Photochromic nanostructures based on diarylethenes with perylene diimide

Article abstract of DOI:10.1021/la9040387

A bisthienylethene-functionalized perylene diimide (BTE-PDI) photochromic dyad was synthesized for self-assembly into 1-D nanotubes by a reprecipitation method. SEM and TEM observations showed that the nanotubes were formed from their 0-D precursors of hollow nanospheres. HR-TEM images revealed that both the nanospheres and the nanotubes have highly ordered lamellar structure, indicating the hierarchical process during assembly. The IR and XRD results revealed that DAE-PDI molecules were connected through intermolecular hydrogen bonds to form building blocks that self-assembled into nanostructures. Electronic absorption and fluorescence spectroscopic results indicated the H-aggregate nature of the self-assembled nanostructures. Competition and cooperation between the dipole-dipole interaction, intermolecular π-π stacking, and hydrophilic/hydrophobic interaction are suggested to result in nanostructures. Reconstruction was found to happen during the morphology transition progress from the 0-D nanospheres to the 1-D nanotubes, which was driven by donor-acceptor dipole-dipole interactions. Green emission at 520 nm originating from the DAE subunit was observed for the aggregates of vesicles and nanotubes, which could be regulated by photoirradiation with 365 nm light, suggesting the nanoaggregates to be photochromic switches.

Full text of DOI:10.1021/la9040387

pubs.acs.org/Langmuir
© 2009 American Chemical Society
Photochromic Nanostructures Based on Diarylethenes with Perylene Diimide
Lulu Ma,† Quanbo Wang,† Guifen Lu,§ Ruiping Chen,‡ and Xuan Sun*,†
†Key Laboratory of Colloid and Interface Chemistry of the Ministry of Education, School of Chemistry and
Chemical Engineering, Shandong University, Jinan 250100, PR China, §School of Chemistry and Chemical
Engineering, Jiangsu University, Zhenjiang 212013, PR China, and ‡State Key Laboratory of Structural
Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences,
Fuzhou 350002, PR China
Received October 24, 2009. Revised Manuscript Received December 4, 2009
A bisthienylethene-functionalized perylene diimide (BTE-PDI) photochromic dyad was synthesized for self-assembly
into 1-D nanotubes by a reprecipitation method. SEM and TEM observations showed that the nanotubes were formed
from their 0-D precursors of hollow nanospheres. HR-TEM images revealed that both the nanospheres and the
nanotubes have highly ordered lamellar structure, indicating the hierarchical process during assembly. The IR and XRD
results revealed that DAE-PDI molecules were connected through intermolecular hydrogen bonds to form building
blocks that self-assembled into nanostructures. Electronic absorption and fluorescence spectroscopic results indicated
the H-aggregate nature of the self-assembled nanostructures. Competition and cooperation between the dipole-dipole
interaction, intermolecular π-π stacking, and hydrophilic/hydrophobic interaction are suggested to result in
nanostructures. Reconstruction was found to happen during the morphology transition progress from the 0-D
nanospheres to the 1-D nanotubes, which was driven by donor-acceptor dipole-dipole interactions. Green emission
at 520 nm originating from the DAE subunit was observed for the aggregates of vesicles and nanotubes, which could be
regulated by photoirradiation with 365 nm light, suggesting the nanoaggregates to be photochromic switches.
1. Introduction
stimulus, light-triggered structural changes in building blocks
affect their self-assembly behaviorand therefore modulate macro-
scopic properties, which has previously rarely been explored.8-13
Actually, the fabrication of new functional supramolecular
assemblies and materials based on photoresponsible molecular
building blocks for understanding the assembly formation
mechanism are still challenging tasks. Herein, we report the
hierarchical supramolecular self-assembly of a photochromic
molecule, a bisthienylethene (BTE) derivative, by a precipitation
method. The morphology of the self-assembly formed in metha-
nol is confirmed to be nanospheres with well-defined lamellar
hollow structures. More interestingly, a morphology transition
took places in the self-assembly process, which induced 0-D
nanospheres to transform into 1-D nanotubes. Although the
red emission of the PDI subunit is quenched by aggregation,
the green emission of the DAE subunit remained strong and can
be modulated by light irradiation, indicating that the material
brings about potential applications in the fields of data storage
and computing.
Mediated by noncovalent interactions (e.g., hydrogen bonding
interactions, π-π stacking, and solvophobic and surface effects),
the self-assembly of atomic/molecular building blocks into large
supramolecular structures offers significant advantages in device
miniaturization, which can fabricate features on the scale of a few
nanometers. To date, numerous interesting materials have been
constructed from a large library of molecular building blocks,
among which amphiphilic molecules with controlled hydrophilic/
hydrophobic interactions can hierarchically self-assemble into
highly organized aggregates with a hollow interior and various
morphologies, especially 0-D and 1-D micro/nano hollow spheres
and tubes with unique multilevel inner structures. These multi-
level structural micro/nanomaterials have spurred great attention
not only because of their fantastic interior architectures but also
for their unique predominance and multifunctionality that are
superior to their same-sized solid counterparts.1-7 Moreover, the
fabrication of smart supramolecular materials bythe introduction
of stimuli-responsive groups into building blocks that are respon-
sive to external stimuli is believed to have significant potential
with respect to actuation, sensing, data storage, and computing.
Whereas light represents perhaps the most attractive external
2. Experimental Section
2.1. Chemicals. Unless stated otherwise, all reagents and
anhydrous solvents were purchased from Aldrich Chemicals
and were used without further purification and drying except as
noted. Column chromatography (CC) was used: SiO2 (200-300
*Corresponding author. Tel: þ86-531-88362326. E-mail: sunxuan@
sdu.edu.cn.
(1) Percec, V.; Dulcey, A. E.; Balagurusamy, V. S. K.; Miura, Y.; Smidrkal, J.;
Peterca, M.; Nummelin, S.; Edlund, U.; Hudson, S. D.; Heiney, P. A.; Duan, H.;
Magonov, S. N.; Vinogradov, S. A. Nature 2004, 430, 764.
(8) Murata, K.; Aoki, M.; Nishi, T.; Ikeda, A.; Shinkai, S. J. Chem. Soc., Chem.
Commun. 1991, 1715.
(9) Murata, K.; Aoki, M.; Suzuki, T.; Harada, T.; Kawabata, H.; Komori, T.;
Ohseto, F.; Ueda, K.; Shinkai, S. J. Am. Chem. Soc. 1994, 116, 6664.
(10) Loos, M. D.; Esch, J. V.; Kellogg, R. M.; Feringa, B. L. Angew. Chem., Int.
Ed. 2001, 40, 613.
€
(2) Antonietti, M.; Forster, S. Adv. Mater. 2003, 15, 1323.
(3) Hill, J. P.; Jin, W. S.; Kosaka, A.; Fukushima, T.; Ichihara, H.; Shimomura,
T.; Ito, K.; Hashizume, T.; Ishii, N.; Aida, T. Science 2004, 304, 1481.
(4) Hartgerink, J. D.; Beniash, E.; Stupp, S. I. Science 2001, 294, 1684.
(5) Uzun, O.; Sanyal, A.; Nakade, H.; Thibault, R. J.; Rotello, V. M. J. Am.
Chem. Soc. 2004, 126, 14773.
(11) Laan, S. V. D.; Feringa, B. L.; Kellogg, R. M.; Esch, J. V. Langmuir 2002,
18, 7136.
(6) Arnt, L.; Tew, G. N. J. Am. Chem. Soc. 2002, 124, 7664.
(12) Jong, J. J. D. D.; Lucas, L. N.; Kellogg, R. M.; Esch, J. H. V.; Feringa, B. L.
Science 2004, 304, 278.
€
(7) Percec, V.; Ahn, C. H.; Ungar, G.; Yeardley, D. J .P.; Mouller, M.; Sheiko, S.
S. Nature 1998, 391, 161.
(13) Hirose, T.; Matsuda, K.; Irie, M. J. Org. Chem. 2006, 71, 7499.
6702 DOI: 10.1021/la9040387
Published on Web 12/28/2009
Langmuir 2010, 26(9), 6702–6707

Ma et al.
Article
mesh). 2,3-Bis(2,3,5-trimethyl-3-thienyl) maleic anhydride was
prepared following a literature procedure.14 N,N0-diamido-1,6,
7,12-tetra(4-tert-butylphenoxy)perylene-3,4/9,10-tetracarboxylic
acid bisimide was prepared according to a procedure similar to
that in the literature.15
2.2. Synthesis of BTE-PDI Dyad 1. Synthesis of the target
BTE-PDI 1 was accomplished in one step by the condensation of
photochromic 2,3-bis(2,3,5-trimethyl-3-thienyl) maleic anhydride
with a stoichiometric amount of the corresponding N,N0-diamido-
1,6,7,12-tetra(4-tert-butylphenoxy)perylene-3,4/9,10-tetracarboxylic
acid bisimide in refluxing toluene in the presence of imidazole as a
catalyst. Details of the synthesis will be described and published
elsewhere.
Figure 1. Schematic illustration of the chemical structure of BTE-
PDI 1 and the possible intermolecular translation-related hydro-
gen bonding.
3. Results and Discussion
2.3. Evaporation Method. The sample was dissolved in
CHCl3 to a concentration of 10-3 mol L-1. The solution (100
3
3.1. Molecule Design. As shown in Figure 1, photochromic
BTE is covalently linked to the bay-substituted perylene tetra-
carboxylic acid bisimide (PDI) on the amino N atom to form the
functional structure of light-regulated fluorescence-switching 1.16
Drastic fluorescence quenching of BTE-PDI dyad 1 compared
with reference compound N,N0-dibutyl-1,6,7,12-tetra(4-tert-
butylphenoxy)pery-lene-3,4/9,10-tetracarboxylic diimide indicates
rapid electron transfer from the -NH2 group to the tetraphenoxy-
substituted PDI within this intramolecular charge-transfer (ICT)
compound, NH2•þ-PDI•--BTEo (open state of BTE).17 Further-
more, polar amino moiety -NH2 remained unsubstituted to exhibit
a hydrophilic effect relative to the solvophilic skeleton of BTE-PDI
1, hence the amphiphilic structure can facilitate the self-assemble
process. Besides, the PDI segment has a strong tendency to
aggregate through π-π overlap, and the intermolecular hydrogen
bonding has a synergistic effect on the formation of extremely stable
aggregations. The unique structural feature of BTE-PDI 1 makes it
an ideal candidate for self-assembly using the synergistic effects of
π-πstacking, microsegregation, intermolecular hydrogen bonding,
and dipole-dipole interaction.
3.2. Self-Assembly of Molecule 1. The aggregation beha-
vior of 1 was subsequently studied by injecting a chloroform
(CHCl3) solution of 1 into methanol (CH3OH) to give a final
CHCl3/CH3OH ratio of 1/30 (v/v). It is important to note that the
growth time played a key role in controlling the self-assembly
process starting from the hollow nanospheres to the tadpolelike
vesicles and nanotubes. Figure 2 shows typical scanning electron
microscopy (SEM) and the corresponding transmission electron
microscopy (TEM) images of 1 with different morphologies.
After the solution was allowed to equilibrate for 3 h at 38 °C,
one drop of the solution was evaporated on the carbon-coated
grid to observe the aggregate behavior in the solid state. Irregular
spherical particles with small defects on the surface are observed
in the SEM images (Figure 2a). The diameter of the spheres
ranges from 800 to 2800 nm. TEM observation (Figure 2b)
confirms that all of the spherical structures are hollow in nature
with a wall thickness of roughly 20-350 nm. Not occasionally, as
revealed in SEM and TEM images (Figure 2a,b), vesicles are not
separately dispersed but cohered one-by-one in a linear way,
forming “pearl necklace” morphology. The adjacent vesicles fuse
with one another and the membranes between them are eroded,
suggesting the growing tendency of the tubes.
μL) was injected into 3 mL of anhydrous methanol (described as
CHCl3/CH3OH (v/v = 1/30) in the text). After the solution was
allowed to equilibrate over 3 h, 4 to 5, and 6 h at 38 °C, one dropof
solution was cast onto the carbon copper grids in order to observe
the aggregate behavior in the solid state. CH3OH was also
converted to acetone or THF when the assemblies were manu-
factured. The nanospheres collected from the suspension were
held at 50 °C for 10 min to evaporate the CH3OH, and the
nanostructure collapsed.
2.4. Characterization. 1H NMR spectra were recorded on a
Bruker DPX 300 spectrometer (300 MHz) in CDCl3 using the
residual solvent resonance of CHCl3 at 7.26 ppm relative to SiMe4
as an internal reference. Matrix-assisted laser desorption/ioniza-
tion time-of-flight (MALDI-TOF) mass spectra were detected on
a Bruker BIFLEX III ultrahigh-resolution Fourier transform ion
cyclotron resonance (FT-ICR) mass spectrometer with R-cyano-
4-hydroxycinnamic acid as the matrix. Elemental analyses were
performed by the Institute of Chemistry at the Chinese Academy
of Sciences. Fourier transform infrared spectra (FT-IR) were
recorded for KBr pellets with 2 cm-1 resolution using a VER-
TEX-70 (Bruker) spectrometer. Absorption spectra were mea-
sured on a Hitachi U-4100 spectrophotometer. Steady-state
fluorescence measurements of a CHCl3 and CHCl3/CH3OH
combined solution of the BTE-PDI compound were performed
on a fluorescence spectrophotometer (Perkin-Elmer LS-50) with
excitation at a wavelength of 488 nm, and the emission spectrum
between 500-700 nm was recorded. A fluorescence microscopy
image of the aggregates was obtained with a mercury lamp and a
40ꢀ objective and captured with a DP70 CCD camera (Japan) on
an Olympus FV 500 instrument (Japan). Excitation was per-
formed with the Ar 488 nm laser, and the emission was monitored
from 600 to 800 nm. Standard lamps used to visualize TLC plates
(Spectroline E-series, 470 μW/cm2) were used to carry out the
ring-closing reaction of 1o to 1c. Transmission electron micro-
scopy images were recorded on a JEOL-100CX II electron
microscope operated at 100 kV. A high-resolution transmission
electron microscopy (HR-TEM) measurement was performed
with a JEOL-2010 working at 200 kV. Scanning electron micro-
scopy images were obtained on a JEOL JSM-6700F. The powder
X-ray diffraction (XRD) patterns were recorded using a Rigaku
D/Max 2200-PC diffractometer with Cu KR radiation (λ =
0.15418 nm) and a graphite monochromator at ambient tempera-
ture. For TEM and HR-TEM imaging, a drop of sample solution
was cast onto a copper grid sprayed with carbon. For SEM
imaging, Au (1 to 2 nm) was sputtered onto these grids to prevent
charging effects and improve image clarity. All calculations were
carried out with the density functional theory (DFT) method at
the B3LYP/LANL2DZ and B3LYP/(6-31þG*, LANL2DZ) le-
vels. All of the calculations were performed using Gaussian 03
program 27 in the IBM P690 system at the Shandong Province
High Performance Computing Centre.
To investigate this tendency, the sample in the combined
CHCl3/CH3OH solvents system is aged for 1 h more and
the intermediate states of the morphology transition are ob-
tained. Many discrete 0-D and 1-D nanostructures are observed
(Figure 3). The typical structure of the intermediates is tadpolelike
(16) Fukaminato, T.; Irie, M. Adv. Mater. 2006, 18, 3225.
€
(14) Irie, M.; Mohri, M. J. Org. Chem. 1988, 53, 803.
(17) Wurthner, F.; Thalacker, C.; Diele, S.; Tschierske, C. Chem.;Eur. J. 2001,
7, 2245.
€
(15) Wurthner, F.; Thalacker, C.; Sautter, A. Adv. Mater. 1999, 11, 754.
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Ma et al.
Figure 2. Typical morphologies of the nanostructures formed by injecting the CHCl3 solution of 1 into CH3OH. (a) SEM of the nanospheres
formed within 3 h. (b) TEM of the nanospheres. (c) SEM of the nanotadpoles formed around 4 h. (d) TEM of the nanotadpoles. (e) SEM of
the nanotubes formed after 5 h. (f) TEM of the nanotubes.
Figure 3. SEM photography of the nanostructures formed by
injecting the CHCl3 solution of 1 into CH3OH and equilibrating
for 5 h. (a)SEMimage withmany0-Dnanostructuresand(b) SEM
Figure 5. Electronic absorption spectra of 1 in CHCl3 (5 ꢀ 10-5
image with many 1-D nanostructures.
mol L-1, -) and its self-assembled nanoscale aggregatesformedin
CHCl3/CH3OH (v/v = 1/30, ---).
3
morphology with a hollow spherical head and a tubular tail,
formed by the corrosion of the membranes between the pearls
(Figure 2c,d), clearly indicating the 1-D growing process. Nano-
tubes with a length of more than 8 μm are obtained by the long-
time stabilization (left undisturbed for more than 5 h at 38 °C) of
the precipitate (Figure 2e,f), which again confirms the 1-D growth
tendency of the vesicles. The surface of the tubes is relatively
smooth and the inner and outer diameters are uniform with a wall
thickness of about 135-150 nm. The progressive growth of the
assembly from vesicles to nanotubes was a natural process that
depended only on time and was similar to some natural biological
growth phenomena. These results provide a very interesting
artificial molecular system in which to mimick the features of
growth in natural systems.
Insight into the aggregation behavior of 1, the well-ordered
lamellar structure, can clearly be identified from the HR-TEM
(high-resolution transmission electron microscopy) micrograph
of a single hollow nanosphere (Figure 4a). The membrane wall
Figure 4. HR-TEM images of typical nanospheres and nanotubes
contains several lamellas in interspaces of the solvents, as illu-
formed in CHCl3 and CH3OH (volume ratio = 1/30). (a) HR-
strated in the enlarged image. The average thickness of each ridge
(darkness in Figures) is roughly 1.7 nm. Interestingly, the mole-
cular arrangement can almost be identified from the magnified
TEM image of the nanospheres and the magnification of the
interlamellar structure of the shell. (b) HR-TEM image of the
nanotubes as well as the amplified structure of the tubular shell.
6704 DOI: 10.1021/la9040387
Langmuir 2010, 26(9), 6702–6707

Ma et al.
Article
image (Figure 4a). According to the thickness of one ridge and the
dimensions of an optimized molecule, molecules may stack
oppositely by intermolecular hydrogen bonding and π-π inter-
actions estimated by the 3-D molecular structural modeling
(Figure 1). One lamella containing two ridges and one interspace
(1.6 nm) (whiteness in Figures) is measured to be about 5.0 nm,
corresponding to the d spacing of the X-ray diffraction results
(XRD, Figure 6). This lamella structure clearly indicates that
molecules of 1 are arranged in an orderly manner into a mono-
layer by noncovalent interactions. When such a monolayer is
formed, extra CH3OH molecules in the organic solvent could be
attracted through hydrogen bonding to 1 or by the permanent
dipole in the layer. Therefore, a repetition of the above process
generates stacked multilayers, as illustrated in Figure 4a.
The HR-TEM image of the nanotubes shows the hollow
interiors of the 1-D structures with a well-defined laminate
structure of the wall (Figure 4b). The width of the striped domains
is not uniform, with the thickness of the ridges ranging from 2.0 to
8.0 nm, which can be attributed to the amalgamation of several
ridges and the loss of interspaces. The homology of the structure
between the nanovesicles and the nanotubes indicates the uniform
nature of the two nanostructures, which again reveals the mor-
phology transition process from the 0-D nanospheres to the 1-D
nanotubes.
UV/vis absorption spectroscopy and X-ray diffraction are used
to clarify the packing of the molecules in the self-assembled
aggregates. Figure 5 displays the electronic absorption spectrum
of 1 in CHCl3 as well as that in combined solvents of CHCl3 and
CH3OH. The aggregation of 1 leads to pronounced changes in the
optical properties with a blue shift (13 nm) relative to that of
the monomeric PDI unit, suggesting that, in spite of the large
steric hindrance induced by the bulky substitutes at the bay
positions, the molecules pack face-to-face with considerable
overlap betweenthe adjacent PDI aromatic rings, which is distinct
for the generally observed J-type aggregates of the tetraphenoxy-
substituted PDIs.5 Such spectroscopic changes arising from the
formation of the aggregates are attributed to the efficient π-π
interaction that proceeds from the ordered molecular packing as
visualized in the HR-TEM results (Figure 4). By prolonging the
aging time of the sample in CHCl3/CH3OH solution to longer
than 6 h, no changes in the absorption spectra are observed, which
may indicate that molecules arrange in the same manner in the
vesicles and nanotubes.
Figure 6. XRD profiles of the hollow nanospheres of 1.
The XRD pattern of the self-assembled vesicles (Figure 6)
shows one diffraction peak at 2θ = 1.79°, which can be ascribed
to the refraction from the lamellar structure of the hollow shell.
The d spacing is therefore 4.94 nm, representing the distance of
two layers containing one interlayer of the lamellar structure,
which is in good agreement with the HR-TEM observation
(Figure 4a). The inset in Figure 6 demonstrates the diffraction
Figure 7. IR spectra of 1 (-) and aggregates (---) in the 400-4000
cm-1 region with 2 cm-1 resolution.
Figure 8. Schematic illustration of nanostructure formation from 1 and the morphology-transition process.
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Ma et al.
in the wide-angle range, where weak peaks at 2θ = 30.76 and 34.72°
are observed and are attributed to the π-π stacking and average
hydrogen bonding distance between neighboring molecules, respec-
tively.18 These results, together with the HR-TEM observation and
the electronic absorption spectrum, indicate that the molecules form
ordered H aggregates in the membrane of the hollow nanostructures
by the synergic π-π and hydrogen bonding interactions.
The FT-IR spectra of 1 as well as that of thenanoaggregates are
compared in Figure 7. The relatively strong, broad band appeared
at 3435 cm-1 in the spectrum of the aggregates, which is absent
from that of 1, apparently originated from the hydrogen bonding
stretching vibration.18-20 In addition, the characteristic CdO
stretching vibration of the BTE subunit in the aggregates shifts
upfield compared with that in 1, which is ascribed to the weaken-
ing of the p-π conjugation between the lone-pair electron on
oxygen and the thiophene caused by hydrogen bonding. There-
fore, the formation of hydrogen bonds between the CdO parts of
the BTE units and the -NH2 groups of the PDIs is proposed as
illustrated in Figure 1. These changes clearly demonstrate the
significant effect of the hydrogen bonding interaction on the
formation of molecular aggregates.
3.3. Possible Mechanism for the Formation of the Nano-
structures of 1. On the basis of the above-described experimental
results, a possible assembly mechanism is thus proposed as shown
in Figure 8,21 including the following steps: (1) neighboring BTE-
PDI molecules are connected through charge-charge interaction,
hydrogen bonding, and π-π interactions to form clusters acting
as building blocks; (2) various building blocks grow into nano- or
microscale assemblies with hollow vesicle morphology by micro-
phase segregation, and (3) the 0-D hollow nanospheres transform
into 1-D nanotubes by the dipole-dipole driving force and the
evaporation of methanol.
As disclosed, for such a strongly polar compound as 1, charge-
charge interactions have a dominating influence on the packing
geometry.17 Repulsion and attraction between the adjacent π-π
stacked molecules and the steric demand of the substituents in the
bay positions lead to a longitudinal offset. Moreover, in the case of
1, intermolecular hydrogen bonding is required in forming the large
overlapped H aggregates as demonstrated in the HR-TEM
observation (Figure 4a) and simulated in Figure 1. Meanwhile,
the lamella morphology of the nanostructures membrane indicates
that microphase separation plays an important role in the molecular
self-assembly process, which is always found in micellar or tube
formation of amphiphilic molecules.2,22 The relatively wide inter-
layer between two adjacent layers as well as the irregular morpho-
logy and rough surface of the nanospheres may indicate that the
building blocks stack in a relatively loose manner. CH3OH may
play a specific role in the formation of the lamella structure because
no tangible morphology can be obtained by changing the CH3OH
into acetone or tetrahydrofuran when manufacturing the assem-
blies. Upon heating, especially when the temperature arrived at
50 °C, the nanospheres collapsed with the evaporation of CH3OH,
which may verify the important effect of CH3OH on the molecular
self-assembly.23
Figure 9. (a) Fluorescence spectra of 1 in CHCl3 and a CHCl3/
CH3OHcombinedsolvent system, withλ= 488nmand [BTE-PDI
1] = 3.0 ꢀ 10-6 mol L-3. The inset shows the fluorescence spectra
3
of 1 in CHCl3 in CH3OH (v/v) from 2 to 10%. (b) Confocal
fluorescence images and fluorescence spectral changes of aggre-
gates of BTE-PDI 1 before (relative strong emission, -) and after
(very weak emission, ---) photoirradiation with 365 nm light for 10
min. (c) Schematic representation of the structures of the open
form 1o (PDI-BTEo) and the closed-form 1c (PDI-BTEc).
Considering the molecular structure of 1, the dipole-dipole
interaction is proposed to be the dominating driving force for the
morphology transition from 0-D to 1-D, similar to the 1-D
growing progress of an ICT compound.24-28 For 1, the main
transition dipole moment is along the long molecular axis
(18) Lu, G. F.; Chen, Yanli; Zhang, Y. X.; Bao, M.; Bian, Y. Z.; Li, X. Y.; Jiang,
J. Z. J. Am. Chem. Soc. 2008, 130, 11623.
(19) Kimura, M.; Muto, T.; Takimoto, H.; Wada, K.; Ohta, K.; Hanabusa, K.;
(24) Xu, J. L.; Wen, L. P.; Zhou, W. D.; Lv, J.; Guo, Y. B.; Zhu, M.; Liu, H. B.;
Li, Y. L.; Jiang, L. J. Phys. Chem. C 2009, 113, 5924.
Shirai, H.; Kobayashi, N. Langmuir 2000, 16, 2078.
(20) Kimura, M.; Kuroda, T.; Ohta, K.; Hanabusa, K.; Shirai, H.; Kobayashi,
N. Langmuir 2003, 19, 4825.
(25) Zhang, X. J.; Zhang, X. H.; Shi, W. S.; Meng, X. M.; Lee, C. S.; Lee, S. T.
Angew. Chem., Int. Ed. Engl. 2007, 46, 1525.
(26) Zhang, X. J.; Zhang, X. H.; Zou, K.; Lee, C. S.; Lee, S. T. J. Am. Chem. Soc.
2007, 129, 3527.
(21) Xu, J. L.; Liu, X. F.; Lv, J.; Zhu, M.; Huang, C. S.; Zhou, W. D.; Yin, X. D.;
Liu, H. B.; Li, Y. L.; Ye, J. P. Langmuir 2008, 24, 4231.
(27) Zhang, C. Y.; Zhang, X. J.; Zhang, X. H.; Fan, X.; Jie, J. S.; Chang, J. C.;
Lee, C. S.; Zhang, W. J.; Lee, S. T. Adv. Mater. 2008, 20, 1716.
(28) Yamamoto, Y.; Fukushima, T.; Suna, Y.; Ishii, N.; Saeki, A.; Seki, S.;
Tagawa, S.; Taniguchi, M.; Kawai, T.; Aida, T. Science 2006, 314, 1761.
(22) Yan, D. Y.; Zhou, Y. F.; Hou, J. Science 2004, 303, 65.
(23) Huang, C. S.; Wen, L. P.; Liu, H. B.; Li, Y. L.; Liu, X. F.; Yuan, M. J.; Zhai,
J.; Jiang, L.; Zhu, D. B. Adv. Mater. 2009, 21, 1.
6706 DOI: 10.1021/la9040387
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Ma et al.
Article
(Figure 8,21), according to the calculation results and consistent
particles with dimension of about 1 to 2 μm with bright-green
emission are observed. This green emission is therefore ascribed to
the fluorescence of the BTE components within the aggregates,
corresponding to the fluorescence spectra of the assembly men-
tioned above. Upon irradiation of the aggregates with 365 nm
light for 10 min, the green emission is dramatically quenched,
suggesting that an efficient molecular photocyclization-induced
(as shown inFigure9c) photochromic transformation arises in the
assembled structures and revealing the superiority of the assem-
blies over the colloidal solutions and amorphous films.37 The
“on” and “off” emission modulated by light stimuli indicates that
the material is a good switch bearing great potential in the fields of
information storage and computing. Details of the photochromic
reaction-induced conformational changes of1 and the subsequent
light-controlled assembly alteration are being carried out in our
laboratory and will be published elsewhere.
with the results interpreted by Wurthner et al.,17 which will direct
€
the morphology transition process. Besides, the dipole-dipole
interaction between the stacked thiophene rings should facilitate
the transition simultaneously.29 Therefore, concomitant with the
evacuation of the solvent interspace, dipole-dipole interactions
act as the major forces driving layers in 0-D structure to fuse
together and finally direct the formation of 1-D nanotubes. The
fusion of vesicles released the curvature energy, leading to a
thermodynamically more stable tubular structure.
3.4. Photochromic Properties of the Assemblies. A fluore-
scence study is carried out to investigate the assembly behavior as
well as the switching performance of the aggregates. As shown in
Figure 9a, the emission spectra of molecularly dissolved 1 display
a mirror-image relationship to the absorption spectrum with a
large Stokes’ shift (25 nm) in CHCl3. Upon additionof CH3OH to
the CHCl3 solution, a gradual decrease in fluorescence intensity
with a maximum at 619 nm was observed, indicating the presence
of a fluorescence quenching effect induced by the strong inter-
molecular π-π stacking as a result of aggregate formation.30-35
When the ratio of the CHCl3 to CH3OH reaches 3%, of which the
well-defined nanostructures (nanospheres and nanotubes)
formed, the emission at 619 nm originating from the PDI core
was quenched almost completely whereas the emission at 520 nm
is observed (inset in Figure 9a). According to the relative BTE
compound investigated previously,36 the emission with a maxi-
mum at 520 nm is ascribed to the fluorescence of the open form of
2,3-bis(2,3,5-trimethyl-3-thienyl)maleic anhydride.
4. Conclusions
A diarylethene-functionalized perylene diimide (BTE-PDI)
photochromic dyad has been designed and self-assembled into
aggregates by a reprecipitation method. Vivid SEM and TEM
images were recorded and confirmed that the molecules are able
to self-assemble into 0-D vesicles and thereafter continually grow
into 1-D tubes. Both the vesicles and the tubes have highly
ordered lamellar structure, indicating the hierarchical process
during assembly formation. The fluorescence of the vesicles can
be regulated by photoirradiation with UV light, suggesting the
aggregates to be good photochromic switches. These findings
provide a simple method for the introduction of stimuli-respon-
sive groups into building blocks to fabricate dynamic and smart
devices on the scale of nanometers, and the progressive growth
demonstrates a promising pathway for constructing an artificial
system that mimicks the features of growth in nature.
The response of the assemblies to light stimulation is studied by
confocal fluorescence microscopy. As displayed in Figure 9b,
(29) Saita, K.; Kobatake, S.; Fukaminato, T.; Nanbu, S.; Irie, M.; Sekiya, H.
Chem. Phys. Lett. 2008, 454, 42.
(30) Liu, S. G.; Sui, G. D.; Cormier, R. A.; Leblanc, R. M.; Gregg, B. A. J. Phys.
Chem. B 2002, 106, 1307.
(31) Yan, P.; Chowdhury, A.; Holman, M. W.; Adams, D. M. J. Phys. Chem. B
2005, 109, 724.
Acknowledgment. We are grateful for financial support by the
Nature Science Foundation of Shandong Province (Y2006B14)
and a grant from the Ph.D. Programs Foundation of the Ministry
of Education of China.
€
(32) Zhang, X.; Chen, Z. J.; Wurthner, F. J. Am. Chem. Soc. 2007, 129, 4886.
€
(33) Schneider, M.; Hangen, J.; Haarer, D.; Mullen, K. Adv. Mater. 2000, 12,
351.
€
(34) Tang, T. J.; Qu, J. Q.; Mullen, K.; Webber, S. E. Langmuir 2006, 22, 26.
(35) Gregg, B. A. J. Phys. Chem. B 2003, 107, 4688.
(36) Me, M.; Sayo, K. J. Phys. Chem. 1992, 96, 7671.
(37) Kasatani, K.; Kambe, S.; Irie, M. J. Photochem. Photobiol., A 1999, 122, 11.
Langmuir 2010, 26(9), 6702–6707
DOI: 10.1021/la9040387 6707