Light-triggered self-assembly of a spiropyran-functionalized dendron into nano-/micrometer-sized particles and photoresponsive organogel with switchable fluorescence

Article abstract of DOI:10.1002/adfm.200901358

The synthesis, self-assembly, and spectroscopic investigations of spiropyran (SP)-functionalized dendron 1 are reported. Under UV light irradiation, assembly of 1 into nano-/microparticles occurs due to the transformation of the closed form of SP into the

Full text of DOI:10.1002/adfm.200901358

www.afm-journal.de
www.MaterialsViews.com
Light-Triggered Self-Assembly of a Spiropyran-
Functionalized Dendron into Nano-/Micrometer-Sized
Particles and Photoresponsive Organogel with
Switchable Fluorescence
By Qun Chen, Yu Feng, Deqing Zhang,* Guanxin Zhang, Qinghua Fan,*
Shuna Sun, and Daoben Zhu
number of molecular switches and
logic gates based on SP derivatives are
reported.[4–10]
The synthesis, self-assembly, and spectroscopic investigations of spiropyran
(SP)-functionalized dendron 1 are reported. Under UV light irradiation,
assembly of 1 into nano-/microparticles occurs due to the transformation of
the closed form of SP into the open merocyanine (MC) form. The formation of
these nano-/microparticles is confirmed by transmission electron microscopy
(TEM) and dynamic light scattering (DLS) experiments in addition to the
confocal laser scanning microscopy (CLSM) measurements. These nano-/
microparticles exhibit relatively strong red emission. It is interesting to note
that the direct cooling of the toluene/benzene solution of 1 to 0 8C leads to gel
formation. Multivalent p–p interactions due to the dendron in 1 may be the
driving-force for the gelation. The UV light irradiation cannot destroy the gel
phase, and in fact, the gel–gel transition is successfully realized. The purple-
blue gel exhibits relatively strong red fluorescence; moreover, the
fluorescence can be reversibly switched by alternating UV and visible light
irradiation. The results clearly indicate that the MC form after aggregation
becomes more stable and fluorescent.
Meanwhile, assemblies of SP com-
pounds and relevant photomodulation have
also attracted attention. In the 1970’s,
Krongauz et al. reported the formation of
MC aggregates (referred to as ‘‘quasicrys-
tals’’) upon UV irradiation of SP molecules
in aliphatic hydrocarbons.[11] They also
concluded that the crystalline cores were
composed of J-aggregate-like stacks of the
MC form based on spectral studies. Sato
et al. reported recently the observation of
micrometer-sized long-lived crystals gener-
ated by prolonged UV irradiation of the
solutions of SP molecules.[12] The aggrega-
tion of the MC form was also observed for
the polymer with SP-containing side
chains.[13] These results indicate that the
MC form tends to aggregate, probably due
to its zwitterionic nature, unlike the closed
form of SP. Additionally, the reversible interconversion between
theclosedandMCformscanalsoinfluencetheassemblyofcertain
polymers.[14] Recent studies from Li et al. show that the MC
aggregates in the hydrophobic cavities of polymer nanoparticles
exhibit strong red emission.[15]
Self-assembly of certain organic molecules, referred to as low-
molecular-weight gelators (LMWGs), through weak intermolec-
ular interactions (such as H-bonding, p–p stacking and van der
Waals interactions) can lead to gelation of organic solvents and
form organogels.[16] Organogels based on LMWGs with functional
groups have been the target of increasing attention in recent years
because of various potential applications as soft materials.[17–30]
Forinstance, photochromicorganogelsfeaturingbisthienylethene
with intriguing optical properties have been studied.[31–33]
Some SP-functionalized macromolecular gels have also been
reported.[34] However, to the best of our knowledge, LMWGs with
the SP moiety still remain rare.[35,36]
1. Introduction
Spiropyran (SP) molecules constitute an important class of
photochromic compounds. It is well known that the closed form of
SP can be transformed into the open (merocyanine, MC) form
under UV light irradiation, and the MC form can revert to the
closed form under visible light irradiation or heating.[1] Because of
their photochromic behavior, SP molecules havebeen investigated
extensively for optical memories, switches, and displays.[2,3]
A
[*] Prof. D. Zhang, Prof. Q. Fan, Q. Chen, Y. Feng, Dr. G. Zhang,
Dr. S. Sun, Prof. D. Zhu
Beijing National Laboratory for Molecular Sciences
CAS Key Laboratories of Organic Solids and
Molecular Recognition and Function
Institute of Chemistry, Chinese Academy of Sciences
Beijing 100190 (PR China)
E-mail: dqzhang@iccas.ac.cn; fanqh@iccas.ac.cn
In this paper, we will describe the synthesis and self-assembly of
a SP-functionalized dendron 1 (Scheme 1). The results show that i)
UV light irradiation of toluene solutions of 1 leads to its self-
assembly into nano-/micrometer-sized particles exhibiting strong
redemission;ii) aphotoresponsive organogelcanbe obtainedwith
Q. Chen, Y. Feng
Graduate School of Chinese Academy of Sciences
Beijing 100190 (PR China)
DOI: 10.1002/adfm.200901358
36
ß 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Funct. Mater. 2010, 20, 36–42

www.afm-journal.de
www.MaterialsViews.com
displayed in Figure 1. It has to be noted that only
wheretheareawasirradiatedbyUVlightdidthe
particles appear.
We also studied the UV-light-triggered
assembly of 1 with different concentrations. It
was interesting to note that the particle size was
also dependent on the concentration of 1.
When the concentration of 1 in toluene was
0.2 mg mLꢁ1, only dots were observed after
irradiating the sample with UV light even for
10 min. Under similar conditions particles with
sizes around 500 nm were detected for the
solutionof1(2.0 mgmLꢁ1)afterexposuretoUV
light for 10 min, as shown in Figure S1 in the
Supporting Information (SI). This was under-
standable: the reduction of the concentration of
1 would lead to the reduction of the concentra-
tion of the corresponding MC form (self-
assembly blocks as to be discussed below) in
solution; accordingly, the decrease of the feed
concentration of the self-assembly blocks would
decrease the particle size.
Both transmission electron microscopy
(TEM) and dynamic light scattering (DLS)
experiments also indicated the formation of
spherical nano-/microparticles after UV light
irradiation. Figure 2 shows the TEM images for
Scheme 1. The synthetic approach to SP-functionalized dendron 1 and the photochromic
reactions under UV and visible light irradiation.
SP-functionalized dendron 1 with switchable fluorescence.
Moreover, it is found that the MC form in the gel phase is
strongly emissive and more stable compared to that in solution,
and accordingly, the organogel based on 1 may be useful for
information storage.
the solution of 1 (20 mg mLꢁ1) after exposure to UV light (365 nm)
for 30 and 60 s. The sizes (based on TEM images) of the formed
spherical particles were approximately 1000 and 3000 nm after UV
light irradiation for 30 and 60 s, respectively. Similarly, spherical
particles with sizes around 250 nm were also generated for the
solution of 1 (2.0 mg mLꢁ1) after exposure to UV light (365 nm) for
2. Results and Discussion
2.1. Synthesis and Light-Triggered Self-Assembly of SP-
Functionalized Dendron 1
The synthesis of SP-functionalized dendron 1 is shown in
Scheme 1. Compounds 2 and 3 were prepared according to
reportedprocedures.[37] Reactionofcompound2withcompound3
in the presence of K2CO3 led to SP-functionalized dendron 1 in
50% yield. The synthesis and characterization data are provided in
the Experimental section.
The solution of 1, prepared by dissolving 20 mg of 1 in 1.0 mL of
toluene and then cooled down to 30 8C, was subjected to confocal
laser scanning microscopy (CLSM) measurements. At the
beginning, no apparent particles were observed in both
fluorescence and bright-field images. However, particles with
nearly spherical shape appeared after exposure to UV light
(365 nm) as shown in Figure 1. The particle size increased by
prolonging the UV light irradiation time, and nanoparticles grew
gradually into micrometer-sized particles. For instance, the
particle size was ꢀ500 nm after the sample was exposed to UV
lightfor10 s,anditbecameꢀ5.0 mmwhentheirradiationtimewas
extended to 120 s. Moreover, these particles generated from 1 after
UV light irradiation exhibit strong red emission, as clearly
Figure 1. CLSM fluorescence images for the toluene solution of 1
(20 mg mLꢁ1) observed under 559 nm laser light excitation immediately
after UV light (365 nm) irradiation for a) 10, b) 30, c) 120, and d) 480 s,
respectively; for UV light irradiation, a mercury lamp with a excitation filter
(BP330-385, Olympus) was used.
Adv. Funct. Mater. 2010, 20, 36–42
ß 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
37

www.afm-journal.de
www.MaterialsViews.com
Scheme 2. The self-assembly propensity of dendron 1 into
particles may further minimize the contact among toluene
molecules and polar MC groups, thus lowering the energy of
the system.
Although the MC form can convert into the closed SP form
under visible light irradiation (for spectral investigations, see
below), the particles formed in the toluene solution of 1 after
exposure to UV light cannot be totally disassembled by further
visible light irradiation. As shown in Figure 3, where the CLSM
images for the solution of 1 (20 mg mLꢁ1 in toluene) are displayed,
the particle morphology in the bright field remains, even after the
solution that was exposed to UV light for 2.0 min was further
irradiated with a 559 nm laser light for 30 min. This implies that
these particle aggregates are relatively stable. However, disas-
semblyoccurredintheseparticleaggregateswhenthesolutionwas
heated to 80 8C, and complete disappearance of these particles was
observed when the solution was kept at 80 8Cfor only 1.0 min. This
is understandable since the self-assembly process is usually
enthalpy-favored and entropy-disfavored, and thus heating will
facilitate the disassembly process.
Figure 4a shows the absorption spectra of the solution of 1
(0.2 mg mLꢁ1, 0.127 mM) before and after UV light irradiation for
2.0 min. The new broad absorption band in the range of 500–
700 nm that appeared after UV light irradiation should be due to
the corresponding MC form. Normally, MC forms exhibit
maximum absorption around 570 nm. The fact that the maximum
absorption of 1 after UV light irradiation appears at 608 nm
together with a shoulder band around 570 nm indicates the
formation of MC aggregates, according to previous studies.[12]
Similarabsorptionspectrawereobtainedforthesolutionsof1with
concentrations of 2 mg mLꢁ1 (1.27 mM), 0.02 mg mLꢁ1 (12.7 mM),
and 0.002 mg mLꢁ1 (1.27 mM).
Figure 2. TEM images of the self-assembly aggregates generated from the
toluene solution of 1 (20 mg mLꢁ1) before (a) and after exposure to UV
light (365 nm) for 30 (b) and 60 s (c) respectively. d) TEM image of the self-
assembled aggregates generated from the toluene solution of
1
(2 mg mLꢁ1) after exposure to UV light for 60 s; samples were prepared
by dropping the respective solutions onto the copper grid and the solvents
were allowed to evaporate at room temperature.
60 s (see Fig. 2). It should be mentioned that no particles were
detected for the solution of 1 before UVirradiation. For the toluene
solution of 1 (2.0 mg mLꢁ1), no DLS signals corresponding to
particles larger than 5.0 nm were detected. After UV irradiation
however, DLS signals due to particles with sizes over 200 nm were
observed (see Fig. S2, SI), indicating the
formation of self-assembled aggregates.[38] All
the investigations with CLSM, TEM, and DLS
indicate the UV-light-triggered self-assembly of
SP-functionalized dendron 1 into spherical
nano-/microparticles and the increase of par-
ticle size with increasing concentrations of 1
and UV irradiation time. It should be noted that
suchnano-/microparticles withsphericalshape
generated from SP compounds in situ after
exposure to UV light were not previously
reported, although formation of aggregates of
SP compounds induced by UV light has been
described.[12,13]
It is known that the MC forms of SP compounds usually exhibit
rather weak fluorescence in the range of 580–800 nm in solution.
However, the particles generated in the solution of 1 after UV light
The UV-light-triggered self-assembly of 1
into particles can be understood as follows:
i) the SP unit in 1 will transform into the
corresponding MC form under UV light
irradiation; ii) the polar MC form is solvophobic
towards toluene, and thus the intermolecular
MC forms tend to aggregate as previously
reported;[12,13] iii) the formation of spherical
Scheme 2. Schematic representation of the self-assembly of SP-functionalized dendron 1 into
particles and network structure within the organogel, and the corresponding transformations
under UV and visible irradiation as well as the corresponding CLSM images.
particles may be related to the structure of the
dendron in 1 as schematically shown in
38
ß 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Funct. Mater. 2010, 20, 36–42

www.afm-journal.de
www.MaterialsViews.com
resulted, as shown in Figure 5. SEM and TEM
images (Fig. 6) of the xerogel of 1 show that
molecules within have self-assembled into long
fibers with widths of about 50 nm, which are
further interconnected to generate a 3D net-
work. Molecules of 1 in the gel phase are
relatively orderly, as indicated by X-ray diffrac-
tion (XRD) analysis (Fig. S3, SI), in which a
signal around 0.778 was detected, correspond-
ing to d-spacings of 11.5 nm. The d value is
relatively large compared to those of normal
organogels, and this may be related to the bulky
dendron group in 1. Other solvents were also
tested to examine the gelation ability of 1.
Besidestoluene, dendron1canalsogelbenzene
(20 mg to 0.02 mg mLꢁ1). However, dendron 1
cannot gel acetonitrile, methanol, ethanol,
dichloromethane, tetrahydrofuran, and ethyl
acetate. Dendron-based gelators were reported,
but intermolecular H-bonds were believed to be
responsible for the gelation processes.[39,40]
Although the gelation mechanism with 1 in
toluene and benzene is not fully clarified at this
stage, multivalent p–p interactions due to the
dendron in 1 may be the driving-force for the
gelation.
Figure 3. a) CLSM bright-field images for the toluene solution of 1 (20 mg mLꢁ1) after UV light
(365 nm) irradiation for 2 min. b) Further visible light (559 nm) irradiation for 30 min, and
c) incubation at 80 8C for 1.0 min.
The SP unit in 1 can be converted to the polar
MC form under UV light irradiation, and such
structural alteration may destabilize the self-
assembled structure and induce a gel–solution
phase transition. However, when the gel was
exposed to UV light for 2.0 min, the gel phase
was not destroyed and the light yellow gel was
Figure 4. a) Absorption spectra of the toluene solution of 1 (0.2 mg mLꢁ1) before and after UV
light (365 nm) irradiation for 2 min. b) Fluorescent spectra of 1 with three different concentrations
(0.002, 0.02, and 0.2 mg mLꢁ1 in toluene) after UV light (365 nm) irradiation for 2 min;
lexc. ¼ 560 nm.
irradiation show red emission, as clearly shown in Figure 1, where
the corresponding CLSM images are displayed. Figure 4b shows
the fluorescence spectra of the solutions of 1 with different
concentrations after UV light irradiation for 2.0 min. Obviously,
the fluorescence intensity of 1 after UV light irradiation increases
significantly as the concentration increases from 0.002 to
0.02 mg mLꢁ1 and 0.02 mg mLꢁ1, along with the red-shift of
the emission peak from 643 to 650 nm and 661 nm. The
fluorescence quantum yields of solutions of 1, however, with
three respective concentrations after UV light irradiation for
2.0 min were similar, that is, 0.05 with respect to rhodamine B.
The red-shift of the fluorescence spectrum by increasing the
concentration of 1 again indicates theformation of MCaggregates.
Two factors may contribute to the relatively strong fluorescence of
the particles: i) the aggregation of MC forms may restrict the
conformational flexibility, which may minimize nonradioactive
relaxation through internal motions of the excited molecules;
ii) the dendron in 1 may function as protective shells for the MC
aggregates (see Scheme 2), and as a result the MC form may be
isolated from nonradioactive decay pathways involving solvents.
transformed into the purple-blue gel asillustrated in Figure5. This
result further suggests that the driving force for the gelation of
toluene (and benzene) with 1 may be the multivalent p–p
interactions due to the dendron in 1. Further visible light
irradiation of the purple-blue gel led to the yellow gel again (see
Fig. 5). Figure 5 also illustrates the transition of the purple-blue gel
into the corresponding solution after heating, which can be
converted to the light yellow gel again after further cooling to 0 8C.
The purple-blue gel shows a broad absorption in the range of
500–700 nm due to the MC aggregates. After exposure to visible
2.2. Gel Formation, Switchable Fluorescence, and Application
Figure 5. Illustration of the gel–gel transformation under alternating UV
(365 nm) and visible light irradiation, and the gel–solution–gel transition
under heating and cooling for the toluene solution of 1 (20 mg mLꢁ1).
When the hot toluene solution of 1 (20 mg mLꢁ1, 12.7 mM) was
directly cooled by ice water to 0 8C, a transparent light yellow gel
Adv. Funct. Mater. 2010, 20, 36–42
ß 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
39

www.afm-journal.de
www.MaterialsViews.com
Figure 7. a) Variation of the transmittance at 580 nm versus the decay time
for the corresponding gel and solution of 1 (20 mg mLꢁ1 in toluene); the
samples were firstly exposed to UV light (365 nm) for 5 min and were kept
under dark conditions after recording each spectrum. b) Illustration of the
recording of ‘‘ICCAS 2008’’ characters on the gel of 1 (20 mg mLꢁ1 in
toluene) by exposure to UV light (365 nm) for 1.0 min, and erasing the
recorded pattern by exposure to visible light for 5.0 min.
Figure 6. a) SEM and b) TEM images of the corresponding xerogel of 1
formed in toluene.
light irradiation for a few minutes, this broad absorption
disappeared because of the transformation of MC into the closed
SP form as expected. The corresponding solution of 1[41] also
exhibits a broad absorption in the range of 500–700 nm after UV
light irradiation. Of particular interest is the fact that the MC form
in the gel phase becomes more stable compared to that in solution
as indicated in Figure 7a, where the plot of the transmittance at
580 nm for the gel and solution versus the decay time is displayed
(the sample was kept under dark conditions after recording each
spectrum). The stable MC form may enable this organogel of 1 to
be used as soft materials for information storage. As illustrated in
Figure 7b, the light yellow gel was covered with a photomask
containing the characters ‘‘ICCAS 2008,’’ and these characters
becameapparentfromtheblue-coloredbackgroundafterexposure
to UV light for 1.0 min. Such a photopattern can last (i.e., still be
distinguished with the naked eye) for at least 12 h. Two pathways
are applicable for erasing the written data and generating the
original gel state. One is to illuminate the gel with visible light, and
the other is to heat the gel, resulting in the solution, followed by
rapid cooling to generate the gel again.
Thepurple-bluegelexhibitsrelativelystrongredfluorescenceas
illustrated in Figure 8. Also, the xerogel shows strong red
fluorescence as indicated by the CLSM image (Fig. 8b). The strong
red fluorescence of the gel can be switched off by additional visible
light irradiation. This is simply because of the conversion of the
MC form into the closed form of SP that emits no intrinsic
fluorescence. Furthermore, the fluorescence of the gel can be
restored. In this way, the fluorescence of the gel can be reversibly
tuned by alternating UV and visible light irradiation as shown in
the inset of Figure 8, where reversible changes of the fluorescence
intensity of the gel at 667 nm is displayed. Therefore, this
organogel can function as a fluorescence switch.
3. Conclusion
In summary, we have described the synthesis, self-assembly, and
spectroscopic studies of the SP-functionalized dendron 1. The
results show that by manipulating the cooling process, the toluene
solution of 1 can lead to different self-assembled structures:
spherical nano-/microparticles in solution by cooling the hot
solution to 30 8C and additional UV light irradiation, and 3D
interconnected fiber-network within an organogel by cooling the
hot solution to 0 8C as schematically shown in Scheme 2.
Multivalent p–p interactions due to the dendron in 1 may be the
driving force for the gelation. These self-assembled structures
were successfully characterized by CLSM, SEM, TEM, and DLS.
The UV light irradiation cannot destroy the gel phase, and in fact
gel–gel transition is successfully realized. The purple-blue gel
exhibits relatively strong red fluorescence; moreover, the fluores-
cencecan bereversibly switchedbyalternating UVandvisiblelight
irradiation. The results clearly indicate that the MC form after
aggregation becomes more stable and strongly fluorescent. These
results provide insights into the design of new MC aggregates,
which may have potential applications in fluorescence imaging,
particularly in biological systems.
4. Experimental
General Procedures: Unless otherwise stated, all starting materials and
reagents were purchased from commercial suppliers and used without
further purification. The solvents used were dried and purified by standard
methods prior to use. 1H and 13C NMR spectra were recorded with Bruker
40
ß 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Funct. Mater. 2010, 20, 36–42

www.afm-journal.de
www.MaterialsViews.com
resulting reaction mixture was extracted with dichloromethane and washed
with water. The organic layer was dried over anhydrous Na2SO4. The
solvents were removed under vacuum, and the residue was purified by
column chromatography on silica gel with CH2Cl2/EtOAc (30/1, v/v) to
give compound 1 as a white solid powder (424 mg, 50%). 1H NMR
(400 MHz, CDCl3, 25 8C, tetramethylsilane: TMS): d ¼ 1.16 (s, 3H), 1.25
(s, 3H), 2.26 (m, 2H), 2.66 (s, 3H), 3.93 (s, 24H), 4.13 (t, J ¼ 6 Hz, 2H),
4.21(t, J ¼ 6 Hz, 2H), 5.08–5.13 (12H), 5.82 (d, J ¼ 10 Hz, 1H), 6.42
(d, J ¼ 9 Hz, 1H), 6.72 (3H), 6.89 (d, J ¼ 10 Hz, 1H), 7.07 (m, 9H), 7.82
(d, J ¼ 1 Hz, 8H), 7.98 (d, J ¼ 8 Hz, 2H), 8.29 (t, J ¼ 1 Hz, 4H); 13C NMR
(100 MHz, CDCl3, 25 8C): d ¼ 166.2, 160.0, 159.7, 159.5, 158.8, 153.6,
142.15, 141.07, 138.8, 138.4, 137.8, 132.1, 128.3, 126.0, 123.5, 122.8,
121.7, 120.4, 120.3, 119.0, 118.8, 118.6, 115.6, 113.7, 113.3, 112.6, 110.3,
107.4, 107.0, 70.3, 70.25, 70.1, 65.4, 64.9, 52.57, 52.53, 29.8, 29.7, 29.3,
25.9, 20.0; MALDI(matrix-assisted laser desorption/ionization)-TOF-MS
(m/z): 1574.2 [M þ H] þ, 1596.3 [M þ Na] þ; Anal. calcd. for C86H80N2O27
:
C, 65.64; H, 5.12; N, 1.78; Found: C, 65.72; H, 5.37; N, 1.99.
Gel Formation: In a typical gelation experiment, a weighed amount of 1
and 1.0 mL of the solvent were placed in a test tube, which was sealed and
then heated until the compound was dissolved. The solution was then
cooled down with ice water.
Acknowledgements
The present research was financially supported by NSFC, the State Basic
Program and Chinese Academy of Sciences. This work was partially
supported by the NSFC-DFG joint project (TRR61). We thank the
anonymous reviewers for their suggestions and comments which enabled
us to significantly improve the manuscript. Supporting Information is
available online from Wiley InterScience or from the authors.
Received: July 22, 2009
Published online: October 26, 2009
[1] V. I. Minkin, Chem. Rev. 2004, 104, 2751.
[2] G. Berkovic, V. Krongauz, V. Weiss, Chem. Rev. 2000, 100, 1741.
[3] W. F. Yuan, L. Sun, H. H. Tang, Y. Q. Wen, G. Y. Jiang, W. H. Huang,
L. Jiang, Y. L. Song, H. Tian, D. B. Zhu, Adv. Mater. 2005, 17, 156.
[4] a) F. M. Raymo, Adv. Mater. 2002, 14, 401. b) F. M. Raymo, S. Giordani,
Proc. Natl. Acad. Sci. USA 2002, 99, 4941. c) F. M. Raymo, R. J. Alvarado,
S. Giordani, M. A. Cejas, J. Am. Chem. Soc. 2003, 125, 2361.
Figure 8. a) Fluorescence spectra of the gel of 1 (20 mg mLꢁ1 in toluene)
before and after UV light (365 nm) irradiation for 5.0 min, lexc. ¼ 560 nm.
The insets show the photo of the gel under UV (365 nm) light illumination
(left), and the reversible change of the fluorescence intensity of the gel at
667 nm by alternating UV and visible light irradiation (right). b) CLSM
image of the corresponding xerogel.
[5] F. M. Raymo, M. Tomasulo, Chem. Soc. Rev. 2005, 34, 327.
[6] F. M. Raymo, M. Tomasulo, Chem. Eur. J. 2006, 12, 3186.
[7] a) S. Silvi, E. C. Constable, C. E. Housecroft, J. E. Beves, E. L. Dunphy,
M. Tomasulo, F. M. Raymo, A. Credi, Chem. Eur. J. 2009, 15, 178.
400MHz spectrometers. Mass spectrometry (MS) were determined with a
BEFLEX III for time-of-flight (TOF) MS. Elemental analysis was performed
on a Carlo-Erba-1106 instrument. The CLSM system, FV-1000-IX81
Olympus (Japan), was employed. XRD data were collected on a Rigaku
D/max-2500 X-ray diffractometer with Cu Ka radiation. For SEM
´
b) J. Andreasson, S. D. Straight, G. Kodis, C. D. Park, M. Hambourger,
M. Gervaldo, B. Albinsson, T. A. Moore, A. L. Moore, D. Gust, J. Am. Chem.
Soc. 2006, 128, 16259.
[8] G. Y. Jiang, Y. L. Song, X. F. Guo, D. Q. Zhang, D. B. Zhu, Adv. Mater. 2008,
20, 2888.
experiments,
a JEOL JSM 6700F field-emission scanning electron
[9] a) X. F. Guo, D. Q. Zhang, Y. Gui, M. X. Wan, J. C. Li, Y. Q. Liu, D. B. Zhu,
Adv. Mater. 2004, 16, 636. b) G. Y. Wen, J. Yan, Y. C. Zhou, D. Q. Zhang,
L. Q. Mao, D. B. Zhu, Chem. Comm. 2006, 3016. c) X. F. Guo, D. Q. Zhang,
D. B. Zhu, J. Phys. Chem. B 2004, 108, 212.
microscope was used, and the freeze-dried xerogel was sputtered with
platinum. TEM measurements were conducted with JEOL 2010 transmis-
sion electron microscopes using an accelerating rate voltage of 120 keV.
DLS experiments were carried out with an ALV5000 Laser Light Scattering
[10] a) X. F. Guo, D. Q. Zhang, D. B. Zhu, Adv. Mater. 2004, 16, 125. b) X. F. Guo,
D. Q. Zhang, H. R. Tao, D. B. Zhu, Org. Lett. 2004, 6, 2491. c) X. F. Guo,
D. Q. Zhang, G. X. Zhang, D. B. Zhu, J. Phys. Chem. B 2004, 108, 11942.
[11] V. A. Krongauz, E. S. Goldburt, Nature 1978, 271, 43.
[12] Y. Onai, M. Mamiya, T. Kiyokawa, K. Okuwa, M. Kobayashi, H. Shinohara,
H. Sato, J. Phys. Chem. 1993, 97, 9499.
Instrument. Absorption spectra were recorded on a JASCO V-570
spectrophotometer. Fluorescence spectra were measured with a Hitachi
F-4500 spectrophotometer.
Synthesis of Compound 1: Compound 2 was prepared according to the
reported procedure [37]. The synthesis and characterization of compound
3 is published elsewhere [37]. A solution of 2 (250 mg, 0.545 mmol), 3
(650 mg, 0.544 mmol), and K2CO3 (700 mg, 5 mmol) in dimethylforma-
mide (DMF, 20 mL) was stirred at room temperature for three days. The
[13] M. Alonso, V. Reboto, L. Guiscardo, A. San Martn, J. C. Rodriguez-Cabello,
Macromolecules 2000, 33, 9480.
Adv. Funct. Mater. 2010, 20, 36–42
ß 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
41

www.afm-journal.de
www.MaterialsViews.com
[14] a) M. C. George, A. Mohroz, M. Piech, N. S. Bell, J. A. Lewis, P. V. Braun,
Adv. Mater. 2009, 21, 66. b) K. Fukushima, A. J. Vandenbos, T. Fujiwara,
Chem. Mater. 2007, 19, 644.
[29] a) P. Gao, C. L. Zhan, M. H. Liu, Langmuir 2006, 22, 775. b) Y. G. Li,
T. Y. Wang, M. H. Liu, Soft Matter, 2007, 3, 1312.
[30] a) A. Ajayaghosh, V. K. Praveen, C. Vijayakumar, Chem. Soc. Rev. 2008, 37,
109. b) A. Ajayaghosh, V. K. Praveen, Acc. Chem. Res. 2007, 40, 644.
c) A. Ajayaghosh, S. J. George, A. P. H. J. Schenning, Top. Curr. Chem. 2005,
258, 83. d) A. Ajayaghosh, S. J. George, J. Am. Chem. Soc. 2001, 123, 5148.
e) A. Ajayaghosh, R. Varghese, V. K. Praveen, S. Mahesh, Angew. Chem, Int.
Ed. 2006, 45, 3261.
[15] a) M. Q. Zhu, L. Y. Zhu, J. J. Han, W. W. Wu, J. K. Hurst, A. D. Q. Li, J. Am.
Chem. Soc. 2006, 128, 4303. b) D. H. Hu, Z. Y. Tian, W. W. Wu, W. Wan,
A. D. Q. Li, J. Am. Chem. Soc. 2008, 130, 15279. c) L. Y. Zhu, W. W. Wu,
M. Q. Zhu, J. J. Han, J. K. Hurst, A. D. Q. Li, J. Am. Chem. Soc. 2007, 129,
3524.
[16] P. Terech, R. G. Weiss, Chem. Rev. 1997, 97, 3133.
[17] N. M. Sangeetha, U. Maitra, Chem. Soc. Rev. 2005, 34, 821.
[18] N. Fujita, Y. Sakamoto, M. Shirakawa, M. Ojima, A. Fujii, M. Ozaki,
S. Shinkai, J. Am. Chem. Soc. 2007, 129, 4134.
[31] a) S. Wang, W. Shen, Y. L. Feng, H. Tian, Chem. Commun. 2006, 1497.
b) L. L. Zhu, X. Ma, F. Y. Ji, Q. C. Wang, H. Tian, Chem. Eur. J. 2007, 13,
9216.
[32] J. J. D. de Jong, P. R. Hania, A. Pagzlys, L. N. Lucas, M. de Loos,
R. M. Kellogg, B. L. Feringa, K. Duppen, J. H. van Esch, Angew. Chem.
Int. Ed. 2005, 44, 2373.
[19] K. Sugiyasu, N. Fujita, S. Shinkai, Angew. Chem. Int. Ed. 2004, 43, 1229.
[20] O. Gronwald, E. Snip, S. Shinkai, Curr. Opin. Colloid Interface Sci. 2002, 7,
148.
[33] M. Akazawa, K. Uchida, J. J. D. de Jong, J. Areephong, M. Stuart, G. Caroli,
W. R. Browneb, B. L. Feringa, Org. Biomol. Chem. 2008, 6, 1544.
[34] A. Garcia, M. Marquez, T. Cai, R. Rosario, Z. B. Hu, D. Gust, M. Hayes,
S. A. Vail, C. D. Park, Langmuir 2007, 23, 224.
[21] J. H. Jung, M. Amaike, K. Nakashima, S. Shinkai, J. Chem. Soc. Perkin Trans.
2 2001, 1938.
[22] J. H. van Esch, B. L. Feringa, Angew. Chem. Int. Ed. 2000, 39, 2263.
[23] F. S. Schoonbeek, J. H. van Esch, B. Wegewijs, D. B. A. Rep, M. P. de Haas,
T. M. Klapwijk, R. M. Kellogg, B. L. Feringa, Angew. Chem. Int. Ed. 1999, 38,
1393.
[35] H. Hachisako, H. Ihara, T. Kamiya, C. Hirayama, K. Yamada, Chem.
Commun. 1997, 19.
[36] Z. J. Qiu, H. T. Yu, J. B. Li, Y. Wang, Y. Zhang, Chem. Commun. 2009, 3342.
[37] X. F. Guo, X. F. Zhang, D. Q. Zhang, Y. C. Zhou, D. B. Zhu, J. Org. Chem.
2003, 68, 5681. The synthesis and characterization of compound 3 is
published elsewhere: Y. Feng, Z. T. Liu, J. Liu, Y. M. He, Q. Y. Zheng,
Q. H. Fan, J. Am. Chem. Soc. 2009, 131, 7950.
[24] M. de Loos, J. van Esch, R. M. Kellogg, B. L. Feringa, Angew. Chem. Int. Ed.
2001, 40, 613.
[25] A. Friggeri, C. van der Pol, K. J. C. van Bommel, A. Heeres, M. C. A. Stuart,
B. L. Feringa, J. van Esch, Chem. Eur. J. 2005, 11, 5353.
[26] R. Wang, C. Geiger, L. H. Chen, B. Swanson, D. G. Whitten, J. Am. Chem.
Soc. 2000, 122, 2399.
[38] For the DLS experiments, a red light (632 nm) was used for signal
detection. Also, it takes a relatively long time to finish each DLS measure-
ment. In order to reduce the influence of disaggregation during the
measurement, the solution of 1 was exposed to UV light for a relatively
long period.
[27] a) J. Wu, T. Yi, T. Shu, M. Yu, Z. Zhou, M. Xu, Y. Zhou, H. Zhang, J. Han,
F. Li, C. Huang, Angew. Chem. Int. Ed. 2008, 47, 1063. b) Y. F. Zhou, M. Xu,
J. C. Wu, T. Yi, J. T. Han, S. Z. Xiao, F. Y. Li, C. H. Huang, J. Phys. Org. Chem.
2008, 21, 338. c) T. M. Shu, J. C. Wu, M. Lu, L. Q. Chen, T. Yi, F. Y. Li,
C. H. Huang, J. Mater. Chem. 2008, 18, 886.
[39] W. D. Jang, T. Aida, Macromolecules 2003, 36, 8461.
[40] W. D. Jang, D. L. Jiang, T. Aida, J. Am. Chem. Soc. 2000, 122, 3232.
[41] As mentioned above, if the hot toluene solution of 1 is not cooled to 0 -C,
gelation cannot occur.
[28] Y. Q. Huang, Y. Lin, G. Zeng, Z. X. Liang, X. L. Liu, X. L. Hong, G. Y. Zhang,
S. C. Tsang, J. Mater. Chem. 2008, 18, 5445.
42
ß 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Funct. Mater. 2010, 20, 36–42