Novel macrocycles bearing dithienylethene units and urea functional groups: Synthesis, structure and photochromic property

Article abstract of DOI:10.1002/cjoc.201300246

Two novel photochromic macrocycles 1 and 2 bearing dithienylethene units and urea building blocks have been synthesized, and their photochromic properties are described. Macrocycle 2 shows good photochromic properties, while the relatively smaller size of

Full text of DOI:10.1002/cjoc.201300246

FULL PAPER
DOI: 10.1002/cjoc.201300246
Novel Macrocycles Bearing Dithienylethene Units and Urea
Functional Groups: Synthesis, Structure and
Photochromic Property†
Tangxin Xiao, Shaolu Li, Xiaoning Zhang, Chen Lin, and Leyong Wang*
Key Laboratory of Mesoscopic Chemistry of Ministry of Education, Center for Multimolecular Chemistry, School of
Chemistry and Chemical Engineering, Nanjing University, Nanjing, Jiangsu 210093, China
Two novel photochromic macrocycles 1 and 2 bearing dithienylethene units and urea building blocks have been
synthesized, and their photochromic properties are described. Macrocycle 2 shows good photochromic properties,
while the relatively smaller size of macrocycle 8b exhibits photochemically inactive properties due to the unfa-
vourable ring conformational constraint. Moreover, the crystal structures of the urea-protected precursor macrocyles
3a, 3b, and 8b are presented.
Keywords photochromism, macrocycles, dithienylethene, urea derivatives, supramolecular chemistry
Introduction
conformation, which prohibits its photocyclization.
Macrocyclic molecules bearing photochromic units
are an intriguing class of compounds, which are capable
of playing the role of basic building blocks for unique
molecular switches and smart materials.[1] Among many
known photochromic compounds, dithienylethene moi-
ety has been proved to be the most promising
switchable unit due to its excellent fatigue resistance
and thermal stability.[2] On accounts of such outstanding
properties, an increasing number of dithienylethene de-
rivatives with enhanced photochromic properties by
introducing some unique functional groups have been
reported in recent years.[3] Moreover, dithienylethene
moiety has shown broad applications in areas ranging
from photo-switchable molecular machines[4] and
photo-responsible supramolecular polymers[5] to bio-
logical systems.[6] Photocyclization of dithienylethene
can proceed only from the antiparallel conformer of
open-isomers, while the photochemical reactivity of
dithienylethene can be hindered when two thienyl rings
are fixed in mirror symmetry (parallel conformer) in the
molecule (Scheme 1).[7] Based on this unique property,
we have already reported a new photochemical ap-
proach to investigate ring-chain mechanism of supra-
molecular polymers by introducing a dithienylethene
unit into bifunctional ureidopyrimidinone (UPy) deriva-
tives.[8] The two UPy functional groups of the target
compound can dimerize intramolecularly in dilute solu-
tion through quadruple hydrogen bonding to form a cy-
clic monomer with two thienyl rings fixed in a parallel
Scheme 1 Photochromic reactions of dithienylethenes
H3C
CH3
CH3
S
R
R
S
S
H3C
S
R
R
parallel
anti-parallel
hv
hv
hv'
CH3
H3C
S
S
R
R
Whereas the fabrication of monomeric or polymeric
dithienylethene derivatives is well documented, macro-
cyclic architecture of dithienylethenes is relatively less
common.[1d,9] Therefore, it is an attractive challenge to
realize self-assembly of macrocyclic molecules bearing
dithienylethene units. In 2012, Iwasawa and cowork-
ers[10] have reported the guest-induced self-assembly of
a macrocyclic boronic ester containing photochromic
diarylethene units, which showed high quantum yield of
photoisomerization due to the favorable conformational
constraint. Macrocyclic host molecules containing urea
groups are also an interesting class of molecular build-
ing blocks, which can self-assemble into unique
three-dimensional nanoscale structures due to hydrogen
*
E-mail: lywang@nju.edu.cn; Fax: 0086-025-83317761
Received March 26, 2013; accepted April 21, 2013; published online May 14, 2013.
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cjoc.201300246 or from the author.
Dedicated to Professor Hongwen Hu on the occasion of his 89th birthday.
†
Chin. J. Chem. 2013, 31, 627—634
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Xiao et al.
FULL PAPER
bonds originated from urea groups.[11] In 2008, Feringa
and coworkers[12] have reported dithienylethene-bisurea-
based low molecular weight gelators which are able to
function as photo responsive organogels that show a
remarkable gel-to-liquid transition upon irradiation by
incorporating urea group into dithienylethene molecules.
Inspired by these, we envisioned that the strategic in-
troduction of dithienylethene units into a urea-based
macrocyclic framework would achieve both photo-
chromic responsiveness and unique self-assembly be-
havior simultaneously. In the present study, two novel
photochromic macrocycles 1 and 2 bearing urea groups
are synthesized, and their structures and photochromic
reactivities are described (Scheme 2).
trometer. L-EM and S-EM photo luminescence spectra
were measured on a Lambda 55 and an Aminco Bow-
man Series 2 luminescence spectrometers. Low-resolu-
tion electrospray ionization mass spectra (LR-ESI-MS)
were obtained on Finnigan Mat TSQ 7000 instruments.
High-resolution electrospray ionization mass spectra
(HR-ESI-MS) were recorded on an Agilent 6210 TOF
LCMS equipped with an electrospray ionization (ESI)
probe operating in positive-ion mode with direct infu-
sion. Matrix-assisted laser desorption/ionization time-
of-flight (MALDI-TOF) mass spectra were recorded in
positive-ion mode using an Autoflex III (BrukerDalton-
ics, Germany) time-of-flight mass spectrometer. Com-
pound 7 was prepared according to procedures reported
previously.[12] Compound 6 was obtained from 7 ac-
cording to the reported literature.[13] Compounds 11[12]
and 10[14] are also reported previously, but the synthetic
routes are different. The main spectra of the compounds,
such as 1H NMR, 13C NMR, MS and CIF file for X-ray
crystal data could be found in the Supporting Informa-
tion.
Scheme 2 Chemical structures of macrocycles 1 and 2
S
S
H N
H N
N H
N H
O
O
Single crystal X-ray analysis
S
S
Single crystal X-ray data were measured on a Bruker
SMART APEX II CCD diffractometer (Mo Kα radia-
tion, λ＝0.71073 Å). Structure solutions and refine-
ments were carried out using the SHELXTL-PC soft-
ware package. Crystallographic data of compounds 3a,
3b and 8b are presented as follows. 3a: colorless,
C48H62N6O2S4, Mr＝883.30, monoclinic, space group
P21/c, a ＝13.2050(12) Å, b ＝17.8440(16) Å, c ＝
11.5850(11) Å, α＝90.00°, β＝91.373(3)°, γ＝90.00°,
V＝2729.0(4) Å3, Z＝2, Dc＝1.196 g•cm−3, T＝291(2)
K, μ＝0.219 mm−1, 4657 measured reflections, 2935
independent reflections, F(000)＝1058, R1 ＝0.0872,
wR2＝0.1108 (all data), R1＝0.0559, wR2＝0.1062 [I＞
2sigma(I)], largest diff. peak and hole 0.261 and −0.191
e•Å−3, goodness-of-fit on F2＝1.097, CCDC-830768. 3b:
colorless, C24H31N3OS2, Mr＝441.65, triclinic, space
group P1, a＝8.9298(11) Å, b＝9.0638(12) Å, c＝
15.832(2) Å, α ＝84.890(2)°, β ＝85.452(3)°, γ ＝
69.210(2)°, V＝1191.6(3) Å3, Z＝2, Dc＝1.281 g•cm−3,
T＝291(2) K, μ＝0.249 mm−1, 4118 measured reflec-
tions, 2472 independent reflections, F(000)＝492, R1＝
0.0749, wR2＝0.1025 (all data), R1＝0.0527, wR2＝
0.0968 [I＞2σ(I)], largest diff. peak and hole 0.443 and
−0.273 e•Å−3, goodness-of-fit on F2＝1.001, CCDC-
830769. 8b: colorless, C36H39N3OS2, Mr＝593.84, or-
thorhombic, space group Pccn, a＝16.2521(17) Å, b＝
35.4053(16) Å, c＝11.6291(12) Å, α＝90.00°, β＝
90.00°, γ＝90.00°, V＝6691.5(10) Å3, Z＝4, Dc＝1.197
g•cm−3, T＝291(2) K, μ＝0.193 mm−1, 6571 measured
reflections, 4781 independent reflections, F(000)＝2568,
R1＝0.0548, wR2＝0.0951 (all data), R1＝0.0405, wR2
＝0.0921 [I＞2σ(I)], largest diff. peak and hole 0.129
and −0.132 e•Å−3, goodness-of-fit on F2 ＝1.052,
CCDC-830847.
1
S
S
N H
N H
H N
H N
O
O
S
S
2
Experimental
General methods
All reactions were performed in atmosphere unless
noted. The commercially available reagents and sol-
vents were either employed as purchased or dried ac-
cording to procedures described in the literature. All
yields were given as isolated yields. NMR spectra were
recorded on a Bruker DPX 300 MHz spectrometer with
internal standard tetramethylsilane (TMS) and solvent
signals as internal references, CDCl3 was used as re-
ceived. UV-Vis spectra were obtained from a Perkin-
Elmer Lambda 25 and a Shimadzu UV-2401 spec-
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Chin. J. Chem. 2013, 31, 627—634

Novel Macrocycles: Synthesis, Structure, and Photochromic Property
＋
1
Synthesis of (4,4'-(cyclopentene-1,2-diyl)bis(5-methyl-
thiophene-4,2-diyl))dimethanol (5)
(%): 905.58 ([M＋Na] , 100%). 3b: H NMR (300
MHz, CDCl3) δ: 6.91 (s, 2H), 5.21 (d, J＝15.3 Hz, 2H),
4.23 (d, J＝10.4 Hz, 2H), 4.11 (d, J＝10.4 Hz, 2H),
3.33 (d, J＝15.3 Hz, 2H), 2.90－2.58 (m, 4H), 2.29 (s,
6H), 2.11－1.94 (m, 2H), 1.20 (s, 9H); 13C NMR (75
MHz, CDCl3) δ: 158.7, 136.5, 135.8, 134.8, 132.9,
131.3, 54.3, 43.9, 37.0, 28.9, 23.5, 14.3; ESI-MS m/z
(%): 464.17 ([M＋Na]＋, 100).
To a solution of 6 (0.46 g, 1.45 mmol) in ethanol (35
mL) was slowly added a solution of potassium boro-
hydride (0.30 g, 5.6 mmol) in ethanol (7 mL) and water
(7 mL). After stirring for 1 h at room temperature, the
reaction mixture was extracted with ether (30 mL×2),
and the combined organic layer was washed with satu-
rated aqueous brine and dried over MgSO4. Removal of
the solvent gave alcohol 5 as a yellow solid (0.38 g,
82%). It was used for the following reaction without any
further purification. 1H NMR (300 MHz, CDCl3) δ: 6.63
(s, 2H), 4.64 (s, 2H), 2.75 (t, J＝7.5 Hz, 4H), 2.09－
1.97 (m, 2H), 1.94 (s, 6H); 13C NMR (75 MHz, CDCl3)
δ: 139.5, 135.5, 135.1, 134.7, 127.0, 60.1, 38.4, 23.1,
14.5.
Synthesis of bis-urea macrocycle 1
The protected macrocycle 3a (0.045 g, 0.051 mmol)
was dissolved in MeOH (10 mL) and a solution of 20%
diethanol amine (5 mL, pH≈2, previously adjusted
with conc. HCl) was added. The mixture was heated at
85 ℃ overnight. After cooled to room temperature,
precipitate was filtered and washed with H2O (5 mL),
MeOH (5 mL), H2O (5 mL) and MeOH (5 mL) to afford
1
3a as an off white solid (0.032 g, 90%). H NMR (300
Synthesis of 1,2-bis(5-(chloromethyl)-2-methylthio-
phen-3-yl)cyclopent-1-ene (4)
MHz, DMSO-d6) δ: 6.57 (s, 4H), 6.37 (t, J＝6.0 Hz,
4H), 4.19 (d, J＝5.8 Hz, 8H), 2.69 (t, J＝7.4 Hz, 8H),
2.02－1.85 (m, 4H), 1.77 (s, 12H); HR-ESI-MS m/z:
711.1934 ([M＋Na]＋).
To a reaction flask (100 mL), 5 (0.40 g, 1.25 mmol)
and dry pyridine (1.0 mL) were dissolved in dry THF
(40 mL) at 0 ℃ under argon. Thionyl chloride (0.37
mL, 5 mmol) was added, and the solution was allowed
to stir for 2 h. The mixture was poured into ice-water
(40 mL) and extracted with ether (30 mL×2). The
combined organic phases were washed with saturated
NaHCO3 (30 mL), dried over anhydrous MgSO4 and
evaporated in vacuo to give 4 as a brown solid (0.38 g,
85%). Since this compound was not very stable in air, it
was used for the next step right away without any fur-
ther purification. 1H NMR (300 MHz, CDCl3) δ: 6.72 (s,
2H), 4.67 (s, 4H), 2.75 (t, J＝7.5 Hz, 4H), 2.09－1.96
(m, 2H), 1.92 (s, 6H).
Synthesis of 1,2-bis(5-(4-(1,3-dioxolan-2-yl)phenyl)-
2-methylthiophen-3-yl)cyclopent-1-ene (12)
The dichloride 7 (0.83 g, 2.5 mmol) was dissolved in
anhydrous THF (20 mL) under a nitrogen atmosphere,
and n-BuLi (3 mL, 2.5 mol•L−1 solution in hexane, 7.5
mmol) was added slowly at 0 ℃. Subsequently the re-
action mixture was allowed to warm to room tempera-
ture and stirred for 1 h. Then B(OC4H9)3 (2.0 mL, 7.5
mmol) was added, followed by stirring for the next 2 h
at room temperature. Degassed aq. Na2CO3 (10 mL of 2
mol•L−1 solution), Pd(PPh3)4 (0.092 g, 0.08 mmol), eth-
ylene glycol (20 drops) and 2-(4-bromophenyl)-1,3-
dioxolane (1.15 g, 5 mmol) were added and the mixture
was heated at reflux with stirring vigorously for 3 h.
Then additional Pd(PPh3)4 (0.046 g, 0.04 mmol) was
added and continued heating with stirring for another 3
h. The reaction mixture was cooled down to room tem-
perature, and extracted with ether (40 mL×2). The
ether extract was dried over MgSO4, and the solvent
was removed in vacuo. The residue was purified by
column chromatography [neutral Al2O3, ethyl acetate/
petroleum ether (V∶V＝7∶1)] to give pure 12 as a
yellow solid (0.67 g, 48%). 1H NMR (300 MHz, CDCl3)
δ: 7.43 (d, J＝8.4 Hz, 4H), 7.43 (d, J＝8.4 Hz, 4H),
7.04 (s, 2H), 5.81 (s, 2H), 4.13－4.02 (m, 8H), 2.84 (t,
J＝7.5 Hz, 4H), 2.13－2.03 (m, 2H), 1.99 (s, 6H); 13C
NMR (75 MHz, CDCl3) δ: 139.3, 136.8, 136.6, 135.4,
134.9, 134.8, 127.0, 125.3, 124.4, 103.6, 65.4, 38.5,
23.1, 14.5.
Synthesis of urea-protected macrocycles 3a and 3b
Triazinanone (0.19 g, 1.2 mmol) was weighed into a
dried round bottom flask (100 mL) under nitrogen and
dissolved in 35 mL anhydrous THF. Then NaH (0.27 g,
7.0 mmol, 60% content) was added to the solution and
the reaction mixture was heated at reflux for 30 min.
The reaction was cooled and a solution of readily pre-
pared dichloride 4 (0.97 g, 1.6 mmol in 40 mL THF)
was added. After the addition was completed, the reac-
tion was heated at reflux for 48 h. Then the reaction was
quenched with H2O (30 mL) and reduced to half of its
original volume under vacuum. The remaining aqueous
solution was extracted with CHCl3 (40 mL×3). The
combined organic layers were washed with brine and
then dried with anhydrous MgSO4. The solution was
reduced in vacuo. The residue was purified by column
chromatography on silica gel and eluted with chloro-
form/ethyl acetate (V∶V＝20∶1) to give white pre-
cipitate 3a (0.071 g, 10%) and 3b (0.085 g, 12%). 3a:
1H NMR (300 MHz, CDCl3) δ: 6.60 (s, 4H), 4.57 (s,
8H), 4.13 (s, 8H), 2.74 (t, J＝7.5 Hz, 8H), 2.10－1.94
(m, 4H), 1.82 (s, 12H), 1.20 (s, 18H); 13C NMR (75
MHz, CDCl3) δ: 156.1, 136.8, 135.0, 134.7, 134.4,
127.3, 61.9, 44.2, 38.5, 28.7, 23.0, 14.2; ESI-MS m/z
Synthesis of 4,4'-(4,4'-(cyclopentene-1,2-diyl)bis(5-
methylthiophene-4,2-diyl))dibenzaldehyde (11)[12]
A solution of diarylethene 12 (1.08 g, 1.94 mmol) in
wet acetone (30 mL) containing pyridinium tosylate
(1.60 g, 6.40 mmol) was refluxed overnight under a ni-
trogen atmosphere. The mixture was cooled to room
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Xiao et al.
FULL PAPER
temperature and water was added. The resultant mixture
was then extracted with diethyl ether (30 mL×2). And
the combined organic extracts were washed with brine
(40 mL) and dried over MgSO4. Removal of the solvent
in vacuo afforded 11 as a yellow solid (0.81 g, 89%). 1H
NMR (300 MHz, CDCl3) δ: 9.97 (s, 2H), 7.84 (d, J＝
8.4 Hz, 4H), 7.62 (d, J＝8.4 Hz, 4H), 7.19 (s, 2H), 2.86
(t, J＝7.5 Hz, 4H ), 2.18－2.06 (m, 2H), 2.04 (s, 6H);
13C NMR (75 MHz, CDCl3) δ: 191.5, 140.2, 138.3,
137.3, 137.2, 134.9, 134.8, 130.5, 126.2, 125.4, 38.6,
23.1, 14.7.
heated at reflux for 48 h. Then the reaction was
quenched with H2O (30 mL) and reduced to half of its
original volume under vacuum. The remaining aqueous
solution was extracted with CHCl3 (80 mL×3). The
combined organic layers were washed with brine and
then dried with anhydrous MgSO4. The solution was
reduced in vacuo. The residue was purified by column
chromatography on silica gel and eluted with chloro-
form/ethyl acetate (V∶V＝10∶1) to give white pre-
cipitate 8a (0.095 g, 10%) and 8b (0.104 g, 11%). 8a:
1H NMR (300 MHz, CDCl3) δ: 7.41 (d, J＝8.4 Hz, 8H),
7.26 (d, J＝8.4 Hz, 8H), 6.93 (s, 4H), 4.50 (s, 8H), 4.19
(s, 8H), 2.84 (t, J＝7.5 Hz, 8H), 2.12 (s, 12H), 2.10－
2.01 (m, 4H), 1.05 (s, 18H); 13C NMR (75 MHz, CDCl3)
δ: 156.4, 139.3, 137.0, 136.7, 135.1, 134.6, 133.7, 128.7,
125.6, 124.4, 62.2, 54.3, 48.9, 38.0, 28.6, 23.3, 14.6;
ESI-MS m/z (%): 1209.75 ([M＋Na] , 100). 8b: H
NMR (300 MHz, CDCl3) δ: 7.18 (d, J＝8.4 Hz, 4H),
6.99 (s, 2H), 6.98 (d, J＝8.4 Hz, 4H), 5.18 (d, J＝15 Hz,
2H), 4.19 (s, 4H), 3.46 (d, J＝15 Hz, 2H), 2.85 (t, J＝
7.5 Hz, 4H ), 2.39 (s, 6H) 2.15－1.99 (m, 2H), 1.25 (s,
9H); 13C NMR (75 MHz, CDCl3) δ: 157.4, 138.3, 136.5,
136.0, 135.6, 135.0, 133.4, 128.8, 127.3, 125.2, 54.3,
49.5, 37.2, 28.9, 23.6, 14.3; ESI-MS m/z (%): 616.50
([M＋Na]＋, 100).
Synthesis of (4,4'-(4,4'-(cyclopentene-1,2-diyl)bis(5-
methylthiophene-4,2-diyl))bis(4,1-phenylene))dimeth-
anol (10)[14]
To a solution of 11 (0.79 g, 1.69 mmol) in ethanol
(45 mL) was added slowly a solution of potassium
borohydride (0.40 g, 7.4 mmol) in ethanol (10 mL) and
water (10 mL). After stirring for 1 h at room tempera-
ture, the reaction mixture was extracted with ether (30
mL×2) and the combined organic extracts were washed
with saturated brine (40 mL) and dried over MgSO4.
Removal of the solvent gave diol 10 as a yellow solid
(0.72 g, 90%). It was used for the following reaction
＋
1
1
without any further purification. H NMR (300 MHz,
CDCl3) δ: 7.48 (d, J＝8.4 Hz, 4H), 7.32 (d, J＝8.4 Hz,
4H), 7.03 (s, 2H), 4.67 (s, 4H), 2.84 (t, J＝7.5 Hz, 4H),
2.15－2.03 (m, 2H), 2.00 (s, 6H); 13C NMR (75 MHz,
CDCl3) δ: 139.7, 139.4, 136.8, 134.8, 134.7, 134.0,
127.6, 125.5, 124.2, 65.1, 38.6, 23.1, 14.5.
Synthesis of bis-urea macrocycle 2
The protected macrocycle 8a (0.059 g, 0.049 mmol)
was dissolved in MeOH (15 mL) and a solution of 20%
diethanol amine (5 mL, pH was ca. 2, previously ad-
justed with conc. HCl) was added. The mixture was
heated at 85 ℃ overnight. After cooled to room tem-
perature, precipitate was filtered and washed with H2O
(5 mL), MeOH (5 mL), H2O (5 mL) and MeOH (5 mL)
to afford the bis-urea macrocycle 2 as an off white solid
(0.037 g, 76%).1H NMR (300 MHz, DMSO-d6) δ: 7.40
(d, J＝8.1 Hz, 8H), 7.18 (d, J＝8.1 Hz, 8H), 7.16 (s,
4H), 6.46 (t, J＝6.0 Hz, 4H), 4.18 (br s, 8H), 2.81 (t,
J＝7.5 Hz, 8H), 2.08－1.87 (m, 4H), 1.95 (s, 12H);
MALDI-TOF-MS m/z (%): 993.841 ([M＋H]＋, 100).
Synthesis of 1,2-bis(5-(4-(bromomethyl)phenyl)-2-
methylthiophen-3-yl)cyclopent-1-ene (9)
To a solution of 10 (0.28 g, 0.60 mmol) in 7 mL
CH2Cl2 at 0 ℃, was added PBr3 (0.11 mL, 1.2 mmol)
and the mixture was stirred at 0 ℃ for 30 min and at
ambient temperature for 90 min. The reaction mixture
was then poured into ice and extracted with CH2Cl2 (20
mL×2). The organic layer was washed with brine, and
dried with anhydrous Na2SO4. The solvent was evapo-
rated in vacuo. The residue was purified by column
chromatography [silica gel, ethyl acetate/ petroleum
ether (V∶V＝1∶6)] to give 9 as a yellow solide (0.25
g, 71%). 1H NMR (300 MHz, CDCl3) δ: 7.48 (d, J＝8.4
Hz, 4H), 7.32 (d, J＝8.4 Hz, 4H), 7.03 (s, 2H), 4.67 (s,
4H), 2.84 (t, J＝7.5 Hz, 4H ), 2.15－2.02 (m, 2H), 2.00
(s, 6H); 13C NMR (75 MHz, CDCl3) δ: 139.0, 136.9,
136.4, 135.1, 134.8, 134.7, 129.7, 125.6, 124.5, 38.5,
33.6, 23.1, 14.6.
Results and Discussion
The synthetic routes of the two macrocycles 1 and 2
are shown in Schemes 3 and 4. Compound 7 can readily
undergo alithium exchange at ambient temperature,
which was quenched with DMF to afford the dialdehyde
6.[13] Reduction of 6 with KBH4 gave diol 5, which was
treated with thionyl chloride in dry pyridine-THF to
give a brown solid compound 4 in 85% yield. Since the
dichloride compound 4 was not stable in air, it was used
right away for the next reaction without any further pu-
rification. Compound 4 was subjected to cyclize with
the triazinanone in THF/NaH to afford both the bis-urea
protected macrocycle 3a in 10% yield (“2＋2” adduct)
and mono-urea protected macrocycle 3b in 12% yield
(“1＋1” adduct) together. The protecting group in 3a
was removed by diethanol amine in methanol to give
Synthesis of urea-protected macrocycles 8a and 8b
Triazinanone (0.25 g, 1.6 mmol) was weighed into
an dried 250 mL round bottom flask under nitrogen and
dissolved in 50 mL of anhydrous THF. Then NaH (0.26
g, 6.5 mmol, 60% content) was added to the solution
and the reaction mixture was heated at reflux for 30 min.
The reaction was cooled and a solution of dibromide 9
(0.97 g, 1.6 mmol in 60 mL anhydrous THF) was added.
After the addition was completed, the reaction was
630
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© 2013 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2013, 31, 627—634

Novel Macrocycles: Synthesis, Structure, and Photochromic Property
Scheme 3 Preparation of macrocycle 1
KBH4
(1) n-BuLi/THF, r.t.
ethanol
OHC
CHO
S
Cl
S
S
Cl
S
S
S
S
HO
OH
6
7
5
N
N
"1+1"
O
N
O
N
HN
NH
S
3b
SOCl2
THF
NaH, THF
S
S
Cl
Cl
S
S
20% diethanol
amine
4
N
N
N
1
O
O
N
N
"2+2"
MeOH, reflux
N
S
S
3a
Scheme 4 Preparation of macrocycle 2
(1) n-BuLi/THF
(2) B(OC4H9)3
Pyridinium tosylate
Acetone, reflux
S
S
O
(3) Na2CO3 aq.
O
Cl
Cl
S
S
O
O
O
12
Br
7
O
PBr3
KBH4
CH2Cl2
S
Ethanol
S
S
S
S
S
OHC
CHO
11
Br
HO
9
10
Br
OH
S
N
O
N
"1+1"
O
N
HN
NH
S
N
8b
NaH, THF
S
S
20% diethanol amine
MeOH, reflux
N
N
N
N
2
"2+2"
O
N
N
O
S
S
8a
© 2013 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2013, 31, 627—634
www.cjc.wiley-vch.de
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Xiao et al.
FULL PAPER
the target bis-urea macrocycle 1 in 90% yield.
Compound 7 was converted into the bis(boronic) es-
ters via n-BuLi/B(OBu)3, which was directly used for
the Suzuki coupling with the ethylene glycol protected
bromobenzaldehydes to give the corresponding diacetal
derivative 12 in 48% yield. Deprotection of 12 with
PPTS in acetone under reflux afforded the formyl-sub-
stituted diarylethene 11 in 89% yield. The diol com-
pound 10 was then obtained by reduction of 11 with
KBH4 in ethanol at room temperature in 90% yield.
Bromination of the diol 10 with PBr3 in CH2Cl2 yielded
dibromide 9 in 71% yield. The dibromide 9 was cy-
clized with the triazinanone in THF/NaH to afford both
the bis-urea protected macrocycle 8a in 10% yield (“2＋
2” adduct) and mono-urea protected macrocycle 8b in
11% yield (“1＋1” adduct) together. The protecting
group in 8a was removed with the use of diethanol
amine in methanol to yield the target bis-urea macrocy-
cle 2 in 76% yield.
The urea-protected macrocycles 3a, 3b, 8a and 8b
were characterized by 1H NMR,13C NMR and MS tech-
niques. Furthermore, single crystals suitable for X-ray
diffraction were obtained by slow evaporation from
hexane/dichloromethane solution of 8b or from hexane
solution of 3a and 3b. The X-ray diffraction study gave
unambiguous assignment of the urea-protected macro-
cyclic structures of 3a, 3b and 8b. The crystal structures
of 3a, 3b and 8b (including part of atomic labeling) are
given in Figure 1. In contrast to the good solubility of
3a and 8a in CHCl3, both macrocycles 1 and 2 are in-
soluble in CHCl3 and only show low solubility in
DMSO. Thus it is hard to perform 13C NMR spectra for
macrocycles 1 and 2. However, macrocycles 1 and 2
were clearly characterized by 1H NMR and HR-ESI-MS
or MALDI-TOF-MS (For spectra, please see Supporting
Information). We have also tried to cultivate crystals for
bis-urea macrocycles 1 and 2 to get insight into the three
dimensional self-assembly behavior induced by urea
groups. However, no single crystal of 1 or 2 suitable for
X-ray diffraction was obtained due to their poor solu-
bilities. In the1H NMR spectrum of macrocycle 1, the
methyl-H, and thienyl-H resonance were observed at δ
1.77 and 6.57 in DMSO-d6, respectively. Similar signals
were observed at δ 1.95 and 7.16 in DMSO-d6 for mac-
rocycle 2. The mass spectra provided further evidence
for the formation of the bis-urea macrocycles. The spec-
tra of macrocycles 1 and 2 showed the m/z ratio at
711.1934 for [1＋Na]＋ and 993.841 for [2＋H]＋, re-
spectively, which were in good consistency with the
theoretic results.
Figure 1 ORTEP view of the compounds (a) 3b, (b) 3a, and (c)
8b with 30% thermal ellipsoids and labeling scheme. Hydrogen
atoms and solvent atoms are omitted for clarity.
spectroscopy. Upon irradiating a mixed CH2Cl2/DMSO
(V∶V＝1∶1) solution of 2 with UV light of 313 nm, a
new band appeared at 529 nm, corresponding to closed-
ring isomers (Figure 2). During this procedure, the col-
orless solution turned pale purple immediately (＜10 s)
and gradually changed to a deep red-purple (1 min).
Upon exposure of the red-purple solution to the visible
light (＞400 nm) for 5 min, the colored solution was
completely bleached, which indicated that the close-ring
form reverted to the open-ring form (Figure 3). That is
to say, the bis-urea macrocycle 2 could show good
photochromic properties, which is consistent to our
original assumption. Moreover, we have also examined
the photochemical reactivity of 8a, the precursor of 2.
Upon irradiating with UV light, 8a quickly changed into
the closed form within 13 s and reverted to the open-
ring form within 65 s upon exposure to visible light
(＞400 nm), indicating that 8a possesses good photo-
chromic property. Although both 8a and 2 are capable
of undergoing photochemical reaction, 8a showed more
sensitive to light irradiating and could accomplish the
photochemical reaction within very short time, which
might be due to the good solubility of 8a and the ten-
dency to adopt antiparallel conformation of the two
thienyl rings. However, no new absorption band was
observed upon irradiation with UV light in the CH2Cl2
solution of macrocycle 8b, which indicated that the two
dithienylethene units in the open-ring form were
The photochromic reaction of dithienylethene
moeity is based on the reversible ring-closing and
ring-opening reactions as shown in Scheme 1. Upon
irradiation with UV light, the open-ring isomer is con-
verted into the closed-ring isomer, which could be con-
verted back into open-ring isomer by irradiating with
visible light. The photo isomerization behavior of the
macrocyclic urea derivative 2 was monitored by UV-vis
632
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© 2013 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2013, 31, 627—634

Novel Macrocycles: Synthesis, Structure, and Photochromic Property
ring constraint and photo-reaction was forbidden.
Moreover, 8b showed some extent of decomposition if
elongating the exposure time upon UV light. Since both
the absorption band of the open form and the closed
form of macrocycle 1 were exhibited in UV region, it is
inconvenient for us to investigate the photoisomeriza-
tion behavior of 1 by using UV-vis spectroscopy (Figure
S26).[15]
Conclusions
In summary, we have successfully prepared two
novel macrocycles 1 and 2 bearing dithienylethene units
and urea groups. In particular, macrocycle 2 shows good
photochromic properties, while the relatively smaller
size of macrocycle 8b exhibits photochemically inactive
properties due to the unfavourable ring conformational
constraint. Further research efforts will focus on grow-
ing single crystals of 1 and 2 and studying their self-
assembly behavior directed by their urea groups. Fur-
thermore, we will also explore the possibilities of func-
tionalization of such macrocycles. This work is now
underway in our laboratory.
Figure 2 UV/Vis absorption spectral changes of 2 (2.5×10−5
mol/L) in DMSO/CH2Cl2 (V∶V＝1∶1) upon 313 nm light irra-
diation at 0, 10, 20, 30, 40, 50, 60, 70 s. The inset shows the color
change of solution before (left) and after (right) UV irradiation.
Acknowledgement
This work was supported by the National Natural
Science Foundation of China (Nos. 20932004,
21072093), and the Natural Science Foundation of
Jiangsu Province (No. BK2011551).
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Chin. J. Chem. 2013, 31, 627—634