Synthesis of oligophenylenes containing hydroxyl group and their solvatochromic behavior

Article abstract of DOI:10.1016/j.tet.2009.02.073

Oligo(p-phenylene)s containing hydroxyl group(s), namely, OPP(n)-OH (n=3, 4, and 5; n denotes the number of benzene rings), HO-OPP(3)-OH, and 1,3,5-tri(4-biphenyl)phenol TBP-OH were synthesized in high yields by the Suzuki coupling reaction. Absorption ma

Full text of DOI:10.1016/j.tet.2009.02.073

Tetrahedron 65 (2009) 3645–3652
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis of oligophenylenes containing hydroxyl group
and their solvatochromic behavior
*
Isao Yamaguchi , Kazuyuki Goto, Moriyuki Sato
Department of Material Science, Faculty of Science and Engineering, Shimane University, 1060 Nishikawatsu, Matsue 690-8504, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Oligo(p-phenylene)s containing hydroxyl group(s), namely, OPP(n)-OH (n¼3, 4, and 5; n denotes the
number of benzene rings), HO-OPP(3)-OH, and 1,3,5-tri(4-biphenyl)phenol TBP-OH were synthesized in
high yields by the Suzuki coupling reaction. Absorption maxima (lmaxs) of OPP(n)-OHs shifted pro-
Received 29 January 2009
Received in revised form 26 February 2009
Accepted 27 February 2009
Available online 5 March 2009
gressively toward long wavelengths due to the expansion of the p-conjugation system with an increase
in the number of benzene rings. Deprotonation of the OH group of OPP(n)-OHs by treatment with NaH
caused a bathochromic shift of lmax. The bathochromic shift of the deprotonated species increased with
the donor numbers (DNs) of the solvents. The emission peak positions of OPP(n)-OH and OPP(n)-ONa
depended on the DN of the solvents; that is, the emission color could be tuned by changing the solvent.
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Hydroxyphenylenes
Phenolate
Donor number
Photoluminescence
Solvatochromism
1. Introduction
OPPs, only a few studies have been conducted on the synthesis of
mono-OH-substituted OPPs OPP(n)-OHs (n denotes the number of
Well-defined conjugated oligomers have attracted considerable
attention due to their nondefected structures for the fabrication of
electronic and optical devices.1 They can also be used as model
compounds for understanding the chemical and physical proper-
ties of related polymeric materials and for investigating structure–
property correlation.
benzene rings).15 Therefore, we conducted a study to synthesize
OPP(n)-OHs and elucidate their chemical properties.
OPP(n)-OH will exhibit unique optical properties after the
deprotonation of the OH group. This is because the solvation be-
havior of deprotonated products, i.e., OPP(n)-OL, is quite different
from that of OPP(n)-OHs. In many cases, the solvation of ionic ar-
omatic compounds containing phenoxy groups significantly affects
their optical properties. For example, Reichardt’s betaine (1)16 and
Brooker’s merocyanines (2)17 exhibit solvatochromism, which de-
pends on solvent polarity.
Oligo(p-phenylene)s (OPPs) are an important class of
p-conju-
gated oligomers because they are useful as luminophores for light-
emitting materials,2 as semiconductors for field-effect transistors,3
as rigid-rod cores for liquid crystalline materials,4 and as amphi-
philic materials for biological applications.5 Recently, OPPs have
been converted into planarized ladder-type materials,6 relatively
large polycyclic aromatic hydrocarbons,7 novel macrocycles,8 and
star-shaped compounds.9
Systematic investigation of OPPs containing various sub-
stituents such as alkyl,10 alkoxy,10 amine,2c,11 carboxylic ester,12
cyano,13 and nitro11a,14 groups has revealed that the chemical and
physical properties of substituted OPPs depend on the type of
substituents and their bonding positions in the OPPs. The sub-
stituents on the OPPs bring about improved solubility in organic
solvents, and the reactivity of the substituents enables the con-
version of OPPs into functional materials. In the case of substituted
Ph
N+
Ph
Ph
Ph
O-
N+
Me
O-
Ph
1
2
It has been reported that OPP(2)-OH and OPP(3)-OH cause
a bathochromic shift of absorption by the deprotonation.18 How-
ever, the absorption of OPP(n)-OHs and OPP(n)-OLs (nꢀ4) and
fluorescence of OPP(n)-OHs and OPP(n)-OLs (nꢀ3) have not yet
been elucidated. An investigation of the chemical properties of
OPP(n)-OHs (nꢀ3) and their deprotonated products would help us
to gain a better understanding of the optical properties of OPPs and
develop new functional materials.
OPPs with hydroxyl groups located at both ends, i.e., HO-
OPP(n)-OHs, can be used in the synthesis of functional polymers.
For example, poly(aryl ether)s synthesized by polymerization using
* Corresponding author. Tel.: þ81 825 326421.
E-mail address: iyamaguchi@riko.shimane-u.ac.jp (I. Yamaguchi).
0040-4020/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2009.02.073

3646
I. Yamaguchi et al. / Tetrahedron 65 (2009) 3645–3652
(ii)
(i)
(a)
Br
Br
OMe
OMe
OH
OPP(3)-OMe, 94%
OPP(3)-OH, 92%
(i)
(iv)
(iii)
(v)
(b)
(c)
(d)
OH
Br
O
O
OH
O
O
Br-OPP(2)-OTHP, 42%
OPP(4)-OTHP, 88%
OPP(4)-OH, 94%
(vi)
(i)
Br
Br
Br
Br
OMe
Br
OH
OH
Br-OPP(3)-OMe, 80%
Br-OPP(3)-OH, 74%
OPP(5)-OH, 78%
(v)
(iv)
(vi)
MeO
OTHP
MeO
OH
HO
OH
O
O
MeO-OPP(3)-OTHP, 85%
MeO-OPP(3)-OH, 96%
HO-OPP(3)-OH, 100%
Scheme 1. Synthesis approaches for hydroxyoligo(p-phenylene)s OPP(n)-OH (n¼3, 4, and 5) and dihydroxy-p-terphenyl HO-OPP(3)-OH. (i) 4-C6H5C6H4B(OH)2, 1.5 mol % of
Pd(PPh3)4, K2CO3 (aq), THF, reflux, 48 h; (ii) BBr3, CH2Cl2, rt, 30 h; (iii) DHP, CSA, CH2Cl2, rt, 18 h, in dark; (iv) HCl, 1,4-dioxane, 100 ꢁC, 12 h; (v) 4-MeOC6H5B(OH)2, 1.5 mol % of
Pd(PPh3)4, K2CO3(aq), THF, reflux, 48 h; (vi) C5H5N$HCl, 180 ꢁC, 12 h.
HO-OPP(4)-OH exhibit photoluminescence with high quantum
yields because they contain p-quaterphenyl.19 However, the syn-
thesis of HO-OPP(n)-OH (nꢀ3) often requires severe reaction
conditions. For example, HO-OPP(3)-OH is synthesized by the hy-
drolysis of terphenyl-4,40-disulfonic acid at 330 ꢁC.19d The Suzuki
coupling reaction is a versatile method for the synthesis of aromatic
oligomeric compounds containing functional groups under mild
reaction conditions.20 In this study, OPP(n)-OHs and HO-OPP(3)-
OH were synthesized by the Suzuki coupling reaction of O-alky-
lated 4-bromophenol derivatives with aromatic boronic acid and
the hydrolysis of the O-alkyl group. It has been reported that the
substituents on the phenoxy ring of 2 considerably affect its optical
properties.17d Therefore, in order to elucidate the effect of the
substituents on the phenoxy ring of OPP(n)-OH on the optical
properties, a branched oligophenylene 1,3,5-tri(4-biphenyl)phenol
TBP-OH was synthesized by the Suzuki coupling reaction using
1,3,5-tribromobenzene as a starting material.
that the Suzuki coupling reaction can be carried out on substrates
containing the OH group.20 In this study, O-alkylated phenols were
used as substrates because O-alkylated compounds have higher
solubility than naked phenols, and therefore, they can be purified
easily. Methods for synthesizing hydroxyoligo(p-oligophenylene)s
OPP(n)-OHs (n¼3, 4, and 5) and dihydroxy-p-terphenyl HO-
OPP(3)-OH are shown in Scheme 1.
The reaction of 4-biphenylboronic acid with 4-bromoanisole
and 4-bromo-40-tetrahydropyranyloxybiphenyl Br-OPP(2)-OTHP
(THP¼tetrahydropyranyl) afforded O-alkylated oligo(p-phenyl-
ene)s OPP(3)-OMe and OPP(4)-OTHP in 94% and 88% yields, re-
spectively. The THP-group-protected compound Br-OPP(2)-OTHP
was synthesized by the reaction between 4-bromobiphenyl-40-ol
and 3,4-dihydro-2H-pyran (DHP). The deprotection of the O-methyl
and O-THP groups of OPP(3)-OMe and OPP(4)-OTHP yielded the
corresponding OPP(n)-OHs (n¼3 and 4) in 92% and 94% yields,
respectively. The method involving the Suzuki coupling reaction
followed by hydrolysis was not used for the synthesis of OPP(5)-
OH. This is because the solubility of OPP(5)-OMe in organic sol-
vents was low, and therefore, it could not be deprotected to
produce OPP(5)-OH. Instead of the above method, the reaction
between 4-bromo-400-hydroxy[1,10:40,100]terphenyl Br-OPP(3)-OH
and 4-biphenylboronic acid was used for the synthesis of OPP(5)-
OH. The yield of OPP(5)-OH (78%) was low apparently because of
the use of the unprotected substrate Br-OPP(3)-OH. The in-
termediate compound Br-OPP(3)-OH was synthesized by the 1:1
Suzuki coupling reaction of 4,40-bromobiphenyl with 4-methoxy-
phenylboronic acid and the hydrolysis of the O-methyl group. The
use of an excess amount of 4,40-bromobiphenyl prevented the 2:1
side reaction with 4-methoxyphenylboronic acid and yielded an
In this study, we report the synthesis of linear oligo(p-phenyl-
ene)s OPP(n)-OHs (n¼3, 4, and 5) and HO-OPP(3)-OH containing
OH group(s) and a branched oligophenylene TBP-OH and describe
their solvatochromic behaviors. We also compare the chemical
properties of OPP(n)-OHs with those of TBP-OH.
2. Results and discussion
2.1. Synthesis
The oligophenylenes were synthesized by the Suzuki coupling
reaction using O-alkylated phenol derivatives as substrates and the
hydrolysis of the O-alkyl group of the coupling products. It is known
OMe
OMe
OH
Br
Br
(ii)
(i)
Br
TBP-OMe, 77%
TBP-OH, 91%
Scheme 2. Synthesis of 1,3,5-tri(4-biphenyl)phenol. (i) 4-C6H5C6H4B(OH)2, 1.5 mol % of Pd(PPh3)4, K2CO3(aq), THF, reflux, 48 h; (ii) BBr3, CH2Cl2, rt, 30 h.

I. Yamaguchi et al. / Tetrahedron 65 (2009) 3645–3652
3647
solvents but completely soluble in polar organic solvents such as
1,4-dioxane, N,N-dimethylformamide (DMF), and dimethyl sulfox-
ide (DMSO) because they contained OH group(s). Although the
solubility of OPP(5)-OH in polar organic solvents was low, it was
possible to perform UV–vis and photoluminescence measurements
on it.
The melting points of OPP(n)-OHs (n¼3 and 4) determined by
DSC measurements were 277 ꢁC and 358 ꢁC, respectively; these
values were higher than those of OPP(n)s reported earlier (212 ꢁC,
n¼3 and 312 ꢁC, n¼4),21 apparently due to intermolecular hydrogen
bonding. The melting points of OPP(n)-ORs (233 ꢁC, n¼3; R¼Me
and 221 ꢁC, n¼4; R¼THP) were lower than those of OPP(n)-OHs
(n¼3 and 4); this result supports the above-mentioned assumption.
The melting points of TBP-OH and TBP-OMe were 216 ꢁC and
113 ꢁC, respectively.
2.2. IR spectra
Figure 1 shows IR spectra of OPP(n)-OHs (n¼3, 4, and 5) and
TBP-OH. The main features of the IR spectra of OPP(n)-OHs are
identical: the absorption peak at 3428 cmꢂ1 is due to O–H
stretching vibrations; the strong peak at 1484 cmꢂ1 is due to phenyl
ring vibrations; and the bands at approximately 820 cmꢂ1 and
760 cmꢂ1 are due to the out-of-plane C–H bending of p-phenylene
and terminal phenyl rings, respectively. These absorption band
positions are similar to those of poly(p-phenylene).22 The in-
tensities of absorptions due to the out-of-plane C–H bending of the
p-phenylene and terminal phenyl rings were used to estimate the
degree of polymerization of poly(p-phenylene).22 The absorption
ratios I820/I760 of OPP(n)-OHs (n¼3, 4, and 5) were 1.4, 2.3, and 3.2,
respectively; they were largely consistent with the number of
p-phenylene rings in these compounds.
In contrast to the broad absorption due to the hydrogen bonding
OH group of OPP(n)-OHs, the absorption due to the O–H stretching
vibration of TBP-OH is observed as a sharp peak at 3524 cmꢂ1. This
observation is attributed to the inhibition of intermolecular hy-
drogen bonding caused by the bulky biphenyl groups at the 2,6-
positions of TBP-OH.
Figure 1. IR spectra of OPP(n)-OH (n¼3, 4, and 5) and TBP-OH.
expected product as a precipitate from the reaction mixture.
Dihydroxy-p-terphenyl HO-OPP(3)-OH was obtained via the two-
step deprotection of MeO-OPP(3)-OTHP, as shown in Scheme 1d.
MeO-OPP(3)-OH could not be deprotected by using BBr3 because of
the low solubility of the substrate in CH2Cl2; hence, it was depro-
tected by using pyridinium hydrochloride.
2.3. 1H NMR data
As shown in Scheme 2, TBP-OH was obtained by the 1:3 Suzuki
coupling reaction of 1,3,5-tribromoanisol with 4-biphenylboronic
acid and the hydrolysis of the methyl group.
The 1H NMR chemical shifts of OPP(n)-OHs (n¼3, 4, and 5) and
their deprotonated species are summarized in Table 1. Deprotona-
tion of the OH group(s) of OPP(n)-OHs and HO-OPP(3)-OH was
carried out by treating them with an excess amount of NaH in
DMSO-d6. The disappearance of the OH signal in the 1H NMR
spectra of solutions of OPP(n)-OHs and NaH indicated that sodium
phenoxidation proceeded quantitatively. The signals due to par-
ticular protons of OPP(n)-ONa shifted to higher magnetic fields as
compared to those of OPP(n)-OH. The changes in the chemical shift
The structures of the newly synthesized compounds OPP(n)-
OHs, HO-OPP(3)-OH, and TBP-OH were determined by 1H and 13
C
NMR spectroscopy and elemental analysis. p-Terphenyl and
p-quaterphenyl were highly soluble in non-polar organic solvents
such as cyclohexane and toluene. In contrast, OPP(n)-OHs (n¼3 and
4) and HO-OPP(3)-OH were sparingly soluble in non-polar organic
Table 1
1H NMR chemical shifts of OPP(n)-OH and HO-OPP(3)-OH as well as their deprotonated products in DMSO-d6
Chemical shift (ppm)
H2
H3
H20
H30
H200
H300
H400
H2%
H3%
H4%
H2&
H3&
H4&
OH
a
a
a
OPP(3)-OH
OPP(3)-ONa
OPP(4)-OH
OPP(4)-ONa
OPP(5)-OH
OPP(5)-ONa
HO-OPP(3)-OH
NaO-OPP(3)-ONa
6.85
6.22
6.86
6.17
6.87
6.20
6.84
6.68
7.54
7.18
7.55
7.18
7.56
7.19
7.51
7.38
7.47
7.42
7.79
7.34
7.29
d
d
d
d
d
d
d
d
d
9.57
d
7.51
7.69
7.52
7.70
7.53
7.60
7.52
7.56
7.73
7.62
7.73
7.64
7.60
7.52
7.64
7.77
d
d
d
d
d
7.81
7.48
7.38
7.37
d
d
d
9.57
d
7.71
7.73
d
7.75
7.47
d
b
d
d
b
b
b
b
d
7.49
7.48
d
7.38
7.37
d
9.58
d
7.73
7.51
7.38
7.74
6.84
6.68
d
d
d
d
d
d
d
d
7.83
d
d
d
9.53
d
d
d
d
d
d
a
Observed in the range of
Observed in the range of
d
d
7.65–7.71.
7.78–7.83.
b

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I. Yamaguchi et al. / Tetrahedron 65 (2009) 3645–3652
0.6
0.5
0.4
0.3
0.2
0.1
0
400
OPP(4)-OH
OPP(5)-OH
OPP(4)-O-
OPP(5)-O-
350
300
OPP(3)-O-
400
Wavelength/ nm
OPP(3)-OH
300
350
450
500
550
5
10
15
Donor number
20
25
30
Figure 2. UV–vis spectra of OPP(n)-OH (n¼3, 4, and 5) (bold curves) and their de-
protonated species (thin curves) in DMSO (1.0ꢃ10ꢂ5 M).
Figure 3. Dependence of lmax of OPP(n)-OH (n¼3 (ꢄ), 4 (:), and 5 (-); dotted line)
and their deprotonated species (solid line) on the DNs of solvents.
Dd increase when the distance of the protons from the ONa group
decreases; that is, Dd is the largest in the case of protons (H3) ad-
jacent to the ONa group. These observations can be attributed to the
electron-donating effect of the ONa group. In contrast, chemical
shifts due to the protons of the terminal phenyl ring are almost
constant after the deprotonation. These data indicated the possi-
bility of the occurrence of a shift of charge from the phenolate
group to the adjacent rings in the deprotonated species. Such
a charge shift in OPP(n)-ONa may significantly affect its optical
properties. In the case of HO-OPP(3)-OH, 1H NMR peak shifts due to
deprotonation were observed. However, Dd of HO-OPP(3)-OH after
deprotonation was smaller than Dd’s of OPP(n)-OHs. This is
apparently because a charge accepting site is limited in the central
phenylene ring.
4-hydroxybiphenyl in a phosphate buffer (pH¼6.76) shifts to
a longer wavelength by 29 nm due to deprotonation.18 To prove
that these observations were due to the deprotonation of the OH
group after treatment with NaH, we confirmed that there was no
change in the absorption spectra of OPP(3)-OMe and OPP(4)-OTHP
after the addition of NaH. The possibility that aggregation con-
tributes to the solvatochromic behavior through the formation of
dimers or other more complex structures can be discarded because
the solutions always obey the Lambert–Beer law over several or-
ders of concentration. In order to observe the bathochromic shift of
lmax, the deprotonation of OPP(n)-OHs was carried out by using
LiOH and KOH instead of NaH. The degree of bathochromic shift
was independent of the type of alkaline metal.
Bathochromic shift attributable to deprotonation depends on
the donor number (DN) of the solvents. As shown in Figure 3, the
lmax values of OPP(3)-OH and OPP(3)-ONa shifted to longer
wavelengths as the DNs of the solvents increased. In contrast to
the small bathochromic shift of OPP(3)-OH with an increase in the
DNs of the solvents, the lmax values of the deprotonated species
move from 292 nm in CH2Cl2 (DN¼0) to 398 nm in DMSO
(DN¼29.8) through to a value of 355 nm in THF (DN¼20.0). The
large Dl value can be attributed to the fact that solvents with
a high DN solvate effectively with Naþ to stabilize the deproto-
nated species in the solutions. Similar solvatochromic behavior
was observed in the case of OPP(n)-OHs (n¼4 and 5) and OPP(n)-
ONas (n¼4 and 5), as shown in Figure 3. In relation to the linear
relationship shown in Figure 3, the absorption positions of
OPP(n)-OHs (n¼3 and 4) and OPP(n)-ONas (n¼3 and 4) in
methanol deviated from the plot. This is consistent with the fact
that solutions of the phenolate ion in hydrogen bonding solvents
cause hypsochromic shift.18a
2.4. UV–vis absorption and solvatochromism
Figure 2 shows the UV–vis spectra of OPP(n)-OHs (n¼3, 4, and
5) in DMSO. The optical data are summarized in Table 2. The
absorption maxima (lmaxs) of OPP(n)-OHs shifted progressively
toward longer wavelengths due to the expansion of the
p-
conjugation system as the number of benzene rings increased. The
lmax values were somewhat higher than those of OPP(n)s (n¼3, 4,
and 5) reported earlier, which is comparable to the fact that
OPP(n)s having an electron-donating alkyl group at the 4-position
exhibit lmax at a longer wavelength than that of the intact
OPP(n)s.10b
The treatment of the DMSO solutions of OPP(n)-OHs (n¼3, 4,
and 5) and HO-OPP(3)-OH with NaH causes bathochromic shift of
lmax by approximately 80 nm. The formation of OPP(n)-ONa and
NaO-OPP(n)-ONa was mainly responsible for the shift of lmax
toward a longer wavelength. It has been reported that lmax of
Table 2
Absorption of OPP(n)-OH, HO-OPP(3)-OH, and TBP-OH as well as their deprotonated productsa
Solvent
DNb
OPP(n)-OH (nm)
OPP(n)-ONa (nm)
HO-OPP(3)-OH (nm)
NaO-OPP(3)-ONa (nm)
OBP-OH (nm)
OBP-ONa (nm)
n¼3
n¼4
n¼5
n¼3
n¼4
n¼5
c
c
c
c
Dichloromethane
1,4-Dioxane
Methanol
THF
DMF
DMSO
0
288
291
289
291
296
297
303
305
303
307
310
314
292
330
313
348
380
383
306
348
324
355
397
398
292
294
293
295
299
302
306
327
321
341
376
377
14.8
19.0
20.0
29.6
29.8
316
298
276
281
283
283
284
264, 356
269, 341
266, 369
400
c
c
315
321
324
357
404
404
402
a
Concentration of solution was 1.0ꢃ10ꢂ5 M.
DN¼donor number.
b
c
Not measured due to low solubility.

I. Yamaguchi et al. / Tetrahedron 65 (2009) 3645–3652
3649
0.4
0.3
0.2
0.1
0
600
t = 0 min
10 min
550
500
450
400
350
300
20 min
30 min
40 min
50 min
60 min
70 min
250
300
350
400
Wavelength/ nm
0
5
10
15
Donor number
20
25
30
Figure 4. Changes of UV–vis spectra of methanol solution of OPP(3)-OH (1ꢃ10ꢂ5 M) in
the presence of aqueous solution of NaOH (0.5ꢃ10ꢂ5 M) with time upon standing
under nitrogen at 30 ꢁC.
Figure 5. Dependence of PL peak position of OPP(n)-OH (n¼3 (ꢄ) and 4 (:); dotted
line) and their deprotonated species (solid line) on the DNs of solvents.
The bathochromic shift of OPP(n)-OHs caused by deprotonation
was significantly affected by the concentration of the base. The
absorption of the methanol solutions of OPP(3)-OH in the presence
of NaOH (aq), which was less than the equimolar amount of
OPP(3)-OH, varied with the time for which they were left to stand
under nitrogen; that is, the absorption due to OPP(3)-ONa de-
creased and that due to OPP(3)-OH increased simultaneously, as
shown in Figure 4. In contrast, the UV–vis spectra of the methanol
solutions of OPP(3)-OH in the presence of an excess amount of the
base remained almost unchanged over time. OPP(n)-OHs (n¼4 and
5) showed similar absorption behavior. These results suggested
that intact OPP(n)-OHs and their deprotonated species in solution
were in equilibrium.
Bathochromic shift caused by deprotonation was observed in
the case of HO-OPP(3)-OH. However, it was smaller than that of
OPP(n)-ONas (n¼3, 4, and 5). In the case of OPP(n)-ONas, the
intramolecular charge shift from the phenoxy groups to the adja-
cent rings appeared to contribute to the bathochromic shift. It may
be assumed that the smaller bathochromic shift of NaO-OPP(3)-
ONa was caused by a slight shift of charge from the phenolate
groups at both ends to the central phenylene ring. This assumption
is in good agreement with the result that the 1H NMR peak shifts of
HO-OPP(3)-OH produced by deprotonation are smaller than those
of OPP(n)-OHs.
phenylene unit in
p-conjugated compounds with a 1,3,5-triphe-
nylbenzene core are twisted by approximately 45ꢁ.23 The twisting
between the adjacent phenylene rings of OPP(n) (3ꢅnꢅ8) is esti-
mated to be approximately 10–37ꢁ.23 As in the case of OPP(n)-
ONas, lmax of the deprotonated species of TBP-OH shifted to
a longer wavelength as the DNs of the solvents increased.
2.5. Photoluminescence
It has been reported that OPPs exhibit photoluminescence (PL)
with
a
high quantum yield.10b,24 Hydroxyoligo(p-phenylene)s
OPP(n)-OHs (n¼3, 4, and 5) and their deprotonated species
OPP(n)-ONas (n¼3, 4, and 5) are photoluminescent in solution. The
PL data are summarized in Table 3. The PL peak positions of OPP(n)-
OHs (n¼3, 4, and 5) were observed at longer wavelengths than
those of OPP(n)s (n¼3, 4, and 5) in solution.10b,24 These observa-
tions are comparable to the fact that OPPs having an electron-do-
nating alkoxy group OPP(n)-OR exhibit PL peaks at longer
wavelengths than OPP(n).10b The quantum yields of the PLs of the
1,4-dioxane solutions of OPP(n)-OHs (n¼3, 4, and 5) were 59, 42,
and 59%, respectively; these values were lower than those of
OPP(n)s (n¼3, 4, and 5) reported earlier.24
The emission peak positions of OPP(n)-OHs and OPP(n)-ONas
depended on the DNs of the solvents; that is, the emission color can
be tuned by changing the solvent. For example, OPP(4)-ONa
exhibited purple, blue, green, and orange emissions after it was
irradiated with UV light in CH2Cl2 (DN¼0), 1,4-dioxane (DN¼14.8),
THF (DN¼20.0), and DMSO (DN¼29.8), respectively, as shown in
Figure 5. Figure 6 shows the dependence of the emission peak
positions of OPP(n)-OHs (n¼3 and 4) on the DNs of the solvents.
Thus, by alternating solvents such as CH2Cl2, which have a small DN
The solutions of TBP-OH exhibited lmax at approximately
280 nm, irrespective of the type of solvent. The wavelength at
which lmax was observed was shorter than that of OPP(3)-OH, al-
though TBP-OH consisted of seven benzene rings. A possible reason
for these observations is that the degree of twisting between the
three biphenyl substituents and the central phenylene unit is larger
than that between the adjacent benzene rings in OPP(n)-OHs. It
has been reported that the three phenyl substituents on the central
Table 3
Photoluminescence data of OPP(n)-OH, HO-OPP(3)-OH, and TBP-OH as well as their deprotonated productsa
Solvent
DNb
OPP(n)-OH (nm)
OPP(n)-ONa (nm)
HO-OPP(3)-OH (nm)
NaO-OPP(3)-ONa (nm)
OBP-OH (nm)
OBP-ONa (nm)
n¼3
n¼4
n¼5
n¼3
n¼4
n¼5
c
c
c
c
c
Dichloromethane
1,4-Dioxane
Methanol
THF
DMF
DMSO
0
357
358
371
364
378
384
380
380
397
386
405
408
357
419
475
456
512
514
377
465
524
495
562
563
344, 357
346, 359
348, 361
347, 361
351, 366
355, 370
14.8
19.0
20.0
29.6
29.8
397
483
410
411
407
435
439
390
393
393
402, 521
404, 520
504
504
503
527
529
c
c
399
409
414
509
d
d
a
Concentration of solution was 1.0ꢃ10ꢂ5 M.
DN¼donor number.
b
c
Not measured due to low solubility.
No photoluminescence.
d

3650
I. Yamaguchi et al. / Tetrahedron 65 (2009) 3645–3652
CH2Cl2
DN = 0
1,4-dioxane
DN = 14.8
THF
DMSO
originate from OPP(3)-OH and OPP(3)-ONa, respectively. The PL
DN = 20.0 DN = 29.8
spectra of the solutions of OPP(3)-OH in the presence of a less
equimolar amount of NaOH changed with the time for which the
solutions were left to stand under nitrogen; that is, absorption due
to OPP(3)-ONa at 475 nm decreased and that due to OPP(3)-OH at
371 nm increased simultaneously. On the other hand, the PL spectra
of the solution of OPP(3)-OH in the presence of an excess amount of
NaOH did not change over time. These observations are consistent
with the UV–vis absorption behavior that depends on the con-
centration of the base, as mentioned above.
Figure 6. Photographs of OPP(4)-ONa when it was irradiated with UV light in CH2Cl2
(DN¼0), 1,4-dioxane (DN¼14.8), THF (DN¼20.0), and DMSO (DN¼29.8).
As mentioned earlier, an increase in the DNs of the solvents
caused the large bathochromic shift of the PL peaks of OPP(n)-ONas
(n¼3, 4, and 5). However, the DNs of the solvents had a small effect
on the peak positions of TBP-OH and TBP-ONa. Their PL peaks
appeared at approximately 390 nm and 500 nm when they were
dissolved in solvents with moderate DNs, such as 1,4-dioxane
(DN¼14.8) and THF (DN¼20), respectively. The PL peak position of
TBP-ONa in 1,4-dioxane was comparable to that of OPP(4)-ONa in
DMSO (DN¼29.8). These observations can be attributed to the
steric effect of the biphenyl substituents at the 2,6-positions that
can stabilize the phenolate anion in the S1-excited state even in
solvents with moderate DN values. It was reported that OPP(n)
adopted more planar configurations in the S1-excited than in the
S0-grand state.25 Hence, in the S1-excited state, the three biphenyl
substituents of TBP-OH could adopt a more planar configuration
with the phenylene core. Because of this configuration, the wave-
length at which the PL peak of TBP-OH appeared at longer than the
wavelengths at which the PL peaks of OPP(n)-OHs appeared;
however, the solutions of TBP-OH showed lmax at shorter wave-
lengths than those of OPP(n)-OHs. The quantum yields of the PLs of
the 1,4-dioxane solutions of TBP-OMe and TBP-OH are 15 and 21%,
respectively.
value, and those such as DMF and DMSO, which have large DN
values, it is observed that the emission peak positions of OPP(n)-
OHs (n¼3 and 4) shifts only by approximately 30 nm. However,
a significantly large shift in the emission peaks of OPP(n)-ONas
(n¼3 and 4) occurred as the DNs of the solvents increased. These
observations are comparable to the results that lmax of OPP(n)-ONa
in solution shifts to a longer wavelength than that of OPP(n)-OH
with an increase in the DNs of the solvents. The remarkable sol-
vatochromic shift of the PL peak position of OPP(n)-ONa appeared
to be due to the charge shift from the phenolate group to the ad-
jacent rings. In addition to the charge shift effect, a large amount of
stabilization energy produced by the solvation of OPP(n)-ONa may
contribute to the solvatochromic red shift as the DNs of the solvents
increase. In the case of anthrylphenoxide anions, the sol-
vatochromic red shift of the PL peak position occurred as the di-
electric constant of the solvents increased.25 In relation to the linear
relationship shown in Figure 5, the emission peak positions of
OPP(n)-OHs (n¼3 and 4) and OPP(n)-ONas (n¼3 and 4) in meth-
anol deviated from the plot. This appear to be due to the assump-
tion that OPP(n)-OHs (n¼3 and 4) and OPP(n)-ONas (n¼3 and 4)
form a hydrogen bond with methanol. It has been reported that
hydroxyarenes such as naphthol cause bathochromic shift of the
fluorescence peak when they form a hydrogen-bonded compex.26
The PL intensities of OPP(n)-ONa decreased as the chain length (n)
increased. These phenomena were significant in the case of organic
solvents that had high DN values, such as DMF and DMSO. For
example, OPP(5)-ONa did not exhibit PL in the solvents. Reasons for
quenching of the PL of OPP(5)-ONa in DMF and DMSO are not
entirely clear.
3. Conclusions
Oligophenylenes containing hydroxyl group(s), namely, OPP(n)-
OHs, HO-OPP(3)-OH, and TBP-OH, were synthesized by the Suzuki
coupling reaction. The OH group contributed to improve the solu-
bility and melting points of OPP(n)-OHs. The treatment of OPP(n)-
OHs with a base produced deprotonated species OPP(n)-ONas,
whose absorption and PL peak positions in solution shifted toward
longer wavelengths with an increase in the DNs of the solvents. The
emission colors of the solutions of OPP(n)-ONas could be tuned by
changing the solvent. The optical properties of the oligophenylenes
containing OH group(s) were significantly affected by the ar-
rangement of their phenylene rings. From the results of this study,
it can be concluded that new luminescent materials can be de-
veloped on the basis of the remarkable solvatochromic behavior of
OPP(n)-ONas.
The concentration of the base significantly affected on the
emission behavior of the solutions of OPP(n)-OHs (n¼3, 4, and 5).
Figure 7 shows the PL spectra of the methanol solutions of OPP(3)-
OH containing different amounts of NaOH. It is observed that the
peak at 371 nm decreases and a new emission peak at 475 nm
appears as the concentration of the base increases. This result
confirms the fact that the emission peaks at 371 nm and 475 nm
(a)
4. Experimental section
4.1. General
Solvents were dried, distilled, and stored under nitrogen. Other
reagents were purchased and used without further purification.
Reactions were carried out with standard Schlenk techniques under
nitrogen.
IR and NMR spectra were recorded on a JASCO FT/IR-660 PLUS
spectrophotometer and a JEOL AL-400 spectrometer, respectively.
Elemental analysis was performed on a Yanagimoto MT-5 CHN
corder. UV–vis and PL spectra were obtained by a JASCO V-560
(b)
(c)
(d)
(e)
350
400 450
Wavelength/ nm
500
550
spectrometer and
a JASCO FP-6200 spectrofluorometer, re-
spectively. Quantum yields were calculated by using a diluted
ethanol solution of 7-dimethylamino-4-methylcoumarin as the
standard.
Figure 7. PL spectra of methanol solutions of OPP(3)-OH (1ꢃ10ꢂ8 M) in the presence
of various amounts of NaOH. (a); 0 M, (b); 0.5ꢃ10ꢂ8 M, (c); 1ꢃ10ꢂ8 M, (d); 2ꢃ10ꢂ8 M,
(e); 3ꢃ10ꢂ8 M.

I. Yamaguchi et al. / Tetrahedron 65 (2009) 3645–3652
3651
4.2. Synthesis of OPP(3)-OMe
solution was stirred at 100 ꢁC for 12 h, the solution was neutralized
with NaOH (aq). The solvents were removed under vacuum and the
resulting solid was washed with water. OPP(4)-OH was collected
by filtration, dried under vacuum, and obtained as a white powder
4-Bromoanisole (1.14 g, 6.1 mmol) and 4-biphenylboronic acid
(1.10 g, 5.5 mmol) were dissolved in 40 mL of dry THF under N2. To
the solution were added K2CO3 (aq) (2.0 M, 20 mL; N2 bubbled
before use), Pd(PPh3)4 (0.10 g, 0.90 mmol), and several drops of the
phase transfer catalyst (Aliquat 336). After the mixture was
refluxed for 48 h, the solvent was removed under vacuum. The
resulting solid was washed with water and dried under vacuum to
give a light yellow solid, which was purified by silica gel column
chromatography (eluent¼CHCl3). The solvent was removed by
evaporation and a resulting solid was dried in vacuo to give OPP(3)-
OMe as a white powder (1.36 g, 94%). 1H NMR (400 MHz, CDCl3):
(0.16 g, 94%). 1H NMR (400 MHz, DMSO-d6):
d 9.57 (s, 1H), 7.68–7.82
(m, 10H), 7.55 (d, J¼8.8 Hz, 2H), 7.48 (t, J¼7.6 Hz, 2H), 7.38 (t,
J¼7.6 Hz, 1H), 6.86 (d, J¼8.8 Hz, 2H). 13C{1H} NMR (100 MHz,
DMSO-d6):
d 157.0, 139.4, 139.1, 138.2, 138.5, 137.2, 130.1, 128.6,
127.3, 127.2, 126.9, 126.6, 126.2, 126.1, 115.6. Anal. Calcd for
C24H18O$0.1H2O: C, 88.91; H, 5.66. Found: C, 88.98; H, 5.70.
Mp¼358 ꢁC.
4.7. Synthesis of Br-OPP(3)-OMe
d
7.63–7.67 (m, 6H), 7.58 (d, J¼8.8 Hz, 2H), 7.46 (t, J¼7.6 Hz, 2H), 7.33
(t, J¼7.6 Hz, 1H), 7.00 (d, J¼8.8 Hz, 2H), 3.87 (s, 3H). 13C{1H} NMR
Br-OPP(3)-OMe was synthesized by the 1:1 Suzuki coupling
(100 MHz, CDCl3):
127.4, 127.2, 127.0, 114.2, 55.4. Mp¼233 ꢁC.
d 159.2, 140.8, 139.7, 139.5, 133.2, 128.8, 128.0,
reaction of 4,40-dibromobiphenyl with 4-methoxyphenylboronic
acid. 1H NMR (400 MHz, CDCl3):
d 7.56–7.62 (m, 8H), 7.55 (d,
J¼8.8 Hz, 2H), 7.00 (t, J¼8.8 Hz, 2H), 3.87 (s, 3H). 13C{1H} NMR
4.3. Synthesis of OPP(3)-OH
(100 MHz, CDCl3):
d 159.3, 140.1, 139.7, 138.2, 133.0, 131.9, 128.6,
128.1, 127.25, 127.16, 121.5, 114.3, 55.4.
A dichloromethane solution (10 mL) of BBr3 (0.80 mL, 8.4 mmol)
was added dropwise to a dichloromethane solution (50 mL) of
OPP(3)-OMe (0.50 g, 1.9 mmol). The solution was stirred at 25 ꢁC
for 30 h. After the solution was washed with water, the solvent was
removed under vacuum. The resulting solid was washed with water
and then chloroform (30 mL). OPP(3)-OH was collected by filtra-
tion, dried under vacuum, and obtained as a white powder (0.34 g,
4.8. Synthesis of Br-OPP(3)-OH
Br-OPP(3)-OMe was dissolved in melting pyridine hydrochloric
acid (20 g) at 180 ꢁC and the solution was stirred at the temperature
for 12 h. After the solution was cooled to room temperature,
a precipitate from the solution was washed with water and
extracted with methanol. The solvent removed under vacuum and
the resulting solid was dried in vacuo to give Br-OPP(3)-OH as
92%). 1H NMR (400 MHz, DMSO-d6):
d 9.57 (s, 1H), 7.65–7.71 (m,
6H), 7.54 (d, J¼8.8 Hz, 2H), 7.47 (t, J¼7.2 Hz, 2H), 7.34 (t, J¼7.2 Hz,
1H), 6.85 (d, J¼8.4 Hz, 2H). 13C{1H} NMR (100 MHz, DMSO-d6):
a white solid (0.28 g, 74%). 1H NMR (400 MHz, CDCl3):
d 7.49–7.61
d
157.2, 139.7, 139.2, 138.0, 130.3, 128.9, 127.6, 127.3, 127.0, 126.4,
(m, 10H), 6.93 (d, J¼8.8 Hz, 2H), 4.84 (s, 1H). 13C{1H} NMR
126.3, 115.7. Anal. Calcd for C18H14O: C, 87.78; H, 5.73. Found: C,
87.70; H, 5.77. Mp¼277 ꢁC.
(100 MHz, CDCl3):
d 157.3, 139.6, 138.9, 136.7, 131.8, 130.2, 128.6,
127.7, 127.0, 126.5, 120.8, 115.8.
4.4. Synthesis of Br-OPP(2)-OTHP
To a dichloromethane suspension (60 mL) of 4-bromo-40-
hydroxybiphenyl (3.00 g, 12.1 mmol) was added 3,4-dihydro-2H-
pyran (3.26 mL, 38.4 mmol) and camphor-10-sulfonic acid (0.082 g,
0.35 mmol). After the suspension was stirred at 25 ꢁC for 18 h in the
dark, the solvent was removed under vacuum. The resulting solid
was extracted with ether and dried over magnesium sulfate. The
solvent was removed under vacuum and the resulting solid was
washed with hexane. Br-OPP(2)-OTHP was collected by filtration,
dried under vacuum, and obtained as a white powder (1.66 g, 42%).
4.9. Synthesis of OPP(5)-OH
OPP(5)-OH was synthesized by the Suzuki coupling reaction of
Br-OPP(3)-OH with 4-biphenylboronic acid. Yield¼78%. 1H NMR
(400 MHz, DMSO-d6):
d 9.58 (s, 1H), 7.78–7.83 (m, 10H), 7.73 (d,
J¼7.6 Hz, 2H), 7.70 (d, J¼8.8 Hz, 2H), 7.56 (d, J¼8.4 Hz, 2H), 7.49 (t,
J¼8.0 Hz, 2H), 7.37 (t, J¼8.0 Hz, 1H), 6.87 (d, J¼8.8 Hz, 2H). Anal.
Calcd for C30H22O$0.15H2O: C, 89.81; H, 5.60. Found: C, 89.81; H,
5.68. Mp¼419 ꢁC.
1H NMR (400 MHz, CDCl3):
d
7.53 (d, J¼8.8 Hz, 2H), 7.47 (t, J¼8.4 Hz,
2H), 7.41 (t, J¼8.8 Hz, 2H), 7.12 (d, J¼8.8 Hz, 2H), 5.47 (t, J¼2.8 Hz,
4.10. Synthesis of MeO-OPP(3)-OTHP
1H), 3.92 (m, 1H), 3.64 (m, 1H), 2.03 (m, 1H), 1.89 (m, 2H), 1.55–1.69
(m, 3H). 13C{1H} NMR (100 MHz, CDCl3):
d 156.8, 139.8, 133.3, 131.8,
MeO-OPP(3)-OTHP was synthesized by Suzuki coupling re-
action of Br-OPP(2)-OTHP with 4-methoxyphenylboronic acid.
128.3, 127.9, 120.8, 116.8, 96.3, 62.0, 30.3, 25.2, 18.7.
Yield¼85%. 1H NMR (400 MHz, CDCl3):
d 7.55–7.61 (m, 8H), 7.14 (d,
4.5. Synthesis of OPP(4)-OTHP
J¼8.4 Hz, 2H), 6.99 (t, J¼8.4 Hz, 2H), 5.48 (t, J¼3.2 Hz, 1H), 3.86 (s,
3H), 3.65 (m, 1H), 2.03 (m, 1H), 1.89 (m, 2H), 1.55–1.70 (m, 3H).
OPP(4)-OTHP was synthesized by the Suzuki coupling reaction
of Br-OPP(2)-OTHP with 4-biphenylboronic acid. Yield¼88%. 1H
13C{1H} NMR (100 MHz, CDCl3):
d 159.1, 156.6, 139.2, 134.2, 133.3,
128.0, 127.0, 116.8, 114.2, 96.4, 62.1, 55.4, 30.4, 25.2, 18.8.
NMR (400 MHz, CDCl3):
d
7.66–7.74 (m, 10H), 7.58 (d, J¼8.8 Hz, 2H),
7.47 (t, J¼7.6 Hz, 2H), 7.37 (d, J¼7.6 Hz, 1H), 7.15 (d, J¼8.8 Hz, 2H),
5.49 (t, J¼2.8 Hz, 1H), 3.96 (m, 1H), 3.65 (m, 1H), 2.04 (m, 1H), 1.90
4.11. Synthesis of HO-OPP(3)-OH
(m, 2H), 1.55–1.71 (m, 3H). 13C{1H} NMR (100 MHz, CDCl3):
d 156.7,
140.7, 140.1, 139.9, 139.7, 139.0, 138.8, 134.0, 128.8, 128.0, 127.5,
HO-OPP(3)-OH was synthesized by stepwise hydrolysis of the
methoxy and THP groups of MeO-OPP(3)-OTHP. Yield¼96%. 1H
127.3,127.1,127.0,116.8, 96.4, 62.1, 30.9, 30.4, 25.2, 18.8. Mp¼221 ꢁC.
NMR (400 MHz, DMSO-d6):
d 9.53 (s, 2H), 7.60 (s, 4H), 7.51 (d,
4.6. Synthesis of OPP(4)-OH
J¼8.8 Hz, 4H), 6.84 (d, J¼8.4 Hz, 4H). 13C{1H} NMR (100 MHz,
DMSO-d6):
d 157.1, 138.1, 130.5, 127.5, 126.3, 115.7. Anal. Calcd for
To a 1,4-dioxane and methanol (v/v¼8:1) solution (90 mL) of
OPP(4)-OTHP was added hydrochloric acid (20 mL). After the
C18H14O2$0.2H2O: C, 81.43; H, 5.31. Found: C, 81.46; H, 5.10.
Mp¼378 ꢁC.

3652
I. Yamaguchi et al. / Tetrahedron 65 (2009) 3645–3652
Org. Chem. 1999, 451–458; (c) Iyoda, M.; Kondo, T.; Nakao, K.; Hara, K.; Ku-
4.12. Synthesis of TBP-OMe
watani, Y.; Yoshida, M.; Matsuyama, H. Org. Lett. 2000, 2, 2081–2083.
9. (a) Deng, X.; Mayeux, A.; Cai, C. J. Org. Chem. 2002, 67, 5279–5283; (b) Cao, X.-Y.;
Zi, H.; Zhang, W.; Lu, H.; Pei, J. J. Org. Chem. 2005, 70, 3545–3653.
10. (a) Berlman, I. B.; Wirth, H. O.; Steingraber, O. J. J. Phys. Chem. 1971, 75, 318–325;
(b) Robert, F.; Winum, J.-Y.; Sakai, N.; Gerard, D.; Matile, S. Org. Lett. 2000, 2,
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Higuchi, A.; Ohnishi, K.; Nomura, S.; Inada, H.; Shirota, Y. J. Mater. Chem. 1992, 2,
1109–1110; (c) Stevens, B.; Biver, C. J., III.; Yuan, D.-C. Chem. Phys. Lett. 1993, 205,
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TBP-OMe was synthesized by the 1:3 Suzuki coupling reaction
of 2,4,6-tribromoanisole with 4-biphenylboronic acid. Yield¼77%.
1H NMR (400 MHz, CDCl3):
d 7.65–7.79 (m, 20H), 7.45–7.50 (m, 6H),
7.25–7.39 (m, 3H), 3.32 (s, 3H). 13C{1H} NMR (100 MHz, CDCl3):
d
154.7, 140.8, 140.6, 140.1, 139.3, 137.6, 136.8, 135.7, 129.7, 128.9,
128.8, 127.5, 127.38, 127.35, 127.1, 127.03, 127.00, 60.8. Mp¼168 ꢁC.
4.13. Synthesis of TBP-OH
TBP-OH was synthesized by the hydrolysis of TBP(3)-OMe by
12. (a) Read, M. W.; Escobedo, J. O.; Willis, D. M.; Beck, P. A.; Strongin, R. M. Org.
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the use of BBr3. Yield¼91%. 1H NMR (400 MHz, CDCl3):
d 7.64–7.77
(m, 20H), 7.40–7.50 (m, 6H), 7.26–7.38 (m, 3H), 5.56 (s, 1H). 13C{1H}
13. (a) Jack Wu, C.-J.; Xue, C.; Kuoa, Y.-M.; Luo, F.-T. Tetrahedron 2005, 61, 4735–
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d 149.2, 140.7, 140.6, 139.8, 139.4, 136.4,
133.5, 129.8, 128.9, 128.8, 128.5, 127.7, 127.55, 127.52, 127.3, 127.15,
127.13, 127.1, 127.0. Mp¼216 ꢁC.
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