Cooperative assembly of binary molecular components into tubular structures for multiple photonic applications

Article abstract of DOI:10.1002/anie.201006681

Take the tube: Tubular structures can be fabricated by the cooperative self-assembly of the binary molecular components TPI and APO (see picture). This method can also be used to make a single binary tube capable of performing multiple photonic functions,

Full text of DOI:10.1002/anie.201006681

Communications
DOI: 10.1002/anie.201006681
Self-Assembly
Cooperative Assembly of Binary Molecular Components into Tubular
Structures for Multiple Photonic Applications**
Qing Liao, Hongbing Fu,* Chen Wang, and Jiannian Yao*
One-dimensional (1D) assemblies of p-stacked conjugated
molecules are of particular interest for miniaturized elec-
tronic[1] and photonic[2] devices. Inspired by the discovery of
carbon nanotubes, hollow tubular structures been intensively
investigated in the past decades.[3] Research into organic
tubes, however, has been slower than that of their inorganic
counterparts. Supramolecular nanotube architectures of
amphiphilic molecules[4a] and peptides[4b] have been con-
structed by a twisted-belt mechanism, while the template-
wetting method has been developed for the preparation of
polymer nanotubes.[5] Nonetheless, the self-assembly of
tubular structures from p-conjugated molecules,[6] especially
from multiple molecular components, remains largely unex-
plored.
The cooperative assembly of multiple p-conjugated
Figure 1. a) Molecular structures of APO and TPI. b) SEM and TEM
components has been recently introduced as an effective
(inset) images of as-prepared binary microtubes. c) Normalized diffuse
reflection absorption (black) and PL (red, lEX =320 nm) spectra of an
ensemble of binary tubes placed on a quartz substrate. d) PL micro-
approach to the fabrication of photo- and/or electroactive
nanostructures,[7] in which adjustable electronic processes,
graph of binary microtubes on a quartz substrate upon excitation with
unfocused UV light (330–380 nm).
such as electron transfer and energy transfer, between
different species allow the realization of novel properties,
such as p/n heterojunctions,[8a] ambipolar charge transport,[8b]
and white-light emission.[9] Herein, we report a supramolec-
ular synthesis of rectangular binary microtubes with precisely
controlled lengths by cooperative assembly of 2,4,5-tripheny-
limidazole (TPI, a ultraviolet-emissive molecule) and 3-
(anthracen-10-yl)-1-phenylpro-2-en-1-one (APO, a green-
emissive and photoactive molecule; Figure 1a). In contrast
to the orthogonal self-assembly that takes place at room
temperature, the cooperative assembly of TPI and APO
mediated by hydrogen bonding has been achieved at 658C,
and leads to 1D growth of homogeneous tubular structures.
As a result of their well-defined facets, rectangular binary
tubes behave as annular microcavities that are capable of
propagating both TPI and APO photoluminescence (PL).
Furthermore, the controllable switching of guided light to a
selected end of a single tube has been demonstrated by the
photoisomerization of APO molecules that was induced
locally upon focused light irradiation.
In a typical preparation, a mixed stock solution (100 mL)
containing both TPI (1 mm) and APO (1 mm) in tetrahydro-
furan (THF) was rapidly injected into deionized water (2 mL)
at 658C under shaking. The mixture was maintained at 658C
for 30 min, and then the hot mixture was slowly cooled to
258C at a rate of 108Chꢀ1. Finally, the precipitates were
centrifugally separated from the colloidal suspension and
washed twice with water prior to vacuum drying.
Scanning electron microscopy (SEM) results (Figure 1b)
reveal that highly monodispersed 1D structures with a
rectangular cross-section were obtained. The open-end fea-
tures suggest that the structures are rectangular hollow tubes
with a wall thickness of approximately 200 nm. These results
are further supported by transmission electron microscopy
(TEM) analysis (Figure 1b, inset). Each individual tube has a
uniform diameter around 800 nm and smooth outer surfaces
along the entire length (60 mm; Figure S1 in the Supporting
Information). Moreover, the well-defined facets of these
tubes are also confirmed by atomic force microscopy (AFM)
measurements (Figure S2).
[*] Dr. Q. Liao, Prof. H. B. Fu, C. Wang, Prof. J. N. Yao
Beijing National Laboratory for Molecular Science (BNLMS)
Institute of Chemistry, Chinese Academy of Sciences
Beijing, 100190 (P. R. China)
E-mail: hongbing.fu@iccas.ac.cn
jnyao@iccas.ac.cn
[**] This work was supported by grants-in-aid from the Natural Science
Foundation of China (nos. 90301010, 20873163, 20803085,
20925309), the Chinese Academy of Sciences (“100 Talents”
program), and the National Research Fund for Fundamental Key
Project 973 (2011CB808402).
Figure 1c shows the diffuse reflection absorption (black)
and PL spectra (red) of an ensemble of tubes placed on a
quartz plate. Two evident absorption peaks at 340 and 440 nm
are observed. The former is due to the S0!S1 transition of the
TPI molecules,[10a] and the latter is a characteristic of the APO
components (Figure S3).[10b] Moreover, besides the TPI band
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201006681.
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at 402 nm, the PL spectrum of tubes excited at 320 nm also
exhibits the PL of APO at 540 nm. Note that APO
components only weakly absorb light at 320 nm (Figure S3).
Considering the good spectral overlap between the TPI
emission and the APO absorption (Figure S3), the APO PL
observed for binary tubes upon excitation at 320 nm might be
a result of Fꢀrster energy transfer (FET) from excited TPI to
APO molecules.[11] Indeed, the decay of TPI PL in binary
tubes (109 ps) is faster than that in pure TPI microrods
(301 ps), and results in an FET efficiency of 0.64 (Figure S4).
According to the absorption analysis of binary tubes re-
dissolved in THF, the contents of TPI and APO are
determined to be (92 ꢁ 3)% and (8 ꢁ 2)%, respectively
(Figure S5). Figure 1d shows the PL micrograph of binary
tubes excited with unfocused UV light (330–380 nm). Blue-
violet PL occurs uniformly along the tube bodies with bright
white spots at both ends. The spatially resolved PL spectra
indicate that the intensity fluctuation across the entire
spectral region is less than 10% at different positions for a
single tube (Figure S6). Furthermore, X-ray diffraction
(XRD) results suggest that binary tubes are highly crystalline,
however, this property is mainly related to the TPI compo-
nent (Figure S7). In fact, no XRD characteristics of APO
component were identified. It is known that besides the
spectral overlap, the FET process also requires a close
distance of about 2–6 nm between the donor and acceptor
molecules.[11] Therefore, the frustrated FET process (effi-
ciency = 0.64) suggests that the APO molecules are distrib-
uted between small crystal grains of TPI matrix in binary
microtubes, which are different from the common molecular
dispersed film doping, where the donor PL can be completely
quenched.
Figure 2. a) Infrared spectra of the TPI rods (top), APO rods (middle),
and binary tubes (bottom). b) Length (hollow circle) and diameter
(solid square) of microtubes plotted as a function of reaction time,
based on SEM analysis of binary microtubes obtained at different
reaction intervals c) 2 min, d) 10 min, e) 1 h, and f) 3 h. The insets
show corresponding high-magnification SEM images. The scale bars
represent 1 mm. g) A schematic model of cooperative self-assembly for
the formation of binary tubular structures.
Individual TPI and APO molecules can self-assemble into
solid microrods by p stacking at 258C (Figure S8); conse-
quently, orthogonal assembly takes place if the mixed solution
is applied (Figure S9). By raising the temperature to 658C,
individual TPI or APO molecules form irregular particles
(Figure S10); remarkably, cooperative self-assembly gener-
ates rectangular binary tubes. Figure 2a shows the IR spectra
of binary tubes, individual TPI, and APO solid rods, and the
rapid growth that results in rectangular tubes with a diameter
of 650 nm and a length of 12 mm at 10 min (Figure 2d).
Further prolongation of the reaction time to longer than
10 min leads to the 1D growth stage. In this stage (Figure 2b),
the tube diameter remains almost constant around 800 nm;
however, the tube length keeps growing as the reaction time is
increased, for example, the length is 30 mm after 1 h (Fig-
ure 2e) and 60 mm after 3 h (Figure 2 f). After the reaction
time exceeds 3 h, both the transverse and longitudinal growth
terminate (Figure 2b). The formation of binary tubes follows
a typical 1D growth process rather than the twisted-belt
mechanism reported for amphiphilic molecules and pep-
tides,[4] or the recently reported “etching” mechanism,[12] in
which crystalline tubular structures are converted from their
solid counterparts by dissolution using either liquid or
gaseous solvents.
following can be observed: 1) the peaks at 3416 cmꢀ1 of N H
ꢀ
stretching observed in TPI rods red-shift to 3349 cmꢀ1 and
become broader and stronger in the binary tubes; 2) the peaks
ꢀ1
=
=
at 1597 (C C stretching) and 1656 cm (C O stretching)
observed in APO rods become weaker in the binary tubes;
ꢀ1
ꢀ
and 3) unsaturated C H stretching at 3052 cm occurs in
ꢀ
both TPI and APO rods; however, saturated C H stretching
at 2904 cmꢀ1 occurs concurrently with the appearance of a
broad feature around 1050 cmꢀ1 typical for C O stretching in
ꢀ
binary tubes. All these features suggest the existence of
ꢀ
intermolecular hydrogen bonding between the N H of TPI
=
and C O of APO in binary tubes.
Temporal SEM analysis was employed to further probe
the formation process of binary tubes (Figure 2c–f). We have
identified three distinctive stages: nucleating aggregation, 1D
growth, and termination (Figure 2b). At an early stage about
2 min after the injection, short and round hollow structures
are already observed with a diameter of 350 nm and a length
of 3 mm (Figure 2c). These initial hollow structures undergo a
Most recently, Jonkheijm et al. demonstrated a close
relationship between the self-assembly process and the
nucleation–growth pathway, where self-assembled molecular
clusters are identified as a high-energy prenucleus.[13] In our
case, the TPI and APO components can be selectively excited
at 320 and 440 nm, respectively. At room temperature, we
found that the dilute mixed solution (ꢂ 4.0 ꢁ 10ꢀ5 m) shows
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only the PL of TPI upon excitation at 320 nm (Figure S11a),
Propagation loss measurements were performed based on
the spatially resolved PL spectra of a single tube by collecting
the PL signal from one of its ends with respect to the distance
travelled (Figure 3a). According to the equation of the
because both the TPI and the APO molecules are separately
free-standing. In contrast, the PL of APO is dominant in the
PL spectrum of the stronger stock solution (1 mm) excited at
320 nm, thus suggesting the exclusive formation of TPI–APO
mixed clusters (Figure S11a), in which the spatial proximity
between TPI and APO molecules ensures the FET process.
Upon selective excitation of APO at 440 nm (Figure S11b),
observation of a severe concentration quenching effect (>
3.0 ꢁ 10ꢀ4 m) confirms that APO clusters are also formed in
the stock solution.[14] Most importantly, if the stock solution is
heated to 658C, the fluorescence signal of APO PL excited at
440 nm reappers with an intensity three times that recorded at
258C, probably because of the dissociation of APO clusters.
Meanwhile, the PL spectrum excited at 320 nm (Figure S11)
indicates that despite the dissociation, some of TPI–APO
mixed clusters remained intact at 658C.
By combining the above results, we propose a cooperative
assembly model for the formation of binary tubes in Fig-
ure 2g. Upon injection, the solvent exchange induces the
nucleation event. At room temperature (path 1), both TPI–
APO mixed clusters and APO clusters can serve as nuclei for
heterogeneous assembly driven by the p-stacking motif of
TPI or APO molecules. Therefore, orthogonal self-assembly
takes place, and leads to TPI and APO solid rods (path 1). At
658C (path 2), the APO clusters are dissociated; only TPI–
APO mixed clusters survive as high-energy nuclei for further
homogeneous cooperative assembly. In the presence of APO
monomers in the hot system, those APO molecules incorpo-
rated at the periphery of mixed clusters might dynamically
exchange on (formation) and off (dissociation) the mixed
clusters,[15] thus serving as a linker for aggregation of mixed
clusters by hydrogen-bonding during the nucleation process.
Although it is not yet fully understood, the aggregation of
nucleates might cause temporary concentration depletion,
which is responsible for the formation of primary hollow
structures (path 2).[16] Once initial hollow structures form, 1D
growth is energetically favorable because of the preferable
adsorption of the growth units of the mixed clusters on the
edge of primary tubular structures (path 2).[17] Note that the
system was maintained at 658C for 30 min after the injection,
and then the system was slowly cooled down at a rate of
108Chꢀ1. In the first 150 min (52 mm long tubes were obtained
as shown in Figure 2b), the temperature is higher than 458C.
Therefore, the TPI–APO mixed clusters play a major role in
both the nucleation and growth processes. The solution that
remains after the centrifugation shows only the absorption
characteristics of APO (nanoparticles according to SEM),
thus suggesting that all the TPI molecules are involved in tube
formation. We also monitored the growth process by measur-
ing the PL spectra excited at 320 nm. It is found that the ratio
Figure 3. a) Spatially resolved PL spectra of out-coupled light at a
distance of 10, 20, 30, 40, 50, and 60 mm (curves from top to bottom)
from the tip of a single tube, recorded by focused 325 nm laser
excitation (see the arrow in the inset). The scale bar is 10 mm.
b) Logarithmic plot of the relative PL intensities at 402 nm (square)
and 540 nm (circle) versus the propagation distance.
optical loss coefficient of guided light in the fundamental
modes of a waveguide [Eq. (1)]:[12c]
a ¼ ꢀ10 logðIout=IinÞ Lꢀ1
ð1Þ
where Iin and Iout are the intensities of incidence and out-
coupled light, respectively, and L is the propagation distance,
the values of a for TPI PL at 402 nm and for APO PL at
540 nm are determined to be 100 and 36 dBmmꢀ1, respec-
tively (Figure 3b). It has been established that the air medium
inside the tubes that have well-defined facets leads to spatial
confinement of guided photons in two dimensions in the thin
tubular wall, thereby forming an annular microcavity.[12b,c] The
travel distance of the guided light in the annular microcavity
is so long that a photon in the UV region from TPI can be
reabsorbed by APO, which then re-emits a photon in the
green region. This so-called remote energy relay (RER)
process results in re-distribution of the guided PL from short
to long wavelengths,[12c] and is the reason why the value of a at
540 nm is much lower than that at 402 nm.
The chalcone derivatives such as APO are photochemi-
cally active, and might undergo either photoisomerization or
photodimerization.[18] We found that the green fluorescence
of an ensemble of APO microrods placed on a quartz plate
can be quenched by exposure to light (UV400) from an Hg
lamp equipped with a band-pass filter (central wavelength:
400 nm, FWHM: 40 nm), probably because of the photo-
isomerization reaction.[18a] The reversible recovery of green
fluorescence can be easily achieved by keeping the irradiated
sample in the dark (Figure S13). Figure 4a shows a schematic
picture of a waveguide switch based on binary microtubes.
Snapshots during the waveguide switch measurement are
presented in Figure S14. Photoisomerization of APO compo-
nents is induced locally by focusing 400 nm light from the Hg
lamp down to the diffraction limit (2 mm) on a selected
position on the tube, as indicated by the circle in Figure 4a.
According to the spatially resolved spectra at the irradiation
between the PL intensities of APO and TPI, IAPO/ITPI
,
increases as the reaction time is extended (Figure S12). The
variation of IAPO/ITPI with time correlates well with that of the
tube length versus time (circles in Figure 2b), thus verifying
the incorporation of APO in the 1D tube growth.
As shown in Figure 1d, these binary microtubes present
typical features of an active waveguide, such as bright PL
spots at the tips and weaker emission from the bodies.[3]
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cavities that are capable of propagating both TPI and APO
PL along the 1D direction. Furthermore, the controllable
switching of guided light to a selected end of a single tube has
been demonstrated by local introduction of photoisomeriza-
tion of APO component upon focused light irradiation. The
strategy described here might be useful for the design and
fabrication of novel optoelectronic devices.
Received: October 25, 2010
Revised: February 18, 2011
Keywords: p conjugation · energy transfer · microtubes ·
.
photonics · self-assembly
[1] a) H. Moon, R. Zeis, E. J. Borkent, C. Besnard, A. J. Lovinger, T.
Siegrist, C. Kloc, Z. N. Bao, J. Am. Chem. Soc. 2004, 126, 15322 –
15323; b) L. Zang, Y. Che, J. Moore, Acc. Chem. Res. 2008, 41,
1596 – 1608.
Figure 4. a) Representation of waveguide switch before (top) and after
(bottom) irradiation of the region marked with a circle by UV400 light
(FWHM: 40 nm). The squares show the excitation point of focused
325 nm laser light for waveguide measurement. b) Out-coupled PL
spectra from the left tip before (black) and after (red) UV400 irradiation
at the region marked with a circle, upon excitation at 325 nm by
focusing the laser on the region marked with a square. c) The switch
cycles (N=number of cycles) of APO PL out-coupled at the left tip
upon UV400 irradiation at the circled region and subsequent recovery in
the dark.
[2] a) Y. S. Zhao, H. B. Fu, A. D. Peng, Y. Ma, Q. Liao, J. N. Yao,
Acc. Chem. Res. 2010, 43, 409 – 418; b) D. OꢂCarroll, I. Lieber-
wirth, G. Redmond, Nat. Nanotechnol. 2007, 2, 180 – 184.
[3] a) J. Hu, M. Ouyang, P. Yang, C. M. Lieber, Nature 1999, 399,
48 – 51; b) J. P. Hill, W. Jin, A. Kosaka, T. Fukushima, H.
Ichihara, T. Shimomura, K. Ito, T. Hashizume, N. Ishii, T. Aida,
Science 2004, 304, 1481 – 1483; c) A. N. Aleshin, Adv. Mater.
2006, 18, 17 – 27; d) Y. S. Zhao, W. S. Yang, D. B. Xiao, X. H.
Sheng, X. Yang, Z. G. Shuai, Y. Luo, J. N. Yao, Chem. Mater.
2005, 17, 6430 – 6435.
[4] a) T. Shimizu, M. Masuda, H. Minamikawa, Chem. Rev. 2005,
105, 1401 – 1443; b) D. T. Bong, T. D. Clark, J. R. Granja, M. R.
Ghadiri, Angew. Chem. 2001, 113, 1016 – 1041; Angew. Chem.
Int. Ed. 2001, 40, 988 – 1011.
[5] M. Steinhart, R. B. Wehrspohn, U. Gꢀsele, J. H. Wendorff,
Angew. Chem. 2004, 116, 1356 – 1367; Angew. Chem. Int. Ed.
2004, 43, 1334 – 1344.
[6] a) Z. C. Wang, C. J. Medforth, J. A. Shelnutt, J. Am. Chem. Soc.
2004, 126, 15954 – 15955; b) J. S. Hu, Y. G. Guo, H. P. Liang, L. J.
Wan, L. Jiang, J. Am. Chem. Soc. 2005, 127, 17090 – 17095; c) Y.
Chen, B. Zhu, F. Zhang, Y. Han, Z. Bo, Angew. Chem. 2008, 120,
6104 – 6107; Angew. Chem. Int. Ed. 2008, 47, 6015 – 6018.
[7] F. J. M. Hoeben, P. Jonkheijm, E. W. Meijer, A. P. H. J. Schen-
ning, Chem. Rev. 2005, 105, 1491 – 1546.
[8] a) N. Sakai, R. Bhosale, D. Emery, J. Mareda, S. Matile, J. Am.
Chem. Soc. 2010, 132, 6923 – 6925; b) P. Jonkheijm, N. Stutz-
mann, Z. J. Chen, D. M. de Leeuw, E. W. Meijer, A. P. H. J.
Schenning, F. Wꢃrthner, J. Am. Chem. Soc. 2006, 128, 9535 –
9540.
[9] a) C. Vijayakumar, V. K. Praveen, A. Ajayaghosh, Adv. Mater.
2009, 21, 2059 – 2063; b) R. Abbel, C. Grenier, M. J. Pouderoijen,
J. W. Stouwdam, P. E. L. G. Leclꢄre, R. P. Sijbesma, E. W.
Meijer, A. P. H. J. Schenning, J. Am. Chem. Soc. 2009, 131,
833 – 843; c) Y. L. Lei, Q. Liao, H. B. Fu, J. N. Yao, J. Am. Chem.
Soc. 2010, 132, 1742 – 1743.
[10] a) Y. S. Zhao, A. D. Peng, H. B. Fu, Y. Ma, J. N. Yao, Adv. Mater.
2008, 20, 1661 – 1665; b) H. D. Becker, K. Andersson, J. Org.
Chem. 1983, 48, 4542 – 4549.
point (Figure S14d), the PL of TPI remain the same as that
before irradiation, while the PL from APO is indeed
quenched. We next checked the effect of UV400 irradiation
at the circled region on the waveguide behavior by excitation
at the region indicated by a square by using focused 325 nm
laser light (Figure 4a). Figure 4b shows the out-coupled
spectra collected at the left tip. The intensity of TPI PL
after UV400 irradiation is about one-third of that before
irradiation. Moreover, the PL of APO out-coupled at the left
tip disappears completely after UV400 irradiation at the circled
region. The inset of Figure 4b shows the CIE coordinates
calculated from the out-coupled PL spectra at the left tip
before (line 1) and after UV400 irradiation (line 2). In sharp
contrast, the out-coupled spectra at the right tip show no
changes in both TPI and APO features. That is, selective
switching of the waveguide to the left tip had been success-
fully realized by using our binary tube.[19] Remarkably, the
APO PL out-coupled at the left tip can be turned on again by
keeping the irradiated sample in the dark. This switch has an
on/off ratio of approximately 20 and can be reversibly
switched over at least seven cycles without any fatigue
(Figure 4c).
In summary, we have reported the preparation of
rectangular binary microtubes with precisely controlled
lengths through cooperative self-assembly of TPI and APO.
We have identified three stages of the formation binary tubes:
nucleating aggregation, 1D growth, and termination. In
particular, TPI–APO mixed clusters play a major role in the
cooperative self-assembly for the nucleation and growth of
binary tubes. These microtubes behave as annular micro-
[11] J. R. Lakowicz, Principles of Fluorescence Spectroscopy, Plenum,
New York, 1999.
[12] a) X. J. Zhang, X. H. Zhang, W. S. Shi, X. M. Meng, C. S. Lee,
S. T. Lee, Angew. Chem. 2007, 119, 1547 – 1550; Angew. Chem.
Int. Ed. 2007, 46, 1525 – 1528; b) Y. S. Zhao, J. J. Xu, A. D. Peng,
H. B. Fu, Y. Ma, L. Jiang, J. N. Yao, Angew. Chem. 2008, 120,
7411 – 7415; Angew. Chem. Int. Ed. 2008, 47, 7301 – 7305; c) Q.
Liao, H. B. Fu, J. N. Yao, Adv. Mater. 2009, 21, 4153 – 4157.
Angew. Chem. Int. Ed. 2011, 50, 4942 –4946
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org 4945

Communications
[13] P. Jonkheijm, P. Van der Schoot, A. Schenning, E. W. Meijer,
2506 – 2509; b) L. W. Yin, Y. Bando, D. Golberg, M. S. Li, Adv.
Mater. 2004, 16, 1833 – 1838.
Science 2006, 313, 80 – 83.
[14] V. Bulovic, A. Shoustikov, M. A. Baldo, E. Bose, V. G. Kozlov,
M. E. Thompson, S. R. Forrest, Chem. Phys. Lett. 1998, 287,
455 – 460.
[15] Y. D. Yin, A. P. Alivisatos, Nature 2005, 437, 664 – 670.
[16] a) B. Mayers, Y. N. Xia, Adv. Mater. 2002, 14, 279 – 282; b) H. X.
Ji, J. S. Hu, Q. X. Tang, W. G. Song, C. R. Wang, W. P. Hu, L. J.
Wan, S. T. Lee, J. Phys. Chem. C 2007, 111, 10498 – 10502.
[17] a) S. M. Yoon, I. C. Hwang, K. S. Kim, H. C. Choi, Angew.
Chem. 2009, 121, 2544 – 2547; Angew. Chem. Int. Ed. 2009, 48,
[18] a) K. Rurack, M. L. Dekhtyar, J. L. Bricks, U. Resch-Genger, W.
Rettig, J. Phys. Chem. A 1999, 103, 9626 – 9635; b) Z. Irena, L.
Tali, K. Menahem, Eur. J. Org. Chem. 2006, 4164 – 4169.
[19] Photoisomerization of APO components might alter the local
TPI crystalline matrix, thus leading to leakage of guided light,
which should be responsible for the selective switch of wave-
guide to the left tip rather than to the right tip (Figure S14).
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