Synthesis and properties of novel photochromic bisthienylethenes containing imidazole and imidazolium derivatives

Article abstract of DOI:10.1016/j.cclet.2014.01.033

A series of bisthienylethenes containing imidazole and imidazolium derivatives have been prepared and the products have been characterized by means of NMR and MS. Their photochromic and fluorescent switch properties have been investigated by UV-vis absorption spectra and fluorescence spectra. The fluorescent emissions of these kinds of photochromic compounds can be simply modulated by varying the imidazole groups, which shows that these compounds may have potential application in the design of fluorescent photochromic materials.

Full text of DOI:10.1016/j.cclet.2014.01.033

Accepted Manuscript
Title: Synthesis and properties of novel photochromic
bisthienylethenes containing imidazole and imidazolium
derivatives
Author: Jia-Qi Zhang Qiao-Chun Wang Lei Zou Chun-Yang
Jia
PII:
S1001-8417(14)00051-5
DOI:
Reference:
http://dx.doi.org/doi:10.1016/j.cclet.2014.01.033
CCLET 2859
To appear in:
Chinese Chemical Letters
Received date:
Revised date:
Accepted date:
16-11-2013
7-1-2014
13-1-2014
Please cite this article as: J.-Q. Zhang, Q.-C. Wang, L. Zou, C.-Y. Jia,
Synthesis and properties of novel photochromic bisthienylethenes containing
imidazole and imidazolium derivatives, Chinese Chemical Letters (2014),
http://dx.doi.org/10.1016/j.cclet.2014.01.033
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Graphical Abstract
Synthesis and properties of novel photochromic bisthienylethenes containing
imidazole and imidazolium derivatives
Jia-Qi Zhanga, Qiao-Chun Wanga, Lei Zoua, ∗, Chun-Yang Jiab
aKey Laboratory for Advanced Materials and Institute of Fine Chemicals, East China University of Science & Technology, Shanghai 200237, China
bState Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054, China
R
R
O
O
HN
N
UV
vis
HN
N
O
O
N
a: R =
S
S
S
S
1aC
1bC
1aO
1bO
R
R
-
-
PF6
PF6
N
N
N
N
UV
vis
N
b: R =
S
S
S
S
2aC
2bC
2aO
2bO
A series of bisthienylethenes containing imidazole and imidazolium derivatives have been prepared, and their photochromic and fluorescent
switch properties have been investigated by UV-vis absorption spectra and fluorescence spectra. Results showed that the fluorescent emission
of this kind of photochromic compounds can be simply modulated by varying the imidazole groups.
∗ Corresponding author.
E-mail address: zoulei@ecust.edu.cn
Page 1 of 7

Original article
Synthesis and properties of novel photochromic bisthienylethenes containing
imidazole and imidazolium derivatives
Jia-Qi Zhanga, Qiao-Chun Wanga, Lei Zoua, ∗, Chun-Yang Jiab
aKey Laboratory for Advanced Materials and Institute of Fine Chemicals, East China University of Science & Technology, Shanghai 200237, China
bState Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054, China
ARTICLE INFO
ABSTRACT
A series of bisthienylethenes containing imidazole and imidazolium derivatives have been
prepared and the products have been characterized by means of NMR and MS. Their
photochromic and fluorescent switch properties have been investigated by UV-vis absorption
spectra and fluorescence spectra. The fluorescent emissions of these kinds of photochromic
compounds can be simply modulated by varying the imidazole groups, which shows that these
compounds may have potential application in the design of fluorescent photochromic materials.
Article history:
Received 16 November 2013
Received in revised form 7 January 2014
Accepted 13 January 2014
Available online
Keywords:
Photochromism
Bisthienylethenes
Imidazole
Fluorescence
1. Introduction
Photochromic compounds have received increasing attention in recent years due to their potential application in optical data storage
and photo-controllable materials [1-9]. In particular, fluorescent photochromic bisthienylethenes currently have been extensively
explored for use as chemosensors and in biological imaging [10-12]. There are many ways to design fluorescent photochromic
bisthienylethenes, including linking fluorophores on the branched chains of the aryl [13-15], and using the fluorophores as the center
ethene bridge [16, 17]. Triaryl(heteroaryl)-imidazoles are one kind of classic chromophores, which are usually used in the field of
photochromic compounds because of their fine optoelectronic properties [18-21]. Herein, we synthesized a series of bisthienylethenes
containing imidazole and imidazolium derivatives, and their photochromic and fluorescent switch properties were investigated (Scheme
1).
2. Experimental
2.1. General methods
N-(4-formylphenyl)-aza-15-crown-5-ether 3 and diketone 5 were synthesized according to the literature [22, 23]. Other reagents were
1
commercially available and used without further purification. H NMR and 13C NMR spectra were recorded on a Bruker AM-400
spectrometer in DMSO-d6 solutions. High resolution mass spectra (HRMS) were recorded on a Waters LCT Premier XE spectrometer
using standard conditions (ESI, 70 eV). UV–vis absorption spectra were measured on a Varian Cary 500 UV–vis spectrophotometer.
Fluorescence emission spectra were measured on a Varian Cary Eclipse Fluorescence spectrophotometer. Fluorescence quantum yields
were recorded on a Fluoro Max-4 spectrofluorometer with a quanta-Φ integrating sphere (Horiba Jobin-Yvon).
2.2. Synthesis of diarylethene 1a
A mixture of formyl azacrown ether 3 (0.96 mmol), ammonium acetate (10 equiv) and diketone 5 (0.96 mmol) in glacial acetic acid
(50 mL) was stirred and heated at reflux for 12 h. Then the mixture was cooled to room temperature and the product precipitated during
neutralization with 5 mol L−1 NH4OH. The crude product was purified through column chromatography on silica using ethyl
o
1
acetate/petroleum ether (3:1) as the eluent. Compound 1a was separated in 38% yield as a yellow solid. Mp 122.1-124.0 C. H NMR
(400 MHz, DMSO-d6): δ 12.09 (s, 1H), 7.80 (d, 2H, J = 8.90 Hz), 6.71 (d, 2H, J = 7.60 Hz), 6.68 (s, 1H), 6.57 (s, 1H), 3.66 (t, 4H, J =
6.00 Hz), 3.60-3.46 (m, 16H), 2.41 (s, 3H), 2.33 (s, 3H), 2.11 (s, 3H), 1.96 (s, 3H). 13C NMR (101 MHz, DMSO-d6): δ 144.71, 135.95,
127.76, 126.75, 111.35, 70.29, 69.53, 69.01, 67.74, 51.95, 14.79, 13.40. ESI-HRMS (m/z): Calcd. for C31H40N3O4S2 ([M+H]+): 582.2460;
∗ Corresponding author.
E-mail address: zoulei@ecust.edu.cn
Page 2 of 7

Found: 582.2465.
2.3. Synthesis of diarylethene 1b
Compound 1b was prepared by an analogous method to that used for 1a and obtained as a white solid in a yield of 25%. Mp 246.7-
247.4 oC. 1H NMR (400 MHz, DMSO-d6): δ 12.36 (s, 1H), 7.91 (d, 2H, J = 8.70 Hz), 7.36-7.30 (m, 4H), 7.10-6.99 (m, 8H), 6.72 (s, 1H),
6.56 (s, 1H), 2.41 (s, 3H), 2.32 (s, 3H), 2.13 (s, 3H), 1.97 (s, 3H). 13C NMR (101 MHz, DMSO-d6): δ 147.00, 146.92, 144.76, 135.16,
134.66, 134.06, 133.50, 132.13, 131.25, 129.60, 129.62, 128.06, 127.22, 126.82, 126.11, 124.77, 124.14, 123.29, 122.88, 14.83, 13.86,
13.50. ESI-HRMS (m/z): Calcd. for C33H30N3S2 ([M+H]+): 532.1881; Found: 532.1887.
2.4. Synthesis of compound 2a
Iodomethane (0.54 mmol) was added to a mixture of 1a (210 mg, 0.36 mmol) and K2CO3 (100 mg, 0.72 mmol) in N,N-
o
dimethylformamide (15 mL), then the mixture was heated under nitrogen atmosphere and stirred at 50 C for 4 h. The solvent was
removed under reduced pressure. The residue was dissolved in ethyl acetate and washed with water and brine. Removal of the solvent led
to the isolation of an off-white solid. The solid was dissolved in acetonitrile (7 mL), and iodomethane (0.34 mL) was added to this
solution. The mixture was heated to reflux for 24 h. The solvent was removed under reduced pressure, and the residue was washed with
diethyl ether. The resulting solid was dissolved in acetonitrile (5 mL), and then saturated NH4PF6 solution was added to the mixture until
the precipitate appeared. The solid was collected by filtration and washed with deionized water. The final product was obtained as a white
solid in a yield of 51 %. Mp 249.2-250.2 oC. 1H NMR (400 MHz, CDCl3): δ 7.53 (d, 1H, J = 8.10 Hz), 6.86 (d, 1H, J = 8.60 Hz), 6.80 (s,
0.64H), 6.57 (s, 0.34H), 3.80 (t, 2H, J = 6.00 Hz), 3.73-3.63 (m, 8H), 3.54 (s, 3H), 2.43 (s, 3H), 2.22 (s, 1H), 1.94 (s, 2H). 13C NMR (101
MHz, DMSO-d6): δ 149.99, 137.18, 131.65, 126.67, 122.12, 111.32, 70.25, 69.57, 68.86, 67.59, 52.08, 34.23, 14.87, 13.33. ESI-HRMS
(m/z): Calcd. for C33H44N3O4S2 ([M+H]+): 610.2773; Found: 610.2773.
2.5. Synthesis of compound 2b
Compound 2b was prepared by a method similar to that used for 2a and obtained as a white powder in a yield of 52 %. Mp 275.1-
276.0 oC. 1H NMR (400 MHz, DMSO-d6): δ 7.65 (d, 1H, J = 8.10 Hz), 7.44 (t, 2H, J = 7.80 Hz), 7.20-7.31 (m, 3H), 7.07 (d, 1H, J = 8.80
Hz), 6.90 (s, 0.61H), 6.64 (s, 0.36H), 3.49 (s, 3H), 2.42 (s, 3H), 2.18 (s, 1H), 1.93 (s, 2H). 13C NMR (101 MHz, DMSO-d6): δ 150.65,
145.74, 137.32, 131.72, 130.06, 126.95, 126.18, 125.36, 121.98, 118.90, 34.14, 14.87, 13.35. ESI-HRMS (m/z): Calcd. for C35H34N3S2
([M+H]+): 560.2194; Found: 560.2191.
3. Results and discussion
3.1. Synthetic strategy and the X-ray structures of 1a
In this work, a series of bisthienylethenes containing imidazole and imidazolium derivatives were prepared by a simple method, and
their photochromic behaviors were investigated in detail. The synthetic route used to obtain diarylethene 1 and 2 is shown in Scheme 2.
N-(4-Formylphenyl)-aza-15-crown-5-ether 3 and diketone 5 were synthesized according to the literatures. Treatment of diketone in acetic
acid with corresponding aldehyde in the presence of NH4Ac afforded target compounds 1a and 1b in yields of 20 % - 40 %. Compound 2
was prepared by compound 1 methylating with CH3I, and then ion exchanging with NH4PF6. All of the target compounds were
characterized by 1H NMR, 13C NMR and HRMS, and the corresponding spectra were shown in Fig. S1-S12 in Supporting information. It
is worth mentioning that the single crystal of 1a was obtained by slow evaporation in THF. The structure of compound 1a was further
determined by X-ray diffraction (Fig. 1), the distance between the reactive carbons (C5-C10) is 3.71 Å for 1a, which is short enough to
undergo photochromic reactions in the single-crystalline phase [24]. Crystal determination data of 1a was shown in Table S1 in
Supporting information with CCDC number 969060.
3.2. Photochromism of compound 1 and 2
Bisthienylethenes 1 and 2 can undergo a reversible photochromic reaction in acetonitrile upon alternating irradiation with UV and
visible light. Changes in the absorption spectra of compound 1 and 2 induced by photo irradiation at room temperature in acetonitrile (c
1×10-5 mol L−1) are shown in Fig. 2. The maximum absorption of compound 1a is observed at 344 nm. Upon irradiation with 365 nm
light, the colorless solution of 1aO gradually turns purple due to the appearance of a new visible absorption band centered at 550 nm,
which is attributed to the formation of the closed-ring form 1aC. The photo-stationary state is attained after about 20 seconds.
Alternatively, the purple solution could be bleached to colorlessness upon irradiation with visible light (λ> 550 nm), indicating that 1aC
returned to the initial state 1aO. Compared to 1aO, the maximum absorption of compound 2aO appeared at 318 nm. And the maximum
absorption of ring-closed isomer 2aC appeared at 576 nm, which is a 26 nm bathochromic shift from 1aC. The possible reason is that the
methylation of the imidazole increased the π-conjugation of the ring-closed isomer 1aC. Similarly, the colorless solutions of 1b and 2b
can turn purple on irradiation with 365 nm UV light, and the color can also be disappeared upon irradiation with the same visible light (λ
Page 3 of 7

> 550 nm). The corresponding spectra changes are shown in Fig. 2b and Fig. 2d. The photochromic properties of diarylethenes 1a, 1b
and 2a, 2b are summarized in Table 1. The thermal stabilities of these diarylethenes were also investigated. After putting the solutions of
open-ring isomers of diarylethenes 1a, 1b and 2a, 2b in acetonitrile at room temperature in the dark for more than one week, no changes
in their colors and spectra were observed. The color of the closed-ring isomers of 1a and 1b were bleached after staying in the dark for
several minutes. However, the color of the closed-ring isomers of 2a and 2b would not change even after several hours, which means that
the N-methylation of the imidazole ring can improve the thermal stability of these diarylethenes with the imidazole ring.
3.3. Fluorescence of the bisthienylethenes
The fluorescence spectra changes of the diarylethene 1 and 2 in acetonitrile at room temperature are shown in Fig. 3. In acetonitrile,
diarylethene 1aO exhibited strong blue emitting fluorescence at 416 nm when excited at 344 nm. After irradiation with 365 nm UV light,
the fluorescence intensity of 1a decreased to 40 % due to the formation of ring-closed isomer. Similar results were obtained when
solutions of the other bisthienylethenes 1b, 2a, and 2b in acetonitrile were irradiated with UV light. The corresponding fluorescence data
of these compounds is summarized in Table 2.
As shown in Table 2, the different substituents and the methylation of the imidazole ring have a great influence on the fluorescent
performances of the bisthienylethenes. Compared to 1b, the fluorescence emission wavelength of 1a was 14 nm red-shifted due to the
difference between the N-(4-phenyl)-aza-15-crown-5-ether and the triphenylamine groups. After the methylation of the imidazole, the
fluorescence emission wavelength of 2a was 4 nm bathochromic shifted from 1a because the methylation extended the π-conjugation. A
much longer bathochromic shift was observed from 2a to 2b, which can reach about 103 nm. In this way, the fluorescence emission
colors could be easily tuned from blue to yellow-green, which were shown in Fig. 4. Moreover, the fluorescence quantum yields of these
bisthienylethenes could be regulated from 26.1 % to 48.4 %, which provided a possible application for biological imaging and cell
staining. According to the above analysis, the light-emitting properties of this kind of diarylethenes could be manipulated by easy
modification of the imidazole group.
4. Conclusion
A series of novel bisthienylethenes containing imidazole and imidazolium derivatives have been prepared, and the crystal structure of
compound 1a was obtained. Their photochromism and fluorescent properties in solution were investigated. It has been demonstrated that
the fluorescent emission wavelength of the photochromic bisthienylethenes could be simply tuned by varying the imidazole groups,
which provides a simple solution for designing the fluorescent photochromic diarylethenes.
Acknowledgment
This work was financially supported by National Basic Research 973 Program (No. 2013CB733700), National Natural Science
Foundation of China (Nos. 21190033, 21302056 and 21072058) and the Open Foundation of State Key Laboratory of Electronic Thin
Films and Integrated Devices (No. KFJJ201311). Professor He Tian is also acknowledged for helpful discussion.
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coordinations, Chem. Commun. 48 (2012) 2095-2097.
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[14] J.J. Zhang, W.J. Tan, X.L. Meng, H. Tian, Soft mimic gear-shift with a multi-stimulus modified diarylethene, J. Mater. Chem. 19 (2009) 5726-5729.
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R
R
O
O
HN
N
UV
vis
HN
N
O
O
N
a: R =
S
S
S
S
1aC
1bC
1aO
1bO
R
R
-
-
PF6
PF6
N
N
N
N
UV
vis
N
b: R =
S
S
S
S
2aC
2bC
2aO
2bO
Scheme 1. Photochromism of diarylethenes 1a, 1b and 2a, 2b.
R
R
-
PF6
1. CH3I K2CO3 DMF
2. CH3I CH3CN
O
O
N
N
NH4OAC
HN
N
R-CHO
+
CH3COOH
3. CH3CN NH4PF6
S
S
S
S
S
S
5
2a R = R1
2b R = R2
1a R = R1
1b R = R2
3 R = R1
O
O
4
R = R2
O
O
N
N
R1 =
R2 =
Scheme 2. Synthetic route for the target compounds.
Fig. 1. Molecular structure of 1a (H atoms have been omitted for clarity).
Page 5 of 7

(b)
(a)
UV vis
0.3
0.2
0.1
0.3
0.2
0.1
UV
vis
vis
UV
vis
UV
0.0
0.3
0.0
0.3
300
400
500
Wavelength (nm)
600
700
300
400
500
Wavelength (nm)
600
700
(c)
(d)
UV
vis
UV
vis
0.2
0.1
0.0
0.2
0.1
0.0
vis
UV
600
vis
UV
600
300
400
500
700
300
400
500
700
Wavelength (nm)
Wavelength (nm)
Fig. 2. Changes in the absorption spectra of compounds 1a (a), 1b (b), 2a (c), and 2b (d) in acetonitrile at room temperature (1×10-5 mol L−1).
(a)
(b)
800
600
400
200
0
600
400
200
0
UV
vis
vis
UV
350
400
450
Wavelength (nm)
500
550
350
400
450
500
550
Wavelength (nm)
(c)
(c)
600
400
200
0
UV
vis
UV vis
200
100
0
400
450
500
550
600
650
350
400
450
Wavelength (nm)
500
550
Wavelength (nm)
Fig. 3. Fluorescent changes of compounds 1a (a), 1b (b), 2a (c), and 2b (d) upon alternate irradiation with UV/vis light in acetonitrile (1×10-5 mol L−1) at room
temperature.
Page 6 of 7

Fig. 4. Fluorescence emission of compounds 1aO, 1bO, 2aO, and 2bO (from left to right) by photo irradiation in acetonitrile (2×10-5 mol L−1) at room
temperature.
Table 1
Absorption parameters and photochromic reactivities of diarylethenes 1a, 1b, 2a, and 2b in acetonitrile.
Φc
λmaxa/nm
λmaxb/nm
Compd.
Conversion at PSS
(ε×104/L mol-1 cm-1)
(ε×104/L mol-1 cm-1)
Φo-c
Φc-o
344 (3.04)
347 (3.43)
318 (2.88)
332 (2.57)
550 (0.15)
553 (0.16)
576 (0.22)
583 (0.17)
0.262
0.351
0.380
0.401
40%
85%
23%
28%
1a
1b
2a
2b
0.033
0.028
0.004
0.005
a Absorption maxima of open-ring isomers.
b Absorption maxima of closed-ring isomers.
c Quantum yields of cyclization reaction (Φo-c) and cycloreversion reaction (Φc-o), respectively.
Table 2
Fluorescence data of diarylethenes 1a, 1b, 2a, and 2b in acetonitrile (1×10-5 mol L−1).
a
Compd.
λex/nm
λem/nm
Φf
Reduction rate(%) b
344
347
317
333
416
402
420
505
26.1
44.8
44.3
48.4
40%
85%
23%
28%
1a
1b
2a
2b
a Absolute fluorescence quantum yields of bisthienylethenes.
b Reduction rate (%) = (F(initial)-F(PSS))/F(initial).
Page 7 of 7