Synthesis of hydroxyoligophenylenes containing electron-donating, electron-accepting groups, or π-deficient aromatic ring and their solvatochromic behavior

Article abstract of DOI:10.1002/poc.3671

We have reported oligo(p-phenylene)s (OPPs) with an OH group located at one end, namely, OPP(n)-OHs (where n is the number of benzene rings). The OPPs exhibited significant solvatochromism; the deprotonation of the OH groups of OPP(n)-OHs, when treated with NaH, caused a bathochromic shift of absorption maxima (λ_max) that increased with the donor numbers (DNs) of the solvents. We assumed that the solvatochromism exhibited by OPP(n)-ONa was attributed to an intramolecular charge shift from the sodium phenoxy group(s) to the adjacent rings. In this study, to investigate the assumption, hydroxyoligophenylenes (R-OPP(n)-OH) with an electron-donating dimethylamino group (n?=?3, R?=?NMe₂), an electron-accepting nitro group (n?=?3, R?=?NO₂), and a π-deficient pyridine ring (n?=?2, R?=?Py) were synthesized by the Suzuki coupling reaction. The deprotonation of the OH group of by treatment with NaH caused a bathochromic shift (Δλ) of λ_max of R-OPP(m)-ONa. The Δλ of the deprotonated species increased with the DNs of the solvents. The emission peak positions of R-OPP(m)-ONa depended on the DNs of the solvents; therefore, the emission color could be tuned by changing the solvent. R-OPP(m)-OH received an electrochemical oxidation of the OH group and OPP unit. The data related to the remarkable solvatochromic behavior of R-OPP(n)-ONa will be useful information for the development of new luminescent materials.

Full text of DOI:10.1002/poc.3671

Received: 9 August 2016
DOI 10.1002/poc.3671
Revised: 1 November 2016
Accepted: 4 November 2016
R E S E A R C H A R T I C L E
Synthesis of hydroxyoligophenylenes containing electron‐
donating, electron‐accepting groups, or π‐deficient aromatic ring
and their solvatochromic behavior
Isao Yamaguchi | Ryosuke Yamaji
Department of Chemistry, Interdisciplinary
Abstract
Graduate School of Science and Engineering,
Shimane University, 1060 Nishikawatsu, Matsue
90‐8504, Japan
We have reported oligo(p‐phenylene)s (OPPs) with an OH group located at one
end, namely, OPP(n)‐OHs (where n is the number of benzene rings). The OPPs
exhibited significant solvatochromism; the deprotonation of the OH groups of
OPP(n)‐OHs, when treated with NaH, caused a bathochromic shift of absorption
maxima (λmax) that increased with the donor numbers (DNs) of the solvents. We
assumed that the solvatochromism exhibited by OPP(n)‐ONa was attributed to an
intramolecular charge shift from the sodium phenoxy group(s) to the adjacent rings.
In this study, to investigate the assumption, hydroxyoligophenylenes (R‐OPP(n)‐
6
Correspondence
Isao Yamaguchi, Department of Chemistry,
Interdisciplinary Graduate School of Science and
Engineering, Shimane University, 1060
Nishikawatsu, Matsue 690‐8504, Japan.
Email: iyamaguchi@riko.shimane‐u.ac.jp
OH) with an electron‐donating dimethylamino group (n = 3, R = NMe ), an
2
electron‐accepting nitro group (n = 3, R = NO ), and a π‐deficient pyridine ring
2
(
n = 2, R = Py) were synthesized by the Suzuki coupling reaction. The deproton-
ation of the OH group of by treatment with NaH caused a bathochromic shift
Δλ) of λmax of R‐OPP(m)‐ONa. The Δλ of the deprotonated species increased
(
with the DNs of the solvents. The emission peak positions of R‐OPP(m)‐ONa
depended on the DNs of the solvents; therefore, the emission color could be
tuned by changing the solvent. R‐OPP(m)‐OH received an electrochemical oxida-
tion of the OH group and OPP unit. The data related to the remarkable
solvatochromic behavior of R‐OPP(n)‐ONa will be useful information for the
development of new luminescent materials.
KEYWORDS
donor number, hydroxyoligophenylene, photoluminescence, solvatochromism, Suzuki
coupling
1
|
INTRODUCTION
namely, OPP(n)‐OHs (where n is the number of benzene
[
16]
rings) and HO‐OPP(3)‐OH, respectively.
The OPPs
Oligo(p‐phenylene)s (OPPs) are an important class of π‐con-
jugated oligomers because they are useful as luminophores
for light‐emitting materials,
effect transistors, as rigid‐rod cores for liquid crystalline
materials,
applications.
taining various substituents has revealed that the chemical
and physical properties of substituted OPPs depend on the
type of substituents used. Recently, we have reported OPPs
with an OH group located at one end and at both ends,
exhibited significant solvatochromism; the deprotonation of
the OH groups of OPP(n)‐OH, when treated with NaH,
caused a bathochromic shift of λmax that increased with the
donor numbers (DNs) of the solvents. Furthermore, the emis-
sion peak positions of OPP(n)‐ONa depended on the DNs of
the solvents; therefore, the emission color could be tuned by
changing the solvent. We assumed that the solvatochromism
exhibited by OPP(n)‐ONa was attributed to an intramolecu-
lar charge shift from the sodium phenoxy group(s) to the
[1–6]
as semiconductors for field‐
[
7]
[
8–10]
and as amphiphilic materials for biological
A systematic investigation of OPPs con-
[
11–15]
[
5]
adjacent rings. In this study, to investigate the assumption,
J Phys Org Chem 2016; 1–8
wileyonlinelibrary.com/journal/poc
Copyright © 2016 John Wiley & Sons, Ltd.
1

2
YAMAGUCHI AND YAMAJI
Me N‐OPP(3)‐OH with electron‐donating dimethylamino
gel column chromatography (eluent = chloroform). The sol-
vent was removed by evaporation and a resulting solid was
2
group and O N‐OPP(3)‐OH with electron–withdrawing
2
nitro group were synthesized via the Suzuki coupling reac-
tion. Furthermore, the presence of a π‐deficient pyridine ring
dried in vacuo to give Me N‐OPP(3)‐OH as a light brown
2
1
powder (0.13 g, 23%). H NMR (400 MHz, DMSO‐d ): δ
6
(
Py) in Py‐OPP(2)‐OH would affect its optical properties
9.51 (s, 1H), 7.63 (d, J = 9.2 Hz, 2H), 7.59 (d, J = 8.4 Hz,
2H), 7.55 (d, J = 8.4 Hz, 2H), 7.51 (d, J = 8.4 Hz, 2H),
6.85 (d, J = 8.4 Hz, 2H), 6.81 (d, J = 8.4 Hz, 2H), 2.94 (s,
because the charge shift from the sodium phenoxide groups
to the adjacent rings depends on the electronic properties of
the accepting site. Elucidation of the substitution (R) effect
on the chemical properties of R‐OPP‐OH may afford funda-
mental information for the synthesis of functional OPPs.
Additionally, elucidation of the optical properties of Me N‐
OPP(3)‐OH, O N‐OPP(3)‐OH, and Py‐OPP(2)‐OH before
and after the deprotonation of the OH groups will lead to a
better understanding of the intramolecular charge shift in
the π‐conjugated oligoarylenes and toward the development
of new functional materials.
13
3H). C NMR (125 MHz, DMSO‐d ): δ 157.0, 149.8,
6
138.2, 137.7, 130.6, 127.4, 127.2, 126.9, 126.3, 125.8,
−1
115.7, 112.7. IR (KBr, cm ): 3398 (OH), 3033, 2923,
2854, 2804, 1610, 1540, 1493, 1356, 1256, 1200, 809. Anal
2
calcd. for C H NO: C, 83.01; H, 6.62; N, 4.84. Found: C,
2
20 19
82.74; H, 6.85; N, 4.63.
2
.3 | Synthesis of Py‐OPP(3)‐OH
Herein, we report the synthesis of Me N‐OPP(3)‐OH,
2
Py‐OPP(2)‐OH was synthesized by the reaction of 4‐
pyridineboronic acid with 4‐bromo‐4′‐hydroxybiphenyl by
O N‐OPP(3)‐OH, and Py‐OPP(2)‐OH as well as their
optical and electrochemical properties before and after the
deprotonation of the OH groups.
2
the procedure that used for the synthesis of Me N‐OPP(3)‐
2
1
OH. Yield = 12%. H NMR (500 MHz, DMSO‐d ): δ 9.74
6
(s, 1H), 8.77 (d, J = 6.5 Hz, 2H), 8.05 (d, J = 6.5 Hz, 2H),
7
.97 (d, J = 9.0 Hz, 2H), 7.79 (d, J = 8.5 Hz, 2H), 7.61 (d,
2
2
|
EXPERIMENTAL
13
J = 8.5 Hz, 2H), 6.90 (d, J = 8.5 Hz, 2H). C NMR
(125 MHz, DMSO‐d ): δ 157.8, 150.1, 146.9, 142.0, 133.6,
6
.1 | General
−
1
129.6, 127.9, 127.8, 126.7, 121.9, 115.9. IR (KBr, cm ):
3076, 2800, 2679, 2617, 1634, 1601, 1489, 1278, 1223,
1177, 1100, 810. Anal calcd. for C H NO: C, 82.57; H,
5
Solvents were dried, distilled, and stored under nitrogen.
Reagents were purchased and used without further purifica-
tion. Reactions were conducted with standard Schlenk tech-
niques under nitrogen.
17 13
.30; N, 5.66. Found: C, 82.29; H, 5.54; N, 5.38.
IR and NMR spectra were recorded on a JASCO FT/IR‐
60 PLUS spectrophotometer and a JEOL AL‐400 spectrom-
6
2
.4 | Synthesis of O N‐OPP(3)‐OH
2
eter, respectively. Elemental analysis was performed on a
Yanagimoto MT‐5 CHN corder. UV‐vis and PL spectra were
obtained by a JASCO V‐560 spectrometer and a JASCO
FP‐6200 spectrofluorometer, respectively. Quantum yields
were calculated by using a diluted ethanol solution of 7‐
diethylamino‐4‐methylcoumarin (Φ = 0.50) as the stan-
Pd(PPh ) (0.045 g, 0.039 mmol) was dissolved in 20 mL of
dry THF under N . 4‐Nitrophenylboronic acid (0.50 g,
3
4
2
3
.0 mmol), 4‐bromo‐4′‐hydroxybiphenyl (0.50 g, 2.0 mmol),
K CO (aq) (2.0 M, 20 mL; N bubbled before use), and
2
3
2
three drops of aliquat336 were added to the solution. After
the mixture was refluxed for 158 h, the solvent was removed
under vacuum. The resulting solid was washed with water
and HCl(aq) (1.0 M, 40 mL) and dried under vacuum to give
a light brown solid, which was washed with acetone for
[
16]
1
dard. The solutions for the H NMR, UV‐vis, and PL mea-
surements of Me N‐OPP(3)‐ONa, O N‐OPP(3)‐ONa, and
2
2
Py‐OPP(3)‐ONa were prepared by treating Me N‐OPP(3)‐
2
OH, O N‐OPP(3)‐OH, and Py‐OPP(3)‐OH with an excess
2
3
0 sec and purified by silica gel column chromatography
amount of NaH under nitrogen. Cyclic voltammetry was per-
(eluent = chloroform). The solvent was removed by
formed with a Hokuto Denko HSV‐110.
evaporation and a resulting solid was dried in vacuo to
give O N‐OPP(3)‐OH as a yeloow powder (0.44 g, 79%).
2
2
.2 | Synthesis of Me N‐OPP(3)‐OH
1
2
H NMR (500 MHz, DMSO‐d ): δ 9.65 (s, 1H), 8.32
6
Pd(PPh ) (0.066 g, 0.057 mmol) was dissolved in 20 mL of
(d, J = 9.5 Hz, 2H), 8.02 (d, J = 9.0 Hz, 2H), 7.86
3
4
dry THF under N . 4‐Dimethylaminophenylboronic acid
(d, J = 8.0 Hz, 2H), 7.76 (d, J = 8.5 Hz, 2H), 7.59
(d, J = 8.5 Hz, 2H), 6.88 (d, J = 9.0 Hz, 2H). C NMR
2
1
3
(0.50 g, 3.0 mmol), 4‐bromo‐4′‐hydroxybiphenyl (0.50 g,
2
.0 mmol), K CO (aq) (2.0 M, 20 mL; N bubbled before
(125 MHz, DMSO‐d ): δ 157.6, 146.5, 146.2, 140.8,
2
3
2
6
use), and three drops of aliquat336 were added to the solu-
tion. After the mixture was refluxed for 113 h, the solvent
was removed under vacuum. The resulting solid was washed
with water and HCl(aq) (1.0 M, 40 mL) and dried under vac-
uum to give a light brown solid, which was purified by silica
135.1, 129.8, 127.8, 127.7, 127.5, 126.6, 124.1, 115.8. IR
−
1
(KBr, cm ): 3430 (OH), 3033, 2924, 2853, 1593, 1506,
1346, 1333, 1268, 1191, 1111, 822. Anal calcd. for
C H NO : C, 74.22; H, 4.50; N, 4.81. Found: C, 74.01;
18
13
3
H, 4.63; N, 4.68.

YAMAGUCHI AND YAMAJI
3
3
3
| RESULTS AND DISCUSSION
.1 | Synthesis
Suzuki
hydroxybiphenyl with 4‐dimethylaminobenzeneboronic acid,
‐nitrophenylboronic acid, 4‐pyridineboronic acid yielded
The
coupling
reaction
of
4‐bromo‐4′‐
4
Me N‐OPP(3)‐OH, O N‐OPP(3)‐OH, and Py‐OPP(2)‐OH
2
2
in 23%, 79%, and 12% yields, respectively (Scheme 1).
The structures of the newly synthesized compounds were
1
13
determined by H and C NMR spectroscopy and elemental
analysis. Me N‐OPP(3)‐OH and O N‐OPP(3)‐OH were
2
2
soluble in dichloromethane, 1,4‐dioxane, tetrahydrofuran
(THF), N,N‐dimethylformamide (DMF), and dimethyl sulf-
oxide (DMSO). However, Py‐OPP(2)‐OH was completely
soluble in DMF and DMSO but sparingly soluble in dichloro-
methane, 1,4‐dioxane, and THF. The solubility of Py‐
OPP(2)‐OH is because of the presence of a hydrophilic pyr-
idine ring.
FIGURE 1 IR spectra of Me N‐OPP(3)‐OH, O N‐OPP(3)‐OH, and Py‐
OPP(2)‐OH
2
2
magnetic fields than those of Me N‐OPP(3)‐OH and O N‐
2
2
1
a
f
OPP(3)‐OH. The H NMR chemical shifts (δ (OH) ~ δ (OH))
of protons in Me N‐OPP(3)‐OH, O N‐OPP(3)‐OH, and
Py‐OPP(2)‐OH and those (δ (ONa) ~ δ (ONa)) of protons
in Me N‐OPP(3)‐ONa, O N‐OPP(3)‐ONa, and Py‐
2
2
a
f
3.2 | IR and NMR spectra
2
2
Figure 1 shows the IR spectra of Me N‐OPP(3)‐OH, O N‐
OPP(2)‐ONa are summarized in Table 1. These chemical
shifts increase with decreasing the distance of the protons
from the ONa group; therefore, they are largest in the case
of protons adjacent to the ONa groups. These observations
can be attributed to the electron‐donating effect of the ONa
groups. These data indicated the possibility of the occur-
rence of a charge shift from the phenolate groups to the adja-
cent rings in the deprotonated species. Such a charge shift in
2
2
OPP(3)‐OH, and Py‐OPP(2)‐OH.
The absorption peaks corresponding to O‐H stretching
vibrations of Me N‐OPP(3)‐OH and O N‐OPP(3)‐OH were
2
2
−
1
observed at approximately 3398 and 3430 cm , respectively.
The observation of the absorptions corresponding to O‐H
stretching vibrations of Py‐OPP(2)‐OH in the range of
1
2
617 to 3076 cm− is attributable to intermolecular hydrogen
bonding between the O‐H‐donating group and the accepting
pyridine ring. The absorption corresponding to the out‐of‐
Me
2
N‐OPP(3)‐OH, O N‐OPP(3)‐OH, and Py‐OPP(2)‐OH
2
significantly may affect their optical properties. The differ-
ences in the chemical shift (Δδ = δ(OH) – δ(ONa)) values
between Me
plane C‐H bending vibrations of p‐phenylene of Me N‐
2
OPP(3)‐OH, O N‐OPP(3)‐OH, and Py‐OPP(2)‐OH was
2
N‐OPP(3)‐OH and Me
2
N‐OPP(3)‐ONa and
2
−
1
observed at approximately 810 cm .
Figure 2 shows the H NMR spectra of Me N‐OPP(3)‐
OH, O N‐OPP(3)‐OH, and Py‐OPP(2)‐OH before and
O
N‐OPP(3)‐OH and O
2
2
N‐OPP(3)‐ONa are nearly the
1
same. The results suggest that the Δδ values are independent
on the electronic properties of the substituent at the 4‐ or 4″‐
positions. By contrast, the Δδ values between Py‐OPP(2)‐
OH and Py‐OPP(2)‐ONa are larger than those between
2
2
after the deprotonation of the OH group. The deprotonation
of the OH group of the compounds was conducted by
treating them with an excess amount of NaH in DMSO‐d6.
The disappearance of the signal corresponding to OH group
Me
N‐OPP(3)‐OH and Me
N‐OPP(3)‐ONa and O N‐
2
2
2
OPP(3)‐OH and O
N‐OPP(3)‐ONa. This difference was
2
1
from the H NMR spectra of solutions of the compounds
apparently due to the presence of the electron‐accepting
pyridine ring that easily induced the shift in charge
from the phenolate groups to the adjacent rings in the
deprotonated species.
indicated that the deprotonation proceeded quantitatively.
The signals corresponding to particular protons of Me N‐
2
OPP(3)‐ONa and O N‐OPP(3)‐ONa shifted to higher
2
SCHEME 1 Synthesis of Me
2
N‐OPP(3)‐OH, O N‐OPP(3)‐OH, and Py‐OPP(2)‐OH
2

4
YAMAGUCHI AND YAMAJI
1
FIGURE 2
H NMR spectra of the DMSO‐d
6
solutions of Me N‐OPP(3)‐OH, O N‐OPP(3)‐
2
2
OH, and Py‐OPP(2)‐OH before and after the
deprotonation of the OH group
TABLE 1 1H NMR chemical shift
3
.3 | UV‐vis absorption and solvatochromism
Figure 3 shows the UV‐vis spectra of Me N‐OPP(3)‐OH,
2
O N‐OPP(3)‐OH, and Py‐OPP(2)‐OH in DMF. The UV‐
2
vis data of OPP(3)‐OH, Me N‐OPP(3)‐OH, O N‐OPP(3)‐
2
2
f
e
d
c
b
a
δH
δH
δH
δH
δH
δH
OH, and Py‐OPP(2)‐OH and their deprotonated species are
Me
Me
2
N‐OPP(3)‐OH
N‐OPP(3)‐ONa
6.85
6.79
8.32
8.25
8.77
8.57
7.55
7.49
8.02
7.94
8.08
7.7
7.63
7.45
7.86
7.7
7.59
7.41
7.76
7.57
7.79
7.56
7.51
7.1
6.85
6.01
6.88
6.09
6.9
summarized in Table 2.
2
The treatment of the DMF solutions of Me N‐OPP(3)‐
2
O
O
2
N‐OPP(3)‐OH
N‐OPP(3)‐ONa
7.59
7.24
7.61
7.22
OH, O N‐OPP(3)‐OH, and Py‐OPP(2)‐OH with NaH
2
2
causes bathochromic shift of λmax by 46, 154, and 118 nm,
respectively. The formation of Me N‐OPP(3)‐ONa, O N‐
Py‐OPP(2)‐OH
Py‐OPP(2)‐ONa
7.97
7.7
2
2
6.12
OPP(3)‐ONa, and Py‐OPP(2)‐ONa was mainly responsible

YAMAGUCHI AND YAMAJI
5
FIGURE 4 Dependence of λmax of Me
2
N‐OPP(3)‐OH (red solid line),
FIGURE 3 UV‐vis spectra of Me
OPP(3)‐OH (blue solid line), Py‐OPP(2)‐OH (green solid line), Me
2
N‐OPP(3)‐OH (red solid line), O
N‐
N‐OPP(3)‐ONa (blue dotted line), and
2
N‐
O N‐OPP(3)‐OH (blue solid line), Py‐OPP(2)‐OH (green solid line),
2
2
Me N‐OPP(3)‐ONa (red dotted line), O N‐OPP(3)‐OH (blue dotted line),
2
2
OPP(3)‐ONa (red dotted line), O
2
and Py‐OPP(2)‐OH (green dotted line) on the DNs of solvents. In the case
that two absorption peaks were observed, the longer wavelength was adopted
for the data point
Py‐OPP(2)‐ONa (green dotted line) in DMF
for the shift of λmax toward a longer wavelength. Similar
solvatochromic behavior was observed in the case of
3
60 nm in CH Cl (DN = 0) to 532 nm in DMSO (DN = 29.8)
2 2
[
17]
OPP(3)‐OH and its deprotonated species reported earlier.
through to a value of 475 nm in THF (DN = 20.0). The large
Δλ value can be attributed to the fact that solvents with a high
DN solvate effectively with Na to stabilize the deprotonated
species in the solutions.
The Δλ value of O N‐OPP(3)‐OH was larger than that of
2
Me N‐OPP(3)‐OH although the Δδ values in the both com-
+
2
pounds are nearly the same. This is because of the resonance
effect of the nitro group in O N‐OPP(3)‐OH. The Δλ value
2
of Py‐OPP(3)‐OH was smaller than that of O N‐OPP(3)‐
2
b~f
b~f
3.4 | Photoluminescence
OH although the Δδ = δ (ONa) – δ (OH) values in Py‐
OPP(3)‐OH are larger than those of O N‐OPP(3)‐OH. The
2
Me N‐OPP(3)‐OH, O N‐OPP(3)‐OH, and Py‐OPP(2)‐OH
2
2
result suggests that charge shift from the phenoxy anion to
the second and third aromatic rings has little influence on
the Δλ. Bathochromic shift attributable to deprotonation
depends on the DN of the solvents. As shown in Figure 4,
the λmax values of Me N‐OPP(3)‐OH, O N‐OPP(3)‐OH,
and their deprotonated species are photoluminescent in solu-
tion. The PL data are summarized in Table 3. The emission
peak positions of Me N‐OPP(3)‐OH, O N‐OPP(3)‐OH,
2
2
and Py‐OPP(2)‐OH and their deprotonated species depended
2
2
on the DNs of the solvents; therefore, the emission color can
and Py‐OPP(2)‐OH and their deprotonated species shifted
be tuned by changing the solvent. For example, Me N‐
2
to longer wavelengths as the DNs of the solvents increased.
OPP(3)‐ONa exhibited purple, blue, and green emissions
after it was irradiated with UV light in 1,4‐dioxane
(DN = 14.8), THF (DN = 20.0), and DMSO (DN = 29.8),
respectively. The quantum yields of the PLs of the THF solu-
tions of Me N‐OPP(3)‐OH, O N‐OPP(3)‐OH, and Py‐
In contrast to the small bathochromic shift of Me N‐
2
OPP(3)‐OH, O N‐OPP(3)‐OH, and Py‐OPP(2)‐OH with
2
an increase in the DNs of the solvents, the λmax values of
the deprotonated species were larger than those of Me N‐
2
2
2
OPP(3)‐OH, O N‐OPP(3)‐OH, and Py‐OPP(2)‐OH. For
OPP(2)‐OH were 30%, 17%, and 34%, respectively, while
those of Me N‐OPP(3)‐ONa, O N‐OPP(3)‐ONa, and
2
example, the λmax value of O N‐OPP(3)‐ONa moves from
2
2
2
TABLE 2 UV‐vis data of Me
2
N‐OPP(3)‐OH, O
2
N‐OPP(3)‐OH, and Py‐OPP(2)‐OH
Me N‐OPP(3)‐ N‐OPP(3)‐
Me
2
N‐OPP(3)‐
2
O
2
O
2
N‐OPP(3)‐
Py‐OPP(2)‐
Py‐OPP(2)‐
b
a
a
a
a
a
a
Solvent
DN
OH, nm
ONa, nm
OH, nm
ONa, nm
OH, nm
ONa, nm
Dichloromethane
0
320 (4.21)
318 (4.09)
321 (4.33)
324 (4.11)
340 (3.60)
260 (4.23), 343 (4.31)
261 (4.04), 342 (4.15)
264 (4.22), 347 (4.14)
272 (4.21), 358 (4.30)
279 (3.61), 414 (3.52)
261 (4.10), 416 (4.00)
303 (4.36), 452 (4.28)
273 (4.32), 353 (4.44),
c
c
c
c
1
,4‐dioxane
14.8
20
318 (3.98)
THF
271 (4.12), 320 (4.01)
271 (4.29), 370 (4.35)
301 (4.30)
377 (4.37)
DMF
26.6
304 (4.07)
308 (4.12)
271 (4.17),
422 (4.21)
4
97 (4.30)
289 (4.22), 319 (4.40),
20 (4.16), 490 (4.22)
DMSO
29.8
328 (4.26)
293 (4.59), 376 (4.45)
273 (4.09), 359 (4.26)
281 (4.55),
415 (4.26)
4
aAbsorption maximum wavelength. Concentration of solution was 5.0 × 10−5 M. logε values are shown in parenthesis.
b
DN indicates donor number.
c
Not measured due to low solubility.

6
YAMAGUCHI AND YAMAJI
TABLE 3 PL data of Me
2
N‐OPP(3)‐OH, O N‐OPP(3)‐OH, and Py‐OPP(2)‐OH
2
Me
2
N‐OPP(3)‐OH,
Me
ONa, nm
2
N‐OPP(3)‐
O
2
N‐OPP(3)‐OH,
O
2
N‐OPP(3)‐ONa,
Py‐OPP(2)‐OH,
Py‐OPP(2)‐ONa,
b
a
a
a
a
a
a
solvent
DN
nm
nm
nm
nm
nm
Dichloromethane
0
400
395
403
415
422
409
396
404
487
490
360
382
391
408
420
360
400
475
503
532
c
c
c
1
,4‐Dioxane
14.8
20
c
THF
389
409
414
501
555
554
DMF
DMSO
26.6
29.8
aEmission peak wavelength. Concentration of solution was 5.0 × 10−5 M.
b
DN indicates donor number.
c
Not measured due to low solubility.
Py‐OPP(2)‐ONa were 5%, 1%, and 8%, respectively. The
Figure 6 shows the dependence of the emission peak
fact that the quantum yields of the PLs of Me N‐OPP(3)‐
positions of Me N‐OPP(3)‐OH, O N‐OPP(3)‐OH, and Py‐
2
2
2
ONa, O N‐OPP(3)‐ONa, and Py‐OPP(2)‐ONa are lower
OPP(2)‐OH and their deprotonated species on the DNs of
2
than those of Me N‐OPP(3)‐OH, O N‐OPP(3)‐OH, and
the solvents. Thus, by alternating solvents such as CH Cl
2
2
2
2
Py‐OPP(2)‐OH is attributed to the ICT in Me N‐OPP(3)‐
and 1,4‐dioxane, which have small DN values, and those
such as DMF and DMSO, which have large DN values, it is
2
ONa, O N‐OPP(3)‐ONa, and Py‐OPP(2)‐ONa. It has been
2
reported that the ICT in π‐conjugated molecules reduces their
observed that the emission peak positions of Me N‐
2
[18]
PL emission efficiencies.
OPP(3)‐OH, O N‐OPP(3)‐OH, and Py‐OPP(2)‐OH shift
2
Figure 5 shows the PL and its excitation spectra of
only by 22 to 60 nm. However, a significantly large shift in
O N‐OPP(3)‐OH and O N‐OPP(3)‐ONa in DMSO. The
the emission peaks of Me N‐OPP(3)‐ONa O N‐OPP(3)‐
2
2
2
2
PL peaks of the compounds appear at the onset position
of their absorption bands, as usually observed with
photoluminescent aromatic compounds. The observation
ONa, and Py‐OPP(2)‐ONa occurred as the DNs of the
solvents increased. These observations are comparable with
the results that λmax of Me N‐OPP(3)‐ONa, O N‐OPP(3)‐
2
2
that the PL peak position for O N‐OPP(3)‐OH was longer
ONa, and Py‐OPP(2)‐ONa in solution shifts to a longer
wavelength than that of Me N‐OPP(3)‐OH, O N‐OPP(3)‐
2
than that for O N‐OPP(3)‐ONa is comparable with the
2
2
2
result that the λmax wavelength for O N‐OPP(3)‐OH was
OH, and Py‐OPP(2)‐OH with an increase in the DNs of
the solvents. The remarkable solvatochromic shift of the PL
peak position of Me N‐OPP(3)‐ONa and O N‐OPP(3)‐
2
longer than that for O N‐OPP(3)‐ONa. The peak wave-
2
lengths (λex) of the excited spectra of the DMF solutions
of O N‐OPP(3)‐OH and O N‐OPP(3)‐ONa were shorter
2
2
ONa appeared to be due to the charge shift from the pheno-
late group to the adjacent ring. In addition to the charge shift
effect, a large amount of stabilization energy produced by the
solvation of Me N‐OPP(3)‐ONa and O N‐OPP(3)‐ONa
2
2
than their λmax. The difference between λex and λmax of
O N‐OPP(3)‐ONa (λex – λ = 100 nm) was considerably
2
max
larger than that of O N‐OPP(3)‐OH (λex – λ
= 25 nm).
2
max
2
2
The large difference between λex and λmax of O N‐OPP(3)‐
2
ONa is probably ascribed to intrachain charge transfer in
the compound.
FIGURE 6 Dependence of PL peak position of Me
solid line), O N‐OPP(3)‐OH (blue solid line), Py‐OPP(2)‐OH (green solid
line), Me N‐OPP(3)‐ONa (red dotted line), O N‐OPP(3)‐OH (blue dotted
line), and Py‐OPP(2)‐OH (green dotted line) on the DNs of solvents. In the
case that two PL peaks were observed, the longer wavelength was adopted for
the data point
2
N‐OPP(3)‐OH (red
2
2
2
FIGURE 5 PL (thin solid curve) and its excitation (thin hashed curve)
spectra of O
2
N‐OPP(3)‐OH and PL (bold solid curve) and its excitation
N‐OPP(3)‐ONa in DMF
(
bold hashed curve) spectra of O
2

YAMAGUCHI AND YAMAJI
7
may contribute to the solvatochromic red shift as the DNs of
the solvents increase.
that the E (1) and E (2) potentials of Me N‐OPP(3)‐OH
pa
pa
2
are more positive and negative than those of O N‐OPP(3)‐
2
OH, respectively, corresponds to the presence of the
electron‐donating dimethylamino group in Me N‐OPP(3)‐
2
3
.5 | Cyclic voltammograms
OH. O N‐OPP(3)‐OH exhibited a peak corresponding to
2
Figure 7 shows cyclic voltammograms of Me N‐OPP(3)‐
the electrochemical reduction of the nitro gourp at ‐0.50 V
2
+
OH, O N‐OPP(3)‐OH, and Py‐OPP(2)‐OH in an acetoni-
(Epa vs. Ag /Ag).
2
trile solution containing [Et N]BF (0.10 M). Me N‐
4
4
2
OPP(3)‐OH, O N‐OPP(3)‐OH, and Py‐OPP(2)‐OH exhib-
2
4
| CONCLUSIONS
ited peaks corresponding to the electrochemical oxidation
of the OH gourp (E (1)) and terphenyl or biphenyl moieties
pa
Hydroxyoligophenylenes (R‐OPP(n)‐OH) with an electron‐
(
E (2)) at 0.75 V and 1.53 V, 0.49 V and 1.59 V, and 0.44 V
pa
donating dimethylamino group (n = 3, R = NMe ), an
+
2
and 1.32 V (Epa vs. Ag /Ag), respectively. The observation
electron‐accepting nitro group (n = 3, R = NO ), and a π‐
2
deficient pyridine ring (n = 2, R = Py) were synthesized by
the Suzuki coupling reaction. The treatment of R‐OPP(n)‐
OH with a base produced the deprotonated species R‐
OPP(n)‐ONa, whose absorption and PL peak positions in
solution shifted toward longer wavelengths with an increase
in the DNs of the solvents. An intramolecular charge shift
from the sodium phenoxy group to the adjacent ring played
an important role in Δλ. R‐OPP(n)‐OH received electro-
chemical oxidation of the OH group and OPP unit. The
oxidation potentials depended on the electric properties of
the substituents at the 4‐ or 4″‐positions. From the results of
this study, it can be concluded that new luminescent materials
can be developed on the basis of the remarkable
solvatochromic behavior of R‐OPP(n)‐OH.
ACKNOWLEDGEMENT
This work was performed under the Cooperative Research
Program of “Network Joint Research Center for Materials
and Devices” (No. 2015291).
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