Photolysis of the BODIPY dye activated by pillar[5]arene

Article abstract of DOI:10.1039/d0ra08611h

Here, a pseudo[3]rotaxane comprising a fluorescent BODIPY derivative and pillar[5]arene was conveniently fabricatedviahost-guest complexation. Importantly, in this system, the efficient photodecomposition of the BODIPY derivative in the presence of pillar

Full text of DOI:10.1039/d0ra08611h

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Photolysis of the BODIPY dye activated by pillar[5]
arene†
Cite this: RSC Adv., 2021, 11, 7454
a
a
a
a
a
*
Haifan Zhang,
and Guoxing Liu
Long Wang, Puyang Dong, Shuqiang Mao, Pu Mao
*
ab
Here, a pseudo[3]rotaxane comprising a fluorescent BODIPY derivative and pillar[5]arene was conveniently
fabricated via host–guest complexation. Importantly, in this system, the efficient photodecomposition of
the BODIPY derivative in the presence of pillar[5]arene was witnessed upon irradiation at 311 nm light,
which was demonstrated via UV-Vis absorption, fluorescence emission, NMR and HR-MS spectroscopy
techniques, but the only BODIPY dye in the absence of pillar[5]arene couldn't undergo
photodegradation. We demonstrated that pillar[5]arene could act as an activator to trigger the
photodegradation reaction of BODIPY derivatives via free radical reactions even without supramolecular
interactions. The present results provide a new strategy for the efficient photolysis of organic dyes.
Received 9th October 2020
Accepted 22nd January 2021
DOI: 10.1039/d0ra08611h
rsc.li/rsc-advances
Superuous organic dyes are one of the most serious contami- macrocycles such as water-soluble cyclodextrins, calixarenes,
nation sources that are discharged at will, which is a cause for crown ethers and cucurbiturils as platforms for the rapid and
concern. The efficient elimination of organic dyes is a hugely broad spectral photodecomposition of aromatic dyes.14
challenging problem that needs and remains to be solved. Most Although there are a few reports on the construction of photo-
approaches, such as membrane separation,1 activated carbon degradable supramolecular assemblies, the fabrication of pho-
adsorption,2 ion exchange on synthetic adsorbent resins3 and toresponsive supramolecular systems equipped with photolysis
coagulation by chemical agents,4 were adopted to dispose of the remains highly unexplored. Consequently, it is still necessary to
organic dye pollution. However, these superuous organic dyes develop novel high-efficiency photolyzable supramolecular
cannot be thoroughly degraded via these conventional materials. Pillararenes (particularly pillar[5]arene and pillar[6]
methods. Light is considered one of the most desirable stimuli arene), as a new type of supramolecular macrocycles, have been
because of its non-invasiveness, easy controllability, low cost, used as a host to construct photodegradable materials.15 For
and ubiquity.5 Owing to the above-mentioned advantages, light instance, Wang et al. prepared a bola-type supra-amphiphilic
is oen utilized as an effective strategy to manage responsive photoresponsive supramolecular material based on water-
materials, which have been applied in numerous research soluble pillar[5]arene, achieving the photodecomposition of
elds, such as separation technology,6 photolithography,7 pho- the 9,10-dialkoxyanthracene group.16
tocontrolled singlet oxygen generation,8 optical memory
Due to excellent photophysical and photochemical proper-
storage,9 and photomodulated control-release of anions.10 ties such as good photostability and uorescence quantum
Among numerous stimuli-responsive systems, photolyzable yield,17 BODIPY dyes have been generally applied in bioimaging
matrices that can irreversibly decompose aer irradiation have and uorescent sensing,18 photodynamic therapy,19 advanced
aroused wide research interests in the design and construction optical materials,20 etc. However, the elimination of surplus and
of photodegradable materials, controlled drug release systems used BODIPY dyes and other uorescent dyes has gradually
and tissue engineering systems.11 The supramolecular method become a major issue to be addressed due to use and waste of
was alternatively used to develop photodegradable materials.12 large amounts of organic dyes applied in living matter.
Recently, Liu et al. developed a photoresponsive amphiphilic Furthermore, some BODIPY derivatives have high cytotoxicity.21
supramolecular assembly that achieved efficient photolysis of Consequently, it is crucial to seek a simple and effective method
anthracene derivatives via calixarene-induced aggregation.13 for dealing with excess and useless organic pollutants. Herein,
Subsequently,
they
employed
several
multi-charged to the best of our knowledge, we rst put forward a new way for
the efficient photolysis of BODIPY dyes via free radical reaction
triggered by P5.
aCollege of Chemistry and Chemical Engineering, Henan University of Technology,
Zhengzhou 450001, P. R. China. E-mail: gxliu@henau.edu.cn; maopu@haut.edu.cn
bCollege of Science, Henan Agricultural University, Zhengzhou, 450002, China
† Electronic supplementary information (ESI) available: Synthesis and
characteristics of new compounds and other data. See DOI: 10.1039/d0ra08611h
The BODIPY dye G-BODIPY and pillar[5]arene (P5) acted as
the guest and host, respectively. Their synthetic routes were
prepared by simple steps, as shown in Scheme 1. 3,4-Dihy-
droxybenzaldehyde (1) reacted with propargyl bromide to
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Scheme 1 The synthesis route of G-BODIPY and P5.
Fig. 1 1H NMR (400 MHz, CDCl3) spectra of (a) P5, (b) assembly G-
BODIPY3P52 and (c) guest G-BODIPY. [P5] ¼ 2[G-BODIPY] ¼ 6 ꢀ
10ꢁ3 mol Lꢁ1
.
obtain compound (2). Subsequently, the reaction of (2) and
pyrrole catalyzed by TFA produced substance (3). Then, (3)
encountered with DDQ, Et3N and BF3$OEt2 in succession to give
compound (4). Finally, the click reaction of (4) and (5) by the
catalyzation of CuSO4$5H2O and sodium ascorbate prepared G-
BODIPY. Macrocyclic host P5 was synthesized by 1,4-dime-
thoxybenzene by the catalyzation of FeCl3.
implying the formation of the host-guest complex G-
BODIPY3P52. Therefore, G-BODIPY and P5 self-assembled to
a [3]pseudorotaxane G-BODIPY3P52 in chloroform (Scheme 2).
To our surprise, as illustrated in Fig. 2a, when the sample
containing G-BODIPY3P52 was irradiated using 311 nm light,
the absorbance at 295 nm and 503 nm (assigned to BODIPY
unit) signicantly declined by 83% (503 nm) with four iso-
sbestic points at 286 nm, 308 nm, 458 nm and 518 nm,
respectively, implying that the BODIPY unit of G-BODIPY was
dramatically destroyed. The photochemical quantum yield
(311 nm light irradiation) of the pseudo[3]rotaxane was deter-
mined to be 0.34, and the test method was added in the ESI.†
However, in the control experiment, only the guest G-BODIPY
expressed no obvious change under the same condition,
It is well-known that a strong binding ability (Ka ¼ 1.2 ꢀ 104
Mꢁ1) exists between P5 and the neutral guests bearing two or
three short alkyl chains with a triazole site and a cyano site at
either end in chloroform.22 Therefore, we speculated that G-
BODIPY would assemble with P5 by an equivalent proportion of
1 : 2 (guest/host) and strong complexation. As displayed in
Fig. S5,† an NMR titration experiment was performed. From the
NMR titration spectroscopy, an apparent upeld shi of the
resonance for methylene in the guest (Ha–d) was observed, and
their integral areas remained unchanged with the continuous
addition of 2 equiv. P5, indicating the 2 : 1 host–guest binding
stoichiometry. The complex stability constant (KS) was deter-
mined as 5.66 ꢀ 106 Mꢁ2 using the 1H NMR single point
method (see Fig. S5 and computational method in ESI†).
Clearly, the assembled model of G-BODIPY and P5 are man-
ifested in Scheme 2. The corresponding proof was provided by
the 1H NMR spectroscopic contrast, indicating the apparent
upeld shi for the resonance of methylene (Ha–d) of the guest,
which implies the occurrence of an assembling behavior and
the formation of
a new supramolecular assembly G-
BODIPY3P52 (Fig. 1). Furthermore, as shown in Fig. S6 and
S7,† the absorbance (at 504 nm) and uorescence intensity (at
517 nm) of G-BODIPY increased slightly with the addition of P5,
Fig. 2 (a) The variation of UV-Vis absorption spectra of G-BODIPY
with P5 upon continuous irradiation of 311 nm. (b) The variation of the
UV-Vis absorption spectra of G-BODIPY upon continuous irradiation
of 311 nm. (c) The variation of UV-Vis absorption spectra of G-BODIPY
with 10 eq. PDME upon continuous irradiation of 311 nm. (d) The
variation of absorbance of G-BODIPY, G-BODIPY with 10 eq. PDME
Scheme 2 Schematic illustration of formation pattern of assembly G- and G-BODIPY with P5 at 503 nm upon continuous irradiation of
BODIPY3P52 and photolysis of the BODIPY guest induced by P5.
311 nm. [G-BODIPY] ¼ 1.0 ꢀ 10ꢁ5 mol Lꢁ1
.
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indicating that its structure exhibited invariability upon irra- photodegradation efficiency was inferior to that of G-
diation at 311 nm. Furthermore, we selected p-phenyl dimethyl BODIPY3P52 (Fig. 3c). More visually, G-BODIPY3P52 man-
ether (PDME), which is 5 equivalents to the host (P5), to evaluate ifested the highest uorescence quenching efficiency (Fig. 3d),
photodegradation performance. As shown in Fig. 2c, the suggesting that P5 induced high-efficiency photolysis of the
absorbance of G-BODIPY/PDME at 503 nm decreased by only BODIPY dye.
43%, suggesting that PDME also inuenced the photo-
Subsequently, to further verify the aforementioned conse-
degradation of the guest to some extent but unsatisfactory. quence, we performed an NMR irradiation experiment for the
More visually, the variation curve of the absorbance at 503 nm sample containing G-BODIPY3P52 in CDCl3. As shown in
belonged to the BODIPY skeleton over irradiation time at Fig. S8,† the resonance of the protons on the BODIPY group (Hk)
311 nm light for only G-BODIPY, G-BODIPY3P52 and G-BOD- in the assembly gradually disappeared with irradiation at
IPY/PDME, as presented in Fig. 2d. Moreover, the color change 311 nm light for 3 h, indicating that the BODIPY group in G-
of the samples containing G-BODIPY, G-BODIPY3P52 and G- BODIPY3P52 was almost completely damaged. In addition, we
BODIPY/PDME in the above irradiation process is visually measured the HR-MS spectra of P5 and G-BODIPY3P52 before
shown in Fig. 2b, a and 2c (inset), which reveal that the sample and aer the irradiation of 311 nm. As shown in Fig. S9–S12,†
containing G-BODIPY3P52 turned from yellow to almost the HR-MS spectra of P5 and G-BODIPY3P52 aer irradiation
+
colorless, while the others did not display a wide variation. The showed the peaks at 768.3761 (assigned to P5 + NH4 ) and
aforementioned investigation clearly illustrated that the inter- 681.3404 (belonged to G-BODIPY) both thoroughly disappeared
vention of P5 caused the best photolysis efficiency of G-BODIPY. and only some small molecular weight peaks were observed,
In addition, we employed a uorescence spectrometer to revealing that P5 and G-BODIPY3P52 were both broken into
conrm if P5 played a vital role in the photolysis of G-BODIPY. pieces. In contrast, when the sample containing only G-BODIPY
As expected, the uorescence of G-BODIPY3P52 at 516 nm was was irradiated by 311 nm light, the resonance of the protons on
quenched by 77%, which was consistent with the absorbance the BODIPY group in the guest did not manifest any change
change (Fig. 3a). Intuitively, strong green uorescence turned (Fig. S13†). In addition, we conducted photoirradiation experi-
out to be very weak and nearly invisible to our eyes in the irra- ments of P5 and PDME via UV-Vis absorption spectra upon
diation process (Fig. 3a, inset). On the contrary, no apparent irradiation at 311 nm, showing that photodecomposition reac-
variation of only G-BODIPY was observed in the uorescence tions of P5 and PDME occurred (Fig. S14 and S15†).
spectrum upon irradiation at 311 nm (Fig. 3b). Meanwhile, no
From the aforementioned investigation, the photolysis of G-
uorescent color and intensity changes were observed from BODIPY was efficiently activated by P5. We presumed that the
photographs before and aer irradiation (Fig. 3b, inset). three investigated manners of degradation were as follow: (a)
Moreover, with regards to BODIPY/PDME, approximately 51% energy transfer (as shown in Fig. S16,† P5 and PDME with
of uorescence intensity was decreased, and its a specic absorbance at 311 nm can absorb 311 nm UV light
into the solution containing G-BODIPY and deliver the absor-
bed light energy to G-BODIPY), (b) reactive oxygen species
(photoreaction of P5 and PDME caused by reactive oxygen
species further triggered the photodecomposition of G-BOD-
IPY), and (c) free radical species (photoreaction of P5 and PDME
caused by the free radical-activated photolysis of G-BODIPY). To
clarify the credible manner, we subsequently performed a series
of control experiments. As displayed in Fig. S17†, we directly
employed a 500 nm wavelength light (which could also generate
heat) on free G-BODIPY and complex G-BODIPY3P52 through
the variation of UV-Vis absorption and emission spectra, and no
changes were observed. The results implied that the degrada-
tion reaction was not caused by heat. Furthermore, the spectral
overlap of UV-Vis absorption of G-BODIPY and uorescence
emission of P5 (Fig. S18†) were performed and displayed almost
very little degree of overlap (Fig. S19†). Thus, we could rule out
the photolysis of the BODIPY dye caused by energy transfer
from P5 to G-BODIPY. Subsequently, we also investigated the
photoirradiation experiments of P5 and G-BODIPY3P52 under
both aerobic and anaerobic conditions. The manifested results
Fig. 3 (a) The variation of the fluorescence spectra of G-BODIPY with
P5 upon continuous irradiation of 311 nm. (b) The variation of the
fluorescence spectra of G-BODIPY upon continuous irradiation of in the photoreactions mentioned above were not photooxida-
311 nm. (c) The variation of the fluorescence spectra of G-BODIPY with
tion reactions caused by oxygen (Fig. S20 and S21†). Then, we
10 eq. PDME upon continuous irradiation of 311 nm. (d) The variation
speculated that the photoreaction of P5 caused by free radicals
of the fluorescence intensity of G-BODIPY, G-BODIPY with 10 eq.
upon irradiation at 311 nm light could further trigger the
photodecomposition reaction of G-BODIPY. To verify our
speculation, we selected TEMPO as a free radical scavenger to
PDME and G-BODIPY with P5 at 516 nm upon continuous irradiation
of 311 nm. [G-BODIPY] ¼ 1.0 ꢀ 10ꢁ5 mol Lꢁ1; excitation at 480 nm; slit
¼ 1, 2.5.
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perform some control experiments. As displayed in Fig. S22b,†
the absorption spectrum of G-BODIPY3P52 in the presence of
TEMPO showed no apparent change in comparison to that of G-
BODIPY3P52 in the absence of TEMPO (Fig. S22a†) upon irra-
diation at 311 nm light. Furthermore, a striking contrast for the
absorbance variation of the pseudo[3]rotaxane at 503 nm in the
presence and absence of TEMPO is presented in Fig. S22c.†
Therefore, the above investigations demonstrated that photo-
reaction of P5 caused by free radicals further triggered photo-
decomposition of G-BODIPY upon irradiation at 311 nm light.
In the control experiments, we selected compound (4) that
lacked the valeronitrile binding site to investigate its photo-
irradiation experiments in the presence and absence of P5 using
UV-Vis absorption and uorescence emission spectra. As shown
in Fig. S23 and S24,† the photolysis of compound (4) in the
presence of P5 without the host–guest complexation was also
achieved upon irradiation at 311 nm light, which further
implied that these photodecomposition reactions were caused
by free radicals and not related to supramolecular interactions.
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Conclusion
In summary, we synthesized a valeronitrile-modied BODIPY
derivative via the “Click” reaction as a guest. Holosymmetric
methoxyl-pillar[5]arene, as the host was prepared, and assem-
bled with the BODIPY guest to form a pseudo[3]rotaxane.
Importantly, pillar[5]arene as an activator could activate the
high-efficiency photolysis of the BODIPY dye via free radical
reactions, and was veried via UV-Vis absorption, uorescence
emission, NMR and HR-MS spectroscopy techniques. Through
a series of control experiments, we also demonstrated that the
photodecomposition reactions caused by free radicals were not
related to supramolecular interactions. The study provides
a new strategy to induce the efficient photodegradation of
residual and useless organic dyes.
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Conflicts of interest
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324–327; (b) M. Vlatkovic, B. L. Feringa and
There are no conicts of interest to declare.
S. J. Wezenberg, Angew. Chem., Int. Ed., 2016, 55, 1001–
1004; (c) J. Leng, G. Liu, T. Cui, S. Mao, P. Dong, W. Liu,
X. Q. Hao and M. P. Song, Dyes Pigm., 2021, 184, 108838.
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Mater., 2017, 5, 1700770; (b) G. Liu, Y. M. Zhang, L. Zhang,
C. Wang and Y. Liu, ACS Appl. Mater. Interfaces, 2018, 10,
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Acknowledgements
We thank the National Natural Science Foundation of China
(No. 21801063), the Science and Technology Foundation of
Henan Province (No. 192102210039), the Colleges and Univer-
sities Key Research Program Foundation of Henan Province 12 (a) N. Kamatham, J. P. Da Silva, R. S. Givens and
(No. 19A150022) and China Postdoctoral Science Foundation
(No. 2018M642767) for their nancial support.
V. Ramamurthy, Org. Lett., 2017, 19, 3588–3591; (b)
N. Kamatham, D. C. Mendes, J. P. Da Silva, R. S. Givens
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