A Bodipy-bearing pillar[5]arene for mimicking photosynthesis: Multi-fluorophoric light harvesting system

Article abstract of DOI:10.1016/j.tetlet.2018.04.016

Herein, we submitted to the original synthesis, characterization, energy transfer mechanism of the Bodipy-bearing pillar[5]arene Bodipy and its reactants by employing of infrared, ¹H, ¹¹B, ¹³C, ¹⁹F-NMRs, UV–vis,

Full text of DOI:10.1016/j.tetlet.2018.04.016

Accepted Manuscript
A BODIPY-bearing pillar[5]arene for mimicking photosynthesis: multi-fluoro-
phoric light harvesting system
Ahmed Nuri Kursunlu, Canan Baslak
PII:
S0040-4039(18)30459-3
https://doi.org/10.1016/j.tetlet.2018.04.016
TETL 49879
DOI:
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
15 February 2018
27 March 2018
10 April 2018
Please cite this article as: Kursunlu, A.N., Baslak, C., A BODIPY-bearing pillar[5]arene for mimicking
photosynthesis: multi-fluorophoric light harvesting system, Tetrahedron Letters (2018), doi: https://doi.org/
10.1016/j.tetlet.2018.04.016
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and
review of the resulting proof before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

A BODIPY-bearing pillar[5]arene for mimicking photosynthesis: multi-fluorophoric
light harvesting system
Ahmed Nuri Kursunlu1, Canan Baslak
Department of Chemistry, University of Selcuk, Campus, 42075, Konya, Turkey
ABSTRACT
Herein, we submitted to the original synthesis, characterization, energy transfer mechanism of
1
the Bodipy-bearing pillar[5]arene Bodipy and its reactants by employing of infrared, H, 11B,
13C, 19F-NMRs, UV-vis, fluorescence spectroscopy, melting point apparatus, CHN elemental
analysis and mass spectroscopy. Preliminary UV-vis, fluorescence and excitation
measurements were carried out in CH2Cl2 and the results revealed an effective fluorescence
resonance energy transfer (FRET) system based on the interaction of pillar[5]arene and
Bodipy derivative. εmax of target molecule reached to a maximum value and it was found as
955 000 M-1cm-1. This fluorescent macromolecule worked well for mimicking a light
harvesting system with an energy transfer efficiency up to 92%.
Keywords: Pillar[5]arene, Bodipy, light harvesting, energy transfer, fluorescence
1Corresponding author:
E-mail address: ankursunlu@gmail.com (A.N.Kurşunlu)
Phone: +90 332 223 3876 Konya/Turkey
1

Light harvesting-capable systems have attracted much interest owing to their
widespread fields in technology and scientific application such as solar energy units,
energy suppliers, nanodevices, memory storages, smart molecules and sensor materials1-
5. Fluorescence resonance energy transfer (FRET) is most famous among energy transfers
carried out in light harvesting systems that the interaction of the donor and acceptor via a
non-radiative transfer of energy from an excited donor fluorophore to a ground state acceptor
6,7. The sunlight is vital for the living cells capable of photosynthesis, similarly, an efficient
energy transfer is very important for the mimicking photosynthetic light-harvesting devices
such as organic light-emitting diodes, fluorescent dye-sensitized solar cells and other
optoelectronic supramolecules. Chemist and biochemists focused on light-harvesting devices
obtained by the combination of donor and acceptor organic groups. Both fluorescent dyes and
macromolecules contributed together towards the improving of the mimicking photosynthetic
light-harvesting systems8-10. Calixarenes, crown ethers, pillararenes etc. as a macromolecule
and Bodipy, phthalocyanine, porphyrin, dansyl chloride etc. as a fluorescent dye were used in
these systems11-18. Among macromolecules, pillararene compounds linked with methylene
bridges at para-positions have multi-terminals and they can be possessed for various
applications such as smart polymer, drug delivery, chemosensor, transmembrane19-22
.
However, pillararenes have been just reported in a few literatures for FRET-based light-
harvesting systems23,24. Ogoshi and co-workers synthesized a pillar[5]arene derivative
including pyrene/perylene for an effective light-harvesting application that a FRET process
carried out from pyrene to perylene depending on the smart interlocked structure25.
To make a more efficient process of the electron-transfer, various donor and acceptor linked
dyads were developed. Among most dyes, Bodipy’s have been extensively used as antenna
molecule in artificial photosynthetic systems due to their excellent properties such as high
molar absorption coefficient, high fluorescence yield, long lifetimes good photostability26-28
.
2

Herein, we summarize a multifluorophoric combination for artificial photosynthesis device.
For this aim, pillar[5]arene bearing ten Bodipy units has been designed as a light harvesting
antennae (Scheme 1). The spectroscopic measurement of compounds show that it can
possibly provide a strategy for the enhancement of light harvesting ability of pillar[5]arene
linked Bodipy moieties making them attractive for various applications. To the best of our
knowledge, this paper is a pioneer study used both pillar[5]arene and Bodipy for the light-
harvesting materials.
Decameric Bodipy-bearing pillar[5]arene (8) (see Scheme 1) was prepared by a Schiff
base condensation between AA/BB-type Bodipy (with amino terminal) and pillar[5]arene
containing ten aldehyde fragments.
FRET property of 8 was investigated by the spectroscopic techniques as UV–Vis and
fluorescence and excitation for mimicking a photosynthetic light-harvesting system. In order
to achieve the synthesis of 8, it was prepared in the several synthetic steps. A boron-
dipyrromethene (5) derivative containing benzylchloro moiety was firstly synthesized. This
compound was converted to benzylazido (6) by sodium azide and then reduced to amino
group (7) for Schiff base reaction. The main framework of 4 was obtained in several steps
from a reaction of 3 and 4-hydroxybenzaldehyde in presence of potassium carbonate. The
details of syntheses of all compounds can be found in the Suppl. Info. Target multi-
fluorophoric compound (8) was obtained from a reaction between Bodipy (7) and
pillar[5]arene in chloroform. To this aim, Bodipy was used in ten equivalent due to decameric
terminals of pillar[5]arene. The chemical structures of the compounds were optionally
1
illuminated by H-NMR, 11B-NMR, 13C-NMR, 19F-NMR, elemental analysis, melting point
and MS.
3

O
O
O
O
O
I
O
O
I
O
O
I
HO
I
I
I
O
O
O
O
10
O
O
O
O
O
O
O
O
O
O
O
O
OH
K2CO3
CI4
BF3.OEt2
O
O
O
paraformaldehyde
O
PPh3
O
O
O
O
O
O
I
I
O
I
O
I
O
I
O
OH
I
2
O
1
3
O
O
O
O
O
4
+
Cl
N
H2N
N3
Cl
H
N
BF3.OEt2,
TEA
H2
O
PPh3
NaN3
LiBr
2
+
Ar, dry DCM
O
Cl
N
N
F
N
N
N
B
B
B
F
F
F
F
F
7
5
6
F
F
B
N
N
F
B
F
N
N
F
F
N
B
N
N
N
N
F
B
N
O
F
O
O
N
N
N
O
O
F
F
O
B
O
O
N
N
O
O
O
O
O
O
O
N
O
O
O
N
O
O
N
N
B
F
N
N
B
F
N
F
F
N
N
N
B
N
N
B
F
N
F
F
F
N
N
B
F
F
8
Scheme 1 Chemical structures of reactants and target supramolecule
The ground-state absorption spectra of Compounds 3, 4, 5, 6, 7 and target compound
(8) initially recorded in dichloromethane (3x10-7 M) in order to examine the assemblies to the
natural photosynthesis system (Fig.1). Fig. 1 shows that free-Bodipy derivatives 5, 6 and 7
exhibited to three main transition around 275, 390 and 530 nm. These transitions assign to
4

π→π*, n→π*, and S0→S1 band of classical Bodipy compounds, respectively. Their
bandwidth at 530 nm and gradually broadened in order 6, 5 and 7. Thus, the molar absorption
coefficients (εmax also significantly changed depending on behaviors of different auxochrome
)
moieties involving the lone pair of electrons while no shift in the absorption maximum. εmax
values are calculated as 450 000 M-1cm-1, 224 000 M-1cm-1 and 151 000 M-1cm-1 for 6, 5 and
7, respectively. Otherwise, the pillar[5]arene derivatives (3 and 4) exhibited a more different
bands. The most important difference between the absorption spectra of 3 and 4 is the
broadening of absorption band around 275 nm (ε = 63 000 M-1 cm-1, 416 300 M-1 cm-1,
respectively). This change can be explained by the binding of 4-hydroxybenzaldehyde
moieties to the skeleton of pillar[5]arene and thus, the increasing number of π-electrons. The
main absorption band of 8 broadened and slightly red-shifted due to intramolecular like other
reactants interactions of pillar[5]arene skeleton with the bonded Bodipy subunits, when
compared to those typically observed for a Bodipy derivative. εmax of 8 reached to a higher
value and calculated as 955 000 M-1cm-1. In addition to, more specific mounds were observed
at 280, 330 and 370 nm owing to multi-electronic transitions in macromolecule as unlike
other reactants.
5

Fig. 1 Absorption spectra of compounds 3, 4, 5, 6, 7 and 8 recorded in CH2Cl2 at 25°C
The emission and excitation spectra recorded in same solvent (CH2Cl2) and concentration (3.
10-7 M) for reactants and target compound are depicted in Fig. 2 and Fig. 3. While the
emission maximum of fluorescent compounds, 5, 6, 7 and 8, almost centered around 540 nm,
their fluorescence intensities are very different values. Moreover, the fluorescent
enhancement in compound 8 can attributed due to the rotation restriction of Bodipy groups
and linked other aromatic fragments. However, it was thought that Bodipy moities are more
effective in this process owing to their excellent π-conjugation.
6

Fig. 2 a) Emission spectra of compounds 3, 4, 5, 6, 7 and 8 recorded in CH2Cl2 in 3. 10-7 M (25°C,
λexc= 475 nm, slit: 3). b) Normalized UV-vis absorption spectra of 4, 7 and fluorescence emission
spectra of 4, 7 and 8 (5°C, λexc= 475 nm, slit: 3).
Fig. 2b shows the normalized UV-vis absorption spectra of compounds 4, 7 and the
fluorescence emission spectra of 4, 7 and 8. The titration experiments for the 4+7 compounds
have now been studied and gave in FigS28. The maximum emission wavelength shifted
slightly to red with the continuously extended π-system.
These results were further photographed under longwave light (365 nm) and daylight (Fig. 3).
The solutions of compounds 3 and 4 are transparent, however, other solutions are bright green
and sparkling yellow due to their excellent fluorescent character. Meanwhile, the
7

corresponding fluorescent color of fluorescent reactant, 7, converted from green to yellow
following to the reaction with other reactants, 4, under longwave. All observations are
consistent with the emission data and the outcome can be explained by an energy transfer
mechanism.
Fig. 3 Corresponding color changes of compound solutions (3, 4, 5, 6, 7 and 8) under longwave (365
nm) and daylight
The FRET efficiency E can be defined as the fraction of the donor de-excited via energy
transfer to the acceptor. In our system, the efficiency E was calculated according to the
following equation:
E = 1 − I/I0
where I and I0 are the fluorescence intensities of the donor in the presence and absence of the
acceptor, respectively23. The I and I0 values were measured as 72 and 1093, respectively and
the efficiency were calculated to be 92% for 8.
This energy transfer mechanism was also supported by the excitation spectra measured
for the fluorescent compounds (5, 6, 7 and 8) (Fig. 4) at the fixed Iem in the 560 nm. Two
8

main band were observed in the excitation spectra and these curves are similar to the
absorption spectrum of compounds. As observed, the excitation curve of reactant 7 broadened
in target compound 8 and this difference was ascribed to the change in the increasing
fluorescent moieties and intramolecular folded-interactions. As a result of these interaction,
an efficient energy transfer carried out between chromophore groups and pillar[5]arene
aromatic subunit. Moreover, the broadness can be explained by the J-aggregated formation
enhanced among ten fluorophoric Bodipy cores15. So, the aggregation cause to a perturbation
in the electronic structure of molecule by the alternation of the ground and excited state
electronic structures.
Fig. 4 Excitation spectrum recorded for compounds 5, 6, 7 and 8 recorded in CH2Cl2 at 25°C
(3.10-7 M, λem=570 nm, slit:3).
9

In conclusion, we have successfully synthesized an efficient FRET system by the combination
of the pillar[5]arene and Bodipy moieties. To the best of our knowledge, this compound is
one of few examples on pillar[5]arenes consisting of Bodipy with alkyl-amino terminal. We
plan to prepare another pillararenes having higher wavelength with different Bodipy to
increase the a more effective FRET system and to illuminate overall shuttling process of the
pillararene macromolecules within Bodipy’s.
Acknowledgements
The authors express their appreciation to Prof. J.-F. Nierengarten and Dr. I. Nierengarten for
helpful discussions. Financial support for this work is provided by the Research Foundation of
Selcuk University (BAP) and is gratefully acknowledged.
References
[1] Wang A., Xuan Y., Energy, 2018, 144: 490-500.
[2] Alghisi D., Ferrari V., Ferrari M., Touati F., Crescini D., Mnaouer A.B., Sensors
Actuators A: Phys., 2017; 263: 305-316
[3] Kursunlu A. N., RSC Adv., 2014; 4: 47690-47696.
[4] Xuan M., Zhao J., Shao J., Li Q., Li J., Green Energy & Environ., 2017;2: 18-22.
[5] Taner B., Kursunlu A. N., Güler E., Spectrochim. Acta Part A: Mol. Biomol. Spec.
2014;118: 903-907.
[6] Qiao F., Yuan Z., Lian Z., Yan C.-Y., Zhuo S., Zhou Z.-Y., Xing L.-B., Dyes Pigments,
146, 2017, 392-397.
10

[7] Suzuki S., Tatsumi D., Tsukamoto T., Honna R., Shimada T., Inoue H., Takagi S.,
Tetrahedron Lett., 2018; 59: 528-531.
[8] Sun J., Hua B., Li Q., Zhou J., Yang J., Org. Lett., 2018; DOI:
10.1021/acs.orglett.7b03612.
[9] Wang S., Ye J.-H., Han Z., Fan Z., Wang C., Mu C., Zhang W., He W., RSC Adv., 2017;
7: 36021-36025.
[10] Arrigo A., Ganga G. L., Nastasi F., Serroni S., Santoro A., Santoni M.-P., Galletta M.,
Campagna S., Puntoriero F., Comptes Rendus Chimie, 2017; 20: 209-220.
[11] a) Deniz Z. Ş., Tarakci K., Gürol I., Ahsen V., Harbeck M., Sensors Act. B: Chem., 2016;
229: 581-586 b) Zhang H., Strutt N. L., Stoll R. S., Li H., Zhua Z., Stoddart J. F., Chem.
Comm. 2011; 47: 11420-11422, 2011 c) Zhang H., Ma X., Nguyen K. T., Zhao Y., Acs Nano,
2013; 7: 7853-7863.
[12] a) Wang Q., Ma F., Tang W., Zhao S., Li C., Xie Y., Dyes Pigments, 2018; 148: 437-443
b) Zhang H., Zhao Y., Chem. Eur. J., 2013; 19: 16862-16879 c) Zhang H., Ma X., Guo J.,
Nguyen K. T., Zhang Q., Wang X.-J., Yan H., Zhu L., Zhao Y., Rsc Advances, 2013; 3: 368-
371.
[13] a) Bayrakcı M., Kursunlu A. N., Güler E., Ertul Ş., Dyes Pigments, 2013; 99: 268-274 b)
Zhang H., Nguyen K. T., Ma X., Yan H., Guo J., Zhua L., Zhao Y., Org. & Biomol. Chem.,
2013; 11: 2070-2074 c) Zhang H., Liu Z., Xin F., Hao A., Chin. J. Org. Chem., 2012; 32:
219-229.
[14] a) Yao Y., Sun Y., Yu H., Chen W., Dai H., Shi Y., Dalton Trans., 2017; 46: 16802-
16806 b) Kursunlu A. N., Acikbas Y., Ozmen M., Erdogan M., Capan R., Analyst, 2017; 142:
3689-3698.
[15] a) Günsel A., Bilgiçli A. T., Kandaz M., Orman E. B., Özkaya A. R., Dyes Pigments,
2014; 102: 169-179 b) Zhang H., Ma X., Nguyen K. T., Zeng Y., Tai S., Zhao Y.,
11

Chempluschem, 2014; 79: 462-469 c) Zhang H., Zhao Y., Chapter 9 Supramolecular
Assemblies from Pillararenes (Micellar, Vesicular and Tubular Formations), Book:
Pillararenes 2016, pp 208-228 Published: 2016.
[16] Kursunlu A. N., Koc Z. E., Obalı A. Y., Güler E., J. Luminescence, 2014; 149: 215-220.
[17] a) Zhou M., Wang X., Huang K., Huang Y., Hu S., Zeng W., Tetrahedron Lett., 2017;
58: 991-994 b) Ji X., Xia D., Yan X., Wang H., Huang F., Acta Polym. Sin., 2017; 9-18 c)
Yao Y., Xue M., Chen J., Zhang M., Huang F., J. Am. Chem. Soc., 2012; 134: 15712-15715
d) Zhang Z., Luo Y., Chen J., Dong S., Yu Y., Ma Z., Huang F., Angew. Chem. Int. Ed. 2011;
50: 1397-1401.
[18] Kursunlu A. N., Deveci P., Guler E., J. Luminescence, 2013; 136: 430-436.
[19] Wheate N. J., Dickson K.-A., Kim R. R., Nematollahi A., Macquart R. B., Kayser V.,
Yu G., Church W. B., Marshi D. J., J. Pharma. Sci., 2016; 105: 3615-3625.
[20] Nierengarten I., Deschenaux R., Nierengarten J.-F., Chimia, 2016; 70: 61-66.
[21] Stepanova V.B., Shurpik D.N., Evtugyn V.G., Stoikov I.I., Evtugyn G.A., Osin Y. N.,
Hianik T., Sensors Act. B Chem., 2016; 225: 57-65.
[22] Yao Y., Jie K., Y. Zhou, Xue M., Tetrahedron Lett. 2014; 55: 3195-3199.
[23] Meng L.-B., Li D., Xiong S., Hu X.-Y., Wang L., Li G., Chem. Commun., 2015; 51:
4643-4646.
[24] Bojtar M., Szakacs Z., Hessz D., Bazso F. L., Kallay M., Kubinyi M., Bitter I., Dyes
Pigments, 2016; 133: 415-423.
[25] Ogoshi T., Yamafuji D., Yamagishi T., Brouwer A. M., Chem. Commun., 2013; 49:
5468-5470
[26] Lv Y., Wei W., Xie Y., J. Chil. Chem. Soc., 2015; 60: 2843-2846.
[27]) M. Formica, V. Fusi, L. Giorgi, M. Micheloni, New fluorescent chemosensors for metal
ions in solution, Coor. Chem. Rev., 2012; 256: 170-192.
12

[28] Ambrosi G., Borgogelli E., Formica M., Fusi V., Giorgi L., Micheloni M., Rampazzo E.,
Sgarzi M., Zaccheroni N., Prodi L., Sensors Actuat. B: Chem., 2015; 207: 1035-1044.
13

14

Highlights
•
•
Results revealed an effective energy transfer based on pillar[5]arene and Bodipy.
εmax of target molecule reached to a maximum value, calculated as 955 000 M-1cm-1.
Macromolecule worked for a light harvesting system with energy transfer up to 92%.
•
15