Photocontrolled reversible room temperature phosphorescence (RTP) encoding β-cyclodextrin pseudorotaxane

Article abstract of DOI:10.1039/c0cc05488g

Photocontrolled reversible room temperature phosphorescence (RTP) emission engendered by the complexation of β-cyclodextrin (β-CD) and α-bromonaphthalene (α-BrNp) can be employed to address the threading and dethreading of the pseudorotaxane formed between β-CD and sodium 2-hydroxy-5-((4-nitrophenyl)diazenyl)benzoate (DAYR) in the ternary system in aqueous solution.

Full text of DOI:10.1039/c0cc05488g

View Online / Journal Homepage / Table of Contents for this issue
Dynamic Article Links
ChemComm
Cite this: Chem. Commun., 2011, 47, 3559–3561
www.rsc.org/chemcomm
COMMUNICATION
Photocontrolled reversible room temperature phosphorescence (RTP)
encoding b-cyclodextrin pseudorotaxanew
Xiang Ma, Jingjing Cao, Qiaochun Wang and He Tian*
Received 10th December 2010, Accepted 25th January 2011
DOI: 10.1039/c0cc05488g
Photocontrolled reversible room temperature phosphorescence
(RTP) emission engendered by the complexation of b-cyclodextrin
(b-CD) and a-bromonaphthalene (a-BrNp) can be employed to
address the threading and dethreading of the pseudorotaxane
formed between b-CD and sodium 2-hydroxy-5-((4-nitrophenyl)-
diazenyl)benzoate (DAYR) in the ternary system in aqueous
solution.
conformation of the CD-azo pseudorotaxane and rotaxane
has not been reported yet. Herein, we construct a b-cyclodextrin,
a-bromonaphthalene (a-BrNp) and sodium 2-methoxy-5-
((4-nitrophenyl)diazenyl)benzoate (a derivative of Alizarine
Yellow R, DAYR, synthesis, see ESIw) ternary system
(Scheme 1). Usually, trans-DAYR can preferentially form
inclusive pseudorotaxane with b-CD. After the trans to cis
isomerization of DAYR, b-CD then includes a-BrNp to
engender the RTP signals. Therefore, the competitive change
of supramolecular complexes and their RTP signal can be
controlled by different photo-irradiations.
1H NMR, absorption, fluorescence, and circular dirchroism
spectroscopies are usually employed to encode the conforma-
tion changes of rotaxane and pseudorotaxane, which continue
to receive considerable interest recently for their potential
application in nanostructured functional materials and
molecular devices.1,2 Cyclodextrins (CD) are known to form
inclusion complexes with a variety of organic compounds in
aqueous solutions.3,4 Room temperature phosphorescence
induced by cyclodextrin (CD-RTP), with the advantages of
good selectivity, long life, large Stokes shifts and consequently
better application in the area of molecular recognition, was
first introduced by Cline Love et al. in 1984,5 and since then
numerous phosphorescence/CD systems, like a-bromo-
naphthalene/b-CD6 system typically, were employed to exploit
their interesting RTP properties. Azobenzene derivatives
undergo a reversible trans–cis photoisomerization of their
NQN double bond and thus were used to construct CD
pseudorotaxanes and rotaxanes.7 In these CD-azobenzene
supramolecular systems, photoisomerization of the azo group
can control the inclusion and exclusion of azobenzene units,
It is well known that trans-azobenzene can be well included
by b-CD with a high association constant (4 104 L molÀ1) in
aqueous solution.10 Like other azobenzene derivatives, the
trans form of DAYR can be well included in the cavity of
CD (ESI, Fig. S1w). However, when trans-DAYR is
transformed to cis-DAYR, it cannot be included very well by
b-CD because of its bulky dimension. So, the threading and
dethreading of DAYR into b-CD (to form pseudorotaxane or
not) can be driven by external photostimuli. b-CD can also
form an inclusion complex with a-BrNp, but of a relatively
lower equilibrium constant (about 103 L molÀ1).6 That is, the
1
which are accompanied with variable H NMR, absorption,
fluorescence of the fluorophore next to azo group8 and
induced circular dirchroism (ICD)9 signals.
However, to the best of our knowledge, using photo-
controlled reversible RTP to recognize the inclusion
Key Labs for Advanced Materials and Institute of Fine Chemicals,
East China University of Science & Technology, Shanghai 200237,
P.R. China. E-mail: tianhe@ecust.edu.cn; Fax: (+86)-21-64252288
w Electronic supplementary information (ESI) available: Experiments
for sample preparation of the ternary system in water. Instructions of
experimental agents, instruments and a brief description of analytical
operation. UV spectra of aqueous a-BrNp, DAYR, binary b-CD/
a-BrNp, b-CD/DAYR, and ternary b-CD/DAYR/a-BrNp solution.
ICD spectra of aqueous binary b-CD/a-BrNp, b-CD/DAYR solution.
RTP spectrum of aqueous ternary b-CD/a-BrNp solution. See DOI:
10.1039/c0cc05488g
Scheme 1 The reversible inclusion of b-CD/DAYR/a-BrNp ternary
system in water.
c
This journal is The Royal Society of Chemistry 2011
Chem. Commun., 2011, 47, 3559–3561 3559

View Online
cyclodextrin. And only very small amount of a-BrNp was
included by b-CD and thus engendered a RTP of weak
intensity. The RTP lifetime of the aqueous b-CD/a-BrNp
solution is about 0.53 ms (ESI, Fig. S8w).
An interesting phenomenon was found in the RTP spectrum
of the ternary system. UV light (360 nm) irradiation of its
aqueous solution makes the RTP signal at around 527 nm (due
to the b-CD/a-BrNp) stronger, as illustrated in Fig. 2A.13 As
the trans-DAYR is photoisomerized to dethread from b-CD,
more b-CD molecules include and induce a-BrNp to enhance
the RTP obviously. The RTP intensity enhancement is so large
as to reach 18.09 times than its original state (157.36 a.u. to
8.70 a.u.). Owing to the reversible trans–cis photoisomeriza-
tion of azo, DAYR can thread and dethread into the cavity of
b-CD to form pseudorotaxane or not upon different UV and
visible irradiation, then the resulting RTP of the b-CD/a-BrNp
could be repeated over many cycles with UV and visible
irradiation alternating between 360 and 430 nm (Fig. 2B).
In summary, a ternary b-CD/DAYR/a-BrNp complex was
constructed. Due to the different inclusion constants of b-CD,
Fig. 1 ICD spectrum of aqueous the ternary b-CD/DAYR/a-BrNp
solution (a), containing little CH3CN, [a-rNp] = 4.0 Â 10À5 M,
[DAYR] = [b-CD] = 2.0 Â 10À3 M), and after irradiation by
360 nm light for 6 min (b), 9 min (c), 12 min (d), 15min (e), then by
430 nm for 15 min (f). The reference aqueous binary DAYR/a-BrNp
solution without b-CD ([a-BrNp] = 4.0 Â 10À5 M, [DAYR] =
2.0 Â 10À3 M) shows no Cotton effect but only the system error of
the measurement (g).
inclusion priority of b-CD is b-CD/trans-DAYR 4 b-CD/
a-BrNp 4 b-CD/cis-DAYR.
The competitive inclusion phenomenon of the b-CD/
DAYR/a-BrNp ternary system was fully characterized by
absorption (ESI, Fig. S4w) and ICD spectra. It was known
that azo groups can be induced to generate an ICD signal
when included into the cavity of CD.11 A negative Cotton
peak at about 374 nm and a positive Cotton peak at about
415 nm exist after a mixing together of the three components
and standing for a short time (Fig. 1), which are respectively
attributed to the p–p* and n–p* transition bands of the
azobenzene group in trans-DAYR, located within b-CD.12
These ICD signals prove pseudorotaxane formation between
trans-DAYR and b-CD.
Prolonged irradiation with 360 nm light to the ternary
system leads to a gradual intensity increase of the Cotton
peak at 374 nm shown in Fig. 1 (curves b, c, d, and e). This is
owing to the trans–cis photoisomerization of DAYR compo-
nent and its subsequent dethreading out of the CD cavity. The
ICD intensity increases by about 240% (from À6.93 mdeg
to À16.61 mdeg) after irradiation within a time of 15 min
(curve e). And the ICD spectral changes can be almost shifted
back by irradiation at 430 nm (curve f). Without the inclusion
inducement effect of b-CD, the reference aqueous binary
DAYR/a-BrNp system solution shows no obvious ICD signal,
as shown in Fig. 1 (curve g).
The room temperature phosphorescence (RTP) spectrum of
b-CD/DAYR/a-BrNp ternary system in aqueous solution12 is
shown in Fig. 2 (there was weak fluorescence emission for this
aqueous ternary system solution because of the heavy atom
effect of a-BrNp). At the originate state, this ternary system
was excited to bring a very weak RTP signal at about 527 nm
(curve a). The reason, as we elucidated above, is that most
b-CD in aqueous solution prefers forming pseudorotaxane
with DAYR because of its higher equilibrium constant with
Fig. 2 (A) RTP spectrum of aqueous ternary b-CD/DAYR/a-BrNp
solution (a), black, containing little CH3CN, [a-BrNp] = 4.0 Â
10À5 M, [DAYR] = [b-CD] = 2.0 Â 10À3 M), and after irradiation
by 360 nm light for 20 min, 30 min, 40 min,..., 120 min (b–p); then by
430 nm for 120 min (l); (B) Changes in the RTP intensity of aqueous
ternary b-CD/DAYR/a-BrNp solution at 527 nm along with changes
in irradiation time and light source. Light sources of 360 and 430 nm
were alternated every 120 min.
c
3560 Chem. Commun., 2011, 47, 3559–3561
This journal is The Royal Society of Chemistry 2011

View Online
b-CD/trans-DAYR 4 b-CD/a-BrNp 4 b-CD/cis-DAYR,
b-CD prefers to form a pseudorotaxane with trans-DAYR,
addressed with a weak RTP signal. Irradiation with UV light
of 360 nm, DAYR photoisomerized from its trans to cis form
and engenders the dethreading of the DAYR pseudorotaxane.
Then the resultant formation of b-CD/a-BrNp binary complex
makes a large increase (more than 18 times) of the RTP
intensity. The RTP emission can be reversibly shifted back
to the original state using irradiation of 430 nm. That is, the
conformational threading and dethreading of the b-CD/
DAYR pseudorotaxane can be addressed with RTP signals,
which can be reversibly controlled by different UV and visible
irradiations. This would be a novel and simple way to encode
the threading-and-dethreading movement of pseudorotaxane.
This work is financially supported by National Basic
Research 973 Program (2011CB808400) and NSFC/China
(20972053 & 20802019). X. Ma acknowledges the support
from the Ph.D. Programs Foundation of Ministry of
Education of China (200802511029), the Fundamental
Research Funds for the Central Universities (WJ0911001)
and the ‘Chen Guang’ project supported by Shanghai
Education Commission and Shanghai Education Development
Foundation.
J. Am. Chem. Soc., 2006, 128, 15374; (c) D. Qu, F. Ji, Q. Wang and
H. Tian, Adv. Mater., 2006, 18, 2035; (d) Q. Wang, X. Ma, D. Qu
and H. Tian, Chem.–Eur. J., 2006, 12, 1088; (e) Y. Liu, L. Yu,
Y. Chen, Y. Zhao and H. Yang, J. Am. Chem. Soc., 2007, 129,
10656; (f) L. L. Zhu, X. Ma, F. Y. Ji, Q. C. Wang and H. Tian,
Chem.–Eur. J., 2007, 13, 9216; (g) C. F. Ke, C. Yang, T. Mori,
T. Wada, Y. Liu and Y. Inoue, Angew. Chem., Int. Ed., 2009, 48,
6675.
4 (a) P. Kuad, A. Miyawaki, Y. Takashima, H. Yamaguchi and
A. Harada, J. Am. Chem. Soc., 2007, 129, 12630; (b) Y. L. Zhao,
W. R. Dichtel, A. Trabolsi, S. Saha, I. Aprahamian and
J. F. Stoddart, J. Am. Chem. Soc., 2008, 130, 11294; (c) F. Y. Ji,
L. L. Zhu, X. Ma, Q. C. Wang and H. Tian, Tetrahedron Lett.,
2009, 50, 597; (d) F. Y. Ji, L. L. Zhu, D. Zhang, Z. F. Chen and
H. Tian, Tetrahedron, 2009, 65, 9081; (e) L. L. Zhu, F. Y. Ji,
Q. C. Wang, X. Ma, Z. F. Chen and H. Tian, Front. Chem. China,
2009, 4, 278; (f) L. L. Zhu, D. Zhang, D. H. Qu, Q. C. Wang,
X. Ma and H. Tian, Chem. Commun., 2010, 46, 2587; (g) L. L. Zhu,
D. H. Qu, D. Zhang, Z. F. Chen, Q. C. Wang and H. Tian,
Tetrahedron, 2010, 66, 1254.
5 (a) S. Scypinski and L. J. C. Love, Anal. Chem., 1984, 56, 322;
(b) R. A. Femia and L. J. C. Love, J. Phys. Chem., 1985, 89, 1897.
6 (a) S. Scypinski and L. J. C. Love, Anal. Chem., 1984, 56, 331;
(b) Y. S. Wei, W. J. Jin, R. H. Zhu, G. W. Xing, C. S. Liu,
S. S. Zhang and B. L. Zhou, Spectrochim. Acta, Part A, 1996, 52,
683; (c) Y. X. Zhu, J. H. Peng and Y. Zhang, Anal. Chim. Acta,
2007, 583, 364.
7 (a) Y. Inoue, P. Kuad, Y. Okumura, Y. Takashima, H. Yamaguchi
and A. Harada, J. Am. Chem. Soc., 2007, 129, 6396; (b) D. Qu,
Q. Wang and H. Tian, Mol. Cryst. Liq. Cryst., 2005, 430, 59;
(c) X. Ma, Q. Wang and H. Tian, Tetrahedron Lett., 2007, 48,
7112.
Notes and references
8 (a) Q. Wang, D. Qu, J. Ren, K. Chen and H. Tian, Angew. Chem.,
Int. Ed., 2004, 43, 2661; (b) D. Qu, Q. Wang, J. Ren and H. Tian,
Org. Lett., 2004, 6, 2085.
9 (a) H. Murakami, A. Kawabuchi, K. Kotoo, M. Kunitake and
N. Nakashima, J. Am. Chem. Soc., 1997, 119, 7605; (b) X. Ma,
Q. Wang, D. Qu, Y. Xu, F. Ji and H. Tian, Adv. Funct. Mater.,
2007, 17, 829.
10 (a) Y. Wang, N. Ma, Z. Wang and X. Zhang, Angew. Chem., Int.
Ed., 2007, 46, 2823; (b) P. B. Wan, Y. G. Jiang, Y. P. Wang,
Z. Q. Wang and X. Zhang, Chem. Commun., 2008, 5710.
11 (a) Y. Liu, Y.-L. Zhao, H.-Y. Zhang, Z. Fan, G.-D. Wen and
F. Ding, J. Phys. Chem. B, 2004, 108, 8836; (b) X. Ma, D.-H. Qu,
F.-Y. Ji and H. Tian, Chem. Commun., 2007, 1409.
12 (a) M. Kodaka, J. Phys. Chem. A, 1998, 102, 8101; (b) X. Zhang
and W. M. Nau, Angew. Chem., Int. Ed., 2000, 39, 544;
(c) B. Mayer, X. Zhang, W. M. Nau and G. Marconi, J. Am.
Chem. Soc., 2001, 123, 5240.
1 (a) V. Balzani, A. Credi and M. Venturi, Molecular Devices and
Machines: Concepts and Perspectives for the Nanoworld,
Wiley-VCH: Weinheim, Germany, 2008; (b) J. P. Sauvage, Chem.
Commun., 2005, 1507; (c) H. Tian and Q. C. Wang, Chem. Soc.
Rev., 2006, 35, 361; (d) G. Wenz, B. H. Han and A. Muller, Chem.
¨
Rev., 2006, 106, 782; (e) E. R. Kay, D. A. Leigh and F. Zerbetto,
Angew. Chem., Int. Ed., 2007, 46, 72; (f) A. Credi and H. Tian, Adv.
Funct. Mater., 2007, 17, 679 (Guest Editorial); (g) X. Ma and
H. Tian, Chem. Soc. Rev., 2010, 39, 70.
2 For examples: (a) E. Katz, O. Lioubashevsky and I. Willner,
J. Am. Chem. Soc., 2004, 126, 15520; (b) S. Saha, K. C. F.
Leung, T. D. Nguyen, J. F. Stoddart and J. I. Zink, Adv. Funct.
Mater., 2007, 17, 685; (c) V. Aucagne, J. Berna, J. D. Crowley,
´
S. M. Goldup, K. D. Hanni, D. A. Leigh, P. J. Lusby,
¨
V. E. Ronaldson, A. M. Z. Slawin, A. Viterisi and D. B. Walker,
J. Am. Chem. Soc., 2007, 129, 11950; (d) S. Silvi, A. Arduini,
A. Pochini, A. Secchi, M. Tomasulo, F. M. Raymo, M. Baroncini
and A. Credi, J. Am. Chem. Soc., 2007, 129, 13378; (e) H. Zhang,
Q. Wang, M. Liu, X. Ma and H. Tian, Org. Lett., 2009, 11, 3234.
3 (a) D. Qu, Q. Wang, X. Ma and H. Tian, Chem.–Eur. J., 2005, 11,
5929; (b) E. J. F. Klotz, T. D. W. Claridge and H. L. Anderson,
13 Preparation and experiments of the aqueous ternary b-CD/DAYR/
a-BrNp system solution see Supplementary Information. The
optimized concentration of DAYR, b-CD and a-BrNp was
propitious to engender the better RTP signals.
c
This journal is The Royal Society of Chemistry 2011
Chem. Commun., 2011, 47, 3559–3561 3561