The effects of phenyl-bridged glucosyltriazolyl groups on the properties of water-soluble diarylethene derivatives

Article abstract of DOI:10.1016/j.tet.2013.12.037

Three water-soluble diarylethenes with glycosyltriazolyl groups and variable phenyl units have been synthesized, and their properties, such as water solubility, photochromism, and fluorescence have been discussed. Upon alternating irradiation with UV and visible light, each of the diarylethenes exhibited favorable photochromism and functioned as fluorescent switches in water. Experimental results showed that their water solubility as well as absorption features, cyclization quantum yields, photoconversion ratios, thermal stability, and fatigue resistance exhibited a strong correlation with the number of phenyl-bridged glucosyltriazolyl groups in diarylethene systems. The absorption maximum, thermal stability, and fatigue resistance were significantly improved, but the water solubility and fluorescent modulation efficiency were suppressed with the increase of the number of phenyl-bridged glucosyltriazolyl groups for these diarylethene derivatives.

Full text of DOI:10.1016/j.tet.2013.12.037

Tetrahedron 70 (2014) 852e858
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Tetrahedron
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The effects of phenyl-bridged glucosyltriazolyl groups on the
properties of water-soluble diarylethene derivatives
*
Shouzhi Pu , Hongliang Liu, Gang Liu, Bing Chen, Zhipeng Tong
Jiangxi Key Laboratory of Organic Chemistry, Jiangxi Science & Technology Normal University, Nanchang 330013, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Three water-soluble diarylethenes with glycosyltriazolyl groups and variable phenyl units have been
synthesized, and their properties, such as water solubility, photochromism, and fluorescence have been
discussed. Upon alternating irradiation with UV and visible light, each of the diarylethenes exhibited
favorable photochromism and functioned as fluorescent switches in water. Experimental results showed
that their water solubility as well as absorption features, cyclization quantum yields, photoconversion
ratios, thermal stability, and fatigue resistance exhibited a strong correlation with the number of phenyl-
bridged glucosyltriazolyl groups in diarylethene systems. The absorption maximum, thermal stability,
and fatigue resistance were significantly improved, but the water solubility and fluorescent modulation
efficiency were suppressed with the increase of the number of phenyl-bridged glucosyltriazolyl groups
for these diarylethene derivatives.
Received 9 September 2013
Received in revised form 16 November 2013
Accepted 12 December 2013
Available online 17 December 2013
Keywords:
Diarylethene
Glycosyltriazolyl group
Water solubility
Photochromism
Fluorescence
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
light in aqueous solution.10a,15 For example, Yi and co-workers
prepared
a new amphiphilic diarylethene, which exhibited
Organic photochromic molecules have gained much attention
for potential applications in optical memories and photo-
switches.1e3 In recent decades, considerable attention has been
focusing on photochromic diarylethenes due to high conversion
efficiency of reversible photochromic reactivity, excellent thermal
stability of both isomers, and remarkable fatigue resistance.4e7 On
one hand, diarylethenes have shown great promise as new mate-
rials for optoelectronic devices and molecular switches.8e12 On the
other hand, their biological applications have not yet been exten-
sively explored, although a few precedent works have been re-
ported.13 For biological applications, it is necessary for
diarylethenes to undergo photocyclization and cycloreversion re-
actions in aqueous solution. Solubility in water is a very important
property to be applied in biological fields, such as biosensors or
drug deliveries. However, most of the reported works are carried
out in organic systems, including the newly developed fluorescent
photochromic diarylethenes for labeling biomolecules.14 During
the past decade, much effort has been focusing on designing and
synthesizing water-soluble diarylethenes, since they have potential
applications in biological field.
switchable fluorescence and formed stable vesicle nanostructures
in aqueous solution.15a Irie and co-workers synthesized diary-
lethene derivatives with hexaethylene glycol side chains and in-
vestigated their self-assembling photochromic behavior in organic
solvents and water.10a,15b,c But their solubility in water was rela-
tively small and the aqueous solutions easily turned turbid upon
heating. Irie and co-workers also developed a simple non-covalent
approach to improve the water solubility of the perfluorinated
diarylethenes.15e The water-insoluble diarylethenes could be en-
capsulated into a water-soluble nanocavitand to induce photo-
chromic performance in aqueous solution. However, this method is
not easy to achieve due to its difficulty in selecting a perfect cav-
itand for each diarylethene molecule. In order to capsulate hydro-
phobic diarylethenes into a cavitand, the entrance diameter and
volume of cavitand should be very large. Belov and co-workers
reported a water-soluble photochromic diarylethene, but the syn-
thetic method was very complex and the total yield was only about
3%.15f As mentioned above, it is strongly desired to develop simple
methods to explore new photochromic systems with good water
solubility.
So far, several amphiphilic photochromic diarylethenes exhibi-
ted favorable photochromism upon irradiation with UV and visible
In a previous work, we have reported that a diarylethene with
two glucosyltriazolyl groups exhibited favorable photochromism in
both water and a PMMA solid film.16 The result inspired us to do
a consecutive research in this work. We have a strong desire
to understand what the relationship is between the molecular
structures and the water solubility of diarylethenes with
* Corresponding author. Tel./fax: þ86 791 83831996; e-mail address: pushouzhi@
tsinghua.org.cn (S. Pu).
0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.12.037

S. Pu et al. / Tetrahedron 70 (2014) 852e858
853
glucosyltriazolyl groups. Therefore, three diarylethenes (1oe3o)
with glucosyltriazolyl groups were synthesized to investigate the
effects of phenyl-bridged glucosyltriazolyl groups on the properties
of these diarylethene derivatives. All of these diarylethene de-
rivatives showed favorable photochromism in both aqueous solu-
tion and PMMA amorphous films. The photochromic reactions of
1oe3o are shown in Scheme 1.
CHN 2400 analyzer. Fluorescent spectra were measured using
a Hitachi F-4500 fluorimeter. Absorption spectra were measured
using an Agilent 8453 UV/vis spectrophotometer. Photoirradiation
was carried out using an SHG-200 UV lamp, CX-21 ultraviolet
fluorescence analysis cabinet, and a BMH-250 Visible lamp. The
required wavelength was isolated by the use of the appropriate
filters. The quantum yields of cyclization/cycloreversion were de-
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
F
HO
HO
OH
OH
S
S
S
S
N
N
N
N
N
N
O
O
N
N
N
N
O
O
1o
1c
O
O
O
N
O
N
OH
OH
OH
OH
HO
HO
HO
HO
HO
HO
OH
OH
F
F
F
F
F
F
F
F
F
F
OH
OH
HO
HO
S
S
S
S
N
N
N
N
N
N
O
O
N
N
UV
Vis
N
O
N
O
O
O
N
OH
OH
N
OH
OH
O
2o
O
HO
HO
2c
HO
HO
HO
HO
OH
OH
F
F
F
F
F
F
F
F
F
F
HO
HO
OH
OH
S
S
S
N
N
N
S
N
N
N
O
N
N
O
O
N
O
N
O
O
O
O
HO
N
OH
OH
HO
N
OH
OH
3c
3o
HO
HO
OH
OH
HO
HO
Scheme 1. Photochromism of 1e3.
2. Experimental
2.1. General
termined by comparing the reaction yield of 1,2-bis(2-methyl-5-
phenyl-3-thienyl)perfluorocyclopentene in hexane.17 Dissolved
ultrasonically 10 mg of diarylethene sample and 100 mg PMMA
into 1.0 mL chloroform, the film was prepared by spin-coating on
the surface of quartz substrate.
Melting points were taken on a WRS-1B melting point appara-
tus. NMR spectra were recorded on a Bruker AV400 (400 MHz)
spectrometer with CDCl3 and tetramethylsilane as the solvent and
tetramethylsilane as an internal standard. Infrared spectra (IR)
were recorded on a Bruker Vertex-70 spectrometer. Elemental
analysis was measured with an elemental analyzer labeled the PE
2.2. Synthesis
Diarylethene 3o was synthesized by the reported method.16 The
synthesis route for diarylethenes 1o and 2o is shown in Scheme 2.
Scheme 2. Synthetic route for 1o and 2o.

854
S. Pu et al. / Tetrahedron 70 (2014) 852e858
2.2.1. 1,2-Bis{2-methyl-5-{4-[5-(2,3,4,6-tetraacetyl-
b
-
D
-glycoside)-3-
122.62, 125.27, 127.19, 128.93, 129.73, 129.22, 133.30, 135.09, 135.59,
141.78, 143.30.
(1,2,3-triazole)]methyl}phenyl-3-thienyl}perfluorocyclopentene
(6). To a stirred THF (90 mL) of compound 4 (0.70 g, 1.3 mmol) and
2-propynyl-2,3,4,6-tetraacetyl-
b-D
-glucoside
(5)16
(1.10
g,
2.2.5. 1-{2-Methyl-5-[5-(2,3,4,6-tetraacetyl-
triazole)]methyl-3-thienyl}-2-{2-methyl-5-{4-[5-(2,3,4,6-tetraacetyl-
-glycoside)-3-(1,2,3-triazole)]methyl}phenyl-3-thienyl}per-
b-D-glycoside)-3-(1,2,3-
2.6 mmol) was added 10.0 mL water containing NaVc (0.03 g,
0.2 mmol) and CuSO4 (0.01 g, 0.1 mmol) at room temperature. The
reaction mixture was stirred for 12 h at room temperature and then
extracted with CH2Cl2. The organic phase was dried over MgSO4,
filtered and evaporated. Column chromatography on SiO2 with
petroleum ether/ethyl acetate (1 : 5) as the eluent afforded 1.13 g of
6 as a light blue solid in 62% yield. Mp 367e368 K; 1H NMR (CDCl3,
b-D
fluorocyclopentene (10). Compound 10 was prepared by a method
similar to that used for compound 6 using compound 9 instead of 4.
Column chromatography on SiO2 with petroleum ether/ethyl ace-
tate (1:5) as the eluent afforded 1.17 g of 10 as a gray solid in 68%
yield. Mp 355e356 K; 1H NMR (CDCl3, 400 MHz),
d (ppm): 1.89 (s,
400 MHz),
d
(ppm): 1.90 (s, 6H),1.95 (s, 6H),1.99 (s, 6H), 2.02 (s, 6H),
3H), 1.91 (s, 3H), 1.95 (s, 3H), 2.00 (s, 3H), 2.01 (s, 3H), 2.03 (s, 3H),
2.04 (s, 3H), 2.05 (s, 3H), 2.08 (s, 3H), 2.09 (s, 3H), 3.72e3.74 (m, 2H),
4.10e4.17 (m, 2H), 4.24e4.28 (m, 2H), 4.66 (d,1H, J¼2.8 Hz), 4.68 (d,
1H, J¼2.8 Hz), 4.81 (d, 2H, J¼12.4 Hz), 4.92 (m, 2H), 4.99 (m, 2H),
5.09 (m, 2H), 5.18 (m, 2H), 5.54 (s, 2H), 5.64 (s, 2H), 7.12 (s, 1H), 7.25
2.07 (s, 6H), 3.72 (m, 2H), 4.13 (d, 2H, J¼12.8 Hz), 4.23 (d, 1H,
J¼4.8 Hz), 4.26 (d, 1H, J¼3.2 Hz), 4.66 (d, 2H, J¼7.6 Hz), 4.81 (d, 2H,
J¼12.4 Hz), 4.91 (d, 2H, J¼12.8 Hz), 4.98 (t, 2H, J¼8.8 Hz), 5.08 (t, 2H,
J¼9.6 Hz), 5.19 (t, 2H, J¼9.2 Hz), 5.53 (s, 4H), 7.30 (d, 6H, J¼9.2 Hz),
7.48 (s, 2H), 7.54 (d, 4H, J¼8.0 Hz); 13C NMR (CDCl3, 100 MHz),
(s, 1H), 7.30 (d, 2H, J¼8.0 Hz), 7.49 (s, 1H), 7.53 (d, 3H, J¼8.8 Hz). 13
C
d
(ppm): 14.49, 20.52, 20.67, 53.75, 61.82, 63.02, 68.35, 71.24, 71.93,
NMR (100 MHz, CDCl3), d (ppm): 14.17, 14.42, 14.47, 20.52, 20.54,
72.76, 99.96, 122.60, 122.98, 125.94, 126.23, 127.54, 128.41, 128.80,
133.89, 134.07, 141.17, 141.82, 144.77, 169.27, 169.36, 170.12, 170.55.
20.70, 21.00, 48.42, 53.74, 60.36, 61.75, 61.79, 63.02, 63.04, 68.31,
71.18, 71.20, 71.90, 71.94, 72.71, 72.73, 99.94, 100.06, 122.28, 122.63,
122.83, 124.93, 125.70, 126.23, 127.78, 128.81, 133.76, 134.14, 134.62,
141.34, 141.76, 143.80, 144.75, 144.84, 169.29, 169.39, 170.14, 170.59.
2.2.2. 1,2-Bis{2-methyl-5-{4-[5-(2,3,4,6-tetrahydroxyl-b-D-glyco-
side)-3-(1, 2, 3-triazole)]methyl}phenyl-3-thienyl}per-
fluorocyclopentene (1o). To a stirred methanol solution (90.0 mL)
containing compound 6 (0.80 g, 0.6 mmol) was added 10.0 mL
aqueous solution containing sodium hydroxide (0.24 g, 6.0 mmol)
at room temperature. The reaction mixture was stirred for 24 h at
room temperature and then evaporated. Column chromatography
on SiO2 with methanol as the eluent afforded 0.59 g of 1o as a blue
solid in 93% yield. Mp 361e362 K; Anal. Calcd for C47H48F6N6O12S2
(%): C, 52.90; H, 4.53; N, 7.88, found: C, 52.98; H, 4.57; N, 7.91; 1H
2.2.6. 1-{2-Methyl-5-[5-(2,3,4,6-tetrahydroxyl-
(1,2,3-triazole)]methyl-3-thienyl}-2-{2-methyl-5-{4-[5-(2,3,4,6-
tetrahydroxyl- -glycoside)-3-(1,2,3-triaz-ole)]methyl}phenyl-3-
thienyl}perfluorocyclopentene (2o). Compound 2o was prepared by
a method similar to that used for compound 1o using compound 10
instead of 6. Column chromatography on SiO2 with methanol as the
eluent afforded 0.56 g of 2o as an orange solid in 95% yield. Mp
350e351 K; Anal. Calcd for C41H44F6N6O12S2 (%):C, 49.69; H, 4.48;
N, 8.48, found: C, 49.76; H, 4.54; N, 8.56; 1H NMR ((CD3)2SO,
b-D-glycoside)-3-
b-D
NMR ((CD3)2SO, 400 MHz),
d (ppm): 1.96 (s, 6H), 2.97 (t, 2H,
J¼8.4 Hz), 3.06 (d, 2H, J¼8.8 Hz), 3.14 (m, 4H), 3.47 (m, 2H), 3.70 (d,
2H, J¼11.6 Hz), 4.26 (d, 2H, J¼7.6 Hz), 4.62 (d, 2H, J¼12.4 Hz), 4.85
(d, 2H, J¼12.0 Hz), 5.61 (s, 4H), 7.38 (d, 4H, J¼8.0 Hz), 7.50 (s, 2H),
7.64 (d, 4H, J¼8.0 Hz), 8.20 (s, 2H); 13C NMR ((CD3)2SO, 100 MHz),
400 MHz), d (ppm): 1.87 (s, 6H), 2.96 (m, 2H), 3.05 (d, 2H,
J¼10.4 Hz), 3.10 (m, 4H), 3.45 (m, 2H), 3.68 (d, 2H, J¼11.6 Hz), 4.24
(d, 2H, J¼11.6 Hz), 4.61 (d, 2H, J¼12.0 Hz), 4.83 (m, 2H), 5.61 (s, 2H),
5.80 (s, 2H), 7.27 (s, 1H, thiophene-H), 7.37 (d, 2H, J¼8.0 Hz,
benzene-H), 7.47 (s, 1H, thiophene-H), 7.63 (d, 2H, J¼8.0 Hz,
benzene-H), 8.17 (s, 1H), 8.20 (s, 1H); 13C NMR ((CD3)2SO, 100 MHz),
d
(ppm): 14.44, 52.84, 61.63, 62.03, 70.60, 73.85, 77.16, 77.48,
102.75, 123.32, 124.76, 125.44, 126.12, 129.38, 132.80, 136.31, 141.57,
141.93, 144.73; IR (KBr,
n
, cmꢀ1): 661, 744, 792, 897, 989, 1020, 1053,
d (ppm): 14.16, 14.20, 23.96, 47.39, 48.84, 52.63, 61.42, 61.68, 61.82,
1079, 1112, 1194, 1229, 1273, 1339, 1415, 1567, 3428; MS calcd for
C
70.38, 73.66, 76.99, 77.32, 102.48, 102.56, 123.02, 124.23, 124.58,
125.92, 127.32, 129.18, 132.58, 136.12, 137.09, 141.39,143.32, 144.53;
47H48F6N6O12S2Naþ [MþNa]þ: 1089.2, found 1089.2.
IR (KBr, n
, cmꢀ1): 531, 644, 990, 1021, 1051, 1080, 1110, 1275, 1342,
2.2.3. 1-(2-Methyl-5-hydroxymethyl-3-thienyl)-2-[2-methyl-5-(4-
hydroxymethyl)phenyl-3-thienyl]perfluorocyclopentene (8). To
1415, 1559, 1642, 3433; MS calcd for
C
43H47F6N6O14S-2
[MþCH3COO]ꢀ: 1049.2, found 1049.7.
a stirred THF of compound 7 (1.00 g, 2.0 mmol) and sodium boro-
hydride (0.15 g, 4.0 mmol) was refluxed for 2 h. After stopping the
reaction, the mixture was washed sequentially by aqueous NaHCO3.
The product was extracted with ether, dried with MgSO4, filtrated,
and evaporated in vacuo. Column chromatography on SiO2 with
petroleum ether/ethyl acetate (1 : 1) as the eluent afforded 0.91 g of
8 as a silver gray solid in 90% yield. Mp 408e409 K; 1H NMR (CDCl3,
3. Results and discussion
3.1. Solubility in water
The solubility of diarylethenes 1oe3o in water were measured
at room temperature according to the known method.18 When
reached a saturation state in water at 300 K, the solubility of 1oe3o
was 0.056, 47.0, and 750 mg mLꢀ1, respectively, indicating that the
water solubility increased with the decrease in the number of
phenyl-bridged glucosyltriazolyl groups in diarylethene systems.
Consequently, the solubility of 1o is the smallest and that of the 3o
is the biggest in water among the three diarylethene derivatives.
400 MHz),
d (ppm): 1.91 (s, 3H, eCH3), 1.92 (s, 3H, eCH3), 4.72 (d,
2H, J¼4.8 Hz, eCH2e), 4.78 (d, 2H, J¼5.6 Hz, eCH2e), 6.99 (s, 1H,
thiophene-H), 7.39 (d, 2H, J¼8.0 Hz, benzene-H), 7.54 (d, 2H,
J¼8.0 Hz, benzene-H).
2.2.4. 1-(2-Methyl-5-azidomethyl-3-thienyl)-2-[2-methyl-5-(4-
azidomethyl)phenyl-3-thienyl]perfluorocyclopentene (9). Compound
9 was prepared by a method similar to that used for compound 4.
Column chromatography on SiO2 with petroleum ether/ethyl ace-
tate (4:1) as the eluent afforded 0.81 g of 9 as a green solid in 91%
3.2. Photochromism of diarylethenes
The photochromic behaviors of 1e3 induced by photoirradiation
were measured at room temperature in both water and PMMA films.
The absorption spectral change of 1 and the color changes of 1e3
induced by photoirradiation in water are shown in Fig.1.1o exhibited
a sharp absorption peak at 292 nm (εmax¼2.5ꢁ104 L molꢀ1 cmꢀ1) in
yield. Mp 368e369 K; 1H NMR (CDCl3, 100 MHz),
d (ppm): 1.92 (s,
3H, eCH3), 1.94 (s, 3H, eCH3), 4.36 (s, 2H, eCH2e), 4.43 (s, 2H,
eCH2e), 7.04 (s, 1H, thiophene-H), 7.28 (s, 1H, thiophene-H), 7.34
(d, 2H, J¼8.4 Hz, benzene-H), 7.56 (d, 2H, J¼8.4 Hz, benzene-H). 13
C
NMR (100 MHz, CDCl3),
d
(ppm):14.51, 14.55, 48.90, 54.37, 120.19,
water, which arose from p/p
* transition.19 Upon irradiation with

S. Pu et al. / Tetrahedron 70 (2014) 852e858
855
Fig. 1. Absorption spectral changes of 1 and color changes of 1e3 upon alternating irradiation with UV and visible light in water at room temperature: (A) spectral changes of 1
(2.0ꢁ10ꢀ5 mol Lꢀ1); (B) color changes of 1e3.
297 nm light, a new visible absorption band centered at 592 nm
(εmax¼4.4ꢁ103 L molꢀ1 cmꢀ1) emerged, while the original peak at
292 nm decreased due to the formation of the closed-ring isomer 1c.
This could be seenwith the naked eyes, as the colorless solution of 1o
turned blue. Alternatively, the blue solution could be bleached
completely upon irradiation with visible light (l>450 nm), indicating
that 1c returned to the initial state 1o. In the photostationary state,
the isosbestic point of 1 was observed at 328 nm, which was in
agreement with the reversible two-component photochromic re-
action scheme. Similar to 1, diarylethenes 2 and 3 also exhibited
favorable photochromism in water. Upon irradiation with 297 nm
light, the colorless solution of 2o turned purple, and that of 3o turned
red due to the formation of the closed-ring isomers 2c and 3c, re-
spectively (Fig. 1B). The absorption maxima of 2c and 3c in water
were observed at 551 and 516 nm, respectively. In the photosta-
tionary state, the isosbestic points of 2 and 3 were observed at 315
and 261 nm, respectively. In the photostationary state, the photo-
conversion ratios from the open-ring to the closed-ring isomers of
the three derivatives were measured by HPLC analysis in methanol
(Fig. 2). It was calculated that the photoconversion ratios of 1e3 were
54% for 1, 48% for 2, and 40% for 3 in the photostationary state.
Compared to diarylethenes with a pyrrole moiety,20 the photo-
conversion ratios of 1e3 decreased significantly in solution, but were
much larger than those of diarylethenes with six-membered aryl
units.21
In PMMA films, 1e3 also showed similar photochromism as
observed in water. The absorption spectral changes of 1 and the
color changes of 1e3 are shown in Fig. 3. Upon irradiation with
297 nm UV light, the colorless 1o/PMMA film turned blue with the
absorption maximum observed at 594 nm. The colorless 2o/PMMA
film turned purple and 3o/PMMA film turned red by irradiating
with UV light. In the photostationary state, the absorption maxima
of 2c and 3c in PMMA films were observed at 557 and 520 nm,
respectively. All colored diarylethene/PMMA films could be
bleached completely by irradiating of visible light with appropriate
wavelength. Compared to those in water, the absorption maxima of
the closed-ring isomers 1ce3c in PMMA films were at longer
wavelengths, with the redshift values of 2 nm for 1c, 6 nm for 2c,
and 4 nm for 3c. The redshift may be attributed to the polar effect of
the polymer matrix as observed for most of the reported
diarylethenes.22
The photochromic parameters of 1e3 in both water and PMMA
films are summarized in Table 1. The results showed that the
number of phenyl-bridged glucosyltriazolyl groups in diarylethene
systems had a significant effect on the photochromic properties of
these water-soluble diarylethenes, including the absorption max-
ima, molar absorption coefficients, and quantum yields of cycliza-
tion/cycloreversion. Among the three compounds, 1, which
contained two phenyl-bridged glucosyltriazolyl groups, had the
Fig. 2. Photoconversion ratios of 1e3 in the photostationary state in methanol mea-
sured by HPLC analysis.
longest absorption maximum in both water and a PMMA film.
When the number of phenyl-bridged glucosyltriazolyl groups de-
creased, the absorption maxima of the diarylethenes shifted to
a shorter wavelength in both water and PMMA films due to re-
ducing the
p-conjugation in diarylethene systems. As a result, 3,
which contained no phenyl-bridged glucosyltriazolyl groups, had
the shortest absorption maximum in both water and a PMMA film.
Compared to those of 3c, the absorption maximum of 1c was red-
shifted by 76 nm in water, and by 74 nm in a PMMA film. The
molar absorption coefficients of the open-ring isomers 1oe3o in-
creased in the order of 2o<3o<1o, and those of 1ce3c increased in
the order of 3o<2o<1o in water. Compared to that of 3c, the molar
absorption coefficient of 1c was twofold larger in water. For 1 with
two phenyl-bridged glucosyltriazolyl groups, the cyclization
quantum yield was 0.30 and its cycloreversion quantum yield was
0.011. In water, the cyclization quantum yields of 1e3 increased in
the order of 2<1<3, and their cycloreversion quantum yields in-
creased in the order of 1<3<2. Therefore, the cycloreversion

856
S. Pu et al. / Tetrahedron 70 (2014) 852e858
Fig. 3. Absorption spectral changes of 1 and color changes of 1e3 upon alternating irradiation with UV and visible light in PMMA films (10%, w/w) at room temperature: (A) spectral
changes of 1; (B) color changes of 1e3.
Table 1
0.0
Absorption spectral properties of 1e3 in both water and PMMA films
Compd lo,max/nma
(ε/L molꢀ1 cmꢀ1
lc,max/nmb
Fc
Conversion
at PSS in
hexane (%)
-0.2
-0.4
-0.6
-0.8
-1.0
-1.2
-1.4
)
(ε/L molꢀ1 cmꢀ1
)
Water
PMMA Water
PMMA Foec Fceo
film
film
1
2
3
292 (2.5ꢁ104) 308
293 (5.9ꢁ103) 260
239 (1.1ꢁ104) 247
592 (4.4ꢁ103) 594
0.30 0.011 54
0.27 0.046 48
0.33 0.020 40
551 (2.2ꢁ103) 557
516 (2.1ꢁ103) 520
a
b
c
Absorption maxima of open-ring isomers.
Absorption maxima of closed-ring isomers.
Quantum yields of cyclization reaction (Foec) and cycloreversion reaction (Fceo),
343 K
1c
respectively.
2c
3c
0
100
200
300
400
500
600
quantum yield of 2 with mono-phenyl-bridged glucosyltriazolyl
group is the largest, and the cyclization quantum yield of 3 with
non-phenyl-bridged glucosyltriazolyl group is the largest among
the three derivatives. As mentioned above, the number of phenyl-
bridged glucosyltriazolyl groups had a great effect on the photo-
reactivity of these diarylethene derivatives.
Time (s)
Fig. 4. Thermal fading of 1ce3c at 343 K in water.
The thermal stability of the open-ring and closed-ring isomers
of 1e3 was tested in water at room temperature and 343 K, re-
spectively. After storing these solutions in water at room temper-
ature in the dark and then exposing them to air for more than 30
days, no changes were detected in colors and UV/Vis spectra for
1e3. No decomposition was detected, when these derivatives were
exposed to air for more than three months. To investigate the effect
of phenyl-bridged glucosyltriazolyl groups on the thermal stability
of the closed-ring isomers 1ce3c, the thermal cycloreversion ki-
netics of 1ce3c at 343 K was examined by the reported method5a,23
(Fig. 4). It could be clearly seen that the thermal fading rate of 3c
was the fastest and that of 1c was the slowest at 343 K. The result
suggested that the number of phenyl-bridged glucosyltriazolyl
groups could be effective to enhance the thermal stability of these
diarylethenes. In addition, the fatigue resistance of 1e3 was ex-
amined in water by alternating irradiation with UV and visible light
in air at room temperature (Fig. 5). The irradiation time was long
enough for coloration to reach the photostationary state. In water,
the coloration/decoloration cycles of 1e3 could be repeated for
more than eight times with 24% degradation of 1c, 58% degradation
of 2c, and 64% degradation of 3c. The result indicated that the
number of phenyl-bridged glucosyltriazolyl groups could effec-
tively enhance the fatigue resistance of these diarylethenes. Com-
pared to the reported diarylethenes,24 the fatigue resistance of 1e3
1.0
0.8
0.6
0.4
0.2
0.0
1
2
3
1
2
3
4
5
6
7
8
9
Cycle number
Fig. 5. Fatigue resistance of 1e3 in water in air atmosphere at room temperature.
Initial absorptance of the sample was fixed to 1.0.
was much poorer, but better than that of diarylethenes with
a benzene moiety.25

S. Pu et al. / Tetrahedron 70 (2014) 852e858
857
3.3. Fluorescence of diarylethenes
Vis UV
160
A
The fluorescence of 1e3 in water was measured at room tem-
perature. As shown in Fig. 6, the emission peaks of 1oe3o were
observed at 504, 406, and 430 nm in water (5.0ꢁ10ꢀ5 mol Lꢀ1),
when excited at 418, 323, and 259 nm, respectively. Among the
three compounds, the emission peak of 1o with two phenyl-
bridged glucosyltriazolyl groups was the longest and that of 2
was the shortest in water. Compared to that of 2o, the emission
peak of 1o was red-shifted by 98 nm in water. 1e3 behaved as
a weak fluorescent switch, when transformed from the open-ring
isomers to the closed-ring isomers by photoirradiation in water.
The emission intensity changes of 1e3 during the process of pho-
toisomerization are shown in Fig. 7. Upon irradiation with 297 nm
UV light, the photocyclization reaction occurred and the emission
intensity of 1 decreased due to the formation of the closed-ring
isomer 1c. When arrived at the photostationary state, its emis-
sion intensity was quenched to ca. 82% in water. Back irradiation
with visible light of appropriate wavelength regenerated the open-
ring isomer 1o and recovered the original emission intensity.
Similar to 1, diarylethenes 2 and 3 displayed analogous fluorescent
switch property by alternating irradiation with UV and visible light.
In the photostationary state, the emission intensity was quenched
to ca. 91% for 2 and 70% for 3, respectively. Compared to the dia-
rylethenes with two thiophene moieties,22c,26 the fluorescent
modulation efficiency of 1e3 decreased remarkably in solution. The
reason could be possibly attributed to the incomplete cyclization
reaction in water as well as to the existence of inactive 1o, 2o, and
3o in parallel conformations.26,27
120
80
40
460
480
500
520
540
560
580
Wavelength (nm)
180
150
120
90
Vis
UV
B
60
30
0
360
390
420
450
1.0
3
2
Wavelength (nm)
1
140
120
100
80
Vis
UV
C
0.8
0.6
0.4
60
350
400
450
500
550
Wavelength (nm)
380
400
420
440
460
480
Fig. 6. Normalized fluorescence emission spectra of 1e3 in water at room
Wavelength (nm)
temperature.
Fig. 7. Emission intensity changes of 1e3 in water (5.0ꢁ10ꢀ5 mol Lꢀ1) by photo-
irradiation at room temperature: (A) 1; (B) 2; (C) 3.
4. Conclusions
structureeproperty relationship for these water-soluble diary-
lethenes, the present results are valuable for the design of novel
diarylethenes with good water solubility and photochromic
properties.
In summary, a new class of water-soluble diarylethenes with
glycosyltriazolyl groups and variable phenyl units has been syn-
thesized to study the effect of the number of phenyl units on their
water solubility, photochromism, and fluorescent behavior. With
the increase of the number of phenyl-bridged glycosyltriazolyl
groups, their photochromic properties, including the absorption
maximum, photoconversion ratio, thermal stability, and fatigue
resistance were significantly enhanced. However, their water sol-
ubility and fluorescent modulation efficiency were remarkably
suppressed. Though a more detailed study on more structural an-
alogs is required to completely elucidate the molecular
Acknowledgements
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 Science
Funds of Natural Science Foundation of Jiangxi Province

858
S. Pu et al. / Tetrahedron 70 (2014) 852e858
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