Diarylethene-based xerogels: The fabrication of more entangled networks driven by isomerization and acidofluorochromism

Article abstract of DOI:10.1039/c8ob00113h

Fully-conjugated styrylbenzoxazoles and styrylbenzothiazoles of BOAF24, BOACl24, BOACl35, BOABr24, BOABr35, BTAF24, BTACl24 and BTABr24 without traditional gelation groups could form organogels. It was found that introduction of chlorine atoms in the 2,4-

Full text of DOI:10.1039/c8ob00113h

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COMMUNICATION
Takeharu Haino et al.
Solvent-induced emission of organogels based on tris(phenylisoxazolyl)
benzene
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DOI: 10.1039/C8OB00113H
Journal Name
ARTICLE
Diarylethenes-based xerogels: the fabrication of more entangled
networks driven by isomerization and acidofluorochromism
Received 00th January 20xx,
Accepted 00th January 20xx
a
a
a
a
a
a
Haoran Wang, Jinyu Zhao, Guojian Yang, Fushuang Zhang, Jingbo Sun, Ran Lu*
DOI: 10.1039/x0xx00000x
Full-conjuagted styrylbenzoxazoles and styrylbenzothiazoles of BOAF24, BOACl24, BOACl35, BOABr24, BOABr35, BTAF24,
BTACl24 and BTABr24 without traditional gelation groups could form organogels. It was found that the introduction of
chlorine atoms in 2,4-positions of phenyl group would improve the gelation abilities, and benzothiazole derivatives
exhibited better gelation abilities than benzoxazoles with similar -skeleton due to the better -electron delocalization.
Interestingly, the organogel of BTACl24 could be destroyed into solution by UV light due to trans-cis isomerization, which
could also induce the morphological changes of xerogels. The smooth organogel nanofibers stretched out lots of thin ‘arms’
to hold together or to catch other nanofibers upon UV irradiation, so more entangled networks were generated. Moreover,
TFA (trifluoroacetic acid) could induce gel-sol transformation on account of the protonation of benzoxazole or
benzothiazole unit, accompanied with the quenching of the emission. BTACl24 exhibited higher performance than
BOACl24 in the detection of TFA because of its strong basicity. The decay time and the detection limit of BTACl24 in
xerogel-based film towards TFA vapor were of 0.7 s and 0.3 ppm, respectively. Therefore, the organogelation of non-
traditional organogelators is powerful way to fabricate multi-stimuli-responsive soft materials, and it provided a new
method to generate more entangled 3D networks through the photochemical reaction in xerogels.
www.rsc.org/MaterialsC
traditional
butylcarbazole,
-gelators based on the derivatives of tert-
1
0
Introduction
Low molecular weight organogels (LMOGs) fabricated from -
-diketone/salicylaldimine difluoroboron
1
1
12
complexes and full-conjugated carbazolevinyl benzoxazole,
and found that the introduction of halogens could improve the
organogelators have received recent attention due to their
13
1
gelation abilities. In order to reveal the effect of halogen on
the self-assembling of full-conjugated systems, we have
synthesized new styrylbenzoxazoles bearing different kinds of
halogens in different positions in benzene rings except for
BOACl4 and BOACl24, which have been reported in previous
work (Scheme 1). It was found that BOAF4, BOACl4 and
BOABr4 bearing one halogen atom could not form any gel in
the tested solvents. The 2,4-dihalogenstyrylbenzoxazoles of
BOAF24, BOACl24 and BOABr24 showed strong gelation
potential
applications
in
optoelectronic
devices,
2
3
chemosensors, field-effect transistors, and so on. It is well-
known that the π-gelators tend to form 1D aggregates directed
4
by intermolecular interactions, especially
followed by intertwine into 3D network, so that the
sensitive to external stimuli of heat, light, chemical, sound and
- interactions,

-gels are
1
4
5
mechanical force. Compared with the traditional -gelators,
the synthesis of the non-traditional organogelator excluding
the auxiliary groups of long alkyl chains, sugar, cholesterol or
6
abilities
than
the
corresponding
3,5-
H-bonding units showed high atom economy. To date, the
dihalogenstyrylbenzoxazoles of BOAF35
BOABr35 respectively. Accordingly,
dihalogenstyrylbenzothiazoles BTAF24 BTACl24 and BTABr24
,
BOACl35 and
design of non-traditional -gelators is still changeling since it is
difficult to balance the intermolecular interactions of full-
conjugated compounds. Park et al. found that the stilbenes
,
the
2,4-
,
were prepared. Interestingly, they showed more excellent self-
assembling abilities compared with styrylbenzoxazoles in
similar structures. Notably, the light-induced trans-cis
isomerization of BTACl24 led to the gel-sol transformation and
the morphologic changes of the xerogel. In detail, lots of thin
‘arms’ were stretched out from the smooth nanofibers, and
they would hold together or caught other nanofibers. The
networks were turned into a crisscross pattern. To the best of
our knowledge, such phenomenon was not reported
elsewhere. It should be noted that the organogel of BTACl24
and BOACl24 could be destroyed upon the addition of TFA,
accompanied with the quenching of the emission on account
bearing -CN or/and -CF self-assembled into nanowires driven
by C-H···F and π-π interactions. Fan reported a series of non-
3
7
traditional -gelators based on dendrons and dendrimers of
8
poly(benzyl ether). Würthner reported a perylenebisimide-
based organogelator lacking long alkyl chains and H-bonding
9
unit. Recently, our group has synthesized a series of non-
a.
Sate Key Laboratory of Supramolecular Structure and Materials, College of
Chemistry, Jilin University, Changchun, P.R. China. E-mail: luran@mail.jlu.edu.cn.
1
13
†
Electronic Supplementary Information (ESI) available: H NMR and C NMR
spectra; HRMS; Photophysical data; UV-Vis absorption spectra; Fluorescent
emission spectra and XRD patterns in solid states. See DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
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of the protonation of benzothiazole and benzoxazole moieties. the eluent, and the yields were in the range of 42-80%. The target
View Article Online
DOI: 10.1039/C8OB00113H
1
13
BTACl24 exhibited higher performance than BOACl24 in the compounds were characterized by H NMR, C NMR, FT-IR and
detection of TFA in solutions and in xerogels on account of its HRMS.
strong basicity. Although pyrene- and anthracene-based
organogels are typical emissive soft materials, exhibiting
Photophysical properties
enhancement of power-conversion efficiency of solar cell, The UV-vis absorption and fluorescence emission spectra of
-
5
circularly polarized luminescence and multi-responsive BOACl4
,
BOACl24 and BOACl35 in CH Cl (1.0

10 M) were
properties, the self-assembling processes were assisted by shown in Figure 1. The absorption bands of BOACl4 BOACl24
traditional gelation groups. Therefore, the organogelation of and BOACl35 appeared at 327 nm, 331 nm and 329 nm,
2
2
15
,

non-traditional organogelators becomes a powerful way to respectively, due to
fabricate multi-stimuli-responsive soft materials, and we fluorescence emission bands at 402 nm, 410 nm and 404 nm
provided a new method to generate more entangled 3D were detected for BOACl4 BOACl24 and BOACl35

-

transitions. Meanwhile, the
,
,
networks through the photochemical reaction in xerogels.
respectively. It suggested that the number and position of
chlorine atom in benzene ring had less effect on the electronic
spectra of styrylbenzoxazole. The slight red-shifts of the
absorption and emission bands for BOACl24 compared with
BOACl4 and BOACl35 were resulted from the conjugation
effects of two chlorine atoms in 2,4-positions of benzene ring.
Similarly, the UV-vis absorption and fluorescence emission
bands of BOABr24 emerged at 334 nm and 401 nm (Figure S1
and Table S1), respectively, giving slight red-shift compared
with the other two bromo-substituted styrylbenzoxazole. For
example, the absorption/emission bands for BOABr4 and
Scheme 1 Molecular structures of styrylbenzoxazole and styrylbenthiazole
derivatives.
Results and discussion
Synthesis
The synthetic routes for (halogenated styryl)-benzoxazoles and
(halogenated styryl)-benzothiazoles were shown in Scheme 2.
They were prepared via Knoevenagel condensation reactions
of 2-methylbenzoxazole/2-methylbenzothiazole with halogen-
substituted benzaldehydes in THF using t-BuOK as catalyst. The
crude products were purified by column chromatography
(silica gel) using ethyl acetate/petroleum ether (v/v =1/10) as
Figure 1. Normalized UV-vis absorption (a) and fluorescence emission (b, ex
325 nm) spectra of BOACl4, BOACl24 and BOACl35 in CH Cl
=
Scheme 2 Synthetic routes for styrylbenzoxazoles and styrylbenthiazoles.
2
2
.
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BOABr35 appeared at 328 nm/399 nm and 329 nm/400 nm, above phenomenon suggested that the gelatioVinew aArbticilleitOynlionef
respectively. In the case of styrylbenzothiazoles, the BOABr24 was stronger than BOABr35DOtoI: 10s.o10m39e/Ce8xOtBe0n0t1.13IHn
absorption and emission bands were red-shifted compared particular, the dichloro-substituted styrylbenzoxazoles
with the styrylbenzoxazole with similar structures on account exhibited relatively strong self-assembling abilities compared
of their good
absorption and emission of BTABr24 emerged at 340 nm and organogels could be formed from BOACl24 and BOACl35 in
20 nm, respectively (Figure S2). The fluorescent quantum petroleum ether, cyclohexane, methanol and ethanol with CGC
-electron delocalization. For instance, the with dibromo-substituted styrylbenzoxazoles since the
4
-
1
-1
yields (Φ ) of the synthesized compounds were in the range of in the range of 2.9-6.7 mg·mL and 5.0-10.0 mg·mL ,
0
F
-
1
.03-0.11 using quinine sulfate in 0.1 mol·L sulfuric acid respectively. Likewise, the gelation ability of BOACl24 was the
solution as the standard (Φ = 57%, Table S1).
strongest among the synthesized chloro-substituted
F
3
styrylbenzoxazoles. It was clear that ca. 2.5
 10 methanol
Self-assembling properties
molecules could be gelated by one BOACl24 molecule, so
1
3
As listed in Table 1 and Table S2, the synthesized BOACl24 could be deemed as a supraorganogelator. Since
styrylbenzoxazole derivatives were soluble in CH Cl , the gelation abilities of 2,4-dihalogen substituted
2
2
chloroform, ethyl acetate, DMF and DMSO. BOAF4
and BOABr4 bearing one halogen atom could not form any styrylbenzoxazoles, we synthesized 2,4-dihalogen-substituted
organogel in the tested solvents. The dibromo-substituted styrylbenzothiazoles (BTAF24 BTACl24 and BTABr24). Among
, BOACl4 styrylbenzoxazoles were better than 3,5-dihalogen substituted
,
styrylbenzoxazoles of BOABr24 and BOABr35 could form them, BTACl24 and BTABr24 could self-assemble into
organogels in n-butanol with criticalgelation concentration organogels in petroleum ether, cyclohexane, methanol,
-1
-1
-1
-1
(
CGC) of 5 mg·mL and 10 mg·mL , respectively, besides ethanol with low CGC of 1.6-2.0 mg·mL and 2.5-6.5 mg·mL ,
ethanol organogel could be generated from BOABr24. The respectively, and they could also be recognized as
a
Table 1 Gelation abilities of styrylbenzoxazole and styrylbenzothiazole derivatives in selected organic solvents.
Solvent
BOAF24
BOACl24
BOACl35 BOABr24
BOABr35
BTAF24
BTACl24
BTABr24
Petroleum ether
Cyclohexane
Methanol
Ethanol
n-Butanol
Toluene
P
G (5.0)
G (6.7)
G (2.9)
G (5.5)
P
S
S
S
S
S
S
G (10.0)
G (9.6)
G (5.0)
G (8.8)
P
S
S
S
S
S
S
P
P
P
P
P
P
P
P
P
G (2.0)
G (1.9)
G (1.8)
S (1.6)
G (6.5)
G (4.0)
G (2.5)
G (3.5)
G (20.0)
P
S
S
S
S
S
S
S
S
G (6.7)
G (12.5)
G (10.0)
G (5.0)
G (10.0)
P
S
S
S
S
S
S
S (10.0)
G (3.7)
P
S
S
S
S
S
P
S
S
S
S
S
S
S
S
S
S
S
P
S
S
S
S
S
CH Cl
2
2
Chloroform
Ethyl acetate
DMF
DMSO
a
-1
I: insoluble; S: soluble; G: stable gel; P: precipitate. CGC: critical gelation concentration (mg·mL ).
Figure 2. SEM images of the xerogels of (a) BOACl24, (b) BOACl35 and (c) BTACl24 obtained from methanol; (d) SEM image of the sample obtained by coating the
solution, which was gained from methanol organogel of BTACl24 upon UV irradiation for 60 s; (e) SEM image of the xerogel of BTACl24 upon UV irradiation for 20 min;
(f) Fluorescence microscopy image of the xerogel of BTACl24 (ex = 365 nm).
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In order to investigate the driving forces during the gel
View Article Online
DOI: 10.1039/C8OB00113H
formation, the time-dependent UV-vis absorption and
-
fluorescent emission spectra of BOACl24 in methanol (1.1 × 10
2
M) upon cooling the hot solution, which was first stimulated
by ultrasound, to room temperature were measured. As
depicted in Figure 3, during the gelation process the intensity
of the absorption at 331 nm decreased gradually and no
spectral shift was detected. Meanwhile, the emission at 410
nm was intensified obviously, accompanied with a slight red-
shift. In the organogel, the emission band emerged at 415 nm.
It suggestedthat the
- interaction had an effect on the
formation of organogel.
To estimate the molecular packing mode in gel state, the
XRD pattern of the xerogel of BOACl24 obtained from
methanol was given in Figure S3, and exhibited several strong
and sharp diffraction peaks. In our previous work, we
determined the single crystal structure of BOACl24 (CCDC
14
1
526199), and found that most of the diffraction peaks in the
simulated XRD pattern based on single crystal structure were
similar to those in xerogel. Therefore, we deemed that the
molecular packing modes were similar in xerogel and in single
crystal. As a result, BOACl24 might adopt a parallel layered
structure in gel phase, in which H-aggregates were formed.
The distance between two adjacent molecular planes was
3
.482 Å in single crystal and a similar diffraction peak
corresponding to a d-spacing of 0.37 nm emerged in xerogel,
meaning the occurrence of π-π interactions. Moreover, we
observed the distances of C-H···Cl (3.165 Å, 3.178 Å, 3.009 Å,
Figure 3. Time-dependent UV-vis absorption (a) and fluorescence emission (b, λex = 320 3.250 Å), C-H···O (2.654 Å, 3.119 Å) and C-H···N (2.811 Å, 2.792
-
2
nm) spectra of BOACl24 upon cooling the hot solution in methanol (1.1 × 10 M),
which was first stimulated by ultrasound to room temperature. The alternation is 15 s,
and the arrows indicate the spectral changes from the sol to gel.
Å, 3.648 Å) in single crystal of BOACl24. It was deduced that
the H-bondings of C-H···Cl, C-H···O and C-H···N might be also
the driving forces to direct the organogelation of BOACl24. It
further suggested that the introduction of halogens would
improve the gelation abilities. Similarly, during the
organogelation of BTACl24, the absorption at 338 nm
decreased gradually. Meanwhile, the emission intensity at 418
nm was red-shifted to 425 nm and its intensity was enhanced
supraorganogelators. The styrylbenzothiazole derivatives
exhibited better gelation abilities than styrylbenzoxazoles with
similar molecular structures. This conclusion could be further
confirmed by the fact that the organogels could be generated
-
1
from BTAF24 in methanol and ethanol with CGC of 6.7 mg·mL
-1
(Figure S4). Therefore, -aggregates were formed from
BTACl24 in the organogel.
Additionally, the single crystal structure of BOACl4 (CCDC
and 12.5 mg·mL , while BOAF24 could form organogel only in
cyclohexane with high CGC of 20 mg·mL . As a result, the
introduction of chlorine atoms in 2,4-position of benzene ring
-
1
1
526206) could provide some information why it could not
and
styrylbenzothiazole would significantly improve the gelation
abilities of non-traditional organogelators based on rigid
the
good
delocalization
of

-electron
in
14
form organogel. The molecules adopted an anti-parallel
layered structure, and the distance between two adjacent
molecular planes was 3.653 Å, so the π-π interactions between
molecules BOACl4 were weaker than those between
molecules BOACl24 in single crystals. The distances of C-H···O

-
conjugated systems. Moreover, the obtained organogels were
stable for several months at room temperature and could be
destroyed upon heating. If the hot solutions were stimulated
by ultrasound again, the organogels could be reformed.
As depicted in Figure 2, SEM images of the xerogels formed
from BOACl24, BOACl35 and BTACl24 in methanol illustrated
that they self-assembled into lots of smooth nanofibers in
diameters of 200-400 nm, which further packed into 3D
networks. It should be noted that more nodes appeared in
xerogel of BTACl24 compared with BOACl24 and BOACl35, so
it was in accordance with the conclusion that the gelation
ability of BTACl24 was better than others.
(2.809 Å, 3.588 Å, 3.631 Å) and C-H···N (2.967 Å, 3.134 Å, 3.534
Å) also illustrated that the H-bondings were weaker in single
crystal of BOACl4 than those in BOACl24. Therefore, BOACl4
could not form organogel was originated from the weak
intermolecular interactions.
Light responsive behaviors of the organogel and xerogel
In our previous work, we have found that the nanofibers
generated from BOACl24 in organogel could curl under UV
14
light, which was driven by light-induced [2+2] cycloaddition.
Therefore, we intended to investigate the light responsive
4
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properties of the gained organogels. Although no visible via the treatment of heat and light. The fluoresceVniecweAertmicleisOsniloinne
macroscopic photomechanic effect was detected for the band at 425 nm for BTACl24 in organogDeOl Iw: 1a0s.10b3lu9/eC-8sOhiBf0te0d113tHo
organogels of BOACl35, BOABr24, BOABr35, BTACl24 and 416 nm in solution gained via heating, and the intensity was
BTABr24, we found the organogels were destroyed into declined 40%. However, the emission intensity at 425 nm for
solutions upon UV irradiation, accompanied with the rapid BTACl24 in solution obtained from organogel induced by UV
disappearance of the nanofibers. As shown in Figure 4 and light was decreased to a quarter of that in organogel, and blue-
Videos S1-S2 (Supporting Information), when 365 nm light was shifted to 407 nm with a newly emerged shoulder at 388 nm.
employed to irradiate the middle part of methanol organogel Thus, new species might be afforded from BTACl24 via
of BTACl24 in a tube from the left side, the irradiated part of photochemical reaction.
1
the gel became transparent. After irradiation for 80 s, the tube
was rotated 180
Consequently, H NMR spectra of BTACl24 in methanol-d4

and further irradiated from left side by UV upon UV irradiation for different time were first measured
light. The middle part in gel was changed into solution (Figure S6), and we found obvious changes in chemical shifts
absolutely when the irradiation time was prolonged to 160 s. and the shapes of the peaks with prolonging UV irradiation.
Even if the tube was shaken slightly or was turned upside However, it was difficult to figure out the changes of the
1
down, the rest part of gel was intact and the solution was signals for H atoms, so H NMR spectra of BTACl24 in DMSO-d6
locked in the middle. After it was placed at room temperature upon UV irradiation were given in Figure 5. We found that the
for 40 d, both the part of gel and the part of solution were still chemical shifts for H1 and H2 in BTACl24 appeared at 7.87
maintained at the original states. It further proved that the ppm and 7.76 ppm, respectively, before UV irradiation, and
organogel was very stable. In addition, the changes of the the coupling constant was 16.0 Hz, suggesting trans-form of
nanofibers in methanol organogel of BTACl24 induced by UV carbon-carbon double bond. After UV irradiated for 15 s, their
light was observed under microscope (Video S3 in Supporting integral values were decreased. Meanwhile, new peaks at 7.97
Information), and they disappeared quickly when 365 nm light ppm and 7.90 ppm with coupling constant of 8.0 Hz emerged,
was turned on.
and could be assigned to H4 and H3, respectively, in cis-form
BTACl24. After irradiated for 80 s, the signals of H1 and H2
disappeared completely. We inferred that trans-cis
isomerization of BTACl24 took place upon exposure under UV
light, which led to the gel-sol transformation of BTACl24
.
Figure 4. The gel-sol transformation of the organogel of BTACl24 in methanol upon
irradiated by 365 nm light for different time, and the tube was rotated 180° after 80 s.
To obtain the insight into the light-induced gel-sol
transformation, the absorption and emission spectral changes
of the methanol organogel of BTACl24 upon exposure to 365
nm light for 1 s were studied (Figure S5a-b). The absorption
band of BTACl24 in methanol organogel was located at 338 nm,
and it was blue-shifted to 301 nm after irradiated by UV light,
accompanied with the significant decrease of the absorption
intensity. It was clear that the light-induced gel-sol
transformation was not the reverse process of organogelation.
As mentioned above, the gel formation of BTACl24 led to the
decrease instead of increase of the absorption intensity at 338
nm, and no spectral shift was detected (Figure S4). Therefore,
we deduced that the reason for the destruction of organogel
1
of BTACl24 induced by UV light was different from gel-sol Figure 5. H NMR spectra of BTACl24 before (a) and after irradiated by 365 nm for 0 s
(
6
a), 15 s (b) 30 s (c) 45 s (d) and 80 s (e) in DMSO-d .
transformation stimulated by heating. Accordingly, the UV-vis
absorption of BTACl24 in solution, which was gained from the
organogel by heating was shown in Figure S5c. It was clear that
the absorption intensity at 338 nm was significantly enhanced
upon the formation of the solution from gel phase by heating.
Therefore, we deemed that photochemical reaction might take
place when the organogel BTACl24 was exposed to UV light.
The fluorescent emission spectra also exhibited different
responsive behaviors in the course of gel-sol transformation
On the other hand, we examined the morphological changes
of the aggregates in wet organogel and in the xerogel upon the
exposure under UV light. Firstly, the sample was prepared by
dropping the solution, which was gained via UV irradiation of
the organogel BTACl24 for 60 s, on silicon wafer. From Figure
d, the aggregates in different shapes, including clews formed
from fibrils, short nanofibers, rugged rods, small blocks and
2
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blobs, were observed. It indicated that the light-induced trans- more entangled supramolecular networks, which has not been
View Article Online
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cis isomerization of BTACl24 could lead to the disassembly of reported elsewhere.
some organogel nanofibers and the destruction of 3D
networks. Interestingly, many thin fibrils with diameter of ca.
0 nm were spit out from the thick fibers (Inset in Figure 2d).
Sensory properties towards acids in organogels and in xerogel-
based films
5
The reason might be that the strains were yielded and
accumulated on the nanofibers during the light-induced
isomerization process. In order to release the strain, more thin
fibrils escaped from the thick fibers. Hence, we deduced that
UV light might result into the morphological change of the
xerogel. As anticipated, after the xerogel BTACl24 was
irradiated by 365 nm light for 20 min, the original smooth
nanofibers stretched out lots of thin ‘arms’. Some ‘arms’ from
neighboring nanofibers might hold together, and some ‘arms’
would stretch to another nanofibers and catch them. As a
result, the networks became in a crisscross pattern (Figure 2e).
What’s more, a lot of blotches emerged on the surface of thick
nanofibers, and they were deemed to be the growing points
for the ‘arms’ so as to release the accumlated strains. It
illustrated that the photochemical reactions of gelators in
xerogels might become a new strategy for the fabrication
Because benzoxazole is a weak base, we intended to
investigate the sensory properties of styrylbenzoxazole
towards acids. Herein, BOACl24 is first selected as a
fluorescent probe on account of its good gelation ability and
intense emission in organogel and in xerogel. As shown in
Figure S7, the methanol organogel of BOACl24 emitted strong
blue fluorescence centered at 415 nm. Upon the addition of
0
.5 equiv. of TFA, the intensity of the emission for BOACl24
was declined and blue-shifted to 410 nm. When 1.0 equiv. of
TFA was added, the organogel was destroyed and the formed
solution exhibited a weak emission at ca. 400 nm. The
emission was further decreased with increasing the amount of
TFA. The solution of BOACl24 was almost non-emissive when
2
.0 equiv. of TFA was added. Therefore, the organogel could
be used as sensory material to detect acid by the naked eye.
Figure 6. (a) Fluorescence emission spectra of BOACl24 in xerogel-based film upon exposure to different amounts of TFA vapor (0-400 ppm, λex = 320 nm).
Inset: The concentration-dependent fluorescence quenching efficiencies of the film upon exposure to different amounts of TFA vapor for 2 s. (b) Time-
course of the fluorescence quenching of BOACl24 in xerogel-based film upon exposure to TFA vapor at 1000 ppm, and the intensity was monitored at 435
nm. (c) Fluorescence emission spectra of BTACl24 in xerogel-based film upon exposure to different amounts of TFA (0-300 ppm, λex = 330 nm). Inset: The
concentration-dependent fluorescence quenching efficiencies of the film upon exposure to different amounts of TFA vapor for 2 s. (d) Time-course of the
fluorescence quenching of BTACl24 in xerogel-based film upon exposure to TFA vapor at 1000 ppm, and the intensity was monitored at 474 nm.
6
| J. Name., 2012, 00, 1-3
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DOI: 10.1039/C8OB00113H
Journal Name
ARTICLE
It is well-known that the luminescent nanofibers-based films BTACl24 towards TFA, two isometric points at 270 nm and 370
usually show sensitive response to analysts due to the high nm emerged, meaning the formation of new species. Hence,
specific surface area as well as efficient exciton migration in 1D we deemed that the benzothiazole might also be protonated
1
6
17
nanostructures.
Therefore, the fluorescent sensory by TFA, which was the reason for the fluorescent quenching.
properties of the xerogel-based film formed from BOACl24 via Meanwhile, we employed an online calculation method
organogelation were investigated. As shown in Figure 6a, the (http://supramolecular.org/) created by P. Thordarson to
1
8a
emission at 435 nm for BOACl24 in the xerogel-based film calculate the binding constant (Ka). Since benzoxazole or
decreased obviously upon exposed to TFA vapor. When the benzothiazole (the host, H) has only one binding site with TFA
concentration of TFA vapor was 400 ppm, the quenching
(the guest, G), the fitter of UV 1:1 system was selected in the
efficiency reached 90%. We found a linear relationship calculation. Based on the plot of the absorption of BOACl24 at
between the quenching efficiency and the concentration of 310 nm, 315 nm and 320 nm versus [G] /[H] in CH Cl (Figure
0
0
2
2
TFA, and the detection limit was estimated to be 0.5 ppm. S8c), the k for BOACl24 with TFA was estimated to be (4.47

a
4
When the nanofibers-based film was exposed to saturated TFA 0.19)

10 M⁻¹. The k for BTACl24 with TFA was (2.31

0.11)
a
5
vapor, the response time of the film was as short as 1.7 s. As a
 10 M⁻¹ according to Figure S9c. It indicated that the basicity
result, such xerogel-based film could detect TFA vapor of BTACl24 was stronger than BOACl24. Moreover, the
quantitatively, sensitively and rapidly. Similarly, the xerogel- fluorescence quenching data for BOACl24 and BTACl24
18
based film of BTACl24 also exhibited excellent fluorescent towards TFA were analyzed using the Stern-Volmer equation,
sensory properties in the detection of TFA. As shown in Figure F /F = 1 + K [Q]
c, the emission at 474 nm for BTACl24 in the xerogel-based where F is the initial emission intensity of probe prior to the
0
sv
6
0
film decreased obviously upon exposed to TFA vapor. When addition of the quencher, F is the emission intensity at given
the concentration of TFA vapor was 300 ppm, the quenching concentration of the quexncher [Q], and Ksv is the Stern-
efficiency reached 95%. Meanwhile, the detection limit and Volmer constant. The calculated Ksv values for BOACl24 and
-
1
-1
the decay time of the xerogel-based film of BTACl24 towards BTACl24 towards TFA were 9278 M and 34325 M ,
TFA vapor were estimated to be 0.3 ppm and 0.7 s, respectively (Figure S8d and S9d). It suggested that BTACl24
respectively. Thus, BTACl24 showed high performance in exhibited stronger affinity with TFA than BOACl24, which was
sensing TFA in xerogel-based film compared with BOACl24
.
consistent with the conclusion made from the online
In order to reveal the fluorescent sensory mechanism and calculation. Moreover, the detection limits (LOD = 3σ/K ) for
sv
the differences in sensory properties of BOACl24 and BOACl24 BOACl24 and BTACl24 towards TFA were measured to be 3.2 ×
-7
-8
towards TFA in xerogels, the electronic spectral titration 10 mol/L and 8.7 × 10 mol/L, respectively. Apparently,
experimental was performed in CH Cl . As shown in Figure S8a, compared with BOACl24 BTACl24 could sense TFA more
the absorption band at 320 nm for BOACl24 decreased sensitively in CH Cl and in xerogel on account of the strong
,
2
2
2
2
gradually and the absorption in the range of 340-420 nm was interaction with TFA.
intensified with increasing the amount of TFA. When 10 equiv.
of TFA was added, new absorption at 355 nm appeared and its
intensity was increased with further increasing the amount of
Conclusions
TFA. The emergence of an isometric point at 330 nm meant
the formation of new species, and we deemed the
benzoxazole unit might be protonated by TFA. Meanwhile, the
fluorescence emission band at 410 nm for BOACl24 decreased
gradually with increasing the amount of TFA, and the strong
blue fluorescence could be quenched completely when 500
equiv. of TFA was added (Figure S8b). Therefore, the emission
quenching of BOACl24 induced by TFA in solution, organogel
state and in xerogel was due to the formation of protonated
BOACl24. On account of the increased electron-withdrawing
ability of protonated benzoxazole, the intramolecular electron
transfer would undergo to quench the emission. BTACl24 gave
similar fluorescence quenching behaviors towards TFA in
In summary, new full-conjugated non-traditional π-gelators
based on styrylbenzoxazoles and styrylbenzothiazoles have
been synthesized. It was found that the introduction of
chlorine atoms at 2,4-position of benzene ring as well as the
existence of benzothiazole with better
-electron
delocalization would enhance the gelation abilities. 3D
networks consisting lots of smooth nanofibers could be
fabricated via organogelation process, and
- interactions
were the main driving forces for the gel formation.
Interestingly, the organogel of BTACl24 coule be destroyed
into solution upon UV irradiation because of the trans-cis
isomerization, which could further lead to the morphological
change of xerogel. The smooth nanofibers stretched out lots of
thin ‘arms’. Some ‘arms’ would hold together, and some ‘arms’
CH Cl (Figure S9b). Besides, in absorption titration process of
2
2
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Journal Name
o
would catch other nanofibers. It should be noted BOACl24 dropwise into the above solution at 0 C. After stirred for 2 h
View Article Online
DOI: 10.1039/C8OB00113H
exhibited strong fluorescence in wet organogel and in xerogel, at 0 C, the mixture was poured into water (200 mL) and light
which could be quenched by TFA. In particular, the decay time yellow solid was collected by filtration. The crude product was
and the detection limit of BOACl24 in xerogel-based film purified by column chromatography (silica gel) using ethyl
towards TFA vapor were of 1.7 s and of 0.5 ppm, respectively, acetate/petroleum ether (v/v =1/10) as the eluent. Flocculus-
and they were decreased to 0.7 s and 0.3 ppm, respectively, like white solid of BOAF4 (0.58 g) was obtained in a yield of
1
for the xerogel-based film of BTACl24 due to its strong basicity. 76%. Mp: 112.0-113.0
Therefore, the organogelation of
organogelators is a powerful way to fabricate multi-stimuli- 8.3 Hz, 2H), 7.40 (p, J = 7.3 Hz, 2H), 7.31 (dd, J = 14.9 Hz, J = 6.0

C. H NMR (400 MHz, DMSO-d ) δ
6
non-traditional (ppm): 7.94-7.88 (t, 2H), 7.84 (d, J = 16.4 Hz, 1H), 7.74 (t, J =
1
3
responsive soft materials and we provided a new method to Hz, 3H) (Figure S10). C NMR (101 MHz, DMSO-d ) δ (ppm):
6
fabricate more entangled supramolecular networks via 162.81 (s), 150.25 (s), 142.17 (s), 138.76 (s), 132.01 (d, J = 3.1
photochemical reactions of

-gelators in xerogels.
Hz), 130.66 (d, J = 8.5 Hz), 125.97 (s), 125.21 (s), 120.07 (s),
16.52 (s), 116.30 (s), 114.17 (s), 111.03 (s) (Figure S11). HRMS,
m/z: calc.: 240.0819, found: 240.0826 (Figure S12). FT-IR (KBr,
1
-
1
Experimental section
Measurement and characterization
cm ): 1602, 1385, 1138, 1068, 992, 953, 862, 819, 539, 513.
E)-2-(2,4-difluorostyryl)benzo[d]oxazole (BOAF24)
By following the synthetic procedure for compound BOAF4
(
1
13
H NMR and C NMR spectra were recorded with a Mercury
,
plus instrument at 400 MHz and 101 MHz using CDCl and
3
BOAF24 was synthesized from 2-methylbenzoxazole (0.38 mL,
.2 mmol), 2,4-difluorobenzaldehyde (0.45 g, 3.2 mmol) and t-
BuOK (0.78 g, 7.0mmol). The crude product was purified by
column chromatography (silica gel) using ethyl
DMSO-d as the solvents. Mass spectra were measured with a
6
3
gas chromatograph mass spectrometer GCMS-QP2010. FT-IR
spectra were obtained with a Nicolet-360 FT-IR spectrometer
by the incorporation of samples into KBr disks. The UV-vis
absorption spectra were obtained using a Mapada UV-1800pc
spectrophotometer. Fluorescence emission spectra were taken
acetate/petroleum ether (v/v = 1/10) as the eluent. Flocculus-
like white solid of BOAF24 (0.56 g) was obtained in a yield of
1
6
8%. Mp: 102.0-103.0

C. H NMR (400 MHz, DMSO-d ) δ
6
on
a
Cary Eclipse Fluorescence Spectrophotometer.
(ppm): 8.10 (dd, J = 15.8 Hz, J = 8.0 Hz, 1H), 7.82 (d, J = 16.6 Hz,
Fluorescence microscopy images were taken on Olympus
Reected Fluorescence System BX51. Scanning electron
microscopy (SEM) measurements were performed on JEOL
JSM-6700F (operating at 5 kV). The samples for SEM
measurements were prepared by casting the organogels on
silicon wafers and dried at room temperature, followed by
coating with gold. X-ray diffraction pattern was obtained on
Empyrean XRD equipped with graphite monochromatized Cu-
1
8
1
1
H),7.78-7.75 (m, J = 5.7 Hz, 2H), 7.45-7.36 (m, 4H), 7.23 (t, J =
13
.6 Hz, 1H) (Figure S13). C NMR (101 MHz, DMSO-d ) δ (ppm):
6
62.40 (s), 150.30 (s), 142.06 (s), 131.02-130.30 (m), 126.22 (s),
25.32 (s), 120.23 (s), 116.51 (s), 113.13 (s), 112.91 (s), 111.19
(s), 105.11 (s) (Figure S14). HRMS, m/z: calc.: 258.0725, found:
-1
2
1
58.0729 (Figure S15). FT-IR (KBr, cm ): 1605, 1385, 1274,
139, 1091, 967, 846, 741, 546.
Kα radiation (λ = 1.5418 Å), employing a scanning rate of (E)-2-(3,5-difluorostyryl)benzo[d]oxazole (BOAF35)
-1
0
.00267 ·s in the 2θ range of 2  to 40 . The sample for XRD
By following the synthetic procedure for compound BOAF4,
BOAF35 was synthesized from 2-methylbenzoxazole (0.38 mL,
measurement was prepared by casting the organogel on
silicon wafer and dried at room temperature.
3
.2 mmol), 3,5-difluorobenzaldehyde (0.45 g, 3.2 mmol) and t-
BuOK (0.78 g, 7.0mmol). The crude product was purified by
column chromatography (silica gel) using ethyl
Preparation of organogels
The hot solutions in selected organic solvents were obtained
by heating. After suffered sonification until the solutions
became translucent, they were aged at room temperature for
acetate/petroleum ether (v/v = 1/10) as the eluent. Flocculus-
like white solid of BOAF35 (0.59 g) was obtained in a yield of
1
7
2%. Mp: 143.0-144.0

C. H NMR (400 MHz, DMSO-d ) δ
6
1
min, and the organogels were formed.
(ppm): 7.82 (d, J = 16.4 Hz, 1H), 7.76 (ddd, J = 12.6, J = 7.3 Hz, J
=
1
1.6 Hz, 2H), 7.65 (dd, J = 8.8 Hz, J = 2.0 Hz, 2H), 7.52 (d, J =
Synthesis
6.4 Hz, 1H), 7.47-7.39 (m, 2H), 7.30 (tt, J = 9.2, 2.3 Hz, 1H)
THF was dried over sodium and benzophenone. CH Cl was
13
2
2
(Figure S16). C NMR (101 MHz, DMSO-d ) δ (ppm): 162.23 (s),
6
dried over calcium hydride. Water was purified with the
Millipore system before used. The other chemicals and
reagents were used as received without further purification.
1
50.30 (s), 142.07 (s), 139.13 (s), 137.49 (s), 126.36 (s), 125.36
(s), 120.32 (s), 117.27 (s), 111.51 (s), 111.25 (s), 111.15 (s),
1
2
1
05.35 (s) (Figure S17). HRMS, m/z: calc.: 258.0725, found:
-
1
58.0731 (Figure S18). FT-IR (KBr, cm ): 1594, 1385, 1165,
072, 948, 859, 549, 518.
(E)-2-(4-fluorostyryl)benzo[d]oxazole (BOAF4)
t-BuOK (0.78 g, 7.0mmol) was added into dry THF (10 mL) and
o
stirred for 10 min at 0 C. Then, 2-methylbenzoxazole (0.38 mL, (E)-2-(3,5-dichlorostyryl)benzo[d]oxazole (BOACl35)
3
0
.2 mmol) was added dropwise and the mixture was stirred at
C for another 10 min. After that, the solution of 4-
By following the synthetic procedure for compound BOAF4
BOACl35 was synthesized from 2-methylbenzoxazole (0.38 mL,
,
o
fluorobenzaldehyde (0.40 g, 3.2 mmol) in THF was added
3
.2 mmol), 3,5-dichlorobenzaldehyde (0.56 g, 3.2 mmol) and t-
8
| J. Name., 2012, 00, 1-3
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Journal Name
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BuOK (0.78 g, 7.0mmol). The crude product was purified by column
column chromatography (silica gel) using
acetate/petroleum ether (v/v = 1/10) as the eluent. Flocculus- like white solid of BOABr35 (0.61 g) was obtained in a yield of
chromatography
(silica
gel)
using
ethyl
View Article Online
DOI: 10.1039/C8OB00113H
ethyl acetate/petroleum ether (v/v = 1/10) as the eluent. Flocculus-
1
like white solid of BOACl35 (0.63 g) was obtained in a yield of 50%. Mp: 191.0-192.0C. H NMR (400 MHz, DMSO-d ) δ
6
1
6
8%. Mp: 144.0-145.0
C. H NMR (400 MHz, DMSO-d ) δ (ppm): 8.13 (s, 2H), 7.87 (s, 1H), 7.80 (d, J = 6.4 Hz, 1H), 7.77 (s,
6
(
7
ppm): 7.97 (d, J = 1.7 Hz, 2H), 7.79 (dd, J = 14.0, J = 8.8 Hz, 2H), 1H), 7.74 (s, 1H), 7.55 (d, J = 16.4 Hz, 1H), 7.46-7.39 (m, 2H)
1
3
.75 (d, J = 7.4 Hz, 1H), 7.64 (t, J = 1.7 Hz, 1H), 7.56 (d, J = 16.4 (Figure S28). C NMR (101 MHz, DMSO-d ) δ (ppm): 162.23 (s),
6
13
Hz, 1H), 7.44 (qd, J = 7.4 Hz, J =3.8 Hz, 2H) (Figure S19).
C
150.29 (s), 142.07 (s), 139.61 (s), 136.82 (s), 134.53 (s), 130.03
NMR (101 MHz, DMSO-d ) δ (ppm): 162.25 (s), 150.31 (s), (s), 126.38 (s), 125.38 (s), 123.53 (s), 120.34 (s), 117.46 (s),
6
1
42.08 (s), 139.10 (s), 136.97 (s), 135.13 (s), 129.23 (s), 126.88 111.17 (s) (Figure S29). HRMS, m/z: calc.: 379.9104, found:
-
1
(
(
(
s), 126.39 (s), 125.39 (s), 120.35 (s), 117.52 (s), 111.18 (s). 379.9104 (Figure S30). FT-IR (KBr, cm ): 1602, 1385, 1166,
Figure S20). HRMS, m/z: calc.: 290.0134, found: 290.0132 1073, 948, 859, 741, 547, 518.
Figure S21). FT-IR (KBr, cm ): 1584, 1559, 1451, 1245, 964,
28, 837, 799, 737, 662.
-1
(
E)-2-(2,4-difluorostyryl)benzo[d]thiazole (BTAF24)
By following the synthetic procedure for compound BOAF4
BTAF24 was synthesized from 2-methylbenzothiazole (0.41 mL,
9
,
(E)-2-(4-bromostyryl)benzo[d]oxazole (BOABr4)
By following the synthetic procedure for compound BOAF4, 3.2 mmol), 2,4-difluorobenzaldehyde (0.45 g, 3.2 mmol) and t-
BOABr4 was synthesized from 2-methylbenzoxazole (0.38 mL, BuOK (0.78 g, 7.0mmol). The crude product was purified by
3
.2 mmol), 4-bromobenzaldehyde (0.59 g, 3.2 mmol) and t- column
BuOK (0.78 g, 7.0mmol). The crude product was purified by acetate/petroleum ether (v/v = 1/10) as the eluent. Flocculus-
column chromatography (silica gel) using ethyl like white solid of BTAF24 (0.37 g) was obtained in a yield of
chromatography
(silica
gel)
using
ethyl
1
acetate/petroleum ether (v/v = 1/10) as the eluent. Flocculus- 42%. H NMR (400 MHz, DMSO-d ) δ (ppm): 8.11 (d, J = 7.9 Hz,
6
like white solid of BOABr4 (0.69 g) was obtained in a yield of 1H), 8.03 (dd, J = 19.9, 8.3 Hz, 2H), 7.66 (s, 2H), 7.54 (t, J = 7.6
1
7
(
2%. Mp: 152.0-153.0

C. H NMR (400 MHz, DMSO-d ) δ Hz, 1H), 7.46 (t, J = 7.5 Hz, 1H), 7.39 (t, J = 10.2 Hz, 1H), 7.22 (t,
6
1
3
ppm): 7.80 (dd, J = 12.0 Hz, J = 10.1 Hz, 3H), 7.74 (dd, J = 11.7 J = 8.3 Hz, 1H) (Figure S31). C NMR (101 MHz, DMSO-d ) δ
6
Hz, J = 8.4 Hz, 2H), 7.65 (d, J = 8.3 Hz, 2H), 7.45-7.37 (m, 3H) (ppm): 166.36 (s), 153.84 (s), 134.62 (s), 130.65 (s), 128.42 (s),
13
(
Figure S22). C NMR (101 MHz, DMSO-d ) δ (ppm): 162.66 (s), 127.12 (s), 126.12 (s), 124.44 (s), 123.20 (s), 122.73 (s), 120.19
6
1
50.27 (s), 142.15 (s), 138.65 (s), 134.63 (s), 132.36 (s), 130.33 (s), 112.99 (d, J = 21.1 Hz), 105.08 (t, J = 26.2 Hz) (Figure S32).
(
s), 126.11 (s), 125.28 (s), 123.66 (s), 120.16 (s), 115.15 (s), HRMS, m/z: calc.: 274.0497, found: 274.0508 (Figure S33). FT-
-1
1
3
1
11.09 (s) (Figure S23). HRMS, m/z: calc.: 300.0019, found: IR (KBr, cm ): 2026, 1605, 1285, 1163, 1074, 952, 860, 547,
-
1
00.0017 (Figure S24). FT-IR (KBr, cm ): 1602, 1385, 1138, 523.
068, 992, 953, 862, 819, 617, 539, 513.
(E)-2-(2,4-dichlorostyryl)benzo[d]thiazole (BTACl24)
(E)-2-(2,4-dibromostyryl)benzo[d]oxazole (BOABr24)
By following the synthetic procedure for compound BOAF4
,
By following the synthetic procedure for compound BOAF4, BTACl24 was synthesized from 2-methylbenzothiazole (0.41
BOABr24 was synthesized from 2-methylbenzoxazole (0.38 mL, mL, 3.2 mmol), 2,4-dicholorobenzaldehyde (0.56 g, 3.2 mmol)
3
.2 mmol), 2,4-dibromobenzaldehyde (0.84 g, 3.2 mmol) and t- and t-BuOK (0.78 g, 7.0mmol). The crude product was purified
BuOK (0.78 g, 7.0mmol). The crude product was purified by by column chromatography (silica gel) using ethyl
column chromatography (silica gel) using ethyl acetate/petroleum ether (v/v = 1/10) as the eluent. Flocculus-
acetate/petroleum ether (v/v = 1/10) as the eluent. Flocculus- like white solid of BTACl24 (0.77 g) was obtained in a yield of
1
like white solid of BOABr24 (0.66 g) was obtained in a yield of 80%. H NMR (400 MHz, DMSO-d ) δ (ppm): 8.13 (d, J = 7.9 Hz,
6
1
5
7%. Mp: 155.0-156.0

C. H NMR (400 MHz, DMSO-d ) δ 1H), 8.10 (d, J = 8.6 Hz, 1H), 8.04 (d, J = 8.0 Hz, 1H), 7.87 (d, J =
6
(
=
8
ppm): 8.05 (d, J = 8.5 Hz, 1H), 8.03 (d, J = 1.9 Hz, 1H), 7.96 (d, J 16.1 Hz, 1H), 7.76 (dd, J = 9.1, J= 7.0 Hz, 2H), 7.54 (ddd, J = 7.0,
13
16.3 Hz, 1H), 7.79 (dd, J = 7.6 Hz, J = 1.4 Hz, 2H), 7.70 (dd, J = J= 5.6, J= 4.7 Hz, 2H), 7.47 (t, J = 7.3 Hz, 1H) (Figure S34).
C
13
.5 Hz, J = 1.8 Hz, 1H), 7.49-7.39 (m, 3H) (Figure S25). C NMR NMR (101 MHz, CDCl ) δ (ppm): 135.48 (s), 134.74 (s), 132.37
3
(
101 MHz, DMSO-d ) δ (ppm): 162.12 (s), 142.03 (s), 135.96 (s), (s), 132.13 (s), 129.96 (s), 127.73 (d, J = 6.6 Hz), 126.56 (s),
6
1
35.60 (s), 133.85 (s), 131.81 (s), 129.81 (s), 126.44 (s), 125.43 125.82 (s), 124.86 (s), 123.18 (s), 121.62 (s) (Figure S35). HRMS,
(
s), 124.02 (s), 120.37 (s), 117.99 (s), 111.33 (s) (Figure S26). m/z: calc.: 305.9906, found: 305.9905 (Figure S36). FT-IR (KBr,
-
1
HRMS, m/z: calc.: 379.9104, found: 319.9109 (Figure S27). FT- cm ): 2025, 1604, 1385, 1163, 1075, 946, 860, 546, 523.
-1
IR (KBr, cm ): 1602, 1385, 1267, 1138, 1068, 993, 952, 862,
41, 517.
E)-2-(3,5-dibromostyryl)benzo[d]oxazole (BOABr35)
(E)-2-(2,4-dibromostyryl)benzo[d]thiazole (BTABr24)
5
By following the synthetic procedure for compound BOAF4
,
(
BTABr24 was synthesized from 2-methylbenzothiazole (0.41
mL, 3.2 mmol), 2,4-dibromobenzaldehyde (0.84 g, 3.2 mmol)
and t-BuOK (0.78 g, 76 mmol). The crude product was purified
by column chromatography (silica gel) using ethyl
acetate/petroleum ether (v/v = 1/10) as the eluent. Flocculus-
By following the synthetic procedure for compound BOAF4
BOABr35 was synthesized from 2-methylbenzoxazole (0.38 mL,
.2 mmol), 3,5-dibromobenzaldehyde (0.84 g, 3.2 mmol) and t-
,
3
BuOK (0.78 g, 7.0mmol). The crude product was purified by
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O rP gl ea na si ce &d Bo i on mo to al e dc juu l sa tr mC ha er mg i ins ts ry
Page 10 of 10
ARTICLE
like white solid of BTABr24 (0.67 g) was obtained in a yield of
Journal Name
H. Shan, Y. Lin, Q. Chen, V. A. Roy and Z. Xu, ACSViAewppArlt.icMle Oantleinre.
Interfaces, 2016, , 18991-18997.
1
5
1
1
7
3%. H NMR (400 MHz, DMSO-d ) δ (ppm): 8.13 (d, J = 7.9 Hz,
8
DOI: 10.1039/C8OB00113H
6
4
5
. (a) Y. Li, K. Liu, J. Liu, J. Peng, A. Xuli Feng and Y. Fang,
Langmuir, 2006, 22, 7016-7020; (b) L. E. Buerkle and S. J.
Rowan, Chem. Soc. Rev., 2012, 41, 6089-6102; (c) H. Peng, D.
L. Ding, T. Liu, X. Chen, L. Li, D. S. Yin and D. Y. Fang, Chem.
Asian J., 2012,
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H), 8.05 (d, J = 8.1 Hz, 1H), 8.00 (d, J = 9.3 Hz, 2H), 7.84 (d, J =
6.0 Hz, 1H), 7.74 (d, J = 16.2 Hz, 1H), 7.69 (d, J = 8.6 Hz, 1H),
1
3
.55 (t, J = 7.6 Hz, 1H), 7.48 (t, J = 7.5 Hz, 1H) (Figure S37).
C
NMR (101 MHz, DMSO-d ) δ (ppm): 165.83 (s), 153.90 (s),
6
7, 1576-1582.
1
(
1
35.87-135.64 (m), 135.16 (d, J = 78.1 Hz), 134.26 (s), 133.66
s), 131.80 (s), 129.66 (s), 127.24 (s), 126.25 (s), 125.63 (s),
25.24 (s), 123.45 (d, J = 17.3 Hz), 122.82 (s) (Figure S38).
HRMS, m/z: calc.: 395.8875, found: 395.8886 (Figure S39). FT-
1
Duan and M. Liu, Chem. Commun., 2012, 48, 7501-7503; (c) X.
Cao, A. Gao, H. Lv, Y. Wu, X. Wang and Y. Fan, Org. Biomol.
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-1
IR (KBr, cm ): 2025, 1604, 1385, 1163, 1074, 946, 860, 547,
23.
5
1
847; (e) G. Qing, X. Shan, W. Chen, Z. Lv, P. Xiong and T. Sun,
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Conflicts of interest
There are no conflicts of interest to declare.
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This work was financially supported by the National Natural
Science Foundation of China (51773076 and 21503090) and
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