Construction of snowflake-shaped dendritic covalent assemblies with rigid conjugated networks

Article abstract of DOI:10.1021/jo3014512

A convergent method for the construction of shape-persistent nanoscale assemblies with conjugated backbones was developed. The copper-free Sonogashira coupling reaction was successfully applied to the formation of multiple covalent connections between conjugated terminals (iodide substituted aryl groups) of AB₂-type outer components and four conjugated terminals (acetylenic bonds) of an inner A₄-type core dendrimer. The conjugated networks in the starting components are expanded during the assembly process to afford nanoscale dendritic conjugated networks of the type A₄(AB ₂)₄, which have a porphyrin core, and longer (3.9 or 4.5 nm) and shorter (1.6 nm) conjugated chains. Fluorescence measurements revealed that singlet energy is effectively transferred in the assemblies from peripheral benzyl ether units and conjugated chains to the free base porphyrin core.

Full text of DOI:10.1021/jo3014512

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pubs.acs.org/joc
Construction of Snowflake-Shaped Dendritic Covalent Assemblies
with Rigid Conjugated Networks
Masatoshi Kozaki,* Shirou Morita, Shuichi Suzuki, and Keiji Okada*
Graduate School of Science, Osaka City University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka 558-8585 Japan
S
* Supporting Information
ABSTRACT: A convergent method for the construction of shape-persistent nanoscale
assemblies with conjugated backbones was developed. The copper-free Sonogashira
coupling reaction was successfully applied to the formation of multiple covalent
connections between conjugated terminals (iodide substituted aryl groups) of AB2-type
outer components and four conjugated terminals (acetylenic bonds) of an inner A4-type
core dendrimer. The conjugated networks in the starting components are expanded
during the assembly process to afford nanoscale dendritic conjugated networks of the
type A4(AB2)4, which have a porphyrin core, and longer (3.9 or 4.5 nm) and shorter (1.6
nm) conjugated chains. Fluorescence measurements revealed that singlet energy is
effectively transferred in the assemblies from peripheral benzyl ether units and conjugated
chains to the free base porphyrin core.
preliminary report, we disclosed a method for the synthesis
INTRODUCTION
■
of a large dendritic porphyrin assembly (Scheme 1).11 Although
this method is undoubtedly effective for the synthesis of an
A4(AB3)4-type dendritic assembly, the yield (15%) could not be
improved in spite of examination of various coupling
conditions.
Organic synthesis is a versatile and reliable bottom-up method
for building well-defined and highly sophisticated nanoscale
architectures.1 Dendrimers are one of the most attractive
nanoscale macromolecular architectures because of their well-
defined molecular size, shape, and arrangement of functional
groups.2 Therefore, the dendrimer architecture is often found
in a variety of molecular devices and machines such as artificial
photosynthetic systems,3,4 bioinspired catalysts,5 and molecular
capsules.6 In addition, dendrimers have been recognized as
attractive modular building blocks for the construction of much
larger and more complicated molecular systems where large
numbers of specifically integrated molecular devices work
cooperatively and synergistically to perform advanced func-
tions.7 Previously, Tomalia et al. reported covalent assemblies
of polyamidoamine (PAMAM)-type dendrimers called “core-
shell tecto(dendrimers)” in which several smaller dendrimers
are covalently attached to the surface of a larger core
dendrimer.7a,b Although higher molecular weight products
were obtained by self-assembly and subsequent covalent bond
formations, it is difficult to use this architecture as a scaffold for
the construction of organized molecular systems, owing to the
structural flexibility of PAMAM-type dendrimers and the wide
size diversity of products. We have recently reported
dendrimers containing rigid conjugated backbones within the
dendritic side chains.8,9 The rigid backbone serves as a scaffold
for the construction of a well-designed assembly within the
dendritic architecture and also serves as a mediator of both
electron- and energy-transfer processes.10 These advantages of
dendritic architectures with conjugated backbones prompted us
to develop a novel methodology for the construction of a larger
covalent dendritic assembly with conjugated backbones using
dendrimers as the key modular building blocks. In our
According to our experience, such low chemical yields are
frequently encountered and are problematic in the preparation
of larger sized dendrimers; poor yields may originate from poor
encounter-probability and also steric interference between the
two cross-coupling components. Therefore, it is quite
important to develop a new general methodology which can
be applied to the synthesis of larger dendrimers in good yields.
We realized that the issue of poor yield can be improved by
converting the couplers to “naked” couplers by extending the
coupling terminals of the iodophenyl or acetylenic moieties or
both. However, extension of the acetylenic moieties may
facilitate not only cross-coupling but also dimerization.12 For
this reason, we examined the extension of the ethynylenephe-
nylene iodide moiety, and using this substrate, we were able to
prepare large dendritic assembly 1 in moderate yield (52%).
Furthermore, we successfully prepared much larger dendritic
assembly 2 in 17% yield. Assembly 2 has a square form with a
diagonal distance of approximately 11 nm (Figure 1).13 In this
paper, we report the synthesis and photophysical properties of
large dendritic assemblies 1 and 2.
RESULTS AND DISCUSSION
■
Synthesis. First, we prepared relatively smaller A4(AB2)4-
type assembly 1 in order to optimize both the coupling
Received: July 11, 2012
Published: October 12, 2012
© 2012 American Chemical Society
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Scheme 1. Construction of a A4(AB3)4-Type Covalent Dendritic Assembly with Conjugated Backbones
conditions and the molecular structures around the reactive
sites in the starting dendritic compounds. Suitable starting
materials for the construction of assembly 1 should be A4-type
core 3 and AB2-type arm 4 (Scheme 2). A4-type core 3 has a
porphyrin center and four conjugated chains terminated by
“shielded” ethynyl couplers that are embedded between 4-(4-
tert-butylbenzyloxy)phenyl groups to suppress any undesired
oxidative homo coupling reactions between the terminal
ethynyl groups. The Y-shaped conjugated network inside
AB2-type arm 4 has an ethynylenephenylene iodide terminal.
This extended terminal acts as a “naked” functional group to
increase reactivity toward the acetylenic terminals of 3 in the
Sonogashira coupling reaction.14
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Scheme 2. Synthesis of A4(AB2)4-Type Assembly 1
A4-type core 3 was prepared according to our previous
report.11 AB2-type arm 4 was synthesized according to the
convergent method shown in Scheme 3. Triethynylbenzene 6
was obtained by selective removal of the TMS groups in AB2-
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Scheme 3. Synthesis of AB2-Type Arm 4
type 1,3,5-triethynylbenzene 515 using potassium carbonate.
The Sonogashira coupling reaction of 6 and phenyl-terminated
dendron 716 gave 8. Removal of the 2-hydroxy-2-propyl group
from the ethynyl terminal was achieved upon the treatment of 8
with sodium hydroxide in toluene to afford 9. Phenyl iodide
10,10a containing a TBS-terminated alkyne, was coupled with 9
by the Sonogashira reaction to afford 11. Expansion of the
conjugated chain was achieved by the removal of the TBS
group in 11 using TBAF followed by Sonogashira coupling with
triazene 13. Then, 14 was heated in iodomethane in the
presence of iodine to afford AB2-type arm 4.17
The 4-fold coupling reaction of A4-type core 3 and AB2-type
arm 4 was investigated under copper-free Sonogashira coupling
conditions, that is, using the combination of Pd(dba)2·CHCl3
and AsPh3 in THF/triethylamine.18 The reaction at room
temperature gave only traces of assembly 1, and when the
reaction mixture was stirred at 40 °C for 24 h, assembly 1 was
obtained in 12% yield. Elongation of the reaction time to 72 h
resulted in considerable improvement of the yield of assembly 1
to 52% (Scheme 2). Although we used similar reaction
conditions for the preparation of the closely related
A4(AB3)4-type assembly (Scheme 1), the isolated yield of the
assembly was only 15%. These results suggest that the
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Figure 1. Molecular structure of A4(AB2)4-type covalent dendritic assembly 2.
reduction of steric hindrance around the iodide terminal of the
conjugated chain in the “naked” coupler is crucial to obtaining
higher yields of the coupling product.
to desired assembly 2 (MW = 16299, calcd for
C1188H1070N4O56). The peak at m/z = 14170 indicates the
formation of T-shaped phenylated assembly 19 (A4(AB2)3 type,
MW = 14168, calcd for C1030H934N4O50) via phenyl group
migration from triphenylarsine. The production of phenylated
byproducts such as 19 is well-known and it is usually easy to
remove such byproducts form palladium-catalyzed coupling
reactions.18,19 Gel permeation chromatography (GPC) should
be an effective method for the separation of assemblies 2 and
19 owing to their large differences in molecular weight (ΔMW
= 2130) and molecular shape. However, when separation of the
mixture was attempted by GPC using chloroform as an eluent,
only a single peak was observed in the elution profile, probably
owing to the intense aggregation of assemblies 2 and 19
(Figure S1 in the Supporting Information). Fortunately, we
found that addition of carbon disulfide and/or triethylamine
effectively suppressed the formation of aggregates during the
GPC separation. The GPC analysis of the mixture was
Next, we turned our attention to preparing much larger
assembly 2 from AB2-type arm 4 and second generation
dendrimer 15 (Figure 1, Scheme 3). Dendrimer 15 was
synthesized according to Scheme 4 from dendron 16 which was
prepared using the previously reported method.10a,16 The
coupling reaction of dendron 16 and A4-type free-base
porphyrin 17 under copper-free Sonogashira coupling con-
ditions gave dendrimer 18. The TBS groups at the ends of the
conjugated chains in dendrimer 18 were removed with TBAF
in THF to afford 15. A mixture of dendrimer 15 and AB2-type
arm 4 was stirred at 45 °C for 3 days in the presence of
Pd2(dba)3·CHCl3 and AsPh3 in THF/triethylamine (5:1, v/v)
to afford a purple solid. The MALDI-TOF mass spectrum of
the solid product shows two intense ion peaks at m/z = 14170
and 16300. The peak at m/z = 16300 is reasonably assignable
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Scheme 4. Synthesis of Assembly 2
performed using chloroform containing various amount of
carbon disulfide. As the result, two partially separated peaks
were obtained when a 1:1 (v/v) mixture of chloroform and
carbon disulfide was used as an eluent. These peaks had longer
retention times relative to the peaks observed in the cases of
other solvent mixtures, indicating that formation of the
aggregate was effectively suppressed in the 1:1 (v/v) mixture
of chloroform and carbon disulfide. The preparative separation
was carried out using a 1:1:0.01 (v/v/v) chloroform−carbon
disulfide−triethylamine mixture to afford assembly 2 in 17%
yield and assembly 19 in 32% yield (Chart 1). These results
clearly demonstrated that the suppression of aggregation is
essential for the isolation of nanoscale assemblies with π-
conjugated backbones.
Spectroscopic Characterization. The chemical structures
of assemblies 1 and 2 were confirmed by means of NMR and
MALDI-TOF mass measurement. Assembly 1 had a relatively
simple NMR spectrum at room temperature in CDCl3 resulting
from its highly symmetric structure and a sharp molecular ion
peak at m/z = 11846 (MW = 11845, calcd for C876H750N4O32)
was observed in its mass spectrum (Figure S2, Supporting
Information). While assembly 2 showed broad and unresolved
NMR signals in CDCl2CDCl2 at room temperature, sharp and
well-resolved signals were observed at 130 °C (Figure 2). This
behavior is typical for large dendritic structures with rigid
backbones and has been previously reported for a number of
dendrimers.8,10 Although NMR signals of the aromatic protons
in the outer components and the core dendrimer were
overlapped, three singlet peaks at 5.10, 5.00, and 4.98 ppm
corresponding to benzyl protons were observed for assembly 2.
The peak at 5.10 ppm and the other singlet signals were
assigned to the benzyl protons for the core and outer
components, respectively, based on comparison of the spectra
of AB2-type arm 4 and dendrimer 15. The observed integral
ratio of these singlet peaks was 64:47 for 2 which is in good
agreement with the expected values (64:48), confirming the 1:4
stoichiometry of the core and outer components in the
assembly. A sharp molecular ion peak at m/z = 16300 for 2
further confirmed the formation of the desired assembly
(Figure S3, Supporting Information).
The UV−vis absorption spectrum of assembly 2 in THF
shows characteristic bands arising from the porphyrin skeleton
(Soret band: λmax = 430 nm (log ε = 5.78); Q-bands: λmax = 525
(4.07), 562 (4.11), and 659 nm (3.66)) along with intense UV
absorption bands due to the branched benzyl ether chains (λmax
= 289 nm (log ε = 5.63)) and conjugated chains (λmax = 366
(5.54), 428 nm, (3.66)) (Figure 3). The intense UV absorption
and characteristic absorption bands for the free base porphyrin
unit were observed for assembly 19. Assembly 1 also has
characteristic absorption bands for the porphyrin core (λmax
=
427, 518, 555, 596, and 650 nm) in addition to the intense
absorption of conjugated chains (364 nm) and benzyl ether
chains (299 nm) (Figure S5, Supporting Information). The
conjugated networks of assemblies 1 and 2 were constructed by
shorter (1.6 nm) and longer phenyleneethynylene chains (3.9
nm for 1 and 4.5 nm for 2) and porphyrin cores that were
encapsulated by the benzyl ether chains. The absorption spectra
indicated that the lowest singlet excitation energy levels
decreased in the sequence of benzyl ether chains > shorter
conjugated chains > longer conjugated chains > porphyrin core.
The excitation energy gradient is helpful for enhancing the
efficiency of excitation energy transfer from outer units to the
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Chart 1
porphyrin core.4,10 To evaluate the efficiency of singlet energy
transfer from the outer units to the central porphyrin core, the
fluorescence spectrum of assembly 2 was measured in degassed
THF at different excitation wavelengths (Figure 4). Excitation
at 430 nm, where light is mainly absorbed by the porphyrin
core,10d,20 results in characteristic fluorescence at 666 and 725
nm with the quantum yield of Φf = 0.109 (Figure 4c). Under
excitation of the benzyl ether chains at 299 nm, a value at which
both the conjugated chain and the porphyrin core have only
weak absorption, an intense fluorescence of the porphyrin core
with the quantum yield of Φf = 0.078 appeared with almost
complete fluorescence quenching of the benzyl ether chains as
shown in Figure 4a, suggesting efficient singlet energy transfer
from excited benzyl ether chains to the porphyrin core
(quantum efficiency: 72%). Furthermore, excitation of the
conjugated chain (λem = 364 nm) also induced porphyrin
fluorescence with the quantum yield ΦF = 0.073, indicating
72% quantum efficiency for energy transfer (Figure 4b). The
excitation spectrum of assembly 2 monitored by porphyrin
emission at 650 nm further supports the efficient excitation
energy transfer from benzyl ether chains and conjugated chains
to the porphyrin core (Figure S6, Supporting Information).
The quantum efficiencies of intramolecular singlet energy
transfer in assemblies 1 and 19 were similarly evaluated by
means of fluorescence spectroscopy in THF (Figures S7 and
S8, Supporting Information). Assembly 1 has quantum
efficiencies of 78% and 86% in the energy transfer from benzyl
ether and conjugated chains to the porphyrin core, respectively.
On the other hand, quantum efficiencies of the energy transfer
from benzyl ether and conjugated chains to the porphyrin core
in assembly 19 are both 93%. These results indicate that
efficient intramolecular singlet energy transfer takes place both
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Figure 4. Florescence spectra of assembly 2, excitation of (a) benzyl
ether chains (λex = 299 nm, *; the intense peak at 598 nm is the
Figure 2. 600 MHz VT 1H NMR spectra of assembly 2 in
CDCl2CDCl2 (*, solvent).
scattered overtone of excitation light), (b) conjugated chains (λex
364 nm), and (c) porphyrin core (λex = 430 nm).
=
dendrimers can serve as “dendritic atoms” in the present
assembly process; that is, each dendrimer has its own valency
and directionality for bonding in addition to its own individual
functionalities. Since various dendrimers with a variety of
properties and geometries are accessible as connecting groups,
the present study provides a powerful tool for the construction
of a broad range of precisely designed nanoscale architectures.
EXPERIMENTAL SECTION
■
4-[3,5-Bis(2-ethynyl)phenyl]-2-methyl-3-butyn-2-ol (6). To
the solution of 515 (3.50 g, 9.92 mmol) in chloroform (250 mL)
and methanol (250 mL) was added potassium carbonate (7.10 g, 51.4
mmol). The mixture was stirred for 1 h at room temperature and
filtered. After the solvent was evaporated under reduced pressure, the
resulting solid was dissolved in dichloromethane. The solution was
washed with brine and dried over anhydrous sodium sulfate. After
filtration, the solvent was evaporated under reduced pressure. The
residue was purified by column chromatography on silica gel (CH2Cl2)
Figure 3. UV−vis spectra of assemblies 2 (solid line) and 19 (dashed
line) in THF.
1
to afford 6 (1.86 g, 90%) as a white solid: mp 79 °C; H NMR (400
MHz, CDCl3) δ 7.52 (t, J = 1.6 Hz, 1H), 7.50 (d, J = 1.6 Hz, 2H), 3.09
(s, 2H), 1.99 (s, 1H), 1.61 (s, 6H); 13C NMR (100 MHz, CDCl3) δ
135.2, 135.1, 123.5, 122.8, 95.2, 81.7, 80.3, 78.5, 65.5, 31.3; IR (KBr)
3296, 3277, 2988, 2934, 1582, 1150, 947, 878, 667, 638 cm−1; MS
(FAB+) m/z 208 (M+); HRMS calcd for C15H12O 208.0889, found
208.0877.
from the benzyl ether chains and the conjugated chains to the
porphyrin core in assemblies 1 and 2.
In summary, we report a novel methodology for the
construction of nanoscale shape-persistent covalent assemblies
with rigid conjugated backbones using dendrimers as modular
building blocks. “Naked” and “shielded” couplers were
incorporated at the ends of conjugated chains in order to
improve the efficiency of the coupling reaction. The method
was successfully applied to the construction of cross-shaped
assembly 2. The T-shaped assembly 19 was formed as a major
byproduct via phenyl group migration under the copper-free
Sonogashira coupling conditions. In general, the separation of
these products (2 and 19) should be easy because of the large
difference in their molecular weights. However, a possible
strong tendency for aggregation between these products
impeded the GPC separation. These results indicate that not
only the preparation, but also purification of large dendrimers
requires new approaches that are unique to nanoscale
assemblies. The cross-shaped assemblies 1 and 2 exhibited
superior UV light absorption and the absorbed photoenergy
was effectively funneled to the central porphyrin core. The
General Procedure for Sonogashira Coupling Reactions.
Before beginning the reactions, all solid samples were dried in vacuo
and THF, triethylamine, and ethyldiisopropylamine were deaerated by
bubbling nitrogen or argon. An oven-dried vessel was charged with an
aryl iodide, a terminal alkyne, and metal catalysts [Pd(PPh3)2Cl2 (or
Pd(PPh3)4) and CuI (Pd2(dba)3·CHCl3 and AsPh3 for copper-free
conditions)]. The vessel was evacuated and backfilled with nitrogen or
argon three times. To the vessel, THF and an amine were added in
this order. The mixture was stirred at room temperature or 60 °C.
After filtration, the solvent was evaporated and the resulting residue
was purified by column chromatography on silica gel. Eluents and
other slight modifications are described below for each material.
Dendron 8. According to the general procedure, 6 (115 mg, 0.55
mmol), 716 (988 mg, 1.27 mmol), Pd(PPh3)2Cl2 (38 mg, 0.054
mmol), and CuI (21 mg, 0.11 mmol) in triethylamine (4 mL) and
THF (40 mL) were reacted at 80 °C overnight. The crude material
was purified by column chromatography on silica gel (hexane/CH2Cl2
= 1:2) to afford 8 (622 mg, 75%): yellow powder; mp 154−155 °C;
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1H NMR (400 MHz, CDCl3) δ 7.66−7.61 (m, 9H), 7.55 (m, 2H),
7.51 (m, 4H), 7.43 (m, 16H), 7.23−7.18 (m, 6H), 7.11−7.05 (m,
12H), 5.11 (s, 8H), 2.01, (s, 1H), 1.62 (s, 6H), 1.34 (s, 36H); 13C
NMR (100 MHz, CDCl3) δ 158.7, 151.1, 144.7, 134.3, 133.9, 132.9,
131.14, 130.97, 130.8, 128.3, 128.2, 128.1, 127.5, 125.6, 123.9, 123.6,
123.5, 122.3, 120.5, 114.2, 97.4, 95.1, 90.5, 89.4, 89.2, 80.6, 70.0, 65.6,
34.6, 31.40, 31.36; IR (KBr) 2961, 1609, 1506, 1232, 1177, 833 cm−1;
MS (FAB+) m/z 1514 (MH+); HRMS calcd for C111H100O5
1512.7571, found 1512.7566. Anal. Calcd for C111H100O5·H2O: C,
87.02; H, 6.71. Found: C, 86.84; H, 6.56.
= 8.5 Hz, 2H), 7.39 (d, J = 8.5 Hz, 2H), 7.24 (d, J = 8.3 Hz, 2H), 3.80
(bs, 4H), 2.04 (bs, 4H); 13C NMR (100 MHz, CDCl3) δ 151.4, 137.4,
133.0, 132.4, 123.2, 120.4, 119.0, 93.7, 91.5, 88.3, 50.9, 46.3, 23.8; IR
(KBr) 2964, 2870, 1497, 1421, 1398, 1319, 1263, 1223, 1132, 1003,
843, 820 cm−1; MS (FAB+) m/z 401.37 (M+); HRMS (FAB+) m/z
calcd for C18H16N3I 401.0389, found 401.0370.
Triazene 14. According to the general procedure, 12 (40 mg, 0.020
mmol), 13 (470 mg, 0.57 mmol), Pd(PPh3)2Cl2 (1.0 mg, 0.0014
mmol), and CuI (0.5 mg, 0.0026 mmol) in triethylamine (2 mL) and
THF (4 mL) were reacted at 65 °C overnight. The crude material was
purified by column chromatography on silica gel (hexane/CH2Cl2 =
1:1) to afford 14 (35 mg, 76%) as a yellow powder: mp 258 °C dec;
1H NMR (400 MHz, CDCl3) δ 7.68−7.63 (m, 15H), 7.53 (s, 6H),
7.48−7.43 (m, 26H), 7.39 (d, J = 8.5 Hz, 2H), 7.34 (d, J = 8.8 Hz,
2H), 7.24−7.19 (m, 6H), 7.12−7.08 (m, 16H), 7.02 (d, J = 8.3 Hz,
2H), 5.13 (m, 12H), 5.12 (s, 4H), 2.04 (bs, 4H), 1.34 (s, 54H); 13C
NMR (100 MHz, CDCl3) δ 158.74, 158.70, 151.4, 151.1, 144.8, 144.7,
134.3, 133.90, 132.93, 132.85, 132.4, 131.3, 131.2, 131.0, 130.8, 129.3,
128.23, 128.19, 128.1, 127.53, 127.50, 125.60, 125.58, 125.3, 123.99,
123.97, 123.5, 123.3, 122.9, 122.5, 122.3, 120.5, 120.4, 119.2, 114.19,
114.16, 97.4, 92.1, 91.1, 90.6, 89.6, 89.4, 89.24, 89.1, 70.0, 34.61, 34.60,
31.4, 23.8; IR (KBr) 2961, 2926, 2868, 1609, 1506, 1396, 1315, 1244,
1177, 1015, 831; MS (FAB+) m/z 2306.0 (M+). Anal. Calcd for
C168H149N3O6: C, 87.50; H, 6.51; N, 1.82. Found: C, 87.42; H, 6.56;
N, 1.88.
Dendron 9. Dendron 8 (500 mg, 0.33 mmol) and sodium
hydroxide powder (132 mg, 3.30 mmol) in dry toluene (50 mL) were
refluxed under argon overnight. The solvent was evaporated and the
crude material was purified by column chromatography on silica gel
(hexane/CH2Cl2 = 1:1) to afford 9 (437 mg, 91%) as yellow powder:
mp 166−167 °C; 1H NMR (400 MHz, CDCl3) δ 7.69−7.68 (m, 1H),
7.65 (d, J = 8.8 Hz, 8H), 7.62 (d, J = 1.7 Hz, 2H), 7.52 (s, 4H), 7.44
(m, 16H), 7.25−7.18 (m, 6H), 7.13−7.07 (m, 12H), 5.12 (s, 8H), 3.12
(s, 1H), 1.33 (s, 36H); 13C NMR (100 MHz, CDCl3) δ 158.7, 151.1,
144.8, 134.7, 133.9, 132.9, 131.1, 131.0, 130.8, 128.2, 128.1, 127.5,
125.6, 123.9, 123.4, 123.0, 122.2, 120.5, 114.1, 97.4, 90.6, 89.21, 89.19,
81.9, 78.5, 69.6, 34.6, 31.3; IR (KBr) 2961, 1609, 1593, 1578, 1506,
1244, 1177, 1109, 1015, 876, 833, 754, 689 cm−1; MS (FAB+) m/z
1456 (M+); HRMS calcd for C108H94O4 1454.7152, found 1454.7136.
TBS Acetylene 11. According to the general procedure, 9 (600
mg, 0.41 mmol), 1010a (470 mg, 0.57 mmol), Pd(PPh3)2Cl2 (29 mg,
0.041 mmol), and CuI (8 mg, 0.042 mmol) in triethylamine (5 mL)
and THF (50 mL) were reacted at 65 °C overnight. The crude
material was purified by column chromatography on silica gel
(hexane/CH2Cl2 = 1:1) to afford 11 (653 mg, 74%) as a yellow
Arm 4. To a thick-walled oven-dried screw-cap tube was added 13
(18 mg, 0.0078 mmol), iodine (2.2 mg, 0.0087 mmol), and
iodomethane (0.5 mL). The tube was flushed with nitrogen or
argon, sealed, and heated at 80 °C overnight. The mixture was cooled
to room temperature and quenched with water. The solution was
extracted with dichloromethane. The extract was washed with sodium
thiosulfate and brine and dried over anhydrous sodium sulfate. After
filtration the solvent was evaporated. The crude material was purified
by column chromatography on silica gel (hexane/CH2Cl2 = 1:1) to
1
powder: mp 129 °C; H NMR (400 MHz, CDCl3) δ 7.67−7.63 (m,
11H), 7.55 (d, J = 8.5 Hz, 4H), 7.52 (s, 4H), 7.47 (s, 2H), 7.44 (m,
24H), 7.42−7.38 (m, 4H), 7.23−7.19 (m, 6H), 7.11−7.09 (m, 12H),
7.01 (d, J = 8.5 Hz, 2H), 5.12 (s, 8H), 5.08 (s, 4H), 1.34 (s, 36H), 1.33
(s, 18H), 0.74 (s, 9H), −0.10 (s, 6H); 13C NMR (100 MHz, CDCl3) δ
158.7, 158.6, 151.1, 151.0, 145.4, 144.7, 134.3, 134.0, 133.9, 132.9,
132.8, 131.1, 131.0, 130.8, 130.7, 128.2, 128.1, 127.5, 127.4, 125.58,
125.55, 124.0, 123.5, 122.3, 120.6, 120.5, 114.2, 104.3, 102.2, 97.4,
90.53, 90.46, 89.4, 89.2, 70.00, 69.95, 34.6, 31.4, 26.0, 16.6, −5.0; IR
(KBr) 2957, 1609, 1506, 1362, 1223, 1177, 1109, 1015, 827, 754 cm−1;
MS (FAB+) m/z 2146.5 (M+); HRMS (FAB+) m/z calcd for
C156H148O6Si 2145.1045, found 2145.1045.
1
afford 4 (16 mg, 88%) as yellow powder: mp 250−251 °C; H NMR
(400 MHz, CDCl3) δ 7.70−7.63 (m, 17H), 7.53 (bs, 6H), 7.44 (s,
24H), 7.34 (d, J = 8.6 Hz, 2H), 7.24−7.21 (m, 10H), 7.11−7.08 (m,
16H), 7.03 (d, J = 8.3 Hz, 2H), 5.12 (m, 12H), 1.34 (s, 54H); 13C
NMR (100 MHz, CDCl3) δ 158.8, 158.7, 151.13, 151.11, 144.9, 144.8,
137.6, 134.3, 133.90, 133.87, 133.1, 132.9, 132.8, 131.4, 131.16,
131.16, 131.0, 130.8, 128.2, 127.53, 127.50, 125.6, 124.0, 123.5, 122.5,
122.3, 120.5, 114.20, 114.18, 97.4, 97.0, 94.5, 91.9, 90.6, 90.1, 89.4,
89.2, 77.2, 70.0, 34.6, 31.4; IR (KBr) 2961, 2926, 1609, 1508, 1246,
1177, 1016, 831, 820 cm−1; MS (FAB+) m/z 2332.8 (M+). Anal. Calcd
for C164H141IO6·H2O: C, 83.72; H, 6.13. Found: C,83.75; H, 6.05.
Assembly 1. An oven-dried vessel was charged with 3 (10.2 mg,
0.0034 mmol), 4 (34.6 mg, 0.0148 mmol), Pd2(dba)3·CHCl3 (1.73
mg, 0.0017 mmol), and AsPh3 (5.0 mg, 0.0163 mmol). The vessel was
evacuated and backfilled with argon three times. To the vessel were
added THF (3.0 mL) and triethylamine (0.6 mL). The mixture was
stirred at room temperature or 40 °C for 3 days. After filtration, the
solvent was evaporated, and the resulting residue was purified by
column chromatography on silica gel (dichloromethane) and then
recycling preparative GPC (JAIGEL-3H and -2H columns, CHCl3) to
afford the assembly 1 (21 mg, 52%) as a purple solid: mp >300 °C; 1H
NMR (400 MHz, CDCl3) δ 8.88 (s, 8H), 8.21 (m, 8H), 7.93 (m, 8H),
7.75−7.57 (m, 76H), 7.55−7.49 (m, 20H), 7.48−7.37 (m, 128H),
7.37−7.31 (m, 24H), 7.23−7.16 (m, 32H), 7.16−6.96 (m, 94H),
5.15−5.11 (m, 64H), 1.35 (m, 288H); 13C NMR (100 MHz, CDCl3)
δ 159.0, 158.9, 151.19, 151.16, 145.1, 145.0, 144.9, 134.3, 134.12,
134.09, 133.21, 133.16, 133.1, 131.4, 131.2, 131.10, 131.06, 130.93,
130.87, 128.2, 128.10, 128.06, 127.49, 127.47, 125.62, 125.60, 125.59,
124.2, 123.6, 122.8, 122.4, 120.8, 120.5, 114.5, 114.4, 114.4, 97.6, 90.7,
89.5, 89.4, 77.2, 70.2, 34.7, 34.7, 31.6, 31.4, 22.7, 14.1; IR (KBr) 2961,
2905, 2866, 1607, 1506, 1227, 1175, 1015, 831 cm−1; MS (MALDI-
TOF) m/z 11846 (M+). Anal. Calcd for C876H750N4O32·2CHCl3: C,
87.27; H, 6.27; N, 0.46. Found: C, 87.52; H, 6.41; N, 0.58.
Terminal Acetylene 12. To the solution of 11 (50 mg, 0.023
mmol) in THF (5 mL) was added 1.0 M TBAF in THF (0.030 mL,
0.030 mmol) and stirred at room temperature overnight. The reaction
was quenched by water and extracted with dichloromethane. The
organic layer was washed with brine and dried over anhydrous sodium
sulfate. The solvent was evaporated and the residue was purified by
column chromatography on silica gel (hexane/CH2Cl2 = 1:1) to afford
12 (45 mg, 96%) as a yellow powder: mp 206−207 °C; 1H NMR (400
MHz, CDCl3) δ 7.67−7.63 (m, 11H), 7.55 (d, J = 8.8 Hz, 4H), 7.52
(s, 4H), 7.47 (s, 2H), 7.43 (s, 16H), 7.42−7.37 (m, 8H), 7.23−7.19
(m, 6H), 7.11−7.04 (m, 16H), 5.12 (s, 8H), 5.08 (s, 4H), 3.07 (s,
1H), 1.34 (s, 36H), 1.33 (s, 18H); 13C NMR (100 MHz, CDCl3) δ
158.7, 151.1, 145.8, 144.8, 134.3, 133.90, 133.87, 132.9, 132.6, 131.2,
131.0, 130.8, 130.7, 128.2, 128.1, 127.6, 127.5, 125.60, 125.58, 124.1,
124.0, 123.5, 122.8, 122.3, 120.6, 119.3, 114.22, 114.18, 97.4, 90.6,
90.1, 89.6, 89.4, 89.2, 86.7, 82.2, 76.7, 70.0, 69.9, 34.6, 31.4; IR (KBr)
2959, 2905, 2866, 1609, 1506, 1464, 1294, 1231, 1177, 1015, 831, 818
cm−1; MS (FAB+) m/z 2032.9 (M+); HRMS (FAB+) m/z calcd for
C150H134O6 2031.0180, found 2031.0179. Anal. Calcd. for
C150H134O6·H2O: C, 87.85; H, 6.68. Found: C, 87.54; H, 6.57.
Triazene 13. According to the general procedure, 1-[2-(4-
ethynylphenyl)diazenyl]pyrrolidine21 (200 mg, 0.678 mmol), 1,4-
diiodobenzene (670 mg, 2.03 mmol), Pd(PPh3)4 (39 mg, 0.034
mmol), and CuI (13 mg, 0.068 mmol) in triethylamine (5 mL) and
toluene (25 mL) were reacted at 40 °C overnight. The crude material
was purified by column chromatography on silica gel (hexane/CH2Cl2
= 1:1) to afford 13 (303 mg, 73%) as a yellow powder: mp 182−183
°C; 1H NMR (400 MHz, CDCl3) δ 7.67 (d, J = 8.3 Hz, 2H), 7.48 (d, J
Dendrimer 18. According to the general procedure, 16 (25 mg,
0.0351 mmol), 17 (299 mg, 0.155 mmol), Pd2(dba)3·CHCl3 (22 mg,
0.021 mmol), and AsPh4 (52 mg, 0.170 mmol) in triethylamine (3
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The Journal of Organic Chemistry
Featured Article
mL) and THF (15 mL) were reacted at 40 °C overnight. The crude
material was purified by column chromatography on silica gel
(CH2Cl2) and then recycling preparative GPC (JAIGEL-3H and
-2H columns, CHCl3) to afford 18 (180 mg, 65%) as a purple powder:
mp 185 °C; 1H NMR (400 MHz, CDCl3) δ (ppm) 8.89 (bs, 8H), 8.22
(d, J = 8.0 Hz, 8H), 7.94 (d, J = 8.0 Hz, 8H), 7.95−7.71 (m, 24H),
7.47 (d, J = 8.5 Hz, 16H), 7.46−7.30 (m, 96H), 7.10−7.06 (m, 24H),
6.94 (d, J = 8.5 Hz, 16H), 6.73 (d, J = 2.0 Hz, 16H), 6.56 (t, J = 2.0
Hz, 8H), 5.00 (s, 16H), 4.97 (s, 32H), 4.87 (s, 16H), 1.30 (m, 216H),
0.70 (s, 36H), −0.14 (s, 24H), −2.73 (bs, 2H); 13C NMR (75 MHz,
CDCl3) δ (ppm) 160.3, 158.6, 158.5, 151.0, 150.9, 145.0, 145.0, 139.4,
134.7, 134.0, 133.7, 133.1, 132.8, 131.1, 130.9, 130.7, 130.3, 130.1,
127.6, 127.5, 125.52, 125.46, 123.1, 120.2, 119.9, 119.7, 114.3, 114.1,
106.2, 104.5, 101.9, 101.6, 97.3, 91.2, 91.1, 90.5, 70.03, 69.96, 69.8,
34.6, 31.4, 31.3, 26.0, 16.6, −5.0; IR (KBr) 2963, 2905, 2965, 1604,
1504, 1458, 1363, 1296, 1247, 1180, 1151, 1109, 1013, 831, 540 cm−1;
MS (MALDI-TOF) m/z 7931.3 ((M + H)+). Anal. Calcd. for
C556H556N4O32Si4·2CH2Cl2: C, 82.75; H, 7.09; N, 0.69. Found: C,
83.02; H, 7.10; N, 0.82.
transfer efficiency, fluorescence quantum yields are relative to zinc
tetraphenylporphyrin or quinine as the external standards.23
ASSOCIATED CONTENT
* Supporting Information
■
S
GPC elution profile, NMR spectra, MALDI-TOF spectra, and
photophysical data. This material is available free of charge via
the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: kozaki@sci.osaka-cu.ac.jp, okadak@sci.osaka-cu.ac.jp.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was partially supported by a Grant-in-Aid for Science
Research (No. 23350022) from the Ministry of Education,
Culture, Sports, Science and Technology, Japan. We thank
Japan Analytical Industry Co., Ltd. for assistance with GPC
separation.
Dendrimer 15. To the solution of 18 (120 mg, 0.015 mmol) in
THF (15 mL) was added 1.0 M TBAF in THF (0.075 mL, 0.075
mmol) and the mixture stirred at room temperature overnight. The
reaction was quenched with water and extracted with dichloro-
methane. The organic layer was washed with brine and dried over
anhydrous sodium sulfate. The solvent was evaporated, and the residue
was purified by column chromatography on silica gel (hexane/CH2Cl2
REFERENCES
1
■
= 1:1) to afford 15 (101 mg, 90%) as a purple solid: mp 202 °C; H
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