.51 (m, 2H),
7.35−7.32 (m, 1H), 6.81−6.78 (d, 1H), 6.64−6.63 (m, 1H), 3.51−
3.46 (q, J = 7.08 Hz, 4H), 3.09 (s, 3H), 2.90 (s, 3H), 1.29−1.26 (t, J =
7.08 Hz, 6H); 13C NMR (100 MHz, CDCl3) δ 163.5, 160.9, 155.3,
151.9, 150.6, 143.3, 143.0, 139.0, 130.7, 129.1, 126.5, 122.2, 108.9,
108.4, 106.0, 98.6, 45.6, 28.3, 19.4, 12.5; SIMS-HRMS m/z calcd for
+
C25H24N4O2 412.1894, found 412.1891.
9-Diethylamino-4-methyl-2-phenyl-[1]benzopyrano[2,3-e]-
pyrazolo[3,4-b]pyridine-6-one (1b): Yellow solid (0.39 g, 69%); mp
218−220 °C; Rf = 0.43 in EA/PA = 1:4; 1H NMR (400 MHz, CDCl3)
δ 8.92 (s, 1H), 8.41−8.38 (m, 3H), 7.58−7.53 (m, 2H), 7.35−7.31 (m,
1H), 6.76−6.74 (d, 1H), 6.56 (s, 1H), 3.49−3.43 (q, J = 7.12 Hz, 4H),
2.67 (s, 3H), 1.27−1.23 (t, J = 7.12 Hz, 6H); 13C NMR (100 MHz,
CDCl3) δ 162.6, 155.0, 152.6, 152.1, 150.9, 145.1, 139.4, 134.0, 129.1,
126.5, 125.9, 120.7, 116.7, 110.3, 109.6, 108.0, 98.3, 45.3, 12.6; SIMS-
HRMS m/z calcd for [C24H22N4O2 + H]+ 399.1816, found 399.1810.
9-Diethylamino-1-methyl-3-phenyl-[1]benzopyrano[4,3-d]-
pyrazolo[3,4-b]pyridine-6-one (2b): Yellow solid (7.2 mg, 1%); mp
211−213 °C; Rf = 0.32 in EA/PA = 1:4; 1H NMR (400 MHz, CDCl3)
δ 9.34 (s, 1H), 8.32−8.30 (d, 1H), 8.15−8.13 (m, 2H), 7.56−7.52 (m,
2H), 7.38−7.34 (m, 1H), 6.77−6.74 (m, 1H), 6.62−6.61 (m, 1H),
3.50−3.45 (q, J = 7.08 Hz, 4H), 3.00 (s, 3H), 1.29−1.25 (t, J = 7.08
Hz, 6H); 13C NMR (100 MHz, CDCl3) δ 161.7, 155.7, 153.5, 152.3,
151.0, 143.1, 141.4, 138.7, 130.2, 129.3, 127.0, 122.7, 109.2, 109.0,
108.9, 105.3, 99.0, 45.3, 20.0, 12.6; GCT-MS m/z calcd for
Synthesis of 9-Diethylamino-5-methyl-1,3-diphenyl-[1]-
benzopyrano[4,3-d]pyrazolo[3,4-b]pyridine-6-one (4c). Com-
pounds 6 (418.5 mg, 1.71 mmol) and 7c (362.5 mg, 1.54 mmol)
were added into anhydrous ethanol (15 mL). The mixture was
refluxed for 15 h, and 4c was obtained by filtration as a yellow solid
(124 mg, 17%): mp 252−253 °C; Rf = 0.51 in EA/PA = 1:4; 1H NMR
(400 MHz, CDCl3) δ 8.36−8.34 (d, 2H), 7.61−7.53 (m, 4H), 7.46−
7.42 (m, 3H), 7.38−7.35 (m, 1H), 7.10−7.08 (d, J = 9.16 Hz, 1H),
6.53 (s, 1H), 6.03−6.01 (d, J = 8.88 Hz, 1H), 3.39−3.33 (q, J = 7.08
Hz, 4H), 3.15 (s, 3H), 1.19−1.15 (t, J = 7.08 Hz, 6H); 13C NMR (100
MHz, CDCl3) δ 163.9, 161.0, 155.3, 152.0, 150.9, 147.5, 143.1, 139.1,
134.9, 132.8, 129.7, 129.1, 128.8, 128.6, 126.8, 122.5, 108.6, 107.4,
106.5, 104.3, 97.3, 45.1, 28.3, 12.5; SIMS-HRMS m/z calcd for
+
C30H26N4O2 474.2050, found 474.2052.
Synthesis of 9-Diethylamino-3,5-dimethyl-1-phenyl-[1]-
benzopyrano[4,3-d]pyrazolo[3,4-b]pyridine-6-one (4d). Com-
pounds 6 (302.5 mg, 1.23 mmol) and 7d (222.4 mg, 1.29 mmol) were
added into anhydrous ethanol (15 mL). The mixture was refluxed for
15 h, and 4d was obtained by filtration as a yellow solid (107 mg,
+
C24H22N4O2 398.1737, found 398.1749.
Synthesis of 9-Diethylamino-2,4-diphenyl-[1]benzopyrano-
[2,3-e]pyrazolo[3,4-b]pyridine-6-one (1c). Compounds 5 (0.22 g,
0.90 mmol) and 7c (0.28 g, 0.12 mmol) were added into anhydrous
ethanol (20 mL). The mixture was refluxed for 8 h, and 1c was
obtained by filtration as a yellow solid (0.31 g, 75%): mp 221−222 °C;
1
22%): mp 220−221 °C; Rf = 0.34 in EA/PA = 1:4; H NMR (400
MHz, CDCl3) δ 7.52−7.49 (m, 2H), 7.43−7.40 (m, 3H), 7.08−7.06
(d, J = 9.12 Hz, 1H), 6.48 (s, 1H), 5.99−5.96 (d, J = 9.16 Hz, 1H),
4.24 (s, 3H), 3.37−3.32 (q, J = 7.12 Hz, 4H), 3.13 (s, 3H), 1.18−1.14
3481
dx.doi.org/10.1021/jo3002722 | J. Org. Chem. 2012, 77, 3475−3482

The Journal of Organic Chemistry
Article
(t, J = 7.08 Hz, 6H); 13C NMR (100 MHz, CDCl3) δ 163.3, 161.2,
155.3, 152.0, 151.0, 146.3, 143.2, 135.2, 132.7, 129.6, 128.6, 107.8,
107.2, 104.8, 104.2, 97.0, 44.9, 34.3, 28.1, 12.6; SIMS-HRMS m/z
(11) Ruiz, M.; Lopez-Alvarado, P.; Giorgi, G.; Menendez, J. C. Chem.
Soc. Rev. 2011, 40, 3445.
(12) (a) Wu, J. S.; Liu, W. M.; Zhuang, X. Q.; Wang, F.; Wang, P. F.;
Tao, S. L.; Zhang, X. H.; Wu, S. K.; Lee, S. T. Org. Lett. 2006, 9, 33.
(b) Lee, S.; Sivakumar, K.; Shin, W. S.; Xie, F.; Wang, Q. Bioorg. Med.
Chem. Lett. 2006, 16, 4596.
(13) (a) Chen, T.; Xu, X. P.; Ji, S. J. J. Comb. Chem. 2010, 12, 659.
(b) Chen, H.; Shi, D. Q. J. Comb. Chem. 2010, 12, 571.
(14) Saiz, C.; Wipf, P.; Mahler, G. J. Org. Chem. 2011, 76, 5738.
(15) Kleinpeter, E.; Lammermann, A.; Kuhn, H. Org. Biomol. Chem.
2011, 9, 1098.
(16) Bai, H. T.; Lin, H. C.; Luh, T. Y. J. Org. Chem. 2010, 75, 4591.
(17) Kolosov, D.; Adamovich, V.; Djurovich, P.; Thompson, M. E.;
Adachi, C. J. Am. Chem. Soc. 2002, 124, 9945.
+
calcd for C25H24N4O2 412.1894, found 412.1891.
ASSOCIATED CONTENT
* Supporting Information
■
S
X-ray structure details for 1a, 1b, 2b, 4a−4d, and 9 (CIF);
photophysical data; electrochemical data; theoretical calcula-
tions and 1H NMR and 13C NMR spectra for new compounds.
This material is available free of charge via the Internet at
http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: wangpf@mail.ipc.ac.cn.
(18) Machado, A. E. D.; de Miranda, J. A. J. Photochem. Photobiol., A
2001, 141, 109.
■
(19) Du, C. Y.; Chen, J. M.; Guo, Y. L.; Lu, K.; Ye, S. H.; Zheng, J.;
Liu, Y. Q.; Shuai, Z. G.; Yu, G. J. Org. Chem. 2009, 74, 7322.
(20) Palsson, L. O.; Wang, C. S.; Batsanov, A. S.; King, S. M.; Beeby,
A.; Monkman, A. P.; Bryce, M. R. Chem.Eur. J. 2010, 16, 1470.
(21) Moss, K. C.; Bourdakos, K. N.; Bhalla, V.; Kamtekar, K. T.;
Bryce, M. R.; Fox, M. A.; Vaughan, H. L.; Dias, F. B.; Monkman, A. P.
J. Org. Chem. 2010, 75, 6771.
Author Contributions
§J.C. and W.L. contributed equally to this paper.
Notes
The authors declare no competing financial interest.
(22) Estrada, L. A.; Neckers, D. C. J. Org. Chem. 2009, 74, 8484.
(23) Shao, J. J.; Guan, Z. P.; Yan, Y. L.; Jiao, C. J.; Xu, Q. H.; Chi, C.
Y. J. Org. Chem. 2011, 76, 780.
(24) Levitus, M.; Zepeda, G.; Dang, H.; Godinez, C.; Khuong, T.-A.
V.; Schmieder, K.; Garcia-Garibay, M. A. J. Org. Chem. 2001, 66, 3188.
(25) Wolak, M. A.; Melinger, J. S.; Lane, P. A.; Palilis, L. C.; Landis,
C. A.; Delcamp, J.; Anthony, J. E.; Kafafi, Z. H. J. Phys. Chem. B 2006,
110, 7928.
(26) Tang, X. L.; Liu, W. M.; Wu, J. S.; Lee, C. S.; You, J. J.; Wang, P.
F. J. Org. Chem. 2010, 75, 7273.
(27) (a) Zhang, Q. M.; Lei, Y. L.; Song, Q. L.; Chen, P.; Zhang, Y.;
Xiong, Z. H. Appl. Phys. Lett. 2011, 98, 243303. (b) Li, N.; Wang, P.
F.; Lai, S.-L.; Liu, W. M.; Lee, C. S.; Lee, S. T.; Liu, Z. T. Adv. Mater.
2010, 22, 527.
ACKNOWLEDGMENTS
■
This work is financially supported by the National Natural
Science Foundation of China (Grant Nos. 61178061,
20903110), the National High Technology Research and
Development Program of China (863 Program) (Grant No.
2011AA03A110), and the Beijing Natural Science Foundation
(Grant No. 2111002).
REFERENCES
■
(1) Schmidt, R. D.; Oh, J. H.; Sun, Y.-S.; Deppisch, M.; Krause, A.-
M.; Radacki, K.; Braunschweig, H.; Konemann, M.; Erk, P.; Bao, Z.;
Wurthner, F. J. Am. Chem. Soc. 2009, 131, 6215.
(2) Karuppannan, S.; Chambron, J. C. Chem.Asian J. 2011, 6, 964.
(3) (a) Wang, P. F.; Xie, Z. Y.; Hong, Z. R.; Tang, J. X.; Wong, O. Y.;
Lee, C. S.; Wong, N. B.; Lee, S. T. J. Mater. Chem. 2003, 13, 1894.
(b) Wang, P. F.; Xie, Z. Y.; Wong, O. Y.; Lee, C. S.; Wong, N. B.;
Hung, L. S.; Lee, S. T. Chem. Commun. 2002, 1404.
̈
̈
(28) (a) Yeh, T. S.; Chow, T. J.; Tsai, S. H.; Chiu, C. W.; Zhao, C. X.
Chem. Mater. 2006, 18, 832. (b) Thomas, K. R. J.; Lin, J. T.; Tao, Y.
T.; Chuen, C. H. Chem. Mater. 2004, 16, 5437.
(29) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.;
Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.;
Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.;
Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.;
Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao,
O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J.
B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R.
E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.;
Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J.
J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.;
Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman,
J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.;
Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.;
Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.;
Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen,
W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03; Gaussian,
Inc.: Wallingford, CT, 2004.
́
(4) (a) Svetlik, J.; Veizerova, L.; Mayer, T. U.; Catarinella, M. Bioorg.
Med. Chem. Lett. 2010, 20, 4073. (b) Chioua, M.; Samadi, A.; Soriano,
E.; Lozach, O.; Meijer, L.; Marco-Contelles, J. Bioorg. Med. Chem. Lett.
2009, 19, 4566.
(5) (a) Mac, M.; Uchacz, T.; Danel, A.; Danel, K.; Kolek, P.; Kulig, E.
J. Fluoresc. 2011, 21, 375. (b) Gondek, E.; Nizioł, J.; Danel, A.;
Szlachcic, P.; Plucinski, K.; Sanetra, J.; Kityk, I. V. Spectrochim. Acta,
́
Part A 2010, 75, 1501. (c) Rurack, K.; Danel, A.; Rotkiewicz, K.;
Grabka, D.; Spieles, M.; Rettig, W. Org. Lett. 2002, 4, 4647.
(6) Tao, Y. T.; Chuen, C. H.; Ko, C. W.; Peng, J. W. Chem. Mater.
2002, 14, 4256.
(7) (a) Dekic, B. R.; Radulovic, N. S.; Dekic, V. S.; Vukicevic, R. D.;
Palic, R. M. Molecules 2010, 15, 2246. (b) Chia, Y. C.; Chang, F. R.;
Wang, J. C.; Wu, C. C.; Chiang, M. Y. N.; Lan, Y. H.; Chen, K. S.; Wu,
Y. C. Molecules 2008, 13, 122. (c) El-Seedi, H. R. J. Nat. Prod. 2007,
70, 118.
(8) (a) Zhang, H.; Yu, T. Z.; Zhao, Y. L.; Fan, D. W.; Xia, Y. J.;
Zhang, P. Synth. Met. 2010, 160, 1642. (b) Yu, T. Z.; Zhang, P.; Zhao,
Y. L.; Zhang, H.; Meng, J.; Fan, D. W.; Chen, L. L.; Qiu, Y. Q. Org.
Electron. 2010, 11, 41. (c) Liu, Z. W.; Helander, M. G.; Wang, Z. B.;
Lu, Z. H. J. Phys. Chem. C 2010, 114, 11931.
(30) Rechthaler, K.; Kohler, G. Chem. Phys. 1994, 189, 99.
(9) (a) Voutsadaki, S.; Tsikalas, G. K.; Klontzas, E.; Froudakis, G. E.;
Katerinopoulos, H. E. Chem. Commun. 2010, 46, 3292. (b) Shao, J.
Dyes Pigm. 2010, 87, 272.
(10) (a) Raikar, U. S.; Tangod, V. B.; Mannopantar, S. R.; Mastiholi,
B. M. Opt. Commun. 2010, 283, 4289. (b) Mannekutla, J. R.;
Mulimani, B. G.; Inamdar, S. R. Spectrochim. Acta, Part A 2008, 69,
419.
3482
dx.doi.org/10.1021/jo3002722 | J. Org. Chem. 2012, 77, 3475−3482