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have been synthesized for deciphering the mechanism of
AIE process,48 while a few other isomers have been re-
ported for exploring their distinguished biological appli-
cations.50,51 The structure diversity and functionality of
TPE stereoisomers are, however, still limited and less
studied in details. The possible reasons are due to their
difficult separation and structure confirmation, which
normally require the use of single crystal X-ray crystal-
lography.
McMurry coupling of 4-aminobenzophenone gave 1,2-
1
2
3
4
5
6
7
8
9
10
1
12
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18
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2
23
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25
26
27
28
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30
31
32
3
34
35
36
37
38
39
40
41
42
43
4
45
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5
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(4-aminophenyl)-1,2-diphenyl ethane (1). Its isomers
could be separated by column chromatography. However,
as confirmed by thin-layer chromatography (TLC), they
undergo isomerization during storage at room tempera-
ture. Reaction of an isomeric mixture of 1 with UPy pre-
cursor (2)65 without the addition of any reactants gave
(Z)-TPE-UPy and (E)-TPE-UPy. Detailed procedures for
their synthesis were provided in the Supporting Infor-
mation (SI). Two separated spots were observed in the
TLC plate using 5% methanol in dichloromethane as
running solvent. The upper and lower spots were sepa-
rated by column chromatography and characterized by
NMR and mass spectroscopies (Figure S1-S8). The
same m/z value of their mass spectra suggests that they
are isomers (Figure S1 and S2). Both TPE-UPy isomers
were very stable, undergoing no isomerization at room
temperature, presumably due to the high activation bar-
rier caused by their large structural difference. It thus
provides good opportunities for studying their structures,
properties and related functionalities.
Supramolecular polymers, which are formed by link-
ing low-molecular-weight units by hydrogen-bonding, π-
π interactions and other reversible noncovalent interac-
tions, play important roles in material science due to
their unique mechanical properties and also reversibility
benefited from the dynamic nature of noncovalent inter-
actions.53 61 Whereas many supramolecular polymers
with various structures and morphologies have been de-
veloped,41 47,62 those fabricated from pure (Z)- and (E)-
isomers of TPE, to the best of our knowledge, have not
yet been explored. In this work, we reported the supra-
molecular polymers constructed by quadruple hydrogen
bonding in pure stereoisomers of ureidopyrimidinone
(UPy)-functionalized tetraphenylethenes ((Z)-TPE-UPy
and (E)-TPE-UPy) (Scheme 1). The isomers can be
macroscopically separated by column chromatography
in high yields. The structures of (Z)-TPE-UPy and (E)-
TPE-UPy were confirmed by 2D COSY and NOESY
NMR spectroscopies. The two molecules show distinct
fluorescence in the aggregate state: (Z)-TPE-UPy exhib-
its green emission while its (E)-counterpart is blue-
emitting. Such difference inspires us to study their pho-
tophysical properties and supramolecular polymerizabili-
ties. Distinct morphologies of particles and nanofibers
were obtained by self-assembly of (Z)-TPE-UPy and
(E)-TPE-UPy, respectively. Our results are rationalized
by spatial configuration of TPE that directs different
supramolecular polymerizability and molecular packing
of the isomers. The heteroatom-containing cavity offered
by the two UPy groups of (Z)-TPE-UPy makes it suita-
ble for Hg2+ coordination. In contrast, the high molecu-
lar weight polymers prepared from (E)-TPE-UPy permit
us to obtain highly fluorescent fibers and 2D/3D pho-
topatterns from their chloroform solutions.
Scheme 1. Synthesis and schematic representation of (Z)-TPE-
UPy and (E)-TPE-UPy.
For correct assignment of the phenyl proton resonanc-
1
1
es, H-1H COSY spectroscopy was carried out. The H-
1H COSY spectrum of the upper TLC was shown in
Figure 1A. The doublet shift at δ 6.99 should correspond
to the resonances of H1 and H2 protons due to the elec-
tron-donating property of the neighboring NH group.
The resonance peak at δ 7.45 should stem from the H3
and H4 protons as it has strong correlation with H1 and
H2 (Figure 1A, solid black cycle). After these assign-
ments, the remaining should belong to the proton reso-
nances of the unsubstituted benzene ring. The integral of
the multiplet at δ 7.08 suggest a relative proton number
of 3, while that at δ 7.03 represents a proton number of 2.
The strong correlations between protons at δ 7.08 sug-
gest that they are H5, H6 and H7 with through-bond cou-
pling (Figure 1A, black dot cycle). Accordingly, the res-
onance at δ 7.03 was assigned to H8 and H9. The full
spectrum and those of the lower TLC fraction are given
in Figure S9-11. However, until this stage, correct as-
signment of the configuration of the products cannot be
made. Fortunately, the distinguishable proton resonances
between the UPy-substituted benzene ring (A) and the
bare one (B) permit us to establish their through-space
correlations. The NOESY spectrum of the lower TLC
As a proof-of-concept, we incorporated 2-ureido-4[1H]-
pyrimidinone (UPy) to TPE-based isomers to endow
them with supramolecular polymerizability. This quad-
ruple hydrogen-bonding motif was developed by Meijer
and widely used for supramolecular polymers due to its
strong binding strength or association constant (5.7×
107 M-1 in CHCl3) and directionality.63 Molecules with
two or more UPy units usually form supramolecular pol-
ymers through ring-chain or isodesmic polymerization
mechanism.64 (Z)-TPE-UPy and (E)-TPE-UPy were
prepared by a two-step reaction route (Scheme 1). First,
2
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