Cucurbit[10]uril-Based [2]Rotaxane: Preparation and Supramolecular Assembly-Induced Fluorescence Enhancement

Article abstract of DOI:10.1021/acs.joc.7b00400

As the cucurbit[n]uril (CB[n]) homologue with the largest cavity size, cucurbit[10]uril (CB[10]) can encapsulate big guests to form interesting host-guest complexes/assemblies. Herein, we report the preparation and fluorescence properties of CB[10]-based

Full text of DOI:10.1021/acs.joc.7b00400

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Article
Cucurbit[10]uril-based [2]Rotaxane: Preparation and
Supramolecular Assembly-Induced Fluorescence Enhancement
Yang Yu, Yawen Li, Xiaoqing Wang, Hao Nian, Le Wang,
Jie Li, Yanxia Zhao, Xiran Yang, Simin Liu, and Liping Cao
J. Org. Chem., Just Accepted Manuscript • Publication Date (Web): 10 May 2017
Downloaded from http://pubs.acs.org on May 12, 2017
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Cucurbit[10]uril-based [2]Rotaxane: Preparation and
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Supramolecular Assembly-Induced Fluorescence Enhancement
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Yang Yu,a,fl Yawen Li,a,fl Xiaoqing Wang,a Hao Nian,a Le Wang,a Jie Li,a Yanxia Zhao,a Xiran
Yang,b Simin Liu,b,* and Liping Caoa,*
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aKey Laboratory of Synthetic and Natural Functional Molecule Chemistry of the Ministry of
Education, College of Chemistry and Materials Science, Northwest University, Xi‘an, 710069, P.
R. China.
E-mail: chcaoliping@nwu.edu.cn
bSchool of Chemistry and Chemical Engineering, Wuhan University of Science and Technology,
Wuhan 430081, P. R. China.
E-mail: liusimin@wust.edu.cn
fl Y.Y. and Y.L. contributed equally to this work.
Table of contents
Abstract
As the cucurbit[n]uril (CB[n]) homologue with the largest cavity size, cucurbit[10]uril (CB[10])
can encapsulate big guests to form interesting host-guest complexes/assemblies. Herein, we
report the preparation and fluorescence properties of CB[10]-based [2]rotaxane (CB[10]•1)
formed from cucurbit[10]uril and dumbbell-like guest 1. This [2]rotaxane (CB[10]•1) is
assembled by C=O•••N+ ion-dipole interactions between oxygen atoms of the carbonyl fringed
portals of CB[10] and the positively charged pyridinium units of 1 via the slipping method under
•
heating at 95 C in DMSO. In contrast, other cucurbit[n]uril (CB[n], n = 6-8) homologues can‘t
form rotaxanes with 1 due to their smaller cavities. The dumbbell-like guest 1 is a poor emitter
in DMSO. Interestingly, the formation of CB[10]•1 renders the restriction of intramolecular
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rotation of TPE, which features a strong fluorescent intensity, long lifetime and high quantum
yield. Furthermore, CB[10]•1 is shown to aggregate plate-like structures with various sizes in
different solvents (DMSO, THF or CHCl3), resulting in a stepwise aggregation-induced emission
enhancement effect. This kind of CB[10]-based [2]rotaxane may be used to fabricate
luminescent systems with unique emission properties.
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Introduction
Luminescent molecules or systems have attracted increasing interest due to their
applications as optical devices,1 photo-induced materials,2 biological applications
(imaging,3 sensor,4 and probes5), photodynamic therapy,6 and molecular machines,7 among
other applications. The self-assembly of luminescent molecules8 through non-covalent
forces cause the change of luminescent properties, including excimer formation,9
fluorescence resonance energy transfer (FRET),10 aggregation-caused quench (ACQ),11
aggregation-induced emission (AIE)/aggregation-induced emission enhancement (AIEE),12
and J-/H-aggregation.13
Inspired by these phenomena, supramolecular scientists,
especially those who are interested in host-guest chemistry and material chemistry, have
developed a series of new design strategies for tuning emission properties via host-guest
recognitions to achieve functional systems, such as near-infrared materials14 and energy
transfer systems.15
Cucurbit[n]urils (CB[n]s),16 a family of pumpkin-shaped macrocyclic molecules bearing
a rigid hydrophobic cavity and two identical carbonyl fringed portals, are of great interest
because of their excellent recognition property in water and wide applications in molecular
recognition,17 self-assembly,18 catalysis,19 bio-sensor,20 drug delivery,21 supramolecular
polymer,22 molecular machine,23 and other supramolecular systems.24 In particular,
CB[n]s are also well known to form complexes with a range of organic fluorophores,
which cause profound changes in increasing fluorescent intensity, lifetime and quantum
yield,25 enhancing photothermal conversion6 and tuning fluorescent color26 through
host-guest interaction with their hydrophobic cavities in water. For examples, Kaifer and
co-workers discovered that CB[7] could form stable host-guest complexes with cyanine
dyes to achieve the emission off-on switch between the H-aggregation and J-aggregation.27
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Galoppini and co-workers described an unprecedented fluorescence enhancement of
viologen derivative bound with two CB[7].25c Ni and co-workers reported a CB[8]
across-linked supramolecular luminescent system with tunable and dynamical
photophysical properties.26
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As the CB[n] homologue with the largest cavity size, cucurbit[10]uril (CB[10]) is unique
because of its ability to bind large guests within its cavity (Figure 1a).28 For examples, Day,
Isaacs, Collins, Wallace and Liu found that CB[10] could encapsulate cucurbit[5]uril,28a
calix[4]arene,28b triazene-arylene oligomer,28c metalloporhyrin,28d platinum/ruthenium/iridium
polypyridyl complexes,28e-g and blue box,28h respectively. However, few reports were involved
with the construction of supramolecular luminescent system from CB[10] as a host in the
solution.28g In this paper, we report the preparation and supramolecular assembly-induced
fluorescence enhancement of rotaxane CB[10]•1 formed from CB[10] and a dumbbell-like guest,
1,1‘-ditetraphenylethenyl-4,4‘-bipyridine-1,1‘-diium dichloride (1), in DMSO. In this case,
CB[10] imposes a structural confinement of guest 1, resulting in the restriction of intramolecular
rotation (RIR) of tetraphenylethylene (TPE) in CB[10]•1 and increasing their electron density by
ion-dipole interactions. These effects together improve fluorescent emission properties of this
rotaxane system. At the same time, CB[10]•1 further exhibits a stepwise aggregation-induced
emission enhancement (AIEE) effect in different solvents (THF or CHCl3).
Results and discussion
Design and synthesis of dumbbell-like guests
As a mechanically interlocked molecule, a rotaxane must have a dumbbell-like molecule as axle
which is threaded through a macrocyclic molecule.29 Recently, cucurbit[n]uril-based rotaxanes
as supramolecular building blocks have been synthesized and used for the construction of
sophisticated supramolecular architectures, such as infinite 1D lines,30 2D networks,31 3D
frameworks,32 and discrete molecular necklaces.33 To prepare CB[10]-based rotaxane, a
dumbbell-like molecule with a suitable recognition site for anchoring CB[10] and two large
enough stoppers is required.
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Figure 1. a) Chemical structure of CB[10]; b) Synthesis of dumbbell-like guests 1-2.
Viologen derivatives as the bis-cationic and aromatic guests are suitable recognition units for
fabricating a mechanically interlocked complex with cucurbit[n]uril, which has a hydrophobic
cavity for aromatic residues and two cyclic carbonyl portals for positively charged pyridinium
units.34 Tetraphenylethylene (TPE) moiety was incorporated for its AIE effect and also acts as
stopper.
Therefore, we designed and synthesized two dumbbell-like guest,
1,1‘-ditetraphenylethenyl-4,4‘-bipyridine-1,1‘-diium dichloride derivatives (1-2), containing a
viologen unit in the middle for binding CB[10] and two TPE units at both terminals as stopper and
fluorophore. As shown in Figure 1b, guests 1-2 were synthesized by the reaction of
corresponding mono-amino TPE with N,N'-bis(2,4-dinitrophenyl) 4,4‘-bipyridine-1,1‘-diium
chloride salt by the Zincke reaction, in 96% yield (See supporting information). We envision
that guests 1-2 would undergo host-guest interaction with CB[n] to generate CB[n]-based rotaxane,
resulting in the change of aggregation and the restriction of intramolecular rotation (RIR) of TPE
to realize fluorescence enhancement.
The preparation of rotaxane CB[10]•1
CB[n] compounds are slightly soluble in water and almost insoluble in common organic solvents,
but solvent-soluble guests that are encapsulated in the cavities of CB[n]s usually can promote the
solubility of CB[n]-based complexes. We found that the dumbbell-like guest 1 (chloride salt)
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was insoluble in water, but soluble in DMSO or MeOH. Therefore, we decided to investigate the
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host-guest recognition of 1 with CB[n] (n = 6-8, 10) by H NMR in DMSO-d6, even though
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CB[n]s had extremely poor solubility in DMSO-d6. It is known that the diameter at the portal of
CB[n] (n = 6-8) is 3.9, 5.4, and 6.9 Å, respectively.16 Because the size of TPE unit is about
7.4-9.0 Å, which is bigger than the size of CB[n] (n = 6-8),35 they can‘t encapsulate 1 even under
heating at high temperature for several weeks. As a result, we failed to gain the rotaxanes from 1
and CB[n] (n = 6-8) via the slipping method (Figure S5).
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Figure 2. 1H NMR spectra (400 MHz, DMSO-d6, rt) for: a) 1; b) 1 (0.5 mM) and CB[10] (0.5 mM)
at 95 •C for 2 days, c) 1 (0.5 mM) and CB[10] (0.5 mM) for 17 days at 95 •C. *Free CB[10] and
#bound CB[10]. Here primed (') denote protons binding with host.
Unlike smaller CB[n] (n = 6-8), CB[10] with the portal diameter of 9.5-10.6 Å and volume of
~870 Å3 could be threaded with the TPE unit to form a rotaxane via the slipping method. We
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observed a slowly-slipping formation process of rotaxane CB[10]•1 by H NMR in DMSO-d6.
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Figure 2 shows the H NMR spectra recorded for guest 1 alone, as an initial mixture of 1 with
CB[10], and as rotaxane CB[10]•1. Initially, the resonance peaks of free 1 didn‘t change at all
when 1 equiv of CB[10] was added into the solution of 1 in DMSO-d6 at room temperature.
Surprisingly, however, some tiny peaks belonging to bound 1 were observed when the mixture
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was heated at 95 C for 2 days. At the same time, the resonance peaks of free and bound CB[10]
became much clearer, indicating that the host-guest complex was coming up (Figure 2b). This
phenomenon suggested that the unsubstituted TPE units of guest 1 were able to reversibly thread
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through CB[10] at higher temperature, and then the dynamic complex became kinetically trapped
as a rotaxane at the lower temperature. The positive result encouraged us to continue this
experiment. Under heating at 95 •C for 17 days, it was showed that the resonance peaks of both
free 1 and free CB[10] nearly disappeared and the resonance peaks of host-guest complex grew up,
which was a strong evidence for the formation of rotaxane CB[10]•1 in 81% yield (Figure 2c and
S6). It also illustrated that the formation of rotaxane CB[10]•1 promoted the solubility of CB[10]
in DMSO. While the resonance peaks (Ha and Hb) of 4,4‘-bipyridine-1,1‘-diium unit were
shifted upfield of 0.93 and 0.74 ppm, the resonance peaks (Hc and Hd) of TPE units near
4,4‘-bipyridine-1,1‘-diium unit slightly shifted downfield of 0.09 ppm and upfield of 0.08 ppm,
respectively. Compared with free CB[10], all the resonance peaks of bound CB[10] showed
slight upfield shift (0.04~0.08 ppm). Based on these NMR shifts, 4,4‘-bipyridine-1,1‘-diium unit
of 1 is exactly anchored inside the cavity of CB[10]. Figure S7 shows side views of the
electrostatic potential energy mapped onto the van der Waals surface of 1 and CB[10]•1 complex.
Obviously, the formation of CB[10]•1 complex results in substantial reduction in the electrostatic
potential at the N atoms on the 4,4'-bipyridine-1,1'-ium unit as a consequence of the C=O•••N+
ion-dipole interactions.17a
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In addition, the COSY and NOESY spectra also revealed the supramolecular assembled
structure of rotaxane CB[10]•1 in the solution (Figure S8-S9). ESI-MS spectrum further showed
that a double-charged peak of rotaxane CB[10]•1 (m/z = 1239.9350) was consistent with the
simulated peak of [CB[10]•1]2+ (m/z 1239.9292, Figure S10). All evidences of NMR and
ESI-MS confirm that CB[10] can slip into the middle of dumbbell-like guest 1 under heating
situation in DMSO, and bind with 4,4‘-bipyridine-1,1‘-diium unit by the C=O•••N+ ion-dipole
interactions to form a stable CB[10]-based [2]rotaxane. However, guest 2 can‘t thread through
CB[10] to form the rotaxane under the same condition, due to the appropriate size of the dimethyl
TPE units (Figure S11).
Aggregation-induced emission enhancement of CB[10]•1
TPE derivatives with unique AIE property have been widely used as building block for fabricating
fluorescent materials.12 Furthermore, the host-guest recognitions have been demonstrated to be
an efficient tool to realize RIR of TPE unit in the limited cavity of host.35-46 Therefore, we
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decided to investigate the fluorescent emission properties of rotaxane CB[10]•1 by fluorescence
experiments. Interestingly, 1 exhibits highly selective fluorescence enhancement with CB[10] in
DMSO solution due to the formation of [2]rotaxane CB[10]•1. As shown in Figure 3a, 1 is
non-fluorescent in DMSO. Meanwhile CB[n] (n = 6-8) have almost no effect on the
fluorescence emission because these hosts can not encapsulate 1. When CB[10] slipped to the
middle of 1 with binding 4,4‘-bipyridine-1,1‘-diium unit to form [2]rotaxane CB[10]•1, however,
the fluorescent emission was obviously turned on with yellow color (ꢀem = 558 nm) (Figure 3a).
This fluorescence turn-on phenomenon could be attributed to the formation of CB[10]•1, which
resulted in the restriction of intramolecular rotation of TPE (First step in Scheme 1).
Furthermore, quantum yields and fluorescence lifetime for CB[10]•1 were measured in DMSO, as
shown in Table S1. The quantum yield of CB[10]•1 increased up to U = 0.50 in DMSO, while
CB[10]•1 displayed only one decay kinetics with contribution from a lifetime of 3.33 ns in DMSO
(Figure S12). UV-vis spectra also showed that only CB[10] can bind 1 to form rotaxane,
resulting in a blue shift (ûꢀ = 32 nm) of the absorption maximun (Figure 3b).
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Figure 3. a) Fluorescence spectra of 1 (10 ꢁM) and b) UV-vis spectra of 1 (50 ꢁM) without and
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with 1 equiv of CB[n] (n = 6-8, 10) in DMSO, under heating at 95 C for 17 days; insert photo:
pictures of 1, 1+CB[6], 1+CB[7], 1+CB[8], and 1+CB[10] in DMSO under a 365 nm lamp. ꢀex =
365 nm; Ex/Em slits = 5/5 nm.
Due to the AIE property of TPE unit, we envisioned that the concentration of CB[10]•1 and the
addition of other solvents with low or high polarity should control the aggregation of CB[10]•1 in
the solution phase to exhibit stronger emission properties. The fluorescence intensity of
CB[10]•1 in DMSO increased linearly as the concentration of CB[10]•1 was gradually increased
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from 2.0 to 28.8 ꢁM, and then showed little changes up to 100 ꢁM, which implies that critical
aggregate concentration of CB[10]•1 in DMSO is around 28.8 ꢁM (Figure S13). Furthermore,
fluorescent emission of 1 and CB[10]•1 were recorded by adding 10 different solvents including
polar and non-polar solvents (Figure 4). 1 showed the best fluorescence enhancement in
1,4-dioxane while CB[10]•1 has the strongest fluorescent emission in CHCl3 (Figure S14-S15).
The quantum yield and lifetime of CB[10]•1 in CHCl3 are U = 0.78 and 2.50 ns (Figure S12). It
is worthy to note that the fluorescent intensity of CB[10]•1 is always stronger than that of 1 in
different solvents, because these relaxation processes of TPE units are severely hindered by the
hydrophobic cavity of CB[10] which enhances the AIE effect. It also indicated that the
formation of CB[10]•1 decrease the solubility in all solvents. Specifically, the fluorescent
intensity of CB[10]•1 in THF or CHCl3 is obviously stronger than that in DMSO, which shows a
stepwise aggregation-induced emission enhancement (Second step in Scheme 1). In order to
investigate the AIE property of CB[10]•1, further tests of the fluorescence were carried out in the
mixed solvent of DMSO/H2O. Figure S16 showed that when increasing the DMSO contents
from 10 to 100%, fluorescent intensity with the emission maximum at 558 nm was increased
gradually, which suggested that CB[10]•1 had strong AIE property. Compared with organic TPE
deriveratives, both 1 and CB[10]•1 showed weak fluorescence in water, probably because the H2O
molecules tend to bipyridine-1,1‘-diium cations, resulting in disassembly of CH•••Œ stacking
between 1 molecules (Figure S17).
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Figure 4. Fluorescence intensity at 600 nm of 1 (10 ꢁM, black column) and CB[10]•1 (10 ꢁM,
red column) in different solvents including 1% DMSO (A = acetone; B = CH2Cl2; C = CHCl3; D =
1,4-dioxane; E = DMF; F = DMSO; G = EA; H = H2O; I = MeOH; J = THF). ꢀex = 365 nm;
Ex/Em slits = 5/5 nm.
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Scheme 1. Cartoon illustrations of a stepwise aggregation-induced emission enhancement of
CB[10]•1.
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Aggregation morphology of 1 and CB[10]•1
In order to further understand the aggregation behaviors of 1 and CB[10]•1, the dynamic light
scattering (DLS) and the scanning electron microscopy (SEM) experiments were utilized. The
aggregation transformation between 1 and CB[10]•1 was evidenced by DLS experiments which
revealed that the diameter (D) of aggregates of CB[10]•1 in DMSO was ~396.1 nm at 0.10 mM
and ~295.3 nm at 0.01 mM, respectively (Figure 5 and S18). These values are ~53 and ~39
times larger than that of 1 alone (~7.5 nm) which is consistent with the size of 1. The DLS study
confirmed again the aggregation of CB[10]•1 in THF or CHCl3 by demonstrating a huge increase
of the hydrodynamic diameter of the species (~955.4 nm in THF; ~1106.0 nm in CHCl3) in the
solution of CB[10]•1 at the same concentration (Figure 5 and S19a). Therefore, the florescence
enhancement of CB[10]•1 after addition of THF or CHCl3 could be attributed to more aggregation
of CB[10]•1, which resulted in further inhibition of the rotation of TPE units in the stacked
structures (Scheme 1).
Figure 5. DLS profiles of 1 (0.10 mM) in DMSO and CB[10]•1 (0.10 mM) in DMSO or THF
including 10% DMSO.
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The morphology of the aggregates formed from the solution of 1 or CB[10]•1 were observed by
SEM (Figure 6). The SEM images in Figure 6a-b show monodispersed spherical structures with
a diameter ranging from 160 nm to 598 nm, probably due to the self-assembly between 1
molecules. As shown in Figure 6c-d, well dispersed plate-like structure of CB[10]•1 instead of
the spherical structure of 1 was observed. It indicated that the formation of [2] rotaxane
CB[10]•1 could turn the spherical self-assembled structure of 1 into the plate-like self-assembled
structure of CB[10]•1, companying with fluorescence enhancement. Interestingly, the dispersed
plate-like structures were combined with each other to form larger stacked structures in THF
(Figure 6e-f) or CHCl3 (Figure S19b-c).
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Figure 6. SEM images of the samples from a) and b) 1 (0.10 mM) in DMSO; c) and d)
CB[10]•1 (0.10 mM) in DMSO; e) and f) CB[10]•1 (0.10 mM) in THF including 10% DMSO.
X-ray crystal structure of 1
To understand the relationship between fluorescence enhancement and aggregation, we
turned to X-ray experiment. We were fortunate to obtain X-ray quality crystals of
red plates from 4:1 (v/v) MeOH/DMF solution by slow vapor diffusion of Pr2O at room
temperature. Firstly, Figure 7a-b illustrate the dimerization of to yield a bimolecular
1 as
i
1
structure 1•1 by CH•••Œ interactions between tetraphenylethylene units (Table S2). The
are about 33.1o.
dihedral angle of two pyridine rings in 4,4‘-bipyridine-1,1‘-diium units of
1
Although the 4,4‘-bipyridine-1,1‘-diium units in two different molecules are not parallel,
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the face-to-face stacking of 1•1 is stabilized by four CH•••Œ interactions among
tetraphenylethylene units. Subsequently, as shown in Figure 7c-d, the dimer 1•1 engages
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other 1•1 dimers through CH•••Œ interactions among tetraphenylethylene units along with
axis (Figure S20a) and axis (Figure S20b), respectively, to form a 3D network-like
arrangement. Therefore, the X-ray structure of further confirms that the aggregation of
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CB[10]•1 could be stabilized by multiple CH•••Œ interactions between tetraphenylethylene
stoppers of CB[10]•1, and exhibit a stepwise AIEE effect in THF or CHCl3.
Figure 7. The crystal structure of 1: a) side view and b) top view of face-to-face stacking dimer
1•1; c) side view and d) top view of stacking networks between 1•1 dimers Color code: N, blue; O,
red; C, gray; H, white. CH•••Œ interactions: green dot line. Chloride ions to balance the charge
are omitted.
Conclusions
In summary, we have designed and synthesized a dumbbell-like guest 1 which is non-fluorescent
but becomes a highly fluorescent [2]rotaxane CB[10]•1 upon host-guest interaction with CB[10]
o
via the slipping method under heating at 95 C in DMSO. The photophysical properties and
aggregation structures of 1 and CB[10]•1 were unambiguously elucidated by fluorescence, UV-vis,
DLS, SEM, and X-ray experiments. We are able to demonstrate that the formation of CB[10]•1
is companied with strong fluorescent intensity, long lifetime and high quantum yield. Compared
with 1, CB[10]•1 also exhibits a stepwise aggregation-induced emission enhancement property in
THF or CHCl3. Therefore, supramolecular assembly strategy to prepare luminescent systems,
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which are easily endowed with multiple emission properties, may find useful application not only
in luminescent materials but also in stimuli-responsive systems and molecular machines.
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Experimental Section
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General Experimental Methods. Starting materials were purchased from commercial
suppliers were used without further purification. CB[n] (n = 6,47 7,48 8,48 1028b) was prepared
according to the published procedure. Melting points were determined using XT-4 apparatus.
IR spectra were recorded on a Bruker IFS 120HR spectrometer and were reported in cmÞ1. 1H
NMR and 13C NMR spectra were done on a Bruker ascend spectrometer at 400 MHz. Electron
Spray Ionization (ESI) mass spectra were acquired by using a Bruker micrOTOF-Q II electrospray
instrument. Fluorescence spectra were recorded on a Horiba Fluorolog-3 spectrometer equipped
with a xenon discharge lamp using 1 cm quartz cells. DLS data was recorded on a Malvern
Zetasizer nano ZS90 spectrometer using a monochromatic coherent He-Ne laser (633 nm) as the
light source and a detector that detected the scattered light at an angle of 90º. SEM images were
obtained on Carl Zeiss SIGMA.
Fluorescence measurement. Fluorescence spectra were obtained with a solution of 1 (3 mL,
10 ꢁM) or CB[10]•1 (3 mL, 10 ꢁM) in a quartz cell. The solution of CB[10]•1 (1.0 mM) in
DMSO was prepared after being heated at 95 oC for 17 days. The different solvents were added
to the DMSO solution of CB[10]•1 (1.0 mM) to make the ratio of DMSO into 1%.
Scanning Electron Microscope measurement. One drop of the solution of 1 (0.10 mM) or
CB[10]•1 (0.10 mM) was placed on the silicon wafer, dried for 1 day under heating at 50 oC.
And the samples were then coated with Au in the ion coater for 90 s. The solution of CB[10]•1
(1.0 mM)in DMSO was prepared after being heated at 95 oC for 17 days. The different solvents
were added to the DMSO solution of CB[10]•1 (1.0 mM) to make the ratio of DMSO into 10%.
Dynamic light scattering measurement. DLS data were obtained with a solution of 1 (1 mL,
0.10 mM) or CB[10]•1 (1 mL, 0.10 mM or 0.01 mM) in a quartz cell. The solution of CB[10]•1
(1.0 mM) in DMSO was prepared after being heated at 95 oC for 17 days. The different solvents
were added to the DMSO solution of CB[10]•1 (1.0 mM) to make the ratio of DMSO into 10%.
Synthetic Procedures. Compound 1. A mixture of 4-(1,2,2-triphenylvinyl)aniline (384 mg,
1.10 mmol) and 1,1'-bis(2,4-dinitrophenyl)-[4,4'-bipyridine]-1,1'-diium chloride (281.8 mg, 0.50
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mmol) in ethanol (25 mL) was heated at reflux for 3 days. After cooling down to room
temperature, the product was precipitated with diethyl ether, and washed with diethyl ether and
acetone to yield 1 as a red solid (427 mg, 0.48 mmol, 96%). M.p. 248-249 ˘C. IR (KBr, cm-1):
3401s, 3108m, 3052m, 3020m, 1630s, 1485m, 1436m, 761w, 698s. 1H NMR (400 MHz,
DMSO-d6): 9.62 (d, J = 6.8 Hz, 4H), 9.01 (d, J = 6.8 Hz, 4H), 7.77 (d, J = 8.6 Hz, 4H), 7.38 (d, J
= 8.6 Hz, 4H), 7.25-7.00 (m, 30H). 13C NMR (100 MHz, DMSO-d6): 148.6, 146.7, 145.5, 142.7,
142.5, 142.5, 140.1, 138.7, 132.3, 130.7, 130.5, 128.2, 128.1, 127.9, 127.2, 127.0, 126.6, 124.2
(only 18 of the 21 resonances expected were observed). HRMS (ESI-TOF) m/z: [1-2Cl-]2+ Calcd
for C62H46N2 409.1825; Found 409.1819.
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Compound 2. A mixture of compound 4-(1-phenyl-2,2-di-p-tolylvinyl)aniline (100 mg, 0.27
mmol) and 1,1'-bis(2,4-dinitrophenyl)-[4,4'-bipyridine]-1,1'-diium chloride (67.9 mg, 0.12 mmol)
in ethanol (10 mL) was heated at reflux for 3 days. After cooling down to room temperature, the
solvent was reduced, and the product was dissolved in acetone and then precipitated with diethyl
ether, and washed with diethyl ether to yield 2 as a red solid (90 mg, 0.10 mmol, 83.3%). M.p.
200-201 ˘C. IR (KBr, cm-1): 3409s, 3021m, 2917m, 1604s, 1499m, 1443m, 1306m, 822w, 668w.
1H NMR (400 MHz, DMSO-d6): 9.63 (d, J = 6.8, 4H), 9.01 (d, J = 6.8, 4H), 7.77 (d, J = 8.6, 4H),
7.35 (d, J = 8.6, 4H), 7.25-6.85 (m, 26H), 2.23 (s, 6H), 2.21 (s, 6H). 13C NMR (100 MHz,
DMSO-d6): 147.0, 145.5, 142.9, 142.4, 139.9, 139.7, 137.8, 136.3, 136.1, 132.3, 130.7, 130.6,
128.8, 128.5, 128.1, 126.8, 126.6, 124.2, 20.8, 20.7. HRMS (ESI-TOF) m/z: [2-2Cl-]2+ Calcd for
C66H54N2 437.2138; Found 437.2144.
Associated Content
Supporting Information
NMR data, ESI-MS data, fluorescent spectra, UV-vis spectra, SEM, DLS, and X-ray data (PDF)
Crystallographic data for CCDC-1511208 (1) (CIF)
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Acknowledgements
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We thank the National Natural Science Foundation of China (21472149 to L.C., 21472143
to S.L.), the Shaanxi Provincial Natural Science Foundation (2016JM2025, 2016JQ2015 to
Y.Z.), and Research Project of Shaanxi Provincial Education Department (15Js112) for
financial support.
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