A first porphyrin liquid crystal with strong fluorescence in both solution and aggregated states based on the AIE-FRET effect

Article abstract of DOI:10.1039/c9sm01174a

Porphyrins are good near-infrared fluorescent materials, but the strong self-assembly stacking resulted in the aggregation-caused quenching (ACQ) effect, limiting their emissive performance in aggregated states. In this work, a novel diphenylacrylonitrile-porphyrin derivative with multiple polyglycol chains on the periphery was designed and synthesized as an excellent near-infrared-emissive liquid crystalline material in both solution and aggregated states, which was first observed for porphyrin liquid crystals. It exhibited a high self-assembly ability with the ordered hexagonal columnar mesophase between 70 and 120 °C approximately. The strong AIE-FRET effect was produced based on the overlap of the emission wavelength of diphenylacrylonitrile and the absorption wavelength of the porphyrin, resulting in the excellent near-infrared emission in both solution and aggregated states. The pseudo Stokes shift was as large as 210 nm and the fluorescence quantum yield reached 0.12 in the solid state. Moreover, this porphyrin liquid crystal displayed low biotoxicity and excellent fluorescence bio-imaging ability in living cells, opening a new application prospect for porphyrin liquid crystalline materials.

Full text of DOI:10.1039/c9sm01174a

Soft Matter
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A first porphyrin liquid crystal with strong
fluorescence in both solution and aggregated
states based on the AIE-FRET effect†
Cite this: Soft Matter, 2019,
15, 8329
ac
Hongyu Guo,a Sining Zheng,a Shibin Chen,a Chenyang Hanab and Fafu Yang
*
Porphyrins are good near-infrared fluorescent materials, but the strong self-assembly stacking resulted
in the aggregation-caused quenching (ACQ) effect, limiting their emissive performance in aggregated
states. In this work, a novel diphenylacrylonitrile–porphyrin derivative with multiple polyglycol chains on
the periphery was designed and synthesized as an excellent near-infrared-emissive liquid crystalline
material in both solution and aggregated states, which was first observed for porphyrin liquid crystals. It
exhibited a high self-assembly ability with the ordered hexagonal columnar mesophase between 70 and
120 1C approximately. The strong AIE-FRET effect was produced based on the overlap of the emission
wavelength of diphenylacrylonitrile and the absorption wavelength of the porphyrin, resulting in the
excellent near-infrared emission in both solution and aggregated states. The pseudo Stokes shift was as
large as 210 nm and the fluorescence quantum yield reached 0.12 in the solid state. Moreover, this
porphyrin liquid crystal displayed low biotoxicity and excellent fluorescence bio-imaging ability in living
cells, opening a new application prospect for porphyrin liquid crystalline materials.
Received 11th June 2019,
Accepted 13th September 2019
DOI: 10.1039/c9sm01174a
rsc.li/soft-matter-journal
no fluorescence in aggregated states for these fluorescent liquid
crystals because of the strong ACQ effect in aggregated states.
1. Introduction
Discotic liquid crystals, as important soft matter materials with Another was that the near-infrared fluorescent liquid crystal
excellent supramolecular self-assembly abilities of liquid–crystalline was seldom reported, which deserved to be investigated
columnar mesophases, have been paid considerable research because the near-infrared materials had the advantages of high
attention based on their distinctive features such as self- tissue penetration, low cell damage and little self-fluorescence
organization into self-healing of organizational defects, one- interference of biological tissues, exhibiting potential applica-
dimensional charge migration, and potential applications in tions in many research fields, such as telecommunications,
thin film transistors, organic light emitting diodes and photo- thermal imaging, biological imaging and so on.29,30 Thus, the
voltaic devices.1–8 Among all kinds of columnar liquid crystals, near-infrared fluorescent liquid crystal with high emission in
the ones with high fluorescence had attracted much attention both solution and aggregated states is still a research challenge
due to the effective combination of intrinsic luminescence in the field of discotic liquid crystals.
capability and supramolecular self-assembly characteristic
On the other hand, it was well known that porphyrins were
within a mesophase.9,10 Up to now, a series of columnar liquid excellent near-infrared-emissive fluorescent materials with broad
crystals with excellent fluorescence had been prepared, such as application prospects.31 Based on their planar conjugated aromatic
Bodipy liquid crystals,11–14 perylene liquid crystals,15–24 tristri- structures, some porphyrin liquid crystals and liquid porphyrins
azolotriazine liquid crystals,25,26 metallomesogens,27,28 etc. were also reported by introducing long alkyl chains on the
Although these fluorescence liquid crystals had been developed periphery of the porphyrin skeleton.32–46 However, although
successfully, however, a survey of the literature suggested two these reported porphyrin liquid crystals exhibited good fluores-
obvious shortcomings for these studies. One was the weak even cence in various organic solutions, they did not exhibit good
fluorescence behaviour in aggregated states due to the strong
a College of Chemistry and Materials Science, Fujian Normal University,
Fuzhou 350007, P. R. China. E-mail: yangfafu@fjnu.edu.cn
b Fujian Key Laboratory of Polymer Materials, Fuzhou 350007, P. R. China
c Fujian Provincial Key Laboratory of Advanced Materials Oriented Chemical
Engineering, Fuzhou 350007, P. R. China
ACQ effect, limiting seriously further applications such as solid
emission and bio-imaging in aqueous solution. Lately, in order
to obtain porphyrin derivatives with solid fluorescence, the AIE
(aggregate-induced emission) phenomena, which were discovered
and studied extensively by Tang’s groups,47–51 were applied in
preparing porphyrin derivatives. Two novel porphyrin derivatives
† Electronic supplementary information (ESI) available. See DOI: 10.1039/
c9sm01174a
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with AIE groups were synthesized and displayed excellent
fluorescence in both solution and aggregated states.52,53 But
no porphyrin liquid crystal with fluorescence in both solution
and aggregated states was presented up to now. In this paper,
the first porphyrin liquid crystal with strong fluorescence in
both solution and aggregated states was designed and synthesized
by introducing polyglycol-diphenylacrylonitrile units onto the
porphyrin skeleton. This novel porphyrin derivative possessed
a good self-assembly ability of the liquid–crystalline hexagonal
columnar mesophase. Moreover, based on the overlap of the
emission wavelength of diphenylacrylonitrile and the absorption
wavelength of the porphyrin, a strong FRET (fluorescence resonance
energy transfer) effect existed between the diphenylacrylonitrile unit
and porphyrin unit. As a result, this novel porphyrin liquid crystal
showed strong fluorescence in both solution and aggregated states.
The excellent fluorescence property was further successfully applied
for fluorescence imaging of living HeLa cells, which was firstly
observed for porphyrin liquid crystalline materials.
2. Results and discussion
2.1. Synthesis and characterization
Scheme 1 The synthetic route for title compound 6.
Diphenylacrylonitrile is a classic AIE group with an emission
wavelength of 425 nm approximately in the aggregated state,54
which was overlapped with an absorption wavelength of
420 nm for the porphyrin skeleton. This overlap of wavelengths
was favourable for the AIE-FRET effect between diphenylacrylo-
nitrile units and porphyrin skeleton in the aggregated state. On
the other hand, the multiple polyglycol chains on the periphery
contributed to the production of liquid crystalline properties
and enhanced hydrophilicity for increasing the bio-imaging
abilities in aqueous solution. The synthetic route is designed as
in Scheme 1. The diphenylacrylonitrile derivatives 3, 4 and 5
were prepared sequentially by using 4-hydroxybenzaldehyde
and compound 1 as starting materials. By the classic condensa-
tion process of the preparation of the porphyrin skeleton,55
diphenylacrylonitrile–porphyrin derivative 6 was synthesized in
a yield of 8.8% after column chromatography. The structure of
target compound 6 was examined by 1H NMR, 13H NMR,
MALDI-TOF-MS and elemental analysis. All spectral signals
were in agreement with its structure (see the ESI†). For example,
the NH of the porphyrin skeleton exhibited a shift at À2.76 ppm
Fig. 1 DSC curves of porphyrin 6 upon second heating and first cooling at
a scanning rate of 10 1C minÀ1
.
Table
1
Transition temperatures (1C) and enthalpies (kJ molÀ1
) of
porphyrin 6
Phase transitiona
Heating scan T(DH)
Cooling scan T(DH)
1
in the H NMR spectrum, certainly suggesting the formation of
Cr–Colh(Colh–Cr)
Colh–Iso(Iso–Colh)
71.4(17.8)
118.9(6.5)
62.2(16.4)
115.4(7.3)
the porphyrin skeleton.
a
Cr = crystalline, Colh = hexagonal columnar phase, Iso = isotropic.
2.2. Mesomorphic studies
The mesomorphic self-assembly property of porphyrin 6 was
studied by differential scanning calorimetry (DSC), polarizing behaviors corresponded to the crystalline-mesophase-isotropic
optical microscopy (POM) and X-ray diffraction (XRD) measure- transition forcefully. The slight hysteresis phenomenon could be
ments. Fig. 1 exhibits the DSC curves of porphyrin 6. The corres- rationally attributed to the viscous material with a large molecular
ponding phase transition temperatures and enthalpy changes are weight. Moreover, the mesophase texture of porphyrin 6 was
summarized in Table 1. It can be seen that porphyrin 6 possessed observed under a POM. Obvious phase transitions of Iso–Col and
two endothermic peaks at 71.4 1C and 118.9 1C upon second Col–Cr were seen during heating and cooling processes. Fig. 2
heating and two exothermic peaks at 62.2 1C and 115.4 1C during displays the mesophase texture at 90 1C upon cooling under POM
first cooling, respectively. These good reversible phase transition observation. The typical pseudo-focal conic fan-shape textures
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Fig. 2 The mesophase texture of porphyrin 6 at 90 1C upon cooling
under POM observation (Â400 times).
suggested the ordered hexagonal columnar mesophase for
porphyrin 6, which was further confirmed by following XRD
analysis. These results of DSC analysis and POM observation
indicated that porphyrin 6 had an excellent self-assembly ability
to form a hexagonal columnar phase at 70–120 1C approximately.
Moreover, the molecular stacking behavior of porphyrin 6
was studied by XRD analysis as shown in Fig. 3. It can be seen
that a sharp scattering peak at 2y = 2.021 and three weak peaks
(2y = 3.501, 4.041 and 5.341) appeared in the small-angle region,
indicating d-spacings of 43.73 Å, 25.25 Å, 21.87 Å and 16.53 Å,
respectively. The ratio for these d-spacings is in accordance
with 1 : 1/O3 : 1/O4 : 1/O7, which can be indexed as the [d100],
[d110], [d200] and [d210] planes of a columnar hexagonal mesophase.
Also, a broad diffuse halo at 2y = 18–281 with a mean distance of
4.4 Å was observed for the molten alkyl chains in the wide-angle
region. These XRD data supported that porphyrin 6 was an
ordered self-assembly hexagonal columnar liquid crystal. More-
over, a couple of weak sharp signals (named h2) between 13.51
and 24.21, and two weak and broad signals in regions of
9.41–12.41 (named h3) and 24.61–26.41 (named h1), respectively,
could be distinguished. The d-spacings for h1, h2 and h3 were
3.3–3.6 Å, 3.6–6.6 Å and 9.3–12.2 Å, approximately. Obviously, h1
could be attributed to the representative intracolumnar-packing
distance of the porphyrin cores. The value of h3 was nearly triple
Fig. 4 The preferred conformation of porphyrin 6.
distance of h1, indicating some kind of three-molecule associa-
tions for the Colh mesophase of porphyrin 6. On the other hand,
the lattice constant (a) was calculated as 50.50 Å, which was
far smaller than the diameter of porphyrin 6 in linear shape
(76 Å approximately), suggesting that the alkyl chains might be
curled and folded or interdigitated in the mesophase. As previous
studies had reported that the beta-octasubstituted porphyrin
derivatives prefer the columnar mesophase and the meso-
tetrasubstituted porphyrins need to increase the number of alkyl
chains to obtain LC mesophases,56–61 it was reasonable to
deduce that the long meso-tetrasubstituted chains of porphyrin
6 adopted the curled and folded shape, which was favourable for
producing the LC mesophase. Furthermore, the number (n) of
molecules in a single disk of the column could be proposed
according to the following formula,62
n = (a2)(O3/2)(hrNA/M)
where the notation ‘‘a’’ is the hexagonal lattice parameter, NA is
Avogadro’s number and M is the molecular mass of the
compound. The thickness [h] of the slice is about 3.4 Å estimated
by h1. Due to only four alkyl chains (less than the usual six or eight
alkyl chains of the columnar mesophase) on the periphery of
porphyrin 6, the density (r) is assumed as 0.7–0.8 g cmÀ3, which
was less than normal r values (0.9–1.0 g cmÀ3).62 After calculation,
the estimated number of molecules (n) in a disk of the columnar
hexagonal state was approximately 1 for porphyrin 6. The estimated
number of molecules (n) was nearly 3 when using h3 for the
thickness [h] of the slice. These XRD analyses suggested that the
Fig. 3 The XRD trace of porphyrin 6 in the mesophase at 90 1C.
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supramolecular arrangement of the mesophase of porphyrin 6 be attributed to the reflections of low and part order of the
might be slightly different from the normal hexagonal columnar layer or columnar arrangement of the phenyl group and diphenyl-
mesophase.
acrylonitrile unit mixed flexible chains. Because the geometry of
The literature had confirmed that, for the purpose of an the trimolecular associations was not well-defined nor their inter-
energy-minimized structure, the meso-substituted phenyl groups distance constant, all the reflections of h1, h2 and h3 were weak and
had a nonplanar conformation with a porphyrin core due to the broad signals. Indeed, this kind of trimolecular stack per unit cell
bulky effect.63,64 Thus, the possible preferred conformation of for the columnar stacking had been observed in a previous
porphyrin 6 is proposed in Fig. 4, in which the three planes of porphyrin liquid crystalline system,65,66 which also possessed bulky
the porphyrin core, phenyl groups and diphenylacrylonitrile aromatic groups on the peripheral flexible chains of the porphyrin
units were not coplanar with each other, surrounded by curled core. On the other hand, it should be clarified that the peripheral
or folded alkyl chains. Based on Fig. 4, an intracolumnar alkyl chains of Fig. 5 were in curled, folded or interdigitated
arrangement of trimolecular stacks per unit cell in the Colh disordered arrays with neighboring disks in the hexagonal
mesophase is proposed in Fig. 5. Although three porphyrin cores columnar mesophase.
per unit cell were in ordered columnar stacking, the phenyl groups
2.3. Photophysical studies
and diphenylacrylonitrile units would stand out of the porphyrin
plane and would invade the planar space of neighboring molecules
due to the requirements of the minimum-energy conformation
and the flexible C3H6 spacers. This stable association was com-
prised of three molecules, with the C3H6 spacers mutually hold-
ing the neighboring molecules, resulting in the three stacking
distances of h3. The stacking distance of h1 could be ascribed to
rapid thermal fluctuations of the conformations of the disks
which eliminates the crystallographic difference among the three
disks in a unit cell. The couple of weak sharp signals (h2) might
The photophysical properties of porphyrin 6 were examined
using UV-vis spectra and fluorescence spectra. The porphyrin
derivative 7 with an OMe group (without the AIE group, as
shown in Scheme 1) was cited as a reference compound for
comparison. Fig. 6 illustrates the UV-vis spectra and fluores-
cence spectra of porphyrins 6 and 7. One can see that both
porphyrins 6 and 7 displayed the absorption peaks at 421, 517,
553, 595 and 652 nm in UV-vis spectra, which were the typical
porphyrin absorption Soret bands and four Q bands. Besides,
porphyrin
6 showed another strong absorption peak at
320–390 nm (Fig. 6A), which could be ascribed to the absorption
of diphenylacrylonitrile units. As to the fluorescence spectra
(Fig. 6B), porphyrins 6 and 7 exhibited a similar fluorescence
emission (excitation at 420 nm) at 640–760 nm, although the
fluorescence intensities fluctuated reasonably. These phenomena
were in accordance with the structure of porphyrin 6, in which the
porphyrin unit and diphenylacrylonitrile units were linked by
Fig. 6 (A) UV-vis absorption spectra of compounds 6 and 7 (5 mM) and
(B) fluorescence spectra (excitation at 420 nm) of compounds 6 and 7
(1 mM) in THF solution.
Fig. 5 The proposed molecular stacking mode for the hexagonal columnar
mesophase of porphyrin 6.
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saturated alkyl chains, resulting in little interaction between these
two structural units.
Furthermore, the AIE behaviors of porphyrin 6, precursor 4 and
reference compound 7 were investigated in THF–H2O mixtures.
Precursor 4 exhibited strong fluorescence at 400–500 nm when H2O
fractions were bigger than 80% in THF/H2O mixtures (see Fig. S11,
ESI†), suggesting the good AIE effect for the structure of the
diphenylacrylonitrile moiety. As expected, it can be seen that the
Soret band absorption of the porphyrin skeleton (400–450 nm) was
overlapped with the scope of fluorescence emission (400–500 nm)
of diphenylacrylonitrile derivative 4 in the aggregated state, which
was favourable for the FRET effect between these two structural
units. On the other hand, the reference compound 7 without an
AIE group showed no AIE property (see Fig. S12, ESI†). Its fluores-
cence decreased obviously with the increase of H2O fraction in
THF/H2O mixtures and almost quenched completely due to the
ACQ effect. However, diphenylacrylonitrile–porphyrin derivative 6
exhibited totally different fluorescence properties by comparison
with precursor 4 and reference compound 7. When excited by the
Soret band (lex = 420 nm), the fluorescence intensities of porphyrin
6 decreased rapidly with the increase of fw in THF–H2O solutions,
suggesting the strong ACQ effect for the aggregated states (Fig. 7A).
The fluorescence of porphyrin 6 was almost quenched completely
in the THF–H2O solution with 90% of H2O. When excited by the
wavelength of the diphenylacrylonitrile unit (lex = 350 nm), the
fluorescence intensities of porphyrin 6 decreased a little with
the increase of fw from 0% to 40%, and then increased with
the increase of fw from 40% to 90%. The fluorescence in the
THF–H2O solutions with 70–90% of H2O was even stronger
than that in pure THF solution. Moreover, unlike Fig. S11 (ESI†)
showing fluorescence changes of precursor 4 in THF–H2O
solutions, no remarkable fluorescence emission was observed
Fig. 7 (A) The fluorescence spectra of porphyrin 6 (1 mM) in the THF/water
mixture with different water fractions (excitation at 420 nm). (B) The
fluorescence spectra of porphyrin 6 (1 mM) in the THF/water mixture with
for the diphenylacrylonitrile unit in all THF–H2O solutions of different water fractions (excitation at 350 nm). Inset: The line plot of
fluorescence intensity change from 0–90% water fractions of porphyrin 6
porphyrin 6 (no emission peak at 400–500 nm) (Fig. 7B). Taking
and the fluorescence photos (under UV365 light) of porphyrin 6 in THF/
into account the outstanding AIE effect of precursor 4 in
water mixtures at fw = 10%, 50% and 90%, respectively.
THF/H2O solution (lex = 350 nm), the strong fluorescence of
porphyrin 6 in THF/H2O solution (lex = 350 nm) could be
attributed to the AIE effect of diphenylacrylonitrile units and
the FRET process between diphenylacrylonitrile and porphyrin
units. As a result, no fluorescence at 400–500 nm appeared
for diphenylacrylonitrile units and excellent fluorescence was
produced in all THF–H2O solutions for porphyrin 6. Based on
these results, a subtle balance could be deduced for the ACQ
effect and AIE-FRET effect. When fw o 40%, the ACQ effect
suppressed the AIE and FRET effect, causing a decrease of
fluorescence. When fw 4 40%, the AIE-FRET effect increased
rapidly and became stronger than the ACQ effect, resulting in a
strong fluorescence in the aggregated state.
In order to confirm further the AIE-FRET effect in the
aggregated state, the fluorescence spectra of porphyrin 6 in
the solid state and mesophase film and reference compound 7
in the solid state were studied as exhibited in Fig. 8. It could be
seen that porphyrin 6 displayed similar fluorescence spectra in
the solid state and mesophase film with the strong fluorescence
Fig. 8 The fluorescence spectra of porphyrins 6 (solid state), 7 (solid
emission at the near-infrared region (650–750 nm). A little red
shift for porphyrin 6 in the mesophase film might suggest the cence photos of porphyrins 6 and 7 in the solid state.
state) and 7 (mesophase film) (excitation at 350 nm). Inset: The fluores-
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Fig. 11 Dark-field image (left), bright-field image (middle) and the merged
images of dark and bright fields (right). lex = 460–550 nm. Scale bar:
50 mm.
Fig. 9 The optimized structure of porphyrin
6 based on the DFT
calculation.
J-aggregation in the mesophase state. But reference compound
7 showed no obvious emission. The inserted fluorescence
pictures also suggested no fluorescence for compound 7 but a
strong red fluorescence for porphyrin 6. This comparison in
solid emission certainly also supported the existence of the
AIE-FRET effect between diphenylacrylonitrile and porphyrin
moieties of porphyrin 6. The pseudo Stokes shift of porphyrin 6
was as large as 210 nm. The fluorescence quantum yield was
0.12 in the solid state, which was outstanding among porphyrin
derivatives. On the other hand, the distance between diphenyl-
acrylonitrile and porphyrin moieties of porphyrin 6 was calculated
as 16.7 Å based on the DFT calculation (as shown in Fig. 9), which
was suitable for producing the FRET effect. Thus, the emission
mechanism in the aggregated state for porphyrin 6 is proposed in
Fig. 10.
Fig. 12 Relative cell viabilities of HeLa cells incubated with different
concentrations of porphyrin 6 for 24 h.
DM IL LED). The G-type excitation/emission components of this
instrument (excitation chip wavelength: 460–550 nm, emission
chip wavelength: 590 nm) were applied to study the red fluores-
cence cell imaging for porphyrin 6. As expected, the strong red
fluorescence imaging was observed for HeLa cells with porphyrin 6
(Fig. 11), indicating the excellent bio-imaging performance of
porphyrin 6 in aqueous solution. On the other hand, the HeLa cell
metabolic activity of porphyrin 6 with MTT assay was investigated
as shown in Fig. 12. The cell viabilities were over 90% at 0–40 mM in
24 h, suggesting the low biotoxicity for porphyrin 6. The excellent
bio-imaging ability of porphyrin 6 might be attributed to not only
the good near-infrared emission in aggregated states but
also the good biocompatibility of multiple polyglycol chains
on the periphery. In a word, these results indicated that the
novel diphenylacrylonitrile–porphyrin derivative 6 possessed
an excellent application potential for near-infrared fluores-
cence bioimaging in living cells.
2.4. Fluorescence imaging of porphyrin 6
Although normal porphyrins showed good near-infrared emission,
they were limited to apply for bio-imaging in aqueous solution due
to the strong ACQ effect. As diphenylacrylonitrile–porphyrin
derivative 6 displayed excellent fluorescence in solution and
the aggregated state based on the AIE-FRET effect, it was
expected to exhibit the bio-imaging ability in aqueous solution.
Thus, fluorescence imaging of porphyrin 6 in vitro HeLa cells
was examined using a fluorescence inverted microscope. After
incubation with porphyrin 6 for 2 h at 37 1C, the HeLa cells were
rinsed with PBS solution. Later, the cells were fastened and
observed under an inverted microscope (Leica inverted microscope
3. Conclusions
In conclusion, a novel diphenylacrylonitrile–porphyrin deriva-
tive with multiple polyglycol chains on the periphery was
designed and prepared as the near-infrared-emissive fluores-
cence liquid crystalline material in both solution and aggre-
gated states. The DSC, POM and XRD studies showed that it
had excellent self-assembly ability with the ordered hexagonal
Fig. 10 The proposed illustration of the AIE-FRET effect for porphyrin 6.
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columnar mesophase between 70 and 120 1C approximately. anhydrous MgSO4, and concentrated. The residue was further
The investigation of the photophysical properties indicated that purified by rapid column chromatography using CH2Cl2/hexane
the novel porphyrin liquid crystal had excellent emission in (1: 1, v/v) as an eluent. Compound 2 was collected as a sticky
both solution and aggregated states. When excited by the solid in a yield of 82%. 1H NMR (400 MHz, CDCl3) d: 9.88 (s, 1H,
wavelength of the diphenylacrylonitrile unit, the fluorescence CHO), 7.83 (d, J = 8.0 Hz, 2H, ArH), 7.03 (d, J = 8.0 Hz, 2H, ArH),
intensities maintained a high level, which were attributed to 4.22 (t, J = 4.0 Hz, 2H, OCH2), 3.90 (t, J = 4.0 Hz, 2H, OCH2),
the cooperative mechanism of AIE and FRET effects between 3.64–3.78 (m, 10H, OCH2), 1.23 (t, J = 4.0 Hz, 3H, CH3).
the diphenylacrylonitrile unit and porphyrin unit based
4.3. Synthesis of compound 3
on the overlap of the emission of diphenylacrylonitrile and
the absorption of the porphyrin. The pseudo Stokes shift of the A mixture of 4-hydroxyphenylacetonitrile (0.14 g, 1.0 mmol),
novel porphyrin liquid crystal was as large as 210 nm and compound 2 (0.28 g, 1.0 mmol) and NaOH (0.10 g, 2.5 mmol) in
the fluorescence quantum yield was 0.12 in the solid state. 30 mL of EtOH solution was stirred for 10 h at room tempera-
Moreover, it exhibited low biotoxicity and excellent fluores- ture. The reaction was monitored by the TLC technique,
cence bio-imaging ability in living cells. In a word, this paper suggesting the disappearance of the materials. After reaction,
reported the first porphyrin liquid crystal with excellent near- 10 mL of HCl solution (1 M) was poured into the reaction
infrared emission in both solution and aggregated states as mixture. The precipitate was formed and filtered. The obtained
well as good fluorescence imaging ability and biocompatibility precipitate was purified by recrystallization in MeOH/CH2Cl2
in living cells, which provided a good strategy for the design (1 : 1, v/v). After dryness, compound 3 was obtained as a pale
and synthesis of novel near-infrared material with excellent yellow solid in a yield of 78%. 1H NMR (400 MHz, DMSO) d: 9.91
self-assembly properties and high fluorescence in both solution (s, 1H, OH), 7.91 (d, J = 12.0 Hz, 2H, ArH), 7.78 (s, 1H, CQCH),
and solid states for application in the bioimaging of living cells. 7.57 (d, J = 8.0 Hz, 2H, ArH), 7.26 (d, J = 8.0 Hz, 2H, ArH), 6.88
(d, J = 8.0 Hz, 2H, ArH), 4.18 (t, J = 4.0 Hz, 2H, OCH2), 3.78 (t, J =
4.0 Hz, 2H, OCH2), 3.40–3.61 (m, 10H, OCH2), 1.10 (t, J = 8.0 Hz,
3H, CH3); MALDI-TOF-MS (C23H27NO5) calcd for m/z = 397.19,
4. Experimental section
4.1. General
found: m/z = 399.04 (MH+), 421.20 (MNa+), 437.63 (MK+).
4.4. Synthesis of compound 4
All chemical reagents were supplied by Aladdin Reagent Co.,
Ltd. and used without further purification. The other organic
solvents and inorganic reagents were purified by standard
anhydrous methods before use. TLC analysis was carried out
by using pre-coated glass plates. Column chromatography was
done by using silica gel (200–300 mesh). NMR spectra were
measured on a Bruker-ARX 400 instrument at 26 1C. Chemical
shifts are reported in ppm with tetramethylsilane (TMS) as an
internal standard. MS spectra were recorded on a Bruker mass
spectrometer. DSC measurements were examined on a Thermal
Analyzer Q100 at a scanning rate of 10 1C minÀ1 under an N2
atmosphere. Mesomorphic texture was observed using a polarization
optical microscope (Leica DMRX) equipped with a temperature-
controlled heating stage (Linkam THMSE 600). X-ray diffraction
(XRD) experiments were performed on a SEIFERT-FPM (XRD7)
diffraction meter using Cu Ka radiation (l = 1.5406 Å) with 40 kV,
30 mA power. UV-Vis spectra were measured on a Varian UV-Vis
spectrometer. Fluorescence spectra were recorded in a conventional
quartz cell (10 Â 10 Â 45 mm) at 25 1C on an Edinburgh
Instruments FS5 spectrometer. The fluorescence absolute FF
values were studied on an Edinburgh Instruments FLS920
Fluorescence Spectrometer with a 6 inch integrating sphere.
Under an N2 atmosphere, a mixture of compound 3 (0.40 g,
1.0 mmol), 1,3-dibromopropane (0.4 g, 2 mmol), and K2CO3
(0.36 g, 2.6 mmol) was stirred and refluxed in 30 mL of dry
MeCN for 20 h. The reaction was monitored by the TLC technique
implying the disappearance of reactants. After reaction, the mixture
was treated with 50 mL of HCl (1 M) and extracted with 30 mL of
CHCl3. The CHCl3 layer was partitioned, washed with 20 mL of
distilled water, dried over anhydrous MgSO4, and then concen-
trated. The residue was treated with 15 mL of MeOH and the
precipitate was obtained. The crude product was further purified by
recrystallization in MeOH/CH2Cl2 (2 : 1, v/v). After dryness, com-
pound 4 was collected as a pale yellow solid in a yield of 69%.
1H NMR (400 MHz, CDCl3) d: 7.83 (d, J = 8.0 Hz, 2H, ArH), 7.57
(d, J = 8.0 Hz, 2H, ArH), 7.34 (s, 1H, CQCH), 6.97 (d, J = 8.0 Hz, 2H,
ArH), 6.94 (d, J = 8.0 Hz, 2H, ArH), 3.50–4.19 (m, 18H, OCH2), 2.30–
2.36 (m, 2H, CH2), 1.20 (t, J = 8.0 Hz, 3H, CH3); MALDI-TOF-MS
(C26H32NO5) calcd for m/z = 519.14, found: m/z = 520.01 (MH+).
4.5. Synthesis of compound 5
Under an N2 atmosphere, a mixture of compound 4 (0.52 g,
1.0 mmol), 4-hydroxybenzaldehyde (0.20 g, 1.6 mmol) and
K2CO3 (0.28 g, 2.0 mmol) was stirred and refluxed in 25 mL
of dry MeCN for 24 h. The reaction was monitored by the TLC
4.2. Synthesis of compound 2
A mixture of 4-hydroxybenzaldehyde (0.4 g, 2.0 mmol), com- technique implying the disappearance of reactants. After reaction,
pound 1 (0.25 g, 2.0 mmol), K2CO3 (0.5 g, 3.7 mmol) and KI the mixture was treated with 30 mL HCl (1 M) and extracted with
(0.1 g, 0.6 mmol) in 40 mL of dry MeCN was stirred and refluxed 30 mL of CHCl3. The CHCl3 layer was partitioned, washed with
for 12 h. After reaction and cooling, 20 mL of HCl solution (1 M) 15 mL of distilled water, dried over anhydrous MgSO4, and then
and 40 mL of CHCl3 were added. Then the CHCl3 layer was concentrated. The residue was treated with 15 mL of MeOH and
partitioned, washed with 20 mL of distilled water, dried over the precipitate was obtained. The crude product was further
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purified by column chromatography using CH2Cl2/hexane and Technology Project (2018-G-44), and the Undergraduate
(1: 1, v/v) as an eluent. After dryness, compound 5 was obtained innovation program of FJNU (2019) was greatly acknowledged.
as a pale yellow solid in a yield of 82%. 1H NMR (400 MHz,
CDCl3) d: 9.87 (s, 1H, CHO), 7.83 (d, J = 8.0 Hz, 4H, ArH), 7.56 (d,
J = 8.0 Hz, 2H, ArH), 7.33 (s, 1H, CQCH), 6.93–7.03 (m, 6H, ArH),
3.48–4.27 (m, 18H, OCH2), 2.28–2.34 (m, 2H, CH2), 1.20 (t, J = 8.0 Hz,
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