Donor-acceptor interactions in red-emitting thienylbenzene-branched dendrimers with benzothiadiazole core

Article abstract of DOI:10.1002/chem.200801694

Synthesis and characterization of dendrimers containing thienylbenzene repeating units, red-emitting benzothiadiazole core, and triarylamine peripheries that bear naphthyl units are reported. The relevant dendrimers of different generations are classified as G_nb (n = 1-3), while the tert-butyl dendrimers G_na with the acceptor alone were also synthesized to serve as control chromophores that avoid donor-acceptor interactions. The resulting dendrimers are capable of harvesting photon energy through efficient energy transfer among donor-acceptor moieties, so that highly luminescent red fluorophores result. Transient fluorescence studies suggest that the energy transfer and its efficiency are approximately unity in all G _a dendrimers, whereas the rate of energy transfer for the G _b dendrimers is suppressed, that is, charge transfer from the core to the periphery is a significant quenching pathway. These dendrimers are amorphous in nature with high glass transition temperatures (176-201°C). Electroluminescent devices were fabricated by using the dendrimers as hole-transporting emitters, and the devices exhibit promising red emission parameters.

Full text of DOI:10.1002/chem.200801694

FULL PAPER
DOI: 10.1002/chem.200801694
Donor–Acceptor Interactions in Red-Emitting Thienylbenzene-Branched
Dendrimers with Benzothiadiazole Core
K. R. Justin Thomas,[a] Tai-Hsiang Huang,[a] Jiann T. Lin,*[a, b] Shin-Chien Pu,[c]
Yi-Ming Cheng,[c] Cheng-Chih Hsieh,[c] and Chou Pi Tai*[c]
Abstract: Synthesis and characteriza-
tion of dendrimers containing thienyl-
benzene repeating units, red-emitting
benzothiadiazole core, and triarylamine
peripheries that bear naphthyl units
are reported. The relevant dendrimers
of different generations are classified
as Gnb (n=1–3), while the tert-butyl
dendrimers Gna with the acceptor alone
were also synthesized to serve as con-
trol chromophores that avoid donor–
acceptor interactions. The resulting
dendrimers are capable of harvesting
photon energy through efficient energy
transfer among donor–acceptor moiet-
ies, so that highly luminescent red fluo-
rophores result. Transient fluorescence
studies suggest that the energy transfer
and its efficiency are approximately
unity in all Ga dendrimers, whereas the
rate of energy transfer for the Gb den-
drimers is suppressed, that is, charge
transfer from the core to the periphery
is
a significant quenching pathway.
These dendrimers are amorphous in
nature with high glass transition tem-
peratures (176–2018C). Electrolumi-
nescent devices were fabricated by
using the dendrimers as hole-transport-
ing emitters, and the devices exhibit
promising red emission parameters.
Keywords: charge transfer · den-
drimers · donor–acceptor systems ·
energy harvesting · luminescence
Introduction
actions. These interactions normally result in crystallinity
and hence deviations of luminescence properties such as
shift in emission color and reduced emission yield.[4] Proto-
typical examples are the perylenediimides, which are often
in a crystalline form that displays less intense emission in
both solid and solution phases. It is also possible to suppress
intermolecular interactions by doping such chromophores
into an amorphous matrix. However, the physically blended
systems, obtained by either evaporation or solution casting,
may lead to uneven distribution of guests. As a result, local-
ized high concentrations can lead to detrimental quenching
effects. Alternatively, an efficient way of controlling molecu-
lar interactions is to deposit them at the molecular level, so
that the chromophores can be organized precisely within the
molecular framework. Dendrimers offer a suitable platform
for such endeavors. In sharp contrast to the bulk properties,
incorporation of a small-band-gap chromophore into the
dendrimer core may enhance the emission features simply
due to prohibition of interchromophore interactions and
possible energy transfer from peripheral chromophores. On
this basis, for typical dendrimers with the emission originat-
ing from the core functional group, the fluorescence quan-
tum yield may rapidly increase with increasing generation,
in the absence of other side effects such as electron-transfer
quenching by the peripheral functional groups (vide infra).
Moreover, multifunctional dendrimers may be beneficial for
Dendrimers are attractive as molecular architectures for
studying energy harvesting properties[1] and for their ability
to encapsulate small band gap chromophores within bulky
peripheral masking units.[2] With a view to applications, the
recently developed site-isolation strategy has greatly extend-
ed their usefulness in the design of functional molecules
with multichromophore units.[3] This approach is beneficial
for avoiding detrimental interchromophore interactions, par-
ticularly for small-band-gap chromophores that are subject
to aggregation because of dipole–dipole or p-stacking inter-
[a] Dr. K. R. J. Thomas, Dr. T.-H. Huang, Prof. Dr. J. T. Lin
Institute of Chemistry
Academia Sinica
Taipei 115 (Taiwan)
E-mail: jtlin@chem.sinica.edu.tw
[b] Prof. Dr. J. T. Lin
Department of Chemistry
National Central University
Chungli 320 (Taiwan)
[c] Dr. S.-C. Pu, Dr. Y.-M. Cheng, C.-C. Hsieh, Prof. Dr. C. P. Tai
Department of Chemistry
National Taiwan University
Taipei 106 (Taiwan)
E-mail: chop@ntu.edu.tw
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charge transport as the dendrimer framework may provide a
facile vectorial contribution to the hopping/migration/trap-
ping pathways.
amine—but the same core structure, namely, the long conju-
gated aromatic segment 4,7-bis(5-phenylthiophen-2-
yl)benzo[c][1,2,5]thiadiazole. The dendrimers with triaryla-
AHCTUNGTRENNUNG
Recently, we and others have demonstrated that peripher-
al triarylamines can be effectively used to encapsulate
small-band-gap cores such as thienylpyrazine,[5] benzothia-
diazole,[6] and peryleneimide.[7] Here we describe the synthe-
sis and characterization of a new family of dendrimers in
which thienylbenzene branches are peripherally decorated
with N-phenylnaphthylamine units and focally converge at a
benzothiadiazole core. In this approach, rigid and conjugat-
ed dendrimers were selected because they potentially have
enhanced thermal stability and fewer nonradiative deactiva-
tion pathways (vide infra). Thienyl[8] and phenylene[9] p-con-
jugated dendrimers have been recently synthesized and their
photophysical properties were found to be unique when
compared to other nonconjugated, flexible dendrimers.
However, to the best of our knowledge, dendrimers having
thienylbenzene repeating units are rare in the literature.
Normally, polythiophenes and thiophene oligomers exhibit
diminished quantum efficiency, partly due to the heavy-
atom effect in combination with oxidative quenching. Re-
placement of one or more thio-
mine peripheries Gnb (n=1–3) have donor–acceptor archi-
tecture and hence are considered to be functional dendrim-
ers, while the tert-butyl dendrimers Gna (n=1–3) with the ac-
ceptor alone serve as control chromophores devoid of
donor–acceptor interactions. Thus, these dendrimers allow
us to unravel the donor–acceptor interactions in a dendritic
environment.
One can perceive a feasible energy-transformation path-
way in these functional dendrimers: First, the energy ab-
sorbed by the periphery may migrate to the core by an effi-
cient energy-transfer pathway, the mechanism of which is
most likely of the Fçrster type, that is, dipole-induced
dipole-transition energy transfer. The energy accumulated at
the core can then be released either as core (red) emission
or deactivated (quenched) by an electron transfer process
from the periphery. In the latter case, it is necessary to
match the redox potentials between periphery and core.
Bearing these concepts in mind, we designed and synthe-
sized dendrimers in which the associated chromophores can
phene moieties by a phenyl unit
improves the fluorescence prop-
erties with a slight compromise
in the emission peak wave-
length.[10] Accordingly, the title
dendrimers, which contain red-
emitting benzothiadiazole as
core, thienylbenzene repeating
units, and triarylamine periph-
eries bearing naphthyl units
should establish an efficient
energy-transfer
framework
leading to highly luminescent
red fluorophores. We used
time-resolved
spectroscopic
methods to unravel the energy-
migration pathways in these
dendrimers. In light of their
high glass transition tempera-
tures (176–2018C), these new
dendrimers may pave a new
avenue for applications in elec-
troluminescent devices.
Results and Discussion
Synthesis and characterization:
Our main focus is on two types
of thienylbenzene-branch-based
dendrimers
having
surface
groups of different natures—
tert-butyl or N-(4-tert-butyl-
phenyl)-N-phenylnaphthalen-1-
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Thienylbenzene-Branched Dendrimers
FULL PAPER
be bifunctional, that is, undergo energy and electron trans-
fer.
were obtained by different routes (Scheme 1), elaborated in
the following.
Generally, in modular dendrimer synthesis, the core unit
and dendrons are prepared separately and finally tethered
together to achieve the dendritic configuration. Conversely,
in our approach, the core unit can be self-assembled in the
final step and the dendron itself generally contains part of
the core segment. Schemes 1 and 2 outline the synthetic
methodologies for the dendrons, while Scheme 3 shows the
synthetic route to the dendrimers. Monodendrons 2a and 2b
The G1a dendron 2a was synthesized from 3,5-di-tert-bu-
tylphenyl trifluoromethanesulfonate by treatment with thio-
phen-2-ylmagnesium bromide in the presence of [Pd-
À
AHCUTNTGERG(NNUN PPh3)2Cl2] as catalyst, and G1b dendron 2b by C N cou-
pling between N-(4-tert-butylphenyl)naphthalen-2-amine
and 2-(3,5-dibromophenyl)thiophene (1) catalyzed by [Pd-
AHCTUNTGRENGUN(N dba)2]/tBu3P. Subsequently, by treatment with nBuLi and
nBu3SnCl, the thiophenyl-substituted dendrons were con-
verted to stannylene derivatives, which were treated with 2-
(3,5-dibromophenyl)thiophene (1) in a [PdACHTUNGTRNEG(UN PPh3)2Cl2]-cata-
lyzed Stille reaction to give G2 dendrons 3 (Scheme 2). The
above two steps were repeated on G2 dendrons to generate
G3 dendrons 4. Finally, the dendrimers were obtained in
moderate to good yield by twofold Stille coupling between
the corresponding stannylene derivatives of the dendrons
and 4,7-dibromobenzothiadiazole (Scheme 3). The dendrim-
ers are red or deep red in appearance and soluble in most
organic solvents. The structural composition of the new
Scheme 1. Synthesis of the first-generation dendrons. dba=trans,trans-di-
benzylideneacetone.
Scheme 3. Preparation of the dendrimers.
compounds was determined by
NMR (1H, 13C) spectroscopy,
mass spectrometry, and elemen-
tal analysis.
Linear optical spectroscopy:
We characterized dendrons and
corresponding dendrimers by
absorption and emission spec-
troscopy. The steady-state pho-
tophysical parameters are listed
in Table 1, and the absorption
and emission spectra of the
dendrimers recorded in CH2Cl2
are displayed in Figures 1–4.
The main absorption for naph-
thylamine dendrons 2b–4b ap-
pears at about 305 nm with a
shoulder peaking at 345 nm.
The shoulder grows into
a
prominent peak for higher gen-
erations. Because the control
dendrons 2a–4a and dendrim-
ers G1a–G3a display
a single
band in the lower wavelength
region at about 340 nm, it is
plausible to assign the 345 nm
Scheme 2. Growth of the higher generation dendrons by an iterative procedure.
Chem. Eur. J. 2008, 14, 11231 – 11241
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J. T. Lin, C. P. Tai et al.
Table 1. Physical properties of the dendrons and dendrimers.
Compd
labs [nm][a]
Tg (Tm) [8C][b]
Td [8C][b,c]
2a
284
–
-
2b
294, 347
349, 496
265, 304, 354, 499
337
305, 345
346, 491
266, 307, 348, 489
346
267, 308, 345
346, 485
265, 306, 343, 488
99
85 (232)
176
86 (191)
170
154 (366)
201
152
197
173
189
320 (331)
330 (355)
425 (450)
340 (375)
425 (463)
500 (530)
427 (440)
502 (530)
450 (471)
505 (527)
340 (361)
G1a
G1b
3a
3b
G2a
G2b
4a
4b
G3a
G3b
[a] Absorption and emission spectra were recorded for dichloromethane
solutions. [b] Scan rate: 108CminÀ1. [d] Onset values and temperature at
5% weight loss in parentheses are reported.
~
*
Figure 2. Absorption spectra of dendrons 2b ( ), 3b ( ), 4b (&) and
~
&
*
naphthylamine terminated dendrimers G1b
( ), G2b ( ), G3b ( ) recorded
band as originating from at least two neighboring units of
the thienylbenzene backbone. As the generation increases,
both the population and effective conjugation length of the
thienylbenzene segment increase, so the intensity of the
peak at 345 nm increases monotonically (Figure 1). Accord-
ingly, the higher energy transition at 305 nm is attributed to
the naphthyl moiety.[11] This assignment is also supported by
the linear correlation observed between the extinction coef-
ficient at 305 nm and the number of naphthalene units in
the dendrimer (Figure 2). The absorption spectra of the den-
drimers display an additional redshifted transition at about
495 nm, which may be attributed to conjugation of benzo-
thiadiazole core and the neighbouring two units of thienyl-
benzene backbone. However, interestingly, the absorption
band originating from the benzothiadiazole core of G1 den-
drimers G1a and G1b is redshifted when compared to the G2
and G3 analogues. We believe that this is attributable to the
proximal conjugative effect of surface groups in G1. As the
generation grows, the peripheral units are located farther
in dichloromethane. Inset shows the linear correlation of the increase in
optical density (305 nm) due to naphthylamine units.
from the core, and significant interaction with the benzo-
thiadiazole unit is prevented.[12]
The emission spectral features recorded for the dendrons
and dendrimers in CH2Cl2 are presented in Figures 3 and 4,
respectively. Close inspection of the emission peak positions
reveals the following trends: The emission profile of the
dendrons shifts bathochromically with increasing generation,
while for the dendrimers the emission peak wavelength is
blueshifted on growth of the dendron. These results can be
plausibly explained if we first elucidate the origin of emis-
sion in dendrons and dendrimers. The dendrimers display
red emission, which is characteristic of the core and corre-
sponds to the absorption at about 495 nm, while for the den-
drons the emission seems to originate from the thienylben-
zene bridges. The latter assumption is reasonable because
dendrons with a higher generation should elongate the con-
jugation of the backbone due to the meta effect and thus
result in a redshift of the emission spectral feature. A similar
~
*
*
Figure 1. Absorption spectra of the control dendrons 2a ( ), 3a ( ), 4a
Figure 3. Normalized emission spectra of tert-butyl dendrons 3a ( ), 4a
~
), G2a
~
&
&
*
*
(&) and dendrimers G1a
(
(
), G3a ( ) recorded in dichlorome-
(&) and tert-butyl dendrimers G1a ( ), G2a ( ), G3a ( ) recorded in di-
thane.
chloromethane.
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Thienylbenzene-Branched Dendrimers
FULL PAPER
sponding to the dendritic core. This result provides direct
evidence that efficient energy transfer takes place from the
triarylamine unit at the periphery to the core. For dendrim-
ers G1b and G2b, negligible residual emission due to the pe-
riphery was resolved in the emission spectra on excitation at
305 nm, which corresponds to the absorption of the surface
naphthylamine groups. For G3b a small donor-component
emission (ca. 470 nm, see Figure 4) is realized in addition to
the strong, red emission of the core, that is, the energy-trans-
fer efficiency decreases slightly in higher generations.
In a steady-state approach, we quantified the energy-
transfer efficiency by comparing the absorption and excita-
tion spectrum (monitored at the emission peak) of the den-
drimers. The efficiency of energy transfer can be readily de-
duced from the excitation spectrum of the energy accept-
or.[11] At a given wavelength, the magnitude of the excitation
spectrum of the energy acceptor (A) is related to the trans-
fer efficiency E and the extinction coefficients of the energy
donor eD and acceptor eA by the expression A=eA +EeD.
Thus, energy-transfer efficiency was deduced to be 99, 95,
and 83% for G1b, G2b, and G3b, respectively. A similar ap-
proach was used for G1a–G3a, and their energy-transfer effi-
ciencies were all calculated to be near unity. Qualitatively,
the results for G1b–G3b seem to fit the trend documented in
the literature, that is, energy-transfer efficiency decreases in
higher generation dendrimers.[14]
Finally, the trend of emission quantum yield between
classes G1a–G3a and G1b–G3b as a function of solvent polarity
also attracts our attention. For example, with increasing sol-
vent polarity from toluene to dichloromethane to dimethyl-
formamide the acceptor (i.e., the dendritic core) emission
yield decreased significantly from 0.72 to 0.23 to 0.01, re-
spectively, for G1b. A similar dependence of emission yield
on solvent polarity was also observed for G2b (0.66, 0.60,
0.06) and G3b (0.84, 0.61, 0.22). Note that as the generation
grows the magnitude of solvent effect on emission yield de-
creases. In contrast, the emission yield changed less signifi-
cantly for G1a–G3a in these three solvents (see Table 3).
Owing to the low ionization potential of naphthylamine in
the Gb series, the results indicate that excited-state electron
transfer may be operative for G1b–G3b dendrimers. If this is
the case, it is possible that dynamics of energy transfer and
electron transfer are two competing pathways. To gain de-
tailed insight into the relaxation dynamics, time-resolved
studies based on the femtosecond fluorescence upconversion
technique were carried out.
Figure 4. Normalized emission spectra of naphthylamine-containing den-
~
~
&
*
*
drons 2b ( ), 3b ( ), 4b (&) and dendrimers G1b
( ), G2b ( ), G3b ( )
recorded in dichloromethane (lex ꢀ375 nm).
effect was previously identified in meta-substituted polyacet-
ylene dendrons and dendrimers.[13] Conversely, on increasing
the generation, the blueshift of the core emission in the den-
drimers may be attributed to a combination of two factors:
1) The aforementioned proximal conjugative effect of sur-
face groups. As the generation grows, the peripheral units
are located farther from the core, and conjugative interac-
tion with the benzothiadiazole unit is reduced. 2) Less sol-
vent (CH2Cl2) perturbation with increasing the dendron size,
so that the core chromophore embedded in higher genera-
tions is subject to a more nonpolar environment.
An interesting aspect of these dendrimers is their efficient
energy-harvesting behavior. As is evident in Figure 5, the
emission of donor part, that is, naphthylamine in 2b, over-
laps well with the absorption of the parent acceptor core (as
in G1a). This fulfils the prerequisite for efficient energy
transfer according to the Fçrster mechanism. In accordance
with this expectation, the emission peak position of den-
drimers G1b–G3b is fairly insensitive to the excitation wave-
length, with most of the emission centered at 640 nm corre-
Transient fluorescence studies: Excited-state relaxation dy-
namics of the dendrons and dendrimers in toluene, dichloro-
methane, and dimethylformamide were measured. The three
solvents were selected on the basis of their different polarity
indices and sufficient solubility for all compounds under in-
vestigation, which allowed us to differentiate between the
energy- and electron-transfer pathways operative in G1b–
G3b. The emission population lifetimes compiled in Table 2
can be summarized as follows: 1) For a given generation the
excited-state lifetime of the tert-butyl dendrons (2a–4a) and
Figure 5. Spectral overlap between naphthylamine donor (2b) and core
acceptor (G1a) in dichloromethane.
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J. T. Lin, C. P. Tai et al.
Table 2. Emission properties of dendrons and dendrimers.
On the contrary, for G1b–G3b excited-state electron trans-
fer takes place from naphthylamine groups to the core chro-
mophore, the efficiency of which, in theory, depends on cou-
pling distance and solvent polarity. With increasing solvent
polarity the energy difference between reactant (neutral
species) and product (charge-transfer species) becomes
larger, and hence the rate of electron transfer (emission
quenching) increases. As a result, the lifetime of G1b is sig-
nificantly shortened in polar solvents. On the other hand,
the electron coupling matrix is reduced, so the rate of elec-
tron transfer decreases with increasing generation, that is,
donor–acceptor distance. This, in combination with the inac-
cessibility of the core to the solvent due to encapsulation of
the core by dendritic wedges, explains the relatively insensi-
tive solvent-polarity-dependent shortening of the lifetime
for G2b and G3b. The result differs from those recently re-
ported for Frꢁchet dendrimers[15] incorporating benzothia-
diazole core and pyrenylamine peripheries, in which charge
transfer from the core to the periphery is a significant
quenching pathway.
Detailed fitting parameters for early-time relaxation dy-
namics at selected wavelengths for all studied dendrimers
are listed in Table 3. Independent of the solvent, the time-
resolved fluorescence of G1a and G2a monitored at less than
500 nm, which is ascribed to the emission of the donor
moiety, was established by a system-response-limited (<
150 fs) decay. As for G3a, the decay is also fast but resolva-
ble and is fitted to be about 300–500 fs, depending on the
solvent. These values correlate well with the early dynamics
monitored at the core emission (see Table 3), which show in-
stant rise (<150 fs) for G1a and G2a and 300–500 fs rise com-
ponents for G3a. The results are consistent with data ob-
tained from steady-state measurements, that is, energy trans-
fer and its efficiency are approximately unity in all Ga den-
drimers.
Toluene
Ff
Dichloromethane
lem Ff
[nm] [%] [ns]
DMF
Ff
lem
t
t
lem
t
[nm]
[%] [ns]
p.l.[a]
[nm] [%]
[ns]
2a
–
360
443
0.12
5.30
–
p.l.[a]
6.23
2b 420
G1a 623
G1b 612
0.18 3.03
0.28
0.54
0.23
0.27
0.15
0.63
442
0.18
0.48
0.72 6.61[a] 645
0.70 5.37[a] 644
7.53[b] 660
4.26[b] 662
7.08[a]
0.003 0.04[a]
3a 391, 408 0.31 1.89
408
482
1.77
5.76
412
498
0.26
0.09
0.56
0.06
0.20
0.08
0.49
0.22
1.44
7.94
3b 445
G2a 615
G2b 615
4a 401
4b 446
G3a 615
G3b 607
0.15 4.22
0.72 5.40[b] 637
0.66 5.44[a] 630
6.34[b] 644
6.49[b]
1.49[b]
2.10
0.61 10.57[b] 644
0.35 1.09
0.16 4.48
409
482
0.26
0.15
0.62
1.54
5.84
423
500
8.64
0.71 5.32[b] 625
0.64 5.83[b] 630
6.42[b] 642
6.59[a]
4.85[a]
0.61 12.01[b] 644
[a] Pulse limit. [b] The population decay dynamics was obtained by moni-
toring at the red core emission.
Table 3. Early dynamics parameters observed for the donor and acceptor
emissions in dendrimers.[a]
tdonor (decay dynamics)
Toluene CH2Cl2 DMF
tacceptor
CH2Cl2
Toluene
352 fs
DMF
329 fs
G3a 309 fs
(0.986)
G2b 409 fs
(0.853)
484 fs
(0.944)
251 fs
(0.932)
4.7 ps
352 fs
(0.964)
240 fs
(0.946)
3.4 ps
511 fs
(À0.435) (À0.486) (À0.473)
216 fs 197 fs 564 fs
(À0.036) (À0.481) (À0.095)
12.1 ps
13.5 ps
(À0.332) (À0.02)
277 fs 218 fs
3.6 ps
1.8 ps
(0.147)
G3b 365 fs
(0.332)
(0.068)
352 fs
(0.630)
5.9 ps
(0.054)
273 fs
(0.683)
4.3 ps
(À0.015)
253 fs
(À0.436) (À0.087) (À0.473)
15.7 ps 4.9 ps 3.8 ps
(À0.07)
(À0.155) (À0.216)
16.1 ps
ACHTUNGTRENNUNG
(0.237)
(0.154)
(0.230)
[a] For clarity, the population lifetime of the acceptor is not included in
this table. For dendrimers G1a, G2a, and G1b the decay times were faster
than the system response of 150 fsÀ1
.
dendrimers (G1a–G3a) is insensitive to solvents. 2) The life-
time of the naphthylamine dendrons (2b–4b) increases as
the solvent polarity increases from toluene to DMF. 3) For
dendrimers G1b–G3b, a reverse trend (c.f. 2b–4b) is wit-
nessed. For lower generation dendrimers such as G1b the
lifetime of core emission rapidly decreases with increasing
solvent polarity. A similar trend was observed in higher gen-
eration dendrimers such as G2b and G3b; however, the de-
crease in lifetime with changing polarity is not as significant.
4) For Gnb dendrimers, the lifetime increases in polar sol-
vents with increasing generation, but in the nonpolar solvent
toluene the excited-state lifetime remains almost the same.
These observations can be rationalized by a mechanism in-
corporating energy- and electron-transfer processes. For the
control compounds G1a–G3a, in which only the core acceptor
unit is present, only very weak interaction of the core chro-
mophore with the solvent and a lack of interchromophore
perturbations are found. The slight alteration observed for
G1a on changing the solvent polarity can be attributed to in-
termolecular solute–solvent interactions. As the generation
grows these intermolecular interactions are prohibited due
to steric inhibition.
For the Gb dendrimers, the addition of a naphthylamine
moiety further elongates the donor–acceptor distance. Thus,
the rate of energy transfer should be suppressed, especially
in the case of G3b, as was confirmed in the steady-state stud-
ies (vide supra). As depicted in Figure 6, the decay of the
Figure 6. Decay dynamics of donor emission (monitored at 470 nm, lex
ꢀ375 nm) for G3b in various solvents.
11236
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Chem. Eur. J. 2008, 14, 11231 – 11241

Thienylbenzene-Branched Dendrimers
FULL PAPER
donor moiety of G3b (i.e., naphthylamine, monitored at
470 nm) consists of a component with a few hundred femto-
seconds and a fast but resolvable component on the order of
several to tens of picoseconds. The ultrafast decay compo-
nent is nearly at the system response limit; therefore, the
fitted time constant listed in Table 3 should not be treated
as a trend to correlate with the solvent parameters. Howev-
er, its value, to a certain extent, seems to reveal solvent de-
pendency. On the other hand, the fast decay component of a
few picoseconds is evidently dependent on solvent polarity;
it decreases from 16.1 ps in toluene to 4.3 ps in DMF. More-
over, the picosecond decay component correlates well with
the rise component of the core emission (monitored at
655 nm, see Figure 7 and Table 3), which was measured to
Figure 8. Decay dynamics of donor emission (monitored at 470 nm, lex
ꢀ375 nm) for G1b, G2b, and G3b in DMF.
Table 1 for relevant parameters). The glass transition tem-
perature for the dendrons and tert-butyl dendrimers G1a–G3a
gradually increases with increasing generation. However, for
the functional dendrimers, after a initial raise in Tg for G2b,
a slight decrease in Tg is observed for G3b. This is probably
due to the mobility induced by the voluminous structure of
G3b. In general, the glass transition temperatures observed
for the dendrimers are higher when compared to commonly
employed amorphous electroluminescent materials 1,4-
bis(1-naphthylphenylamino)biphenyl (NPB) and 1,4-bi-
s(phenyl-m-tolylamino)biphenyl (TPD).[16]
Figure 7. Rise dynamics of acceptor emission (monitored at 655 nm, lex
ꢀ375 nm) for G3b in various solvents.
Electrochemical and electroluminescence studies: Electro-
chemical studies revealed that the dendrimers are bipolar in
nature. Oxidation due to the peripheral amine groups and
reduction due to the central benzothiadiazole core were ob-
served in the cyclic voltammograms of the dendrimers at
about 0.4 and À1.7 V respectively (Table 4). For the G3b
be 15.7, 4.9, and 3.8 ps in toluene, CH2Cl2 and DMF, respec-
tively. This result clearly indicates a precursor–successor
type of relationship between donor and acceptor moieties.
We thus attribute this picosecond decay component to
energy dissipation of the excited donor moiety through
energy/electron transfer to the core (acceptor) moiety. As
such, it is reasonable to ascribe the decay component on a
timescale of a few hundred femtoseconds to vibrational and/
or solvent relaxation dynamics following Franck–Condon
excitation. Note that, on monitoring at 655 nm (see
Figure 7), in addition to the picosecond rise component, a
certain system-response-limited rise component is attributed
to direct core excitation. Similar results were obtained for
G2b, except that the relaxation dynamics of the donor are
faster (12.1, 4.7 and 3.4 ps in toluene, CH2Cl2 and DMF, re-
spectively; see Figure 8 and Table 3). First-generation G1b
exhibits a system-response-limited (<150 fs) decay for the
donor moiety in three studied solvents, consistent with the
trend of transfer efficiency of G3b <G2b <G1b deduced from
steady-state studies (vide supra).
Table 4. Redox properties of the amino-substituted dendrons and den-
drimers.
compd Eox (DEp) [mV][a] Ered [mV][a] HOMO [eV][b] LUMO [eV]
2b
G1b
3b
G2b
4b
G3b
389 (55)
430 (86)
430 (85)
437 (83)
420 (108)
421 (89)
–
5.189
À1697 (70) 5.230
5.230
–
3.103
–
3.144
–
–
À1656 (63) 5.237
–
5.220
5.221
À1716 (i)
3.084
[a] Potentials are quoted with reference to ferrocene as internal standard;
scan rate: 100 mVsÀ1; i: irreversible. [b] Frontier orbital energies were
deduced from Eorb =4.8+Eox/red
.
benzothiadiazole reduction is irreversible, possibly due to in-
accessibility of the core at the electrode surface. This so-
called dendritic effect has been well documented for a wide
array of redox-responsive dendrimers.[17] The HOMO and
LUMO energies derived from the redox potentials are on
the order of 5.2 and 3.1 eV respectively.
Thermal properties: The thermal properties of the com-
pounds were studied by both thermogravimetric analysis
and differential scanning calorimetry measurements (see
All the aforementioned properties make these dendrimers
attractive candidates for electroluminescence applications.
Chem. Eur. J. 2008, 14, 11231 – 11241
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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11237

J. T. Lin, C. P. Tai et al.
Co.) as stationary phase in a column 30 cm long and 2.0 cm in diameter.
The 1H NMR spectra were measured on a Bruker AC300 or AMX400
spectrometer. Mass spectra were recorded on a JMS-700 double-focusing
mass spectrometer (JEOL, Tokyo, Japan). Elemental analyses were per-
formed on a Perkin-Elmer 2400 CHN analyzer. Cyclic voltammetry ex-
periments were performed with a BAS-100 electrochemical analyzer. All
measurements were carried out at room temperature with a conventional
three-electrode configuration consisting of a glassy carbon working elec-
trode, a platinum wire auxiliary electrode, and a nonaqueous Ag/AgNO3
reference electrode. The E1/2 values were determined as (Eap +Epc)/2,
where Eap and Ecp are the anodic and cathodic peak potentials, respective-
ly. The potentials are quoted against ferrocene internal standard. The sol-
vent in all experiments was dichloromethane and the supporting electro-
lyte was 0.1m tetrabutylammonium hexafluorophosphate. Electronic ab-
sorption spectra were obtained with a Perkin Elmer Lambda 900 UV/
Vis/NIR spectrophotometer on dichloromethane solutions. Emission
spectra were recorded in deoxygenated solutions at 298 K with a Jobin
Yvon SPEX Fluorolog-3 spectrofluorometer. The emission spectra were
collected on samples with o.d.<0.1 at the excitation wavelength. The
spectra were corrected for instrumental response. UV/Vis spectra were
checked before and after irradiation to monitor possible sample degrada-
tion. Emission maxima were reproducible to within 2 nm. Luminescence
quantum yields Fem were calculated by using Coumarin 1 as primary
standard (Fem =0.99 in ethyl acetate) for blue fluorophores or 4-dicyano-
methylene-2-methyl-6-p-diethylaminostyryl-4-H-pyran (DCM, Fem =0.40
in acetonitrile) as secondary reference for red fluorophores.[11]
Since dendrimers G1b and G2b exhibit good thermal stability,
vapor deposition was successful for these two compounds
despite their high molecular weights. Two types of devices
were made from the above two dendrimers: 1) ITO/G1b or
G2b/TPBI/LiF/Al and 2) ITO/NPB/G1b or G2b/TPBI/LiF/Al
(ITO=indium tin oxide, TPBI=1,3,5-tris(N-phenylbenzimi-
dazol-2-yl)benzene). The triple-layer devices were found be
better than the double-layer devices in all respects. This in-
dicates that better balance in charge transport and more ef-
ficient recombination are achieved with an additional hole-
transporting layer consisting of NPB. The I–V–L curves for
the devices are displayed in Figure 9. The devices fabricated
from G1b displayed pure red emission with chromaticity co-
ordinates x=0.61, y=0.34, maximum luminance of
8500 cdmÀ2, and external quantum efficiency of 1.84% at a
current density of 20 mAcmÀ2.
Nanosecond lifetime studies were performed with an Edinburgh FL 900
photon-counting system with a hydrogen-filled or nitrogen lamp as exci-
tation source. The emission decays were analyzed by the sum of exponen-
tial functions, which allows partial removal of instrument time broaden-
ing and consequently affords a temporal resolution of about 200 ps. The
setup of picosecond dynamical measurements consists of a femtosecond
Ti:sapphire oscillator (82 MHz, Spectra Physics). The fundamental train
of pulses was pulse-selected (Neos, model N17389) to reduce its repeti-
tion rate to typically 0.8–8 MHz, and then used to produce second har-
monics (375–425 nm) as an excitation light source. A polarizer was
placed in the emission path to ensure that the polarization of the fluores-
cence was set at the magic angle (54.78) with respect to the pump laser to
eliminate fluorescence anisotropy. An Edinburgh OB 900 L time-corre-
lated single-photon counting system was used as detector, with a tempo-
ral resolution of about 15 ps. The fluorescence upconversion measure-
ments were performed by using a femtosecond optically gated system
(FOG-100, CDP). The fundamental of a Ti:sapphire laser (Spectra Phys-
ics) at 750–850 nm with an average power of 0.5 W and a repetition rate
of 82 MHz was used to produce second harmonics (SH) at 375–425 nm
by focusing onto a 0.5 mm-thick BBO type-I crystal. The SH was then
separated from the fundamental pulses with a dichroic mirror and used
as pump pulses. The pump pulses were focused onto a rotating cell, and
the optical path length was 1.0 mm. The resulting fluorescence was col-
lected by an achromatic lens and then focused on another BBO type-I
crystal (0.5 mm). The optically delayed remaining fundamental pulses
were also focused on the BBO crystal and used as gate pulses for sum-
frequency generation. A half-wave plate was placed in the pump beam
path to ensure that the polarization of the pump laser was set at the
magic angle (54.78) with respect to the probe laser to eliminate fluores-
cence anisotropy. The up-converted signal was then separated by an F/4.9
Figure 9. I–V–L characteristics observed for the devices fabricated with
dendrimers G1b and G2b.
Conclusion
In summary, we have designed and synthesized new red-
emitting dendrimers with thienylbenzene backbones, naph-
thylamine peripheries, and benzothiadiazole cores. These
donor–acceptor molecules exhibit efficient energy transfer
and are highly luminescent red fluorophores. Energy-trans-
fer dynamics, monitored by transient fluorescence studies,
reveal that these rigid meta-substituted dendrimers are sig-
nificantly different from flexible dendrimers having similar
donor–acceptor architecture (benzothiadiazole/triarylamine)
and Frꢁchet branches. Additionally, their amorphous nature
with high glass transition temperatures (176–2018C) opens
an avenue for application in electroluminescent devices.
(f=380 mm) single monochromator (CDP2022) and detected by
a
photon-counting photomultiplier tube (R1527P, Hamamatsu). The cross-
correlation between SH and the fundamental had a full width at half-
maximum (fwhm) of about 150 fs, which was chosen as a response func-
tion of the system.
2-(3,5-Dibromophenyl)thiophene (1): A mixture of 1,3,5-tribromoben-
zene (3.15 g, 10 mmol), 2-thienylmagnesium bromide (1.87 g, 10 mmol,
freshly prepared from 2-bromothiophene and magnesium), [Pd-
Experimental Section
AHCTUNGTRENN(GNU PPh3)2Cl2] (70 mg), and tetrahydrofuran (70 mL) was heated at 708C for
General information: All reactions and manipulations were carried out
under N2 by standard inert-atmosphere and Schlenk techniques. Solvents
were dried by standard procedures. All column chromatography was per-
formed under N2 on silica gel (230–400 mesh, Macherey-Nagel GmbH &
24 h. After cooling, the reaction mixture was poured into ice water. It
was extracted with diethyl ether and evaporated to leave a tan solid,
which was adsorbed on silica gel and subjected to column chromatogra-
phy. After the first fraction containing the unconverted 1,3,5-tribromo-
11238
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Chem. Eur. J. 2008, 14, 11231 – 11241

Thienylbenzene-Branched Dendrimers
FULL PAPER
benzene the desired compound was eluted with hexanes. Colorless solid.
Yield: 1.34 g (42%). 1H NMR (300 MHz, CDCl3, 258C): d=7.07 (t, J=
4.7 Hz, 1H), 7.28 (d, J=3.5 Hz, 1H), 7.32 (d, J=4.7 Hz, 1H), 7.54 (t, J=
2.1 Hz, 1H), 7.64 ppm (d, J=2.1 Hz, 2H); 13C NMR (75 MHz, CDCl3,
258C): d=123.3, 124.6, 126.4, 127.5, 128.2, 132.5, 137.7, 140.9 ppm;
HREIMS calcd for C10H6Br2S: 315.8557; found: 315.8556.
amounts of methanol. The red solid obtained was dissolved in CH2Cl2
and subjected to column chromatography on silica gel. The desired com-
pound was obtained by elution with hexanes/dichloromethane (2/1) in
67% yield. 1H NMR (400 MHz, CDCl3, 258C): d=1.38 (s, 36H), 7.39–
7.41 (m, 4H), 7.53 (d, J=1.8 Hz, 4H), 7.89 (s, 2H), 8.13 ppm (d, J=
3.8 Hz, 2H); 13C NMR (100 MHz, CDCl3, 258C): d=31.5, 35.0, 120.5,
122.3, 123.9, 125.2, 125.8, 128.6, 133.5, 128.3, 146.8, 151.4, 152.6 ppm;
FABMS: m/z 676.2 [M]+; elemental analysis calcd (%) for C42H48N2S3: C
74.51, H 7.15, N 4.14; found: C 74.32, H 7.03, N 4.20.
N-(4-tert-Butylphenyl)naphthalen-1-amine: A mixture of naphthalen-1-
amine (1.72 g, 12 mmol), 1-tert-butyl-4-bromobenzene (2.13 g, 10 mmol),
[PdACHTUNGTRENNUNG(dba)2] (58 mg), tBu3P (30 mg), tBuONa (1.44 g, 15 mmol) and tolu-
ene (30 mL) was stirred at room temperature overnight. After the reac-
tion was complete, as evidenced by the disappearance of 1-tert-butyl-4-
bromobenzene, it was quenched by addition of water and extracted with
diethyl ether. The organic extracts were collected, washed with brine,
and evaporated to leave a pale yellow syrup. It was purified by column
chromatography on silica gel by eluting with hexanes/dichloromethane
(3/1). Colorless solid. Yield: 2.4 g (87%). 1H NMR (300 MHz,
[D6]acetone, 258C): d=1.30 (s, 9H), 7.07 (d, J=8.5 Hz, 2H), 7.29–7.51
(m, 8H), 7.86 (d, J=8.1 Hz, 1H), 8.20 ppm (d, J=8.5 Hz, 1H); 13C NMR
(75 MHz, [D6]acetone, 258C): d=31.8, 34.6, 114.3, 118.6, 122.1, 123.1,
125.8, 126.6, 126.7, 126.9, 128.1, 129.1, 135.8, 141.1, 143.2, 143.7 ppm;
HREIMS calcd for C20H21N: 275.1674; found: 275.1671.
5-{5-[4-(5-{3,5-Bis[N-(4-tert-butylphenyl)-N-(naphthalen-1-yl)amino]phe-
nyl}thiophen-2-yl)benzo[c]ACHTUNGTRNEUNG
[1,2,5]thiadiazol-7-yl]thiophen-2-yl}-N1,N3-
bis(4-tert-butylphenyl)-N1,N3-bis(naphthalen-1-yl)benzene-1,3-diamine
(G1b): A mixture of dendron 2b (2.83 g, 4 mmol) and tetrahydrofuran
(50 mL) was cooled to À758C, and n-butyl lithium (2.8 mL, 1.6m in hex-
anes) added dropwise over 10 min. Over 1 h it was slowly allowed to
warm to 08C. After stirring at this temperature for 30 min, it was again
cooled to À758C. Tributyltin chloride (1.63 g, 5 mmol) was added and the
mixture allowed to stir at room temperature overnight. It was quenched
by addition of ice water and extracted with diethyl ether. The combined
organic extracts were dried over anhydrous MgSO4 and evaporated to
dryness to leave the stannylene derivative. It was immediately mixed
2-(3,5-Di-tert-butylphenyl)thiophene (2a): A solution of 3,5-di-tert-butyl-
phenyl trifluoromethanesulfonate (3.38 g, 10 mmol), thiophen-2-ylmagne-
sium bromide (2.25 g, 12 mmol, freshly prepared from 2-bromothiophene
with 4,7-dibromobenzothiadiazole (0.53 g, 1.8 mmol), [Pd
(14 mg), and DMF (10 mL). The resulting mixture was heated at 808C
for 18 h. red solid formed. After cooling the mixture, methanol
ACHTUNGTRENNUNG(PPh3)2Cl2]
A
and magnesium), [PdACHTUNGTRENNUNG(PPh3)2Cl2] (70 mg, 0.1 mmol), and tetrahydrofuran
(40 mL) was added to complete the precipitation. The solids were collect-
ed by filtration and washed with liberal amounts of methanol. The red
solid obtained was dissolved in CH2Cl2 and subjected to column chroma-
tography on silica gel. The desired compound was obtained by elution
with hexanes/dichloromethane (1/1). Yield: 2.0 g (72%). 1H NMR
(400 MHz, CDCl3, 258C): d=1.24 (s, 36H), 6.44 (t, J=2.1 Hz, 2H), 6.76
(d J=2.1 Hz, 4H), 6.80–6.84 (m, 8H), 6.96 (d, J=3.7 Hz, 2H), 6.99–7.03
(m, 8H), 7.26 (dd, J=7.3, 1.1 Hz, 4H), 7.33–7.39 (m, 8H), 7.45 (dt, J=
7.3, 1.1 Hz, 4H), 7.60 (s, 2H), 7.67 (d, J=8.1 Hz, 4H), 7.85 (d, J=8.5 Hz,
4H), 7.88 (d, J=3.7 Hz, 2H), 7.92 ppm (d, J=8.1 Hz, 4H); 13C NMR
(100 MHz, CDCl3, 258C): d=31.4, 34.1, 11.3, 113.2, 121.8, 124.3, 124.4,
125.2, 125.7, 126.0, 126.2, 126.3, 127.0, 128.3, 128.4, 131.2, 135.2, 135.4,
138.3, 143.2, 144.7, 145.1, 145.7, 149.5, 152.4 ppm; FABMS: m/z 1545.6
[M+H]+; elemental analysis calcd (%) for C106H92N6S3: C 82.34, H 6.00,
N 5.44; found: C 81.84, H 5.81, N 5.37.
was refluxed under nitrogen atmosphere for 24 h. After cooling, the reac-
tion mixture was quenched with ice water and extracted with diethyl
ether (3ꢂ50 mL). The combined organic extract was dried over anhy-
drous MgSO4 and evaporated to dryness to leave a colorless viscous
liquid. It was purified by column chromatography on silica gel with hex-
anes as eluant. Yield: 2.12 g (78%). 1H NMR (300 MHz, CDCl3, 258C):
d=1.35 (s, 18H), 7.05–7.08 (m, 1H), 7.24–7.29 (m, 2H), 7.36 (d, J=
3.8 Hz, 1H), 7.43 ppm (d, J=1.8 Hz, 1H); 13C NMR (75 MHz, CDCl3,
258C): d=31.4, 34.9, 120.7, 121.8, 122.8, 124.3, 127.8, 133.7, 145.7,
151.3 ppm; HREIMS calcd for C18H24S: 272.4482; found: 272.4474.
N1,N3-Bis(4-tert-butylphenyl)-N1,N3-bis(naphthalen-1-yl)-5-(thiophen-2-
yl)benzene-1,3-diamine (2b): A mixture of 2-(3,5-dibromophenyl)thio-
phene (3.18 g, 10 mmol), N-(4-tert-butylphenyl)naphthalen-1-amine
(5.78 g, 21 mmol), [PdACHTUNGTRENNUNG(dba)2] (116 mg), tBu3P (60 mg), tBuONa (2.88 g,
30 mmol), and toluene (40 mL) was stirred at 808C overnight. After
quenching with water, it was extracted with diethyl ether. The combined
organic extracts were dried over anhydrous MgSO4 and evaporated to
dryness to yield a pale yellow solid. It was purified by column chroma-
tography on silica gel with hexanes/dichloromethane (4/1) as eluant. Pale
yellow solid. Yield: 6.1 g (86%). 1H NMR (300 MHz, CDCl3, 258C): d=
1.27 (s, 18H), 6.50 (t, J=2.1 Hz, 1H), 6.72 (d, J=2.1 Hz, 2H), 6.83–6.88
(m, 5H), 6.92–6.93 (m, 1H), 7.02–7.08 (m, 5H), 7.29 (d, J=7.1 Hz, 2H),
7.36–7.41 (m, 4H), 7.48 (t, J=7.1 Hz, 2H), 7.69 (d, J=8.1 Hz, 2H), 7.87
(d, J=8.1 Hz, 2H), 7.95 ppm (d, J=8.5 Hz, 2H); 13C NMR (75 MHz,
CDCl3, 258C): d=31.4, 34.1, 111.3, 112.8, 121.8, 123.1, 124.3, 124.4, 125.6,
125.9, 126.2, 127.0, 127.5, 128.3, 131.2, 135.2, 125.6, 143.2, 144.6, 144.7,
145.1, 149.4 ppm; FABMS: m/z 707.2 [M+H]+; elemental analysis calcd
(%) for C50H46N2S: C 84.94, H 6.56, N 3.96; found: C 84.75, H 6.69, N
3.88.
5,5’-[5-(Thiophen-2-yl)-1,3-phenylene]bis[2-(3,5-di-tert-butylphenyl)thio-
phene] (3a): 3a was prepared by following a procedure similar to that
described above for G1a with the exception that 2-(3,5-dibromophenyl)th-
iophene was used instead of 4,7-dibromobenzothiadiazole. Colorless
solid. Yield: 82%. 1H NMR (300 MHz, CDCl3, 258C): d=1.38 (s, 36H),
7.12 (dd, J=3.8, 3.8 Hz, 1H), 7.30 (d, J=3.8 Hz, 2H), 7.33 (d, J=3.8 Hz,
1H), 7.38–7.41 (m, 4H), 7.44 (d, J=3.8 Hz, 1H), 7.48 (d, J=1.8 Hz, 4H),
7.75 (d, J=1.8 Hz, 2H), 7.79 ppm (t, J=1.8 Hz, 1H); 13C NMR (75 MHz,
CDCl3, 258C): d=31.5, 34.9, 120.4, 121.9, 122.1, 122.3, 123.8, 123.9, 124.6,
125.3, 128.1, 133.5, 135.8, 142.2, 143.6, 145.6, 151.5 ppm; FABMS: m/z
700.1 [M]+; elemental analysis calcd (%) for C46H52S3: C 78.80, H 7.48;
found: C 78.59, H 7.25.
5-{5-[3-(5-{3,5-Bis[N-(4-tert-butylphenyl)-N-(naphthalen-1-yl)amino]phe-
nyl}thiophen-2-yl)-5-(thiophen-2-yl)phenyl]thiophen-2-yl}-N1,N3-bis(4-
tert-butylphenyl)-N1,N3-bis(naphthalen-1-yl)benzene-1,3-diamine
(3b):
4,7-Bis[5-(3,5-di-tert-butylphenyl]thiophen-2-yl)benzo[c]
ACHTUNGTREN[NUNG 1,2,5]thiadiazole
3b was prepared by following a procedure similar to that described
above for G1b with the exception that 2-(3,5-dibromophenyl)thiophene
was used instead of 4,7-dibromobenzothiadiazole. Pale yellow solid.
(G1a): solution of 2-(3,5-di-tert-butylphenyl)thiophene (2.73 g,
A
10 mmol) in tetrahydrofuran (50 mL) was cooled to À758C and n-butyl
lithium (6.9 mL, 1.6m in hexanes, 11 mmol) added dropwise over 10 min.
After stirring at this temperature for 30 min, it was again cooled to
À758C. Tributyltin chloride (3.58 g, 11 mmol) was added and the mixture
allowed to stir at room temperature overnight. It was quenched by addi-
tion of ice water and extracted with diethyl ether. The combined organic
extracts were dried over anhydrous MgSO4 and evaporated to dryness to
leave the stannylene derivative. It was immediately mixed with 4,7-dibro-
1
Yield: 79%. H NMR (300 MHz, CDCl3, 258C): d=1.24 (s, 36H), 6.45 (t,
J=2.1 Hz, 2H), 6.71 (d, J=2.1 Hz, 2H), 6.80–6.83 (m, 8H), 6.88 (d, J=
3.7 Hz, 2H), 6.99–7.07 (m, 9H), 7.12 (d, J=3.7 Hz, 2H), 7.25–7.30 (m,
6H), 7.33–7.40 (m, 8H), 7.43–7.53 (m, 7H), 7.67 (d, J=8.1 Hz, 4H), 7.85
(d, J=8.5 Hz, 4H), 7.92 ppm (d, J=8.1 Hz, 4H); 13C NMR (75 MHz,
CDCl3, 258C): d=31.4, 34.1, 111.2, 113.1, 121.8, 122.3, 123.8, 124.1, 124.3,
124.4, 125.3, 125.7, 126.0, 126.2, 127.0, 128.0, 128.3, 131.2, 135.2, 135.4,
135.5, 142.2, 143.2, 143.4, 144.6, 144.7, 145.1, 149.5 ppm; FABMS: m/z
1569.8 [M+H]+; elemental analysis calcd (%) for C110H96N4S3: C 84.14, H
6.16, N 3.57; found: C 83.79, H 6.07, N 3.50.
mobenzothiadiazole (1.47 g, 5 mmol), [PdACTHUNRGTNEG(UN PPh3)2Cl2] (35 mg), and DMF
(15 mL). The resulting mixture was heated at 808C for 18 h. A red solid
formed. After cooling the mixture, methanol (40 mL) was added to com-
plete the precipitation. The solids were filtered and washed with liberal
Chem. Eur. J. 2008, 14, 11231 – 11241
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11239

J. T. Lin, C. P. Tai et al.
4,7-Bis(5-
phen-2-yl)benzo[c]ACHTUNGTRENNUNG
G
144.7, 145.1, 149.6 ppm; MALDI MS: m/z 3297.6 [M+H]+; elemental
analysis calcd (%) for C230H196N8S7: C 83.80, H 5.99, N 3.40; found: C
83.67, H 5.98, N 3.46.
in 74% yield from 3a and 4,7-dibromobenzothiadiazole as described for
G1a. 1H NMR (400 MHz, CDCl3, 258C): d=1.39 (s, 72H), 7.32 (d, J=
3.8 Hz, 4H), 7.40 (t, J=1.8 Hz, 4H), 7.42 (d, J=3.8 Hz, 4H), 7.51 (d, J=
1.8 Hz, 8H), 7.54 (d, J=3.8 Hz, 2H), 7.80 (t, J=1.8 Hz, 2H), 7.82 (d, J=
1.8 Hz, 4H), 7.92 (s, 2H), 8.14 ppm (d, J=3.8 Hz, 2H); 13C NMR
(100 MHz, CDCl3, 258C): d=31.5, 34.9, 120.3, 121.7, 121.9, 122.1, 123.8,
124.7, 125.2, 125.5, 128.5, 133.5, 135.3, 135.7, 139.1, 142.1, 144.5, 145.5,
151.4, 152.4 ppm; FABMS: m/z 1533.9 [M]+; elemental analysis calcd
(%) for C98H104N2S7: C 76.71, H 6.83, N 1.83; found: C 76.56, H 6.80, N
1.76.
Dendrimer G3b was obtained in 75% yield as described above for G1b
from 4b and 4,7-dibromobenzothiadiazole. Red solid. 1H NMR
(400 MHz, CDCl3, 258C): d=1.21 (s, 144H), 6.46 (s, 8H), 6.54 (s, 2H),
6.71 (d, J=2.1 Hz, 16H), 6.79–6.88 (m, 40H), 6.98–7.02 (m, 32H) 7.13 (t,
J=2.1 Hz, 6H), 7.26 (d, J=7.3 Hz, 12H), 7.32–7.46 (m, 62H), 7.51–7.58
(m, 10H), 7.65 (d, J=8.1 Hz, 18H), 7.79–7.84 (m, 22H), 7.89–7.96 (m,
18H), 8.18 ppm (s, 2H); 13C NMR (100 MHz, CDCl3, 258C): d=31.4,
34.1, 111.3, 111.7, 113.2, 121.8, 124.2, 124.4, 125.7, 126.0, 126.2, 127.0,
128.3, 131.2, 135.2, 143.2, 144.7, 145.1, 149.6 ppm; MALDI MS: m/z
6726.5 [M+H]+; elemental analysis calcd (%) for C466H392N18S15: C 83.22,
H 5.88, N 3.75; found: C 82.98, H 5.91, N 3.62.
5-(5-{3-[5-(4-{5-[3,5-Bis(5-
1-yl)amino]phenyl}thiophen-2-yl)phenyl]thiophen-2-yl}benzo[c]-
ACHTUNGTRENNUNG[1,2,5]thiadiazol-7-yl)thiophen-2-yl]-5-(5-{3,5-bis[N-(4-tert-butylphenyl)-
ACHTUNGTREN{NGNU 3,5-bis[N-(4-tert-butylphenyl)-N-(naphthalen-
N-(naphthalen-1-yl)amino] phenyl}thiophen-2-yl)phenyl}thiophen-2-yl)-
N1,N3-bis(4-tert-butylphenyl)-N1,N3-bis(naphthalen-1-yl)benzene-1,3-di-
ACHTUNGTRENNUNGamine (G2b): G2b was obtained in 75% yield as described above for G1b
from 3b and 4,7-dibromobenzothiadiazole. Red solid. 1H NMR
(400 MHz, CDCl3, 258C): d=1.23 (s, 72H), 6.45 (t, J=2.1 Hz, 4H), 6.73
(d, J=2.1 Hz, 8H), 6.81–6.84 (m, 16H), 6.89 (d, J=3.7 Hz, 4H), 7.00–
7.04 (m, 16H), 7.15 (d, J=3.7 Hz, 4H), 7.26 (dd, J=7.3, 1.1 Hz, 8H),
7.33–7.52 (m, 28H), 7.62–7.68 (m, 12H), 7.83–7.87 (m, 10H), 7.92 (d, J=
8.5 Hz, 8H), 8.09 ppm (d, J=3.7 Hz, 2H); 13C NMR (100 MHz, CDCl3,
258C): d=31.5, 34.2, 11.4, 113.3, 122.0, 122.2, 124.3, 124.6, 125.5, 125.8,
126.1, 126.3, 126.4, 127.1, 128.5, 128.7, 131.3, 135.4, 135.6, 135.7, 139.3,
142.3, 143.4, 144.8, 145.3, 149.7, 152.7 ppm; MALDI MS: 3273.7 [M+H]+;
elemental analysis calcd (%) for C226H192N10S7: C 82.95, H 5.91; N 4.28;
found: C 82.79, H 5.87, N 4.23.
Acknowledgement
We thank Academia Sinica, National Taiwan University, and National
Science Council for financial support.
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(3,5-dibromophenyl)thiophene as described above for 3a. 1H NMR
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7.32 (d, J=3.8 Hz, 4H), 7.36 (d, J=3.8 Hz, 1H), 7.39 (t, J=1.8 Hz, 4H),
7.44 (d, J=3.8 Hz, 4H), 7.46–7.50 (m, 13H), 7.81 (s, 8H), 7.85 ppm (s,
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8.14 ppm (d, J=3.8 Hz, 4H); 13C NMR (100 MHz, CDCl3, 258C): d=
31.4, 34.8, 120.3, 121.7, 121.8, 122.0, 123.8, 124.1, 124.7, 125.0, 125.3,
125.6, 128.0, 128.5, 133.5, 135.4, 135.6, 136.0, 139.1, 142.2, 143.1, 143.6,
144.5, 145.6, 151.4, 152.4 ppm; MALDI MS: m/z 3247.1 [M]+; elemental
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(400 MHz, CDCl3, 258C): d=1.22 (s, 72H), 6.72 (d, J=2.1 Hz, 8H),
6.80–6.83 (m, 16H), 6.88 (d, J=3.7 Hz, 4H), 6.99–7.02 (m, 16H), 7.13–
7.15 (m, 5H), 7.27 (d, J=7.2 Hz, 8H), 7.32–7.39 (m, 21H), 7.42–7.51 (m,
11H), 7.57 (d, J=1.5 Hz, 4H), 7.66 (d, J=8.5 Hz, 8H), 7.74 (s, 3H), 7.84
(d, J=8.1 Hz, 8H), 7.92 ppm (d, J=8.5 Hz, 8H); 13C NMR (100 MHz,
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125.7, 126.0, 126.2, 127.0, 128.3, 131.2, 135.2, 135.4, 135.6, 142.1, 143.2,
11240
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Chem. Eur. J. 2008, 14, 11231 – 11241

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Received: August 14, 2008
Revised: September 26, 2008
Published online: November 7, 2008
Chem. Eur. J. 2008, 14, 11231 – 11241
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www.chemeurj.org
11241