Fluorination of the tetraphenylethene core: Synthesis, aggregation-induced emission, reversible mechanofluorochromism and thermofluorochromism of fluorinated tetraphenylethene derivatives

Article abstract of DOI:10.1039/c9tc00511k

The Suzuki-Miyaura cross-coupling reactions of bromoalkenes with fluorophenylboronic acids afforded 17 fluorinated tetraphenylethene (FTPE) compounds that have only fluorine substituent(s) directly on the tetraphenylethene (TPE) core with different number

Full text of DOI:10.1039/c9tc00511k

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Nguyên T. K. Thanh, Xiaodi Su et al.
Fine-tuning of gold nanorod dimensions and plasmonic properties using
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Journal of Materials Chemistry C
ARTICLE
Fluorination of the tetraphenylethene core: synthesis,
aggregation-induced emission, reversible mechanofluoro-
chromism and thermofluorochromism of fluorinated tetraphenyl-
ethene derivatives
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
Hao Zhanga, Yong Nie*a, Jinling Miao*a, Dengqing Zhangb, Yexin Lia, Guangning Liua,
www.rsc.org/
Guoxin Suna, Xuchuan Jiang*a
The Suzuki-Miyaura cross-coupling reactions of bromoalkenes with fluorophenylboronic acids afforded 17 fluorinated
tetraphenylethene (FTPE) compounds that have mere fluorine substituent(s) directly on the tetraphenylethene (TPE) core
with different number and substitution position of the fluorine atom(s). The X-ray structures of four FTPEs show that these
FTPE derivatives have C-H···F and C-H···π hydrogen bonds in the crystal packing. DFT calculations indicate that both the
HOMO and LUMO orbitals of the FTPEs essentially have lower energy levels than those of the parent TPE, and the energy
gaps are highly dependent on the substitution pattern. These FTPEs exhibit aggregation-induced emission characteristics
as most TPE derivatives but the aggregation process was found to be gradual and time-dependent. The emission
wavelengths of both aggregates from tetrahydrofuran/H2O and solids, and the corresponding emission quantum yields of
the solid samples vary with different substitution pattern. In addition, two examples of these FTPEs show reversible
mechanofluorochromic and thermofluorochromic property (the latter was only shown on silica gel), while the parent TPE
does not exhibit mechanochromism under the same conditions.
the rotation of the C-C single bonds dissipates the excitation
energy leading to very weak emission or even no emission;
whereas in aggregated states the rotation is restricted by
Introduction
Aggregation induced emission (AIE) has been proven to be one
of the best solutions to aggregation caused quenching (ACQ)
multiple intermolecular C-H···π and/or other interactions that
activates radiative relaxation channel and thus the strong
emission. It has been revealed that different chemical
modifications of the TPE structure can afford tunable emission
colours in all the entire visible spectrum.5-8 Meanwhile, the AIE
luminogens especially the TPE derivatives often show multi-
stimuli-responsiveness towards external stimuli such as
temperature, pressure, light etc., because of the internal
structural characteristics and molecular packing.
On the other hand, fluorination has been known as an
important and efficient modification method for synthesizing
organic optoeelctronic materials, medicine and pesticides
because of the unique characteristics of fluorine atom (small
atomic radius and greatest electronegativity),9-17 and
fluorinated materials generally have lower energy levels for
HOMO and LUMO orbitals than their non-fluorinated
counterparts, and thus higher oxidative stability and often
optimized electronic properties. Meanwhile, fluorine atom is
prone to participate in intra- or intermolecular interactions for
the molecular packing, thereby influencing the spectroscopic
property of the resulting materials.
which is
a problem of traditional organic luminescent
materials. AIE was proposed by Tang et al. in 2001 and has
thus far shown potential applications in luminescent materials,
chemical sensing, biological sensing/imaging and other fields.1-
4 A large variety of compounds have been found to exhibit the
AIE effect, and they generally can be divided into several
categories as heterocycle rings, pure hydrocarbon aromatics,
ethenyl derivatives, metal clusters and complexes and others.5
Among the many types of AIE luminogens the
tetraphenylethene (TPE) derivatives are considered the
archetypical and easy-to-prepare system. The working
mechanism for the TPE derivatives is regarded as the
intramolecular restriction of rotation (RIR): in dilute solution
aInstitute for Smart Materials & Engineering, School of Chemistry and Chemical
Engineering, University of Jinan, No. 336 Nanxinzhuang West Road, 250022 Jinan,
P. R. China.* E-mail address: chm_niey@ujn.edu.cn (YN), chm_miaojl@ujn.edu.cn
(JM), ism_jiangxc@ujn.edu.cn (XJ).
bCollege of Chemistry, Chemical Engineering and Biotechnology, Donghua
University, 2999 North Renmin Road, Songjiang, 201620 Shanghai, P. R. China
Considering the importance of TPEs and fluorinated
materials, it would be of interest to study the fluorine
†Electronic Supplementary Information (ESI) available: Synthetic details of new
compounds, crystal data and structure refinement, selected bond lengths and
torsion angles, diagrams of the frontier MOs and energy gaps, CIE1931 diagrams,
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with an absolute quantum yield of 23%).18
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Although there has been a few reporDtsOIc:o10n.c10e3r9n/iCn9gTtCh0e05A11IEK
property of FTPEs (including few examples with F and other
groups on the TPE core19-21 or few examples with F in the
vicinity of the TPE core22), and a number of reports on the
synthetic methodologies of some FTPEs or usage of some
FTPEs as synthetic intermediates,23-32 there is currently no
systematic study on the fluorination effect on the structure
and property of the corresponding FTPEs especially those with
mere F atom(s) on the TPE core. In this paper we have
synthesized 17 FTPEs with F atom(s) on the TPE core,
displaying various substitution patterns. The structural and
optical properties of these FTPEs show that the fluorination of
the TPE core influences the molecular packing and electronic
structures as well as the optical properties, to a different
extent, depending on the substitution pattern. Moreover,
some derivatives exhibit reversible mechanofluorochromism
and thermofluorochromism, which are not observed for the
parent TPE.
Results and Discussion
Synthesis and characterization
Seventeen FTPEs were conveniently prepared by the Suzuki-
Miyaura cross-coupling reactions of the corresponding
fluorinated phenylboronic acid with triphenylbromoethene, or
(fluorinated) 1,1-dibromoethene precursors (Scheme 1),
respectively. The FTPE products were characterized by NMR
Scheme 1 Synthetic routes to FTPEs with one, two, three and four fluorinated phenyls.
(1H, 13C, 19F) and mass spectra, and in some cases (1b
, 1c, 1e
substitution effect in fluorinated TPE (FTPE) molecular
systems. Another point of the FTPEs is that with only fluorine
atom(s) on the TPE core, it may be possible to obtain stable
blue or deep blue emitters with high emission efficiency (the
solid parent TPE exhibits a blue emission band at 439 nm, with
and 4a) single crystal X-ray analyses. It should be noted that,
although most of the FTPEs were obtained in moderate to
good yields, in some cases good yields were not possible under
Fig. 1 Molecular Structures of 1b, 1c, 1e and 4a, ellipsoids are drawn at the 30% probability for non-hydrogen atoms.
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Table 1 Information on the hydrogen bonding interactions in 1b, 1c, 1e and 4a.
View Article Online
DOI: 10.1039/C9TC00511K
Compounds
1b
D–H···
A
d(H···A) [Å]
2.66
2.96
2.97
2.44
2.53
2.96
2.43
2.62
d(D···A) [Å]
3.442
3.787
3.807
3.343
3.416
3.778
3.239
3.511
3.364
3.254
∠
(D–H···A) [°]
C(14)-H(14)···F(1)
C(5)-H(5)[1]···Cg1a
C(8)-H(8)[1]···Cg2b
C(24)-H(24)···F(1')
C(26)-H(26)···F(1)
C(8)-H(8)[1]···Cg3c
C(13)-H(13)···F(1)
C(26)-H(26)···F(2)
C(8)-H(8)···F(2)
142
149
151
164
158
148
146
160
133
150
1c
1e
4a
2.66
2.42
C(22)-H(22)···F(4)
aCg1: Centorid of phenyl (C15-C16-C17-C18-C19-C20), bCg2: Centorid of phenyl (C21-C22-C23-C24-C25-C26), cCg3: Centorid of phenyl (C21-C22-C23-C24-C25-C26).
the
same/similar
conditions
because
of
the X-ray structures of 1b, 1c, 1e and 4a
hydrodeboronation of the 2-fluorinated or 2,6-difluorinated
phenylboronic acids under basic conditions (basic conditions
are normally utilized for the Suzuki reactions).33
To understand the structure and molecular packing of the
FTPEs, single crystals of four compounds were grown and their
X-ray structures were determined, as shown in Fig. 1. The
crystals all crystallize in the chiral space group P21, as the
parent TPE.34,35 It should be noted that due to the light atoms
(C/H/F) in the molecules and the X-ray radiation (Mo-Kα) used,
the Flack parameters are not satisfactory, and the absolute
configurations (M or P) of the crystals are not determined. In
the present structures, the C-F bond lengths fall into the range
1.248~1.363 Å, and the C=C bond lengths lie in the range
1.337~1.370 Å, comparable to that of 1.359 Å reported for the
parent TPE (for selected bond lengths, and torsional angles of
These FTPEs exhibit different substitution patterns with
different number and substitution position of the F atoms on
the TPE core, which represent four different types of
fluorination of the TPE skeleton: fluorination of one, two,
three and four phenyl rings. It should be pointed out that this
list is not exhaustive, as we were not intended to synthesize all
the possible combinations of FTPE derivatives, rather, by the
limited number of compounds, to try to get the regularity of
the effects of fluorination on the structures and properties of
the resulting products.
1b
,
1c
,
1e and 4b, see Table S5). Although the C=C bond is not
Fig. 2 Weak intermolecular interactions of 1b, 1c, 1e and 4b in the crystal.
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Table 2 Photophysical data for the FTPE derivatives.
apparently influenced by fluorination, the conformation of the
phenyl rings and the molecular packings are significantly
affected. In the present structures, as is well known, weak
intermolecular interactions involving F atoms are present, as
shown in Fig. 2, and the related information is listed in Table 1.
The C-H···F hydrogen bonding interactions are found in all the
four structures, and C-H···π interactions are exhibited further
for molecules of 1c and 1e in the crystals, which is very
different from that of TPE crystals. In the structure of the
parent TPE, it is the multiple C-H···π intermolecular
interactions that block the conformation of the four phenyl
rings. 34,35
bλem
(nm)
τ
(ns)
aλabs(nm)
bϕ
jkF (s-1)
kknr (s-1)
1a 237, 301 444f
1b 239, 309 445f
0.21
1.40f 1.50x108 5.64x108
1.24f 2.02x108 6.05x108
0.25
(0.22i)
0.09
1c 234, 306 439f
1d 237, 300 450f
1e 237, 300 438f
1f 238, 299 448f
0.46f 1.96x108 1.98x109
n. a.
n. a.
n. a.
n. a.
0.15
0.05
n. a.
0.23
n. a.
0.15
0.06
0.05
0.02
0.54
n. a.
n. a.
n. a.
n. a.
n. a.
n. a.
n. a.
n. a.
n. a.
n. a.
n. a.
n. a.
1g n. a.
1h 239, 309 446f
455e
0.98f 1.53x108 8.67x108
0.30f 1.67x108 3.17x108
DFT calculations on the electronic structures
1i n. a.
1j n. a.
448f
469h
To gain insight into the electronic structures, density
functional theory (DFT) calculations were performed at the
B3LYP/6-31G(d,p) level of theory. As shown in Tables S6 and
S7, for all the 17 FTPE structures both the HOMO and LUMO
orbitals are delocalized over the whole molecules, with the
fluorine atom(s) involved, to a different extent. All the energy
levels of the HOMO orbitals (-5.37 ~ -5.64 eV) are lower than
that of the parent TPE (-5.33 eV, calculated at the same level
of theory), and the energy levels of the LUMO orbitals are
also lowered (-1.23 ~ -1.57 eV) relative to that of the parent
n. a.
0.86f 2.67x108 8.95x108
n. a. n. a. n. a.
n. a.
n. a.
1k 234, 309 440f
2a n. a.
490c
2b 233, 308 455g
3a 234, 306 456h
3b 234, 305 442h
4a 234, 307 444h
4b 233, 305 434d
1.25g 1.20x108 6.80x108
0.91h 6.59x107 1.03x109
0.84h 5.95x107 1.13x109
0.42h 4.76x107 2.33x109
1.50d 3.60x108 3.07x108
a) Measured in THF solutions, 2 × 10-5 mol/L; b) Measured in solids; c) λex = 330 nm; d)
λex = 350 nm; e) λex = 370 nm; f) λex = 372 nm; g) λex = 375 nm; h) λex = 380 nm; i) crystal;
j) Radiative decay rate in solid, kF = ϕ/τ; k) Nonradiative decay rate in solid, knr = 1/τ- kF.
TPE (-1.22 eV) except those for 1a (-1.20 eV), which is
comparable to that of the parent TPE. As to the energy gaps
between the HOMO and LUMO orbitals, the values for the
FTPE lie in the range 4.04~4.28 eV (for comparison, that for the
parent TPE is calculated to be 4.11 eV), with the smallest for
4b (4.04 eV) and the largest (4.28 eV) for 2a
.
Moreover, the different number and substitution position
of the F atom(s) show different influence on the calculated
energy gaps. Even with one fluorinated phenyl ring, the energy
gap values fall into in the range 4.08 eV (1h) ~ 4.26 eV (1j). For
those with two, three or four fluorinated phenyl rings, the
energy gap values also vary with the different substitution
pattern. This suggests the complexity of the influence of the
fluorination of the TPE core on the electronic structure of
corresponding FTPEs. On the other hand, it may be possible to
precisely tune the electronic property by choosing the suitable
substitution pattern.
Absorption spectra
The absorption spectra of 13 FTPEs were measured in THF
solutions at room temperature, as shown in Fig. 3, and the
corresponding data are listed in Table 2. The absorption
maxima are in the range 296-309 nm, similar to but slightly
blue shifted when compared to that of the parent TPE (314 nm
in THF).36 This indicates that the fluorination of the TPE core
with different substitution pattern does not significantly affect
the absorption property.
Aggregation-induced emission
Fig. 3 Absorption spectra of 1a-1k (a) and 2a-4b (b) in THF solutions (2 × 10-5
mol/L).
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Fig. 4 PL spectra of 1b in THF/water with different fw (c = 1 × 10-4 mol/L, λex = 300
nm); Inset: photographs of 1b in THF solution (a) and THF/water (fw = 90%) (b)
under ambient light (A) and UV light of 365 nm (B).
Fig. 5 PL spectra of 2b in THF/water mixtures with different fw (c = 2.5 × 10-5
mol/L, λex = 300 nm); Inset: photographs of 2b in THF solution (2.5 × 10-5 mol/L)
(a) and fw = 97.5% mixture (b) under visible light (A) and UV light of 365 nm (B).
The photoluminescence spectra of four FTPEs, namely, 1b, 2b,
3b and 4b were examined at room temperature, in both
solution (THF) and aggregated states (Figs. 4-7, Table 3). All the
four FTPEs emit weakly in solutions, whereas the
corresponding samples in aggregated states show strong
emissions as expected, exhibiting AIE characteristics. However,
as they have different substitution pattern of F atom(s), the
emission of the aggregates show different trends. For 1b, the
emission wavelengths were at 486 nm with fw = 85% and 487
nm with fw = 90%, respectively, while with fw = 90% an
emission at 484 nm (30 min after mixing) was observed with
the intensity further increased indicating the time dependence
of the aggregation within the observed time interval. The
photos clearly display the color difference (Fig. 4).
The THF solution of 2b emitted at 356 nm, which was
weakened when water was added, till fw = 80% only a much
weaker emission at 354 nm was detected (Fig. 5). With the
addition of water, the molecules gradually aggregated and the
emission of single molecules of 2b became weaker but the
aggregates also emitted weakly at this stage. With higher
water fractions the emissions of the aggregates red-shifted
and the intensity increased dramatically, first to 480 nm with
fw = 90%, then 482 nm with fw = 95%, finally to 480 nm with fw
= 97.5% and the emission intensity further increased after 40
min, but the emission wavelengths remained essentially
unchanged. The corresponding photos show the color
difference. For 3b, the emission wavelengths were at 482, 484
and 482 nm with fw = 80%, 85 and 90%, respectively. The
sample with fw = 90% exhibited a slightly blue-shifted emission
(478 nm) after 40 min and the intensity also increased. The
Fig. 6 PL spectra of 3b in THF/water mixtures with different fw (c = 5 × 10-5 mol/L,
λex = 300 nm); Inset: photographs of 3b in 5 × 10-5 mol/L THF solution (a) and fw
=
90% mixture (b) under visible light (A) and UV light of 365 nm (B).
corresponding photos are shown in Fig. 6. In the case of 4b
,
the emissions were at 472 nm with fw = 90% and 466 nm with
fw = 97.5%. The corresponding photos also display the color
difference (Fig. 7).
In all the experiments, it was found that in the THF/H2O
mixtures, the aggregates could exhibit a significant increase in
the emission intensity only with certain fraction of water (fw
around 90%). The aggregates with different water fractions
show different emission wavelengths (466-487 nm) when
compared to the corresponding samples in solution (354-372
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Fig. 7 PL spectra of 4b in THF/water mixtures with different fw (c = 2.5 × 10-5
mol/L, λex = 300 nm); Inset: photographs of 4b in 2.5 × 10-5 mol/L THF solution (a)
and fw = 97.5% mixture (b) under visible light (A) and UV light of 365 nm (B).
Table 3 PL emission wavelengths of 1b, 2b, 3b and 4b measured in THF/water
mixtures with different water fractions (fw).
PL emission wavelength (nm)
Compounds
0%a
372
356
360
363
80%a 85% 90% 95% 97.5%
1b
2b
3b
452
354
482
564
486
487
480 482 480
482
472
484
4b
466
a weakly emissive
nm), apart from the emission intensity. After
fw = 85% the emission wavelengths did not vary much
suggesting the similarity of the respective aggregates. But the
emission intensity still increased or the emission wavelengths
shifted within certain extended time, in the cases of 2b and 3b
.
Fig. 8 Emission spectra of 1a-1c (a), 1d-1k (b), and 2a-4b (c) in the solid state.
Fluorescence spectra in the solid state
The emission spectra for all of the solid FTPEs were measured
at room temperature (Fig. 8). The emission wavelengths and
the corresponding absolute quantum yields are listed in Table
2. The emission wavelengths vary from 429 nm (4b) to 490 nm
(2a) with the majority falling into or near the range 440-450
nm. The quantum yields of the samples also vary. The
difference in molecular packing and the calculated energy gap
values mentioned above may explain the difference in the
emission wavelengths and even the quantum yields of the
samples. To look at more details, FTPEs with one fluorinated
phenyl ring, 1a-c, emitted at very similar wavelength of ~440
nm, whereas 1d-k fluoresced at wavelengths from 438 nm to
450 nm, with the exception of 1j, at 469 nm.
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As to those with two, three or four fluorinated phenyl rings,
2a exhibits an emission band centered at 490 nm, whereas 4b
displays an emission at 429 nm, red-shifted relative to that of
the parent TPE (439 nm),18,37 and the quantum yield of 4b
(54%) is the highest of this series, much higher than that of
23%18 or 25%36 for the parent TPE. In the cases of the other
FTPEs, either comparable to, or lower than that of the parent
TPE, exhibiting the significant influence of fluorination of the
TPE core. Fig. S1 illustrates the CIE1931 diagrams and the
chromaticity coordinates of the solid samples, among which
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DOI: 10.1039/C9TC00511K
the emission of several compounds (1e, 1k and 4a) is relatively
pure blue (according to CIE1931 the chromaticity coordinate of
pure blue is (0.14, 0.08).38 The emission lifetimes of 11 solid
samples (Table 2) are estimated to be from 0.30 (1i) to 1.5 ns
(
4b) (Table S8, Figs. S5-S15), indicating that the emissions are
Fig. 9 Normalized PL spectra of 1b (before grinding), ground 1b and 1b ground
then heated (λex = 372 nm); Inset: photographs of 1b (before grinding, a) and
ground 1b (b) under UV of 365 nm.
of fluorescence nature, as expected. For most of the FTPEs, the
radiative decay rates (kF) are smaller than the corresponding
nonradiative decay rates (knr) except those of 4b, which
exhibits the longest lifetime and greatest emission efficiency in
this series and the kF is greater than the knr, implying the
relatively better utilization of the excited state energy through
the radiative channel because of the relatively more restriction
of intramolecular rotation in its molecular packing.
Mechanofluorochromism
The powder samples of 1b and 4b, with relatively high
emission efficiency in the solid state, were selected as
examples to test the mechanofluorochromism. The solids of 1b
and 4b were ground in a mortar, and the emission spectra
were measured to compare with that of 1b and 4b (before
grinding), respectively. As shown in Fig. 9 and Table 4, in the
case of 1b, after being ground the solid exhibited an emission
at 451 nm, slightly red-shifted relative to that of 1b (448 nm).
After annealing (100 oC, 20 min) the sample showed
anemission at 448 nm showing the reversible
mechanofluorochromism, the photos shown in Fig. 9 display
the fluorescent images before and after being ground. As
shown in Fig. 10 and Table 4, in the case of 4b, after being
ground the solid exhibited an emission at 459 nm, much red-
shifted relative to that of 4b (434 nm). After annealing (100 oC,
20 min) the sample exhibited an emission at 434 nm, also
showing the reversible mechanofluorochromism. The photos
shown in Fig. 10 display the fluorescent images before and
after being ground.
Fig. 10 Normalized PL spectra of 4b (before grinding, λex = 350 nm), ground 4b
(λex = 370 nm) and 4b ground heated (λex = 350 nm); Inset: photographs of 4b
(before grinding, a) and ground 4b (b) under ultraviolet light of 365 nm.
Contrary to such results, the parent TPE does not exhibit
mechanochromism.20 The difference in mechanochromism
may be ascribed to the different solid state molecular packings
when the F atoms are involved compared to that in the parent
TPE and hence the different responses towards the mechanical
force. The present two examples, though limited in number,
suggest that with more F atoms, the mechanofluorochromism
property could be more significant.
Thermofluorochromismn
The DSC and TGA analyses (Figs. S2 and S3) of 1k show that the
phase transition (melting) temperature is 164.4 oC, and the 5%
weight loss temperature is 235 oC, indicating its thermal
stability. In addition, the powder samples of the parent TPE, 1b
and 4b, respectively, were investigated under UV light (365
nm) while being heated (all below the corresponding melting
points). No obvious emission colour change was observed
(from the photographs, Fig. S4a) for all the samples from room
temperature to 130oC. When the temperature increases the
molecules have higher energy and more degree of freedom to
tune the conformations, usually the emissions of TPE
compounds could get weaker and red-shifted, presumably the
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emission color change was too small to be observed within the cases of the parent TPE and 1b, the emissioVniewluArmticilne Oannlcinee
o
o
DOI: 10.1039/C9TC00511K
temperature range tested.
obviously reduced even at 60 C, and nearly quenched at 75 C,
whereas in the case of 4b, under the same conditions, the
o
emission luminance was not obviously reduced at 60 C, and
only partially weakened at 80 oC, with the emission colour
turning to somewhat cyan. The emissions of all the three
composites were recovered, when the samples were stored at
room temperature for 4-5 hours.
Table 4 PL emission wavelengths of 1b and 4b
.
In these composite samples, the F atoms of the FTPE
molecules may form weak hydrogen bonding interactions with
the OH groups of silica gel. The molecule of 1b has only one F
atom, thus similar to that of the parent TPE (with silica gel),
such hydrogen bonds between 1b and TPE and silica gel,
respectively, are very weak; while 4b has four F atoms located
on the 4-positions of the phenyl rings forming relatively
stronger hydrogen bonds with silica gel than those of 1b and
TPE. Small amount of water on the silica gel plates may also
play some role but could be only minor. Thus, the influence of
the change of temperature on the emissions showed drastic
difference among these samples, which are exemplified by the
corresponding emission spectra (Fig. 11).
As shown in Fig. 11, the emission spectra of the three
composite samples exhibit an obvious weakening in intensity
and a red shift in the emission maxima, as the temperature
o
o
changes from 30 C to 80 C. The difference is that for parent
TPE- and 1b-silica gel composites, the weakening of the
o
o
intensity at 80 C is ca. one sixth of that at 30 C and the shift
of the emission wavelength is 12 and 26 nm, respectively,
whereas 4b-silica gel composite shows an intensity weakening
o
of ca. one third of that at 30 C, and an the emission maxima
change of 13 nm. This type of interesting phenomenon is
rarely reported for organic molecules39 and holds promise in
the development of solid-state fluorescent temperature
sensors.40
Conclusions
We have prepared a series of FTPEs with pure F atom(s) on the
TPE core and studied the fluorine effect on the structures and
optical property (absorption, aggregation-induced emission,
mechanofluorochromism and thermofluorochromism). It
appears that the influence of the fluorination of the TPE core is
dependent on the substitution pattern (the number and
substitution position of the F atoms). Fluorine atom tends to
participate in intermolecular interactions that would
significantly change the molecular packing modes of the FTPEs
compared to that of the parent TPE, thus the different
substitution patterns have an influence that is more
complicated than would be expected especially when other
types of interactions (other than F atom interactions) are
present. From the examples shown here it may be possible to
find suitable combination of F atoms on the TPE core or even
more complex TPE derivatives to tune the properties. The easy
synthesis, good emission quantum yields and reversible
mechanofluorochromic and thermofluorochromic properties
of some examples imply that promising materials may be
expected for device applications.
Fig. 11 PL spectra of the parent TPE (a, λex = 380 nm), 1b (b, λex = 372 nm) and 4b
(c, λex = 350 nm) on silica gel plates being heated from 30 to 80 oC.
Interestingly, composite samples, prepared by drying a few
drops of solutions of the parent TPE, 1b and 4b, respectively,
on silica gel plates, showed very different changes (Fig. S4b)
from those of the above-mentioned powder samples. In the
PL emission wavelength (nm)
Compounds
ground
Powder and then heated
Powder ground
Powder
1b
4b
448
434
451
459
448
434
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Journal of Materials Chemistry C
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Journal Name
ARTICLE
22. H. Wu, Y. Jiang, Y. Ding, Y. Meng, Z. Zeng, C. Cabanetos, G.
Conflicts of interest
There are no conflicts to declare.
View Article Online
Zhou, J. Gao, J. Liu and J. Roncali, Dyes Pigments, 2017, 146
,
DOI: 10.1039/C9TC00511K
323-330.
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Journal of Materials Chemistry C
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DOI: 10.1039/C9TC00511K
Substitution patterns in fluorinated tetraphenylethenes affect the emission properties, mechano- and
thermofluorochromism, compared to those of the parent TPE.