Self-assembled star-shaped aza-BODIPY mesogen affords white-light emission

Article abstract of DOI:10.1039/c9nj04755g

A novel multifunctional star-shaped aza-BODIPY mesogen was synthesized by a click reaction. This star-shaped aza-BODIPY mesogen undergoes self-assembly into a hexagonal columnar phase in its bulk state and spherical gels in organic solvents. Based on the

Full text of DOI:10.1039/c9nj04755g

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Self-assembled star-shaped aza-BODIPY mesogen
affords white-light emission†
Chao Liu,‡a Wei Ding,‡a Yuantao Liu,a Hongmei Zhaoa and Xiaohong Cheng
Cite this: New J. Chem., 2020,
44, 102
ab
*
A novel multifunctional star-shaped aza-BODIPY mesogen was synthesized by a click reaction. This star-shaped
aza-BODIPY mesogen undergoes self-assembly into a hexagonal columnar phase in its bulk state and spherical
gels in organic solvents. Based on the investigation of the absorption and emission spectra and surface
morphologies, J-aggregates are observed in their liquid crystalline (LC), gel and solid states, while H-aggregates
are observed in n-hexane solution. Additionally, this star-shaped aza-BODIPY mesogen acts as a chemosensor
toward CNꢀ ions via a nucleophilic addition reaction, and the corresponding addition product can yield white
light emission (WLE) upon doping with blue dye. This star-shaped aza-BODIPY mesogen is represented as the
first example of an aza-BODIPY derivative with LC, organogel and white light emission properties.
Received 18th September 2019,
Accepted 18th November 2019
DOI: 10.1039/c9nj04755g
rsc.li/njc
B100 nm red shift in the absorption region of 600–800 nm.17 Thus,
aza-BODIPY shows all the important features of BODIPY such as
1. Introduction
The self-assembly of organic dyes has provided a powerful tool narrow absorption and emission bands with high molar absorption
to design novel nano-functional materials with distinct optical coefficients and fluorescence quantum yields in the visible-NIR
and electrochemical properties. By controlling the non-covalent region which are essential for their applications in photodynamic
interactions of photo- and redox-active dye molecules, extended therapy (PDT), sensors and photosynthetic model systems.18 The
superstructures up to mesophase materials and organogels1 relatively easy access to specific derivatives has now enabled
with controlled exciton coupling and energy transport in p-stacked aza-BODIPYs to be applied in diverse technologies extending
materials2,3 can be realized. Among the materials realized so far, from real-time fluorescence imaging to solar energy materials, and
J-aggregates4 have attracted considerable attention because of optoelectronic devices. To date, although a few BODIPY based liquid
their excellent photophysical characteristics with strong and crystals and organogels with excellent photophysical performance
narrow J-bands, a long exciton lifetime and high fluorescence have been reported,19–21 to the best of our knowledge, aza-BODIPY
quantum yields.5 J-aggregates have been found in several based liquid crystals and organogels have never been reported.
p-conjugated systems, such as oligo(p-phenylenevinylenes) (OPVs),6 Therefore it is significantly worthwhile to develop aza-BODIPY based
porphyrins,7 merocyanines,8 boradiazaindacenes (BODIPYs),9 LCs and organogels with the purpose of obtaining novel functional
perylene bisimides,10 and 8-aza-boradiazaindacenes (aza-BODIPY) materials.
dyes.11,12 A few examples of J-aggregates have also been observed
Click chemistry namely Cu(I) catalyzed azide–alkyne cycloaddi-
in thermotropic liquid-crystalline (LC) phases of perylene tion (CuAAC)22 provides an easy access to obtain novel aza-BODIPY
bisimides,2b,13,14 porphyrins,15 and ionic cyanine dyes.16 Dye NIR dyes for various applications. For example click reactions have
aggregates are capable of producing new optical or electronic been used for the attachment of multi-donor BODIPY chromo-
functions that are not possible in a single dye molecule. There- phores to a central aza-BODIPY acceptor as a dendritic BODIPY
fore, it is very important to study the aggregation states of dyes. antenna for light harvesting.23 A new triad (BDP-ADP-C60) in
Aza-BODIPY dye is derived from BODIPY where the meso-carbon which an ADP (Aza-boron-dipyrrin) core is covalently linked to a
is replaced by nitrogen. Compared with BODIPY, aza-BODIPY shows BDP (a monostyryl boron-dipyrrin) moiety via a click reaction and a
C
60 unit using the Prato reaction in its two side arms can serve as an
artificial photosynthetic model.24 The water-soluble aza-BODIPY
derivatives are synthesized by attaching tetraethylene-glycerol groups
to the central aza-BODIPY via a click reaction which could serve as
near-infrared (NIR) emitting fluorescent probes.25
a Key Laboratory of Medicinal Chemistry for Natural Resources,
Chemistry School of Chemical Science and Technology, Yunnan University,
Kunming, 650091, P. R. China
b School of Chemistry and Chemical Engineering, Yangtze Normal University,
Fuling, 408100, P. R. China. E-mail: xhcheng@ynu.edu.cn;
Fax: +86 871 65032905
White-light emissive materials have drawn widespread
attention owing to their potential in day-to-day lighting systems
and display media.26–28 In general, white-light emission can be
fabricated by mixing three primary colors (red, green and blue)29
† Electronic supplementary information (ESI) available. See DOI: 10.1039/
c9nj04755g
‡ Both authors contributed equally to this work.
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or two complementary colors (yellow and blue)30 via a dry or emission) were studied on UNIC UV2600A and HITACHI F-7000
solution process. So far as we know, no aza-BODIPYs have been spectrophotometers.
used to generate WLE materials.
SEM experiments were performed on a ZEISS SIGMA 300
Considering the great potential application of aza-BODIPYs, scanning electron microscope (SEM, GER). All pictures were
here the first example of a star-shaped aza-BODIPY columnar taken digitally. For sample preparation, the gel was placed on
mesogen consisting of an aza-BODIPY core surrounded by four an aluminium foil for some time until the gel became dry, and
flexible 1,2,3-triazole dendritic paddles was synthesized effi- then the sample was gold plated. Finally the sample was used
ciently via the CuAAC click reaction. This compound undergoes for SEM analysis.33
self-assembly into a thermotropic hexagonal columnar meso-
The small-angle powder diffraction (SAXS) experiment was
phase and spherical organogels. Optical and morphological performed in transmission mode with synchrotron radiation at
investigation unveils that J-aggregates can be observed in its the 1W2A SAXS beamline and the beamline BL16B1 at the
LC, solid and gel states, while H-aggregates can be observed in Shanghai Synchrotron Radiation Facility (SSRF).34 A modified
its hexane solution. Furthermore this compound can serve as a Linkam hot stage with thermal stability within 0.2 1C was used,
chemosensor toward the cyanide ion (CNꢀ), which is the most with a hole for the capillary drilled through the silver heating
toxic inorganic anion for living organisms, via nucleophilic block and mica windows attached to it on each side. The
addition.31 Most interestingly, the obtained addition product samples were held in a poly(imide) (Kapton) film. A MarCCD
can yield white light emission upon doping with thiophene 165 detector was used. The q calibration and linearization were
acetylene bolaamphiphile. Thus LC, organogel and WLE proper- verified using several orders of layer reflections from silver
ties were observed simultaneously in this aza-BODIPY derivative. behenate. Positions and intensities of the diffraction peaks
were measured using PeakSolvet (Galactic).
For electron density reconstruction, Fourier reconstruction
of the electron density was carried out using the general
formula for 2D periodic systems:
2. Results and discussion
2.1. Materials and methods
E(xy) = Shk sqrt[I(hk)] exp[i2p(hx + ky) + Fhk]
Commercially available reagents are used as received. Solvents were
dried and distilled prior to use based on previously reported
For the centrosymmetric structures considered in this work,
procedures.32 1H NMR and 13C NMR spectra were recorded on
the phase angle F can take up the values of 0 or p. The choice of a
phase combination was initially made depending on the merit of
Bruker-DRX-400 and Bruker-DRX-600 spectrometers. Elemental
analysis was performed by using an Elementar VARIO EL elemental
each reconstructed electron density map obtained using the most
analyzer. Thin-layer chromatography (TLC) was carried out on
intense reflections, combined with the additional knowledge of
aluminum plates pre-coated with 5735 silica gel 60 PF254 (Merck).
the molecules (molecular shape, length, volume of each part and
Column chromatography was performed with Merck silica gel 60
the distribution of electron density among the different moieties).
(230–400 mesh). A Mettler heating stage (FP 82 HT) was used for
polarizing optical microscopy (POM, Optiphot 2, Nikon) and DSC
2.2. Synthesis
data were recorded with a DSC 200 F3 Maia calorimeter (NETZSCH)
at 10 K minꢀ1. Their optical properties (UV-vis and fluorescent
The target compound ADP/12 was synthesized by the Michael
reaction and the click reaction23 as the key steps (Scheme 1).
Benzaldehyde 1 and acetophenone 2 were obtained by etherifi-
cation of 4-hydroxybenzaldehyde and 4-hydroxyacetophenone
with propargyl bromide, respectively. Benzaldehyde 1 reacted
with acetophenone 2 giving diaryl a,b-unsaturated ketone 3.
Nitromethane was added to the a,b-unsaturated ketone 3 via
Michael addition. The obtained 1,3-diaryl-4-nitrobutanone 4 was
condensed with ammonium acetate giving aza-dipyrrin 5. Com-
plexation of aza-dipyrrin 5 with BF3ꢁEt2O in the presence of
diisopropylethylamine (DIPEA) gave terminal alkyne 6. The final
product ADP/12 was obtained by a click reaction between the
terminal alkyne 6 and azide 7.
2.3. Mesomorphic properties
The mesomorphic behavior of ADP/12 was investigated by polarizing
optical microscopy (POM), differential scanning calorimetry (DSC)
and X-ray diffraction (XRD). The phase transition is summarized
in Fig. 1. The color of the sample was deep blue, under POM, and
Scheme 1 Synthesis of compounds ADP/12. Reagents and conditions:
(i) 3-bromopropyne, acetone, K2CO3, 90 1C, 8 h, 93%; (ii) 3-bromopropyne,
DMF, K2CO3, 90 1C, 8 h, 94%; (iii) C2H5OH, KOH, H2O, RT, 6 h, 89%;
(iv) CH3NO2, (C2H5)2NH, CH3OH, reflux, 12 h, 76%; (v) NH4OAc, C2H5OH,
no texture could be observed. The sample had high viscosity but
could flow under shearing. Upon heating the sample to 99.4 1C,
80 1C, 48 h; (vi) BF3ꢁEt2O, DIPEA, CH2Cl2, RT, 10 h, 31%; (vii) tert-butanol, THF,
H2O, sodium ascorbate, CuSO4ꢁ5H2O, RT, 12 h, 75%.
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Table 1 Gelation test results of compounds ADP/12a
Solvent
ADP/12
Solvent
ADP/12
Ethyl acetate
Acetone
DMF
Toluene
Acetonitrile
Dichloromethane
G
P
G
S
P
S
Chloroform
n-Hexane
Petroleum ether
1,4-Dioxane
Methanol
S
S
P
S
P
P
Ethanol
a
G = gel, S = soluble, and P = precipitation.
molecule organizes into a one-dimensional (1D) disk-like stratum,
and then the 1D disks stake into columns which further arrange into
a 2D hexagonal columnar mesophase. It is worth noting that the
intercolumnar distance (namely the lattice parameter a = 4.34 nm) of
ADP/12 is much smaller than the fully extended molecular length
(L = 6.8 nm, calculated by MM235). In this way, the discotic molecule
should be tilted with respect to the cross-section of each disk-like
stratum. From the longitudinal offset, the tilt superposition angle in
the column was estimated to be y = 421 in the Colhex phase with
respect to the long axis of the column.3 Such a packing model (Fig. 2)
is in correspondence with p-stacked aggregates with a J-type
parallel stacking mode in the LC state based on the spectral
studies (see Fig. 4 in the section of photophysical properties and
aggregation in LC, gel and solvents).
Fig. 1 Structure of compound ADP/12 with transition temperatures (T/1C)
and the associated enthalpy values as determined by DSC (peak tempera-
tures, 10 K minꢀ1); Cr = crystal; Colhex = hexagonal columnar phase; and
Iso = isotropic liquid.
the viscosity of the sample was suddenly lost and the sample
changed into flowing liquid. Upon cooling the sample to 75.4 1C,
the sample showed high viscosity again. The DSC curve of ADP/12
is shown in Fig. S1 (ESI†). During the heating cycle, it showed a
mesophase–isotropic transition with an enthalpy change of
0.39 kJ molꢀ1 at 99.4 1C, while during the cooling cycle, it showed
an isotropic– liquid mesophase transition with an enthalpy
change of 1.05 kJ molꢀ1 at 75.4 1C. This is in accordance with
the POM observation, and therefore ADP/12 is an enantiotropic
(thermodynamically stable) room temperature LC.
2.4. Gel self-assembly
The mesomorphic phase was further investigated with SAXS.
The XRD pattern of the columnar phase of the compound ADP/12
showed three small-angle reflections, and their reciprocal spacings
in a ratio of 1 : 31/2 : 2, which are consistent with the 10, 11, 20
reflections of the hexagonal lattice with p6mm symmetry. The
number of molecules (m) in the slice of the columns with a height
of h = 0.45 nm (the maximum of the measured diffuse wide-
angle scattering ddiff) is 1 (Table S3, ESI†). This indicates that one
The gelation test of the compound ADP/12 was performed in several
organic solvents as shown in Table 1. The gels were prepared by
cooling the heated solution of ADP/12 (10 mg mlꢀ1) quickly below
20 1C or slowly down to room temperature. And the method ‘‘stable
to inversion of the container’’36 was used to judge gel formation.
The compound ADP/12 could form gels in organic solvents such
as ethyl acetate and DMF. The morphologies of the xerogels were
observed by SEM. The SEM image of the xerogel formed in EA
Fig. 2 Colhex/p6mm phase of ADP/12 (a) XRD patterns at T = 55 1C; (b) reconstructed electron density map of the Colhex/p6mm phase; (c) snapshot of
the Colhex/p6mm phase after MD annealing; and (d) the model for the Colhex phase.
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Fig. 3 SEM images of the xerogels (a) ADP/12 in ethyl acetate; scale bar is 20 mm, (b) ADP/12 in DMF; scale bar is 10 mm, and the inset shows ADP/12 in
DMF; scale bar is 1 mm.
showed irregular nanospheres with an average diameter of 6–20 mm polarity exhibiting 688–697 nm for solvents like CH2Cl2, THF,
(see Fig. 3), while the xerogel formed in DMF showed more regular toluene and DMF,whereas the fluorescence spectra of ADP/12
nanospheres with an average diameter of 4 mm.
exhibit a positive solvatochromism (red-shifted) with an increase
of the polarities of the solvents from 731 nm (CH2Cl2) to 734 nm
(toluene) to 735 nm (THF) and 744 nm (DMF) with Stokes shifts
of 41–47 nm. ADP/12 shows fluorescence quantum yields (FFL)
from 0.37 to 0.39 in different polarity organic solvents relative to
rhodamine B in ethanol (FFL = 0.67). Interestingly, a broad spectrum
with a blue-shifted absorption band of ADP/12 in n-hexane
(1 ꢂ 10ꢀ6–5 ꢂ 10ꢀ5 M) was observed, while the luminescence
was totally quenched, indicating that H-aggregates were formed
in n-hexane. Furthermore, the SEM image (Fig. 4d) of ADP/12 in
n-hexane reveals the presence of irregular spherical aggregates
(an average diameter of 7–9 mm), which were different in both
the shape and size as observed from the morphologies for the
xerogels (Fig. 3). The UV-vis absorption spectrum of ADP/12 in
the film, LC (40 1C) and gel states was also recorded. The film
exhibits a broad and intensive absorption band in the range of
600–750 nm with an absorption maximum at 713 nm. The
absorption peaks in the solid and LC states are red-shifted by
25 nm and 23 nm, respectively, compared to those in THF
solution, which indicated the formation of p-stacked aggregates
with a J-type parallel stacking mode in the solid and LC states.
Combining all experimental evidence, different packing models
of ADP/12 have been proposed in Scheme 2.
2.5. Photophysical properties and aggregation in LC,
gel and solvents
Dye aggregates with a narrow absorption band that is shifted to
a longer wavelength (bathochromically shifted) compared with
the monomer absorption band are usually referred to as Scheibe
aggregates or J-aggregates (J denotes Jelley).37,38 Aggregates with
absorption bands shifted to a shorter wavelength (hypsochromi-
cally shifted) compared with the monomer band are termed as H-
aggregates39 (H denotes hypsochromic shift). For the compound
ADP/12, the UV-vis absorption and fluorescence spectra in THF
solution (1 ꢂ 10ꢀ5 M) are shown in Fig. S3 (ESI†). ADP/12 shows a
Q-band between 600 and 750 nm with an absorption maximum at
694 nm, which coincides with that of other aza-BODIPY dyes.40
The emission spectrum is nearly a mirror image of the absorption
spectrum, and the maximum emission in THF is at 735 nm.
To gain an insight into the solvatochromic behavior of ADP/12,
the UV-vis absorption and fluorescence emission were investigated
in different organic solvents (see Fig. 4), and the photophysical
data are summarized in Table 2. As shown in Fig. 4a, the UV-vis
absorption spectrum of ADP/12 is less influenced by the solvent
2.6. Chemosensor behavior
The active meso CQN bond of aza-BODIPY is prone to nucleo-
philic attack by anions. Therefore, aza-BODIPY can serve as an
Table 2 UV-vis absorption and fluorescence spectroscopy data of ADP/12
(1 ꢂ 10ꢀ5 M) at 20 1C
Stokes shiftsb (nm)
a
Comp.
State
lex/nm
lem/nm FFL
ADP/12 THF
694
659
688
693
697
713
735
—
731
734
744
—
—
—
—
0.38 41
c
n-Hexane
—
—
CH2Cl2
Toluene
DMF
0.37 43
0.38 41
0.39 47
Film
—
—
—
—
—
—
—
—
LC (40 1C) 711
Gel (EA) 707
Gel (DMF) 704
Fig. 4 (a) The absorption spectra of ADP/12 in different solvents and
(b) the emission spectra of ADP/12 in different solvents. (c) The absorption
spectra of ADP/12 in different states and (d) the SEM images of ADP/12
solution in n-hexane.
a
b
Relative to rhodamine B in ethanol (FFL = 0.65) as the standard.
Stokes shifts = lem ꢀ lex. Not measured.
c
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fluorescence spectra of ADP/12 in the presence of other anions
but there was no significant change in both the absorption and
fluorescence spectra.
To assess the binding properties of ADP/12 to CNꢀ, fluores-
cence titration curves of ADP/12 were obtained in THF solution.
Upon increasing the addition amount of CNꢀ (from 1 to 10 equiv.),
the emission intensity of ADP/12 at 726 nm slowly decreased while
the emission band at 630 nm increased (Fig. 5b). For a better
understanding of the coordination of ADP/12 with CNꢀ, fluores-
cence titration in the case of varying mole fractions of CNꢀ ion
in THF solution was carried out. The fluorescence Job’s plot
analysis showed 1 : 1 stoichiometry between ADP/12 and CNꢀ
(Fig. S5b, ESI†). The detection limit of ADP/12 to CNꢀ was
measured based on 3s/k to be 3.69 ꢂ 10ꢀ5 mol Lꢀ1 41
.
It is
well-known that some food contains cyanogenic glycosides,
such as bitter almond,42 cassava43 and sprouting potato.44 The
cyanide is generated by enzymatic hydrolysis of cyanogenic glyco-
sides when their tissues are damaged. So we further explored the
Scheme 2 Proposed packing models for the self-assembly of ADP/12.
anion sensor based on a chemical reaction.31a Thus we tested potential application of ADP/12 for determining cyanide in a food
the anion sensing behavior of aza-BODIPY with various anions. sample. Thus, direct detection of CNꢀ was further studied on a
After ten equivalents of different anions, including Brꢀ, Clꢀ, Iꢀ, sprouting potato. The sprouting potato was cut into fresh slices at
HSO4ꢀ, NO2ꢀ, N3ꢀ, CO32ꢀ, NO3ꢀ, Fꢀ, H2PO4ꢀ, AcOꢀ and CNꢀ, room temperature. After being incubated with ADP/12 solution,
were added to ADP/12 solution (1 ꢂ 10ꢀ5 M), respectively, a it did not show any significant change in color under daylight
change in the color from blue to light yellow under daylight (Fig. 6a and c). However, a remarkable yellow–green color was
(Fig. S4b, ESI†) and yellow colour emission under UV light observed under UV light (365 nm) (Fig. 6b and d). According to
could be observed with the naked eye in the presence of CNꢀ, a previous report, the CQN bond of aza-BODIPY can undergo a
while no visible color changes were noticed in the case of the nucleophilic addition reaction with CNꢀ.31a Therefore a nucleo-
other anions (Fig. 5c). This indicates that compound ADP/12 philic addition product ADP-CN was supposed to be formed.
can be used as a specific sensor for CNꢀ.
However many efforts to run the 1H NMR experiment for this
The fluorescence profiles of ADP/12 in the presence of 10 equiv. nucleophilic addition product failed. Only unclear and broader
1
of the selected anions in THF solution were investigated. Upon the peaks were observed in the H NMR spectra for this nucleophilic
addition of CNꢀ, the absorption spectrum of ADP/12 was largely addition product. Therefore we have turned to verify the nucleophilic
quenched at 694 nm and enhanced at 445 nm (Fig. S4a, ESI†). addition product between intermediate 6 and CNꢀ. Intermediate 6
The fluorescence of ADP/12 was largely quenched at 726 nm and contained the same CQN bond of aza-BODIPY but without a triazole
significantly enhanced at 630 nm (Fig. 5a). We also tested the group and a flexible alkyl chain. The results showed that compound 6
Fig. 5 (a) The fluorescence response of ADP/12 upon addition of different anions. (b) Fluorescence titration spectra of ADP/12 in THF (1 ꢂ 10ꢀ5 M) upon
addition of different amounts of CNꢀ (TBACN) ion (0–10 equiv.) (lex = 430 nm), and (c) the samples with addition of different metal ions, under irradiation
with 365 nm light.
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Fig. 6 Photographs taken under ambient light (a and c) and UV light (b and d): (a and b) a freshly cut potato slice; (c and d) after incubating the potato
slice with ADP/12 solution.
showed similar spectral changes as compound ADP/12 (Fig. S6, ESI†) added into 6, the peak of the alkyne protons completely disappeared.
1
upon addition of different anions. The H NMR spectra of 6 in the The methylene protons of OCH2 appeared as four sets of singlets in
absence and presence of different equivalents of TBACN (tetrabutyl- the region of 4.61–4.75 ppm (Fig. 7d). With the disappearance of
ammonium cyanide) in CDCl3 were recorded as shown in Fig. 7. The alkyne protons, the small coupling between alkyne protons and
1H NMR spectrum of compound 6 showed that the CH protons of the ArOCH2 methylene became much weaker. When 6 and TBACN
pyrrole rings appeared at 6.99 ppm. The aryl protons appeared as two formed a 1 : 1 mixture, the small coupling completely disappeared,
sets of multiplets in the region of 8.03–8.08 ppm and 7.06–7.10 ppm, and thus the methylene protons of OCH2 appeared as singlets
and the methylene of the OCH2 protons appeared as multiplets at instead of multiplets. Based on this experiment, it could be
4.76–7.79 ppm and the alkyne protons appeared as two singlets at concluded that a nucleophilic addition reaction between the
2.60 ppm and 2.57 ppm. The intermediate 6 is a symmetrical CQN bond of aza-BODIPY and CNꢀ ion could be observed,
compound. After addition of CNꢀ ion to the intermediate 6, and after the nucleophilic addition reaction with CNꢀ, addition
the resulting product 6-CN showed an asymmetric structure products 6-CN and ADP-CN could be obtained.
(Fig. S7, ESI†). Thus the CH protons of the pyrrole rings changed
2.7. White light emission
into two singlets at 6.54 ppm and 6.64 ppm, respectively. The aryl
protons changed into eight sets of doublets in the region of Both the addition products 6-CN and ADP-CN obtained by the
6.81–8.16 ppm (Fig. 7b–d). Upon increasing the amount of above mentioned nucleophilic addition reactions between CNꢀ
cyanide ions, the peak of the alkyne protons gradually reduced ion and the intermediate 6 or ADP/12 were separated and their
and the peak of the methylene protons of N–CH2 from TBACN optical properties were studied. Both 6-CN and ADP-CN emitted
gradually increased (Fig. 7a–d). When 1.0 equiv. of CNꢀ was yellow colours in THF (500–800 nm). Their CIE coordinates
Fig. 7 1H NMR (400 MHz, CDCl3) spectra of (a) free compound 6; (b) 0.4 equiv. of CNꢀ added into 6; (c) 0.7 equiv. of CNꢀ added into 6; and (d) 1.0 equiv.
of CNꢀ added into 6.
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such a columnar aza-BODIPY liquid crystal shows great potential
in many fruitful applications.
Conflicts of interest
There are no conflicts to declare.
Fig. 8 (a) Emission spectrum of the gel of ADP-CN (1 ꢂ 10ꢀ5 M) + 2ET/12
(1 ꢂ 10ꢀ5 M); the inset shows the photo of the 2ET/12, ADP-CN + 2ET/12,
ADP-CN solutions in THF under 365 nm UV light and (b) the CIE coordinates
of ADP-CN + 2ET/12.
Acknowledgements
This work was financially supported by the National Natural
Science Foundation of China (No. 21865038 and 21664015) and
the program for Innovative Research Team (in Science and
Technology) in University of Yunnan Province (2018FY001(-012)).
We thank beamline 1W2A at the Beijing Accelerator Laboratory
and beamline BL16B1 at the Shanghai Synchrotron Radiation
Facility (SSRF), China.
were found to be (0.59, 0.41) (Fig. S9, ESI†) and (0.56, 0.43)
(Fig. 8), respectively. Therefore, they could generate white-light
emission upon blending with a dopant emitting complemen-
tary color (blue emission). We selected our previously reported
blue emissive 5,50-bis(phenylethynyl)-2,20-bithiophene-based
bolaamphiphile 2ET/1245 as a dopant. The CIE coordinates of
6-CN and 2ET/12 (0.14, 0.23) or ADP-CN and 2ET/12 can be
connected in line with the coordinates of the white light area.
The absorption spectrum of 6-CN showed a band around
394–568 nm and ADP-CN showed two bands around 403–597 nm
and 697–800 nm, respectively. The emission spectra of 2ET/12
showed emission peaks centered at 465 nm. The partial overlap of
the spectrum of 2ET/12 and 6-CN (or ADP-CN) indicated energy
transfer from 2ET/12 to 6-CN (or ADP-CN) solutions (in THF) and
also possibility to tune their emission colors (Fig. S8, ESI†).
Two mixtures were prepared by doping 0.01 mL of 2ET/12 solution
(1 ꢂ 10ꢀ4 mol Lꢀ1 in THF) into 3.5 mL 6-CN or ADP-CN solution
(1 ꢂ 10ꢀ5 mol Lꢀ1 in THF). The emission spectrum of the two
mixtures covered the spectral range of 400–750 nm (Fig. 8a). The
CIE coordinates were found to be (0.33, 0.31) for 2ET/12 + 6-CN
(Fig. S9, ESI†) or (0.33, 0.33) for 2ET/12 + ADP-CN, respectively
(Fig. 8b). The CIE coordinates of 2ET/12 + 6-CN were quite close to
those of the ideal white light emission (0.33, 0.33), while the CIE
coordinates of 2ET/12 + ADP-CN were those of the ideal white light
emission.46 Such anion tunable WLE should have great potential
for detection of the most toxic inorganic anion CNꢀ in living
organisms and fabrication of stimuli responsive devices.
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