FRET-capable supramolecular polymers based on a BODIPY-bridged pillar[5]arene dimer with BODIPY guests for mimicking the light-harvesting system of natural photosynthesis

Article abstract of DOI:10.1039/c5cc00398a

AA/BB-type and A₂/B₃-type FRET-capable supramolecular polymers based on a BODIPY-bridged pillar[5]arene dimer and two BODIPY derivative guests have been successfully constructed and their application in mimicking the light-harvesting

Full text of DOI:10.1039/c5cc00398a

ChemComm
View Article Online
View Journal | View Issue
COMMUNICATION
FRET-capable supramolecular polymers based on
a BODIPY-bridged pillar[5]arene dimer with
BODIPY guests for mimicking the light-harvesting
system of natural photosynthesis†
Cite this: Chem. Commun., 2015,
1, 4643
5
Received 15th January 2015,
Accepted 5th February 2015
a
a
a
a
a
Lu-Bo Meng, Dongqi Li, Shuhan Xiong, Xiao-Yu Hu, Leyong Wang* and
Guigen Li
DOI: 10.1039/c5cc00398a
bc
www.rsc.org/chemcomm
2 3
AA/BB-type and A /B -type FRET-capable supramolecular polymers attracting great interest from biologists and chemists. So far, lots of
based on a BODIPY-bridged pillar[5]arene dimer and two BODIPY artificial light-harvesting systems based on fluorescence (or F ¨o rster)
derivative guests have been successfully constructed and their resonance energy transfer (FRET) have been developed, most of
2b,d,6
application in mimicking the light-harvesting system of natural which were constructed by covalent donor–acceptor models.
photosynthesis was studied.
Although impressive achievements have been made in this field,
non-covalent artificial light-harvesting systems have been much
7
Energy issues are a global concern for human beings. Because of less frequently explored. Recently, with the rapid development of
the excessive consumption of fossil fuels, severe environmental supramolecular chemistry, more and more efforts were contributed
pollution, and increasing pressure for energy supply, the search for towards developing such non-covalent artificial light-harvesting
8
9
economical and clean energy sources is a highly challenging and systems, and among them crown ethers (CEs), cyclodextrins (CDs)
8,10
urgent task. Fortunately, solar energy is a very promising energy and host–guest complexes containing multiple hydrogen bonds
source, which is nearly inexhaustible and distributes all over the were frequently employed as building scaffolds.
earth. However, one difficult problem is how to take full advantage
As a new class of macrocyclic hosts, pillararenes, which are
of sunlight and convert it into other forms of energy we can cyclized by several hydroquinone monomers linked with methylene
conveniently use. In this regard, nature provides us with a fantastic bridges at para-positions, possess many advantages, including
lesson: photosynthesis, which is a natural process, takes place in facile preparation, selective functionalization, unique host–guest
11
plants, algaes and cyanobacteria and plays a significant role in life chemistry, and so on. These properties make pillararenes excel-
on this planet. Based on photosynthesis, sunlight can be converted lent host molecules for constructing rotaxanes, supramolecular
into chemical energy that is stored in carbohydrate molecules, such polymers, and vesicles, which are widely applied as fluorescent
1
12
13
14
as sugars. Generally, the absorption and transfer of solar energy is sensors, drug delivery systems, and other functional materials.
1a,2
the first and a vital step in the process of photosynthesis.
However, until now, pillararene-based artificial light-harvesting
Therefore, mimicking the photosynthetic light-harvesting system systems have never been reported except for the only example of
15
with synthetic models is significantly meaningful not only for our a pillar[5]arene-based FRET system reported by Ogoshi in 2013, in
understanding of the function and mechanism of photosynthesis which a mechanically interlocked [2]rotaxane was fabricated based
but also in the development of potential applications in terms of on a di-pyrene appended pillar[5]arene and an axle with a perylene
3
organic light-emitting diodes (OLED), dye-sensitized solar cells stopper, and an effective FRET process occurred from pyrene to
3a,4
5
(DSSC),
and other optoelectronic devices. This area is currently perylene due to the smart interlocked structure, suggesting a
potential application for mimicry of the light-harvesting system.
In order to develop ideal light-harvesting systems, which generally
possess three key factors, namely intense and broad absorption in
the range of the solar spectrum, fast and efficient energy transfer
a
Key Laboratory of Mesoscopic Chemistry of MOE, Center for Multimolecular
Organic Chemistry, School of Chemistry and Chemical Engineering, Nanjing
University, Nanjing 210093, China. E-mail: lywang@nju.edu.cn;
Fax: +86-25-83597090; Tel: +86-25-83592529
from ‘‘antenna’’ complexes to the ‘‘reaction center’’, and good
b
c
16
Institute of Chemistry and BioMedical Sciences, School of Chemistry and Chemical photostability, herein we prepared a boron-dipyrromethene
Engineering, Nanjing University, Nanjing, 210023, China
(BODIPY)-bridged pillar[5]arene dimer (H, as donor, for detailed
Department of Chemistry & Biochemistry, Texas Tech University, Lubbock, Texas
9409-1061, USA
Electronic supplementary information (ESI) available: Experimental details,
synthesis, see Scheme S1, ESI†) and two BODIPY derivatives with
mono-styryl/di-styryl group substituents (G1 or G2, as acceptors, for
detailed synthesis, see Scheme S2, ESI†) to construct AA/BB-type
7
†
NMR spectra, 2D NOESY, SEM images, fluorescence excitation spectra, Job plots
and specific viscosities. See DOI: 10.1039/c5cc00398a
2 3
or A /B -type FRET-capable supramolecular polymers and further
This journal is ©The Royal Society of Chemistry 2015
Chem. Commun., 2015, 51, 4643--4646 | 4643

View Article Online
Communication
ChemComm
1
Fig. 1 H NMR (300 MHz, CDCl
3
, 298 K) spectra of (a) 4 mM H, (b) G1CH
(
[G1] = [H] = 4 mM, [G1]/[H] = 1 : 1), and (c) 4 mM G1 (blue italics represent
complexed host and guest and the solvent peaks are marked with asterisks).
signals for uncomplexed host and guest, indicating a slowly-
exchanging system on the NMR timescale. As shown in Fig. 1b,
after complexation, all proton signals became broad, and the
signals of the phenyl protons (H , H , and H ), methylene
1
2
3
protons (H
4
), and methoxyl protons (H
5
6
and H ) from the
pillar[5]arene dimer H shifted downfield slightly. Meanwhile,
the signals derived from the triazole protons (H and H ) of G1
shifted upfield slightly and the signals of the methylene protons
, H , H , and H ) from G1 shifted upfield remarkably due to
a
b
(H
c
f
d
e
the shielding effect of the electron-rich cavities of pillar[5]arene.
These results clearly demonstrated that both of the pillar[5]arene
motifs in H were fully threaded by guest G1 with the protons Ha,
Scheme 1 Chemical structures of H, G1, G2 and G0 and the cartoon
representation of the construction of two kinds of FRET-capable func-
tional supramolecular polymers.
b c f d e
H , H , H , H , and H in the pillar[5]arene cavities. Similar
complexation-induced chemical shift changes could be observed
1
investigated their application for mimicking a photosynthetic from the H NMR spectrum of G2CH (2: 3 molar ratio) (Fig. S17,
light-harvesting system (Scheme 1). The neutral guests bearing ESI†). Moreover, 2D NOESY experiments were also performed
two or three short alkyl chains with a triazole site and a cyano (Fig. S18 and S19, ESI†) and the NOE correlation signals marked
1
2a
site at either end (unit G0) were designed due to their strong with circles confirmed the above binding mode.
4
À1
binding ability towards pillar[5]arene (K = (1.2 Æ 0.2) Â 10 M in
2D diffusion-ordered NMR spectroscopy (DOSY) experiments
a
17
chloroform). BODIPY dyes, which are perfectly competent for the were further performed to investigate the self-assembly behavior
requirements of ideal light-harvesting systems, were chosen as the of H and G1 or G2 during linear or cross-linked supramolecular
chromophores, since they have a high absorption coefficient, high polymerization. A plot of diffusion coefficient against concen-
18
fluorescence yields and remarkable photostability. Particularly, tration (Fig. 2a) shows that as the concentration of H increased
they are conveniently derivatized to cover the entire visible from 5 to 40 mM, the measured weight-average diffusion coeffi-
À10
spectrum and energy transfer can efficiently take place between cient of G1CH decreased remarkably from 2.37 Â 10
to
1
9
À10
2
À1
well-designed analogues. In this work, two kinds of assemblies 0.51 Â 10 m s , and a similar observation could also be
exhibited very strong absorption in a broad region from 300 to seen for G2CH with the diffusion coefficient decreasing from
À10
À10
2
À1
700 nm and showed slightly different FRET effects. To the best of 1.93 Â 10
to 0.31 Â 10
m s (Fig. 2b). These results clearly
our knowledge, this is the first example of pillar[5]arene-based
supramolecular polymers for mimicking the light-harvesting
system of natural photosynthesis. Although the transfer efficiency
was not as high as those of covalent models, the results we achieved
(51% for G1CH and 63% for G2CH) were comparable with
previous artificial architectures. Therefore, the present study
developed a novel supramolecular model for mimicking the
light-harvesting system.
The host–guest complexations between compounds H and
1
G1 or G2 were first investigated by H NMR. Fig. 1 shows the
proton NMR spectra of H, G1, and G1CH (1 : 1 molar ratio), in
3
Fig. 2 DOSY (400 MHz, 298 K) plots of solutions in CDCl of: (a) G1CH
which a new species is observed, along with the corresponding (1 : 1 molar ratio) and (b) G2CH (2 : 3 molar ratio) at multiple H concentrations.
4
644 | Chem. Commun., 2015, 51, 4643--4646
This journal is ©The Royal Society of Chemistry 2015

View Article Online
ChemComm
Communication
reveal that larger polymeric structures gradually formed from
small oligomers to linear supramolecular polymers (G1CH) or
large-sized cross-linked supramolecular aggregates (G2CH),
17a
which was intrinsically concentration dependent.
Moreover,
SEM micrographs (Fig. S20, ESI†) of a rodlike fiber drawn from
a very concentrated solution of G1CH or G2CH in chloroform
provided further direct physical evidence for the formation of
such supramolecular polymers, which generally resulted from the
entanglement of linear or cross-linked macro-sized aggregates.
Specific viscosities of two polymers were further measured and
the critical polymerization concentration (CPC) values were
8.8 mM for G1CH and 9.6 mM for G2CH (Fig. S24, ESI†).
In order to develop the application of these two assemblies for
mimicking the light-harvesting system, photophysical properties
of these compounds were initially examined via their ground-state
UV-vis absorption and steady-state fluorescence spectroscopy in
chloroform. Fig. 3a shows the normalized UV-vis absorption spectra
of compounds H, G1, G2 and complexes G1CH and G2CH. For
Fig. 4 Changes in the fluorescence emission spectra of H (10 mM) upon
gradual addition of (a) G1 (lex = 470 nm) and (b) G2 (lex = 490 nm) in
single BODIPY derivatives H, G1 or G2, only one intense and CHCl . The attached pictures are the corresponding changes in fluores-
3
narrow absorption band is exhibited in the range of 400–700 nm cence emission color.
(peaks at 503, 570 and 642 nm for H, G1, and G2, respectively), and
the maximum absorption wavelength redshifted gradually with the
continuously extended p-system by introducing one or two styryl G2 shifted towards the red region much more than that of G1 as
groups. As expected, the spectra of G1CH and G2CH were discussed above.
essentially equal to the superposed patterns of the two individual
After studying the individual properties of H, G1, and G2, the
components, suggesting that there was no interaction between excited-state interactions of complexes G1CH and G2CH were
6d
donor H and acceptors G1 or G2 in the ground-state. Moreover, further investigated by fluorescence titration experiments. The
with the addition of an absorption band in the range of 300– excitation wavelengths of H were chosen as 470 nm for G1CH
4
00 nm, the whole spectra of G1CH and G2CH spanned a very and 490 nm for G2CH to avoid the excitation of G1 or G2 at the
broad region from 300 to 700 nm, which overlapped with the most same time. With gradual addition of G1, the emission peak of H at
intense radiation domain of sunlight. 522 nm decreased gradually, while the emission peak of G1 at
As shown in Fig. 3b, upon excitation at different wave- 595 nm appeared and then increased remarkably (Fig. 4a). When
lengths, the fluorescence emission of compounds H, G1, 1.0 equiv. of G1 was added to the H solution, the intensities of both
and G2 showed signals at 522, 595 and 669 nm, respectively, H and G1 showed almost no change, indicating a 1 : 1 stoichio-
which were also as sharp as those in their absorption spectra. metry of G1 :H which was in good accordance with their chemical
9a
In particular, the absorption spectrum of G1 overlapped with structures. A similar phenomenon could also be observed for
the fluorescence emission spectrum of H in the range of 500– complex G2CH, except that the stoichiometry of G2 :H was about
600 nm just as in our design goals, which perfectly satisfied one 2 : 3, corresponding to the designed structures as well. The above
of the basic principles for an excellent FRET donor–acceptor stoichiometry was also supported by Job plot experiments (Fig. S22
system. In contrast, the overlap between the spectra of G2 and and S23, ESI†). In addition, compared with the strong fluorescence
H was overwhelmingly smaller because the absorption band of intensity (2862 counts) of G1, the intensity (1009 counts) of
G2 turned out to be much weaker, probably due to the smaller
overlap of its absorption spectrum with the fluorescence emission
spectrum of H (Fig. 3b). Moreover, changes in fluorescence emis-
sion color before and after the addition of the guests could be easily
distinguished by the naked eye. The above results clearly demon-
strated that an efficient FRET effect from donor H to acceptors G1
or G2 existed in both supramolecular complexes.
To further confirm the energy transfer process, the fluores-
cence excitation spectra of G1CH and G2CH were recorded by
monitoring the emission at 595 nm corresponding to G1 and at
669 nm for G2 (Fig. S21, ESI†). In the fluorescence excitation
spectra of both G1CH and G2CH, all absorption bands of the
parent compounds could be observed. Moreover, the similarity
between the excitation and the absorption spectra provided
Fig. 3 (a) Normalized UV-vis absorption spectra of H, G1, G2 and the G1CH
1:1 molar ratio) and G2CH (2 : 3 molar ratio) complexes in CHCl . (b) Normalized
UV-vis absorption spectra of G1, G2 and fluorescence emission spectra of
(
3
2
b
H (lex = 490 nm), G1 (lex = 560 nm), and G2 (lex = 630 nm) in CHCl
3
.
further evidence for energy transfer.
This journal is ©The Royal Society of Chemistry 2015
Chem. Commun., 2015, 51, 4643--4646 | 4645

View Article Online
Communication
ChemComm
The FRET efficiencies were further calculated to be 51% for
G1CH and 63% for G2CH (for details see ESI†). Although the
fluorescence intensity of G2 increased less than that of G1,
the energy transfer efficiency of G2CH was actually a little
higher than that of G1CH, which was out of our expectation.
We speculated that the greater number of binding sites (G2 vs.
G1 = 3 vs. 2) towards the pillar[5]arene dimer H might result in
the stronger complexation between G2 and H, which may
explain the difference in energy transfer efficiency.
5 (a) K. Kikuchi, H. Takakusa and T. Nagano, TrAC, Trends Anal.
Chem., 2004, 23, 407; (b) D. Holten, D. F. Bocian and J. S. Lindsey,
Acc. Chem. Res., 2001, 35, 57; (c) S. Saha and J. F. Stoddart,
Chem. Soc. Rev., 2007, 36, 77; (d) V. Balzani, A. Credi and
M. Venturi, Chem. – Eur. J., 2008, 14, 26.
6
(a) O. A. Bozdemir, S. Erbas-Cakmak, O. O. Ekiz, A. Dana and
E. U. Akkaya, Angew. Chem., Int. Ed., 2011, 50, 10907; (b) J. Y. Liu,
Y. Huang, R. Menting, B. Roder, E. A. Ermilov and D. K. Ng, Chem.
Commun., 2013, 49, 2998; (c) B. Rybtchinski, L. E. Sinks and
M. R. Wasielewski, J. Am. Chem. Soc., 2004, 126, 12268; (d) X. Zhang,
Y. Xiao and X. Qian, Org. Lett., 2007, 10, 29.
7
8
(a) P. D. Frischmann, K. Mahata and F. Wurthner, Chem. Soc. Rev.,
2013, 42, 1847; (b) Y. Ishida, T. Shimada, D. Masui, H. Tachibana,
H. Inoue and S. Takagi, J. Am. Chem. Soc., 2011, 133, 14280.
G. Bottari, O. Trukhina, M. Ince and T. Torres, Coord. Chem. Rev.,
2012, 256, 2453.
In summary, we have successfully prepared a BODIPY-bridged
pillar[5]arene dimer H and two BODIPY derivative guests G1 and
G2 to construct AA/BB-type and A /B -type FRET-capable supramo-
2
3
lecular polymers for mimicking the photosynthetic light-harvesting
system. Both assemblies exhibited very strong absorption in a
broad region from 300 to 700 nm. Due to the high complexation
stability of the host–guest pair, they showed efficient FRET effects
and the transfer efficiencies were 51% for G1CH and 63% for
G2CH, which are comparable with previous artificial models. To
the best of our knowledge, this is the first example of pillar[5]arene-
based supramolecular assemblies for mimicking the light-
harvesting system. Therefore, this work not only provided a novel
model for fabricating artificial light-harvesting systems but also
extended the potential applications of pillararenes in the field of
optoelectronic materials.
9 (a) Z.-Y. Gu, D.-S. Guo, M. Sun and Y. Liu, J. Org. Chem., 2010,
5, 3600; (b) R. Menting, J. T. Lau, H. Xu, D. K. Ng, B. Roder and
7
E. A. Ermilov, Chem. Commun., 2012, 48, 4597.
1
1
1
1
0 (a) F. Loiseau, G. Marzanni, S. Quici, M. T. Indelli and S. Campagna,
Chem. Commun., 2003, 286; (b) H. Q. Peng, J. F. Xu, Y. Z. Chen,
L. Z. Wu, C. H. Tung and Q. Z. Yang, Chem. Commun., 2014,
50, 1334.
1 (a) T. Ogoshi, S. Kanai, S. Fujinami, T.-a. Yamagishi and
Y. Nakamoto, J. Am. Chem. Soc., 2008, 130, 5022; (b) M. Xue,
Y. Yang, X. Chi, Z. Zhang and F. Huang, Acc. Chem. Res., 2012,
45, 1294.
2 (a) J. Wu, S. Sun, X. Feng, J. Shi, X. Y. Hu and L. Wang, Chem.
Commun., 2014, 50, 9122; (b) S. Sun, X.-Y. Hu, D. Chen, J. Shi,
Y. Dong, C. Lin, Y. Pan and L. Wang, Polym. Chem., 2013, 4, 2224;
(
c) P. Wang, X. Yan and F. Huang, Chem. Commun., 2014, 50, 5017.
3 (a) G. Yu, M. Xue, Z. Zhang, J. Li, C. Han and F. Huang, J. Am. Chem.
Soc., 2012, 134, 13248; (b) Y. Cao, X.-Y. Hu, Y. Li, X. Zou, S. Xiong,
C. Lin, Y.-Z. Shen and L. Wang, J. Am. Chem. Soc., 2014, 136, 10762;
We are grateful for the financial support from the National Basic
Research Program of China (2014CB846004 and 2013CB922100),
the National Natural Science Foundation of China (No. 21472089
and 21202083), and the National Science Foundation of Jiangsu
(
c) Q. Duan, Y. Cao, Y. Li, X. Hu, T. Xiao, C. Lin, Y. Pan and L. Wang,
J. Am. Chem. Soc., 2013, 135, 10542; (d) X.-Y. Hu, K. Jia, Y. Cao, Y. Li,
S. Qin, F. Zhou, C. Lin, D. Zhang and L. Wang, Chem. – Eur. J., 2015,
21, 1208; (e) Y. Yao, M. Xue, J. Chen, M. Zhang and F. Huang, J. Am.
(No. BK20140595).
Chem. Soc., 2012, 134, 15712.
1
4 (a) N. Song, D. X. Chen, Y. C. Qiu, X. Y. Yang, B. Xu, W. Tian and
Y. W. Yang, Chem. Commun., 2014, 50, 8231; (b) L. Chen, W. Si,
L. Zhang, G. Tang, Z. T. Li and J. L. Hou, J. Am. Chem. Soc., 2013,
135, 2152; (c) Y. Guan, M. Ni, X. Hu, T. Xiao, S. Xiong, C. Lin and
L. Wang, Chem. Commun., 2012, 48, 8529; (d) X.-Y. Hu, P. Zhang,
X. Wu, W. Xia, T. Xiao, J. Jiang, C. Lin and L. Wang, Polym. Chem.,
2012, 3, 3060; (e) Z. Zhang, Y. Luo, J. Chen, S. Dong, Y. Yu, Z. Ma and
F. Huang, Angew. Chem., Int. Ed., 2011, 50, 1397.
Notes and references
1
(a) D. A. Bryant and N.-U. Frigaard, Trends Microbiol., 2006, 14, 488;
b) V. Balzani, A. Credi and M. Venturi, ChemSusChem, 2008, 1, 26.
(
2
(a) J. Barber and B. Andersson, Nature, 1994, 370, 31; (b) F. D’Souza,
P. M. Smith, M. E. Zandler, A. L. McCarty, M. Itou, Y. Araki and O. Ito,
J. Am. Chem. Soc., 2004, 126, 7898; (c) X. Hu, A. Damjanovi ´c , T. Ritz
and K. Schulten, Proc. Natl. Acad. Sci. U. S. A., 1998, 95, 5935; 15 T. Ogoshi, D. Yamafuji, T.-a. Yamagishi and A. M. Brouwer, Chem.
d) E. Maligaspe, N. V. Tkachenko, N. K. Subbaiyan, R. Chitta, Commun., 2013, 49, 5468.
M. E. Zandler, H. Lemmetyinen and F. D’Souza, J. Phys. Chem. A, 16 F. Arteaga-Larios, A. Cosultchi and E. P ´e rez, Energy Fuels, 2004,
009, 113, 8478; (e) T. Renger and E. Schlodder, J. Photochem. Photo- 19, 477.
biol., B, 2011, 104, 126; ( f ) N. Krausz, W.-D. Schubert, O. Klukas, 17 (a) C. Li, K. Han, J. Li, Y. Zhang, W. Chen, Y. Yu and X. Jia,
(
2
P. Fromme, H. T. Witt and W. Saenger, Nat. Struct. Biol., 1996, 3, 965.
(a) S.-C. Lo and P. L. Burn, Chem. Rev., 2007, 107, 1097;
Chem. – Eur. J., 2013, 19, 11892; (b) X. Wang, H. Deng, J. Li,
K. Zheng, X. Jia and C. Li, Macromol. Rapid Commun., 2013, 34, 1856.
3
4
(
(
b) G. M. Farinola and R. Ragni, Chem. Soc. Rev., 2011, 40, 3467; 18 (a) G. Ulrich, R. Ziessel and A. Harriman, Angew. Chem., Int. Ed.,
c) Y. Tao, C. Yang and J. Qin, Chem. Soc. Rev., 2011, 40, 2943.
(a) J.-K. Lee and M. Yang, Mater. Sci. Eng., B, 2011, 176, 1142;
2008, 47, 1184; (b) A. Coskun and E. U. Akkaya, J. Am. Chem. Soc.,
2005, 127, 10464.
(
2
b) Y. Koyama, T. Miki, X.-F. Wang and H. Nagae, Int. J. Mol. Sci., 19 (a) K. Umezawa, Y. Nakamura, H. Makino, D. Citterio and K. Suzuki,
009, 10, 4575; (c) A. Hagfeldt, G. Boschloo, L. Sun, L. Kloo and
J. Am. Chem. Soc., 2008, 130, 1550; (b) K. Rurack, M. Kollmannsberger
and J. Daub, Angew. Chem., Int. Ed., 2001, 40, 385.
H. Pettersson, Chem. Rev., 2010, 110, 6595.
4
646 | Chem. Commun., 2015, 51, 4643--4646
This journal is ©The Royal Society of Chemistry 2015