Specific solvatochromism of D-π-A type pyridinium dyes bearing various counter anions in halogenated solvents

Article abstract of DOI:10.1016/j.tet.2012.12.033

Donor-π-acceptor type pyridinium dyes OD1-OD4 bearing various counter anions (X^-=Cl^-, Br^-, I^-, or BPh ^4-) have been designed and developed to gain greater insight into the influences of the electronic structures of D-π-A type pyridinium dye on the specific solvatochromism in halogenated solvents: the intramolecular charge transfer absorption bands of the dyes OD1-OD4 in halogenated solvents show a large bathochromic shift compared with those in the non-halogenated solvents. This study revealed that the halogenated solvents can significantly enhance the intramolecular charge transfer characteristics of D-π-A type pyridinium dye with soft counter anion, leading to large bathochromic shift of absorption band in halogenated solvents, which is in good agreement with an increase in the energy of halogen-halide anion interaction for the type of the halogen atom of halogenated solvents.

Full text of DOI:10.1016/j.tet.2012.12.033

Accepted Manuscript
Specific solvatochromism of D-π-A type pyridinium dyes bearing various counter
anions in halogenated solvents
Yousuke Ooyama, Yuichiro Oda, Tomonobu Mizumo, Joji Ohshita
PII:
S0040-4020(12)01875-3
10.1016/j.tet.2012.12.033
TET 23845
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 8 November 2012
Revised Date: 5 December 2012
Accepted Date: 6 December 2012
Please cite this article as: Ooyama Y, Oda Y, Mizumo T, Ohshita J, Specific solvatochromism of D-π-A
type pyridinium dyes bearing various counter anions in halogenated solvents, Tetrahedron (2013), doi:
10.1016/j.tet.2012.12.033.
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Specific solvatochromism of D-π-A type
pyridinium dyes bearing various counter
anions in halogenated solvents
Yousuke Ooyama,* Yuichiro Oda, Tomonobu Mizumo, and Joji Ohshita*
Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University, Higashi-hiroshima
739-8527, Japan
Fax: (+81) 82-424-5494
E-mail: yooyama@hiroshima-u.ac.jp
jo@hiroshima-u.ac.jp
N
N
nBu
N
nBu
X
OD1: X = Cl
OD2: X = Br
OD3: X = I
OD1 OD2 OD3
OD4
In CH2Br2
OD4: X = BPh4

ACCEPTED MANUSCRIPT
Tetrahedron
1
TETRAHEDRON
Pergamon
Specific solvatochromism of D-π-A type pyridinium dyes bearing
various counter anions in halogenated solvents
Yousuke Ooyama,* Yuichiro Oda, Tomonobu Mizumo, and Joji Ohshita**
Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University, Higashi-Hiroshima 739-8527, Japan
–
Abstract— Donor-π-acceptor type pyridinium dyes OD1–OD4 bearing various counter anions (X– = Cl–, Br–, I–, or BPh4 ) have been
designed and developed to gain greater insight into the influences of the electronic structures of D-π-A type pyridinium dye on the specific
solvatochromism in halogenated solvents: the intramolecular charge transfer absorption bands of the dyes OD1–OD4 in halogenated
solvents show a large bathochromic shift compared with those in the non-halogenated solvents. This study revealed that the halogenated
solvents can significantly enhance the intramolecular charge transfer characteristics of D-π-A type pyridinium dye with soft counter anion,
leading to large bathochromic shift of absorption band in halogenated solvents, which is good agreement with an increase in the energy of
halogen-halide anion interaction for the type of the halogen atom of halogenated solvents. © 2012 Elsevier Science. All rights reserved
that the bathochromic shifts of ICT absorption band in
Introduction
halogenated solvents such as dichloromethane and
dibromomethane are larger than those in non-halogenated
solvents of similar dielectric constant (εr) values.24 The
specific solvatochromism of dyes in halogenated solvents is
also observed for neutral (non-ionic) D-π-A dyes having
strong electron-withdrawing group.31 However, there have
been few efforts to clarify the influences of halogenated
solvent on the large bathochromic shifts, although the
specific solvatochromism is of a great interest from an
academic viewpoint, together with a practical importance
such as development of sensors for halogenated organic
compounds.32 Thus, recently, we investigated the specific
solvatochromic behaviors of D-π-A type pyridinium dye
bearing an iodide ion as the counter anion. It was found that
the bathochromic shifts of ICT absorption band in iodinated
solvents such as iodobenzene and diiodomethane are larger
than those in chlorinated and brominated solvents.30
Solvatochromic dyes have received considerable
attention over many years because of a fundamental interest
in photochemistry and their application as environmental
probes for determination of local polarity in macrosystems
(e.g. membrances, polymers, and sol-gel matrices) and
detection of volatile organic compounds.1–12 Among the
various types of solvatochromic dyes, donor-π-acceptor (D-
π-A) type pyridinium dyes having diphenyl or dialkyl
amino group as electron donor and pyridinium ring as
electron acceptor linked by a π-conjugated bridge, and
bearing a halide anion as counter anion are known well to
show negative solvatochromism (i.e., the dye shows a
hypsochromic shift of the intramolecular charge-transfer
(ICT) absorption band with increasing solvent polarity).13–
30
Almost all chemists may understand that the negative
solvatochromism would be ascribed to the change of the
electronic ground-state structure of the pyridinium dye on
changing of solvent polarity; with increasing solvent
polarity the ground state is more stabilized than the excited
state because the ground state is more dipolar than the
excited state, and this produces a hypsochromic shift.1, 18, 19
In our previous study we have mentioned another
interesting characteristic of D-π-A type pyridinium dyes is
In this study, to gain greater insight into the influences of
the electronic structures of D-π-A type pyridinium dye on
the specific solvatochromism in halogenated solvents, we
have designed and synthesized D-π-A type pyridinium dyes
OD1–OD4 having diphenylamino group as an electron
donor and pyridinium ring as an electron acceptor linked by
carbazole as a π-conjugated bridge, and bearing various
–
counter anions (X– = Cl–, Br–, I–, or BPh4 ). The dyes OD1–
———
* Corresponding authors. Tel.: +81 82 424 7689; fax: +81 82 424 5494; e-mail: yooyama@hiroshima-u.ac.jp (Y. Ooyama), jo@hiroshima-u.ac.jp (J.
Ohshita)

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2
Tetrahedron
OD4 showed the specific solvatochromism, leading to large
bathochromic shift of ICT absorption band in halogenated
solvents. Furthermore, it was found that bathochromic
shifts of ICT absorption bands become larger in order of
solvents were also observed in the cases of OD1–OD3
(Table 1). It is worthy to note here that the specific
solvatochromism strongly depends on the counter anion of
the dyes OD1–OD4, that is, the bathochromic shifts of ICT
absorption band become larger in order of soft counter
–
soft counter anion Cl– < Br– < I– < BPh4 . The influences of
–
halogenated solvents on the large bathochromic shifts of
anion Cl– < Br– < I– < BPh4 . In fact, as shown in Fig. 1c,
1
ICT absorption band are studied on the basis of H NMR
the ICT absorption bands of the four dyes in
dibromomethane show the large bathochromic shifts in
order of OD1 < OD2 < OD3 < OD4. The color of OD1
and OD2 in dibromomethane is orange, but the color of
OD3 and OD4 in dichloromethane is reddish-orange (Fig.
2b). Fig. 3 clearly indicates that the wavenumbers (ν) of
absorption maxima for the ICT bands of the dyes OD1–
OD4 depend on the type of halogen atom of halogenated
solvents and the counter anion of the dyes. On the other
hand, among polar solvents (εr > 20), the ICT absorption
bands of OD1–OD4 in ethanol appear at wavelengths
longer than those of OD1–OD4 in the aprotic solvents such
as acetone, acetonitrile and DMSO (Table 1). It was
suggested that the bathochromic shift of ICT absorption
band in ethanol is contributable to stronger ICT
characteristics, which are induced by the hydrogen bonding
between hydroxyl group of ethanol and the counter anion
of OD1–OD4.
measurements and theoretical calculations. Here we discuss
the specific solvatochromism from the viewpoint of the
enhanced ICT characteristics of the D-π-A pyridinium dyes
in halogenated solvents.
Results and discussion
The D-π-A type pyridinium dyes OD1–OD3 were
prepared from diphenyl-[7-(5-pyridin-4-yl-thiophen-2-yl)-
9H-carbazol-2-yl]-amine 133 and the corresponding n-butyl
halide (Scheme 1). The dye OD3 was metathesized to the
corresponding tetraphenylborate salt OD4 by precipitation
from acetonitrile/water NaBPh4.
nBuX
N
N
N
N
Acetonitrile
or
Toluene
nBu
N
nBu
N
nBu
X
Table 1. Solvatochromic spectral data of OD1–OD4
OD1: X = Cl
OD2: X = Br
OD3: X = I
λ
abs [nm]b
max
εra
NaBPh4
No.
Solvent
OD3
OD4: X = BPh4
OD1 OD2 OD3 OD4
Acetonitrile/Water
1
2
3
4
5
6
7
8
1,4-dioxane
tetrachloromethane
toluene
2.22
2.24
2.38
4.40
4.59
4.81
5.32
5.45
5.47
5.69
7.52
7.77
8.93
442
442
445
488
459
475
485
482
497
475
467
477
443
481
480
443
455
440
438
460
464
470
474
486
479
497
480
474
479
458
488
487
443
455
440
438
c
c
–
–
–
–
Scheme 1. Synthesis of D-π-A type pyridinium dyes OD1–OD4 bearing
various counter anions.
c
c
bromoform
iodobenzene
chloroform
diiodomethane
bromobenzene
fluorobenzene
chlorobenzene
THF
dibromomethane
dichloromethane
acetone
ethanol
acetonitrile
DMSO
459
475
473
480
470
461
464
438
472
468
464
480
477
494
472
463
470
440
475
473
443
455
440
438
The solvatochromic spectral data of OD1–OD4 are
summarized in Table 1 and the spectra of OD3 in various
solvents are shown in Fig. 1a (see Table S1 in Supporting
Information for the molar extinction coefficients of OD1–
OD4). Fig. 2a shows color changes of OD3 in various
solvents. The color of OD3 in 1,4-dioxane, THF, acetone,
and DMSO is yellow, but the color of OD3 in
dichloromethane, dibromomethane, and diiodomethane is
reddish-orange. The pyridinium dyes OD1–OD4 show
absorption maxima at around 460–530 nm attributable to
ICT excitation from diphenylamino group to pyridinium
ring. The ICT absorption bands of the four dyes exhibit a
general negative solvatochromism in non-halogenated
solvents; with decreasing solvent polarity from DMSO (εr =
47.24) to toluene (εr = 2.38), for example, the ICT
absorption band of OD3 shifts from 438 nm to 459 nm. On
the other hand, the dyes OD1–OD4 showed the specific
solvatochromism, leading to large bathochromic shift of
ICT absorption band in halogenated solvents: although the
εr value of dibromomethane (εr = 7.77) is very close to that
of THF (εr = 7.52), the ICT absorption band of OD3 in
dibromomethane occurs at 481 nm compared with 443 nm
in THF. Moreover, as shown in Fig. 1b, the ICT absorption
band in iodinated solvents such as iodobenzene and
diiodomethane shows bathochromic shifts compared with
those in chlorinated and brominated solvents. The large
bathochromic shifts of ICT absorption band in iodinated
9
10
11
12
13
14
15
16
21.10 443
25.3 455
36.64 441
17
47.24 438
a
b
Dielectric constant (ref. 34). The longest wavelength absorption
maximum. c Poorly soluble

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Tetrahedron
3
(a)
in Toluene
in CHCl3
in PhBr
in THF
in CH2Br2
in Ethanol
in DMSO
350
400
450
500
550
600
Wavelength / nm
(b)
Fig. 3. Plots of the experimental absorption maximum wavenumber (ν)
of OD1–OD4 against the εr value of CH2Cl2, CH2Br2, and CH2I2.
in CH2Cl2
in CH2Br2
in CH2I2
in PhCl
in PhBr
in PhI
To elucidate the influences of solvent polarity on the ICT
bands of OD1–OD4, semi-empirical MO calculations of
the dye cation were carried out by the INDO/S method35
using the SCRF Onsager Model after geometrical
optimizations using the MOPAC/AM1 method.36 The
calculated absorption data are collected in Table 2. For all
the solvents used, the calculations show that the first
excitation bands of the dye cation are mainly assigned to a
transition from HOMO to LUMO, where HOMO is mostly
localized on the diphenylamino-carbazole moiety and
LUMOs are mostly localized on the pyridinium moiety
(Figs. 4a and b). The changes in the calculated electron
density accompanying the first electron excitation are
shown in Fig. 4c, which reveals that the ICT occurs from
the diphenylamino-carbazole moiety to the pyridinium
moiety. The calculation demonstrates that with decreasing
solvent polarity from DMSO to 1,4-dioxane the ICT
absorption bands show bathochromic shifts from 373 nm to
453 nm (Table 2). In order to see the influence of solvent
polarity on the ICT absorption bands more explicitly, the
wavenumbers (ν) of the experimental absorption maxima
for the ICT bands of OD3 and the calculated absorption
maxima for the ICT bands of the dye cation are plotted
against the εr value of solvent in Fig. 5a and Fig. 5b,
respectively. The plot of the calculated absorption
maximum against εr shows that the wavenumber increases
dramatically with the increase in εr value from 1,4-dioxane
(εr = 2.22) to dichloromethane (εr = 8.93), while in the
range of εr value between dichloromethane (εr = 8.93) and
DMSO (εr = 47.24) the wavenumber is increased gradually
(Fig. 5b). On the other hand, the profile of plot of the
experimental absorption maximum against εr differs
considerably from that of the calculation: the ICT
absorption bands of OD3 in halogeneted solvents are
400
450
500
550
600
Wavelength / nm
(c)
OD1
OD2
OD3
OD4
400
450
500
550
600
Wavelength / nm
Fig. 1. Absorption spectra of a) OD3 in various solvents, b) OD3 in
halogenated solvents, and c) OD1–OD4 in CH2Br2.
(a)
1,4-dioxane
acetone DMSO
THF
(b)
CHCl3
CH2I2
CH2Br2 CH2Cl2
OD1
OD2
OD3
OD4
Fig. 2. (a) Solvatochromic properties of OD3 in various solvents.
(b) Specific solvatochromic properties of OD1–OD4 in CH2Br2.

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4
Tetrahedron
located in the low-wavenumber range (Fig. 5a). In addition,
as shown in Fig. 5c, the plot of the experimental absorption
maximum against solvent polarity parameter ET(30) is the
profile similar to the plot of Fig. 5a. However, when the
plots of halogeneted solvents and alcohol solvents are
excluded from the plot of Fig. 5a, the profile of the plot of
Fig. 5a is similar to that of Fig. 5b. This result clearly
shows that with increasing solvent polarity of non-
halogenated solvents, the ICT absorption band of OD1–
OD4 shows a hypsochromic shift, that is, the dyes OD1–
OD4 in non-halogenated solvents exhibit
a general
negative solvatochromism.
(a)
(b)
(c)
Fig. 4. (a) HOMO and (b) LUMO of the dye OD cation. The red and
blue lobes denote the positive and negative phases of the coefficients of
the molecular orbitals. The size of each lobe is proportional to the MO
coefficient. (c) Calculated electron density changes accompanying the
first electronic excitation of the dye cation. The black and white lobes
signify decrease and increase in electron density accompanying the
electronic transition, respectively. Their areas indicate the magnitude of
the electron density change. (Light blue, green, blue, and red balls
correspond to hydrogen, carbon, nitrogen, and oxygen atoms,
respectively.)
Fig. 5. Plots of (a) the experimental and (b) calculated absorption
maximum wavenumber (ν) of OD3 against εr value of solvent. (c) Plots
of the experimental absorption maximum wavenumber (ν) of OD3
against solvent polarity parameter ET(30). The numbers correspond to
those of Tables 1 and 2, respectively. The circles in black, orange, blue,
red, purple, and green show non-halogenated solvents, fluorobenzene,
chlorinated solvents, brominated solvents, iodinated solvents, and
ethanol, respectively.
Table 2. Calculated absorption spectra for the dye OD cation
No.
1
2
3
4
5
6
7
8
Solvent
λmax [nm]
453
447
442
405
403
404
396
398
400
397
391
389
391
380
379
377
373
CI componenta
1,4-dioxane
tetrachloromethane
toluene
HOMO→LUMO (72%)
HOMO→LUMO (72%)
HOMO→LUMO (71%)
HOMO→LUMO (70%)
HOMO→LUMO (70%)
HOMO→LUMO (70%)
HOMO→LUMO (70%)
HOMO→LUMO (70%)
HOMO→LUMO (70%)
HOMO→LUMO (70%)
HOMO→LUMO (69%)
HOMO→LUMO (69%)
HOMO→LUMO (69%)
HOMO→LUMO (69%)
HOMO→LUMO (69%)
HOMO→LUMO (69%)
HOMO→LUMO (69%)
bromoform
iodobenzene
chloroform
diiodomethane
bromobenzene
fluorobenzene
chlorobenzene
THF
dibromomethane
dichloromethane
acetone
ethanol
acetonitrile
9
In order to investigate the influence of solvent on the
electronic ground-state structure of OD1–OD4, the 1H
NMR measurements in acetone-d6 of a high εr value and
THF-d8 of a relatively low εr value as the non-halogenated
solvents, and in CD2Cl2 as the halogenated solvent were
performed. The 1H NMR spectra of OD3 in acetone-d6,
10
11
12
13
14
15
16
17
DMSO
a
The transition is shown by an arrow from one orbital to another,
followed by its percentage CI (configuration interaction) component.

ACCEPTED MANUSCRIPT
Tetrahedron
5
THF-d8, and CD2Cl2 are shown in Fig. 6. Remarkable
withdrawing
group
such
as
rhodanine
and
differences were observed between the halogenated and
non-halogenated solvents: the chemical shifts of Ha, Hb, Hc,
Hd, He, and Hf show upfield shifts on changing solvents
from acetone-d6 or THF-d8 to CD2Cl2. It is worth noting
that these chemical shifts in CD2Cl2 show significantly
upfield shifts compared to those in THF-d8, although the εr
value of CH2Cl2 is close to that of THF. Awwadi et al have
demonstrated by theoretical and crystallographic studies for
halogen-halide anion interaction between the halide anion
and the halogen atom of halogenated solvents.37 For the
type of the halogen atom of halogenated solvents, the
energy of halogen-halide anion interaction follows the
order F < Cl < Br < I. Therefore, it is apparent that the
observed upfield shifts of Ha, Hb, Hc, Hd, He, and Hf on
changing solvents from acetone-d6 or THF-d8 to CD2Cl2 are
attributed to a shift of the electronic structure of OD1–OD4
depending on the order of halogen-halide anion interaction
for the type of the halogen atom of halogenated solvents. In
fact, the bathochromic shifts of ICT absorption band of
OD1–OD4 in iodinated solvents such as iodobenzene and
diiodomethane are larger than those in chlorinated and
brominated solvents (Table 1 and Fig. 1b), which is good
agreement with an increase in the energy of halogen-halide
anion interaction for the type of the halogen atom of
halogenated solvents. A more interesting result was
obtained when a comparison is made for the 1H NMR
spectra of OD1–OD4 in acetone-d6 and CD2Cl2 (Figs. 7
and 8). There are little differences in these chemical shifts
among the dyes OD1–OD4 in acetone-d6, which
adequately reflects the very similar ICT absorption bands
of OD1–OD4 in acetone (Table 1). On the other hand, the
chemical shift of Ha for the dyes OD1–OD4 in CD2Cl2
depends on the type of counter anion of the dyes, that is,
the chemical shift of Ha show the upfield shifts in order of
dicyanomethylene units.31 Consequently, our results
demonstrate that the halogen-halide anion interaction plays
some non-negligible role here, but this interaction is surely
not responsible for the specific solvatochromism in
halogenated solvents, but only for the systematic shift
within the series of dyes with various counter anions.
j
k
e
f
i
d
g
b
a
N
N
nBu
N
c
h
d
I
nBu
OD3
(a) Acetone-d6
a
i
j
b
k
h
c e
f
g
(b) THF-d8
(c) CD2Cl2
9.5
9.0
8.5
8.0
δ/ppm
7.5
7.0
Fig. 6. 1H NMR spectra of OD3 in (a) acetone-d6, (b) THF-d8, and (c)
CD2Cl2.
(a) OD1
i
j
k
f
h
e
b
a
g
c
d
(b) OD2
(c) OD3
–
soft counter anion Cl– < Br– < I– < BPh4 . Moreover, the
chemical shifts of Hb, Hc, and Hd for the dye OD4 in
CD2Cl2 show significantly upfield shifts compared to those
for the dyes OD1–OD3 in CD2Cl2, which adequately
reflects the ICT absorption bands of the dyes OD1–OD4 in
dichloromethane: the ICT absorption bands of the four dyes
in halogenated solvents show the large bathochromic shifts
in order of OD1 < OD2 < OD3 < OD4 (Table 1). Awwadi
et al have also showed that the energy of halogen-halide
anion interaction for the type of the halide anion of counter
anions follows the order I– < Br– < Cl– < F–, which is in
contrast to that for the type of halogen atoms of
halogenated solvents. However, the bathochromic shifts of
ICT absorption band of the four dyes in halogenated
solvents become larger in order of soft counter anion of the
BPh
3
m
l
(d) OD4
n
l
m
n
9.5
9.0
8.5
8.0
δ/ppm
7.5
7.0
Fig. 7. 1H NMR spectra of OD1–OD4 in acetone-d6.
(a) OD1
j
i
k
h
b
a
e
f
c
g
d
–
dyes OD1–OD4; Cl– < Br– < I– < BPh4 (Fig. 3), which is
(b) OD2
exactly opposite to an increase in the energy of halogen-
halide anion interaction for the type of the halide anion of
counter anions. Nevertheless, the 1H NMR spectra of OD1–
OD4 in CD2Cl2 indicate that the halogenated solvents can
significantly enhance the ICT characteristic of D-π-A type
pyridinium dye with soft counter anion, leading to large
bathochromic shift of ICT absorption band in halogenated
solvents. On the other hand, the specific solvatochromism
of dyes in halogenated solvents is also observed for neutral
(non-ionic) D-π-A dyes having strong electron-
(c) OD3
(d) OD4
BPh
3
m
l
n
l
m
n
9.5
9.0
8.5
8.0
δ/ppm
7.5
7.0
Fig. 8. 1H NMR spectra of OD1–OD4 in CD2Cl2.

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6
Tetrahedron
Conclusions
NMR (500 MHz, acetone-d6): δ = 0.84 (t, J = 7.0 Hz, 3H),
1.01 (t, J = 7.5 Hz, 3H), 1.26–1.32 (m, 2H), 1.48–1.52 (m,
2H), 1.74–1.81 (m, 2H), 2.13–2.17 (m, 2H), 4.42 (t, J = 7.0
Hz, 2H), 4.85 (t, J = 7.0 Hz, 2H), 6.98 (dd, J = 1.5 and 8.0
Hz, 1H), 7.08–7.12 (m, 2H), 7.14–7.18 (m, 4H), 7.24 (d, J
= 1.5 Hz, 1H), 7.32–7.37 (m, 4H), 7.91 (dd, J = 1.5 and 8.5
Hz, 1H), 8.13 (d, J = 8.5 Hz, 1H), 8.31 (d, J = 8.5 Hz, 1H),
8.38 (d, J = 1,5 Hz, 1H), 8.72 (d, J = 7.0 Hz, 2H), 9.22 (d, J
= 7.0 Hz, 2H) ppm. 13C NMR (500 MHz, CDCl3): δ = 13.5,
13.8, 19.4, 20.4, 31.1, 33.6, 42.8, 60.6, 103.6, 108.0, 116.8,
117.1, 118.4, 120.7, 121.8, 123.3, 124.4, 124.6, 126.8,
128.9, 129.3, 141.2, 143.3, 144.4, 147.8, 148.4, 157.1 ppm.
HRMS (ESI): calcd. for [M–Cl]+ 524.30602; found
524.30609.
In order to gain greater insight into the influences of the
electronic structures of D-π-A type pyridinium dye on the
specific solvatochromism in halogenated solvents, we have
designed and synthesized D-π-A type pyridinium dyes
OD1–OD4 bearing various counter anions (X– = Cl–, Br–, I–,
–
or BPh4 ). The dyes OD1–OD4 showed the specific
solvatochromism, leading to large bathochromic shift of
ICT absorption band in halogenated solvents. It was found
that the bathochromic shifts of ICT absorption band of
OD1–OD4 in iodinated solvents are larger than those in
chlorinated and brominated solvents, which is good
agreement with an increase in the energy of halogen-halide
anion interaction for the type of the halogen atom of
halogenated solvents. The 1H NMR study indicates that the
halogenated solvents can significantly enhance the ICT
characteristic of D-π-A type pyridinium dye with soft
counter anion, leading to large bathochromic shift of ICT
absorption band in halogenated solvents. Furthermore, this
study revealed that the bathochromic shifts of ICT
absorption band of the four dyes in halogenated solvents
become larger in order of soft counter anion of the dyes
4.3. Synthesis of 1-butyl-4-(9-butyl-7-(diphenylamino)-
9H-carbazol-2-yl)pyridinium bromide (OD2)
A solution of 1 (0.35 g, 0.75 mmol) and 1-bromobutane
(8.2 g) in dry acetonitrile (90 ml) was stirred at 80 ˚C for 4
days. After concentrating under reduced pressure, the
resulting residue was subjected to reprecipitation from
CH2Cl2-hexane to give OD2 (0.40 g, yield 89 %) as dark
brown solids; decomposition 263 °C. IR (ATR): ν = 1623
–
OD1–OD4; Cl– < Br– < I– < BPh4 , which is exactly
1
opposite to an increase in the energy of halogen-halide
anion interaction for the type of the halide anion of counter
anions. Consequently, our results demonstrate that the
halogen-halide anion interaction plays some non-negligible
role here, but this interaction is surely not responsible for
the specific solvatochromism in halogenated solvents, but
only for the systematic shift within the series of dyes with
various counter anions. Further studies on the specific
solvatochromism of D-π-A type pyridinium dyes bearing
various counter anions are now in progress to gain greater
insight into the influences of number of halogen atoms of
halogenated solvents on the specific solvatochromism.
cm-1. H NMR (500 MHz, acetone-d6): δ = 0.84 (t, J = 7.5
Hz, 3H), 1.01 (t, J = 7.5 Hz, 3H), 1.26–1.34 (m, 2H), 1.46–
1.53 (m, 2H), 1.76–1.81 (m, 2H), 2.13–2.17 (m, 2H), 4.44
(t, J = 7.0 Hz, 2H), 4.87 (t, J = 7.5 Hz, 2H), 6.98 (dd, J =
1.5 and 8.0 Hz, 1H), 7.08–7.12 (m, 2H), 7.15–7.18 (m, 4H),
7.24 (d, J = 1.5 Hz, 1H), 7.33–7.37 (m, 4H), 7.92 (dd, J =
1.5 and 8.0 Hz, 1H), 8.13 (d, J = 8.5 Hz, 1H), 8.31 (d, J =
8.0 Hz, 1H), 8.42 (d, J = 1,5 Hz, 1H), 8.74 (d, J = 7.0 Hz,
2H), 9.26 (d, J = 7.0 Hz, 2H) ppm. 13C NMR (500 MHz,
CDCl3): δ = 13.5, 13.9, 19.4, 20.4, 31.1, 33.6, 42.9, 60.6,
103.6, 108.0, 116.8, 117.1, 118.4, 120.7, 121.8, 123.3,
124.4, 124.6, 126.8, 128.8, 129.3, 141.1, 143.3, 144.3,
147.7, 148.4, 157.1 ppm. HRMS (ESI): calcd. for [M–Br]+
524.30602; found 524.30621.
Experimental section
4.1. General
4.4. Synthesis of 1-butyl-4-(9-butyl-7-(diphenylamino)-
9H-carbazol-2-yl)pyridinium iodide (OD3)
TG-DTA was performed with a SII TG/DTA 6200. IR
spectra were recorded on a Perkin Elmer Spectrum One
FT-IR spectrometer by ATR method. High-resolution mass
spectral data were acquired on a Thermo Fisher Scientific
A solution of 1 (0.3 g, 0.64 mmol) and 1-iodobutane (7.1 g)
in dry acetonitrile (90 ml) was stirred at 80 ˚C for 70 h.
After concentrating under reduced pressure, the resulting
residue was subjected to reprecipitation from CH2Cl2-
hexane to give OD3 (0.33 g, yield 79 %) as orange solids;
1
LTQ Orbitrap XL. H NMR and 13C NMR spectra were
1
recorded on
a
Varian-500 (500 MHz) FT NMR
decomposition 276 °C. IR (ATR): ν = 1620 cm-1. H NMR
spectrometer with tetramethylsilane as an internal standard.
Absorption spectra of solution (2×10–5 M – 7×10–5 M) were
observed with a Hitachi U-2910 spectrophotometer.
(500 MHz, acetone-d6): δ = 0.84 (t, J = 7.5 Hz, 3H), 1.01 (t,
J = 7.5 Hz, 3H), 1.28–1.32 (m, 2H), 1.48–1.53 (m, 2H),
1.76–1.82 (m, 2H), 2.12–2.17 (m, 2H), 4.37 (t, J = 7.0 Hz,
2H), 4.86 (t, J = 7.5 Hz, 2H), 6.98 (dd, J = 1.5 and 8.0 Hz,
1H), 7.06–7.12 (m, 2H), 7.14–7.18 (m, 4H), 7.24 (d, J = 1.5
Hz, 1H), 7.32–7.37 (m, 4H), 7.92 (dd, J = 1.5 and 8.5 Hz,
1H), 8.13 (d, J = 8.0 Hz, 1H), 8.31 (d, J = 8.5 Hz, 1H), 8.41
(d, J = 1,5 Hz, 1H), 8.74 (d, J = 7.0 Hz, 2H), 9.22 (d, J =
7.0 Hz, 2H) ppm. 13C NMR (500 MHz, acetone-d6): δ =
13.8, 14.2, 20.1, 21.0, 31.9, 34.1, 43.2, 61.3, 105.0, 109.8,
117.8, 118.1, 119.7, 121.6, 122.9, 124.2, 125.3, 125.4,
127.3, 130.3, 130.5, 142.2, 144.2, 145.2, 148.9, 149.1,
4.2. Synthesis of 1-butyl-4-(9-butyl-7-(diphenylamino)-
9H-carbazol-2-yl)pyridinium chloride (OD1)
A solution of 1 (0.35 g, 0.75 mmol) and 1-chlorobutane
(19.3 g) in dry toluene (50 ml) was stirred at 80 ˚C for 7
days. After concentrating under reduced pressure, the
resulting residue was subjected to reprecipitation from
CH2Cl2-hexane to give OD1 (0.17 g, yield 41 %) as yellow
solids; decomposition 256 °C. IR (ATR): ν = 1623 cm-1. 1H

ACCEPTED MANUSCRIPT
Tetrahedron
7
157.9 ppm. HRMS (ESI): calcd. for [M–I]+ 524.30602;
References
found 524.30609.
1. Reichardt, C. Solvents and Solvent Effects in Organic
Chemistry, WILEY-VCH, Weinheim, 2003.
2. Dawber, J. G.; Williams, R. A. J. Chem. Soc., Faraday Trans.
1 1986, 82, 3097–3112.
4.5. Synthesis of 1-butyl-4-(9-butyl-7-(diphenylamino)-
9H-carbazol-2-yl)pyridinium tetraphenylborate (OD4)
3. Dawber, J. G.; Williams, R. A. J. Chem. Soc., Faraday Trans.
1993, 89, 55–57.
4. Reichardt, C. Chem. Soc. Rev. 1992, 21, 147–153.
5. Laus, G.; Schottenberger, H.; Wurst, K.; Schütz, J.; Ongania,
K.-H.; Horvatch, U. E. I.; Schwärzler, A. Org. Biomol. Chem.
2003, 1, 1409–1418.
6. Masternak, A.; Wenska, G.; Milecki, J.; Skalski, B.; Franzen,
S.; J. Phys. Chem. A 2005, 109, 759–766.
7. Sarkar, A.; Trivedi, S.; Pandey, S. J. Phys. Chem. B 2008,
OD3
tetraphenylborate salt OD4 as dark brown solids by
precipitation from acetonitrile/water NaBPh4;
was
metathesized
to the
corresponding
decomposition 187 °C. IR (ATR): ν = 1621, 732, 702 cm-1.
1H NMR (500 MHz, acetone-d6): δ = 0.84 (t, J = 7.5 Hz,
3H), 1.00 (t, J = 7.5 Hz, 3H), 1.25–1.31 (m, 2H), 1.45–1.50
(m, 2H), 1.76–1.82 (m, 2H), 2.12–2.17 (m, 2H), 4.41 (t, J =
7.0 Hz, 2H), 4.77 (t, J = 7.5 Hz, 2H), 6.75–6.79 (m, 3H),
6.92–6.97 (m, 6H), 6.98 (dd, J = 2.0 and 8.5 Hz, 1H), 7.09–
7.12 (m, 2H), 7.14–7.17 (m, 4H), 7.24 (d, J = 2.0 Hz, 1H),
7.33–7.36 (m, 10H), 7.89 (dd, J = 2.0 and 8.5 Hz, 1H), 8.13
(d, J = 8.5 Hz, 1H), 8.30–8.32 (m, J = 8.5 Hz, 2H), 8.65 (d,
J = 7.0 Hz, 2H), 9.06 (d, J = 7.0 Hz, 2H) ppm. 13C NMR
(500 MHz, acetone-d6): δ = 13.8, 14.1, 20.1, 21.0, 31.9,
34.0, 43.2, 61.4, 105.0, 109.6, 117.8, 118.1, 119.8, 121.7,
122.3, 122.9, 124.2, 125.3, 125.5, 126.00, 126.02, 126.05,
126.07, 127.3, 130.3, 130.5, 137.01, 137.03, 137.04, 137.05,
142.2, 144.2, 145.1, 148.9, 149.1, 157.9, 164.4, 164.8,
165.2, 165.6 ppm. HRMS (ESI): calcd. for [M–BPh4]+
524.30602; found 524.30591.
112, 9042–9049.
8. Huang, Y.; Cheng, T.; Li, F.; Luo, C.; H. Huang, C.; Cai, Z.;
Zeng, X.; Zhon, J. Eur. J. Org. Chem. 2008, 4475–4481.
9. Aimi, J.; Nagamine, Y.; Tsuda, A.; Muranaka, A.; Uchiyama,
M.; Aida, T. Angew. Chem. 2008, 120, 5231–5234; Angew.
Chem. Int. Ed. 2008, 47, 5153–5156.
10. Bolz, I.; Schaarschmidt, D.; Rüffer, T.; Lang, H.; Spange, S.
Angew. Chem. 2009, 121, 7576–7579; Angew. Chem. Int. Ed.
2009, 48, 7440–7443.
11. Bureš, F.; Pytela, O.; Kivala, M.; Diederich, F. J. Phys. Org.
Chem. 2011, 24, 274–281.
12. (a) Kulinich, A. V.; Derevyanko, N. A.; Mikitenko, E. K.;
Ishchenko, A. A. J. Phys. Org. Chem. 2011, 24, 732–742; (b)
Hrobárik, P.; Hrobáriková, V.; sigmundová, I.; Zahradník, P.;
Fakis, M.; Polyzos, I.; Persephonis, P. J. Org. Chem. 2011, 76,
8726–8736; (c) Giordano, L.; Shvadchak, V. V.; Fauerbach, J.
A.; Jares-Erijman E. A.; Jovin, T. M. J. Phys. Chem. Lett.
2012, 3, 1011–1016.
13. (a) Gawinecki, R.; Trzebiatowska K. Polish J. Chem. 2001,
75, 231–239; (b) Turshatov, A. A.; Möbius, D.; Bossi, M. L.;
Hell, S. W.; Vedernikov, A. I.; Lobova, N. A.; Gromov, S. P.;
Alfimov, M. V.; Zaitsev, S. Y. Langmuir 2006, 22, 1571–
1579; (c) Hrobárik, P.; Horváth, B.; Sigmundová, I.;
Zahradník, P.; Malkina, O. L. Magn. Reson. Chem. 2007, 45,
942–953.
14. Coe, B. J.; Harris, J. A.; Hall, J. J.; Brunschwig, B. S.; Hung,
S.-T.; Libaers, W.; Clay, K.; Coles, S. J.; Horton, P. N.; Light,
M. E.; Hursthouse, M. B.; Garín, J.; Orduna, J. Chem. Mater.
2006, 18, 5907–5918.
15. Jacques, P. J. Phys. Chem. 1986, 90, 5535.
16. Gaines, G. L. Jr. Angew. Chem. 1987, 99, 346–348; Angew.
Chem. Int. Ed. 1987, 26, 341–342.
4.6. Computational methods
The semi-empirical calculations were carried out with the
WinMOPAC Ver. 3.9 package (Fujitsu, Chiba, Japan).
Geometry calculation of compound 2 in the ground state
was made using the AM1 method.36 The geometry was
completely optimized (keyword PRECISE) by the
eigenvector following routine (keyword EF). Experimental
absorption spectra of the compound was compared with
their absorption data by the semi-empirical method
INDO/S
(intermediate
neglect
of
differential
overlap/spectroscopic)35 using the SCRF Onsager Model.
All INDO/S calculations were performed using single
excitation full SCF/CI (self-consistent field/configuration
interaction), which includes the configuration with one
electron excited from any occupied orbital to any
unoccupied orbital, where 100 configurations were
considered [keyword CI (15 15)].
17. Testoni, F. M.; Riberio, E. A.; Giusti, L. A.; Machado, V. G.
Spectrochim. Acta A 2009, 71, 1704–1711.
18. Botrel, A.; Beuze, A.; Jacques, P.; Strub, H. J. Chem. Soc.
Faraday Trans. 1984, 80, 1235–1252.
19. Morley, J. O.; Morley, R. M.; Docherty, R.; Charlton, M. H.;
J. Am. Chem. Soc. 1997, 119, 10192–10202.
20. Huang, Y.; Cheng, T.; Li, F.; Luo, C.; Huang, C. H.; Cai, Z.;
Zeng, X.; Zhon, J. J. Phys. Chem. B 2002, 106, 10031–10040.
21. Panigrahi, M.; Dash, S.; Patel, S.; Behera, P. K.; Mishra, B. K.
Spectrochim. Acta A 2007, 68, 757–762.
Keywords: Pyridinium dye; Solvatochromism; Donor-pi-
acceptor system; Halogenated solvent; Halogen-halide
anion interaction
Acknowledgments
22. Dumur, F.; Mayer, C. R.; Dumas, E.; Miomandre, F.; Frigoil,
M.; Sécheresse, F. Org. Lett. 2008, 10, 321–324.
23. Abdel-Halim, S. T.; Awad, M. K. J. Mol. Struct. 2009, 920,
323–341.
24. Ooyama, Y.; Asada, R.; Inoue, S.; Komaguchi, K.; Imae, I.;
Harima, Y. New J. Chem. 2009, 33, 2311–2316.
25. Hrobárik, P.; Sigmundová, I.; Zahradník, P.; Kasák, P.; Arion,
V.; Franz, E.; Clays, K. J. Phys. Chem. C 2010, 114, 22289–
22302.
This work was supported by the Japan Society for the
Promotion of Science (JSPS) (Grants-in-Aid for Scientific
Research (B) (23350097) and (C) (24550225)). Y. O. also
acknowledges the UBE Foundation.
26. Hou, J.; Wu, X. Synth. Met. 2011, 161, 1194.

ACCEPTED MANUSCRIPT
8
Tetrahedron
27. Gáplovský, A.; Donovalová, J.; Magdolen, P.; Toma, S.;
Zahradník, P. Spectrochim. Acta A 2002, 58, 363–371.
28. Laage, D.; Thompson, W. H.; Blanchard-Desce, M.; Hynes, J.
T. J. Phys. Chem. A 2003, 107, 6032–6046.
Kawano, Y.; Carvalho, L. R. F. Sens. Actuators B Chem.
2008, 131, 646–651.
33. (a) Ooyama, Y.; Inoue, S.; Nagano, T.; Kushimoto, K.;
Ohshita, J.; Imae, I.; Komaguchi, K.; Harima, Y. Angew.
Chem. 2011, 123, 7567–757; Angew. Chem. Int. Ed. 2011, 50,
7429–7433; (b) Ooyama, Y.; Nagano, T.; Inoue, S.; Imae, I.;
Komaguchi, K.; Ohshita, J.; Harima, Y. Chem. Eur. J. 2011,
17, 14837–14843.
34. Lide, D. R. ed., CRC Handbook of Chemistry and Physics,
83rd ed., CRC, 2002.
35. (a) Ridley, J. E.; Zerner, M. C.; Theor. Chim. Acta 1973, 32,
111–134; (b) Ridley, J. E.; Zerner, M. C.; Theor. Chim. Acta
1976, 42, 223–236; (c) Bacon, A. D.; Zerner, M. C.; Theor.
Chim. Acta 1979, 53, 21–54.
36. Dewar, M. J. S.; Zoebisch, E. G.; Healy, E. F.; Stewart, J. J. P.
J. Am. Chem. Soc. 1985, 107, 3902–3909.
37. (a) Awwadi, F. F.; Willett, R. D.; Peterson, K. A.; Twamley,
B. Chem. Eur. J. 2006, 12, 8952–8960; (b) Awwadi, F. F.;
Willet, R. D.; Peterson, K. A.; Twamley, B. J. Phys. Chem. A
2007, 111, 2319–2328;
29. Sarkar, A.; Trivedi, S.; Pandey, S. J. Phys. Chem. B 2003,
107, 7896–7902.
30. Ooyama, Y.; Kushimoto, K.; Oda, Y.; Tokita, D.; Yamaguchi,
N.; Inoue, S.; Nagano, T.; Harima, Y.; Ohshita, J.
Tetrahedron 2012, 68, 8577–8580.
31. (a) Dentani, T.; Kubota, Y.; Funabiki, K.; Jin, J.; Yoshida, T.;
Minoura, H.; Matsui, M.; New J. Chem. 2009, 33, 93–101; (b)
Baheti, A.; Singh, P.; Thomas, K. R. J. Dyes Pigm. 2011, 88,
195–203; (c) Hagimori, M.; Mizunuma, N.; Yokota, K.;
Nishimura, Y.; Suzuta, M.; Tai, C.-K.; Wang, B.-C.; Wang,
S.-L.; Shih, T.-L.; Wu, H.-H.; Kawashima, K.; Kawashima,
S.; Tominaga, Y. Dyes Pigm. 2012, 92, 1069–1074; (d) Fakis,
M.; Hrobárik, P.; Stathatos, E.; Giannetas, V.; Persephonis, P.
Dyes Pigm. 2013, 96, 304–312.
32. (a) Masila, M.; Sargent, A.; Sadik, O. A. Electroanalysis
1998, 10, 312–320; (b) Li, R. W. C.; Ventura, L.; Gruber, J.;