Technical Field
The present invention relates to viologen derivatives
as an electrochromic material having improved stability and
lifetime, a metal oxide electrode including the same, and an
electrochromic device using the viologen derivative as an
electrochromic material.
Background Art
In general, the so-called "electrochromism" is a
phenomenon in which a color change arises depending on
potentials of an applied electric field. Use of the
electrochromism results in production of electro-
photoswitchable devices such as electrochromic devices,
information memory devices, and solar cells. Typical
electrochromic materials include inorganic metal oxides such
as tungsten trioxide (WO3) , nickel oxide (NiO) and titanium
dioxide (TlO2) , and organic electrochromic materials
including bipyridinium salt (viologen) derivatives, quinone
derivatives such as anthraquinone and azine derivatives such
as phenothiazine.
Though the electrochromism was known in 1961,
practical use and commercial mass production of
electrochromic devices have been limited because of their
shortcomings, such shortcomings being that it is difficult
to realize multiple colors, coloring/bleaching rates are
low, it is difficult to accomplish complete bleaching, and
electrochromic materials tend to be damaged easily during
repeated coloring/bleaching cycles due to their poor
stability.
US Patent No. 5,441,827 (Graetzel et al.) discloses a
device such as a photocell, photochromic device or an

electrochromic device, having high surface area of an
electrode, high concentration of electroactive materials,
high efficiency and fast response speed, the device being
manufactured by coating an electroactive organic material,
as a monolayer, onto the surface of a nanoporous metal oxide
thin film electrode obtained by sintering metal oxide
nanoparticles. The device substantially solves the problems
with which electrochromic devices according to the prior art
are faced.
PCT International Publication No. WO 98/352 67
(Fitzmaurice et al.) discloses an electrochromic device
capable of repeating coloring/bleaching cycles 10,000 times
or more at room temperature, the device being a more
specified version of the above-mentioned metal oxide thin
film-based electrochromic device. However, lifetime of
electrochromic devices should be increased to 100,000 cycles
or more in order to commercialize electrochromic devices and
to expand application of electrochromic devices.
Disclosure of the Invention
Viologen compounds are those containing 4,4'-
bipyridinium, and have three oxidation states, i.e., bipm2+,
bipm+ and bipm0, as represented by the following scheme:

Particularly, the redox reaction of bipm24 ↔ bipm+
occurs at redox potential E1 and is reversible. Though the
redox reaction of bipm+ ↔ bipm0 occurs at redox potential of
E2, it is frequently irreversible. Bipm0 is chemically
unstable and thus tends to react with molecular oxygen or
other solvent molecules to be transformed into a molecule

having a different chemical structure, thereby losing its
function as an electrochromic material. Redox reactions of a
bipyridinium ion occur at E1 and E2, in turn. However, the
half wave potentials E1 and E2 are merely the voltage values
where oxidation rate becomes equal to reduction rate so as
to accomplish a dynamic equilibrium state. Moreover, redox
reactions occur not only at the half wave potentials but
continuously occur at any other potentials, and each of
bipm2+, bipm+ and bipm0 is present at different mole
fractions. Distribution of each chemical species according
to potential follows the Boltzman Distribution. Therefore,
the present inventors have made an attempt to decrease the
mole fraction of bipm0 at the half wave potential E1 by
increasing AE that is a potential difference, between E1 and
E2. We thought that a decrease in the mole fraction of bipm0
species at the half wave potential E1 might result in
improvement in lifetime of electrochromic device's, because
the state of bipm0 is chemically unstable and has a strong
tendency toward irreversible redox reactions.
Under these circumstances, we introduced various
regulator groups into viologen derivatives to increase ∆E. .
As a result, we found an electrochromic material based on a
viologen derivative and ' an electrochromic device showing
higher optical density and having an improved lifetime.
According to an aspect of the present invention, there
is provided an electrochromic material including a viologen
compound having a regulator group linked to 4,4'-
bipyridinium having three types of oxidation states, i.e.,
bipm2+, bipm+ and bipm0, as represented by the following
scheme, the regulator group being capable of increasing ∆E
that is a potential difference between E1 and E2:


wherein each of E1 and E2 represents a redox potential.
According to another aspect of the present invention,
the re is provided an electrochromic material including a
viologen compound having an electropositively charged
cationic regulator group linked to 4,4'-bipyridinium.
According to still another aspect of the present
invention, there is provided an electrochromic material
including a viologen compound having a redox couple
regulator group linked to 4,4'-bipyridinium, the redox
couple regulator group being capable of forming a redox
couple electrically with a bipyridinium ring.
According to still another aspect of the present
invention, there are provided a metal oxide electrode coated
with the above-described electrochromic material and an
electrochromic device including the .same electrochromic
material.
According to still another aspect of the present
invention, the present invention provides a compound
represented by the following formula 1:

wherein each of R1, R2, R4 and R5 independently or
simultaneously represents H, a C1-C6 alkyl group, OH, OR9"',
CN, NO2, COOH, CO2R97, CONH2, CONR982 or NR982 (preferably, each
of R1, R2, R4 and R5 represents H) ; each of R97 and R9B
represents a C1-C6 alkyl group, preferably a C1-C2 alkyl

group; and either or both of linker 1 and linker 2 may be
present, as necessary.
Typical examples of the compound represented by
formula 1 include a compound represented by the following
formula 1-1:

wherein each of R1, R2, R4 and R5 independently or
simultaneously represents H, a C1-C6 alkyl group, OH, OR97,
CN, NO2, COOH, CO2R97, CONH2, CONR982 or NR982 (preferably, each
of R1, R2, R4 and R5 represents H) ; and each of R97 and R98
represents a C1-C6 alkyl group, preferably a C1-C2 alkyl
group.
Hereinafter, the present invention will be explained
in more detail.
A viologen compound has a structure in which two
pyridinium rings are attached to each other as depicted in
the following scheme:

When a viologen compound is present in the state of
bipm2+, two pyridinium rings are orthogonal to each other and
has no resonance structure between them. Therefore, the
state of bipm2+ is a very stable, colorless and transparent

state. However, while bipm2+ accepts an electron to be
reduced to the state of bipm+, two pyridinium rings rotate
to be present on the same plane and electric charges are
delocalized according to the occurrence of the resonance
between two pyridinium rings, thereby producing a deep
color. In the state of bipm0, two pyridinium rings form a
complete planar structure and steric hindrance is generated
between 3,3'-hydrogen atoms, thereby making the molecule
unstable. In this state, other molecules such as solvent
molecules may cause addition-elimination reactions on carbon
atoms of the ring. Therefore, the viologen compound may be
transformed into completely different types of molecules or
may be subjected to ring opening in the presence of heat or
light to be decomposed into completely different molecules,
such transformations being irreversible. The resultant
compound does not have electrochromic activity any longer.
Additionally, when the viologen molecule has a planar
structure, an. aromatic-aromatic stacking phenomenon'- may
occur due to pi-pi (π-π) interactions. Therefore, adjacent
viologen molecules aggregate among themselves. Each of the
states of bipm+ and bipm0 having a planar structure is a
high-energy state by nature. Aggregation of high-energy
molecules may cause a self-quenching phenomenon and side
reactions including polymerization reactions, followed by an
irreversible transformation of an electrochromic material
resulting in reduced lifetime in an electrochromic device.
Because such collapses and irreversible changes in
viologen derivatives occur largely in the state of bipm0, it
is necessary to minimize the mole fraction occupied by bipm0
at a drive voltage in order to obtain an electrochromic
viologen derivative having longer lifetime.
To accomplish this, according to the technical gist of
the present invention, a bipyridinium ion is provided with a

regulator group at its end, the regulator group being
suitable to stabilize the state of bipm+ and to prevent bipm+
from being transformed into bipm0. Such regulator groups can
increase ∆E that is a potential difference between E1
(electrochemical potential where a transformation into bipm+
occurs) and E2 (electrochemical potential where a
transformation into bipm0 occurs).
The regulator group preferably increases ∆E by 0.04V
or more.
Relative mole fractions of various chemical species
follow the Boltzman Distribution, wherein the number of each
chemical species is in direct proportion to the electric
current used for redox reactions. More particularly, the
electric current used for redox reactions at each electric
potential is determined by the following formula (see, Allen
J. Bard, and Larry R. Faulkner, "Electrochemical Methods:
Fundamentals and Applications", John Wiley & Sons, 1980,'
Chap. 6) :
I - nFAC0* ( π Do σ ) 1/2 (σt)
wherein
I is the maximum current resulting from redox
reactions at a given applied potential;
n is the number of electrons coming in and out
according to redox reactions,-
F is the Faraday constant;
C0 is the concentration of an oxidative/reductive
species in solution;
D0 is a diffusion coefficient; and
X(σt) is an electric current function resulting from
reversible charge transfer.
Particularly, (π ) 1/2X (π t) is a function having an
exponential relationship with an electric potential
difference between applied potential and half wave

potential. More particularly, whenever the applied potential
varies from the E1/2 (half-wave potential) value by 20 mV,
the function, (it) 1/2x ( σt) decreases in the ratio of about
1/2. In other words, whenever AE increases by 20 mV (0.02V),
the mole fraction of bipm0 at the applied voltage decreases
in the ratio of 1/2. Therefore, when ∆E varies by 40 mV or
more, the mole fraction of bipm0 decreases by 1/4 or less of
the initial value, and thus it is possible to observe a
significant increase in the lifetime of an electrochemical
device.
According to the present invention, the regulator
group capable of increasing ∆E includes: (1) an cationic
functional group; and (2) an additional redox-coupled
functional group capable of forming a redox couple
electrically with a bipyridinium ring.
An electric potential where redox reactions occur is
determined by the energy level; of each oxidation state under
a given electric field.
A cationic regulator group increases positive charge
density in the whole molecule and changes the charge density
of a bipyridinium ring at each oxidation state, thereby
changing energy level at each oxidation state. Because a
change in energy level at each oxidation state is followed
by a change in redox potentials, it is possible to control
∆E. Additionally, cationic properties increased by a
cationic regulator group can decrease aggregation of
adjacent viologen molecules due to the effect of repulsive
force between molecules having the same charge. Furthermore,
such increased cationic properties can inhibit a self-
quenching phenomenon and side reactions including
polymerization reactions. As a result, it is possible to
increase the lifetime of a viologen derivative.
Meanwhile, when the regulator group is an additional

redox-coupled functional group capable of forming a redox
couple electrically with a bipyridinium ring, a change in
redox states of the regulator group affects the charge
distribution of the whole molecule and changes the redox
potential of a bipyridinium ring. Therefore, it is possible
to increase the lifetime of an electrochromic viologen
derivative.
Such regulator groups may be linked directly to a
viologen derivative without any linker or may be attached to
a viologen derivative by means of a linker (linker 1).
Additionally, the viologen derivative according to the
present invention may further comprise an anchor group
capable of anchoring to a metal oxide electrode so as to
show its function sufficiently when it is coated on the
metal oxide electrode for an electrochromic ' device. Such
anchor groups may be linked directly to a viologen
derivative without any linker or may be attached to a
viologen derivative by means of a linker (linker 2), in the
same manner as the regulator group.
. Therefore, according to a preferred embodiment of the
present invention, there is provided a viologen derivative
as an electrochromic material, the viologen derivative being
[regulator group]-[linker 1]-[bipyridinium (bipm)]-[linker
2]-[anchor group], as depicted in the following formula:

The cationic regulator groups that may be used in the
present invention include substituted pyridinium derivatives
represented by the following formula 2, substituted
quinolinium derivatives represented by the following formula
3, substituted imidazolium derivatives represented by the

following formula 4 and tetraalkylammonium derivatives
represented by the following formula 5:

wherein each of R1, R2, R3, R4 and R5 independently or
simultaneously represents H, a C1-C6 alkyl group, OH, OR97,
CN, NO2, COOH, CO2R97, CONH2, CONR982 or NR982 (preferably, each
of R1, R2, R4 and R5 represents H, and R3 represents N(CH3)2 or
OR97) ; and each of R97 and R98 represents a C1-C6 alkyl group,
preferably a C1-C2 alkyl group.

wherein each of R6, R7, R8, R9, R10, R11 and R12
independently or simultaneously represents H, a C1-C6 alkyl
group, OH, OR97, CN, NO2, COOH, CO2R97, CONH2, CONR982 or NR982
(preferably each of R6, R7, R9, R10, R11 and R12 represents H,
and R8 represents N(CH3)2 or OR97); and each of R97 and R98
represents a C1-C6 alkyl group, preferably a C1-C2 alkyl
group.
[formula 4]


wherein each of R13, R14, R15 and R16 independently or
simultaneously represents H or a C1-C6 alkyl group
(preferably, each of R13, R15 and R16 represents H and R14
represents a C1-C6 alkyl group).

wherein each of R17, R18 and R19 independently or
simultaneously represents H or a C1-C12 alkyl group,
preferably a C1-C4 alkyl group.
The redox couple-functional groups that may be used in
the present invention include ferrocene derivatives
represented by the following formula 6; azine derivatives
represented by the following formulae 7 and 8, including
phenothiazines, phenoxazines and phenazines; quinone
derivatives represented by the following formulae 9-13,
including benzoquinones, hydroquinones, naphtoquinones,
anthraquinones and acenaphthene quinones (formula 13) ; and
multicyclic aromatic compounds including pyrenes represented
by the following formula 14, perylenes represented by the
following formula 15 and dancyls represented by the
following formula 16:
[formula 6]
substituted ferrocene regulator groups


wherein each of R20 to R28 independently or
simultaneously represents H or a C1-C6 alkyl group
(preferably, all of R20 to R28 simultaneously represents H or
methyl); X represents CH2, O, S, NH, NR98 or CO2; and R98
represents a C1-C6 alkyl group, preferably a C1-C2 alkyl
group.
[formula 7]
substituted azine regulator groups

wherein X represents S, O or Se; each of R29 to R36
independently or simultaneously represents H, a C1-C6 alkyl
group, OH, OR97, CN, NO2, COOH, CO2R97, CONH2, CONR982 or NR982
(preferably, each of R29, R30, R32, R33, R35 and R36 represents
H and each of R31 and R34 represents Br, NR982 or OR9"7) ; and
each of R97 and R98 represents a C1-C6 alkyl group, preferably
a C1-C2 alkyl group,
[formula 8]
substituted azine regulator groups


wherein each of R37 to R45 independently or
simultaneously represents H, C1-C6 alkyl group, OH, OR97, CN,
NO2, COOH, CO2R97, CONH2, CONR982 or NR982 (preferably, each of
R37, R40, R41 and R44 represents H, each of R38, R39, R42 and R43
represents Br, NR982 or OR97, and R45 represents a C1-C6 alkyl
group) ; and each of R97 and R98 represents a C1-C6 alkyl
group, preferably a C1-C2 alkyl group,
[formulae 9-12]
substituted quinone regulator groups



wherein each of R46 to R63 independently or
simultaneously represents H, a C1-C6 alkyl. group, OH, OR97,
CN, NO2, COOH, CO2R97, CONH2, CONR982 or NR982 (preferably, all
of R46 to R63 simultaneously represents H) ; X represents CH2,
0, S, NH, NR98 or CO2 (wherein the position of X may be
either of a-position and b-position of anthracene in the
case of anthraquinone) ; and each of R37 and R98 represents a
C1-C6 alkyl group, preferably a C1-C2 alkyl group,
[formula 13]
substituted acenaphthene quinone regulator groups

wherein X represents CH2, O, S, NH, NR98 or CO2; each of
R84 to R88 independently or simultaneously represents H, a
C1-C6 alkyl group, OH, OR97, CN, NO2, COOH, CO2R97, CONH2,
CONR982 or NR982 (preferably, all of R84 to R88 simultaneously

represents H) ; and each of R97 and R98 represents a C1-C6
alkyl group, preferably a C1-C2 alkyl group.
[formula 14]
substituted pyrene regulator groups

wherein X represents CH2, O, S, NH, NR98 or CO2; each of
R64 to R72 independently or simultaneously represents H, a
C1-C6 alkyl group, OH, OR97, CN, NO2, COOH, CO2R97, CONH2,
CONR982 or NR982 (preferably, all of R64 to R72 simultaneously
represents H) ; and each of R97 and R98 represents a C1-C6
alkyl group, preferably a C1-C2 alkyl group,
[formula 15]
substituted perylene regulator groups

wherein X represents CH2, O, S, NH, NR98 or CO2; each of
R73 to R83 independently or simultaneously represents H, a
C1-C6 alkyl group, OH, OR97, CN, NO2, COOH, CO2R97, CONH2,
CONR982 or NR982 (preferably, all of R73 to R83 simultaneously

represents H) / and each of R97 and R98 represents a C1-C6
alkyl group, preferably a C1-C2 alkyl group.
[formula 16]
substituted dancyl regulator groups

wherein each of R89 to R94 independently or
simultaneously represents H, a C1-C6 alkyl group, OH, OR97,
CN, NO2, COOH, CO2R97, CONH2, CONR982 or NR982 (preferably, all
of R89 to R94 simultaneously represents H) ; each of R95 and R96
independently or simultaneously represents H or a C1-C6
alkyl group, preferably a C1-C2 alkyl group;and each of R97
and R98 represents a C1-C6 alkyl group, preferably a C1-C2
alkyl group.
Anchor groups that may be used in the present
invention include phosphonic acid represented by the
following formula 17, salicylic acid represented by the
following formula 18, boronic acid represented by the
following formula 19, iminodiacetic acid represented by the
following formula 20 and ortho-dihydroxyaryl (catechol)
represented by the following formula 21:



wherein X may be 0, NH, NR98, S or CO, and R98
represents a C1-C6 alkyl group, preferably a C1-C2 alkyl
group.
As described above, regulator groups or anchor groups
may be linked directly to a bipyridinium ring without any
linker or linked to a bipyridinium ring by means of a
linker. When a linker is used, the linker (linker 1, linker
2) may be an C1-C4 alkyl chain represented by the following
formula 22, xylene (-CH2-Ar-CH2-) represented by the
following formula 23, 1,3,5-triazine (C3N3) represented by
the following formula 24, or a substituted aromatic ring
represented by the following formula 25. When the linker is
an aromatic ring linker, the link may be present at ortho-,
meta- and para-positions.


wherein X may be 0, NH, NR38, S or CO, and R98
represents a C1-C6 alkyl group, preferably a C1-C2 alkyl
group.
Counterions of the viologen derivative according to
the present invention may include Cl-, Br-, BF4-, PF6-, ClO4-
and (CF3SO2)2N-.
In general, electrochromic materials according to the
present invention may be prepared as follows: 4,4'-
bipyridine is reacted with one equivalent of an anchor group
to obtain a unit formed of bipyridine having an anchor group
at one end thereof, i.e., a unit of bipyridinium-(linker)-
anchor group. The anchor group may be protected with an
ester or ketal protecting group, etc. To accomplish the
link, various types of reactions including a nucleophilic

substitution reaction, esterification reaction, addition-
elimination reaction and metal catalytic reaction may be
used depending on the kind of linker. When an addition-
elimination reaction or metal catalytic reaction is used,
the link can be made without any linker. Next, a regulator
group is linked to the pyridine ring remaining in the
resultant unit of bipyridinium-(linker)-anchor group,
directly without any linker or by using a linker, to form a
molecule of regulator group-bipyridinium-anchor group. Then,
deprotection of the anchor group may be performed to
activate the molecule, if necessary. By doing so, it is
possible to obtain an electrochromic material having a
regulator group, which is capable of being bonded to an
electrode.
The electrochromic device according to the present
invention includes a first electrode disposed on a
transparent or translucent substrate, a second electrode and
an electrolyte, wherein at least one of the.first.electrode,
second electrode and electrolyte includes the electrochromic
material according to the present invention. .
The electrodes and the electrochromic device may be
manufactured by conventional methods known to one skilled in
the art, except that the electrochromic material according
to the present invention is used (see, US Patent No.
5,441,827 and PCT International Publication No. WO
98/35267).
Hereinafter, a preferred embodiment of the method for
manufacturing the electrochromic device according to the
present invention will be described.
A nanoporous metal oxide electrode that may be used in
the present invention is prepared as follows:
Nanocrystalline metal oxide particles having an average
particle size of 2-200 nm were suspended in an organic

solvent along with an organic binder to form a paste. Metal
oxides that may be used include oxides of a metal selected
from the group consisting of titanium, zirconium, hafnium,
chrome, molybdenum, tungsten, vanadium, niobium, tantalum,
silver, zinc, strontium, iron (Fe2+ and Fe3+) , nickel and
perovskites thereof. Preferably, the metal oxide is TiO2,
WO3, MOO3, ZnO, SNO2, indium-doped tin oxide or indium-doped
zinc oxide. The organic binder has a molecular weight of
between several thousands and several millions. Particular
examples of the organic binder include- alkyl cellulose,
dextran, PMMA (poly (methyl methacrylate)) and Carbowax. The
organic solvents that may be used include methanol, ethanol,
isopropyl alcohol, dimethylglycol dimetylether,
propyleneglycol propylether, propylene glycolmethylether
acetate and terpineol. The paste is printed on the surface
of a conductive electrode by using a printing method such as
screen printing, stencil printing, spin coating or doctor
blading. The conductive electrode may be an ITO or FTO- thin
film electrode coated on the surface of glass, or a metal
electrode such as gold, silver, aluminum, copper, chrome,
chrome/silver, alloy or silver/palladium alloy. Then, the
resultant assembly of [metal oxide nanoparticle-organic
binder/conductive electrode] is sintered at high temperature
so as to burn out the organic binder and thus to form
nanopores, while the metal oxide nanoparticles are
interconnected to form a porous metal oxide electrode. Then,
the electrochromic material according to the present
invention is coated on the resultant system of [nanoporous
metal oxide electrode/conductive electrode] by using a self-
assembly process, thereby providing a working electrode for
an electrochromic device.
Counter electrodes that may be used include a
nanoporous metal oxide electrode obtained as described

above, an ITO or FTO thin film electrode coated on the
surface of glass, or a metal electrode such as gold, silver,
aluminum, copper, chrome, chrome/silver alloy or
silver/palladium alloy. A white reflective plate may be
optionally inserted between the working electrode and the
counter electrode. The white reflective plate may be formed
by coating titania or silica nanoparticles having a size of
between 200 nm and 600 nm on the surface of counter
electrode and then sintering the coated electrode at a
temperature of 200 °C or higher.
The electrochromic device according to the present
invention may be manufactured by laminating the working
electrode with the counter electrode, obtained as described
above, by means of an adhesive, injecting an electrolyte and
sealing the device. Electrolytes that may be used include
liquid electrolytes containing a lithium salt or
tetraalkylammonium salt dissolved in a solvent, ionic
liquids, gelled lithium salt electrolytes, gelled ionic
liquids and mixtures thereof.

Brief Description of the Accompanying Drawings
FIG. 1 is a graph showing variations in redox
potentials of the viologen derivatives obtained from Example
1 and Comparative Examples 1 and 2.
FIG. 2 is a schematic view showing the structure of an
electrochromic device including a metal oxide electrode
coated with the viologen derivative obtained from Example 1.
Best Mode for Carrying Out the Invention
Reference will now be made in detail to the preferred
embodiments of the present invention. It is to be understood
that the following examples are illustrative only and the
present invention is not limited thereto.

Example 1: 2- (( α ' (4 ''' -N,N-dimethylpyridinium) -4'' - α -
)-4,4'-bipyridinium) -ethyl phosphonic acid trichloride salt
(III) (PV-DMAP)

[Reaction Scheme 1]
I
1- (4' -Bromomethyl-benzyl) -4-dimethylamino-pyridinium
bromide (I) :
30 ml of THF solution containing 1 g of 4-
dimethylaminopyridine dissolved therein was added gradually
to 100 ml of THF solution containing 4.32 g of dibromo-p-
xylene dissolved therein at 4°C and the mixture was reacted
for 2 hours to form precipitate. After filtration, the
precipitate was dried under vacuum to obtain 3.23 g of
compound (I).
1H-NMR (DMSO-d6; ppm) : 8.43(2H), 7.48 (2H), 7.39(2H),
7.06(2H), 5.42(2H), 4.70(2H), 3.18(6H); MS(LC): m/z=305 (M+) .
N- (phosphono-2-ethyl) -4 ' ' -dimethylamino-pyridinitim-

4,4' -bipyridinium tribromide (II) :
4.60 g of compound (I) prepared as described above and
4.00 g of N-(diethylphosphono-2-ethyl)-4,4'-bipyridinium
bromide were dissolved in 100 ml of CH3CN and the reaction
mixture was reacted under reflux for 24 hours. After
filtration, the precipitate was dried under vacuum to obtain
6.81 g of compound (II) .
1H-NMR (D2O; ppm): 9.22 (2H), 9.19(2H), 8.64(2H),
8.60(2H), 8.09(2H,d), 7.60(2H,d), 7.48(2H), 6.93(2H),
6.00(2H), 5.42(2H), 5.07(2H), 4.17(4H), '3.23(6H), 2.86(2H),
1.29(6H).
N- (phosphono-2-ethyl) -4' ' -dimethylamino-pyridinium-4,4' -
bipyridinium trichloride (III):
6.81 g of compound (II) prepared as described above
was dissolved in 50 ml of 6N HC1 and reacted under reflux
for 24 hours. After evaporation of the solvent,
recrystallization was performed by using H2O, „ MeOH , and THF
to obtain 5.98 g of compound (III).
1H-NMR (D2O; ppm): 9.23 (4H) , 8.63(4H), 8.12 (2H),
7.65(2H), 7.53(2H), 6.03(2H), 5.45(2H), 5.01(2H), 3.26(6H),
2.57 (2H) MS(LC): m/z=489 (M+) .
[Experimental Example]
Measurement of redox potentials of viologen
derivative>
The redox potentials of compound (III) in solution
were measured by cyclic voltametry. Particularly, cyclic
current-voltage curve was determined in aqueous 0. 5M KCl
solution by using a glassy carbon electrode as a working
electrode, Pt electrode as a counter electrode and Ag/AgCl
as a reference electrode. As shown in the following Table 1
and FIG. 1, it was possible to observe the first stage of
reduction at -0.520 V (E1, reversible) and the second stage
of reduction at -0.975 V (E2, irreversible).

Ti(0-iPr)4 was hydrolyzed to form a colloidal
dispersion of TiO2 nanoparticles. The nanoparticles that
were initially formed had an average size of 7 nm. The
nanoparticles were autoclaved at 200 °C for 12 hours to
increase the average size to 12 mm. The solvent was
distilled under reduced pressure to the concentration of 160
g/1. Then 40 wt% of Carbowax 20000 (poly(ethylene oxide)
having an average molecular weight of 20,000) based on the
weight of TiO2 was added to the solution, thereby forming
white titania sol slurry with high viscosity. The slurry was
printed on an ITO transparent electrode by using a screen
printing process and the printed electrode was sintered at a
high temperature of 450°C to provide a transparent electrode
based on TiO2 having nanopores as a working electrode. As a
counter electrode, an antimony-doped tin oxide (Sb-doped
SNO2) electrode was formed in a similar manner. The surface
of the counter electrode was further coated with Ti02
nanoparticles present in the rutile phase by using a screen
printing process and then sintered to form a reflective
plate.
The transparent working electrode obtained as
described above was immersed in 50 ml of 10 mM aqueous
solution of compound (III) for 30 minutes and then washed
with 50 ml of ethanol two times. The working electrode was
dried at room temperature for 4 hours, and then a
thermosetting adhesive was applied on the working electrode
so as to be integrated with the counter electrode. Gamma-
butyrolactone solution containing 10mM of LiClO4 was
injected as an electrolyte and the resultant device was
sealed by UV curing. The resultant electrochromic device

(FIG.2) developed deep blue purple color at 1. OV and showed
no deterioration even after 500,000 times of
coloring/bleaching cycles.
Comparative Example 1: 2- (4-Benzyl-, 4 ' -bipyridinium)
ethyl phosphonic acid dichloride salt (VI) (PVB)
[Reaction Scheme 2]

3.12 g of 4,4' -Dipyridyl was mixed with 5.10 g of
bisethyl-2-bromoethyl phosphonate and the mixture was
reacted for 12 hours at room temperature. 300 ml of cold
diethylether was added thereto, followed by stirring for
additional 1 hour and filtration of precipitate. The
precipitate was washed with 50 ml of diethylether three
times and dried under vacuum to obtain 6.21 g of compound
(IV) .
To 400 ml of CH3CN containing 6.21 g of compound (IV)
dissolved therein, 3.70 g of benzyl bromide was added. Next,
the mixture was stirred under reflux for 6 hours at 80°C.
The reaction mixture was cooled to room temperature and
poured into 300 ml of cold diethylether, followed by
stirring for additional 1 hour and filtration of

precipitate. The precipitate was washed with 50 ml of CH3CN
three times and dried under vacuum to obtain 7.4 4 g of
compound (V).
1H-NMR (DMSO-d6; ppm) : 9.58 (2H) , 9.45(2H), 8.83 (4H).,
7.65(2H), 7.46(3H), 5.99(2H), 4.91(2H), 4.02(4H)f 2.76(2H),
1.21(6H).
7.44 g of compound (V) was dissolved in 150 ml of 6N
HC1 and reacted under reflux for 24 hours. After evaporation
of the solvent, recrystallization was performed by using H20,
MeOH and THF to obtain 5.27 g of compound (VI).
1H-NMR (DMSO-d6; ppm): 9.59 (2H) , 9.43(2H), 8.84 (2H),
8.80(2H), 7.65(2H), 7.46(3H), 5.98(2H), 4.89(2H), 2.63(2H).
As shown in Table 1 and FIG. 1, compound (VI) showed
the first reduction at -0.586 V (E1, reversible) and the
second reduction at -0.879 V (E2, irreversible), under the
same conditions as Example 1. An electrochromic device was
manufactured in the same manner as Example- 1, except that
compound (VI) was used instead of compound (III). The
resultant electrochromic device showed intense bluish purple
color at 1.0V and showed deterioration after 10,000 times of
coloring/bleaching cycles.
Comparative Example 2: 4,4" -bipyridinium-bis (diethyl
phosphonic acid) dichloride salt (VIII) (PVP)
[Reaction Scheme 3]


3.12 g of 4,4'-Dipyridyl was mixed with 10.1 g of
diethyl-(2-bromoethyl) phosphonate and the mixture was
reacted for 12 hours at room temperature, .500 ml of cold
diethylether was added thereto, followed by stirring for
additional 1 hour and filtration of precipitate. The
precipitate was washed with 50 ml of diethylether three
times and dried under vacuum to obtain 11.6 g of compound
(VII). 11.6 g of compound (VII) obtained as described above
was dissolved in 100 ml of 6N HCl and reacted under reflux
for 24 hours. After evaporation of the solvent,
recrystallization was performed by using H2O, MeOH and THF
to obtain 6.85 g of compound (VIII).
As shown in Table 1 and FIG. 1, compound (VIII) showed
the first reduction at -0.630 V (E1, reversible) and the
second reduction at -0.955 V (E2, irreversible), when an
Ag/AgCl reference electrode was used. An electrochromic
device was manufactured in the same manner as Example 1,
except that compound (VIII) was used instead of compound
(III). The resultant electrochromic device developed deep

blue color at 1.3V and showed deterioration after 10,000
times of coloring/bleaching cycles.

Industrial Applicability
As can be seen from the foregoing, the viologen
derivative according to the present invention is provided
with a suitable regulator group capable of increasing ∆E at
one end thereof. The viologen derivative can increase the
lifetime of an electrochromic device by 3-10 times at a low
drive voltage of 1.0V. Additionally,. the electrochromic
material according to the present invention shows ah
improved optical density compared to conventional
electrochromic materials.
While this invention has been described in connection
with what is presently considered to be the most practical
and preferred embodiment, it is to be understood that the
invention is not limited to the disclosed embodiment and the
drawings. On the contrary, it is intended to cover various
modifications and variations within the spirit and scope of
the appended claims.

We-Claim:
1. An electrochromic material, which comprises a viologen
compound having a regulator group linked to 4,4'-bipyridinium
wherein the regulator group is at least one selected from a
cationic group such as herein described and an additional redox-
coupled functional regulator group such as herein described being
capable of forming a redox couple electrically with a bipyridinium
ring.
2. The electrochromic material as claimed in claim 1, wherein
the viologen compound optionally comprises a counterion, the
counterion being CI-, Br-, BF4-, PF6-, ClO4- or (CF3SO2)2N-.
3. The electrochromic material as claimed in claim 1, wherein
the regulator group is linked directly to 4,4'-bipyridinium
without any linker, or linked to 4,4'-bipyridinium by means of a
linker (linker 1) such as herein described.
4. The electrochromic material as claimed in claim 1, wherein
an anchor group capable of being bonded to a metal oxide electrode
is optionally linked to 4,4'-bipyridinium, the anchor group being
linked directly to 4,4'-bipyridinium without any linker, or linked
to 4,4'-bipyridinium by means of a linker (linker 2).
5. The electrochromic material as claimed in claim 1, wherein
the cationic group is selected from the group consisting of
functional groups represented by the following formulae 2 to 5:


wherein each of R1, R2, R3, R4 and R5 independently or
simultaneously represents H, a C1-C6 alkyl group, OH, OR9-, CN, NO2,
COOH, CO2R97, CONH2, CONR982 or NR982; and each of R97 and R98 represents
a C1-C6 alkyl group.

wherein each of R6, R7, R5, R9, R10, R11 and R12 independently or
simultaneously represents H, a C1-C6 alkyl group, OH, OR97, CN, NO-,
COOH, CO2R97, CONH2, CONR952 or NR982; and each of R97 and R98 represents
a C1-C6 alkyl group.

wherein each of Rl3, R14, R15 and R16 independently or
simultaneously represents H or a C1-C6 alkyl group.


wherein each of R17, R18 and R19 independently or simultaneously
represents H or a C1-C12 alkyl group.
6. The electrochromic material as claimed in claim 1, wherein
the additional redox-coupled functional regulator group is
selected from the group consisting of functional groups
represented by the following formulae 6 to 16:

wherein each of R20 to R25 independently or simultaneously
represents H or a C1-C6 alkyl group; X represents CH2, O, S, NH,
NR98 or CO2; and R98 represents a C1-C6 alkyl group.


wherein X represents S, O or Se; each of R29 to R36
independently or simultaneously represents H, a C1-C6 alkyl group,
OH, OR37, CN, NO2, COOH, CO2R97, CONH2, CONR982 or NR982; and each of R97
and R58 represents a C1-C6 alkyl group.

wherein each of R37 to R45 independently or simultaneously
represents H, a C1-C6 alkyl group, OH, OR97, CN, NO2, COOH, CO2R97,
CONH2, CONR982 or NR962; and each of R97 and R98 represents a C1-C6
alkyl group.


wherein each of R46 to R63 independently or simultaneously
represents K, a C1-C6 alkyl group, OH, OR97, CN, NO2, COOH, CO:R97,
CONH2, CONR982 or NR982; X represents CH2, O, S, NH, NR98 or CO2; and
each of R97 and R93 represents a C1-C6 alkyl group.


wherein X represents CH2, O, S, NH, NR98 or CO2; each of R34 to
R88 independently or simultaneously represents H, a C1-C6 alkyl
group, OH, OR97, CN, NO2, COOH, CO2R97, CONH2, CONR982 or NR962; and
each of R97 and R98 represents a C1-C6 alkyl group.

wherein X represents CH2, O, S, NH, NR98 or CO2; each of R64 to
R72 independently or simultaneously represents H, a C1-C6 alkyl
group, OH, OR97, CN, NO2, COOH, CO2R97, CONH2, CONR982 or NR982; and
each of R97 and R98 represents a C1-C6 alkyl group.


wherein X represents CH2, O, S, NH, NR98 or CO2; each of R73 to
R83 independently or simultaneously represents H, a C1-C6 alkyl
group, OH, OR97, CN, NO2, COOH, CO2R97, CONH2, CONR982 or NR982; and
each of R97 and R98 represents a C1-C6 alkyl group.

wherein each of R89 to R94 independently or simultaneously
represents H, a C1-C6 alkyl group, OH, OR97, CN, NO2, COOH, CO2R97,
CONH2, CONR982; or NR982; each of R95 and R96 independently or
simultaneously represents H or a C1-C6 alkyl group; and each of R97
and R98 represents a C1-C6 alkyl group.
7. The electrochromic material as claimed in claim 4, wherein
the anchor group is selected from the group consisting of

functional groups represented by the following formulae 17 to 21:

wherein X represents O, NH, NR98, S or CO, and R98 represents a
C1-C6 alkyl group.
8. The electrochromic material as claimed in claim 3 or 4,
wherein the linker is represented by any one formula selected from
the group consisting of the following formulae 22 to 25:


wherein n is an integer of between 1 and 4.
[formula 23]

wherein X represents O, NH, NR98 S or CO, and R98 represents a
C1-C6 alkyl group.
9. A compound represented by the following formula 1:

wherein each of R1, R2, R4 and R5 independently or
simultaneously represents H, a C1-C6 alkyl group, OH, OR97, CN, NO2,
COOH, CO2R97, CONH2, CONR982 or NR982; each of R97 and R98 represents a
C1-C6 alkyl group; and either or both of linker 1 and linker 2 may
be present, as necessary.

10. The compound as claimed in claim 9, wherein the compound
is represented by the following formula 1-1:

wherein each of R1, R2, R4 and R5 independently or
simultaneously represents H, a C1-C6 alkyl group, OH, OR97, CN, NO2,
COOH, CO2R97, CONH2, CONR982 or NR982; and each of R97 and R98 represents
a C1-C6 alkyl group.
11. A metal oxide electrode coated with an electrochromic
material as defined in any one of claim 1.
12. An electrochromic device comprising a first electrode
disposed on a transparent or translucent substrate, a second
electrode and an electrolyte, wherein at least one of the first
electrode, second electrode and electrolyte comprises an
electrochromic material as defined in claim 1.

The invention discloses an electrochromic material, which
comprises a viologen compound having a regulator group linked to
4,4'-bipyridinium, wherein the regulator group is at least one
selected from a cationic group such as herein described and an
additional redox-coupled functional regulator group such as herein
described being capable of forming a redox couple electrically
with a bipyridinium ring.