Supramolecular Coordination Polymer Formed from Artificial Light-Harvesting Dendrimer

Article abstract of DOI:10.1021/jacs.5b08092

We report the formation of supramolecular coordination polymers formed from multiporphyrin dendrimers (P_ZnP_M; M = FB or Cu), composed of the focal freebase porphyrin (P_FB) or cupper porphyrin (P_Cu) with eight zinc porphyrin (P_Zn) wings, and multipyridyl porphyrins (PyP_M; M = FB or Cu), P_FB or P_Cu with eight pyridyl groups, through multiple axial coordination interactions of pyridyl groups to P_Zns. UV-vis absorption spectra were recorded upon titration of PyP_FB to P_ZnP_FB. Differential spectra, obtained by subtracting the absorption of P_ZnP_FB without guest addition as well as the absorption of PyP_FB, exhibited clear isosbestic points with saturation binding at 1 equiv addition of PyP_FB to P_ZnP_FB. Job's plot analysis also indicated 1:1 stoichiometry for the saturation binding. The apparent association constant between P_ZnP_FB and PyP_FB (2.91 × 10⁶ M^-1), estimated by isothermal titration calorimetry, was high enough for fibrous assemblies to form at micromolar concentrations. The formation of a fibrous assembly from P_ZnP_FB and PyP_FB was visualized by atomic force microscopy and transmission electron microscopy (TEM). When a 1:1 mixture solution of P_ZnP_FB and PyP_FB (20 M) in toluene was cast onto mica, fibrous assemblies with regular height (ca. 2 nm) were observed. TEM images obtained from 1:1 mixture solution of P_ZnP_FB and PyP_FB (0.1 wt %) in toluene clearly showed the formation of nanofibers with a regular diameter of ca. 6 nm. Fluorescence emission measurement of P_ZnP_M indicated efficient intramolecular energy transfer from P_Zn to the focal P_FB or P_Cu. By the formation of supramolecular coordination polymers, the intramolecular energy transfer changed to intermolecular energy transfer from P_ZnP_M to PyP_M. When the nonfluorescent PyP_Cu was titrated to fluorescent P_ZnP_FB, fluorescence emission from the focal P_FB was gradually decreased. By the titration of fluorescent PyP_FB to nonfluorescent P_ZnP_Cu, fluorescence emission from P_FB in PyP_FB was gradually increased due to the efficient energy transfer from P_Zn wings in P_ZnP_Cu to PyP_FB.

Full text of DOI:10.1021/jacs.5b08092

Subscriber access provided by UNIV OF NEBRASKA - LINCOLN
Article
Supramolecular Coordination Polymer Formed
from Artificial Light-Harvesting Dendrimer
Hosoowi Lee, Young-Hwan Jeong, Joo-Ho Kim, Inhye Kim, Eunji Lee, and Woo-Dong Jang
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.5b08092 • Publication Date (Web): 08 Sep 2015
Downloaded from http://pubs.acs.org on September 15, 2015
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a free service to the research community to expedite the
dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts
appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been
fully peer reviewed, but should not be considered the official version of record. They are accessible to all
readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered
to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published
in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just
Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor
changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers
and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors
or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Journal of the American Chemical Society is published by the American Chemical
Society. 1155 Sixteenth Street N.W., Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 9
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Table of contents graphic
40x42mm (300 x 300 DPI)
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 2 of 9
1
2
3
4
5
6
7
8
9
Supramolecular Coordination Polymer Formed from Artificial Light-
Harvesting Dendrimer
Hosoowi Lee,a Young-Hwan Jeong,a Joo-Ho Kim,a Inhye Kim,b Eunji Lee,*,b Woo-Dong Jang*,a
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
aDepartment of Chemistry, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 120-749, Korea.
bGraduate School of Analytical Science and Technology, Chungnam National University, 99 Daehak-ro, Yuseong-gu,
Daejeon 305-764, Korea.
ABSTRACT: We report the formation of supramolecular coordination polymers formed from multiporphyrin dendrimers
(PZnPM; M = FB or Cu), composed of the focal freebase porphyrin (PFB) or cupper porphyrin (PCu) with eight zinc porphy-
rin (PZn) wings, and multipyridyl porphyrins (PyPM; M = FB or Cu), PFB or PCu with eight pyridyl groups, through multi-
ple axial coordination interactions of pyridyl groups to PZns. UV/Vis absorption spectra were recorded upon titration of
PyPFB to PZnPFB. Differential spectra, obtained by subtracting the absorption of PZnPFB without guest addition as well as
the absorption of PyPFB, exhibited clear isosbestic points with saturation binding at 1 equivalent addition of PyPFB to
PZnPFB. Job’s plot analysis also indicated 1:1 stoichiometry for the saturation binding. The apparent association constant
between PZnPFB and PyPFB (2.54 x 106 M-1), estimated by isothermal titration calorimetry (ITC), was high enough for fi-
brous assemblies to form at micromolar concentrations. The formation of a fibrous assembly from PZnPFB and PyPFB was
visualized by atomic force microscopy (AFM) and transmission electron microscopy (TEM). When a 1:1 mixture solution
of PZnPFB and PyPFB (20 µM) in toluene was cast onto mica, fibrous assemblies with regular height (ca. 2 nm) were ob-
served. TEM images obtained from 1:1 mixture solution of PZnPFB and PyPFB (0.1 wt%) in toluene clearly showed the for-
mation of nanofibers with a regular diameter of ca. 6 nm. Fluorescence emission measurement of PZnPM indicated effi-
cient intramolecular energy transfer from PZn to the focal PFB or PCu. By the formation of supramolecular coordination
polymers the intramolecular energy transfer changed to intermolecular energy transfer from PZnPM to PyPM. When the
non-fluorescent PyPCu was titrated to fluorescent PZnPFB, fluorescence emission from the focal PFB was gradually de-
creased. By the titration of fluorescent PyPFB to non-fluorescent PZnPCu, fluorescence emission from PFB in PyPFB was
gradually increased due to the efficient energy transfer from PZn wings in PZnPCu to PyPFB.
based chromophores in LHCs create a sequence of photo-
chemical processes, i.e., light absorption, energy migra-
INTRODUCTION
tion and energy transfer to reaction center, charge separa-
tion, and electron transfer.20 To mimic LHCs, synthetic
chemists have synthesized multiporphyrin-incorporated
molecules for efficient light absorption, directed energy
transfer, charge separation, and photo-catalytic
reactions.15,19,22-29 In addition to covalent approaches, sci-
entists have also attempted to create porphyrin-based
supramolecular assemblies that mimic LHCs.12,19,27,30-33 For
example, Herz et al. reported porphyrin nanorings as the
biomimetic example of light-harvesting antenna.32 Hupp
et al. reported porphyrin-based metal-organic frameworks
to achieve efficient light-harvesting and ultrafast energy
migration.33 We recently reported artificial light harvest-
ing dendrimers with multiple zinc porphyrin (PZn) wings
connected to the focal freebase porphyrin (PFB).30 These
porphyrin dendrimers exhibited very efficient energy
transfer from the PZn wings to the focal PFB. Moreover,
formation of host-guest complexes between the porphyrin
dendrimers and pyridyl-bearing porphyrins enabled pho-
tophysical switching from energy transfer to electron
transfer. Such supramolecular assembly-based photo-
The formation of supramolecular polymers is consid-
ered as an emerging technology in the fields of structural,
electronic, biomedical, and biomimetic functional mate-
rials science.1-3 Various molecular interactions, including
multiple hydrogen bonds, host-guest inclusions, π-π in-
teractions, metal-coordination interaction, and so on,
have been applied to build supramolecular polymers.4-8
Among various interactions, metal-coordination interac-
tion is particularly interesting because metal-coordination
bonds form highly directional and controllable manner.9-11
Metalloporphyrins often form well-ordered supramolecu-
lar architectures through the axial coordination interac-
tion between the central metal ion and pyridyl ligands.12
The biological importance and relevance of porphyrins
have made multiporphyrin arrays of great interest from a
biomimetic standpoint.13-19 Especially, natural light har-
vesting antenna complexes (LHCs) in plants and bacteria
are composed of a great number of self-assembled por-
phyrin-based chromophore units that efficiently absorb
visible photons to initiate the conversion of solar energy
to vital energy sources.20,21 Large number of porphyrin-
ACS Paragon Plus Environment

Page 3 of 9
Journal of the American Chemical Society
physical switching would provide critical benefits for the cuvette with a path length of 1 cm at ambient temperature.
1H NMR spectra were recorded at 25 °C on a Bruker DPX
400 and a Bruker Avance 600 spectrometer and 13C NMR
spectra were recorded at 25 °C on a Bruker DPX 400 spec-
trometer. 2D-DOSY NMR spectra were recorded at 25 °C
on a Bruker Avance 600 spectrometer. MALDI-TOF-MS
was performed on a Bruker Daltonics LRF20 with
dithranol (1,8,9-trihydroxyanthracene) as the matrix. Gel
permeation chromatography (GPC) was performed on JAI
model LC9021 equipped with JAIGEL-2H and JAIGEL-3H
columns using CHCl3 as the eluent. Isothermal titration
calorimetry (ITC) were performed on a Microcal VP-ITC.
Atomic force microscopy (AFM) images were obtained
using a VEECO MULTIMODE instrument. Transmission
Electron Microscopy (TEM) images were taken using a
JEOL JEM_3011 HR and a JEOL JEM-1400.
1
2
3
4
5
6
7
8
design of effective porphyrin-based functional nano-
materials.34,35 In this context, we demonstrate the for-
mation of supramolecular coordination polymers formed
from artificial light-harvesting porphyrin dendrimers
(PZnPM; M = FB or Cu; Scheme 1) and pyridyl-bearing
porphyrins (PyPM; M = FB or Cu; Scheme 1 and 2).
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
UV/Vis Titration. UV/Vis absorption spectra of PZnPFB
and PyPFB were recorded upon titration of PyPFB. Then,
differential spectra were obtained by subtracting the ab-
sorption of PZnPFB without PyPFB addition as well as the
absorption of PyPFB. Because a fixed volume of PyPFB
solution was continuously added, the total absorption of
PyPFB could be numerically calculated from the standard
solution. The total volume of mixture solution increased
gradually, but the concentration of PZnPFB gradually de-
creased upon continuous addition of PZnPFB solution.
Therefore, the final spectra were divided into dilution
factors for each titration step to display the UV/Vis titra-
tion spectra and binding isotherms.
Isothermal Titration Calorimetry (ITC). ITC exper-
iments were conducted on a Microcal VP-ITC at 25 °C.
For ITC measurements, toluene solutions of PZnPFB (4.2 x
10-5) M and PyPFB (5.4 x 10-4 M) were prepared. Both solu-
tions were degassed at 25 °C before measurements. Six
microliters of PyPFB solution in the injection syringe was
successively injected to PZnPFB solution in the cell 30
times with an injection interval of 450 sec. The ‘one-set-
of-sites’ binding model in Microcal Origin 7.0 software
was used for data analysis.
Transmission Electron Microscopy (TEM). A drop
of each sample in toluene was placed on a carbon-coated
copper grid and allowed to evaporate under ambient con-
ditions. A drop of uranyl acetate solution (2 wt%) was
placed on the surface of the sample-loaded grid for stain-
ing. The sample was deposited for at least 1 min, and ex-
cess solution was wicked off by filter paper. The speci-
men was observed using a JEOL_JEM_3011 HR operating
at 300 kV and a JEM-1400 operating at 120 kV. Data were
analysed using Gatan Digital Micrograph software.
Scheme 1. Chemical structures of multiporphyrin den-
drimers (PZnPM) and multipyridyl porphyrins (PyPM) and
schematic illustration of supramolecular polymers.
EXPERIMETAL SECTION
Materials and Measurements. All commercially
available reagents were reagent grade and used without
further purification. CH2Cl2, n-hexane, and tetrahydrofu-
ran (THF) were freshly distilled before each use. UV/Vis
absorption spectra were recorded on a JASCO V-660 spec-
trometer. Fluorescence spectra were measured by a
JASCO FP-6300 spectrophotometer and spectral sensitivi-
ty was corrected by comparison with well-known chro-
mophores such as rhodamine and coumarin dyes. All
spectral measurements were carried out using a quartz
Synthesis. PZnPFB was prepared by previously reported
procedures.16 The synthesis of PyPM is outlined in Figure
2.
PZnPCu: PZnPFB (17 mg, 0.0023 mmol) was dissolved in
CH2Cl2 (100 mL). A methanol (10 mL) solution of
Cu(OAc)2 (4.7 mg, 0.024 mmol) was then added to the
PZnPFB solution. The reaction mixture was stirred at 25 °C
for 2 h. The mixture was evaporated for dryness and puri-
fied over column chromatography on silica gel using
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 4 of 9
CH2Cl2 as an eluent. A freeze-drying procedure using was added to the mixture solution and stirred for 48 h at
1
2
3
4
5
6
7
8
benzene was then performed to give PZnPCu as pink pow-
der. MALDI-TOF-MS m/z: calcd for C468H508CuN36O24Zn8,
7613.32 [M+ + Na]; found, 7614.858.
25 °C. The reaction mixture was poured into distilled
water and extracted with CH2Cl2. The extract was dried
over anhydrous NaSO4 and then chromatographed on
silica gel using CH2Cl2 and n-hexane as eluents to give 3
(460 mg, 86%). H NMR (400 MHz, CDCl3, 25 °C) δ =
9.841 (s, 1 H), 7.84 (s, 2 H), 4.181 (s, 3 H), 0.265 (t, 18 H).
1: 4-hydroxybenzaldehyde (6 g, 49.54 mmol), NaIO4 (21.19
g, 99.09 mmol), and NaCl (11.58 g, 198.15 mmol) were dis-
solved in AcOH/H2O (9:1) solution (150 mL). KI (16.45g,
99 mmol) was slowly added to the mixture solution over 1
h at 25 °C. Then, the mixture solution was stirred for 2
day at 25 °C. The reaction mixture was poured into dis-
tilled water and extracted using EtOAc. The extract was
further washed with aqueous NaHCO3. The combined
extract was dried over anhydrous NaSO4 and passed
through celite. The solution was evaporated to dryness
and then purified by recrystallization using EtOAc and n-
hexane to give 1 as yellowish powder (10.85 g, 59%). 1H
NMR (400 MHz, CDCl3, 25 °C) δ = 9.744 (s, 1 H), 8.203 (s,
2 H), 6.256 (s, 1 H).
1
4: 3 (0.64 g, 1.93 mmol) was dissolved in propionic acid (15
mL). Freshly distilled pyrrole (0.13 mL, 1.93 mmol) was
added to the reaction mixture and refluxed for 4 h. The
reaction mixture was poured into distilled water and ex-
tracted with CH2Cl2. The combined extract was dried over
anhydrous NaSO4 and then evaporated to dryness. The
residue was chromatographed on silica gel using CH2Cl2
as an eluent to give crude porphyrin product. The puri-
fied porphyrin was dissolved in toluene (30 mL) and ex-
cess of nickel(II) acetylacetonate was added. The mixture
was refluxed for overnight and then poured into distilled
water. The mixture solution was extracted with CH2Cl2
and washed with water. The combined extract was dried
over anhydrous NaSO4 and then chromatographed on
silica gel using CH2Cl2 as an eluent to give 4 as dark red
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
O
H
O
H
O
H
O
H
i
ii
iii
I
I
I
I
OH
OH
OMe
2
TMS
3: TMS =
OMe
TMS
CH3
Si CH3
CH3
1
1
solid (410 mg, 55%). H NMR (400 MHz, CDCl3, 25 °C) δ =
8.744 (s, 8 H), 8.017 (s, 8 H), 4.316 (s, 12 H), 0.26 (s, 72 H);
MALDI-TOF-MS m/z: calcd for C88H100N4NiO4Si8, 1558.53
[M+]; found, 1560.283.
N
N
OMe
X
OMe
X
N
N
X
X
5: To a THF (30 mL) solution of 4 (410mg, 0.26 mmol),
tetrabutylammonium fluoride (13 mL; 10% THF solution)
was slowly added at 0°C and the reaction mixture was
stirred for 24 h at 25 °C. The reaction mixture was poured
into distilled water and then extracted with CH2Cl2. The
combined extract was dried oer anhydrous Na2SO4 and
then purified over column chrvomatography on silica gel
using CH2Cl2 as an eluent to give 5 as red solid (110 mg,
N
N
N
N
N
N
N
Ni
N
iv, v
vii
M
OMe
MeO
OMe
X
MeO
X
N
N
OMe
X
OMe
X
N
N
6: M = Ni
PyPFB: M = H2
PyPCu: M = Cu
viii
ix
4: X = TMS
5: X = H
vi
1
43%). H NMR (400 MHz, CDCl3, 25 °C) δ = 8.772 (s, 8 H),
Scheme 2. Synthesis of PyPM. Reagents and conditions; i)
NaIO4, NaCl, KI, AcOH/H2O, 2 day, 25 °C, ii) K2CO3, CH3I,
DMF, 13 h, 25 °C, iii) Pd(PPh3)2Cl2, CuI, trimethylsilylacety-
lene, diisopropylamine, 48 h, 25 °C, iv) pyrrole, propionic
acid, reflux, 4 h, v) nickel(II) acetylacetonate, toluene, reflux,
12 h, vi) tetrabutylammonium fluoride, THF, 24 h, 25 °C, vii)
Pd(PPh3)2Cl2, 3-iodopyridine, diisopropylamine/THF (2:1), 2
day, 70 °C, viii) H2SO4, CH2Cl2/MeOH/THF (5:1:1), 30 m,
25 °C, ix) Cu(OAc)2•H2O, MeOH/CH2Cl2, 3 h, 25 °C.
8.096 (s, 8 H), 4.356 (s, 12 H), 3.369 (s, 8 H); MALDI-TOF-
MS m/z: calcd for C64H36N4NiO4, 982.2 [M+]; found,
982.638.
6: 5 (250 mg, 0.25 mmol), Pd(PPh3)2Cl2 (0.89 mg, 0.001
mmol), and 3-iodopyridine (1.02 g, 5 mmol) were dis-
solved in diisopropyl amine/THF (2:1) mixture (30 mL).
The mixture solution was stirred for 30 m at 60 °C. CuI
(0.2 mg, 0.001 mmol) was then added to the mixture solu-
tion and further stirred for 2 days at 70 °C. Then the reac-
tion mixture was poured into distilled water and extract-
ed with CH2Cl2. The combined extract was evaporated to
dryness and purified over recrystallization from CH2Cl2/n-
hexane to give 6 as a red solid (330 mg, 82%). MALDI-
TOF-MS m/z: calcd for C104H60N12NiO4, 1599.42 [M+];
found, 1599.214.
2: Under N2 atmosphere, 1 (10.01 g, 26.77 mmol), K2CO3
(5.55 g, 40.16 mmol) were dissolved in N,N-
dimethylformamide (DMF; 95 mL). CH3I (3.3 mL, 53.54
mmol) were added to the mixture solution and stirred for
13 h at 25 °C. The reaction mixture was poured into dis-
tilled water (800 mL). The solid precipitation was col-
lected and washed with distilled water. The residue was
dissolved in CH2Cl2 and dried over anhydrous NaSO4 and
evaporated to dryness to give 2 as yellowish powder (10.15
PyPFB: To a CH2Cl2 (50 mL) solution of 6 (330 mg, 0.21
mmol), sulfuric acid (1 mL), methanol (10 mL), and THF
(10 mL) were added and stirred for 30 min at 25 °C. The
reaction mixture was poured into aqueous NaHCO3 and
extracted with CH2Cl2. The combined extract was puri-
fied over column chromatography on silica gel using
CH2Cl2 as an eluent to give PyPFB. 1H NMR (400 MHz,
CDCl3, 25 °C) δ = 9.016 (s, 8 H), 8.839 - 8.836 (m, 8 H),
8.819 - 8.816 (m, 8 H), 8.580 (m, 8 H), 8.572 - 8.569 (m, 8
1
g, 98%). H NMR (400 MHz, CDCl3, 25 °C) δ = 9.812 (s, 1
H), 8.269 (s, 2 H), 3.929 (s, 3 H).
3: 2 (0.87 g, 2.24 mmol), Pd(PPh3)2Cl2 (7.8 mg, 0.01 mmol),
and CuI (2.1 mg, 0.01 mmol) were dissolved in diisoprop-
ylamine (3 mL) and stirred for 1 h at 25 °C under N2 at-
mosphere. Trimethylsilylacetylene (0.8 mL, 5.6 mmol)
ACS Paragon Plus Environment

Page 5 of 9
Journal of the American Chemical Society
H), 8.396 (s, 8 H), 4.500 (s, 12 H), -2.813 (s, 2 H); 13C NMR
changes, we expected that PyPM and PZnPM would form
1
2
3
4
5
6
7
8
(400 MHz, CDCl3, 25 °C) δ = 162.08, 152.51, 149.24, 143.41,
139.68, 138.82, 137.64, 123.36, 120.36, 118.25, 115.68, 91.19,
88.48, 62.18; MALDI-TOF-MS m/z: calcd for C104H62N12O4,
1543.51 [M+]; found, 1542.703.
fibrous coordination polymers at 1:1 stoichiometry as illus-
trated in Scheme 1. The eight PZn wings linked to the me-
so-phenyl groups of PZnPM, which are conformationally
orthogonal to the plane of PFB or Pcu. Therefore, four PZns
are located onto the half side of PZnPM. In the same re-
spect, eight pyridyl groups are linked to the meso-phenyl
groups of core porphyrins in PyPM. Considering the three
dimensional structures of PZnPM and PyPM, only four
pyridyl groups in a PyPM can simultaneously interact with
the PZns in a PZnPM. When PZnPM and PyPM form 1:1 co-
ordination complex, four pyridyl groups and PZns are still
remained in opposite side, and thus it forces the multiple
axial coordination interactions of pyridyl groups to PZns
continuously, resulting in the fibrous supramoelcular co-
ordination polymer. If an excess amount of PyPM was
added to PZnPM, the fibrous assembly may be shortened
by insertion of PyPM into polymer chain, which might
become the terminal of the supramolecular polymers. If
the amount of PyPM addition exceeds two equivalents,
PZnPM and PyPM may form a sandwich-type 1:2 assembly.
PyPCu: To a CH2Cl2 (100 mL) solution of PyPFB (10.8 mg,
0.007 mmol), Copper(II) acetate monohydrate (3.1 mg,
0.02 mmol) and methanol (3 mL) were added and stirred
for 3 h at 25 °C. The reaction mixture solution was
poured into water and extracted with CH2Cl2. The com-
bined extract was purified over column chromatography
on silica gel using CH2Cl2 as the eluent to give PyPCu.
MALDI-TOF-MS m/z: calcd for C104H60CuN12O4, 1604.42
[M+]; found, 1604.273.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
RESULTS AND DISCUSSION
Multiporphyrin dendrimers and multipyridyl den-
drimers were synthesised for the formation of supramo-
lecular coordination polymers. The synthesis of PZnPFB
was carried out by previously reported procedures.16
Cupper ion was inserted to PZnPFB using Cu(OAc)2 to get
PZnPCu. The synthesis of PyPM is outlined in Scheme 2.
First, 3,5-diiodo-4-hydroxy benzaldehyde (1) was prepared
from 4-hydroxy benzaldehyde. Then, the hydroxyl group
of 1 was methylated using CH3I to get 2. Trimethylsilyla-
cetylene (TMS-acetylene) groups were introduced to 2
through Sonogashira’s coupling reaction to obtain 3.36
Acid catalysed annulation reaction of 3 with pyrrole and
successive oxidation was performed to obtain porphyrin.
To prevent cupper insertion in next step, nickel(II) acety-
lacetonate was reacted to get TMS-acetylene bearing
nickel porphyrin (4). After the deprotection of TMS
group, 3-iodopyridine was introduced through So-
nogashira’s coupling reaction to get 6. Finally, PyPFB and
PyPCu were prepared by demetallation and successive
cupper coordination. The porphyrins were characterized
by NMR and MALDI-TOF-MS analysis.
The pyridyl groups in PyPM can be bound to the PZns in
PZnPM as axial ligands for the formation of supramolecular
assemblies.37-40 Because PZnPM and PyPM have eight PZns
and pyridyl groups respectively, the stoichiometry for
saturation binding would be 1:1. UV/Vis spectral changes
upon titration of PyPFB to PZnPFB were measured in tolu-
ene at 25 °C to investigate the dynamics of supramolecu-
lar assembly formation. Because the absorption bands of
PyPFB and PZnPFB overlapped widely (Figure S1a), differen-
tial spectra were recorded by subtracting the absorption
spectra of both pure PyPFB and PZnPFB from that of mix-
ture solutions. As shown in Figure 1a, the differential
spectra exhibited clear isosbestic points at 414.5, 543.5,
and 574.0 nm upon successive addition of PyPFB, indicat-
ing binding of pyridyl groups to PZns to generate a new
type of self-assembled species. As expected, the maxi-
mum spectral changes were observable at 1 equivalent
addition of PyPFB. The binding isotherm reached a maxi-
mum value at 1 equivalent addition, and then the value
decreased gradually (Figure 1b). Job’s plot analysis (Figure
S1b) also indicated 1:1 stoichiometry of saturation bind-
ing.41 Based on the molecular shapes and absorption
Figure 1. a) Differential absorption spectra upon titration of
PyPFB (0-2.2 eq.) to PZnPFB in toluene at 25 °C and b) binding
isotherms of the UV/Vis titration monitored at 424 nm and
408 nm.
Thermodynamics of the self-assembly process were in-
vestigated by isothermal titration calorimetry (ITC). The
isothermal titration curve exhibited strong exothermic
peaks for each injection of PyPFB to PZnPFB (Figure 2).
Exothermic peaks gradually decreased and finally disap-
peared by successive addition of PyPFB. Because the titra-
ACS Paragon Plus Environment

Journal of the American Chemical Society
tion curve matched that for typical 1:1 binding host-guest
Page 6 of 9
1
2
3
4
5
6
7
8
systems, we used a simple 1:1 binding model to estimate
thermodynamic parameters.42-44 Curve fitting revealed
apparent ∆H°, ∆G°, ∆S° and association constant (Kass
)
values of -5.95 x 104 J/mol, -9.37 x 103 J/mol, -171 J/molK,
and 2.54 x 106 M-1, respectively. The association constant
was high enough for a fibrous assembly to form at mi-
cromolar concentrations.
1H NMR study was conducted to confirm supramolecu-
lar coordination polymer formation. As shown in Figure 3,
both PZnPFB and PyPFB exhibits relatively sharp 1H signals,
whereas 1:1 mixtures of PZnPFB and PyPFB exhibit signifi-
cant broadening of signals, indicating that the conforma-
tional fluctuations become slower than the NMR time-
scale due to formation of large supramolecular polymers.
Moreover, the degree of broadening increases by increas-
ing concentration of 1:1 mixture. Diffusion coefficients (D)
of PZnPFB, PyPFB, and 1:1 mixture of PZnPFB and PyPFB were
measured by 2D DOSY NMR spectroscopy (Figure S2). As
a result, D value of PZnPFB and PyPFB showed 1.06 x 10-8
m2s-1 and 1.11 x 10-8 m2s-1, whereas 1:1 mixture of PZnPFB and
PyPFB exhibited relatively lower D value of 7.19 x 10-9 m2s-1
than those of PZnPFB and PyPFB at the same concentration
(1.57 mM). When concentration was increased to 7.86
mM, the D value of 1:1 mixture was greatly decreased to
2.62 x 10-9 m2s-1 with broad distribution, indicating con-
centration dependent molecular size increasing of supra-
molecular coordination polymer.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1
Figure 3. H NMR spectra (600 MHz, toluene-d8, 298 K) of
PZnPFB, PyPFB, and supramolecular polymer formed from 1:1
ratio of PZnPFB, PyPFB with different concentrations (1.57, 3.93,
and 7.86 mM).
The formation of a fibrous assembly from PZnPFB and
PyPFB was visualized by atomic force microscopy (AFM)
and transmission electron microscopy (TEM). For AFM
observations, a 1:1 mixture solution of PZnPFB and PyPFB
(20 µM) in toluene was cast onto mica. As shown in Fig-
ure 4a, fibrous assemblies with regular height (ca. 2 nm)
were observed. The 1:1 mixture solution of PZnPFB and
PyPFB (0.1 wt%) was stained with 2 wt% uranyl acetate for
TEM observation. Considering the expected thickness of
assembled fibers consisting of rigid porphyrin parts and
fully extended geometry of peripheral alkyl chains, the
measured thickness about 2 nm in AFM image seems to
be attributed to the flattening of nanofibers due to the
substrate effect. However, additional TEM observation of
1:1 mixture solution of PZnPFB and PyPFB (0.1 wt%) clearly
showed the formation of nanofibers with a regular diame-
ter of ca. 6 nm (Figure 4b) which is reasonable as com-
pared to the cross-sectional dimension of 1D fibrils.
Figure 4. Microscopic observations of supramolecular poly-
mer; a) AFM and b) TEM images.
Figure 2. Result of isothermal titration calorimetry upon
titration of PyPFB to PZnPFB in toluene at 25 °C.
ACS Paragon Plus Environment

Page 7 of 9
Journal of the American Chemical Society
PyPCu was titrated to fluorescent PZnPFB. The strong
1
2
3
4
5
6
7
8
emission of PZnPFB decreased gradually in response to the
addition of PyPCu (Figure 5d). Notably, the decrease in
fluorescence intensity of PyPFB was stopped after two
equivalent addition of PyPCu, indicating excess PyPM ad-
dition makes 1:2 complexes. The results of fluorescence
titration experiments consistent with our assumption that
intramolecular energy transduction changes to intermo-
lecular energy transduction by the formation of supramo-
lecular coordination polymers.
9
10
11
12
13
14
15
CONCLUSIONS
Fibrous supramolecular coordination polymers were
formed from artificial light-harvesting multiporphyrin
dendrimers and multipyridyl porphyrins through axial
coordination interactions of pyridyl groups to PZn. For-
mation of coordination polymers greatly reduced intra-
molecular energy transfer within the artificial light har-
vesting dendrimer, and a new pathway of intermolecular
energy transfer became predominant. Such a molecularly
modulated energy transfer phenomena can be used as a
motif in the design of new photofunctional materials.
Figure 5. Emission changes by supramolecular assembly
formations; a) Emission spectra of PZnPFB, PZnPCu, PyPFB
and PyPCu, b) emission changes of PZnPFB by successive addi-
tion of PyPCu, c) emission changes of PZnPCu by successive
addition of PyPFB, d) emission changes of PZnPFB by succes-
sive addition of PyPCu. All emission spectra were measured
in toluene at 25 °C.
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
,
In our previous reports, we have demonstrated the effi-
cient energy transfer from PZns to the focal PFB in PZnPFB.
Upon excitation at 414 nm, PZnPFB exhibited intense emis-
sion bands around 650 and 720 nm, originating from the
focal PFB with a very weak shoulder around 600 nm from
the PZn wings (Figure 5a), where the energy transfer effi-
ciency was estimated to be 94%.30 The efficient energy
transfer dynamics in PZnPFB can be changed by the for-
mation of supramolecular assembly with PyPFB. Figure 5b
shows fluorescence emission changes of PZnPFB in re-
sponse to the addition of PyPFB upon excitation at 414 nm.
According to the addition of PyPFB, the emission band
around 600 nm, originated from PZn wings, completely
vanished, and the emission bands around 650 and 720 nm
from PFB were slightly red shifted. Notably, the emission
maximum wavelengths were coincident with those from
PyPFB. This observation suggests that the excitation en-
ergy of PZn wings flows to the PyPFB due to formation of a
fibrous assembly. In other words, intramolecular energy
transfer from PZn wings to the focal PFB in PZnPFB changes
to intermolecular energy transfer to the PyPFB. The
change in energy transfer was more distinctly observable
when non-fluorescent cupper porphyrins (PCu) were
used.45 For this experiment, we newly prepared non-
fluorescent PZnPCu and PyPCu. As shown in Figure 5a,
PZnPCu exhibited very weak fluorescence emission from
PZns around 580 and 630 nm due to efficient energy trans-
fer from PZns to the non-fluorescent focal PCu. When
PyPFB was added to PZnPCu, strong emission peaks were
generated at 655 and 724 nm, coincident with the emis-
sion bands of PyPFB (Figure 5c). In contrast, the weak
emission from PZn wings, around 570 and 630 nm, was
further decreased. Due to formation of coordination pol-
ymers, the excitation energy of PZn wings in PZnPCu flows
to PyPFB instead of the focal PCu in dendrimer. However,
we cannot absolutely exclude the direct excitation of
PyPFB in this experiment. Therefore, non-fluorescent
ASSOCIATED CONTENT
Supporting Information. . Additional spectral data (Figures
S1−2). This material is available free of charge via the Internet
at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
wdjang@yonsei.ac.kr
Author Contributions
All authors have given approval to the final version of the
manuscript
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENT
This work was supported by the Mid-Career Researcher Pro-
gram (2014R1A2A1A10051083) funded by the National Re-
search Foundation (NRF) of Korea.
REFERENCES
(1) Aida, T.; Meijer, E.; Stupp, S. Science 2012, 335, 813.
(2) Yang, L.; Tan, X.; Wang, Z.; Zhang, X. Chemical reviews
2015, 115, 7196.
(3) Ma, X.; Tian, H. Acc. Chem. Res. 2014, 47, 1971.
(4) Dong, S.; Zheng, B.; Wang, F.; Huang, F. Acc. Chem. Res.
2014, 47, 1982.
(5) de Greef, T. F.; Meijer, E. Nature 2008, 453, 171.
(6) Saeki, A.; Koizumi, Y.; Aida, T.; Seki, S. Acc. Chem. Res.
2012, 45, 1193.
(7) Yan, X.; Cook, T. R.; Pollock, J. B.; Wei, P.; Zhang, Y.; Yu, Y.;
Huang, F.; Stang, P. J. J. Am. Chem. Soc. 2014, 136, 4460.
(8) Liu, Y.; Huang, Z.; Tan, X.; Wang, Z.; Zhang, X. Chem.
Commun. 2013, 49, 5766.
(9) Wei, P.; Yan, X.; Huang, F. Chem. Soc. Rev. 2015, 44, 815.
(10) Albrecht, M. Nat. Chem. 2014, 6, 761.
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 8 of 9
(11) Li, W.; Kim, Y.; Li, J.; Lee, M. Soft Matter 2014, 10, 5231.
(43) Lin, F.; Zhan, T.-G.; Zhou, T.-Y.; Zhang, K.-D.; Li, G.-Y.; Wu,
J.; Zhao, X. Chem. Commun. 2014, 50, 7982.
(44) Song, N.; Chen, D.-X.; Qiu, Y.-C.; Yang, X.-Y.; Xu, B.; Tian,
W.; Yang, Y.-W. Chem. Commun. 2014, 50, 8231.
(45) Schick, G. A.; Schreiman, I. C.; Wagner, R. W.; Lindsey, J. S.;
Bocian, D. F. J. Am. Chem. Soc. 1989, 111, 1344.
1
2
3
4
5
6
7
8
(12) Satake, A.; Kobuke, Y. Tetrahedron 2005, 61, 13.
(13) Choi, M. S.; Aida, T.; Yamazaki, T.; Yamazaki, I. Angew.
Chem. 2001, 113, 3294.
(14) Choi, M. S.; Aida, T.; Yamazaki, T.; Yamazaki, I. Chem. Eur.
J. 2002, 8, 2667.
(15) Imahori, H. J. Phys. Chem. B 2004, 108, 6130.
(16) Jang, W.-D.; Lee, C.-H.; Choi, M.-S.; Osada, M. J.
Porphyrins Phthalocyanines 2009, 13, 787.
(17) Uetomo, A.; Kozaki, M.; Suzuki, S.; Yamanaka, K.-i.; Ito, O.;
Okada, K. J. Am. Chem. Soc. 2011, 133, 13276.
9
(18) Hajjaj, F.; Yoon, Z. S.; Yoon, M.-C.; Park, J.; Satake, A.; Kim,
D.; Kobuke, Y. J. Am. Chem. Soc. 2006, 128, 4612.
(19) Wasielewski, M. R. Acc. Chem. Res. 2009, 42, 1910.
(20) Hu, X.; Damjanović, A.; Ritz, T.; Schulten, K. Proc. Natl.
Acad. Sci. USA. 1998, 95, 5935.
(21) Scholes, G. D.; Fleming, G. R.; Olaya-Castro, A.; van
Grondelle, R. Nat. Chem. 2011, 3, 763.
(22) Aratani, N.; Kim, D.; Osuka, A. Acc. Chem. Res. 2009, 42,
1922.
(23) Brodard, P.; Matzinger, S.; Vauthey, E.; Mongin, O.;
Papamicaël, C.; Gossauer, A. J. Phys. Chem. A 1999, 103,
5858.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(24) Choi, M. S.; Yamazaki, T.; Yamazaki, I.; Aida, T. Angew.
Chem. Int. Ed. 2004, 43, 150.
(25) Hori, T.; Aratani, N.; Takagi, A.; Matsumoto, T.; Kawai, T.;
Yoon, M. C.; Yoon, Z. S.; Cho, S.; Kim, D.; Osuka, A. Chem.
Eur. J. 2006, 12, 1319.
(26) Yang, J.; Yoon, M.-C.; Yoo, H.; Kim, P.; Kim, D. Chem. Soc.
Rev. 2012, 41, 4808.
(27) Kim, D.; Heo, J.; Ham, S.; Yoo, H.; Lee, C.-H.; Yoon, H.;
Ryu, D.; Kim, D.; Jang, W.-D. Chem. Commun. 2011, 47,
2405.
(28) Neuhaus, P.; Cnossen, A.; Gong, J. Q.; Herz, L. M.;
Anderson, H. L. Angew. Chem. Int. Ed. 2015, 54, 7344.
(29) Kondratuk, D. V.; Perdigão, L. M.; Esmail, A. M.; O'Shea, J.
N.; Beton, P. H.; Anderson, H. L. Nat. Chem. 2015, 7, 317.
(30) Jeong, Y. H.; Son, M.; Yoon, H.; Kim, P.; Lee, D. H.; Kim, D.;
Jang, W. D. Angew. Chem. 2014, 126, 7045.
(31) Krishna Kumar, R.; Balasubramanian, S.; Goldberg, I. Inorg.
Chem. 1998, 37, 541.
(32) Parkinson, P.; Knappke, C. E.; Kamonsutthipaijit, N.;
Sirithip, K.; Matichak, J. D.; Anderson, H. L.; Herz, L. M. J.
Am. Chem. Soc. 2014, 136, 8217.
(33) Son, H.-J.; Jin, S.; Patwardhan, S.; Wezenberg, S. J.; Jeong,
N. C.; So, M.; Wilmer, C. E.; Sarjeant, A. A.; Schatz, G. C.;
Snurr, R. Q.; Farha, O. K.; Wiederrecht, G. P.; Hupp, J. T. J.
Am. Chem. Soc. 2013, 135, 862.
(34) Yoon, H.; Lee, C. H.; Jang, W. D. Chem. Eur. J. 2012, 18,
12479.
(35) Yoon, H.; Lim, J. M.; Gee, H.-C.; Lee, C.-H.; Jeong, Y.-H.;
Kim, D.; Jang, W.-D. J. Am. Chem. Soc. 2014, 136, 1672.
(36) Sonogashira, K.; Tohda, Y.; Hagihara, N. Tetrahedron Lett.
1975, 16, 4467.
(37) Zhang, Z.; Hu, R.; Liu, Z. Langmuir 2000, 16, 1158.
(38) Chambron, J. C.; Harriman, A.; Heitz, V.; Sauvage, J. P. J.
Am. Chem. Soc. 1993, 115, 6109.
(39) Kobuke, Y.; Miyaji, H. J. Am. Chem. Soc. 1994, 116, 4111.
(40) Williams, D. E.; Rietman, J. A.; Maier, J. M.; Tan, R.;
Greytak, A. B.; Smith, M. D.; Krause, J. A.; Shustova, N. B. J.
Am. Chem. Soc. 2014, 136, 11886.
(41) Connors, K. A. Binding constants: the measurement of
molecular complex stability; Wiley-Interscience, 1987.
(42) Lee, H. H.; Choi, T. S.; Lee, S. J. C.; Lee, J. W.; Park, J.; Ko, Y.
H.; Kim, W. J.; Kim, K.; Kim, H. I. Angew. Chem. 2014, 126,
7591.
ACS Paragon Plus Environment

Page 9 of 9
Journal of the American Chemical Society
Insert Table of Contents artwork here
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
8
ACS Paragon Plus Environment