Photo-controlled molecular recognition of α-cyclodextrin with azobenzene containing polydiacetylene vesicles

Article abstract of DOI:10.1039/b820894h

Herein, photo-controlled inclusion and exclusion reaction of azobenzene-containing polydiacetylene vesicles with α-cyclodextrin were used to act as driving force to induce chromatic transition of PDA vesicles, which provided a novel model system that comb

Full text of DOI:10.1039/b820894h

View Article Online / Journal Homepage / Table of Contents for this issue
COMMUNICATION
www.rsc.org/chemcomm | ChemComm
Photo-controlled molecular recognition of a-cyclodextrin with azobenzene
containing polydiacetylene vesiclesw
Xin Chen,a Lei Hong,b Xian You,a Yali Wang,a Gang Zou,*a Wei Sua and Qijin Zhanga
Received (in Cambridge, UK) 21st November 2008, Accepted 19th January 2009
First published as an Advance Article on the web 13th February 2009
DOI: 10.1039/b820894h
Herein, photo-controlled inclusion and exclusion reaction of
azobenzene-containing polydiacetylene vesicles with a-cyclodextrin
were used to act as driving force to induce chromatic transi-
tion of PDA vesicles, which provided a novel model system
that combines photochemistry and host–guest chemistry for a
photo-stimulus-responsive vesicle.
a-CD.7 However, when the trans-azobenzene is transformed to
the cis-azobenzene, a-CD cannot include the bulky cis form
any more due to the mismatch between the host and guest.
Therefore, the host–guest assembly and disassembly between
the azobenzene and a-CD by an external photo-stimulus can
act as a driving force to induce a chromatic transition of the
azobenzene containing PDA vesicles. To the best of our
knowledge, the light-triggered red-to-blue chromatic response
of the PDA materials has not yet been realized. In this
communication, we attempted to make use of photo-
controlled inclusion and exclusion reaction of the azobenzene-
containing PDA vesicles with a-CD to fabricate a novel
light-triggered colorimetric transition system (Fig. 1).
Biological systems such as cell membranes and chameleons
adapt to their surroundings by undergoing reversible struc-
tural and functional changes in response to external stimulus.
Polydiacetylene (PDA) exhibits intense chromatic switch from
blue to red in response to external stimuli including tempera-
ture, pH, ions, solvent, stress or ligand interaction.1 These
colorimetric changes can be easily perceived by the UV-
absorption spectrum, fluorescence or even the naked eye,
which makes PDA an ideal candidate for sensing materials.2
To date, PDA materials in the forms of liposomes, vesicles and
films have been synthesized.3 However, most of these
chromatic responses are irreversible, and limit their applica-
tion in sensing. To the best of our knowledge, only a few PDA
materials with reversible chromatic responses have been
reported.4 Although significant efforts have been given to the
issue,1,4 the exact mechanism of blue-to-red and red-to-blue
colorimatic transition have not yet been clearly explained.
Cyclodextrins are intriguing molecules because they form
inclusion complexes with a variety of substances.5 Different
binding specificities of a-, b- and g-cyclodextrins make these
substances attractive model systems for studying ligand–
receptor interactions. For instance, Kim et al. observed that
a-cyclodextrin (a-CD) disrupted the ordered structures of
PDA vesicles by forming inclusion complexes and induced
blue-to-red color transition of PDAs in a selective and pre-
dictable way.6 However, these chromatic transitions of PDA
induced by a-CD were irreversible.
To realize the photo-controlled inclusion and exclusion reac-
tion, a diacetylene monomer (10,12-pentacosadiynoic acid, DA)
containing a p-nitrophenyl azobenzene moiety (NADA) was
synthesized in analogy to the previous procedure.1f NADA/DA
complex vesicles with mol ratios of NADA : DA = 1 : 5 were
prepared following similar procedures as in ref. 1h (as shown in
Fig. 1). As expected, the resulting NADA/DA complex vesicles
could be polymerized under 254 nm light irradiation for 10 min
at room temperature. The transparent colorless NADA/DA
complex vesicles solution was converted into blue PNADA/PDA
complex vesicles solution upon UV irradiation. A strong
blue-to-red color transition was observed for PNADA/PDA
vesicles solution mixing with 2 mM a-CD solution. This
colorimetric transition can be ascribed to the inclusion reaction
of a-CD with the PNADA/PDA vesicles. UV-Vis absorbance
spectra shown in Fig. 2 confirmed that the observed color
changes were mainly related to specific association of a-CD
with the azobenzene moiety within the PNADA/PDA matrix.
Fig. 2(a) shows the blue-to-red colorimetric transition of the
PNADA/PDA vesicles induced by a-CD. It was apparent
in UV-Vis spectra, that the ratio between the absorbance
at B540 nm (red band) and 630 nm (blue band) increased in
the presence of NADA within the complex vesicles. These
quantitative colorimetric responses (%CR) data are shown in
Fig. 2(b), which depicts the blue-to-red chromatic kinetics of
the pure PDA vesicles and PNADA/PDA complex vesicles
with a-CD. These blue-to-red color changes were more pro-
nounced (higher %CR and more rapid response) in the
presence of NADA within the complex vesicles. We must
point out that the stronger colorimetric responses of the
PNADA/PDA vesicles with a-CD supported the proposal
that these colorimetric changes were indeed mainly related to
specific association of a-CD with the azobenzene moiety.
Further evidences for above interpretation were provided by
the analysis of the colorimetric transitions induced by
As we know, two isomers of azobenzene mesogen, the trans
and cis forms, can be reversibly switched to each other upon
photo-irradiation. Driven by hydrophobic and van der Waals
interactions, the trans-azobenzene can be well-recognized by
a CAS Key Laboratory of Soft Matter Chemistry, Department of
Polymer Science and Engineering, Key Laboratory of Optoelectronic
Science and Technology in Anhui Province, University of Science and
Technology of China, Hefei, Anhui, 230026, PR China.
E-mail: gangzou@ustc.edu.cn; Fax: 86-551-3601704;
Tel: 86-551-3601698
b Foreign Languages Department, Graduate University of Chinese
Academy of Sciences, NO. 19, Yuquan Road, Beijing, 100049
w Electronic supplementary information (ESI) available: Synthesis
details, characterization and spectral data. See DOI: 10.1039/b820894h
ꢀc
This journal is The Royal Society of Chemistry 2009
1356 | Chem. Commun., 2009, 1356–1358

View Article Online
Fig. 1 Illustration of photo-controlled inclusion and exclusion reaction of azobenzene-containing PDA vesicles with a-CD.
be observed upon 365 nm irradiation. All the above results
confirmed that the observed colorimetric transitions were
directly related to the specific inclusion and exclusion reaction
of a-CD with the trans-azobenzene moiety within the PDA
matrix, instead of the PDA matrix itself. Previous work has
reported that a-CD could form an inclusion complex with
trans-azobenzene species, while it scarcely interacts with the
cis-azobenzene moiety because of the mismatch between the
host and guest.7a a-CD can form an inclusion complex with
trans-azobenzene isomers due to specific association of a-CD
with the trans azobenzene moiety and induce a blue-to-red
colorimetric transition of the PDA matrix. Upon irradiation
with 365 nm light for 30 min, the azobenzene moiety switched
from the trans to the cis state due to the photoisomeriza-
tion. As discussed above, a-CD might be excluded out of
azobenzene group due to the mismatch between the host and
guest when the trans azobenzene moiety was photo-isomerized
to the cis state. Therefore, the previous changes in conforma-
tion order of the side chain within the polydiacetylene matrix
induced by a-CD could be completely recovered and PDA
matrix would concomitantly return back to the blue form.
In order to prove the above idea, 2D-NOESY experiments
were performed for PNADA/PDA vesicles/a-CD complex
before and after 365 nm light irradiation. The NOESY
spectrum for PNADA/PDA vesicles/a-CD complex before
365 nm light irradiation demonstrated correlation peaks
between protons in the a-CD cavity and protons in the
trans-azobenzene moiety (as shown in Fig. 3(a)), indicating
that a-CD formed an inclusion complex with the trans-
azobenzene moiety within the complex vesicles. After
365 nm irradiation for 30 min, no correlation peaks between
protons in the a-CD cavity and protons of the azobenzene
moiety were observed (as shown in Fig. 3(b)), indicating
host–guest disassembly between the azobenzene moiety and
a-CD.7b If the NOESY signals had been collected for long
time, the thermal isomerization reaction of the azobenzene
moiety should lead to partly inevitable recovery of cis to trans
Fig. 2 (a) UV-Vis spectra of PNADA/PDA vesicles solution with no
or 2 mM a-CD solution added; (b) quantitative colorimetric response
kinetics behavior of pure PDA vesicles and PNADA/PDA com-
plex vesicles with a-CD; (c) Photograph of PNADA/PDA vesicles
mixing with a-CD for 20 min and then irradiated with 365 nm light
for 30 min; (d) UV-Vis spectra of PNADA/PDA vesicles/a-CD
mixing solution before and after 365 nm light irradiation for
30 min.
inclusion and exclusion reaction of a-CD with the azobenzene
moiety within the complex vesicles. When mixing with 2 mM
a-CD solution for 20 min, the PNADA/PDA complex vesicles
solution turned red as mentioned above. Subsequently upon
irradiation with 365 nm light for 30 min, the red PNADA/
PDA complex vesicles solution turned back to dark blue
(as shown in Fig. 2(c)). This colorimetric change could be
easily perceived by the UV-absorption spectrum, as the ratio
between the absorbance at B540 and 630 nm decreased
(as shown in Fig. 2(d)). This can be ascribed to the disassembly
of a-CD and guest molecules, and the changes in conforma-
tion order of the side chain within the PDA matrix induced by
a-CD could be completely recovered. However, for pure PDA
vesicles, no obvious red-to-blue colorimetric transitions could
ꢀc
This journal is The Royal Society of Chemistry 2009
Chem. Commun., 2009, 1356–1358 | 1357

View Article Online
has been used to act as a driving force to induce the chromatic
transition of PDA vesicles. Our work provides a novel system
that combines photo-chemistry and host–guest chemistry for a
photo-stimulus-responsive vesicle system. We hope this model
system would be also valuable in understanding the chromatic
transition mechanism of the PDA materials.
This work was supported by the National Natural Science
Foundation of China (Nos: 50703038, 50533040 and
50773035), Specialized Research Fund for the Doctoral
Program of Higher Education (No. 20070358065), the Chinese
Academy of Sciences (kjcx3.syw.H02 and kjcx2-yw-m11)
and the National Basic Research Program of China
(No. 2006cb302900).
Fig. 3 2D-NOESY spectra of PNADA/PDA vesicles/a-CD complex
(a) before and (b) after 365 nm light irradiation for 30 min.
transition of the azobenzene moiety. Here, the interaction
between a-CD and PDA matrix was weak and hardly affected
these colorimetric transitions. The NOESY results well con-
firmed the mechanism that the colorimetric transitions in
response to the external photo-stimuli were directly related
to the specific inclusion and exclusion reaction of a-CD with
the azobenzene moiety within the PDA matrix instead of the
PDA matrix itself.
Notes and references
1 (a) Q. Cheng and R. C. Stevens, Langmuir, 1998, 14, 1974;
(b) S. Kolusheva, T. Shahal and R. Jelinek, J. Am. Chem. Soc.,
2000, 122, 776; (c) R. R. Chance, Macromolecules, 1980, 13, 396;
(d) K. Tashiro, H. Nishimura and M. Kobayashi, Macromolecules,
1996, 29, 8188; (e) D. H. Charych, J. O. Nagy, W. Spevak and
M. D. Bednarski, Science, 1993, 261, 585; (f) Q. Ye, X. You,
G. Zou, X. W. Yu and Q. J. Zhang, J. Mater. Chem., 2008, 18,
2775; (g) Q. Ye, G. Zou, X. You, X. W. Yu and Q. J. Zhang, Mater.
Lett., 2008, 62, 4025; (h) X. Chen, G. Zou, Y. Deng and
Q. J. Zhang, Nanotechnology, 2008, 19, 195703.
2 (a) H. Peng, J. Tang, L. Yang, J. Pang, H. S. Ashbaugh,
C. J. Brinker, Z. Yang and Y. Lu, J. Am. Chem. Soc., 2006, 128,
5304; (b) M. A. Reppy and B. A. Pindzola, Chem. Commun., 2007,
43, 17; (c) C. G. Ferguson, R. D. James, C. S. Bigman,
D. A. Shepard, Y. Abdiche, P. S. Katsamba, D. G. Myszka and
G. D. Prestwich, Bioconjugate Chem., 2005, 16, 1475;
(d) S. Kolusheva, J. Friedman, I. Angel and R. Jelinek, Bio-
chemistry, 2005, 44, 12077; (e) G. Y. Ma and Q. Cheng, Langmuir,
2006, 22, 6743.
3 (a) S. Y. Okada, R. Jelinek and D. Charych, Angew. Chem., Int. Ed.,
1999, 38, 655; (b) J. Song, J. S. Cisar and C. R. Bertozzi, J. Am.
Chem. Soc., 2004, 126, 8459; (c) D. J. Ahn, E. Chae, G. S. Lee,
H. Shim, T. Chang, K. Ahn and J. Kim, J. Am. Chem. Soc., 2003,
125, 8976; (d) H. Tachibana, R. Kumai, N. Hosaka and Y. Tokura,
Chem. Mater., 2001, 13, 155; (e) A. Sellinger, P. M. Weiss,
A. Nguyen, Y. F. Lu, R. A. Assink, W. L. Gong and
C. J. Brinker, Nature, 1998, 394, 256.
4 (a) H. Peng, J. Tang, J. Pang, D. Chen, L. Yang, H. S. Ashbaugh,
C. J. Brinker, Z. Yang and Y. Lu, J. Am. Chem. Soc., 2005, 127,
12782; (b) Z. Yuan, C. W. Lee and S. H. Lee, Angew. Chem., Int.
Ed., 2004, 43, 4197; (c) H. Park, J. Lee, H. Choi, D. J. Ahn and
J. M. Kim, Adv. Funct. Mater., 2007, 17, 3447; (d) O. J. Dautel,
M. Robitzer, J. P. Lere-Porte, F. Serein-Spirau and J. J. E. Moreau,
J. Am. Chem. Soc., 2006, 128, 16213; (e) Q. Huo, S. Wang,
A. Pisseloup, D. Verma and R. M. Leblanc, Chem. Commun.,
1999, 1601; (f) U. Jonas, K. Shah, S. Norvez and D. H. Charych,
J. Am. Chem. Soc., 1999, 121, 4580; (g) J. M. Kim, J. S. Lee,
H. Choi, D. Sohn and D. J. Ahn, Macromolecules, 2005, 38, 9366.
5 (a) F. Ortega-Caballero, C. Rousseau, B. Christensen, T. E. Petersen
and M. Bols, J. Am. Chem. Soc., 2005, 127, 3238; (b) M. Miyauchi and
A. Harada, J. Am. Chem. Soc., 2004, 126, 11418; (c) M. A. Hossain,
H. Mihara and A. Ueno, J. Am. Chem. Soc., 2003, 125, 11178;
(d) B. J. Ravoo and R. Darcy, Angew. Chem., Int. Ed., 2000, 39,
4324; (e) E. Engeldinger, D. Armspach and D. Matt, Angew. Chem.,
Int. Ed., 2001, 40, 2526; (f) T. Ogoshi, Y. Takashima, H. Yamaguchi
and A. Harada, J. Am. Chem. Soc., 2007, 129(16), 4878.
Furthermore, the PNADA/PDA vesicles solution in the
presence of a-CD were irradiated with UV (365 nm) and visible
light (435 nm) for 10 min alternately. The photo-induced
partially reversible chromatic response of the PNADA/PDA
vesicles in the presence of a-CD were observed.
Upon 365 nm light irradiation, the absorbance at B540 nm
(red band) decreased, while the absorbance at B630 nm (blue
band) increased dramatically. However, when we switched the
light irradiation to 435 nm, the absorbance at B540 nm
slightly increased, while the absorbance at B630 nm slightly
decreased; see Fig. 4. On alternating irradiation of the solution
with UV and visible light, this partially reversible chromatic
response was observed. Unfortunately, upon irradiation at
435 nm for a sufficient time, the absorbance at 540 and 630 nm
could not return back to the initial value. The above results
indicated that the inclusion complex of a-CD with the
PNADA/PDA vesicles was less stable and exclusion reaction
of a-CD with the azobenzene moiety within PDA matrix
occurred in response to UV irradiation.
In conclusion, the photo-controlled inclusion and exclusion
reaction of azobenzene-containing PDA vesicles with a-CD
Fig. 4 (a) UV-Vis spectra and (b) absorption maximum at ca. 660 nm
for PNADA/PDA vesicles with a-CD upon alternating irradiation
with 365 and 435 nm light: (i) the mixing solution under 365 nm light
irradiation for 10 min; (ii) subsequent irradiation of (i) with 435 nm
light for 10 min; (iii) subsequent irradiation of (ii) with 365 nm light for
10 min; (iv) subsequent irradiation of (iii) with 435 nm light for 10 min;
(v) subsequent irradiation of (iv) with 365 nm light for 10 min;
(vi) subsequent irradiation of (v) with 435 nm light for 10 min.
6 (a) S. Lee and J. M. Kim, Macromolecules, 2007, 40, 9201;
(b) J. M. Kim, J. S. Lee, J. S. Lee, S. Y. Woo and D. J. Ahn,
Macromol. Chem. Phys., 2005, 206, 2299.
7 (a) Y. P. Wang, N. Ma, Z. Q. Wang and X. Zhang, Angew. Chem.,
Int. Ed., 2007, 46, 2823; (b) C. Luo, F. Zuo, X. Ding, Z. Zheng,
X. Cheng and Y. Peng, J. Appl. Polym. Sci., 2008, 107, 2118;
(c) G. Alvarez-Lorenzo, S. Deshmukh, L. Bromberg,
´
T. A. Hatton, I. Sandez-Macho and A. Concheiro, Langmuir,
2007, 23, 11475.
ꢀc
This journal is The Royal Society of Chemistry 2009
1358 | Chem. Commun., 2009, 1356–1358