Synthesis of π-conjugated, pyridine ring functionalized bis-terpyridines with efficient green, blue, and purple emission

Article abstract of DOI:10.1016/j.tet.2008.06.106

A large variety of rigid, π-conjugated, pyridine ring functionalized bis-terpyridines are synthesized efficiently using tandem Miyaura/Suzuki-type cross-coupling reaction. Photophysical property study reveals that the absorption and luminescent properties

Full text of DOI:10.1016/j.tet.2008.06.106

Tetrahedron 64 (2008) 9108–9116
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis of
p
-conjugated, pyridine ring functionalized bis-terpyridines
with efficient green, blue, and purple emission
,
a,b,
*
Fu-She Han a, Masayoshi Higuchi a , Dirk G. Kurth
*
a Functional Modules Group, Organic Nanomaterials Center, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan
b Max-Planck-Institute of Colloids and Interfaces, Research Campus Golm, D-14424 Potsdam, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 6 June 2008
Received in revised form 30 June 2008
Accepted 30 June 2008
Available online 3 July 2008
A large variety of rigid,
p-conjugated, pyridine ring functionalized bis-terpyridines are synthesized
efficiently using tandem Miyaura/Suzuki-type cross-coupling reaction. Photophysical property study
reveals that the absorption and luminescent properties of the obtained bis-terpyridines are profoundly
affected by the nature of the functional groups at the peripheral pyridine and the spacers. Namely, by
tailoring precisely the structures, the light-emitting efficiencies of bis-terpyridines can be enhanced
significantly with quantum yields (Ff) of up to 0.62, and the emission colors can be tuned to display
distinct colors including purple, bright blue, and bright green. Consequently, the novel bis-terpyridines
are attractive ligands for the assembly of new metallo-supramolecule based functional materials.
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords:
Synthesis
Terpyridine
Suzuki coupling
Light-emission
Supramolecule
Polymer
Functional materials
1. Introduction
assemblies.1,3 Thus, synthesis of tailored terpyridine modules has
become a fundamental step in the construction of high perfor-
Terpyridines have now evoked widespread interest as functional
modules within the domain of supramolecular and coordination
chemistry, as well as materials science.1 This type of compounds
has a rich coordination chemistry and generally high binding af-
finity toward a large variety of transition and rare earth metal
cations, giving rise to diverse metallo-supramolecular assemblies
with distinct photophysical, photochemical, electrochemical, cata-
lytic, and magnetic properties.1 In addition, metallo-supramolecu-
lar assemblies derived from terpyridines possess a well-defined
stereochemistry in contrast to many other modules,1,2 which is of
importance when structure–property relationships are under
consideration.
Among the unique properties of terpyridine compounds, their
luminescent properties upon coordination with metal ions are
particularly attractive due to high potential for technological ap-
plications as light-emitting devices and probes in a large spectral
range.1,3 So far, many complexes have been investigated and it has
been well demonstrated that the choice of ligand affects profoundly
the luminescent properties of the resulting supramolecular
mance metal coordination based functional materials, and indeed,
several groups have devoted their efforts to this subject.4 So far,
monotopic terpyridines have been investigated in some detail. As
an important contribution, Araki’s4a and Siegel’s4d groups have
improved significantly the emission properties of monotopic ter-
pyridine compounds by means of structural modification. Polytopic
terpyridines have recently attracted considerable interest owing to
the advantage of constructing metallo-supramolecular polymers
systems.1e However, only a few examples have been reported.4b,5
Furthermore, the available compounds show only a weak efficiency
with F
f<0.20 in general,5 and is limited to purple or blue emitting
colors with a wavelength maximum at around 400ꢀ40 nm.4,5
Therefore, development of novel polytopic terpyridines with high
efficiency as well as other emission colors remains an important
challenge.
To this end, we have paid particular attention to rigid,
p-con-
jugated bis-terpyridines because back-to-back ditopic ligands are
very useful for the fabrication of structurally well-defined rod-like
metallo-supramolecular polymers, avoiding ring formation as
detected in flexible6a or some rigid angular type analogues.6b On
the other hand, considering that substituent in the ligand perturbs
the photophysical and electronic properties not only of the free
ligands4 but also the final metal complexes,7 we focused on the
investigation into a range of functionalized bis-terpyridines by
* Corresponding authors. Tel.: þ81 29 860 4744; fax: þ81 29 860 4721.
E-mail addresses: higuchi.masayoshi@nims.go.jp (M. Higuchi), kurth@mpikg.mpg.
de (D.G. Kurth).
0040-4020/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2008.06.106

F.-S. Han et al. / Tetrahedron 64 (2008) 9108–9116
9109
O
O
2. Results and discussion
2.1. Synthesis of various bis-terpyridines
O
O
NaOH,
H2O/MeOH,
RT, 82%
+
N
N
Br
N
N
Scheme 1 outlines the Kro¨hnke approach we utilized here to
synthesize compounds 6 and 7. The reference compound 5 is
commercially available from Aldrich. The bromo-substituted com-
pound 6, which has one phenylene group as spacer, was prepared in
two steps involving a Claisen–Schmidt aldol condensation of ben-
zene-1,4-dialdehyde (1) and 2-acetyl-6-bromopyridine (2), fol-
O
Br
Br
3
2
1
lowed by
a
Michael-type bis-addition of the resulting
I
R
diazachalcone (3) with pyridinium iodide salt (4).9 Nucleophilic
substitution reaction of 6 with excess NaOMe gave the dimethoxyl
derivative 7.
N
N
N
N
N
4
O
N
N
NH4OAc, EtOH
For the synthesis of the symmetrically and unsymmetrically
substituted derivatives 10–15 (Scheme 2), which are bridged by
two phenylene units, we have previously developed an efficient
protocol by employing Suzuki-type cross-coupling dimerization11
or a two-step coupling reaction by applying sequentially Miyaura
boronic ester formation13 and Suzuki coupling reaction,14 since
versatile synthesis of these structural variants are troublesome
according to the conventional Kro¨hnke method owing to the lim-
ited availability of starting dialdehyde and 2-acetylpyridine
derivatives.15
39%
R
5 R = H
6 R = Br
NaOMe,
dioxane,
94%
7 R = OMe
Scheme 1. Synthesis of substituted bis-terpyridines with one phenylene unit as spacer.
appending functional groups at the pyridine periphery and/or by
incorporating heteroaromatics into the spacer region. Such com-
pounds are in sharp contrast to the unsubstituted and carbon-ar-
omatic ring bridged bis-terpyridines frequently reported in
previous work.1,8 However, for the synthesis of structurally diverse
bis-terpyridines, a general synthetic protocol is highly desired since
the conventional approaches such as the Kro¨hnke method,9 and
substitution or coupling reaction of suitably functionalized
mono-terpyridines is often limited in yield and functional group
compatibility.7c,10 Herein, we describe a highly efficient and broadly
applicable protocol for the synthesis of various novel bis-terpyr-
idines using palladium-catalyzed tandem Miyaura- and Suzuki-
type cross-coupling reactions,11 which has been shown to be
potential for the synthesis of such type of compounds,12 and the
investigation of the photophysical properties of the compounds
synthesized.
On the basis of our previous work, the tandem Miyaura/Suzuki
cross-coupling protocol was further employed to synthesize other
types of bis-terpyridines, 17–24, featuring the presence of a bent
spacer by incorporating various aromatic groups into the spacer
region (Scheme 3). While a stepwise procedure is routinely appli-
cable,11 here, we examined the two-step in situ strategy (Route A
and Route B), and found eventually that Route A was even more
efficient to access the desired products than the stepwise pro-
cedure, although Route B was less effective for heteroaromatic 16
due possibly to the ease of protonolysis of boronic esters formed
from N- and S-heteroaromatic dibromides 16 and diboron 9.13a
Thus, mono-terpyridine 8a (or 8b and 8c) was reacted with
1.1 equiv of bis(pinacolato)diboron 9 under Miyaura conditions13
(5 mol % PdCl2(PPh3)2, 3.0 equiv of KOAc, DMF (or DMSO)), until the
starting terpyridines 8a–c had disappeared as monitored by TLC.
Br
O
O
O
O
R1
R2
B
B
N
N
N
N
9
N
N
PdCl2(PPh3)2,
K2CO3, DMSO
N
2
N
N
R2
R1
R2
R1
10 R1 = R2 = H (86%)
8a R1 = R2 = H
11 R1 = R2 = OMe (76%)
12 R1 = R2 = CN (51%)
13 R1 = H, R2 = OMe (76%)
8b R1 = R2 = OMe
8c R1 = R2 = CN
8d R1 = H, R2 = OMe
1) 9 (1.1 equiv),
R
R
PdCl2(PPh3)2,
KOAc, DMSO,
80 °C
N
N
N
N
2) 8b or 8c
2
PdCl2(PPh3)2
K2CO3, DMSO
80 - 120 °C
N
N
14 R = OMe (58%)
15 R = CN (65%)
Scheme 2. Synthesis of symmetrically and unsymmetrically substituted ditopic bis-terpyridines with two phenylene units as spacer.11

9110
F.-S. Han et al. / Tetrahedron 64 (2008) 9108–9116
Br
N
N
N
Ar
R
R
8a R = H
8b R = OMe
8c R = CN
Br
Br
16
1) 9, Pd(0),
KOAc,Solvent
1) 9, Pd(0),
KOAc, Solvent
2)
Br
Ar
Route B
Route A
2) 8a, Pd(0),
K2CO3
Br
16
Pd(0), K2CO3
Ar
N
N
R
N
R
N
N
R
N
R
C8H17
(61%)
(59%)
(32%)
17 R = H,
18 R = OMe, Ar =
19 R = CN,
(48%)
22 R = H,
23 R = H,
Ar =
S
20 R = H,
21 R = H,
Ar =
Ar =
(47%)
(59%)
(38%)
Ar =
N
S
S
S
S
S
24 R = OMe, Ar =
(26%)
Scheme 3. Synthesis of ditopic bis-terpyridines with diverse spacers.
Then, the reaction vessel was recharged in situ with 0.5 equiv of
dibromo compounds 16, 5 mol % of PdCl2(PPh3)2, and 3.0 equiv of
K2CO3, and the mixture was further heated until the dibromo
substrates had disappeared. Purification of the reaction mixture
afforded the desired 17–24 in moderate to good yields. The struc-
tures of these compounds were determined by standard spectro-
scopic techniques, including 1H and 13C NMR, and mass analysis.16
It is now evident that the synthetic protocol presented here is quick
and broadly applicable to a large variety of substrates including
mono-terpyridine precursors having electron-rich (e.g., 8b) and
deficient groups (e.g., 8c), as well as diverse classes of dibromo-
aromatic coupling partners such as carbon-aromatic (10–15, 17–
19), N- and S-heteroaromatic (20–24), and sterically hindered
aromatic compounds (22).
It should be noted that, while coupling reaction of 8a–c with 1,4-
dibromobenzene was also effective, purification of the resulting
products was difficult due to the poor solubility. To compare with
the fairly good solubility of bis-terpyridines 17–19 derived from the
bent 1,3-dibromobenzene, the poor solubility of the analogues
prepared from linear-shaped 1,4-dibromobenzene is due probably
to the highly symmetric structures.
behavior, a general observation is that, when compared to refer-
ence compound 5, the maximum absorption band (labs) of the bis-
terpyridines having carbon-aromatic (6, 7, 10–15, and 17–19) and
N-heteroaromatic spacers (20) is around 300 nm, which is red-
shifted slightly (ca. 10ꢀ4 nm) by appending either the electron-
donating OMe or electron-withdrawing Br and CN substituents at
the peripheral pyridines (Table 1). In sharp contrast, the labs red
shifts significantly to ca. 370 nm by introducing a thiophene group
in the spacer region (21), and moves further to more than 400 nm
when a bi-thiophene group (23 and 24) is incorporated (Table 1 and
Fig. 1). It should be noted that, while interposing a thiophene ring
without substituent at 3- or 4-position in the spacer region leads to
a large red-shift of lmax, attaching an octyl alkyl chain at the 3-
position of thiophene unit moves the absorption maximum from
370 to 321 nm as a comparison of 21 and 22 shows, indicating
substitution at the 3- or 4-position of thiophene ring affects
markedly on the absorption behavior of bis-terpyridine derivatives.
This observation is attributed obviously to the introduction of
a long alkyl chain, which causes a twist between the thiophene and
phenylene rings, and ultimately, resulting in a decreased p-conju-
gation between the aromatic rings.7c,17 It should also be mentioned
that, extending the length of spacer generally shifts the labs toward
longer wavelength, the labs of compounds 17–19, whose two ter-
pyridine moieties are bridged by three contiguous but angularly
connected phenylene rings, are slightly shifted toward shorter
wavelength to compare with compounds 10, 11, and 15, whose two
terpyridine moieties are bridged by two linearly linked phenylene
2.2. Photophysical properties
2.2.1. UV–vis absorption property
With a diverse class of novel bis-terpyridines in hand, we next
investigated their photophysical properties. For the absorption

F.-S. Han et al. / Tetrahedron 64 (2008) 9108–9116
9111
Table 1
displaying a purple color (Table 1, and Fig. 2). Compounds 21 and
22, which contain one thiophene ring in the spacer region, exhibit
bright blue emission color with lem at ca. 450 nm for 21. More
excitingly, by further increasing the number of thiophene from one
to two units, the emitting wavelength of 23 and 24 is red-shifted to
more than 500 nm paired with a shoulder at ca. 470 nm, showing
that a large Stokes’ shift occurred (>90 nm). Consequently, the
emission colors of 23 and 24 are bright green. The green emission of
polytopic terpyridines has not been reported in the literature so far.
Thus, our results show that the emission color of this class of
compound can be tuned from purple via blue to green by structural
modification. On the basis of these results, we believe that the
emission color can be further extended to red by tuning the
structure of the ligands.
To elucidate the effect of spacers on the photophysical proper-
ties, the electronic states of compounds 10, 17, and 21, which rep-
resent the types of spacers with different nature such as linear 10
vs angular 17, and carbon-aromatic 17 vis heteroaromatic 21, were
calculated using MOPAC/AM1 and PM5, respectively. The HOMO
and LUMO molecular orbitals for 10 were deduced from its X-ray
structure,7a,11 while those for compounds 17 and 21 were calculated
by fixing the dihedral angle between the terpyridine unit and the
Absorption and emission properties of various bis-terpyridines
labs (nm)a (log
3
)
lem
Ffc
b
5
6
7
292 (4.79)
297 (4.85)
298 (4.84)
310 (4.78)
313 (4.95)
313 (4.92)
314 (4.92)
298 (4.78)
288 (4.84)
310 (5.01)
295 (4.82)
290 (4.86)
360
357
373
371
376
371
371
384
364
371
381
364
445, 457
441, 384
500, 472
505, 474
0.13
0.08
0.22
0.37d
0.54
0.62
0.59
0.41
0.23
0.36
0.21
0.58
0.44
0.42
0.20
0.31
10
11
13
14
15
17
18
19
20
21
22
23
24
370, 280 (4.66,4.41)
321, 280 (4.65,4.64)
403, 280 (4.61,4.63)
410, 305 (4.69,4.67)
a
In 1ꢁ10ꢂ5 M CH2Cl2 solution.
b
In 5ꢁ10ꢂ7 M CH2Cl2 solution with absorbance <0.1. The excitation wavelength
was 290 nm for compounds 17 and 20; 300 nm for 5–7 and 10–15; 310 nm for 11;
320 nm for 22; 370 nm for 21; 400 nm for 23; and 410 nm for 24.
c
Determined relative to bis-terpyridine 5, Ff¼0.13.
d
Ff¼0.49 in reported literature (see Ref. 5a).
units. The absorption spectral change is presumably due to the fact
that an angular connection may introduce an additional steric in-
teraction between the two terpyridine fragments, which prohibits
an effective planar conjugation of the aromatic rings as compared
to the linearly connected analogues.4d
The molar absorptivity (log 3 in Table 1) also correlates with the
substituents and spacers. As listed in Table 1, we observe clearly
that introduction of either electron-donating (OMe) or electron-
withdrawing group (Br and CN) increases the molar absorptivity as
compared to 5. As for the effect of spacer, compounds with carbon-
aromatic and N-heteroaromatics in the spacer region show an en-
hanced molar absorptivity, which is decreased, however, after
replaced by S-heteroaromatics 21–24.
2.2.2. Emission property
The light-emitting property of various bis-terpyridines is also
investigated. As can be seen from Table 1, photoluminescence of the
obtained bis-terpyridines is affected prominently by the nature of
spacers and substituents. Thus, the maximum emission band (lem
)
of the carbon-aromatic (6, 7, 10–15, and 17–19) and N-hetero-
aromatic ring (20) bridged compounds is located at about 370 nm,
Figure 2. Emission colors of selected compounds 10, 21 and 24 (from left to right) in
CH2Cl2 excited with a 365 nm UV lamp (top) and their corresponding emission spectra
in 5ꢁ10ꢂ7 M CH2Cl2 solution (bottom). The small peaks in the emission spectra are due
to an optical artifact (excitation wavelength: 310, 370, and 410 nm for compounds 10,
21, and 24, respectively).
Figure 1. UV–vis spectra of selected bis-terpyridines 7, 21, and 23 in CH2Cl2
(1ꢁ10ꢂ5 M).

9112
F.-S. Han et al. / Tetrahedron 64 (2008) 9108–9116
thiophene-bridged compounds as seen from their photophysical
properties.
As for the emission efficiency, we observed that in general, at-
tachment of electron-donating OMe group to the pyridine ring or
extending appropriately the conjugation length of the spacers give
rise to an increased quantum yield (Ff).18 Accordingly, among the
16 representatives, compounds 11, 13, and 14 (Table 1), which have
an extended spacer as well as electron-donating OMe groups at
pyridine periphery, and 20, which contains a pyridine ring, exhibit
a significantly increased Ff of larger than 0.54, with a maximum Ff
of up to 0.62 for 13, in contrast to Ff¼0.13 of reference compound 5.
Compounds, which are modified either by extending the spacer
only or by appending electron-donating group only (10, 15, 18, 21,
and 22), also show high efficiencies ranging from 0.36 to 0.44. In
addition, the fluorescence intensity of these compounds is in-
creased by 4–6 times as compared to compound 5 (Fig. 3). However,
electron-withdrawing groups, such as Br and CN, generally lead to
a decreased emission efficiency when 6 and 7, 14 and 15, and 18 and
19 are parallelly compared. It should be noted that, while Ff in-
creases when the length of the spacer is extended, incorporation of
a second thiophene ring causes a decrease in Ff as a comparison of
21 and 23 shows. However, on the basis of the principal rules ob-
served, the quantum yield of the green emitters was increased ef-
fectively from 0.20 for 23 to 0.31 for 24 by introducing OMe
functionalities.
Figure 3. Effect of bis-terpyridine structures on the emission intensity referenced to 5.
The spectra are measured in 5ꢁ10ꢂ7 M CH2Cl2 solution.
collected phenylene ring to 27.976ꢃ based on the X-ray structure
of 10.
The results showed that using either AM1 or PM5 method, the
HOMO and LUMO of the linear-shaped 10 are located on the phe-
nylene ring as denoted with pph and
p
*
ph, respectively. Thus, the
transition.
2.2.3. Solvent effect on the photophysical properties
lowest energy absorption for 10 is due to the pph
–
p
*
ph
To examine the solvent effect on the photophysical property,
several selected compounds were investigated in various solvent
systems. The results show that the photophysical behavior of the
angular bis-terpyridine derivatives such as 17, 18, and 20 are similar
to the linear-shaped compounds such as 6, 10, and 13 in different
solvent systems, indicating that the photophysical properties are
less dependent on the shape of spacers. Thus, for a clear discussion
of the effect of substituents and the length of spacers on the pho-
tophysical properties, the UV–vis and fluorescence data of five
representatives 6, 10, 13, 21, and 23 are compared in more detail. As
can be seen from the data collected in Table 2, the absorption
maximum for each compound is essentially identical in aprotic
polar CH3CN and CH2Cl2, and in protic MeOH. However, use of non-
polar cyclohexane shifts the band toward shorter wavelength of
about 10 nm. Only a negligible difference is observed for the ab-
sorption intensity (data not shown) by varying the solvents except
that 13 and 23 show a relatively large decrease in 3max associated
with a broadened band shape in MeOH solution. This is due
probably to the poor solubility of 13 and 23 in MeOH as seen from
the somewhat opaque solution. Also, the emission efficiencies (data
not shown) are less influenced by changing the solvent except for
13 and 23 whose emission intensity decrease to about half in MeOH
compared to that in other solvents mainly due to the solubility
problem, although hydrogen bonding is possibly an additional
factor as being observed in some individuals of mono-
terpyridines.4c
For angular 17, the HOMO orbital is mainly located on the central
phenylene ring (pc–ph), while the LUMO appears mainly on the
phenylene ring linked to the terpyridine unit (
sequently, the lowest energy band for 17 is attributed mostly to
intramolecular charge transfer (ICT) of pc–ph to ph–tpy. The dif-
p
*
ph–tpy), and con-
p
*
ferent energy transition states between 10 and 17 are consistent
with their optimized conformers, where the dihedral angle be-
tween the two directly linked phenylene rings in 107a and 17 are
27.302ꢃ and ca. 46.282ꢃ, respectively. Thus, the larger dihedral
angle exhibited in 17 results in a smaller
p-conjugation when
compared to 10, giving rise to an increased energy gap between the
LUMO and HOMO for 17 (8.170 eV) as compared to that of 10
(7.841 eV). These calculated results are in good agreement with the
observed absorption property with 17 showing a lmax of ca. 22 nm
shorter than 10 (Table 1).
Somewhat different from 10 and 17, compound 21 containing
a thiophene ring in the spacer region leads to a conjugation be-
tween the thiophene and phenylene rings. Both the HOMO and
LUMO orbitals are located on the conjugated region consisting of
phenylene/thiophene/phenylene rings with the major part on
thiophene ring, as represented by pptp and
the lowest energy absorption in the case of 21 is a local transition of
pptp to ptp. Due to the large conjugation, the energy gap between
p ptp, respectively. Thus,
*
p
*
the LUMO and HOMO is significantly decreased to 7.360 eV, and
ultimately, leading to a red-shifted emission and absorption for the
Table 2
Effect of solvent polarity on the photophysical properties of various bis-terpyridinesa
Solvent
6
10
13
21
23
labs (nm)
lem (nm)
labs (nm)
lem (nm)
labs (nm)
lem (nm)
labs (nm)
lem (nm)
labs (nm)
lem (nm)
b
C6H12
288
297
295
297
348, 357
357
359
298
361, 375
371
375
308
313
311
314
361, 375
371
374
362, 279
370, 280
368, 279
370, 280
439, 417
445, 427
447
394, 275
403, 281
400, 275
403, 280
486, 459
500, 472
486c
CH2Cl2
CH3CNb
MeOHb
310, 299
308, 297
311, 299
360
380
381
452
490c
a
Measured in 1ꢁ10ꢂ5 M for UV–vis absorption (labs) and 5ꢁ10ꢂ7 M for emission (lem), respectively. The excitation wavelength was 300 nm for 6, 10, and 13, 370 nm for 21,
and 400 nm for 23.
b
Containing 10% CH2Cl2 due to the poor solubility of the compounds in pure MeOH, CH3CN, and cyclohexane (C6H12).
Middle position of a broad band.
c

F.-S. Han et al. / Tetrahedron 64 (2008) 9108–9116
9113
Figure 4. Emission spectra of bis-terpyridine 21 excited at 370 nm in 5ꢁ10ꢂ7 M so-
lution in various solvents.
Figure 5. Lippert–Mataga plot for 6, 10, 13, 21, and 23 in different solvents. The dif-
ference between the maximal wavenumbers of absorption and fluorescence spectra
(
Dn) is plotted as a function of solvent polarity according to Lippert’s function (D
f).4e,19
In contrast, the emission wavelength for each compound de-
pends on the solvent. Upon increasing the solvent polarity19 from
cyclohexane via CH2Cl2 and CH3CN to MeOH without considering
the protic nature of MeOH,4c the emission maximum shifts grad-
ually toward longer wavelength as seen from the data in Table 2 and
the emission spectra of a representative example 21 depicted in
Figure 4. This bathochromic shift is more pronounced when the
length of spacer for bridging the two terpyridine moieties in-
Lippert’s solvent polarity parameter, 3 and n are the dielectric con-
stant and the refractive index of the medium, respectively, a is the
effective radius of the Onsager cavity of a compound, h and c cor-
respond to Planck’s constant and the velocity of light, respectively.
No good correlation is found for most cases with the Dn values in
cyclohexane exhibiting a large deviation from the curve fitting.
However, plots of the spectral shifts in CH2Cl2, CH3CN, and MeOH
show a satisfactory linear correlation with solvent polarity as
depicted in Figure 5. Generally, the spectral shifts of 6, 10, and 13,
which have one or two phenylene units in the spacer region as well
as different substituents in the pyridine rings such as electron-
deficient Br (6), neutral H (10), and electron-rich OMe groups (13),
are moderately sensitive to the solvent polarity. In contrast, com-
pounds 21 and 23 having thiophene spacers exhibit a considerable
spectral shift upon increasing the solvent polarity. Assuming
a value of 9–11 Å (ca. 5 Å for half molecule4e) for the effective radius
of the Onsager cavity, Dm for 6, 10, 13, 21, and 23 deduced from the
Lippert–Mataga equation is about 2.0ꢀ0.3, 2.1ꢀ0.3 (for compounds
10 and 13), 3.8ꢀ0.5, and 3.2ꢀ0.4 D, respectively. These results fur-
ther indicate that the magnitude of the bathochromic shift corre-
lates mainly with the type of spacers, while effect of the
substituents is weak.
creases, showing an enlarged Dn
(
nHex nMeOH) of ca. 958,1358,1454,
ꢂ
and 1857 cmꢂ1 for compounds 6, 10, 13, and 21, respectively. On the
other hand, the bathochromic effect of substitution in pyridine
periphery on the emission property is rather weak when unsub-
stituted 10 and OMe modified ligands 13 are compared. These re-
sults indicate that the excited states of bis-terpyridine compounds
are stabilized as a consequence of increasing solvent polarity, and
the magnitude of stabilization is correlated mainly with the length
of spacer.
Equally interesting to the spectral shift, another noticeable
feature of the fluorescence spectra is the strong solvent de-
pendence of the emission band shape. As a representative example,
compound 21 shows an unstructured, relatively broad emission
profile in polar solvent such as MeOH and CH3CN as can be seen in
Figure 4. By decreasing the solvent polarity, e.g., from CH3CN via
CH2Cl2 to cyclohexane, the observed band shape becomes gradually
more structured, giving rise to two distinctly resolved bands in
non-polar cyclohexane. Such a behavior combined with solvent-
dependent response of the spectral shift (vide supra) is well known
in electron donor–acceptor dyads20 and has also been noted for
3. Conclusion
In summary, novel rigid,
p-conjugated bis-terpyridines having
a bis-terpyridine compound,7c and is attributed to close
p–
*
p in-
various substituents and aromatic spacers were synthesized using
a one-pot Suzuki-type cross-coupling strategy. The synthetic pro-
tocol is simple, quick, and applicable to access a large number of
new bis-terpyridine derivatives. The photophysical properties of
the obtained compounds are presented. On the basis of our results,
we can make several principal conclusions: (i) the maximum ab-
sorption (labs) is affected significantly by the types of spacers, and
ultimately, labs can be tuned to cover a range from ca. 300 nm to
more than 400 nm; (ii) molar absorptivity is mainly influenced by
the electronic properties of the substituents at the pyridine pe-
riphery, although an additional contribution of the spacer is
observed. Thus, appending an electron-donating OMe group results
teractions and the formation of a fluorescent intramolecular charge
transfer (ICT) sate in polar solvent, which is destabilized in non-
polar solvent.21
2ðDmÞ2
Dn
¼
Dnabs
ꢂ
Dnem
¼
D
f þ Const:
(1)
hca3
ꢀ
ꢁ
3
ꢂ 1
n2 ꢂ 1
D
f ¼
ꢂ
(2)
2n2 þ 1
2
3
þ 1
To estimate the dipole moment difference (Dm) between the
ground and excited state of the functionalized bis-terpyridines,
plots of the difference between the maximal wavenumber (1/
wavelength) of the absorption and fluorescence spectra (Dn) as
in
a
markedly enhanced extinction coefficient exceeding
105 Mꢂ1 cmꢂ1; (iii) the affecting tendency of substituents and
spacers on photoluminescent property is in consistent with the
absorption behavior. Thus, lem can be tuned to span the region from
ca. 370 nm to more than 500 nm by changing the spacer, and the
a function of solvent polarity (
D
f) are made according to the Lippert–
Mataga function as shown in Eqs. 1 and 2,4e,19 where
D
f is the

9114
F.-S. Han et al. / Tetrahedron 64 (2008) 9108–9116
emission efficiency (Ff) is significantly increased to 0.62 by
appending OMe group. Consequently, the newly synthesized bis-
terpyridines exhibit three distinct emission colors, namely, purple,
bright blue, and bright green. In addition, we have shown that the
fluorescence spectra of the bis-terpyridines are dependent on the
solvent polarity. Thus, these novel compounds are promising can-
didates for the construction of metallo-supramolecular based light-
emitting polymers. Further work concerning the photophysical
properties of the polymer materials is currently underway in our
laboratory.
was refluxed for 2 days under N2 atmosphere. Solvent was evapo-
rated under reduced pressure and the residue was suspended in
200 mL CHCl3. The suspension was then washed with H2O (50 mL)
for three times. The organic layer was separated, dried over MgSO4,
filtered, concentrated, and purified by column chromatography on
activated basic Al2O3 (hexane/CH2Cl2¼9:1 then pure CH2Cl2) to give
7 (161 mg, 96%) as white powder; mp>300 ꢃC; 1H NMR (CDCl3)
d¼8.78 (s, 2H), 8.77 (s, 2H), 8.75 (d, 2H, J¼8.1 Hz), 8.69 (d, 2H,
J¼8.0 Hz), 8.30 (d, 2H, J¼7.5 Hz), 8.04 (s, 4H), 7.87 (br t, 2H,
J¼7.5 Hz), 7.78 (t, J¼7.5 Hz), 7.36 (dd, 2H, J1¼7.5 Hz, J2¼4.8 Hz), 6.84
(d, 2H, J¼8.1 Hz), 4.13 (s, 6H); MALDI-MS: m/z (%)¼601 (100)
[MþH]þ; HRMS found m/z: 601.2359 [MþH]þ; C38H29N6O2 re-
quires: 601.2352.
4. Experimental section
4.1. General methods
4.2. General procedure for the synthesis of symmetric bis-
terpyridines via Suzuki-type dimerization (10–13)
Unless otherwise noted, all reagents were of reagent grade and
were used without purification. Reaction solvents were dehydrated
and were purchased from Wako or Kanto Chemical Co., Inc.
Deionized H2O was used in the experiment where required. 1H
NMR and 13C NMR spectra were recorded at 300 and 75 MHz, re-
spectively, on a JEOL AL 300/BZ instrument. Chemical shifts were
given relative to TMS. Mass spectra (MS) were measured by using
AXIMA-CFR, Shimadzu/Kratos TOF Mass spectrometer. High reso-
lution mass spectra (HRMS) were measured by using Shimadzu
LCMS-IT-TOF spectrometer. UV–vis spectra were recorded using
a Shimadzu UV-2550 UV–vis spectrophotometer. Emission spectra
To
a
30 mL DMSO solution of mono-terpyridine (8a–d,
(102 mg,
0.773 mmol) was added bis(pinacolato)diboron
9
0.402 mmol), K2CO3 (320 mg, 2.318 mmol), and PdCl2(PPh3)2
(27 mg, 0.039 mmol). The solution was stirred at 80–120 ꢃC under
an argon atmosphere until the starting material had disappeared as
monitored by TLC. The catalyst was removed by filtration and
washed with CHCl3 after the reaction mixture was cooled to room
temperature. The filtrate was then washed with H2O (50 mL) for
five times, and the organic layer was dried over MgSO4, filtered,
concentrated, and purified by column chromatography on activated
basic Al2O3 (hexane/CH2Cl2 4:1 then pure CH2Cl2) to give the
dimerized products 10–13.
were
measured
using
Shimadzu
RF-5300PC
spectro-
fluorophotometer. MeOH, CH3CN, CH2Cl2, and cyclohexane for
photophysical measurement are special solvents for luminescent
analysis and were purchased from Kanto Chemical Co., Inc. Ana-
lytical thin layer chromatography (TLC) was performed using Merck
aluminum oxide 60 F254 neutral or silica gel 60 F254 coated on
aluminum sheets (20ꢁ20 cm). Flash column chromatographic
4.2.1. Symmetric bis-terpyridine 10
White powder, 86% yield from 8a; 1H NMR (CDCl3)
d¼8.82 (s,
4H), 8.75 (ddd, 4H, J1¼5.4 Hz, J2¼1.8 Hz, J3¼0.9 Hz), 8.69 (d, 4H,
J¼7.8 Hz), 8.04 (d, 4H, J¼8.1 Hz), 7.89 (td, 4H, J1¼8.1 Hz, J2¼1.8 Hz),
7.83 (d, 4H, J¼8.4 Hz), 7.37 (dd, 4H, J1¼7.8 Hz, J2¼4.8 Hz); 13C NMR
separations were performed on silica gel 60N (neutral, 40–100
mM),
Kanto Chemical Co. Inc., or activated alumina oxide (75
mM), Wako.
(CDCl3)
d
¼156.3, 156.1, 149.7, 149.2, 141.1, 137.7, 136.9, 127.8, 127.6,
4.1.1. Synthesis of dibromo-bis-terpyridine (6)
123.8, 121.4, 118.8; MALDI-MS: m/z (%)¼617 (100) [MþH]þ; HRMS
To a 200 mL MeOH solution of benzene-1,4-dicarboxaldehyde 1
(3.62 g, 26.99 mmol) was added 2-acetyl-6-bromopyridine
found m/z: 617.2470 [MþH]þ; C42H29N6 requires: 617.2454.
2
(10.80 g, 53.98 mmol) and 10% aqueous NaOH (2.16 g in 20 mL H2O)
at room temperature, and the mixture was stirred at room tem-
perature overnight. The precipitate formed was collected by fil-
tration, and washed sequentially with H2O and MeOH for three
times, respectively. The slight yellow solid was then dried in vacuo
to give diazachalcone 3 (10.5 g, 78%), which was used directly for
the following reaction without further purification. To a 200 mL
EtOH solution of crude 3 (7.1 g, 14.26 mmol) was added pyridinium
iodide salt 4 (9.3 g, 28.53 mmol) and NH4OAc (54.0 g, 0.70 mol).
The solution was refluxed for 60 h and then cooled to room tem-
perature. The precipitate formed upon cooling was collected by
filtration, and washed sequentially with H2O and MeOH for three
times, respectively. The crude product was purified by column
chromatography on basic Al2O3 (CH2Cl2/hexane 5:1 then pure
CH2Cl2) to give 6 (3.88 g, 39%) as white powder; mp>300 ꢃC; 1H
4.2.2. Symmetric bis-terpyridine 11
White powder, 76% yield from 8b; 1H NMR (CDCl3)
d
¼8.72 (s,
4H), 8.30 (d, 4H, J¼7.2 Hz), 7.98 (d, 4H, J¼8.4 Hz), 7.87 (d, 4H,
J¼8.4 Hz), 7.78 (t, 4H, J¼7.8 Hz), 6.83 (d, 4H, J¼8.1 Hz), 4.12 (s, 12H);
13C NMR (CDCl3)
127.7, 127.4, 118.6, 114.2, 111.1, 53.3; MALDI-MS (%): m/z¼737 (100)
[MþH]þ; HRMS found m/z: 737.2875 [MþH]þ; C46H37N6O4 re-
quires: 737.2876.
d
¼163.8, 156.1, 153.9, 139.4, 130.8, 128.8, 127.8,
4.2.3. Symmetric bis-terpyridine 13
White powder, 76% yield from 8d; 1H NMR (CDCl3)
d¼8.78 (d,
2H, J¼1.8 Hz), 8.76 (d, 2H, J¼1.8 Hz), 8.75 (ddd, 2H, J1¼4.2 Hz,
J2¼1.8 Hz, J3¼0.9 Hz), 8.70 (dt, 2H, J1¼7.8 Hz, J2¼1.2 Hz), 8.30 (dd,
2H, J1¼7.2 Hz, J2¼0.8 Hz), 8.02–8.00 (m, 4H), 7.91 (dd, 2H, J1¼7.5 Hz,
J2¼1.8 Hz), 7.87–7.84 (m, 4H), 7.78 (dd, 2H, J1¼8.1 Hz, J2¼7.2 Hz),
7.37 (ddd, 2H, J1¼7.5 Hz, J2¼4.8 Hz, J3¼1.2 Hz), 6.84 (dd, 2H,
NMR (CDCl3)
d
¼8.82 (d, 2H, J¼1.9 Hz), 8.77 (d, 4H, J¼1.8 Hz), 8.66
(dd, 4H, J1¼7.7 Hz, J2¼0.9 Hz), 8.06 (s, 4H), 7.90 (dt, 2H, J1¼7.7 Hz,
J2¼1.8 Hz), 7.45 (t, 2H, J¼7.7 Hz), 7.55 (dd, 2H, J1¼7.7 Hz, J2¼0.9 Hz),
7.38 (ddd, 2H, J1¼7.7 Hz, J2¼4.8 Hz, J3¼0.9 Hz); 13C NMR (CDCl3)
J1¼8.1 Hz, J2¼0.8 Hz); 13C NMR (CDCl3)
¼163.7, 156.4, 156.1, 156.0,
d
153.7, 149.6, 149.1, 141.1, 139.4, 138.2, 136.9, 127.8, 127.7, 123.8, 121.4,
118.7 (2C), 114.1, 111.2, 53.3; MALDI-MS: m/z (%)¼677 (100)
[MþH]þ; HRMS found m/z: 677.2652 [MþH]þ; C44H33N6O2 re-
quires: 677.2665.
d
¼157.6, 156.3, 156.1, 154.6, 149.9, 149.3, 141.7, 139.2, 139.1, 136.8,
128.1, 128.0, 123.9, 121.4, 120.1, 119.5, 119.3; MALDI-MS: m/z
(%)¼699 (100) [MþH]þ; HRMS found m/z: 699.0347 [MþH]þ;
C
36H23Br2N6 requires: 699.0330.
4.3. General procedure for the synthesis of unsymmetric bis-
terpyridines via tandem Miyaura/Suzuki coupling (14 and 15)
4.1.2. Synthesis of dimethoxyl bis-terpyridine (7)
To a 60 mL dioxane solution of 6 (200 mg, 0.287 mmol) was
added NaOMe (1.0 M solution in MeOH, 1.72 mmol). The solution
To a 8 mL DMSO solution of 8a (100 mg, 0.258 mmol) was added
bis(pinacolato)diboron
9 (72 mg, 0.283 mmol), KOAc (76 mg,

F.-S. Han et al. / Tetrahedron 64 (2008) 9108–9116
9115
0.773 mmol), and PdCl2(PPh3)2 (9.0 mg, 0.013 mmol). The solution
was stirred at 80 ꢃC under argon atmosphere for 12 h. The reaction
vessel was recharged with K2CO3 (107 mg, 0.773 mmol), 8b (or 8c)
(0.258 mmol), and Pd catalyst (5 mol %) after being diluted with
additional 8 mL DMSO. The mixture was then heated at 80–120 ꢃC
until 8b (or 8c) had disappeared as monitored by TLC. The catalyst
was removed by filtration and washed with CHCl3 after the reaction
mixture was cooled to room temperature. The filtrate was then
washed with H2O (50 mL) for five times, and the organic layer was
dried over MgSO4, filtered, concentrated, and purified by column
chromatography on activated basic Al2O3 to give 14 and 15,
respectively.
4.4.2. Spacer tunable bis-terpyridine 18
White powder, 59% yield from 8b and 1,3-dibromobenzene; 1H
NMR (CDCl3)
d
¼8.72 (s, 4H), 8.29 (d, 4H, J¼7.5 Hz), 7.97 (d, 4H,
J¼8.1 Hz), 7.96 (s, 1H), 7.86 (d, 4H, J¼8.1 Hz), 7.77 (t, 4H, J¼8.1 Hz),
7.71 (dd, 2H, J1¼6.9 Hz, J2¼1.2 Hz), 7.62 (t, 1H, J¼6.9 Hz), 6.83 (d, 4H,
J¼7.5 Hz), 4.11 (s, 12H); 13C NMR (CDCl3)
¼163.7, 156.0, 153.8,
d
149.5, 141.7, 141.3, 139.4, 138.5, 129.5, 127.9, 127.8, 126.5, 126.1, 118.6,
114.2, 111.1, 53.3; MALDI-MS (%): m/z¼813 (100) [MþH]þ; HRMS
found m/z: 813.3207 [MþH]þ; C52H41N6O4 requires: 813.3207.
4.4.3. Spacer tunable bis-terpyridine 19
White powder, 32% yield from 8c and 1,3-dibromobenzene; 1H
NMR (CDCl3)
d
¼8.90 (s, 4H), 8.88 (dd, 4H, J1¼8.4 Hz, J2¼1.2 Hz),
4.3.1. Unsymmetric bis-terpyridine 14
8.07–8.03 (m, 8H), 8.00 (s, 1H), 7.91 (dd, 4H, J1¼6.9 Hz, J2¼2.1 Hz),
White powder, 58% yield from 8a and 8b; 1H NMR (CDCl3)
7.78 (dd, 4H, J1¼7.8 Hz, J2¼1.2 Hz), 7.73 (dd, 2H, J1¼6.9 Hz,
d
¼8.82 (s, 2H), 8.75 (ddd, 2H, J1¼5.7 Hz, J2¼1.8 Hz, J3¼0.9 Hz), 8.72
J2¼1.2 Hz), 7.65 (d, 1H, J¼6.9 Hz); 13C NMR (CDCl3)
¼157.6, 154.3,
d
(s, 2H), 8.70 (d, 2H, J¼7.8 Hz), 8.29 (dd, 2H, J1¼7.5 Hz, J2¼0.9 Hz),
8.05 (d, 2H, J¼7.5 Hz), 7.97 (d, 2H, J¼7.2 Hz), 7.90 (ddd, 2H,
J1¼J2¼7.8 Hz, J3¼1.8 Hz), 7.87 (d, 2H, J¼8.7 Hz), 7.81 (d, 2H,
J¼6.9 Hz), 7.76 (d, 2H, J¼7.8 Hz), 7.37 (dd, 2H, J1¼J2¼6.6 Hz), 6.83 (d,
150.8, 142.5, 141.2, 137.9, 136.8, 133.6, 130.8, 129.6, 128.3, 128.1,
127.9, 126.7, 124.3, 120.3, 117.3; MALDI-MS (%): m/z¼793 (100)
[MþH]þ; HRMS found m/z: 815.2391 [MþNa]þ; C52H28N10Na re-
quires: 815.2396.
2H, J¼7.8 Hz), 4.12 (s, 6H); 13C NMR (CDCl3)
¼163.6, 156.3, 156.0,
d
155.9, 153.7, 149.7, 149.4, 149.2 (2C), 141.0, 139.4, 138.4, 137.7, 136.9,
127.9, 127.7 (2C), 127.6, 123.9, 121.4, 118.7, 118.6, 114.1, 111.1, 53.3;
MALDI-MS (%): m/z¼677 (100) [MþH]þ; HRMS found m/z:
677.2652 [MþH]þ; C44H33N6O2 requires: 677.2665.
4.4.4. Spacer tunable bis-terpyridine 20
White powder, 47% yield from 8a and 2,6-dibromopyridine; 1H
NMR (CDCl3)
d
¼8.83 (s, 4H), 8.76 (ddd, 4H, J1¼0.9 Hz, J2¼1.8 Hz,
J3¼4.8 Hz), 8.69 (dt, 4H, J1¼0.9 Hz, J2¼8.1 Hz), 8.34 (d, 4H, J¼8.4 Hz),
8.08 (d, 4H, J¼8.4 Hz), 8.04 (d, 1H, J¼8.7 Hz), 7.92–7.81 (m, 6H), 7.36
(ddd, 4H, J1¼0.9 Hz, J1¼4.8 Hz, J3¼7.5 Hz); 13C NMR (CDCl3)
4.3.2. Unsymmetric bis-terpyridine 15
White powder, 65% yield from 8a and 8c; 1H NMR (CDCl3)
d
¼156.5, 156.2, 149.9, 149.2, 140.1, 139.2, 137.6, 136.8, 127.9, 127.7,
d
¼8.90 (s, 2H), 8.88 (dd, 2H, J1¼8.1 Hz, J2¼1.2 Hz), 8.83 (s, 2H), 8.76
127.6, 123.8, 121.4, 119.0, 118.9; MALDI-TOF MS: m/z 693.9 (100)
[MþH]þ.
(dd, 2H, J1¼3.6 Hz, J2¼0.9 Hz), 8.70 (d, 2H, J¼8.1 Hz), 8.08–8.01 (m,
6H), 7.92–7.87 (m, 4H), 7.85 (d, 2H, J¼8.1 Hz), 7.78 (dd, 2H,
J1¼7.8 Hz, J2¼1.2 Hz), 7.37 (ddd, 2H, J1¼J2¼7.5 Hz, J3¼1.8 Hz); 13C
4.4.5. Spacer tunable bis-terpyridine 21
NMR (CDCl3)
d
¼157.6, 156.5, 156.2, 154.3, 149.2, 141.9, 140.9, 137.9,
Pale yellow powder, 59% yield from 8a and 2,5-dibromothio-
136.8 (2C), 133.6, 132.7, 130.8, 128.8, 128.4, 128.0 (2C), 127.9, 127.7,
124.4, 123.8, 121.4, 120.3, 118.9, 117.3; MALDI-MS (%): m/z¼667
(100) [MþH]þ; HRMS found m/z: 667.2383 [MþH]þ; C44H27N8 re-
quires: 667.2359.
phene; 1H NMR (CDCl3)
d
¼8.79 (s, 4H), 8.75 (br d, 4H, J¼4.8 Hz),
8.68 (d, 4H, J¼7.8 Hz), 7.97 (d, 4H, J¼8.4 Hz), 7.88 (ddd, 4H,
J1¼0.9 Hz, J2¼1.8 Hz, J3¼7.8 Hz), 7.79 (d, 4H, J¼8.4 Hz), 7.43 (s, 2H),
7.36 (ddd, 4H, J1¼0.9 Hz, J2¼4.8 Hz, J3¼7.5 Hz); 13C NMR (CDCl3)
d
¼156.3, 156.1, 149.5, 149.2, 143.5, 137.6, 136.9, 135.0, 127.9, 126.1,
4.4. General procedure for the two-step in situ synthesis of
spacer tunable bis-terpyridines (17–24)
124.7, 123.8, 121.4, 118.6; MALDI-TOF MS: m/z 698.1 (100) [M]þ.
4.4.6. Spacer tunable bis-terpyridine 22
To a 40 mL DMSO solution of terpyridine 8a (or 8b,c, 200 mg)
was added bis(pinacolato)diboron 9 (1.1 equiv), KOAc (3.0 equiv),
and PdCl2(PPh3)2 (5 mol %). The solution was degassed and stirred
at 80 ꢃC under argon atmosphere for 6 h. The reaction vessel was
recharged in situ with K2CO3 (3.0 equiv), dibromo coupling partner
16 (0.5 equiv), and PdCl2(PPh3)2 (5 mol %). The mixture was then
heated at 80–100 ꢃC until the dibromo compound had disappeared
as monitored by TLC. The catalyst was removed by filtration and
washed thoroughly with CHCl3 after the reaction mixture was
cooled to room temperature. The filtrate was washed with H2O (ca.
70 mL) for five times, and the organic layer was separated, dried
over MgSO4, then filtered, concentrated, and purified by column
chromatography on activated basic Al2O3 (CH2Cl2/hexane¼4:1–9:1,
then pure CH2Cl2) to give the target compounds 17–24.
Pale yellow powder, 48% yield from 8a and 2,5-dibromo-3-
octylthiophene; 1H NMR (CDCl3)
d
¼8.82–8.75 (m, 8H), 8.69 (d, 4H,
J¼7.8 Hz), 8.06–7.76 (m, 11H), 7.65 (d, 2H, J¼8.1 Hz), 7.36 (br t, 4H,
J¼6.3 Hz), 2.75 (t, 2H, J¼7.5 Hz), 1.72 (m, 2H), 1.28 (m, 10H), 0.88 (t,
3H, J¼6.6 Hz); 13C NMR (CDCl3)
¼156.3 (2C), 156.0, 149.7 (2C),
d
149.2, 141.8, 141.0, 140.5, 137.7, 137.3 (2C), 136.9, 135.4, 135.1, 129.6,
127.8, 127.6, 127.5, 126.4, 125.9, 123.8, 121.4, 118.7 (2C), 118.5, 31.9,
31.1, 29.7, 29.4, 29.3, 29.1, 22.6, 14.1; MALDI-TOF MS: m/z 833.5
(100) [MþNa]þ.
Acknowledgements
We thank the Ministry of Education, Culture, Sports, Sciences,
and Technology, Japan for financial support.
4.4.1. Spacer tunable bis-terpyridine 17
References and notes
White powder, 61% yield from 8a and 1,3-dibromobenzene; 1H
NMR (CDCl3)
d
¼8.82 (s, 4H), 8.75 (ddd, 4H, J1¼4.8 Hz, J2¼1.8 Hz,
1. For recent reviews, see: (a) Cooke, M. W.; Hanan, G. S. Chem. Soc. Rev. 2007, 36,
1466; (b) Constable, E. C. Chem. Soc. Rev. 2007, 36, 246; (c) Kurth, D. G.; Higuchi,
M. Soft Matter 2006, 2, 915; (d) Medlycott, E. A.; Hanan, G. S. Chem. Soc. Rev.
2005, 34, 133; (e) Andres, P. R.; Schubert, U. S. Adv. Mater. 2004, 16, 1043.
2. Mortimer, R. J.; Dyer, A. L.; Reynolds, J. R. Displays 2006, 27, 2 and references
therein.
3. For recent research articles, see: (a) Cooke, M. W.; Hanan, G. S.; Loiseau, F.;
Campagna, S.; Watanabe, M.; Tanaka, Y. J. Am. Chem. Soc. 2007, 129, 10479; (b)
Camerel, F.; Ziessel, R.; Donnio, B.; Bourgogne, C.; Guillon, D.; Schmutz, M.;
Iacovita, C.; Bucher, J. P. Angew. Chem., Int. Ed. 2007, 46, 2659; (c) Song, B.;
J3¼0.9 Hz), 8.69 (d, 4H, J¼7.5 Hz), 8.05 (d, 4H, J¼8.7 Hz), 7.98 (s, 1H),
7.89 (dt, 4H, J1¼7.5 Hz, J2¼1.8 Hz), 7.83 (d, 4H, J¼8.7 Hz), 7.71 (dd,
2H, J1¼7.5 Hz, J2¼1.2 Hz), 7.60 (t, 1H, J¼7.2 Hz), 7.37 (ddd, 4H,
J1¼7.5 Hz, J2¼6.3 Hz, J3¼0.9 Hz); 13C NMR (CDCl3)
¼156.3, 156.0,
d
149.7, 149.1, 141.7, 141.1, 137.5, 136.8, 129.4, 127.8, 127.7, 126.5, 126.0,
123.8, 121.4, 118.7; MALDI-MS (%): m/z¼693 (100) [MþH]þ; HRMS
found m/z: 715.2563 [MþNa]þ; C48H32N6Na requires: 715.2563.

9116
F.-S. Han et al. / Tetrahedron 64 (2008) 9108–9116
Wang, G.; Tan, M.; Yuan, J. J. Am. Chem. Soc. 2006, 128, 13442; (d) Carlson, C. N.;
Kuehl, C. J.; Da-Re, R. E.; Veauthier, J. M.; Schelter, E. J.; Milligan, A. E.; Scott, B.
L.; Bauer, E. D.; Thompson, J. D.; Morris, D. E.; John, K. D. J. Am. Chem. Soc. 2006,
11. Han, F. S.; Higuchi, M.; Kurth, D. G. Org. Lett. 2007, 9, 559 and references therein.
12. Okamura, R.; Wada, T.; Aikawa, K.; Nagata, T.; Tanaka, K. Inorg. Chem. 2004, 43,
7210.
´
128, 7230; (e) Laine, P. P.; Bedioui, F.; Loiseau, F.; Chiorboli, C.; Campagna, S.
13. (a) Ishiyama, T.; Itoh, Y.; Kitano, T.; Miyaura, N. Tetrahedron Lett. 1997, 38, 3447;
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the weak signals caused by their somewhat poor solubility. However, mass
spectrometry revealed characteristic peaks of m/z¼717.21 (Mþ), 779.9 (Mþ),
and 900.6 (Mþ) corresponding to 12, 23, and 24, respectively.
17. Fang, Y.; Taylor, N. J.; Laverdie`re, F.; Hanan, G. S.; Loiseau, F.; Nastasi, F.; Cam-
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18. The quantum yields (Ff) were evaluated according to the method described in
the literature using compound 5 in dichloromethane (Ff¼0.13, see Ref. 5a) as
standard, see: Brooks, J.; Babayan, Y.; Lamansky, S.; Djurovich, P. I.; Tsyba, I.;
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19. The Lippert’s function
D
f is used to evaluate the solvent polarity without
f of cyclohexane, CH2Cl2, CH3CN,
considering the protic nature of MeOH. The
D
and MeOH are 0.00, 0.21, 0.305, and 0.309, respectively. These parameters are
taken from Ref. 4d and following reference: Ababneh, A. M.; Large, C. C.;
Georghiou, S. J. Appl. Sci. Res. 2007, 3, 1288.
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1009 and references therein.
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