Amide- and urea-functionalized dithienylethene: Synthesis, photochromism, and binding with halide anions

Article abstract of DOI:10.1021/ol202491e

A versatile amide- and urea-functionalized dithienylethene has been successfully synthesized. Upon irradiation with UV or visible light, the compound showed excellent fatigue resistance. As a synthetic receptor, the dithienylethene displayed switchable af

Full text of DOI:10.1021/ol202491e

ORGANIC
LETTERS
2011
Vol. 13, No. 22
6022–6025
Amide- and Urea-Functionalized
Dithienylethene: Synthesis,
Photochromism, and Binding with
Halide Anions
Ziyong Li, Chan Zhang, Yanliang Ren, Jun Yin,* and Sheng Hua Liu*
Key Laboratory of Pesticide and Chemical Biology, Ministry of Education, College of
Chemistry, Central China Normal University, Wuhan 430079, PR China
yinj@mail.ccnu.edu.cn; chshliu@mail.ccnu.edu.cn
Received September 14, 2011
ABSTRACT
A versatile amide- and urea-functionalized dithienylethene has been successfully synthesized. Upon irradiation with UV or visible light, the
compound showed excellent fatigue resistance. As a synthetic receptor, the dithienylethene displayed switchable affinities for Clꢀ and Brꢀ anions
when the UV/vis light was introduced. The switchable binding ability also had good reversibility.
In the past 40 years, anion recognition by synthetic
receptors has grown to be an abundant and inspired
research field, developing into a distinct branch of supra-
molecular chemistry due to the essential roles that anions
play in a wide variety of biological, clinical, and environ-
mental sciences.1,2 Traditional anion receptors have stable
structural configuration and binding ability; hence, mod-
ification of the structure has been the popular approach to
changing the binding ability. However, the adjustment of
binding ability using a simple method has proven to be a
challenging project.
Dithienylethene is a classical molecular switch system
that has been widely applied in molecular devices and
optical memory storage media.3 In view of the change of
structural configuration that can be easily obtained by
irradiation with UV/vis light, the introduction of the
dithienylethene unit has been thought to be helpful to form
the switchable synthetic receptor. Specifically, the varying
recognition ability for guests can be controlled by UV/vis
light. At present, synthetic receptors based on the dithie-
nyletheneunithave attracted someattention. Forexample,
Tian and co-workers recently reported two dithieny-
lethene-based fluorescence sensors, which efficiently de-
tected mercury(II) and fluoride ions.4 In our recent
(1) Sessler, J. L.; Gale, P. A.; Cho, W.-S. Anion Receptor Chemistry;
RSC Publishing: Cambridge, U.K., 2006.
(2) For selected reviews, see: (a) Gale, P. A.; Garcia-Garrido, S. E.;
Garric, J. Chem. Soc. Rev. 2008, 37, 151–190. (b) Piepenbrock, M-O. M.;
Lloyd, G. O.; Clarke, N.; Steed, J. W. Chem. Rev. 2010, 110, 1960–2004.
(c) Li, A. F.; Wang, J. H.; Wang, F.; Yun-Bao Jiang, Y. B. Chem. Soc.
Rev. 2010, 39, 3729–3745. (d) Ballester, P. Chem. Soc. Rev. 2010, 39,
3810–3830. (e) Kang, S. O.; Llinares, J. M.; Day, V. W.; Bowman-James,
K. Chem. Soc. Rev. 2010, 39, 3980–4003. (f) Duke, R. M.; Veale, E. B.;
Pfeffer, F. M.; Kruger, P. E.; Gunnlaugsson, T. Chem. Soc. Rev. 2010,
39, 3936–3953. (g) Amendola, V.; Fabbrizzi, L.; Mosca, L. Chem. Soc.
Rev. 2010, 39, 3889–3915. (h) Gale, P. A. Acc. Chem. Res. 2011, 44, 216–
226. (i) Haynes, C. J. E.; Gale, P. A. Chem. Commun. 2011, 47, 8203–
8209. (j) Dydio, P.; Lichosyt, D.; Jurczak, J. Chem. Soc. Rev. 2011, 40,
2971–2985.
(3) (a) Molecular Switches; Feringa, B. L., Ed.; Wiley-VCH: Weinheim,
Germany, 1990. (b) Irie, M. Chem. Rev. 2000, 100, 1685–1716. (c) Tian, H.;
Yang, S. Chem. Soc. Rev. 2004, 33, 85–97. (d) [4]Tian, H.; Feng, Y. L.
J. Mater. Chem. 2008, 18, 1617–1622.
(4) Zou, Q.; Jin, J.; Xu, B.; Ding, L.; Tian, H. Tetrahedron 2011, 67,
915–921.
r
10.1021/ol202491e
Published on Web 10/25/2011
2011 American Chemical Society

Scheme 1
research, we have also developed some work based on the
use of dithienylethene as a chemosensor by the introduc-
tion of the imidazole ligand.5 However, we still know very
little about these compounds, especially in the field of
switchable molecular recognition. This has provided the
motivation to study this system. We have therefore synthe-
sized an amide- and urea-functionalized dithienylethene,
as shown in Scheme 1. Its photochromism and recognition
properties have been well investigated. The photochromic
properties indicated that the compound had high cycliza-
tion quantum yield and excellent fatigue resistance. At the
same time, in its role as a synthetic receptor dithienylethene
displayed switchable affinities for Clꢀ and Brꢀ anions
upon irradiation with UV/vis light.
The anion receptor 1 was synthesized with a good yield
by treatment of 4,40-(cyclopent-1-ene-1,2-diyl)bis(5- meth-
ylthiophene-2-carbonyl chloride) with 1-(2-aminophenyl)-
3-phenylurea (see Supporting Information: Scheme S1).
The structure was fully confirmed by NMR spectroscopy,
elemental analysis, and mass spectrometry. In the 1H
NMR, the hydrogen bond donors (NH) exhibited three
different resonance signals, at 8.24, 9.29, and 9.99 ppm.
The photochromic behavior of compound 1 induced by
photoirradiation in DMSO was measured at room tem-
perature. As shown in Figure 1, the absorption maximum
of compound 1 was observed at 273 nm (ε = 3.84 ꢁ 104 L
molꢀ1 cmꢀ1) as a result of a πꢀπ* transition.6 Upon
irradiation with 302 nm UV light, the colorless solution
turned purple and a new absorption band at 542 nm (ε =
0.10ꢁ 104 L molꢀ1 cmꢀ1) appeared due tothe formation of
the corresponding ring-closed isomer 1c. Moreover, a well-
defined isosbestic point was observed at 327 nm, which
indicated that compound 1 was cleanly converted to the
photocyclized product. Upon irradiation with visible light
(λ > 402 nm), the colored 1c underwent a cycloreversion
reaction and returned to the initial colorless ring-opened
isomer 1o. In particular, compound 1 showed very good
reversibility, and no apparent deterioration was observed
after repeating the above process seven times, which
indicated that the compound 1 had very excellent fatigue
Figure 1. Absorption spectral changes of dithienylethene 1 by
photoirradiation in DMSO (2.0 ꢁ 10ꢀ5 mol/L). (Inside) Fatigue
resistance of dithienylethene 1 in DMSO.
resistance. The cyclization and cycloreversion quantum
yields of 1 were 0.43 and 0.0077, respectively.
Simultaneously, the photochromic process demon-
strated by 1 has been characterized by means of NMR
spectrometry (see Supporting Information: Figure S2). In
the open-ring state, compound 1 showed three different
NH signals at 9.99 (amide-Ha), 9.26 (urea-Hc), and 8.20
(urea-Hb) ppm. When the d6-DMSO solution of 1 under-
went UV light irradiation and achieved a photostationary
state, the amide-Ha and urea-Hb showed the 0.04 and 0.03
ppm upfieldshifts, respectively, asa resultofthechanges of
structural configuration between the two isomers. How-
ever, no obvious change was observed in the urea-Hc,
possibly due to the greater distance from the reactive
center. Furthermore, from the integrated area of the NH
signals, the photocyclization yield was calculated to be
34%.
Figure 2. ESI mass spectra of 1 (A), 1 Cl (B), and 1 Br (C).
3
3
The amide and urea functional groups, well-known for
their ability to interact with anions, were used as indicators
1
for halide anions using H NMR spectroscopy. For the
fluoride anion, the resonance signals (Ha, Hb, and Hc) of
the multiple hydrogen bond donors exhibited the same
(5) Huang, S. Y.; Li, Z. Y.; Li, S. S.; Yin, J.; Liu, S. H. Dyes Pigm.
2012, 92, 961–966.
(6) Li, Z. X.; Liao, L. Y.; Sun, W.; Xu, C. H.; Zhang, C.; Fang, C. J.
Phy. Chem. C 2008, 112, 5190–5196.
Org. Lett., Vol. 13, No. 22, 2011
6023

downfield shifts (see Supporting Information: Figure S3).
When the concentration of fluoride anions exceeded the
equivalent concentration of dithienylethene, all the NH
signals completely disappeared. However, a new signal at
around 16.00 ppm (See Supporting Information: Figure
S4) wasobservedwhenthe fluoride anion reached 5.0 times
the equivalent dithienylethene concentration, due to the
formation of [FHF]ꢀ, a result in good agreement with
previous reports.8 Similar downfield shifts of all NH
resonance signals were observed in the titration experi-
ments with chloride and bromide anions (see Supporting
Information: Figures S5 and S6), which can be attributed
to the formation of complexes between receptor 1 and
anions. The existence of the complexes was further con-
firmed by ESI mass spectroscopy. In Figure 2, the peaks at
800.8 and 846.7 (m/z) proved the presence of the 1:1
complexes 1 Cl and 1 Br. For the iodide anion, however,
3
3
no obvious chemical shifts were observed even when 10.0
equiv of iodide anion were added; the ESI mass spectro-
scopy still supported the formation of the 1:1 complex 1 I
3
(see Supporting Information).
The binding behaviors of 1 in the photostationary state
were further explored for halide anions. Figure 3 shows
the changes of chemical shifts when compound 1, in the
photostationary state, was allowed to bind with bromide
anions. As shown, the Ha, Hb, and Hc in the open-ring
isomer 1o displayed the same downfield shifts as in the
original state. At the same time, similar chemical shifts for
Figure 4. Top views of the energy-minimized structures for
complexes 1o Cl (A), 1c Cl (B), 1o Br (C), and 1c Br (D).
3
3
3
3
The association constants (K) of the receptor with halide
anions represent a very important parameter for evaluat-
ing the binding affinity. For 1o and 1c, analysis by the
nonlinear least-squares method7 was consistent with a 1:1
host/guest binding stoichiometry, which was in good
agreement with the ESI mass spectroscopy. In addition,
the values of K were determined by fitting the changes in
NMR chemical shifts. The binding constants with 1o and
1c were calculated to be 68.4 and 57.9 Mꢀ1 for the chloride
anion and 13.6 and 13.1 Mꢀ1 for the bromide anion,
respectively. From the association constants of 1o and 1c
for chloride and bromide anions, we can draw the conclu-
sion thattheopen-ringisomer1ohad greater affinities than
the closed-ring isomer 1c, a result attributed to the change
of structural configuration. This result told us that the
binding ability of the receptor was switchable by the very
simple method of photoirradiation.
0
Ha , Hb , and Hc were also obtained for the closed-ring
0
0
isomer 1c. Interestingly, Ha in 1o showed larger shifts than
0
Ha in 1cwhile Hb and Hc represent contrasting behavior to
0
0
Hb and Hc . This interesting phenomenon was also found
when we studied the binding with chloride anions in the
photostationary state. Finally, iodide anions did not pro-
duce any obvious changes, not only for the open-ring state
but also the closed-ring state (see Supporting Information:
Figures S9 and S10).
Subsequently, we optimized the energy-minimizedstruc-
tures of these complexes by theoretical calculation. As can
be observed from Figure 4, the open-ring complexes 1o Cl
3
and 1o Br revealed similar structural configurations while
the closed-ring complexes 1c Cl and 1c Br had an analo-
3
3
3
gous binding model. According to Figure 4A, the two
reactive carbons of 1o Cl are present in the antiparallel
conformation and the dithienylethene unit showed C2
symmetry. After the photochromic reaction, the cyclopen-
tene ring and thiophene rings were in a plane, and the
3
Figure 3. Partial 1H NMR spectra (400 MHz in DMSO at 298 K)
of 1 upon addition of 0ꢀ10 equiv of Bu4NBr after irradiation
with UV (302 nm) light.
dithienylethene unit of 1c Cl had an axially symmetrical
structure. Therefore, compared with 1o Cl, the 1c Cl had
a larger cavity, which was the reason why the open-ring
3
3
3
(8) Kang, S. O.; Powell, D.; Day, V. W.; Bowman-James, K. Angew.
Chem., Int. Ed. 2006, 45, 1921–1925.
(7) Hirose, K. J. Inclu. Phenom. Macro. Chem. 2001, 39, 193–209.
6024
Org. Lett., Vol. 13, No. 22, 2011

isomerpossessed higher affinity for the chlorideanion than
the closed-ring isomer. In addition, the distances from the
chlorineatom tothe hydrogen atomsofthehydrogen bond
donors further prove this suggestion. In Figure 4(A), the
distances between the chlorine atom and hydrogen atoms
were 2.70ꢀ2.71 (Cl Ha), 2.41ꢀ2.42 (Cl Hb), and
3 3 3
3 3 3
˚
2.32ꢀ2.33 A (Cl Hc). In contrast, 1c Cl had distances
3 3 3
3
from the chlorine atom to the hydrogen atoms of 4.24
˚
(Cl Ha ), 3.70 (Cl Hb ), and 2.45 A (Cl Hc ), as
0
0
0
3 3 3 3 3 3 3 3 3
shown in Figure 4B.
Similar results were also achieved from the energy-mini-
Figure 5. Fatigue resistance of switchable affinity for chloride
anion (A) and bromide anion (B).
mized structures of complexes 1o Br and 1c Br. In
3
3
Figure 4C, the distances between the bromine and hydrogen
atoms were 2.73ꢀ2.75 (Br Ha), 2.54ꢀ2.58 (Br Hb),
3 3 3
3 3 3
˚
and 2.40ꢀ2.43 A (Br Hc). In the closed-ring complexes
indicated that the compound had good reversibility, ex-
cellent fatigue resistance, and high cyclization quantum
yield. This was followed by an investigation of the recogni-
tion properties of the open- and closed-ring isomers as
anion receptors for halide anions. Using photoirradiation
with UV/vis light, we have shown that the compound has
switchable affinity for chloride and bromide anions and
that the switchable recognition function could be repeated
ten times without any decay. The results indicated that the
adjustment of the binding ability can be easily achieved
by this type of simple photoirradiation. Therefore, our
studies have supplied an alternative model for the design of
novel supramolecular hosts with a switchable recognition
function.
3 3 3
0
1c Br, the distances were 3.89ꢀ4.09 (Br Ha ), 2.87ꢀ3.00
3
3 3 3
˚
0
0
(Br Hb ), and2.35ꢀ2.38 A (Br Hc ). The data indicated
3 3 3
3 3 3
that the open-ring isomer possessed higher affinity for bro-
mine anions than the closed-ring isomer, just as for chloride.
As has been mentioned, compound 1 showed excellent
reversibility between the open-ring isomer and closed-ring
isomer. Now the question arises astowhether this excellent
reversibility can be achieved in its recognition ability for
halide anions. Therefore, we next studied the switchable
affinity for chloride and bromide anions using NMR
spectrometry. Upon irradiation with visible light (>402
nm), the NH signals of the closed-ring isomer gradually
weakened and disappeared after irradiation for 50 min (see
Supporting Information: Figures S15 and S16). Such
changes corresponded to the changes of recognition ability
and increasing affinity for chloride and bromide anions.
Moreover, further irradiation with UV light reduces the
affinity. Satisfyingly, the switchable process could be
repeated ten times without any decay, as can be seen from
Figure 5. This indicated that the amide- and urea-functio-
nalized dithienylethene synthetic receptor showed repea-
table switching of its recognition ability for halide anions
using photocontrol.
Acknowledgment. This work was supported by the Na-
tional Natural Science Foundation of China (Nos.
20931006, 21072070) and Program for Changjiang Scho-
lars and Innovative Research Team in University (No.
IRT0953).
Supporting Information Available. Details on the syn-
thesis, characterization, anion binding and NMR, MS
spectra are available in the Supporting Information. This
material is available free of charge via the Internet at
http://pubs.acs.org.
In summary, an amide- and urea-functionalized dithie-
nylethene was synthesized. Its photochromic properties
Org. Lett., Vol. 13, No. 22, 2011
6025