Photo-responsive cyclodextrin/anthracene/Eu3+ supramolecular assembly for a tunable photochromic multicolor cell label and fluorescent ink

Article abstract of DOI:10.1039/c9sc00026g

A photo-responsive supramolecular assembly was successfully constructed through the stoichiometric 2?:?1 non-covalent association of two 4-(anthracen-2-yl)pyridine-2,6-dicarboxylic acid (1) units in one γ-cyclodextrin (γ-CD) cavity, followed by the subsequent coordination polymerization of the γ-CD·1₂ (1₂ = two 1) inclusion complex with Eu(iii). Interestingly, owing to the photodimerization behavior of anthracene units and the excellent luminescence properties of Eu(iii), the Eu³⁺?γ-CD·1₂ system showed multicolor fluorescence emission from cyan to red by irradiation for 0-16 minutes. Moreover, white light emission with CIE coordinates (0.32 and 0.36) was achieved at 4 min. Importantly, white light-containing multicolor emission could be obtained in water, solid films and living cells. Especially, the Eu³⁺?γ-CD·1₂ system could tag living cells with marvelous white fluorescence and display no obvious cytotoxicity. Thus, this supramolecular assembly offers a new pathway in the fields of tunable photochromic fluorescent ink and cell labelling.

Full text of DOI:10.1039/c9sc00026g

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Photo-responsive Cyclodextrin/Anthracene/Eu3+
Supramolecular Assembly for a Tunable Photochromic
Multicolor Cell Label and Fluorescent Ink
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
Weilei Zhou,a Yong Chen,a Qilin Yu,a,c Peiyu Li,a Xuman Chena and Yu Liu*a,b
www.rsc.org/
A photo-responsive supramolecular assembly was successfully constructed through the stoichiometric 2:1 non-covalent
association of two 4-(anthracen-2-yl)pyridine-2,6-dicarboxylic acid (1) in one -cyclodextrin (-CD) cavity, followed by the
subsequent coordination polymerization of γ-CD·12 (12 = two 1) inclusion complex with Eu(III). Interestingly, owing to the
photodimerization behavior of anthracene units and the excellent luminescence property of Eu(III), the Eu3+γ-CD·12
system showed multicolor fluorescence emission from cyan to red by irradiating for 0 - 16 minutes. Moreover, white light
emission with CIE coordinates (0.32, 0.36) was achieved at 4 min. Importantly, white light-containing multicolor emission
could be obtained in water, solid film and living cells. Especially, the Eu3+γ-CD·12 system could tag living cells with
marvelous white fluorescence and display no obvious cytotoxicity. Thus, this supramolecular assembly offers a new
pathway in the field of tunable photochromic fluorescence ink and cell labelling.
Introduction
supramolecular assembly. Recently, we constructed
a
host−guest complexes by dipolar dyes styrylpyridiniums and
cucurbituril in which the white-light emission was obtained by
the addition of cucurbit[7]urils to methylated styrylpyridiniums
for adjusting the stacking direction in water.12
Pseudorotaxanes and rotaxanes as one typical species of
molecular machines are challenging and interesting due to
their mechanically interlocked topologies1 and unique
photophysical properties, leading to the widely applications in
biomedicine2, nanotechnology3, smart materials4 and so on. In
particular, functional fluorescent rotaxanes5 are of major
importance, which draw more and more attentions by
scientists and engineers. Multicolor emission, especially white-
light emission, have various applications in solid-state lighting6
and display media owing to their superior color fidelity and
low color distortion.7 Generally, white light emission could be
achieved by different methods in inorganic and organic
materials.7b,8 Among them, the mixing of several fluorophores
with complementary emission colors become a popular
strategy,9 and the dynamic reversible property of
supramolecular system and molecular assembly strategy
played an important role. For instance, Tian et al.10 reported a
white-light emission supramolecular assembly by changing the
excitation wavelength and host−guest interactions in water.
Tao et al.11 reported a white-light emission supramolecular
polymer based on cucurbituril and oligo (p-phenylenevinylene)
by altering different amounts of cucurbit[8]urils in
Materials in response to externally photo-modulating,
accompanied with the changes in physicochemical properties
have draw much attention to extensively research because of
potential applications in the various fields. Among all kinds of
the stimuli-responsive artificial devices, it is beneficial to
design luminescent materials based on lanthanide ions due to
their unique luminescence properties, such as long-lived
excited states, visible-light emission and narrow emission
bandwidths, which could be easy to distinguish from shorter-
lived (ns-based) autofluorescence from biological material.13
Although the multicolor luminescence has been reported
several times recently, the studies on the in-situ technique are
still rare,7c particularly photo-tuning single lanthanide ion for
multicolor luminescence including white light in aqueous
solution remains a challenge. Herein, combining photo-tunable
luminescent lanthanide,13c photo-erasable fluorescent ink14
and cell imaging15 of our previous reports, we designed a light-
sensitive rotaxane network in aqueous solution from γ-
cyclodextrin (γ-CD), 4-(anthracen-2-yl)pyridine-2,6-dicarboxylic
acid (1) and Eu(III) as showed in Fig. 1. The complexation of -
CD with 1 in 1:2 molar ratio led to the formation of a
pseudo[3]rotaxane in aqueous solution. Furthermore, Eu(III)
could coordinate with the carboxylic groups of
pseudo[3]rotaxanes resulting in the formation of
supramolecular network assembly. Significantly, the multicolor
fluorescence emission varying from cyanwhitered could
a. College of Chemistry, State Key Laboratory of Elemento-Organic Chemistry,
Nankai University.
b. Collaborative Innovation Center of Chemical Science and Engineering, Tianjin
300072, P. R. China.
c. Key Laboratory of Molecular Microbiology and Technology, College of Life
Sciences, Nankai University.
Electronic
Supplementary
Information
(ESI)
available:
See
DOI: 10.1039/x0xx00000x
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be achieved by irradiating the pseudorotaxane network for 0 - experiments at 25°C. Electrospray ionization massVsiepweAcrtticrlae O(EnlSinIe-
16 minutes, and these white light-containing multicolor MS) were measured by Agilent 6520 DQO-I:T1O0.F1-0M39S/C. 9QSCu0a0n0t2u6mG
emission consequently enabled the potential applications of yields were measured by an Edinburgh Instruments FS5 near-
pseudorotaxane network as tunable photochromic infrared spectrometer, with a 450 W xenon lamp as the
fluorescence ink and cell labelling. This supramolecular excitation source. The 0.1 mM Eu3+γ-CD·12 (pH=9) solution
approach to obtain multicolor and white light emission by were used to measure the quantum yield of irradiation for 0
controlling the photoirradiation time would provide a new min with an excitation of 365 nm, and the collection range was
strategy for smart optical materials.
from 345 nm to 800 nm. The quantum yield of Eu3+γ-CD·12
solution after irradiation for 4 min and 16 min were
respectively measured with an excitation of 290 nm, and the
collection range was from 260 nm to 800 nm. Human lung
adenocarcinoma cells (A549 cells, purchased from the Cell
Resource Center, China Academy of Medical Science, Beijing,
China) were cultured in F12 medium containing 10 % fetal
bovine serum (FBS). A549 cells were seeded in 96-well plates
o
(5×104 cell mL–1, 0.1 mL per well) for 24 h at 37 C in 5 % CO2,
and then incubated with Eu3+γ-CD·12 ([Eu3+]= 2 μM, [γ-CD] =
4 μM, [12] = 8 μM) for another 24 h. The relative cellular
viability was determined by MTT assay. A549 cells were
seeded in 6-well plates (5×104 cell mL–1, 2 mL per well) for 24 h
at 37 oC in 5% CO2. The cells were incubated with the
corresponding solution for 12 h. After removing the medium,
the cells were washed with phosphate buffer solution for
three times and fixed with 4 % paraformaldehyde for 15 min.
Finally, the cells were subjected to observation by a confocal
laser scanning microscope.
Fig.
1
Schematic illustration of -cyclodextrin/anthracene/Eu3+
supramolecular assembly and tunable lanthanide luminescence
driven by reversible photo-cyclodimerization.
Synthesis of 3
Experimental
A three neck flask was charged with 4 (181.2 mg, 0.6 mmol), 5
(111.0 mg, 0.5 mmol), K2CO3 (400.5 mg, 2.89 mmol), toluene
(50 mL) and H2O (12.5 mL), the resulting solution was
degassed via three freeze-pump-thaw cycles. Pd(PPh3)4 (107.2
mg, 0.0926 mmol) was then added under an argon
Materials and methods
All chemicals were commercially available unless noted
otherwise. Compound 4 was prepared according to the
literatures procedure.16 Compounds 2, 5 and 6 were purchased
from Heowns. NMR spectroscopy was recorded on a Brucker
AV400 spectrometer. Fluorescence spectroscopy was recorded
in a conventional quartz cell (light path 10 mm) on a Varian
Cary Eclipse equipped with a Varian Cary single-cell peltier
atmosphere. The mixture was refluxed for about
1 h
(monitored by TLC) resulting in a turbid solution. After the
solvent was removed under vacuum, CH2Cl2 (50 mL) was added
and washed with H2O. The organic layer was dried with
anhydrous Na2SO4 and filtered. Then removal of CH2Cl2 under
vacuum, the residue was purified by column chromatography
on SiO2 with CH2Cl2 as eluent to give light yellow solid (110.2
o
accessory to control temperature at 25 C. UV/Vis spectra and
the optical transmittance were recorded at 25 C in a quartz
1
o
mg, 61 %). H NMR (400 MHz, CDCl3) δ 8.70 (s, 2H), 8.57 (s,
1H), 8.47 (d, J = 15.7 Hz, 2H), 8.17 (d, J = 8.8 Hz, 1H), 8.05 (s,
2H), 7.83 (d, J = 8.7 Hz, 1H), 7.54 (s, 2H), 4.56 (dd, J = 14.0, 6.9
Hz, 4H), 1.51 (t, J = 7.0 Hz, 6H). 13C NMR (101 MHz, CDCl3) δ
163.9, 149.8, 148.2, 131.8, 131.5, 131.2, 130.3, 130.1, 128.7,
127.3, 127.2, 126.6, 125.3, 125.2, 125.0, 124.5, 122.4, 98.9,
61.5, 13.2. HR-MS (ESI): m/z calcd for C25H21NO4: 400.1549
[M+H]+, found: 400.1547 (Fig. S1-S3).
cell (light path 10 mm) on
a
Shimadzu UV-3600
spectrophotometer equipped with a PTC-348WI temperature
controller. High-resolution Transmission electron microscopy
(TEM) images were acquired using a Tecnai 20 high-resolution
transmission electron microscope operating at an accelerating
voltage of 200 keV. The sample for high-resolution TEM
measurements was prepared by dropping the solution onto a
copper grid. The grid was then air-dried. Scanning electron
microscopy (SEM) images were obtained using a Hitachi S-
3500N scanning electron microscope. Dynamic Light Scattering
(DLS) spectroscopy was examined on a laser light scattering
spectrometer (BI-200SM) equipped with a digital correlator
(TurboCorr) at 636 nm at a scattering angle of 90°. The
hydrodynamic diameter (Dh) was determined by DLS
Synthesis of 1
Sodium hydroxide (30.3 mg, 0.75mmol) was dissolved in water
(10 mL) and 10 mL THF solution of 3 (50.4 mg, 0.125 mmol)
was added. The resulting suspension was stirred at 100 °C
overnight and cooled to room temperature. After removal of
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THF under vacuum, the pH was adjusted to 1 using 37%
aqueous hydrogen chloride solution. The resulting precipitate
was filtered off, washed with water (3 x 30 mL) and dried
under vacuum. The product was obtained as a yellow solid
(37.4 mg, 74 %). 1H NMR (400 MHz, DMSO) δ 8.81 (s, 2H), 8.68
(s, 3H), 8.29 (d, J = 8.9 Hz, 1H), 8.14 (d, J = 6.5 Hz, 2H), 8.05 (d, J
= 9.6 Hz, 1H), 7.64 – 7.51 (m, 2H). 13C NMR (101 MHz, DMSO) δ
166.0, 150.2, 149.8, 145.9, 132.9, 132.5, 132.1, 131.5, 131.4,
130.0, 128.7, 128.6, 128.2, 128.0, 126.8, 126.5, 124.9, 124.2.
HR-MS(ESI): m/z calcd. for C21H13NO4: 344.0924 [M+H]+, found:
344.0918 (Fig. S4-S6) .
View Article Online
DOI: 10.1039/C9SC00026G
Determination of association constant (K)
In the UV-vis titration experiments, the association constant
(Ka) for a stoichiometric 1:2 complex (γ-CD·12) of γ-CD with 1
was calculated by using the non-linear least-squares fit of the
titration data according to the following formula with the
Origin program.17
Scheme 1. Synthetic scheme of 1 and the structure of 2
1 was prepared in 74 % yield via a Suzuki reaction of diethyl 4-
bromopyridine-2,6-dicarboxylate with 2-anthraceneboronic acid
under a alkaline condition, followed by a subsequent hydrolysis
reaction(Scheme 1). It was reported that the γ-CD cavity could
accommodate two 2-anthryl groups, and the 1 : 2 inclusion complex
had four possible configurations including syn or anti head-to-tail
(HT) and head-to-head (HH) isomers in aqueous solution.18 Herein,
the similar phenomenon was observed in aqueous solution. Fig S7a
showed the UV-vis absorption and fluorescence emission of 1. The
UV-vis spectra (Fig. 2a, S7b) showed that, with the stepwise
addition of γ-CD, the 1Bb band of 1 at 260-280 nm gradually
decreased, indicating the conformational change from the J-
aggregate of self-assembled 1 to the H-aggregate of diploid 1 due to
where ΔAobs is the UV-vis absorption change of 1 upon
addition of γ-CD. K1 and K2 are the first-order bonding constant
and the second-order bonding constant, respectively. ɛΔHG is
the molar absorption coefficient changes between the γ-CD·1
inclusion complex and 1. ɛΔHG2 is the molar absorption coefficient
changes between the γ-CD·12 inclusion complex and 1. [G0] is
the initial concentration of guest molecule.
1
the inclusion of γ-CD cavity.18 In addition, the La band of 1 at 410
Preparation of Eu complex
nm showed a little bathochromic shift, and its intensity decreased.
Moreover, two apparent isosbestic points at 319 nm and 400 nm
were also observed. These phenomena jointly indicated the
conversion of free 1 to the γ-CD·12 inclusion complex.19 Accordingly,
the association constants (Ka) between 1 and γ-CD were calculated
to be Ka1 = 4.38  102 M-1 and Ka2 = 5.58  104 M-1 at 25°C by
analyzing the sequential changes in UV-vis spectra (ΔA) of 1 at
Europium(III) nitrate hexahydrate (Eu(NO3)3·6H2O) was
purchased from Energy Chemical. A certain amount of
Eu(NO3)3 was dissolved in deionized water, then added to the
aqueous solution of 1 or γ-CD·12 to prepare the Eu complex in
situ. Preparation of Eu3+γ-CD·12, i.e. Eu complex of γ-CD·12,
as an example: A solution of Eu(NO3)3 (2 mM) was prepared in
deionized water, then 45 µL of the Eu(NO3)3 solution was varying concentrations of γ-CD using a nonlinear least-squares
added to the aqueous solution of γ-CD·12 (0.1 mM, 3 mL) to
obtain the Eu3+γ-CD·12 solution (0.1 mM).
curve-fitting method according to literature reports (Fig. 2a and Fig.
S7c).17 The Job’s plot gave an inflection point at a molar ratio of
0.667, corresponding to a 1:2 host-guest inclusion stoichiometry
(Fig. S8), which was consistent with the previously reported result.19
To further prove the inclusion, 1H NMR spectra (Fig. S9a, b) showed
that the anthracene protons shifted upfield 0.375-0.4 ppm upon the
complexation with γ-CD. In the circular dichroism spectra (Fig. S10),
the γ-CD·12 inclusion complex (green line) showed a positive Cotton
effect peak at 350-400 nm and a negative Cotton effect peak at
400-450 nm, indicating the formation of a pseudo[3]rotaxanes.19c In
the fluorescence spectra (Fig. 2b), the fluorescence intensity of 1
appreciably decreased with the gradual addition of γ-CD, due to the
π-π stacked of 1 in the hydrophobic γ-CD cavity. Considering the
structure of 1 that has a bulky negatively charged substituent at 2-
Results and discussion
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position, we deduced that two units of 1 tended to adopt a syn or
anti head-to-tail (HT) conformation upon inclusion by γ-CD.
CD. In addition, the circular dichroism spectrum (Fig. S10) of γ-CD·12
after UV irradiation was obviously different from that before UV
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DOI: 10.1039/C9SC00026G
irradiation. The ESI-MS spectrum of Eu3+γ-CD·12 after irradiation
under 365 nm in water showed a clear signal at m/z 1981.1
assigned to the [2]rotaxane, while the ESI-MS spectrum of a highly
concentrated THF solution of 1 after irradiation under 365 nm
showed a signal at m/z 689.1 assigned to the dimer of 1 (Fig. S14,
S15). No ESI-MS signal of photooxidized product was observed for
the case of either
1 or γ-CD·12. These phenomena jointly
demonstrated that two discrete units of 1 in a γ-CD cavity
converted into a dimer, i.e. γ-CD·12 complex converted to a
[2]rotaxane, after UV light irradiation, and the photodimerized
product was the principal product. Therefore, a possible emission
mechanism could be deduced as follow: the photo-dimerization of
two accommodated anthracene groups in the γ-CD cavity destroyed
the large conjugated structure of γ-CD·12, allowing the match of the
lowest triplet state of ligand to the first excited state of lanthanide
ion. As a result, the characteristic fluorescence of Eu3+ was
presented.13c
Fig. 2 (a) Absorption spectra and (b) emission spectra of 1 (0.2 mM)
with (red) and without (black) γ-CD (0-0.3 mM) at pH 9.0 in
water(25 °C). (c) Emission spectra of γ-CD·12 (0.2 mM) upon
addition of Eu3+ (from 0 to 3eq) at pH 9.0 in water (25 °C, λex =365
nm) (d) Emission spectra of Eu3+γ-CD·12 system (black) and
Eu3+[2]rotaxanes (red) at 25 °C. Inset: photo image of fluorescence
in pH 9.0 aqueous solution under UV light. (λex=254 nm, 254 nm
used as an excitation source).
It was well reported that pyridine-2,6-dicarboxylic acid (DPA)
could strongly coordinate lanthanide ions with a ratio of 3:1.20
Similarly, the fluorescence spectral experiments showed the 1:3
coordination stoichiometry between Eu3+ and 1, which was
consistent with our previous observation (Fig. S11).13c Possessing
two terminal DPA units, γ-CD·12 complex also showed the similar
coordination behaviors with lanthanide ions (Fig. 2c). With the
gradual addition of Eu3+ to γ-CD·12 complex, no characteristic
fluorescence of Eu3+ could be observed, but the fluorescence at 480
nm, assigned to the intrinsic blue fluorescence of ligand, gradually
quenched (Fig. 2c, 2d black line), similar to the previously report.13c
A possible reason may be that a large aromatic conjugate system in
the antenna molecule led to a mismatch between the lowest triplet
state of ligand and the first excited state of lanthanide. It is well-
documented that anthracenes are photoresponsive and be apt to
photodimerization under UV irradiation.21 However, after
irradiating the aqueous solution of Eu3+γ-CD·12 under N2 for 16
min at 365 nm with an intensity of 50 W, the resultant solution
presented four characteristic emissions (Fig. 2d, red line) of Eu3+ at
590 nm (5D07F1), 615 nm (5D07F2), 645 nm (5D07F3) and 680
nm (5D07F4),13 which was quite similar to that of Eu3+23 (Fig. S12).
This means that an energy transfer (ET) process occurred from
pyridine-2,6-dicarboxylic acid (DPA) to Eu3+.13c In the 1H NMR
spectra, the proton signals at 7.0-7.6 ppm assigned to the
anthanence group in 1 displayed an upfield shift (Fig. S9), indicating
that two accommodated groups may undergo a dimerization after
the UV light irradiation.19c Moreover, the ROESY spectrum (Fig. S13)
also showed the clear NOE(Nuclear Overhauser Effect) correlations
between the dimeric anthanence groups and the inner protons of γ-
Fig. 3 (A) Emission spectra (λex = 290 nm) of Eu3+γ-CD·12 ([12]=0.1
mM, [Eu3+]=0.03 mM) at initial state (a) and after photoirradiation
for (b) 2 min, (c) 4 min, (d) 8 min, and (e) 16 min in pH=9.0 aqueous
solution at 25 °C; (B) CIE 1931 chromaticity diagram. The black dots
signify the luminescent color coordinates for the corresponding
states a (0.22, 0.32), b (0.27, 0.34), c (0.32, 0.36), d (0.39, 0.38), and
e (0.43, 0.38). (C) The images of the corresponding states under UV
irradiation (λex = 365 nm), and (D) the features of fluorescent inks
based on the Eu3+γ-CD·12-doped PVA (The molar ratio is 1:500)
film under UV irradiation (λex = 365 nm).
Significantly, Eu3+γ-CD·12 showed the different emission color
with the changes of light irradiation times. Without the light
irradiation, Eu3+γ-CD·12 only emitted the intrinsic blue
fluorescence of ligand (Fig. 3A) at 490 nm. After irradiating the
solution of Eu3+γ-CD·12 under N2 at 365 nm for 16 min, the
fluorescence emission of Eu3+ gradually enhanced, and the emission
color changed in an order of cyan (0 min)  pale yellow (2 min) 
white (4 min)  orange (8 min)  red (16 min). Moreover, an
obvious white-light point with the CIE coordinate (0.32, 0.36) was
observed in the CIE 1931 chromaticity diagram (Fig. 3B). A possible
reason may be that, with the continuous irradiation of UV light
irradiation, Eu3+γ-CD·12, which emitted the cyan fluorescence,
gradually converted to Eu3+[2]rotaxane that emitted the red
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fluorescence. Therefore, at different time points, the Eu3+γ-CD·12
system existed as the mixtures of blue-light species Eu3+γ-CD·12
and red-light species Eu3+[2]rotaxane with different ratios, leading
to the multi-color emission including white light. In addition,
fluorescence lifetime experiments showed that the decay curve in
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DOI: 10.1039/C9SC00026G
pH 9.0 water followed
a double exponential decay with a
fluorescence lifetimes at τ1 = 1.10 ns and τ2 = 5.97 ns at initial state,
and no fluorescence lifetimes of lanthanide ions were observed. But
the Eu3+γ-CD·12 showed the fluorescence lifetimes of lanthanide
ions at τ1 = 251.88 µs and τ2 = 993.46 µs after photoirradiation for
16 min (Fig. S16). The quantum yields were 3.12 % at initial state,
2.67 % at 4 min and 15.74 % at 16 min. In the emission spectra of
Eu3+γ-CD·12 without photoirradiation, i.e. the case where the
sample is made up and no irradiation, no appreciable emission color
changes were observed (Fig. S17a), indicating that the different
emission colors are due to the irradiation induced rotaxane
formation rather than a simply slow coordination event. In the
irradiation study of Eu3+13 complex (i.e. no CD present), very slight
color changes were observed after irradiating Eu3+13 complex only,
indicating that the CD is required for the different emission colors
because CD can not only increase the solubility of the guest, but
also accelerate the dimerization (Fig. S17b). Meanwhile, the
changes of absorption spectra and the excitation spectra Eu3+γ-
CD·12 with the photoirradiation were shown in Figs S17c-d.
Furthermore, the morphology of Eu3+[2]rotaxane was investigated
by scanning electron microscopy (SEM) and transmission electron
microscopy (TEM) (Fig. S18-S19). In SEM and TEM images, free 1
existed as a number of needle-like nanofibers, and γ-CD·12 showed
the morphology as irregular blocks. However, the morphology of
Eu3+γ-CD·12 before and after UV light irradiation both existed as
thin films. In addition, the zeta potentials of free 1, γ-CD·12, Eu3+γ-
CD·12 were measured to be 29.44 mV, 10.63 mV and 4.45 mV
(Fig. S20), respectively, indicating that the coordination of Eu3+
decreased the surface electronegativity of 1 or γ-CD·12.
Benefitting from the photo-controlled multicolor emission
property, Eu3+γ-CD·12 could be used as a tunable photochromic
fluorescence ink. In a typical test, some characters were written
with the solution of Eu3+γ-CD·12-doped PVA as ink on an ordinary
glass piece, and these characters emitted blue fluorescence under
the UV lamp after being dried in air (Fig. 3). When irradiation with
the UV light (365 nm) from 0 min to 4 min, the characters emitted
white fluorescence, which further turned red after irradiation for 16
min. Interestingly, these multi-color characters could keep stable
for at least 72 h without any appreciable fading. Therefore, the
tunable photochromic multi-color emission property will enable the
application of Eu3+γ-CD·12 assembly as novel anti-counterfeiting
materials in which the information and the state could be
effectively written and read out by simply alternating the UV
irradiation time.
Fig. 4 Absorption spectral changes of Eu3+γ-CD·12 (0.1 mM) upon
irradiation (a) at 365 nm and (b) at 254 nm in PBS at 25 °C (pH=7.2,
inset: the upper and lower images for the fluorescence images of
changing at an excitation source of 254 nm and 365 nm,
respectively). Fluorescence spectral changes of Eu3+γ-CD·12 upon
photoirradiation (c) at 365 nm and (d) at 254 nm in PBS at 25 °C (λex
= 365 nm)
In addition to fluorescence ink, the Eu3+γ-CD·12 assembly could
also be used as photo-modulated multicolor fluorescence labelling
for living cells. Firstly, we study the luminescence behavior under
physiological conditions in PBS buffer (PH=7.2). Similarly, the
assembly Eu3+γ-CD·12 exhibits red luminescence (at 254 nm) and
the white luminescence (at 365 nm) after the light irradiation (Fig.
4a, S21a). Accordingly, UV−vis absorption measurement and
fluorescence spectrum were performed to monitor the
photodimerization process of anthracene. Irradiation of the Eu3+γ-
CD·12 under N2 with 365 nm light using a portable UV lamp (6 W)
decreased the intensity of absorption bands at 373 nm (assigned to
π-π* transition bands of anthracene units) and the fluorescence
intensity at 494 nm was gradually declined, indicating that the
photodimerization disrupted the conjugation of anthracene units
(Fig. 4a, 4c).21,22 Fluorescence lifetime decay curve of Eu3+γ-CD·12
in PBS buffer (pH=7.2) also showed the fairly high fluorescence
lifetimes of lanthanide ion up to τ1 = 543.50 µs and τ2 = 1204.91 µs
after photoirradiation (Fig. S22). Moreover, the reversibility of such
luminescence properties is highly desired for wide applications and
thus we examined its reversibility. When Eu3+[2]rotaxane was
irradiated at 254 nm for 120 s, a reconversion to the parent species
Eu3+γ-CD·12 occurred, as confirmed by UV−vis absorption
measurement and fluorescence spectrum (Fig. 4b, 4d). Significantly,
cycle tests showed that the external-stimuli-responsive
transformation is repetitive (Fig. S21b, S23). The solution of free 1
and Eu3+13 quickly precipitated as shown in Fig. S21c.
Simultaneously, the fluorescence of Eu3+13 is very weak, and red
fluorescence is not observed after irradiated at 365 nm for 3 h or
even longer (Fig. S21a). We then treated human lung
adenocarcinoma cells (A549 cells) with the Eu3+γ-CD·12 assembly
for 24 h. The cytotoxicity of the assembly was evaluated by using a
standard MTT assay. As shown in Fig. S24, over 90% cell viability is
observed after incubation of A549 cells with the assembly at
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concentrations ranging from 1 to 16 µM for 24 h, thus confirming We thank NNSFC (21672113, 21432004,View2A1r7tic7le2O0n9lin9e,
DOI: 10.1039/C9SC00026G
the low cytotoxicity of the assembly. Confocal laser scanning 21861132001 and 91527301) for financial support.
microscopy revealed that the cells initially emitted blue Notes and references
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Conclusions
In conclusion, we have successfully constructed a photo-
tunable supramolecular assembly from γ-CD, anthracene-
modified DPA and lanthanide metal via the time-dependent
photo-crosslink reaction. The resultant supramolecular
assembly possessed dual emission properties, i.e. a red-light
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Conflicts of interest
There are no conflicts to declare.
Acknowledgements
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View Article Online
DOI: 10.1039/C9SC00026G
Photo-responsive
Cyclodextrin/Anthracene/Eu3+
Supramolecular Assembly for a Tunable
Photochromic Multicolor Cell Label and
Fluorescent Ink
Weilei Zhou,a Yong Chen,a Qilin Yu,a,c Peiyu Li,a Xuman Chena
and Yu Liu*a,b
A
photoresponsive supramolecular assembly was constructed and
presented multi-color fluorescence emissions in several environments
including solution, PVA and living cell.