A multi-addressable molecular switch based on a novel diarylethene with an imidazo [4,5-f] [1,10] phenanthroline unit

Article abstract of DOI:10.1002/poc.3257

A novel unsymmetrical diarylethene with an imidazo [4,5-f] [1,10] phenanthroline unit has been synthesized, and its properties including photochromism and fluorescence have been investigated. It showed favorable photochromism and functioned as notable fluorescence switches by photoirradiation in both solution and a poly (methylmethacrylate) film. Moreover, the interaction between the phenanthroline unit of its closed-ring isomer with trifluoroacetic acid caused a notable change in its absorption, accompanied by an evident color change from magenta to slateblue. Its fluorescence could be modulated by trifluoroacetic acid and triethylamine. By adding enough amount of trifluoroacetic acid in chloroform, its emission peak hypochromatic shifted from 501 nm to 456 nm, and the intensity increased significantly with a concomitant change of color from bright cyan to bright blue. However, its emission intensity decreased notably by 95% with a fluorescence color change from bright cyan to dark gray by the addition of triethylamine. Copyright

Full text of DOI:10.1002/poc.3257

Research Article
Received: 28 July 2013,
Revised: 2 November 2013,
Accepted: 8 November 2013,
Published online in Wiley Online Library: 17 December 2013
(wileyonlinelibrary.com) DOI: 10.1002/poc.3257
A multi-addressable molecular switch based on
a novel diarylethene with an imidazo [4,5-f]
[1,10] phenanthroline unit
Panpan Rena, Renjie Wanga, Shouzhi Pua*, Gang Liua and Congbin Fana
A novel unsymmetrical diarylethene with an imidazo [4,5-f] [1,10] phenanthroline unit has been synthesized, and its properties
including photochromism and fluorescence have been investigated. It showed favorable photochromism and functioned as no-
table fluorescence switches by photoirradiation in both solution and a poly (methylmethacrylate) film. Moreover, the interaction
between the phenanthroline unit of its closed-ring isomer with trifluoroacetic acid caused a notable change in its absorption,
accompanied by an evident color change from magenta to slateblue. Its fluorescence could be modulated by trifluoroacetic acid
and triethylamine. By adding enough amount of trifluoroacetic acid in chloroform, its emission peak hypochromatic shifted from
501nm to 456nm, and the intensity increased significantly with a concomitant change of color from bright cyan to bright blue.
However, its emission intensity decreased notably by 95% with a fluorescence color change from bright cyan to dark gray by the
addition of triethylamine. Copyright © 2013 John Wiley & Sons, Ltd.
Keywords: photochromism; diarylethene; phenanthroline; molecular switches; chemical stimuli
transmembrane transport.[34] Irie et al. reported that a digital
switch based on a diarylethene skeleton could be controlled at
INTRODUCTION
Photochromic materials have attracted much attention as most
promising candidates for optical memories, photo-switches, logic
circuit, and chemical sensors.[1–7] Among all photochromic
compounds, diarylethene derivatives are one of the most
attractive families because of their excellent thermal stability,[8–10]
remarkable fatigue resistance,[11–13] and non-destructive.[14,15]
Upon irradiation with different wavelength lights, photochromic
compounds are capable of undergoing clean interconversions
between two perceptibly different states. Such changes have
already led to their applications in a wide variety of consumer
products such as toys, cosmetic products, photochromic inks for
security markings, ophthalmic and sunglass lenses, optical
filters,[2,16] and so on. In the past several decades, many new
diarylethene systems with different heteroaryl moieties were
explored. Among them, most of the central ethene containing
bridging units were 3-benzothienyl[17,18] and 2-thienyl[19] groups,
with just a few reports concerning other heteroaryl moieties, such
as 3-pyrolyl,[20] 4-thiazolyl,[21,22] 4-oxazolyl,[23] 4-pyrazolyl,[24]
3-indolyl,[25,26] furan,[27] benzofuran,[28] and so on. Benzofuran is a
fascinating aryl because of its relative lower aromatic stabilization
energy that can be potential to improve the thermal stability of
diarylethenes.[29] Although many diarylethene derivatives have
hitherto been reported, unsymmetrical diarylethenes with a
benzofuran moiety are relatively rare.
the single-molecule level by photoirradiation.[35] In a previous
work, we found that diarylethenes with a rhodamine unit
exhibited multi-addressable fluorescent switching characteristics
by chemical and optic dual inputs stimuli.[36] As mentioned in the
previous text, these molecular switches mainly relies on the inte-
gration of fluorescent dye and photochromic diarylethene into
one molecular skeleton, in which the photochromic diarylethene
component is attached covalently to the fluorescent partner. This
is an efficient strategy to construct fluorescent molecular
switches at the present stage.
Phenanthroline is an intriguing compound as fluorescence
ligand because its nitrogen atoms in 1 and 10 positions can co-
ordinate with transition metals. Yam and coworkers developed
a
series of photochromic 5,6-dithienyl-1,10-phenanthroline
ligands,[37] which could be coordinated with different metal
centers to tune the photochromism with a wide variety of differ-
ent metal complexes.[38–41] In addition, the phenanthroline can
be modified to form imidazo [4,5-f] [1,10] phenanthroline
compounds, in which the NH group in imidazole ring is able to
act as fluorimetric sensor for anions.[42] For instance, Wang
et al. reported a Eu(III) complex containing imidazo [4,5-f] [1,10]
phenanthroline, in which the addition of F–, HSO4–, and AcO–
caused significant changes in the absorption and emission
spectra.[43] Zheng et al. developed a chemosensor based on
polypyridyl metal complex with a terpyridine/phenyl imidazo
Generally, diarylethene derivatives undergo a reversible trans-
formation from the open-ring isomer to the closed-ring isomer,
which accompanied by decreasing and recovering of fluores-
cence emission intensity. Based on the reversible changes in their
fluorescence by external stimuli, the corresponding networks, in-
cluding diarylethene[30] and some other complex systems,[31–33]
have been constructed. For example, Piao et al. developed a
multi-responsive fluorescent molecular switch containing
* Correspondence to: S. Z. Pu, Jiangxi Key Laboratory of Organic Chemistry,
Jiangxi Science and Technology Normal University, Nanchang 330013, China.
E-mail: pushouzhi@tsinghua.org.cn
a P. Ren, R. Wang, S. Pu, G. Liu, C. Fan
Jiangxi Key Laboratory of Organic Chemistry, Jiangxi Science and Technology
Normal University, Nanchang, China
terpyridine that can serve as
a detector for metal-ion
J. Phys. Org. Chem. 2014, 27 183–190
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P. REN ET AL.
[4,5-f]-phenanthroline hybrid that functioned as an effective
detector for dihydrogen phosphate anion and ferrous cation.[44]
In this work, we developed a new hybrid photochromic
diaylethene with an imidazo [4,5-f] [1,10] phenanthroline
unit, in which the fluorescent phenanthroline partner was
directly linked to the diarylethene moiety by a C–C σ bond.
The synthesized diarylethene is 1-(2-methyl-3-benzofuranyl)-2-
[5-(4-(1H-imidazo [4,5-f] [1,10] phenanthroline-2-yl)phenyl)-2-
methylthien-3-yl]perfluorocyclopentene (1O). The molecular
structures and photochromic scheme of diarylethene 1 is shown
in Scheme 1.
1O. The structures of 1O and 2O were confirmed by elemental
analysis, nuclear magnetic resonance (NMR), and infrared (IR)
(Experimental Section).
Photochromism of diarylethenes
As shown in Fig. 1(A), 1O exhibited a sharp absorption peak at
355 nm (ε, 3.46 × 104 L molÀ1 cmÀ1) in chloroform, which was
ascribed to the π → π* transition.[47] Upon irradiation with
365 nm light, the colorless solution of 1O turned magenta and
a new visible absorption band was observed at 546 nm
(ε, 2.08 × 104 L molÀ1 cmÀ1) because of the formation of the
closed-ring isomer 1C. Alternatively, the colored solution was
bleached entirely by irradiation with visible light (λ > 450 nm),
and the absorption spectrum returned to the initial state. When
arrived at the photostationary state, a clear isosbestic point of
diarylethene 1O was observed at 372 nm, which supported the
reversible two component photochromic reaction scheme.[48]
The photochromic parameters of 1 and precursor 2 in both
chloroform and poly methyl-methacrylate (PMMA) films are
summarized in Table 1. Compared with 2, the molar absorption
coefficients of both the open-ring and closed-ring isomers of 1
RESULTS AND DISCUSSION
Synthesis of diarylethenes
The synthetic route for diarylethene 1O is shown in Scheme 2.
First, the diarylethene aldehyde derivative 2O was prepared by
the reported method.[45,46] Then, 2O was separately cyclized
with 1,10-phenanthroline-5,6-dione (9) to give the asymmetric
diarylethene 1O. Finally, the raw product was obtained by
filtration, and then recrystallized from methanol to give the pure
Scheme 1. Photochromism of diarylethene 1
Scheme 2. Synthetic route for diarylethene 1O
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A NEW MULTI-ADDRESSABLE MOLECULAR SWITCH
0.8
2.4
1.8
1.2
0.6
0.0
Vis
UV
Vis
0.6
UV
UV
Vis
0.4
0.2
0.0
380 s
200
100
50
10
0
1600 s
1000
500
200
80
UV
Vis
0
300
400
500
600
700
300
400
500
600
700
Wavelength (nm)
Wavelength (nm)
(A)
(B)
Figure 1. Absorption spectral and color changes of diarylethene 1 by photoirradiation with UV/Vis in chloroform (C = 2.0 × 10À5 mol LÀ1) and PMMA
films (10%, w/w) at room temperature: (A) in chloroform; (B) in a PMMA film
Table 1. Absorption spectral properties of diarylethenes 1 and 2 in chloroform (C = 2.0 × 10À5 mol LÀ1) and in PMMA films
(10%, w/w) at room temperature
Compd
λ
o,max/nma (ε/L molÀ1 cmÀ1
)
λ
c,max/nmb (ε/L molÀ1 cmÀ1
)
Φc
PR/%d
Chloroform
PMMA film
Chloroform
PMMA film
Φo-c
Φc-o
1
2
355 (3.46 × 104)
332 (2.82 × 104)
347
329
546 (2.08 × 104)
544 (1.81 × 104)
553
547
0.26
0.35
0.05
0.03
84
75
aAbsorption maxima of open-ring isomers.
bAbsorption maxima of closed-ring isomers.
cQuantum yields of open-ring (Φo-c) and closed-ring isomers (Φc-o), respectively.
dPhotoconversion ratios of diarylethenes 1 and 2 (PR%) in the photostationary state.
were notably increased, but its cyclization quantum yield
(Φo-c = 0.26) was much lower than that of 2 (Φo-c = 0.35). In
addition, the photoconversion ratios from open-ring to
closed-ring isomers of diarylethenes 1 and 2 were analyzed
by 1H NMR spectral in MeOD and CDCl3 in the photostationary
state, as shown in Figs. S1 and S2. It can be easily calculated
that the photoconversion ratios in the photostationary state
are 84% for 1 and 75% for 2.
In a PMMA film, diarylethene 1 also showed similar photochro-
mism as observed in chloroform (Fig. 1(B)). Upon irradiation with
365 nm ultraviolet (UV) light, the colorless film containing
diarylethene 1O turned magenta, with a new broad absorption
band centered at 553 nm due to the formation of the closed-ring
isomer 1C. The colored diarylethene/PMMA film reverted to
colorless upon irradiation of visible light with appropriate
wavelength (λ > 450 nm). Compare with that in chloroform, the
absorption maxima of the closed-ring isomer in a PMMA film
was observed at longer wavelength, with the bathochromic shift
value of 7 nm for 1C. The result is in good agreement with the
date for most of the reported diarylethenes.[49–51] The reason
may be ascribed to polar effect of the polymer matrix and the
stabilization of molecular arrangement in solid medium.
decay process of the closed-ring isomer 1C was measured in
acetonitrile at 298 K, 313 K, and 328 K, and the result is shown
in Fig. S3. According to the Arrhenius equation, the activation
energy of the thermal reversion of 1C was calculated with the
value of 37.5 kJ molÀ1. The half-life time of 1C at 298 K was
1.9 h for 1C. Compared with the reported diarylethene with two
pyrrole rings (32.5 kJ molÀ1 at 298 K), 1C showed elevated
activation energy, but it was lower as compared with that of the
1,2-bis(2-naphtyl)cyclopentene (121 kJ molÀ1 at 298 K).[52] The
fatigue resistance of 1 and 2 was examined in both chloroform
and PMMA films by alternating irradiating with UV and visible
light in air at room temperature, as shown in Fig. S4. In chloroform,
the coloration and decoloration cycles of diarylethenes 1 and 2
can be repeated at least 100 times with 62% degradation of 1C
and 14% of 2C, which may result from the formation of an
epoxide.[53] However, the fatigue resistance of 1 and 2 in the solid
state is very strong. After 200 repeat cycles, the two diarylethenes
1 and 2 still exhibited excellent photochromism with only 9%
degradation of 1C and 7% degradation of 2C in PMMA films. This
remarkable improvement may result from effectively suppressing
the oxygen diffusion.[1]
Furthermore, the photochromism property of diarylethene
1 could be modulated by acid/base stimuli in chloroform.
Because the imidazo [4,5-f] [1,10] phenanthroline moiety con-
tains three nitrogen atoms and a NH group, it can be protoned
with acid and then neutralized with base in the solution. The
molecular structural and color changes between 1C and 1C′ in
chloroform are illustrated in Fig. 2. Addition of trifluoroacetic
acid (TFA) to the solution of 1O in chloroform produced a
In addition, the thermal stability of the open-ring and closed-
ring isomers of 1 was tested in acetonitrile at both room
temperature and at 353 K. We stored these solutions in acetoni-
trile at room temperature in the dark and then exposed them
to air for more than a week, and no changes have been observed
in the UV/Vis spectra of diarylethene 1. At 353 K, the diarylethene
1 still showed excellent thermal stability for more than 8 h. The
J. Phys. Org. Chem. 2014, 27 183–190
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P. REN ET AL.
Figure 2. The structural and color changes between 1O, 1C, and 1O′, 1C′ in chloroform (C = 2 × 10À5 mol LÀ1
)
protonated 1O′, and 1O′ could return to 1O by neutralization
with triethylamine base. Similarly, addition of TFA (55.0 μL,
3.71 × 10À4 mol LÀ1) to the solution of 1C produced a protonated
diarylethene 1C′ in photostationaryl state. As has been observed
for the reported diarylethenes,[54–56] the magenta solution (1C)
changed to a slateblue one (1C′) by protonation, and the
absorption maximum bathochromic shifted from 546 to
552 nm (Fig. S5). The slateblue solution of 1C′ either returned
entirely back to magenta 1C after neutralization with the
shift. The emission intensity of diarylethene 1O is much stronger
than that of 2O in both solution and PMMA films. The fluores-
cence quantum yields of 1O and 2O were determined as 0.032
and 0.006, respectively, using anthracene (0.27 in acetonitrile) as
a reference. The results indicated that the imidazo [4,5-f] [1,10]
phenanthroline moiety could significantly enhance the emission
intensity and fluorescence quantum yield, as compared with the
unsubstituted parent diarylethene 2O.
In general, the open-ring isomer of diarylethene emits rela-
tively strong fluorescence, but the fluorescence of closed-ring
isomer is inactive.[57,58] As has been observed for most of the
reported diarylethenes,[59–62] 1O exhibited a remarkable fluores-
cent switch in both solution and a PMMA film during the process
of photoisomerization (Fig. 4). The emission intensity of 1O was
decreased by photocyclization upon irradiation with UV light.
In chloroform, the emission intensity in a photostationary state
decreased by 90% with a concomitant change of color from
bright cyan to dark gray. Back irradiation of the appropriate
wavelength of visible light (λ > 450 nm) regenerated the open-
ring isomer 1O and recovered the original emission spectra. In
a PMMA film, 1O also showed similar fluorescence switching
property as observed in chloroform solution. Upon irradiation
triethylamine (TEA) (55.0 μL, 1.97 × 10À4 mol LÀ1
) or gets
bleached entirely (1O′) upon irradiation with visible light.
Fluorescence of diarylethenes
The fluorescence spectra of 1O and 2O were measured in
chloroform and PMMA films. Because diarylethene 2O showed
very weak fluorescence, we only discuss the fluorescence property
of 1 in this paper. Figure 3 shows the fluorescence spectra of
diarylethenes 1O and 2O in both chloroform (2.0×10À5 mol LÀ1
)
and PMMA films (10%, w/w) at room temperature. Compared with
that in chloroform (λex = 345 nm), the emission peak of 1 in a
PMMA film (λex = 361nm) exhibited an obvious hypochromatic
540
5000
4000
360
1O
3000
2000
1000
0
1O
180
2O
2O
0
420
480
540
600
660
400
440
480
520
560
Wavelength (nm)
Wavelength (nm)
(A)
(B)
Figure 3. Fluorescence emission spectra of diarylethenes 1O and 2O in both chloroform solution (C = 2.0 × 10À5 mol LÀ1) and PMMA films (10%, w/w)
at room temperature; (A) in chloroform, excited at 345 nm and 371 nm; (B) in PMMA films, excited at 361 nm
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A NEW MULTI-ADDRESSABLE MOLECULAR SWITCH
5000
3750
2500
1250
0
540
360
0
10
15
25
35
55
120
260s
Vis
UV
0
5
20
100
280
540 s
Vis
UV
UV
180
0
420
480
540
600
660
400
450
500
550
Wavelength (nm)
Wavelength (nm)
(A)
(B)
Figure 4. Fluorescence emission spectra of diarylethene 1O in both chloroform solution (C = 2.0 × 10À5 mol LÀ1) and a PMMA film (10%, w/w) at room
temperature: (A) in chloroform, excited at 345 nm; (B) in a PMMA film, excited at 361 nm
with UV light, the emission intensity of 1O decreased
significantly by 62% in a photostationary state. The residual
fluorescence may be attributed to the incomplete cyclization
reaction, as well as to the existence of parallel conformation.[63]
In addition, the switchable fluorescent cycles of 1 could be
repeated at least 50 times in both solution and a PMMA film,
indicating that it could be considered as a promising candidate
for fluorescent modulation switches.[64,65]
1O′, its emission peak hypochromatically shifted from 501 nm to
456 nm along with the addition of TFA increased from 0.1μL to
55.0 μL, and its intensity increased significantly by 3-fold larger
with a concomitant change of color from bright cyan to bright blue
(Fig. 5(A) and (C)). The emission intensity kept unchanged when
the addition of TFA was more than 55.0 μL (3.71 × 10À4 mol LÀ1).
At the saturation state, the fluorescent quantum yield of 1O′ was
determined as 0.021. Upon irradiation with 365 nm UV light, the
emission intensity of 1O′ decreased remarkably because of
the formation of the non-fluorescent closing-ring isomer 1C′
(Fig. S6). Furthermore, diarylethene 1O could be deprotonated
to produce diarylethene 1O′′ by neutralization with TEA due
to the existence of NH group in imidazole moiety. When
addition of TEA in chloroform (1.0 μL, 3.59 × 10À6 mol LÀ1) to
It should be noted here that the fluorescence of 1O could be
modulated by the stimulation of acid and base. Figure 5 shows
the emission spectral changes of diarylethene 1O in chloroform
(2.0 × 10À5 mol LÀ1) by alternating addition of TFA and TEA.
When addition of TFA in chloroform (0.1 μL, 6.75 × 10À7 mol LÀ1
)
to the solution of 1O produced the N-protonated diarylethene
540
1400
2.8
1.0
1O
0.8
2.4
1200
450
0.6
2.0
0.4
1000
360
1.6
0.2
0.0
800
1.2
0
40
80
120
160
TEA ( L)
270
180
90
0
10
20
30
40
50
60
600
400
200
0
1OTFA (
L)
TEA
605
0
400
440
480
520
560
600
640
440
495
550
660
Wavelength (nm)
Wavelength (nm)
(A)
(B)
(C)
Figure 5. Changes in fluorescence and color of 1O by the stimulation of acid and base in chloroform when excited at 345 nm: (A) emission spectral
changes for 1O by the addition of TFA; (B) emission spectral changes for 1O by the addition of TEA; (C) photos of fluorescence changes for 1O. Inset
shows the fluorescent modulation efficiency of 1O as a function of the concentration of TFA and TEA, respectively
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P. REN ET AL.
the solution of 1O, the emission intensity of 1O′′ decreased sharply
by 71%; then further added enough amount of TEA (154.0μL,
5.52 × 10À4 mol LÀ1), the emission intensity of 1O′′ could decrease
by 95%, accompanied with a notable fluorescence color change
from bright cyan to dark gray (Fig. 5(B) and (C)). This characteristic
could be potentially applied in fluorescent switches and chemical
sensors.[36,54,55,66,67]
Figure 6. The combinational logic circuits equivalent to the truth table
given in Table 2: I1 (365 nm ultraviolet light), I2 (450 nm visible light), I3
(TFA), and O1
Furthermore, the emission intensity of the diarylethene 1O
bearing an imidazo [4,5-f] [1,10] phenanthroline unit could be
modulated by either acid or light stimuli. As a result, the fluores-
cence of 1 by external stimuli can be described with the aid of
binary logic by light and pH as input signals. The multi-mode
fluorescence switching principle of diarylethene 1 is summarized
in Scheme 3. As shown in Fig. 6, a 365 nm UV light (I1), a 450 nm
visible light (I2), and TFA (I3) are selected as the three inputs,
whereas the emission intensity at 456 nm is noted as one output.
The output signal can be regarded as on when the emission
intensity at 456 nm is larger than three times of the original
value, but off when it is less than three times. Hence, we can
use the binary digits (1 or 0) instead of the two levels (on and
off). As a result, the diarylethene 1 can read a string of three
inputs and write one output. When the input string is 000,
corresponds to the “off” states for all I1, I2, and I3. Under this
conditions, the output signal O1 is off and the output digit is
0. All the possible strings of the three inputs are listed in
Table 2.
enough amount of TEA,
a high-fluorescence quenching
efficiency was achieved with an effective fluorescence change
from bright cyan to dark gray. But its fluorescence enhanced
dramatically by addition enough amount of TFA, accompanied
with a concomitant change of color from bright cyan to bright
blue. The diarylethene has desirably multiple modulation func-
tion in its fluorescence, which make it a potential candidate as
fluorescent switches and chemical sensors.
EXPERIMENTAL SECTION
General
All solvents used were spectroscopic grade and were purified by
distillation before use. NMR spectra were recorded on a Bruker AV400
(400 MHz) spectrometer with CDCl3 as the solvent and tetramethylsilane
as an internal standard. IR spectra were recorded on a Bruker Vertex-70
spectrometer. Melting point was taken on a WRS-1B melting point appa-
ratus. Absorption spectra were measured using an Agilent 8453 UV/VIS
spectrophotometer. Photoirradiation was carried out using a SHG-200
UV lamp, CX-21 UV fluorescence analysis cabinet, and a BMH-250 visible
lamp. The required wavelength was isolated by the use of the appropri-
ate filters. Fluorescence spectra were measured by using a Hitachi F-4600
spectrophotometer.
CONCLUSIONS
In conclusion, a multi-addressable fluorescence switch based on
a new diarylethene with an imidazo [4,5-f] [1,10] phenanthroline
unit was constructed successfully. The fluorescence of the
diarylethene could be multiply modulated by light, acid, and
base in solution. Upon irradiation with UV light or addition
Scheme 3. Schematics of molecular structures and fluorescence changes of diarylethene 1O with proton and optic stimuli
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A NEW MULTI-ADDRESSABLE MOLECULAR SWITCH
Table 2. Truth table for all possible strings of three binary-input data and the corresponding output digit
Input
Outputa
In1 (UV)
In2 (Vis)
In3 (TFA)
0
0
0
1
0
1
1
1
0
0
1
0
1
0
1
1
0
1
0
0
1
1
0
1
0
1
0
0
1
0
0
1
aAt 456 nm, the emission intensity above three times of the original value of 1O (501 nm) is defined as 1, otherwise defined as 0.
CDCl3, ppm): δ 1.87 (s, 3H), 2.15 (s, 3H), 4.01–4.16 (m, 4H), 5.83 (s, 1H),
7.19 (s, 1H), 7.21À7.30 (m, 1H), 7.33 (s, 1H,) 7.38 (s, 1H,) 7.40–7.59
(m, 5H ); 13C NMR (100 MHz, CDCl3, TMS): δ = 13.33, 14.84, 63.74, 65.34,
103.33, 111.04, 119.98, 122.72, 123.62, 123.70, 124.38, 124.67, 125.36,
125.60, 126.04, 126.23, 127.15, 130.51, 135.45, 138.88, 140.68, 154.21,
156.13; IR (ν, KBr, cmÀ1): 748, 800, 988, 1128, 1195, 1265, 1340, 1383,
1459, 3360.
Synthesis
The synthesis method of two diarylethenes 1O and 2O was shown in
Scheme 2, and experimental details were carried out as following.
3-Bromo-2-methyl-5-(4–1,3-dioxolane-phenyl)thiophene (4)
Compound 3 (1.20 g, 4.27 mmol),[68] glycol (1.42 mL, 25.61 mmol), and
p-toluenesulfonic acid (0.02 g, 4.27 mmol) was dissolved in benzene
(120 mL). Under the Dean–Stark condition, the reaction mixture was
refluxed overnight, and then washed with NaHCO3 (5% (w/v),
2 × 50 mL) aqueous. The combined benzene layers were dried, filtered,
and evaporated in vacuum to give 1.30 g 4 as a yellow solid in 93% yield.
M.p. 93–94°C; 1H NMR (400MHz, CDCl3, TMS): δ 2.41 (s, 3H), 3.94–4.15
(m, 4H), 5.81 (s, 1H), 7.12 (s, 1H), 7.46–7.53 (m, 4H); 13C NMR (100 MHz,
CDCl3, TMS): δ 14.88, 65.36, 103.39, 109.98, 125.29, 125.42, 125.90,
127.14, 127.57, 130.51, 134.04, 134.33, 137.48, 140.67; IR (ν, KBr, cmÀ1):
686, 718, 791, 814, 941, 970, 1016, 1079, 2876.
1-(2-Methyl-1-benzofuran-3-yl)-2-[2-methyl-5-(4-benzaldehyde)
-3-thienyl]perfluorocyclopentene (2O)
Compound 7 (2.27 g, 4.12 mmol), pyridine (0.37 g, 4.74 mmol), and
p-toluenesulfonic acid (1.57 g, 8.25 mmol) were dissolved in acetone
(50 mL) and water (10 mL). The reaction mixture was refluxed overnight
at 333 K, and then washed with NaHCO3 (10% (w/v), 2 × 20 mL) aqueous.
The combined acetone layers were dried, filtered, and evaporated in
vacuum to give 0.27 g 2O as a violet solid in 13% yield. Calcd for
C
26H16F6OS (%): Calcd C, 61.66; H, 3.18; Found C, 61.71; H, 3.25; M.p.
109–110 °C; 1H NMR (400 MHz, CDCl3, ppm): δ 1.92 (s, 3H), 2.15 (s, 3H),
7.22–7.44 (m, 4H), 7.45 (s, 1H), 7.68 (d, 2H, J = 8.0 Hz), 7.89 (d, 2H,
J = 8.0 Hz), 9.99(s, 1H); 13C NMR (100 MHz, CDCl3, TMS): δ 13.31, 14.82,
105.40, 111.09, 119.92, 123.67, 124.36,124.65, 125.81, 126.20, 130.49,
135.48, 138.85, 140.66, 143.36, 154.20, 156.11, 191.22; IR (ν, KBr, cmÀ1):
471, 619, 744, 802, 823, 894, 985, 1192, 1276, 1337, 1455, 1600, 1697,
2748, 3413, 3480, 3687.
(2-Methy-1-benzofuran-3-yl) perfluorocyclopentene (6)
To
a stirred tetrahydrofuran (THF) solution (100 mL) containing
compound 5 (3.10 g, 14.69 mmol) was slowly added 6.73 mL n-BuLi
(2.4 M solution in hexanes) at 195 K under nitrogen atmosphere. After
40 min, the C5F8 (2.10 mL, 0.136 mol LÀ1) was added quickly to the
reaction mixture, and kept stirring for 2 h at 195 K under nitrogen atmo-
sphere. Then the reaction mixture was extracted with diethyl ether and
evaporated in vacuum. The residue was purified by column chromatog-
raphy by using petroleum ether as the eluent to give 3.50 g 6 as yellow
oil liquid in 74% yield. 1H NMR (400 MHz, CDCl3, ppm): δ 2.50 (s, 3H),
7.25–7.35 (m, 2H), 7.48 (d, 1H, J = 8.0 Hz), 7.54 (d, 1H, J = 8.0 Hz); 13C
NMR (100 MHz, CDCl3, TMS): δ 13.78, 111.22, 122.58, 124.88, 126.16,
128.92, 133.44, 154.31, 154.39; IR (ν, KBr, cmÀ1): 564, 744, 800, 972,
1041, 1130, 1205, 1282, 1456, 1601, 1700, 2970, 3676.
1,10-Phenanthroline-5,6-dione (9)
To a stirred concentrated sulfuric acid (60 mL) and concentrated nitric
acid (30 mL) containing compound 1,10-phenanthroline (5.00 g,
27.76 mmol) and potassium bromide (9.91 g, 83.30 mmol) at 273 K for
20 min, and then gradually heated up to 403 K and reflux 3 h. After
cooling at room temperature, the solution was poured into plenty of
crushed ice; the resulting mixture was neutralized to pH = 7.0 with
sodium carbonate, and then the extract was washed successively with
water and brine. The organic extracts were concentrated and
recrystallized from methanol to give 5.10 g 9 as a yellow solid in 87%
yield. M.p. 260–261 °C; 1H NMR (400 MHz, CDCl3, TMS): δ 7.58–7.61
(m, 2H), 8.51 (d, 2H, J = 8.0 Hz), 9.11 (d, 2H, J = 8.0 Hz). 13C NMR
(100 MHz, CDCl3, TMS): δ = 124.75, 125.60, 129.34, 131.22, 131.70,
134.17. 137.27, 155.20, 155. 96, 156.35, 163.39, 189.53; IR (ν, KBr, cmÀ1):
739, 1459, 1561, 1576, 1686, 3061.
1-(2-Methyl-1-benzofuran-3-yl)-2-[2-methyl-5-(4–1,3-dioxolane-phe-
nyl)-3-thienyl]perfluorocyclopentene (7)
To a stirred anhydrous THF containing 4 (1.77 g, 5.44 mmol) was added
dropwise a 2.49 mL n-BuLi (2.4 M solution in hexanes) at 195 K under
argon atmosphere. After the mixture has been stirred for 30 min, com-
pound (2-methy-1-benzofuran-3-yl)perfluorocyclopentene (6) (1.76 g,
5.44 mmol) in solvent of anhydrous THF was added. The reaction was
further stirred at 195 K for 2 h, and the reaction was allowed to slowly
warm to the room temperature. The reaction was quenched with distilled
water. The product was extracted with diethyl ether, dried with MgSO4,
and concentrated under reduced pressure. The crude product was
purified by column chromatography by using (petroleum ether/ethyl
acetate = 6:1) as the eluent to afford to 2.27 g compound 7 as a violet
solid in 76% yield. 1H NMR (400 MHz, CDCl3, ppm): δ 1H NMR (400 MHz,
1-(2-Methyl-1-benzofuran-3-yl)-2-[2-methyl-5-(4-phenyl)-1H-imidazo
[4,5-f][1,10]phenanthroline]perfluorocyclopentene (1O)
To a stirred acetic acid solution (15 mL) containing compound 2O (0.21 g,
0.42 mmol), 1,10-phenanthroline-5,6-dione (9) (0.10 g, 0.46 mmol), and
ammonium acetate (0.57 g, 7.36 mmol) at 353 K for 3 h. Then ice water
J. Phys. Org. Chem. 2014, 27 183–190
Copyright © 2013 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/poc

P. REN ET AL.
was poured in, and a yellow solid of crude product was obtained by filtra-
tion. Further, 0.17 g 1O was recrystallized from ethanol as a pale yellow
solid in 59% yield. Calcd for C38H22F6N4OS (%): Calcd C, 65.51; H, 3.18;
N, 8.04; Found C, 65.42; H, 3.27; N, 8.16; M.p. 213–214 °C; 1H NMR
(400 MHz, CDCl3, ppm): δ 1.83 (s, 3H), 2.18 (s, 3H), 7.21–7.30 (m, 3H ),
7.43 (t, 3H, J = 8.0 Hz), 7.53 (s, 1H), 7.61 (d, 4H, J = 8.0 Hz), 7.99 (d, 2H,
J = 8.0 Hz), 8.57 (s, 1H), 8.84 (s, 1H); 13C NMR (100 MHz, CDCl3, TMS):
δ 10.53, 11.81, 12.51, 63.98, 103.49, 109.28, 114.61, 114.86, 117.90,
121.42, 121.60,121.93, 122.39, 122,77, 123.08, 123.49, 123.92,
124.14,124.51, 124.79, 124.93, 125.27, 125.77, 127.22, 128.18, 132.80,
140.01, 140.69,141.66, 145.92, 149.11, 152.80, 154.87; IR (ν, KBr, cmÀ1):
575, 748, 802, 894, 985, 1055, 1116, 1190, 1250, 1271, 1342, 1398, 1453,
1486, 1635, 3435.
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This work was supported by the National Natural Science
Foundation of China (21162011, 21262015), the Project of Jiangxi
Advantage Sci-Tech Innovative Team (20113BCB24023), the
Project of Jiangxi Natural Science Foundation (20114BAB203007,
20132BAB203005), and the Project of the Science Funds of Jiangxi
Education Office (KJLD12035, GJJ11026, GJJ12587).
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