FIELD OF INVENTION
[0001] The present disclosure broadly relates to the field of polymers, specifically
to diketopyrrolopyrrole polymers. The present disclosure also relates to a process of
preparing diketopyrrolopyrrole polymers. In addition, the present disclosure relates
5 to electrochromic materials comprising the diketopyrrolopyrrole polymers and a
device comprising the same.
BACKGROUND OF THE INVENTION
[0002] Electrochromic (EC) materials change color in response to electric field.
10 These materials find their use in many areas, such as flexible electrochromic devices
(ECDs), for example in reflective blinds, displays, smart windows, sensors, and
reflection windows, to mention a few. Also, regulating infrared and thermal radiation
is crucial for energy-saving and temperature management in homes, offices, aircraft,
and vehicles. Compared to thermochromic and photochromic materials,
15 electrochromic windows are the most adaptable and can be actively controlled for
energy-saving purposes, adaptive camouflage, civilian and military applications. In
general, electrochromic active materials made of metal oxides, small organic
molecules, and conjugated polymers are coated on two transparent electrodes
separated by an electrolyte. However, such windows do not allow for tunable control
20 of IR transmission independent of visible region modulation.
[0003] Electrochromic devices operate like batteries, with one electrode acting as an
anode and the other acting as a cathode. When no voltage is applied, the cell is in a
colored state, while a positive voltage applied to the cell achieves a bleached state
with high transmission in the visible region. These cells require complementary
25 materials, where one is oxidized, and the other is reduced. The visible region optical
modulation of state-of-the-art electrochromic windows is high, while the ones
involving near infra-red (NIR) and mid-IR are minimal. Therefore, there is a need
for ECDs that can modulate IR radiation for heat control, night vision, and optical
attenuation, which allows control over IR transmission with little or no visible light
30 variation.
2
[0004] Additionally, fibre-optic communication networks utilize a variable optical
attenuator (VOA) that is crucial in controlling light intensity, primarily in the NIR
region at the wavelengths of 1.31 and 1.55 μm, where silica optical fibers are the
most transparent. VOAs are utilized for tunable control of optical signal intensity,
5 maintaining constant signal output, and regulating signal powers for varying active
channels in amplified wavelength-division-multiplexed networks.
[0001] Current VOAs that are either in development or commercially available are
based on several mechanisms, including polymer-dispersed liquid crystals (PDLC),
mechanical optical, microelectromechanical (MEM), and thermo-optic attenuators.
10 The major challenges are to create flexible, lightweight attenuators with a fast
response time and minimal moving parts while obtaining large NIR contrast with
high visible transparency. Therefore there is a need for electrochromic materials
suitable for use as variable optical attenuators which are also capable of exhibiting
high NIR coloration efficiencies.
15
SUMMARY OF THE INVENTION
[0005] In an aspect of the present disclosure, there is provided a polymer of Formula
I
20 Formula I
wherein, R1 and R2 are independently selected from hydrogen, C1-12 alkoxy, halogen,
cyano, amino, C1-12 alkyl, C2-12 alkenyl, C2-12 alkynyl, C1-12 haloalkyl, C3-12
cycloalkyl, C6-12 aryl, C2-12 heterocyclyl or C3-12 heteroaryl, provided that, at least
one of R1 and R2 is C1-12 alkoxy; R3 and R4 are independently selected from
25 hydrogen, halogen, cyano, amino, C1-25 alkyl, C2-25 alkenyl, C2-25 alkynyl, C1-12
3
alkoxy, C1-12 haloalkyl, C3-12 cycloalkyl, C6-12 aryl, C2-12 heterocyclyl, C3-12
heteroaryl, or –(R’-O)m-R”, wherein, R’ and R” are independently selected from C1-
12 alkyl, C2-12 alkenyl, C2-12 alkynyl, C1-12 haloalkyl, or C1-12 alkoxy; m is in a range
of 1 to 10; and n is in a range of 30 to 70.
5 [0006] In another aspect of the present disclosure, there is provided a process of
preparing the polymer of Formula I as disclosed herein, the process comprising
contacting a compound of Formula II with a compound of Formula III to undergo
polymerization in the presence of a catalyst and a first solvent to obtain the polymer,
wherein, R1 and R2 are independently selected from hydrogen, C1-12 alkoxy, halogen,
10 cyano, amino, C1-12 alkyl, C2-12 alkenyl, C2-12 alkynyl, C1-12 haloalkyl, C3-12
cycloalkyl, C6-12 aryl, C2-12 heterocyclyl or C3-12 heteroaryl, provided that, at least
one of R1 and R2 is C1-12 alkoxy; R3 and R4 are independently selected from
hydrogen, halogen, cyano, amino, C1-25 alkyl, C2-25 alkenyl, C2-25 alkynyl, C1-12
alkoxy, C1-12 haloalkyl, C3-12 cycloalkyl, C6-12 aryl, C2-12 heterocyclyl, C3-12
15 heteroaryl, or –(R’-O)m-R”, wherein R’and R” are independently selected from C1-
12 alkyl, C2-12 alkenyl, C2-12 alkynyl, C1-12 haloalkyl, or C1-12 alkoxy; m is in a range
of 1 to 10; n is in a range of 30 to 70; and X’ and X” are leaving group.
[0007] In one another aspect of the present disclosure, there is provided an
20 electrochromic substrate comprising the polymer of Formula I as disclosed herein,
and a substrate, wherein the polymer is coated on the substrate.
[0008] In yet another aspect of the present disclosure, there is provided a process of
preparing the electrochromic substrate as disclosed herein, the process comprising:
mixing the polymer of Formula I as disclosed herein, in a second solvent to obtain a
25 first solution; and coating the first solution on a substrate in the presence of an inert
gas to obtain the electrochromic substrate.
4
[0009] In more aspect of the present disclosure, there is provided an electrochromic
device comprising: a) the polymer of Formula I or the electrochromic substrate as
disclosed herein, as a primary electrochromic component; b) a gel electrolyte; and c)
a counter electrode.
5 [0010] These and other features, aspects, and advantages of the present subject
matter will be better understood with reference to the following detailed description
and appended claims. This summary is provided to introduce a selection of concepts
in a simplified form. This summary is not intended to identify key features or
essential features of the claimed subject matter, nor is it intended to be used to limit
10 the scope of the claimed subject matter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Figure 1 depicts the absorbance profiles for a) polymers P1, P2 and P3; the
data at the voltage maxima for b) polymer 1 (P1); c) polymer 2 (P2); and d) polymer
15 3 (P3) in different electrolytes, in accordance with an implementation of the present
disclosure.
[0012] Figure 2 depicts estimation of standard switching times with a) square
voltage pulses applied as a function of pulse width; and b) resulting changes in
optical density, in accordance with an implementation of the present disclosure.
20 [0013] Figure 3 depicts a representation of evaluating the performance of polymers
P1, P2, P3 in various electrolytes by fitting their changes in optical density as a
function of pulse width and fitting the data using Equation 2, in accordance with an
implementation of the present disclosure.
[0014] Figure 4 depictsradar plots summarizing figures of merit and electrochromic
25 performances of a) polymer 1 (P1); b) polymer 2 (P2); and c) polymer 3 (P3) in
different electrolytes, in accordance with an implementation of the present
disclosure.
[0015] Figure 5 depicts open circuit memory test for a) polymer 3 (P3); b) polymer
2 (P2); and c) polymer 1 (P1), in optimized electrolyte composition at 1500 nm and
0.8V (vs Ag+
30 /Ag), in accordance with an implementation of the present disclosure.
5
[0016] Figure 6 depicts the working electrochromic optical attenuator setup
comprising the polymer of the present disclosure coated on a substrate, in accordance
with an implementation of the present disclosure.
[0017] Figure 7 depicts linear dynamic ranges of optical attenuation as a function of
voltage (vs Ag+
5 /Ag) for a) polymer 1 (P1); b) polymer 2 (P2); and c) polymer 3 (P3)
in optimized electrolyte composition at 1500 nm, in accordance with an
implementation of the present disclosure.
[0018] Figure 8 depicts optical attenuation and cycling stability tests for polymers
P1, P2, and P3 at 0.8V (vs Ag+
/Ag) at 1500 nm, in accordance with an
10 implementation of the present disclosure.
[0019] Figure 9 depicts attenuation vs voltage plots for a) polymer 4 (P4) and b)
polymer 5 (P5), in accordance with an implementation of the present disclosure.
[0020] Figure 10 depicts cycling stability plots of attenuation vs time for a) polymer
4 (P4); and b) polymer 5 (P5), in accordance with an implementation of the present
15 disclosure.
DESCRIPTION OF THE INVENTION
[0021] Those skilled in the art will be aware that the present disclosure is subject to
variations and modifications other than those specifically described. It is to be
understood that the present disclosure includes all such variations and modifications.
20 The disclosure also includes all such steps, features, compositions, and compounds
referred to or indicated in this specification, individually or collectively, and any and
all combinations of any or more of such steps or features.
Definitions
[0022] For convenience, before further description of the present disclosure, certain
25 terms employed in the specification, and examples are delineated here. These
definitions should be read in the light of the remainder of the disclosure and
understood as by a person of skill in the art. The terms used herein have the meanings
recognized and known to those of skill in the art, however, for convenience and
completeness, particular terms and their meanings are set forth below.
6
[0023] The articles “a”, “an” and “the” are used to refer to one or to more than one
(i.e., to at least one) of the grammatical object of the article.
[0024] The terms “comprise” and “comprising” are used in the inclusive, open sense,
meaning that additional elements may be included. It is not intended to be construed
5 as “consists of only”.
[0025] Throughout this specification, unless the context requires otherwise the word
“comprise”, and variations such as “comprises” and “comprising”, will be
understood to imply the inclusion of a stated element or step or group of element or
steps but not the exclusion of any other element or step or group of element or steps.
10 [0026] The term “including” is used to mean “including but not limited to”.
“Including” and “including but not limited to” are used interchangeably.
[0027] The term “optical contrast” used herein refers to the measure of the difference
between the intensities of light reflected by a sample and its surrounding material. In
the present disclosure, the term “optical contrast” refers to the changes in optical
15 density (absorbance) between bleached and coloured electrochromic states of the
polymer of Formula I. The polymer of Formula I of the present disclosure exhibits
optical contrast (∆OD) in a range of 0.2 to 0.5.
[0028] The term “switching energy” used herein is also referred to as “switching
energy per electrochromic event” and is estimated using the equation SE=QV/A
having unit as Jm-2
20 , Q is the charge obtained from chronoamperometry
measurements by integrating the current vs time plots, V is the voltage applied in a
square pulse and A is the active area.
[0029] The term “optical attenuation” used herein refers to a reduction in the
intensity of the light beam (or signal) with respect to the distance travelled through
25 a transmission medium. In optics, attenuation refers to the rate at which the light
signal decreases in intensity and is calculated from the spectro-electrochemistry
profiles obtained by linearly ramping the potential, which was converted to optical
attenuation (dB) using the equation: Optical attenuation (dB) = 10(ΔOD).
[0030] The term “substrate” used herein refers to a material over which the polymer
30 of the present disclosure is coated, so as to obtain an electrochromic substrate. The
7
substrate of the present disclosure may possess maximum transparency and optical
passivation. Examples of substrate include but not limited to indium tin oxide.
[0031] Ratios, concentrations, amounts, and other numerical data may be presented
herein in a range format. It is to be understood that such range format is used merely
5 for convenience and brevity and should be interpreted flexibly to include not only
the numerical values explicitly recited as the limits of the range, but also to include
all the individual numerical values or sub-ranges encompassed within that range as
if each numerical value and sub-range is explicitly recited. For example, a
temperature range of 60 ℃ to 100 ℃ should be interpreted to include not only the
10 explicitly recited limits of 60 ℃ to 100 ℃, but also to include subranges, such as 61
℃ to 100 ℃, 80 ℃ to 100 ℃, 65 ℃ to 100℃ and so forth, as well as individual
amounts, including fractional amounts, within the specified ranges, such as 67 ℃,
71 ℃, 85.5 ℃, 95 ℃, and 98 ℃, for example.
[0032] Unless defined otherwise, all technical and scientific terms used herein have
15 the same meaning as commonly understood by one of ordinary skill in the art to
which this disclosure belongs. Although any methods and materials similar or
equivalent to those described herein can be used in the practice or testing of the
disclosure, the preferred methods, and materials are now described. All publications
mentioned herein are incorporated herein by reference.
20 [0033] As discussed in the background there is a need for electrochromic materials
which would effectively modulate IR radiation and variable optical attenuator. The
existing attenuators operate based on mechanisms such as polymer-dispersed liquid
crystals (PDLC), mechanical optical, microelectromechanical (MEM), and thermooptic attenuators, however, the challenges of obtaining flexible and lightweight
25 attenuators with a fast response time and minimal moving parts persists. For this
purpose, the conjugated polymers having diketopyrrolopyrrole based backbone are
suitable materials as they provide precise control of color purity, saturation and
brightness, by directly manipulating the redox nature of the backbone. Moreover, the
electrochromic devices resulting from the usage of such conjugated polymers are
30 flexible and can conform to any substrate size and shape with minimal modifications
in their manufacturing protocols. Accordingly, the present disclosure provides a
8
polymer of Formula I which are active electrochromic materials, which exhibit millisecond response times, low energy consumption per switching event, high NIR
coloration efficiencies, low optical loss, and optimal optical attenuation values at a
low switching voltage.
5 [0034] In an embodiment of the present disclosure, there is provided a polymer of
Formula I,
Formula I
wherein, R1 and R2 are independently selected from hydrogen, C1-12 alkoxy, halogen,
10 cyano, amino, C1-12 alkyl, C2-12 alkenyl, C2-12 alkynyl, C1-12 haloalkyl, C3-12
cycloalkyl, C6-12 aryl, C2-12 heterocyclyl or C3-12 heteroaryl, provided that, at least
one of R1 and R2 is C1-12 alkoxy; R3 and R4 are independently selected from
hydrogen, halogen, cyano, amino, C1-25 alkyl, C2-25 alkenyl, C2-25 alkynyl, C1-12
alkoxy, C1-12 haloalkyl, C3-12 cycloalkyl, C6-12 aryl, C2-12 heterocyclyl, C3-12
15 heteroaryl, or –(R’-O)m-R”, wherein, R’ and R” are independently selected from C1-
12 alkyl, C2-12 alkenyl, C2-12 alkynyl, C1-12 haloalkyl, or C1-12 alkoxy; m is in a range
of 1 to 10; and n is in a range of 30 to 70.
[0035] In an embodiment of the present disclosure, there is provided a polymer of
Formula I as disclosed herein, wherein R1 and R2 are independently selected from
20 hydrogen, or C1-6 alkoxy, provided that, at least one of R1 and R2 is C1-6 alkoxy; R3
and R4 are independently selected from hydrogen, C12-25 alkyl, or –(R’-O)m-R”, R’
and R” are independently selected from C1-12 alkyl, m is in a range of 1 to 5; and n
is in a range of 30 to 70.
[0036] In an embodiment of the present disclosure, there is provided a polymer of
25 Formula I as disclosed herein, wherein R1 and R2 are independently selected from
hydrogen, or C1-2 alkoxy, provided that, at least one of R1 and R2 is C1-2 alkoxy; R3
and R4 are independently selected from C18-22 alkyl, or -(C2H4O)3-CH3; and n is 30
9
to 70. In another embodiment of the present disclosure, R1 and R2 are independently
selected from hydrogen, or C1 alkoxy, provided at least one of R1 and R2 is C1 alkoxy;
R3 and R4 are independently selected from C19-21 alkyl, or -(C2H4O)3-CH3; and n is
30 to 70.
5 [0037] In an embodiment of the present disclosure, there is provided a polymer of
Formula I as disclosed herein, wherein the polymer is selected from a) poly- 3-(5’-
(2,5-bis(2-octyldodecyl)-3,6-dioxo-4-(thiophen-2-yl)-2,3,5,6-
tetrahydropyrrolo[3,4-c]pyrrol-1-yl)-3-methoxy-[2,2’-bithiophen]-5-yl)-6-(4-
methoxythiophen-2-yl)-2,5-bis(2-octyldodecyl)-2,5-dihydropyrrolo[3,4-c]pyrrole10 1,4-dione; b) poly- 3-(5’-(2,5-bis(2-(2-(2-methoxyethoxy)ethoxy)ethyl)-4-(4-
methoxythiophen-2-yl)-3,6-dioxo-2,3,5,6-tetrahydropyrrolo[3,4-c]pyrrol-1-yl)-3’-
methoxy-[2,2’-bithiophen]-5-yl)-2,5-bis(2-octyldodecyl)-6-(thiophen-2-yl)-2,5-
dihydropyrrolo[3,4-c]pyrrole-1,4-dione; and c) poly- 3,6-bis(4-methoxythiophen-2-
yl)-2,5-bis(2-octyldodecyl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione.
15 [0038] In an embodiment of the present disclosure, there is provided a polymer of
Formula I as disclosed herein, wherein the polymer has weight average molecular
weight (Mw) in a range of 70 to 95 kg/mol; number average molecular weight (Mn)
in a range of 30 to 65 kg/mol; and polydispersity index (PDI) in a range of 1.2 to 2.5.
In another embodiment of the present disclosure, wherein the polymer has weight
20 average molecular weight (Mw) in a range of 78 to 93 kg/mol; number average
molecular weight (Mn) in a range of 35 to 62 kg/mol; and polydispersity index (PDI)
in a range of 1.3 to 2.3.
[0039] In an embodiment of the present disclosure, there is provided a polymer of
Formula I as disclosed herein, wherein the polymer is an active electrochromic
25 material.
[0040] In an embodiment of the present disclosure, there is provided a polymer of
Formula I as disclosed herein, wherein the polymer exhibits optical contrast in a
range of 0.2 to 0.5. In another embodiment of the present disclosure, the polymer
exhibits optical contrast in a range of 0.23 to 0.47.
30 [0041] In an embodiment of the present disclosure, there is provided a polymer of
Formula I as disclosed herein, wherein the polymer exhibits switching energy in a
10
range of 3 to 9. In another embodiment of the present disclosure, the polymer exhibits
switching energy in a range of 3.5 to 8.5.
[0042] In an embodiment of the present disclosure, there is provided a polymer of
Formula I as disclosed herein, wherein the polymer exhibits optical attenuation in a
5 range of 0.2 to 8 dB. In another embodiment of the present disclosure, the polymer
exhibits optical attenuation in a range of 0.2 to 5 dB.
[0043] In an embodiment of the present disclosure, there is provided a process for
preparing the compound of Formula I as disclosed herein, the process comprising:
contacting a compound of Formula II with a compound of Formula III to undergo
10 polymerization in the presence of a catalyst and a first solvent to obtain the polymer,
wherein, R1 and R2 are independently selected from hydrogen, C1-12 alkoxy, halogen,
cyano, amino, C1-12 alkyl, C2-12 alkenyl, C2-12 alkynyl, C1-12 haloalkyl, C3-12
cycloalkyl, C6-12 aryl, C2-12 heterocyclyl or C3-12 heteroaryl, provided at least one of
R1 and R2 is C1-12 alkoxy;
15
R3 and R4 are independently selected from hydrogen, halogen, cyano, amino, C1-25
alkyl, C2-25 alkenyl, C2-25 alkynyl, C1-12 alkoxy, C1-12 haloalkyl, C3-12 cycloalkyl, C6-
12 aryl, C2-12 heterocyclyl, C3-12 heteroaryl, or –(R’-O)m-R”, wherein R’and R” are
independently selected from C1-12 alkyl, C2-12 alkenyl, C2-12 alkynyl, C1-12 haloalkyl,
20 or C1-12 alkoxy; m is in a range of 1 to 10; n is in a range of 30 to 70; and X’ and X”
are leaving group.
[0044] In an embodiment of the present disclosure, there is provided a process for
preparing the compound of Formula I as disclosed herein, wherein X’ and X” are
independently selected from halogen, 4,4,5,5-tetramethyl-1,3,2-dioxaborolane, or
25 combinations thereof. In another embodiment of the present disclosure, wherein X’
11
and X” are independently halogen. In one another embodiment of the present
disclosure, X’ and X” are independently bromine.
[0045] In an embodiment of the present disclosure, there is provided a process for
preparing the compound of Formula I as disclosed herein, wherein the compound of
5 Formula II and Formula III are independently selected from 3,6-bis(5-bromo-4-
methoxythiophen-2-yl)-2,5-bis(2-(2-(2-methoxyethoxy)ethoxy)ethyl)-2,5-
dihydropyrrolo[3,4-c]pyrrole-1,4-dione, 2,5-bis(2-octyldodecyl)-3,6-bis(5-(4,4,5,5-
tetramethyl-1,3,2-dioxaborolan-2-yl)thiophen-2-yl)-2,5-dihydropyrrolo[3,4-
c]pyrrole-1,4-dione, or 3,6-bis(5-bromo-4-methoxythiophen-2-yl)-2,5-bis(2-
10 octyldodecyl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione.
[0046] In an embodiment of the present disclosure, there is provided a process for
preparing the compound of Formula I as disclosed herein, wherein the first solvent
is selected from tetrahydrofuran, toluene, or combinations thereof.
[0047] In an embodiment of the present disclosure, there is provided a process for
15 preparing the compound of Formula I as disclosed herein, wherein the catalyst is
selected from tris(dibenzylideneacetone)dipalladium(0) (Pd2(dba)3),
tetrakis(triphenylphosphine)palladium(0) (Pd(PPh3)4), bis(1,5-cyclooctadiene
nickel(0) (Ni(COD)2), or combinations thereof. In another embodiment of the
present disclosure, the process involves the use of an auxiliary ligand; and the
20 auxiliary ligand is 1,5-cyclooctadiene.
[0048] In an embodiment of the present disclosure, there is provided a process for
preparing the compound of Formula I as disclosed herein, wherein contacting is
carried out at a temperature in a range of 60 to 100℃. In another embodiment of the
present disclosure, the contacting is carried out at a temperature in a range of 65 to
25 95℃.
[0049] In an embodiment of the present disclosure, there is provided an
electrochromic substrate comprising the polymer of Formula I as disclosed herein,
and a substrate, wherein the polymer is coated on the substrate.
[0050] In an embodiment of the present disclosure, there is provided an
30 electrochromic substrate as disclosed herein, wherein the substrate is indium tin
oxide (ITO).
12
[0051] In an embodiment of the present disclosure, there is provided an
electrochromic substrate as disclosed herein, wherein the polymer forms a film on
the substrate. In another embodiment of the present disclosure, the film is in a
thickness in a range of 60 to 300 nm. In one another embodiment of the present
5 disclosure, the film is in a thickness in a range of 90 to 200 nm.
[0052] In an embodiment of the present disclosure, there is provided a process of
preparing the electrochromic substrate as disclosed herein, the process comprising:
a) mixing the polymers of Formula I as disclosed herein in a second solvent to obtain
a first solution; and b) coating the first solution on a substrate in the presence of an
10 inert gas to obtain the electrochromic substrate.
[0053] In an embodiment of the present disclosure, there is provided a process of
preparing the electrochromic substrate as disclosed herein, wherein the second
solvent is selected from tetrachloroethane, chloroform, or combinations thereof.
[0054] In an embodiment of the present disclosure, there is provided a process of
15 preparing the electrochromic substrate as disclosed herein, wherein coating is carried
out by spray coating, dip coating, or drop casting. In another embodiment of the
present disclosure, coating is carried out by spray coating, or drop casting.
[0055] In an embodiment of the present disclosure, there is provided a process of
preparing the electrochromic substrate as disclosed herein, wherein coating the first
20 solution on a substrate is carried out at a pressure in a range of 20 to 30 psi.
[0056] In an embodiment of the present disclosure, there is provided an
electrochromic device comprising: a) the polymer of Formula I as disclosed herein
or the electrochromic substrate as disclosed herein, as primary electrochromic
component; b) a gel electrolyte and c) a counter electrode.
25 [0057] In an embodiment of the present disclosure, there is provided an
electrochromic device as disclosed herein, wherein the counter electrode comprises
a minimally color changing polymer selected from optionally substituted poly-3,4-
dihydro-2H,7H-[1,4]dioxepino[2,3-c]pyrrole.
[0058] Although the subject matter has been described in considerable detail with
30 reference to certain examples and implementations thereof, other implementations
are possible.
13
EXAMPLES
[0059] The disclosure will now be illustrated with working examples, which is
intended to illustrate the working of disclosure and not intended to take restrictively
5 to imply any limitations on the scope of the present disclosure. Unless defined
otherwise, all technical and scientific terms used herein have the same meaning as
commonly understood to one of ordinary skill in the art to which this disclosure
belongs. Although methods and materials similar or equivalent to those described
herein can be used in the practice of the disclosed methods and compositions, the
10 exemplary methods, devices and materials are described herein. It is to be understood
that this disclosure is not limited to particular methods, and experimental conditions
described, as such methods and conditions may apply.
[0060] The forthcoming examples illustrate the synthesis of polymer of Formula I
which are the active electrochromic materials, with sub-second response times, low
15 energy consumption per switching event, high NIR coloration efficiencies, low
optical loss, and an optical attenuation value. The examples also provide an
electrochromic substrate and an electrochromic device comprising the polymer of
Formula I.
Materials and Methods:
20 [0061] For the purpose of the present disclosure, the raw materials methanol,
chloroform, toluene, dichloromethane, hexane, sodium bisulfate, and potassium
carbonate were purchased from SD fine chem limited. Bromine, and cyclooctadiene
(COD) were purchased from Spectrochem. 2,2’-bipyridyl, lithium bis
(trifluoromethanesulfonyl)imide(LiTFSI), tetrabutylammonium
25 trifluoromethanesulfonate (TBAOTf), tetrabutylammonium
hexafluorophosphate(TBAPF6), tetrabutylammonium perchlorate(TBAClO4), and
tetrabutylammonium tetrafluoroborate (TBABF4) were acquired from TCI
chemicals. Tris(dibenzylideneacetone)dipalladium(0) (Pd2(dba)3), bis(1,5-
cyclooctadiene nickel(0) (Ni(COD)2) were purchased from Sigma Aldrich.
30 Pd(PPh3)4 was synthesized as per the literature procedure (Coulson, D. R.; Satek, L.
C.; Grim, S. O. Tetrakis(triphenylphosphine)palladium(0). Inorg. Synth. Inorganic
14
Syntheses. Vol. 13. p. 121. doi:10.1002/9780470132449). 3,6-bis(4-
methoxythiophen-2-yl)-2,5-bis(2-octyldodecyl)-2,5-dihydropyrrolo[3,4-c]pyrrole1,4-dione, 3,6-bis(4-methoxythiophen-2-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-
dione, were synthesized by known methods.
5 EXAMPLE 1
Preparation of Polymer of Formula I
[0062] The process of preparing the polymer of Formula I comprises contacting a
compound of Formula II with a compound of Formula III to undergo polymerization
in the presence of a catalyst and a first solvent to obtain the polymer,
10
wherein, R1 and R2 are independently selected from hydrogen, C1-12 alkoxy, halogen,
cyano, amino, C1-12 alkyl, C2-12 alkenyl, C2-12 alkynyl, C1-12 haloalkyl, C3-12
cycloalkyl, C6-12 aryl, C2-12 heterocyclyl or C3-12 heteroaryl, provided that, at least
one of R1 and R2 is C1-12 alkoxy; R3 and R4 are independently selected from
15 hydrogen, halogen, cyano, amino, C1-25 alkyl, C2-25 alkenyl, C2-25 alkynyl, C1-12
alkoxy, C1-12 haloalkyl, C3-12 cycloalkyl, C6-12 aryl, C2-12 heterocyclyl or C3-12
heteroaryl, or –(R’-O)m-R”, wherein R’ and R” are independently selected from C1-
12 alkyl, C2-12 alkenyl, C2-12 alkynyl, C1-12 haloalkyl, or C1-12 alkoxy; m is in a range
of 1 to 10; n is in a range of 30 to 70; and X’ and X” are leaving group.
20 [0063] The polymers of the present disclosure prepared by said process are:
Polymer 1: poly- 3-(5’-(2,5-bis(2-octyldodecyl)-3,6-dioxo-4-(thiophen-2-yl)-
2,3,5,6-tetrahydropyrrolo[3,4-c]pyrrol-1-yl)-3-methoxy-[2,2’-bithiophen]-5-yl)-6-
(4-methoxythiophen-2-yl)-2,5-bis(2-octyldodecyl)-2,5-dihydropyrrolo[3,4-
c]pyrrole-1,4-dione
15
Polymer 2: poly- 3-(5’-(2,5-bis(2-(2-(2-methoxyethoxy)ethoxy)ethyl)-4-(4-
methoxythiophen-2-yl)-3,6-dioxo-2,3,5,6-tetrahydropyrrolo[3,4-c]pyrrol-1-yl)-3’-
methoxy-[2,2’-bithiophen]-5-yl)-2,5-bis(2-octyldodecyl)-6-(thiophen-2-yl)-2,5-
5 dihydropyrrolo[3,4-c]pyrrole-1,4-dione
Polymer 3: poly- 3,6-bis(4-methoxythiophen-2-yl)-2,5-bis(2-octyldodecyl)-2,5-
dihydropyrrolo[3,4-c]pyrrole-1,4-dione
16
Synthesis of compounds of Formula II and Formula III
Synthesis of 3, 6-bis(5-bromo-4-methoxythiophen-2-yl)-2,5-bis(2-octyldodecyl)-
2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (Compound A)
[0064] 3, 6-bis(5-bromo-4-methoxythiophen-2-yl)-2,5-bis(2-octyldodecyl)-2,5-
5 dihydropyrrolo[3,4-c]pyrrole-1,4-dione was prepared and was used in the
preparation of polymer of Formula I.
Compound A
[0065] A 100-mL round bottom oven dried Schlenk flask was purged with
10 nitrogen gas. 3,6-bis(4-methoxythiophen-2-yl)-2,5-bis(2-octyldodecyl)-2,5-
dihydropyrrolo[3,4-c]pyrrole-1,4-dione (200 mg, 0.21 mmol) was added to the flask
and dissolved in 20 mL chloroform. The reaction was cooled to 0 ℃ in an ice-bath
and covered with aluminium foil. While stirring, Br2 (bromine, 0.025 mL, 0.47
mmol) (diluted in 10 mL chloroform) was added dropwise to the reaction over 20
15 minutes. A drastic colour change was observed after the addition of Br2. The progress
of the reaction was monitored by TLC in dichloromethane (DCM):hexane. After
consumption of all starting materials (monitored by TLC, approx. 90 minutes), the
reaction mixture was treated with saturated NaHSO4 solution and extracted with
chloroform. The organic part was dried under vacuum and the obtained product was
20 recrystallized from methanol to yield 3,6-bis(5-bromo-4-methoxythiophen-2-yl)-
2,5-bis(2-octyldodecyl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (Compound A)
as dark red solid (210 mg, 90%). 1H NMR (400 MHz, CDCl3) δ (ppm) 8.86 (s, 2H,
thienyl proton), 4.05 (s, 6H, -O-CH3), 3.94 (dd, 4H, -N-CH2-), 1.94-1.92 (m, 2H, -
CH<), 1.30-1.22(m, 64H, alkyl protons), 0.86 (t, 12H, -CH3). 13C{1H} NMR (100
25 MHz, CDCl3) δ (ppm) 161.6 (carbonyl carbon), 156.4 (-C-Br), 139.5 (thienyl
carbon), 127.6, 122.7, 108.1 (aromatic carbon), 98.2 (-C-Br), 59.5 (-O-CH3), 46.5,
32.1, 30.2, 29.9, 29.8, 29.7, 29.6, 29.5, 26.3 (alkyl carbon), 14.4 (-CH3).
17
Synthesis of 3, 6-bis(5-bromo-4-methoxythiophen-2-yl)-2,5-bis(2-(2-(2-
methoxyethoxy)ethoxy)ethyl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione
(Compound B)
5 Compound B
[0066] A 100-mL round bottom oven dried Schlenk flask was purged with
nitrogen gas. 2,5-bis(2-(2-(2-methoxyethoxy)ethoxy)ethyl)-3,6-bis(4-
methoxythiophen-2-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (100 mg, 0.15
mmol) was added to the flask. 15 mL chloroform was added to dissolve the starting
10 material. The reaction flask was cooled to 0 ℃ in an ice-bath and covered with
aluminium foil. While stirring, Br2 (0.018 mL, 0.33 mmol, diluted with 8 mL
chloroform) was added dropwise to the reaction over 20 minutes. A drastic colour
change was observed after the addition of Br2. The progress of the reaction was
monitored by TLC in DCM:Hexane. After consumption of all starting materials
15 (monitored by TLC, approx. 40 minutes), the reaction mixture was treated with
saturated NaHSO4 solution and extracted with chloroform. The organic part was
dried under vacuum and product was recrystallized from hexane to yield the desired
product (Compound B), as dark red solid (106 mg, 88%) as shown in figure 2.
1H
NMR (500 MHz, CDCl3) δ (ppm) 8.70 (s, 2H, thienyl proton), 4.21 (t, 4H, -N-CH2-
20 CH2-O-), 4.03 (s, 6H, -OCH3), 3.78 (t, 4H, -N-CH2-CH2-O-), 3.65-3.62 (m, 4H),
3.60-3.55 (m, 8H), 3.49-3.46 (m, 4H), 3.34 (s, 6H, -O-CH3).
Compound C: 2,5-bis(2-octyldodecyl)-3,6-bis(5-(4,4,5,5-tetramethyl-1,3,2-
dioxaborolan-2-yl)thiophen-2-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione
18
Compound C
[0067] Compound C was synthesized by a known method (Kanimozhi, C et al., J.
Am. Chem. Soc. 2012, 134, 16532−16535).
5 Preparation of Polymer 1 - P1:
[0068] In a 100 mL oven-dried Schlenk flask, 3,6-bis(5-bromo-4-
methoxythiophen-2-yl)-2,5-bis(2-octyldodecyl)-2,5-dihydropyrrolo[3,4-c]pyrrole1,4-dione (Compound A, 116 mg, 0.10 mmol) and 2,5-bis(2-octyldodecyl)-3,6-
bis(5-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)thiophen-2-yl)-2,5-
10 dihydropyrrolo[3,4-c]pyrrole-1,4-dione (Compound C, 120 mg, 0.10 mmol) were
added containing 15 mL of anhydrous toluene (solvent). After completing three
freeze–pump–thaw cycle, Pd2(dba)3:Pd(PPh3)4 (3 mg, 1 mol%, 1:1 ratio) catalyst was
added quickly to the reaction flask under dark condition. The flask was covered with
aluminium foil to protect from light. A degassed solution of aqueous K2CO3
15 (potassium carbonate, 0.35 mL, 2M) was added quickly and this mixture was purged
again with nitrogen for 10 min. This mixture was refluxed at 95 ℃ for 40 h. After
having been quenched with a few drops of methanol, the reaction mixture was cooled
to room temperature. The organic layer was evaporated and extracted with
chloroform. The concentrated polymer solution was then added dropwise into
20 vigorously stirring methanol (in cold conditions) to get the formed polymer 1
precipitated. The precipitate was then collected by filtration, purified via Soxhlet
extraction for 6 h with methanol and hexane and was finally collected with
chloroform. Then the chloroform solution was removed under a vacuum to obtain a
dark green solid of polymer 1 (114 mg, yield 62%). 1H NMR (400 MHz, CDCl3) δ
25 (ppm) 9.26-9.11 (m, thienyl protons), 8.57-8.44 (m, thienyl protons), 4.20-3.84 (m,
-NCH2-, -OCH3), 2.05 (bs, -CH<), 1.24 (bs, alkyl proton), 0.86 (m, -CH3). 13C{1H}
19
NMR (100 MHz, CDCl3) δ (ppm) 161.9, 161.4, 161.3, 161.1, 155.8, 150.0, 141.4,
140.8, 139.5, 138.3, 137.7, 137.4, 136.8, 135.8, 132.1, 130.4, 129.9, 129.4, 129.0,
128.7, 128.4, 126.3, 126.0, 124.9, 114.3, 109.6, 108.5 (aromatic), 59.4 (-OCH3
attached to thiophene), 58.9, 38.2, 38.0, 37.7, 32.1, 32.0, 30.2, 29.9, 29.8, 29.7, 29.5,
26.5, 26.4, 26.3, 22.8, 22.7 (alkyl), 14.2 (-CH3). GPC; Mw = 92.3 kg.mol-1
5 , Mn = 49.3
kg.mol-1
, PDI = 1.87.
Synthesis of Polymer 2- P2:
[0069] A 100 mL oven-dried Schlenk flask was cooled under vacuum and purged
with nitrogen. To the flask, 3,6-bis(5-bromo-4-methoxythiophen-2-yl)-2,5-bis(2-(2-
10 (2-methoxyethoxy)ethoxy)ethyl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione,
(Compound B, 120 mg, 0.14 mmol) and 2,5-bis(2-octyldodecyl)-3,6-bis(5-(4,4,5,5-
tetramethyl-1,3,2-dioxaborolan-2-yl)thiophen-2-yl)-2,5-dihydropyrrolo[3,4-
c]pyrrole-1,4-dione (Compound C, 164 mg, 0.14 mmol) were added in a flask
containing 14 mL of anhydrous toluene (solvent). The Schlenk flask was charged
15 with nitrogen through a freeze–pump–thaw cycle three times. After completing the
cycle, Pd2(dba)3:Pd(PPh3)4 (4 mg, 1 mol %, 1:1 ratio) catalyst were added quickly to
the reaction flask under dark condition and the flask was covered with aluminium
foil. A degassed aqueous solution of K2CO3 (0.45 mL, 2M) was added quickly and
this mixture was purged again with nitrogen for 10 min. This mixture was refluxed
20 at 95 ℃ for 36 h. After having been quenched with a few drops of methanol, the
reaction mixture was cooled to room temperature. The organic layer was evaporated
and the concentrated polymer solution was precipitated by slowly adding into
vigorously stirring methanol (in cold conditions). The precipitate was collected by
filtration, purified via Soxhlet extraction for 5 h with methanol, hexane and was
25 finally collected with chloroform. Then the chloroform solution was removed under
a vacuum to obtain a dark green solid of Polymer 2 (125 mg, yield 68%). 1H NMR
(500 MHz, CDCl3) δ (ppm) 9.28-8.92 (m, thienyl proton), 4.34-4.01 (m, -N-CH2-, -
O-CH3), 3.87-3.46 (m, -OCH2CH2-), 2.04-1.92 (m, -CH<), 1.29-1.16 (m, alkyl
protons), 0.88-0.84 (m, -CH3). 13C{1H} NMR (100 MHz, CDCl3) δ (ppm) 162.1,
30 161.4, 160.8, 141.5, 141.0, 140.5, 138.9, 138.6, 137.6, 137.1, 136.7, 136.0, 135.0,
134.9, 132.4, 131.9, 130.9, 130.0, 129.5, 128.5, 128.9, 128.6, 127.6, 126.4, 125.4,
20
124.7, 109.1, 108.2 (aromatic), 77.4, 72.4, 72.1, 71.7, 70.7, 70.5, 69.2, 59.4,
(alkoxy), 59.2 (-OCH3 attached to thiophene), 46.5, 42.3, 42.2, 38.5, 38.2, 37.9, 33.9,
32.3, 32.1, 31.4, 31.2, 30.2, 30.1, 29.8, 29.7, 29.5, 26.5, 26.3, 22.7 (alkyl), 14.3 (-
CH3). GPC; Mw = 79.8 kg.mol-1
, Mn = 35.3 kg.mol-1
, PDI = 2.25.
5
Synthesis of Polymer 3- P3:
[0070] A 100 mL oven-dried Schlenk flask was cooled under vacuum and purged
with nitrogen. To this Schlenk flask, bis(1,5-cyclooctadiene nickel(0) (Ni(COD)2)
(catalyst, 83 mg, 0.30 mmol) and 2,2’-bipyridyl (46 mg, 0.30 mmol) was added in a
10 glove box with nitrogen. The flask was taken out from glove box and immediately
connected with Schlenk line under high nitrogen flow. A solvent mixture of
anhydrous THF (tetrahydrofuran):toluene (10 mL, 1:1 vol ratio) was added to the
flask. 3,6-bis(5-bromo-4-methoxythiophen-2-yl)-2,5-bis(2-octyldodecyl)-2,5-
dihydropyrrolo[3,4-c]pyrrole-1,4-dione (Compound A, 250 mg, 0.23 mmol) was
15 added to the flask. After that, few drops of 1,5-cyclooctadiene (COD) was added.
The flask was covered with aluminium foil and the polymerization proceeded at 65
℃ for 48 h. After cooling down to room temperature, the THF was removed and
polymer was extracted with CHCl3(chloroform). The concentrated polymer solution
was precipitated by slowly adding into vigorously stirring methanol (in cold
20 condition). The precipitate was collected by filtration, purified via Soxhlet extraction
for 8 h with methanol, hexane and finally collected with chloroform. Then the
chloroform solution was removed under vacuum to obtain a dark green solid of
Polymer 3 (112 mg, yield 65%). 1H NMR (500 MHz, CDCl3) δ (ppm) 9.23-8.90 (m,
thienyl proton), 4.32-3.88 (m, -N-CH2-, -O-CH3), 2.09-1.92 (m, -CH<), 1.25-1.14
(m, alkyl proton), 0.86 (bs, -CH3). 13C{1
25 H} NMR (100 MHz, CDCl3) δ (ppm) 161.8,
161.6, 161.2, 141.4, 140.8, 139.5, 138.4, 137.7, 135.0, 132.0, 129.7, 129.6, 129.4,
129.1, 128.9, 128.8, 128.7, 128.4, 126.3, 126.2, 114.3, 109.1 (aromatic), 59.1 (-
OCH3 attached to thiophene), 46.6, 46.5, 46.4, 38.6, 38.2, 37.9, 32.1, 31.3, 30.3,
30.2, 29.9, 29.8, 29.6, 29.5, 26.5, 26.3, 23.0, 22.9, 22.6 (alkyl), 14.3 (-CH3). GPC;
Mw = 87.7 kg.mol-1
, Mn = 61.8 kg.mol-1
30 , PDI = 1.42.
21
Comparative polymers
Polymer 4 and Polymer 5 (P4 and P5)
[0071] For the purpose of the present disclosure, the polymer 4 and polymer 5 were
considered as comparative polymers and prepared by known methods (Kanimozhi,
5 C.; et al.,. Phys. Chem. Chem. Phys., 2014, 16, 17253—17265.).
10
Polymer 4 Polymer 5
EXAMPLE 2
Preparation of electrochromic substrate
15 [0072] Electrochromic substrate comprising the polymer (Example 1) along with
a substrate was prepared as explained herein. In an example, an electrochromic
substrate comprising polymer 1 coated on indium tin oxide as a substrate was
prepared. The polymer 1 (i.e) 4mg/mL of polymer was added in second solvent, a
mixture of 1,1,2,2 tetrachloroethane (TCE)/chloroform in a 50:50 (volume: volume)
20 to obtain a first solution. The first solution was then spray coated on indium tin oxide
using a stream of Argon (Ar) gas at a pressure of 25psi to obtain the electrochromic
substrate of P1 (ES1). Similarly, the electrochromic substrate 2 (ES2) was prepared
using polymer 2. In another example, the first solution of polymer, P3 (4mg/ml) in
chloroform (second solvent) was spray coated on indium tin oxide to obtain
25 electrochromic substrate 3 (ES3). Chloroform was used to dissolve the polymer P3,
since the solubility of the polymer was found to be significantly altered upon
introducing methoxy (OMe) groups on all the thiophene groups present in the
backbone compared to the other polymers.
[0073] The polymer coated on the substrate formed a film on the substrate and the
30 thickness was maintained in a range of 60 to 300 nm, and more particularly 150 nm.
22
The polymers were always spray coated by tracking their optical density which was
maintained around 0.5 (±0.05) a.u. The thickness of the spray coated films were
measured and it was found that the films spray coated to obtain an optical density of
0.5 (±0.05) a.u., frequently yielded 150 (±8) nm thick films. While a lower thickness
5 of 59 nm did not yield sufficient coverage of films on the substrate, higher
thicknesses of 300nm were achieved but mostly resulted in substandard NIR
electrochromic performance.
EXAMPLE 3
10 Properties of polymers and electrochromic substrates
[0074] The electrochemistry and spectro-electrochemistry experiments for these
polymers were carried out in electrolytes of varying anions. The electrolytes that
displayed optimal performance were screened out for further studies involving
optical attenuation. Electrolytes were selected from lithium bis
15 (trifluoromethanesulfonyl)imide(LiTFSI), tetrabutylammonium
trifluoromethanesulfonate (TBAOTf), tetrabutylammonium
hexafluorophosphate(TBAPF6), tetrabutylammonium perchlorate(TBAClO4), and
tetrabutylammonium tetrafluoroborate (TBABF4). The electrochromic substrates of
Example 2 were used as the working electrodes and the electrochemical and
20 spectrochemical analysis were carried out.
Electrochemical Measurements
[0075] Cyclic voltammetry (CV) was carried out on Autolab potentiostat in a
custom-made electrochemical cell which could support solution as well as thin filmbased electrochemistry experiments using electrochromic substrate (polymer/ITO)
25 as the working electrodes (ES1 or ES2 or ES3), platinum coil as the counter
electrode, and a Ag+
/Ag non-aqueous reference electrode in 0.1 M acetonitrileelectrolyte (TBABF4, TBAClO4, TBAPF6, TBAOTf, LiTFSI). The reference
electrode was prepared by dipping a silver wire in a glass tube of 10 mM silver
triflate (AgOTf) in 0.1 M of acetonitrile/salt as a fill solution. The reference electrode
30 was calibrated each time before the start of experiments against ferrocene as an
external standard (E1/2 = 86 (±6) mV vs Ag+
/Ag, E1/2=0.54 V vs SHE). The
23
electrochemical measurement cell was sealed and purged with Ar (argon) gas for 15
min before experiments. The area and thickness of the working electrodes were
confined to ∼1 cm2
and 150 (±8) nm, unless specified. The samples were
electrochemically preconditioned for three cycles to equilibrate ion ingress and
5 release. After that, the linear evolution of absorbance spectra as a function of applied
electrochemical potential (Vs Ag+
/Ag) was acquired in electrolytes containing BF4
-
,
ClO4
-
, PF6
-
, OTf-
, and TFSIanions and NIR contrast and visible interferences were
analysed.
Spectro electrochemistry measurements
10 [0076] Spectro-electrochemical characterizations and optical attenuation
experiments were carried out in a custom designed in situ cell capable of measuring
electrochemical and optical measurements simultaneously. Spectral profiles were
acquired using Ocean Optics instrument consisting of Ocean FX-XR1-ES and
NIR512−2.5 visible and NIR photodetectors capable of ultrafast acquisition. ITO
15 electrodes were cut into 2.5 cm × 2.5 cm and subjected to standard cleaning
procedures before experiments. The polymers were spray coated onto the ITO
substrates to obtain electrochromic substrates as defined in Example 2. The area of
contact in the cell defined the active area which was about 1.1cm2
. Adequate
measures were taken to ensure that the area of analysis aligned with the beam path
20 in the cell holder. While the electrochromic (ITO/polymer) substrate was used as the
working electrode, a coiled Pt and AgNO3/Ag were used as counter and reference
electrodes.
[0077] All cyclic voltammograms were recorded in 0.1 M dry acetonitrile/salt
solutions at a scan rate of 100 mV/s on Autolab instrument. Linear optical profiles
25 as a function of applied electrochemical potential were acquiesced for every 500 ms
using the OceanView software interface. Chrono-absorptiometry- based experiments
were carried out by applying a fixed potential corresponding to the ion insertion
while simultaneously monitoring the changes in absorbance of the wavelength of
interest. A square wave pulse with 5s of ‘on’ time and 5s of ‘off’ time was employed
30 for the switching experiments. The On and Off times specified the amount of time
the voltage was applied/removed on the electrochromic polymer. The data from
24
chrono-absorptiometry experiments were used to estimate figures of merit like
coloration efficiencies, contrast ratio, switching times, and switching energy per
event.
Absorbance profile
5 [0078] Absorbance profiles obtained for the electrochromic substrates (ES1, ES2,
and ES3) comprising the polymers P1, P2, and P3 respectively are depicted in Figure
1a. Figure 1 illustrates the spectro-electrochemistry profiles of the polymers as a
function of different electrolytes. The profiles were obtained by linearly ramping the
voltage from -0.4V to 0.8V at a scan rate of 100mV/s. The data at the voltage maxima
(0.8V vs Ag+
10 /Ag) are depicted for b) ES1 having polymer P1; c) ES2 having polymer
P2; and d) ES3 having polymer P3 in different electrolytes.
Estimation of Electrochromic Figure-of-merit
[0079] The electrochromic performance for all the polymers incorporated in
electrochromic substrates were studied by monitoring the differences in optical
15 density at wavelengths (1500 nm) where maximum changes were measured. The
films were switched between their neutral (semi-transparent) and p-doped
(transparent) states using a square-wave potential step corresponding to ion insertion
(Vs Ag+
/Ag) as a function of time.
a) The optical contrast ΔOD was obtained by considering the changes in
20 optical density (Absorbance) between bleached and coloured
electrochromic states.
b) The Coloration efficiency (CE) was estimated using the equation:
CE=𝛥𝑂𝐷
𝑄𝑑
(cm2
/C) (1)
where ΔOD is the ratio of change in OD between bleached and coloured
25 states. Qd is the charge injected per unit area.
c) Switching times were estimated from the chrono-absorptiometry
measurements. The coloration/bleaching times were estimated by
considering the time taken to achieve 95% of the maximum contrast and
vice-versa.
25
d) Standard switching times (t95): The standard switching time were
estimated by varying the pulse width of the input square pulse voltage
while monitoring the changes in optical density in Figure 2. Figure 2a is
a representative figure depicting the estimation of standard switching
5 time as a function of pulse width and Figure 2b depict the corresponding
changes in optical density. The maximum changes in optical density were
plotted as a function of pulse width (ν) in Figure 3. Since the physical
processes in the film of the electrochromic substrate resembled a
capacitor in terms of charging, the data was fitted using an equation 2
10 which represents the charging equation of a capacitor.
𝐴(𝑡) = 𝐴𝑜(1 − 𝑒
−𝑏𝑡) (2)
e) Switching energy per event: The switching energy per electrochromic
event was estimated using the formula
𝑆𝐸 =
𝑄𝑉
𝐴
(𝐽 𝑚2
15 ⁄ ) (3)
Q is the charge obtained from chronoamperometry measurements by
integrating the current vs time plots. V is the voltage applied in a square pulse
and A is the active area.
20 [0080] Table 2 provides a summary of Figures of merit such as NIR optical contrast
(ΔOD), coloration efficiency (CE, cm2
/C), standard switching time (t95), Coloration
time (tcol), switching energy (SE, J/m2
) estimated from Chrono-absorptiometry plots
in various electrolytes and are summarized as radar plots (Figure 4) for the polymers
P1, P2, and P3, respectively. Table 2A and Figure 4a summarize the properties of
25 polymer 1 (P1); Table 2B and Figure 4b for the polymer 2 (P2) and Table 2C and
Figure 4c for the polymer 3 (P3).
Open-circuit memory tests
[0081] One of the main advantages of the electrochromic material is its open-circuit
memory or electrochromic memory. Open-circuit memory or electrochromic
memory is defined as the ability to maintain the electrochromic (reduced/oxidized)
states for a sufficient period of time in the absence of driving voltage. Excellent
15 optical memory effect would reduce the power consumption of electrochromic
devices by minimizing the need to apply frequent refreshing voltage. Therefore the
electrochromic substrates (ES1, ES2 and ES3) comprising the polymers (P1, P2 and
P3) were subjected to open-circuit memory tests. The electrochromic substrates were
switched to their oxidized states in optimized electrolyte compositions by applying
20 a voltage of 0.8V for 5s and then the retention of the oxidized state was monitored
under no bias (open circuit potential). As seen in Figure 5, P1 exhibited a retention
time of 43 min (Figure 5c) while P2 and P3 exhibited a retention time of 40 min and
120 min (Figures 5b and 5a), respectively. In general, the electron deficient nature
of the diketopyrrolopyrrole lactam ring would destabilize the radical cationic states
25 formed on the conjugated backbone. However, in the polymers of the present
disclosure (P1, P2 and P3) the presence of methoxy groups which are strongly
electron donating in nature, stabilized the radical cations formed. This was well
Polymer, P3
Figure of Merit TFSI- OTf- PF6
- ClO4
- BF4
-
Optical Contrast
(ΔOD)
0.45 0.24 0.43 0.37 0.23
Standard Switching
Time (t95 (s))
0.69 0.45 0.6 0.87 0.51
Coloration Efficiency
(CE, cm2
/C)
429 472 505 370 436
Coloration time
(tcol (s))
1.04 0.86 1.37 2.95 1.28
Switching energy
(J/m2
)
8.22 3.93 6.77 8 4
28
reflected in the remarkable retention time and a switching energy per event of 8J/m2
for polymer P3 which was much desired for practical applications involving low
power and fast NIR switching electrochromic applications.
Variable optical attenuation and switching experiments
5 [0082] The electrochromic substrates (ES1, ES2 and ES3) comprising the polymers
(P1, P2 and P3) were found to display a large and variable contrast in the NIR region
1300-1500 nm, relevant for fiber optic communications, where the absorption of
fiber optic cables was minimal for the mentioned wavelengths. The polymers P1, P2,
and P3 displayed variable optical attenuation, which was found to be tunable by
10 modulating the applied bias. The optical attenuation (dB) is calculated using the
equation 4 below.
Optical attenuation (dB) = 10(ΔOD) (4)
[0083] Figure 6 depictsthe working electrochromic optical attenuatorsetup, wherein
602 represents the electrochromic substrate, 604 and 606 represent the reference and
15 counter electrodes respectively, 608 and 610 are the inlet and the outlet for
electrolytes respectively, 612 is the optical path. Further as seen in Figure 7, P1
displayed a maximum of 4.2 dB (Figure 7a), while P2 and P3 showed a maximum
attenuation of 4.5 dB, and 5.1dB, (Figure 7b and 7c), respectively. P3 displayed a
lower onset of oxidation and a higher linear dynamic range (LDR) of -50mV and
20 5dB.
[0084] Additionally, the stability of optical attenuation was monitored by subjecting
the polymers to a continuous bias dependent cycling stability test. As seen in Figure
8, the polymers P1, P2 and P3 displayed stable attenuation over 200 cycles in
optimized electrolyte composition.
25
EXAMPLE 5
Comparative polymers P4 and P5
30 [0085] Electrochemistry and spectro-electrochemistry experiments were carried
out on polymers P4 and P5 without alkoxy i.e ‘OMe’ (methoxy) substitution as
present in the polymers P1, P2 and P3 of the present disclosure and the destabilizing
29
effect was studied. It was understood that OMe substitution rendered the polymers
P1, P2 and P3 of the present disclosure with increased radical cation stability. The
attenuation vs voltage plots (Figures 9a and 9b) and cycling stability (Figures 10a
and 10b) for polymers P4 and P5 without OMe substitution did not exhibit a linearity
5 and showed a decreased cycling stability. Thus this confirmed that the polymers
having OMe substitution on the thiophene units where oxidation was proposed to
take place had increased radical cation stability compared to the polymers without
OMe. Therefore it was evident that the structural aspects of the polymers as disclosed
herein are important for obtaining desired electrochromic materials for opto -
10 electronic and electrochemical applications.
EXAMPLE 6
Electrochromic Device
15 [0086] An electrochromic device was fabricated having dual polymer, wherein the
polymer or the electrochromic substrate of the present disclosure was taken as a
primary electrochromic component. A counter electrode comprising a minimally
color changing polymer such as alkyl substituted poly-3,4-dihydro-2H,7H-
[1,4]dioxepino[2,3-c]pyrrole was used in the device. In the electrochromic device, a
20 gel electrolyte was used between the primary electrochromic component and the
counter electrode. The gel electrolyte was made using poly methyl methacrylate
(PMMA) as a gelator, propylene carbonate as a solvent and an electrolyte consisting
of desired cations/anions.
25 ADVANTAGES OF THE PRESENT DISCLOSURE
[0087] The present disclosure provides a polymer of Formula I which are alkoxy
derivatives of a diketopyrrolopyrrole-based (DPP) polymeric compounds. The
alkoxy based polymers exhibit an optical contrast in a range of 0.2 to 0.5; and
switching energy in a range of 3 to 9. The polymers of the present disclosure are
30 found to be efficient variable optical attenuator with optical attenuation in a range of
0.2 to 5 dB. The presence of alkoxy group on the polymer provides the polymer
radical cation stability and thus exhibit an improved optical attenuation. The present
30
disclosure also provides an electrochromic substrate comprising the polymer coated
on a substrate. The present disclosure also provides an electrochromic device
comprising the polymer of the present disclosure along with a minimally color
changing polymer. Electrochromic device of the present disclosure finds its
5 application in defense sectors, smart constructions, aviation, fiber-optics
communication, and flexible/printed optoelectronic industries.
31
I/We Claim:
1. A polymer of Formula I
5 Formula I
wherein,
R1 and R2 are independently selected from hydrogen, C1-12 alkoxy, halogen,
cyano, amino, C1-12 alkyl, C2-12 alkenyl, C2-12 alkynyl, C1-12 haloalkyl, C3-12
cycloalkyl, C6-12 aryl, C2-12 heterocyclyl, or C3-12 heteroaryl, provided that, at
10 least one of R1 and R2 is C1-12 alkoxy;
R3 and R4 are independently selected from hydrogen, halogen, cyano, amino,
C1-25 alkyl, C2-25 alkenyl, C2-25 alkynyl, C1-12 alkoxy, C1-12 haloalkyl, C3-12
cycloalkyl, C6-12 aryl, C2-12 heterocyclyl, C3-12 heteroaryl, or –(R’-O)m-R”,
wherein, R’ and R” are independently selected from C1-12 alkyl, C2-12 alkenyl,
15 C2-12 alkynyl, C1-12 haloalkyl, or C1-12 alkoxy; m is in a range of 1 to 10; and
n is in a range of 30 to 70.
2. The polymer as claimed in claim 1, wherein R1 and R2 are independently
selected from hydrogen, or C1-6 alkoxy, provided that, at least one of R1 and R2
is C1-6 alkoxy;
20 R3 and R4 are independently selected from hydrogen, C12-25 alkyl, or –(R’-O)mR”, wherein, R’ and R” are independently selected from C1-12 alkyl; m is in a
range of 1 to 5; and n is in a range of 30 to 70.
3. The polymer as claimed in claim 1, wherein, R1 and R2 are independently
selected from hydrogen, or C1-2 alkoxy, provided that, at least one of R1 and R2
25 is C1-2 alkoxy;
32
R3 and R4 are independently selected from C18-22 alkyl, or -(C2H4O)3-CH3; and
n is 30 to 70.
4. The polymer as claimed in claim 1, wherein the polymer is selected from
a. poly- 3-(5’-(2,5-bis(2-octyldodecyl)-3,6-dioxo-4-(thiophen-2-yl)-
5 2,3,5,6-tetrahydropyrrolo[3,4-c]pyrrol-1-yl)-3-methoxy-[2,2’-bithiophen]-
5-yl)-6-(4-methoxythiophen-2-yl)-2,5-bis(2-octyldodecyl)-2,5-
dihydropyrrolo[3,4-c]pyrrole-1,4-dione;
b. poly- 3-(5’-(2,5-bis(2-(2-(2-methoxyethoxy)ethoxy)ethyl)-4-(4-
methoxythiophen-2-yl)-3,6-dioxo-2,3,5,6-tetrahydropyrrolo[3,4-c]pyrrol10 1-yl)-3’-methoxy-[2,2’-bithiophen]-5-yl)-2,5-bis(2-octyldodecyl)-6-
(thiophen-2-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione; and
c. poly- 3,6-bis(4-methoxythiophen-2-yl)-2,5-bis(2-octyldodecyl)-2,5-
dihydropyrrolo[3,4-c]pyrrole-1,4-dione.
5. The polymer as claimed in claim 1, wherein the polymer has weight average
15 molecular weight (Mw) in a range of 70 to 95 kg/mol; number average molecular
weight (Mn) in a range of 30 to 65 kg/mol; and polydispersity index (PDI) in a
range of 1.2 to 2.5.
6. The polymer as claimed in claim 1, wherein the polymer is an active
electrochromic material.
20 7. The polymer as claimed in claim 1, wherein the polymer exhibits optical contrast
in a range of 0.2 to 0.5.
8. The polymer as claimed in claim 1, wherein the polymer exhibits switching
energy in a range of 3 to 9.
9. The polymer as claimed in claim 1, wherein the polymer exhibits optical
25 attenuation in a range of 0.2 to 5 dB.
10. A process of preparing the polymer as claimed in claim 1, the process
comprising:
contacting a compound of Formula II with a compound of Formula III to
undergo polymerization in the presence of a catalyst and a first solvent to obtain
30 the polymer,
33
wherein, R1 and R2 are independently selected from hydrogen, C1-12 alkoxy,
halogen, cyano, amino, C1-12 alkyl, C2-12 alkenyl, C2-12 alkynyl, C1-12 haloalkyl,
C3-12 cycloalkyl, C6-12 aryl, C2-12 heterocyclyl, or C3-12 heteroaryl, provided at
5 least one of R1 and R2 is C1-12 alkoxy;
R3 and R4 are independently selected from hydrogen, halogen, cyano, amino,
C1-25 alkyl, C2-25 alkenyl, C2-25 alkynyl, C1-12 alkoxy, C1-12 haloalkyl, C3-12
cycloalkyl, C6-12 aryl, C2-12 heterocyclyl, C3-12 heteroaryl, or –(R’-O)m-R”,
wherein R’and R” are independently selected from C1-12 alkyl, C2-12 alkenyl, C2-
10 12 alkynyl, C1-12 haloalkyl, or C1-12 alkoxy; m is in a range of 1 to 10;
n is in a range of 30 to 70; and X’ and X” are leaving group.
11. The process as claimed in claim 10, wherein X’ and X” are independently
selected from halogen, 4,4,5,5-tetramethyl-1,3,2-dioxaborolane, or
combinations thereof.
15 12. The process as claimed in claim 10, wherein the compound of Formula II and
Formula III are independently selected from 3,6-bis(5-bromo-4-
methoxythiophen-2-yl)-2,5-bis(2-(2-(2-methoxyethoxy)ethoxy)ethyl)-2,5-
dihydropyrrolo[3,4-c]pyrrole-1,4-dione, 2,5-bis(2-octyldodecyl)-3,6-bis(5-
(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)thiophen-2-yl)-2,5-
20 dihydropyrrolo[3,4-c]pyrrole-1,4-dione, or 3,6-bis(5-bromo-4-
methoxythiophen-2-yl)-2,5-bis(2-octyldodecyl)-2,5-dihydropyrrolo[3,4-
c]pyrrole-1,4-dione.
13. The process as claimed in claim 10, wherein the first solvent is selected from
tetrahydrofuran, toluene, or combinations thereof.
25 14. The process as claimed in claim 10, wherein the catalyst is selected from
tris(dibenzylideneacetone)dipalladium(0) (Pd2(dba)3),
34
tetrakis(triphenylphosphine)palladium(0) (Pd(PPh3)4), bis(1,5-cyclooctadiene
nickel(0) (Ni(COD)2), or combinations thereof.
15. The process claimed in claim 10, wherein contacting is carried out at a
temperature in a range of 60 to 100℃.
5 16. An electrochromic substrate comprising the polymer as claimed in claim 1 and
a substrate, wherein the polymer is coated on the substrate.
17. The electrochromic substrate as claimed in claim 16, wherein the polymer forms
a film on the substrate.
18. The electrochromic substrate as claimed in claim 16, wherein the film is in a
10 thickness range of 60 to 300 nm.
19. A process of preparing the electrochromic substrate as claimed in claim 16, the
process comprising:
a. mixing the polymer as claimed in claim 1 in a second solvent to obtain a
first solution; and
15 b. coating the first solution on a substrate in the presence of an inert gas to
obtain the electrochromic substrate.
20. The process as claimed in claim 19, wherein the second solvent is selected from
tetrachloroethane, chloroform, or combinations thereof.
21. The process as claimed in claim 19, wherein coating is carried out by spray
20 coating, dip coating, or drop casting.
22. The process as claimed in claim 19, wherein coating the first solution on a
substrate is carried out at a pressure in a range of 20 to 30 psi.
23. An electrochromic device comprising:
a. the polymer as claimed in claim 1 or the electrochromic substrate as
25 claimed in claim 16, as a primary electrochromic component;
b. a gel electrolyte; and
c. a counter electrode.
24. The device as claimed in claim 23, wherein the counter electrode comprises a
minimally color changing polymer selected from optionally substituted poly30 3,4-dihydro-2H,7H-[1,4]dioxepino[2,3-c]pyrrole.