Carbazole-based π-conjugated polyazomethines: Effects of catenation and comonomer insertion on optoelectronic features

Article abstract of DOI:10.1016/j.polymer.2017.05.039

A series of carbazole-based polyazomethines have been synthesized under micro-wave irradiation and without transition-metal based catalyst. The impact of both the catenation brought by the carbazole subunits and the insertion of a co-monomer, i.e. 3,4 ethylene dioxythiophene (EDOT), on the optical and electrochemical properties have been studied. Among the different polyazomethines synthesized, the best in terms of optical and electrochemical properties has been found to be the one with the azomethine function linked in positions 2,7 of carbazole subunits. Upon the insertion of the EDOT comonomer, an increase of the molecular weight and a red-shift in the absorption spectra has been observed, corresponding to a diminution of the electronic gap.

Full text of DOI:10.1016/j.polymer.2017.05.039

Accepted Manuscript
Carbazole-based π-conjugated polyazomethines: Effects of catenation and
comonomer insertion on optoelectronic features
G. Garbay, L. Muccioli, A. Hanifa, G. Hadziioannou, C. Brochon, E. Cloutet
PII:
S0032-3861(17)30514-1
10.1016/j.polymer.2017.05.039
JPOL 19699
DOI:
Reference:
To appear in: Polymer
Received Date: 16 February 2017
Revised Date: 28 April 2017
Accepted Date: 15 May 2017
Please cite this article as: Garbay G, Muccioli L, Hanifa A, Hadziioannou G, Brochon C, Cloutet E,
Carbazole-based π-conjugated polyazomethines: Effects of catenation and comonomer insertion on
optoelectronic features, Polymer (2017), doi: 10.1016/j.polymer.2017.05.039.
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ACCEPTED MANUSCRIPT
Carbazole-based π-conjugated polyazomethines:
effects of catenation and comonomer insertion on
optoelectronic features
G. Garbaya,b,c L. Mucciolib,d, A. Hanifaa,b,c, G. Hadziioannoua,b,c, C. Brochon*a,b,c and E.
Cloutet*a,b,c
aCentre National de la Recherche Scientifique (CNRS), Laboratoire de Chimie des Polymères
Organiques (LCPO), UMR 5629, B8 allée Geoffroy Saint Hilaire, 33615 Pessac Cedex, France.
bUniversity of Bordeaux, Laboratoire de Chimie des Polymères Organiques (LCPO),UMR 5629,
B8 allée Geoffroy Saint Hilaire, 33615 Pessac Cedex, France
cInstitut Polytechnique de Bordeaux (IPB), Laboratoire de Chimie des Polymères Organiques
(LCPO), UMR 5629, B8 allée Geoffroy Saint Hilaire, 33615 Pessac Cedex, France
dUniversity of Bologna, Department of Industrial Chemistry « Toso Montanari », Viale
Risorgimento 4, 40136 Bologna, Italy
Keywords: Polyazomethines; Carbazole; Copolymer; Organic Electronics;
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Graphical Abstract
Abstract
A series of carbazole-based polyazomethines have been synthesized under micro-wave
irradiation and without transition-metal based catalyst. The impact of both the catenation brought
by the carbazole subunits and the insertion of a co-monomer, i.e. 3,4 ethylene dioxythiophene
(EDOT), on the optical and electrochemical properties have been studied. Among the different
polyazomethines synthesized, the best in terms of optical and electrochemical properties has
been found to be the one with the azomethine function linked in positions 2,7 of carbazole
subunits. Upon the insertion of the EDOT comonomer, an increase of the molecular weight and a
red-shift in the absorption spectra has been observed, corresponding to a diminution of the
electronic gap.
Introduction
π-conjugated polymers are nowadays recognized as a full class of semi-conductors for
electronics and optoelectronics devices, such as OLED[1–3], OFET[4–6], and solar cells.[7–10]
Despite being assumed to be non-fluorescent[11], conjugated polyazomethines (-C=N-) are
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interesting alternatives to their polyvinylene counterparts, partially due to their isoelectronic
properties compared with their carbon analogues.[12,13] More importantly, conjugated
polyazomethines are easily synthesized via a condensation reaction. This implies the formation
of water as the only by-product, a synthesis without the need of stringent reaction conditions and
interestingly in the absence of transition metal catalyst.[14] This is a very important aspect in
view of the applications of polymers in organic electronics, because such catalysts can be
considered as impurities for the final device, altering their properties.[15,16] By avoiding the
presence of metals in the final product, the polymer can then be purified through classical
precipitation (simply by washing off residual monomers). In addition, such a reaction can be
carried out under micro-wave irradiation in order to reduce reaction time and energy
consumption, a procedure generally referred to as microwave-assisted organic synthesis
(MAOS).[17,18] This kind of process has been used to obtain monomers presenting an
azomethine function, for biological application for example.[19] While azomethines were first
synthesized in 1923 and polyazomethines in 1950[12,20–23], they have only recently attracted
an increased interest, in particular for polymers composed of fluorene moieties in regard to their
optical and physical properties, such as versatile color, and good chemical and electrochemical
resistance.[24–32] Alternatively, if well balanced hole and electron mobilities are sought,
carbazole groups can be used to replace fluorene.[33] However, although π-conjugated polymers
containing 3,6- or 2,7-substituted carbazole moieties have been quite extensively studied
showing original optoelectronic features according to their chemical nature and insertion in a
polymer chain, such as a high conductivity or a good optical absorption, literature is scarce on
carbazole-based polyazomethines.[29],[34]
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In this paper, we report the synthesis of various carbazole-based conjugated polyazomethines
with specific emphasis on the catenation effects, along with a 3,4-ethylene dioxythiophene
(EDOT) comonomer insertion on the optical features. Notably, fully alternated copolymers of
approximately 5 kg.mol-1 composed of 2,7-carbazole and EDOT subunits allow the reduction of
electrochemical bandgap down to 1.83 eV, a value quite promising for photovoltaic
applications.[35]
Experimental
Materials and methods
Tetrahydrofuran (THF), methylene chloride (CH2Cl2), toluene, dimethylsulfoxide (DMSO)
and diethylether (Et2O) were purified from a solvent purification system (MBraun MB-SPS-800)
prior to use. Chloroform (CHCl3) and N,N-dimethylformamide (DMF) were dried over calcium
hydride (CaH2) and distilled prior to use. Unless otherwise specified, all other solvents and
chemicals were purchased from commercial suppliers (Alfa Aesar, Sigma-Aldrich, TCI, Acros
Organics) and used as received. All reactions were carried out under argon at 1 atmosphere
unless mentioned otherwise.
Characterizations
1
Precursors and polymers were characterized by IR, HRMS, H and 13C NMR in order to
determine their chemical structures. NMR spectra were recorded on a Bruker 400 MHz
spectrometer from a deuterated chloroform, methylene chloride or dimethyl sulfoxide (CDCl3,
CD2Cl2 or DMSO-d6) solution. IR spectra were recorded with Bruker Tensor 27 spectrometer
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using a 0.6 mm-diameter beam and a 4 cm−1 resolution. Samples were analyzed with the
attenuated total reflectance (ATR) method. High resolution mass spectroscopy analyses were
performed on an AutoSpec-Waters spectrometer (EI). Molecular weights of the polymers were
measured by SEC at 25 °C with CHCl3 as eluent, using a Malvern Viscotek TDAmax system,
and PS standards were used for calibration. Differential scanning calorimetry (DSC) analyses
were performed on a TA unit at a heating speed of 20°C.min-1 for 5 mg of sample.
Thermogravimetric analysis (TGA) was performed on a TA-Q500 unit from 25°C to 700°C with
a heating speed of 10°C.min-1 under nitrogen flow. Absorption and photoluminescence spectra
were recorded for a polymer solution (0.01 g L−1 in CHCl3) and a polymer film casted from a
CHCl3 solution (10 g L−1) using the spectrophotometers UV-3600, Shimadzu and Fluoromax-4,
Horiba Scientific, respectively. Energetic levels were evaluated by cyclic voltammetry in
electrolyte solutions of 0.1 M TBAPF6 in CHCl3. Platinum/titanium electrodes were used both
as counter electrode and as working electrode, and a silver wire was used as reference electrode.
The obtained potentials were recalibrated adding ferrocene in the solution.
Computational details
All calculations were carried out with the PBE0 density functional using either Orca 3.03 or
Gaussian09 C.01 packages.[36,37] Torsional potentials for the rotation about the C-N=R and R-
C=N single bonds were evaluated with constrained minimizations of monomers, employing the
TZVP basis set. The first torsion showed four local minima and the second two minima – see SI
Figure S59. Azomethine dimers at all the possible 512 conformations, as identified by the
minima in the torsional potentials, were first optimized with the PM6 semi-empirical method,
fixing the C-N dihedrals to -150,-40,+40,+150 degrees, and the R-C dihedrals to either 0 or 180
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degrees. Subsequently, PBE0/3-21G* geometry optimizations were performed, removing the
constraints in the dihedral values, in order to relax the structure to the closest local minimum.
Finally PBE0/Def2-SVP calculations were performed at the PBE0/3-21G* equilibrium geometry
to obtain the energies ꢀꢁ employed for calculating thermal-averaged properties (see discussion).
〈 〉
The Boltzmann weighted averages were calculated at 300 K with the equation ꢂ =
ꢊꢋꢌ
ꢊꢋꢌ
ꢁꢍꢋ
ꢄꢅ /(ꢇ ꢉ)
ꢁꢍꢋ ꢂꢁꢃꢄꢅ /(ꢇ ꢉ)
/
ꢃ
.
ꢈ
ꢈ
ꢆ
ꢆ
∑
∑
The ground-state geometries of most stable dimers were further optimized with the def2-TZVP
basis set. These geometries were employed as input for excited state energies calculations,
carried out with the def2-SVP basis set and the Tamm Dancoff Approximation to time-
dependent density functional theory. In all the calculations, the branched di-octyl side chain was
replaced with a methyl group.
Syntheses of monomers and polymers
9-Heptadecanylcarbazole (1): Carbazole (31 mmol) and potassium hydroxide (2.61 g, 46.5
mmol) were solubilized in dry DMSO (40 mL). The reaction mixture was heated at 80°C for one
hour before adding dropwise a solution of 9-Heptadecane p-toluenesulfonate (16.5 g, 60 mmol)
in 60 mL of dry DMSO. After being allowed to cool down at room temperature, the reaction
mixture was poured into 300 mL of water and extracted three times with 100 mL of diethylether,
dried over magnesium sulfate with the solvent removed under vacuum. The white powder was
purified by flash chromatography in cyclohexane to afford white crystals (yield: 85%).
1H NMR (400 MHz, CD2Cl2):
δ (ppm) 8.10 (s, 2H); 7.59 (s, 1H); 7.43 (s, 3H); 7.20 (s, 2H), 4.59
(tt, J = 10.1, 5.0 Hz, 1H); 2.28 (m, 2H); 1.96 (m, 2H) 1.30-0.90 (m, 28H); 0.82 (t, J = 7.0 Hz,
6H).
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Heptadecan-9-ol (2): In a 250 mL three neck flame-dried, magnesium turnings (2.21 g, 91
mmol) was put into dry diethylether (60 mL). After 30 min a solution of bromooctane (15 mL,
87 mmol) in diethylether (45 mL) was then added dropwise and the reaction mixture was
allowed to stir for 1 more hour. Finally, a solution of ethyl formate (3 mL, 37.1 mmol) was
added dropwise and stirred at room temperature overnight. The reaction mixture was poured in
water (300 mL) and extracted 3 times with 150 mL of ethyl acetate, dried over magnesium
sulfate and the solvent was removed under vacuum to give a white solid which was used for the
next step without further purification.
9-Heptadecane p-Toluenesulfonate (3): P-toluenesulfonyl chloride (14.7 g, 77 mmol) in
CH2Cl2 (60 mL) was added dropwise to a solution of heptadecan-9-ol (2) (18.00 g, 70 mmol) and
triethylamine (Et3N) (24.4 mL, 181 mmol) in CH2Cl2 (90 mL) in a dry 250 mL flask. The
mixture was stirred for 2 hours, 250 mL of water was added, and the mixture was extracted three
times with CH2Cl2 (3x150 mL). The organic phase was washed with water, dried (Na2SO4), and
concentrated under reduced pressure. The crude product was purified by silica-gel flash
chromatography (cyclohexane-ethyl acetate, 95-5 as eluent) to give 22.5 g of colorless oil, which
crystallized as the title product (yield: 78 %).
1H NMR (400 MHz, CDCl3):
δ (ppm) 7.78 (d, J = 8.3 Hz, 2H), 7.31 (d, J = 8.0 Hz, 2H), 4.54 (p,
J = 6.0 Hz, 1H), 2.43 (s, 3H), 1.55 (m, 4H), 1.21 (m, 24H), 0.88 (t, 6H).
13C NMR (101 MHz, CDCl3):
δ
(ppm) 144.38, 134.97, 129.74, 127.85, 84.78, 70.82, 34.26,
31.97, 29.48, 29.42, 29.28, 24.81, 22.78, 21.71, 14.23.
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FT-IR (ATR):
ν
= 2954, 2923, 2852, 1598, 1521, 1495, 1465, 1354, 1305, 1173, 1097, 1020, 895,
816, 766, 720, 662, 575, 554 cm-1.
9-Heptadecanyl-3,6-diformylcarbazole (4): In a 100 mL flask, 10 mL of DMF (130 mmol) was
mixed with 12 mL of phosphoryl trichloride (125 mmol) at 0°C. At the same time, previously
alkylated carbazole 1 (2 g, 4.9 mmol) was solubilized in 20 mL of methylene chloride. After
warming up at room temperature, the carbazole solution was added to the mixture and the
reaction was heated at reflux temperature. After 65 hours the reaction mixture was allowed to
cool down at room temperature, poured into water and extracted with methylene chloride. The
crude product was then purified via silica column chromatography with a mixture of
cyclohexane/ethyl acetate (90/10) to afford a yellow powder (yield: 45%).
1H NMR (400 MHz, CD2Cl2, ppm):
δ (ppm) 10.12 (s, 2H), 8.70 (d, J = 5.6 Hz, 2H), 8.03 (dd, J =
17.9, 8.4 Hz, 2H), 7.69 (dd, J = 68.2, 8.2 Hz, 1H), 4.68 (tt, J = 10.2, 5.1 Hz, 1H), 2.30 (m, 2H);
2.01 (m, 2H) 1.32-0.89 (m, 28H); 0.81 (t, J = 7.0 Hz, 6H).
13C NMR (101 MHz, CDCl3, ppm):
103.32, 57.42, 33.78, 31.68, 29.25, 29.23, 29.04, 26.79, 22.54, 14.01.
δ (ppm) 192.41, 121.13, 113.17, 112.51, 110.54, 107.08,
FT-IR (ATR): ν
= 2923, 2860, 1700, 1442, 1319, 1305, 1220, 1154, 1075, 945, 753, 620, 587 cm-
1
.
HRMS (EI+, m/z) [M]+ calculated (%) for C58H86Br2N2O2: 1000.5056, found 1000.5031
9-Heptadecanyl-3,6-dinitrocarbazole (5): In a 50 mL flask, copper nitrate hemipentahydrate
(CuNO3.H2O) (6.3 g, 27.1 mmol) was solubilised in a mixture of acetate anhydride (30 mL) and
acetic acid (15 mL). Then 9-Heptadecanylcarbazole 1 (5 g, 12.3 mmol) was slowly added under
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high agitation and was mixed during 3 hours at room temperature. The reaction mixture was then
poured into 100 mL of cold water, filtered and washed with water. The powder was then purified
by column chromatography in (cyclohexane/ethyl acetate - 9/1) to afford a yellow powder.
1H NMR (400 MHz, CD2Cl2):
δ (ppm) 9.10 (s, 2H); 8.42 (dd, J = 15.9, 8.6 Hz, 2H); 7.75 (d, J =
8.0 Hz, 2H), 7.62 (dd, J = 67.9, 9.2 Hz, 2H); 4.67 (tt, J = 10.2, 5.1 Hz, 1H); 2.26 (m, 2H); 2.02
(m, 2H) 1.32-0.91 (m, 28H); 0.79 (t, J = 7.0 Hz, 6H).
13C NMR (101 MHz, CD2Cl2):
δ (ppm) 146.91; 142.22; 123.38; 122.80; 118.09; 112.86; 110.48;
58.79; 34.09; 32.25; 29.75; 29.70; 29.58; 27.18; 23.12; 14.34.
9-Heptadecanyl-3,6-diaminocarbazole (6): In a 50 mL flask, 2.5 g of previously synthesized
dinitrocarbazole 5 were mixed with 107 mg of palladium on charcoal (1.0 mmol). Then 12 mL of
ethanol was added and the reaction was heated at reflux temperature during one hour. 3.5 mL
were then added to the reaction and heated at 55°C during 36 hours. After cooling down the
reaction, the crude mixture was filtered and washed with ethanol. Finally the filtrate was dried
and purified two times with silica column chromatography, first in toluene and then in a mixture
of cyclohexane/ethyl acetate (95/5), to give a light brown compound (yield: 62%).
1H NMR (400 MHz, CDCl3):
δ (ppm) 7.29 (s, 3H), 7.16 (s, 1H), 6.87 (s, 2H), 4.37 (tt, J = 10.2,
5.1 Hz, 1H), 3.58 (s, 4H), 2.18 (m, 2H), 1.83 (m, 2H), 1.30-0.89 (m, 28H), 0.83 (t, J = 7.0 Hz
6H).
13C NMR (101 MHz, CDCl3, ppm):
δ (ppm) 137.97, 129.18, 128.37, 115.77, 115.32, 109.45,
106.20, 56.26, 34.01, 31.91, 31.07, 29.57, 29.46, 29.32, 26.91, 22.73, 14.21.
= 3207, 2923, 2850, 1786, 1736, 1603, 1577, 1465, 1335, 1127, 807 cm-1
FT-IR (ATR):
ν
HRMS (EI+, m/z) [M]+ calculated (%) for C29H45N3: 435.36135, found 435.36181
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4,4’-Dibromo-2-nitrobiphenyl (7): In a 500 mL flask, 4,4′-Dibromobiphenyl (10 g, 32 mmol)
was mixed with acetic acid (200 mL). A mixture of sulphuric acid and nitric acid (respectively
16 mL and 8 mL) was then added dropwise. The reaction mixture was heated at 110°C for 1
hour, allowed to cool down at room temperature, poured into 300 mL of water and filtered. The
yellow solid was purified by recrystallization in methanol to obtain a pale yellow solid which
was used in the next step without further purification.
2,7-dibromo-9-H-carbazole (8): In a 100 mL flame-dried flask, 4,4’-Dibromo-2-nitrobiphenyl
(10 g, 28 mmol) was solubilized in 35 mL of triethyl phosphite (P(OEt)3). The reaction was
mixed overnight at 160°C. The reaction mixture was then allowed to cool down at room
temperature and P(OEt)3 was distilled off under vacuum, followed by a flash chromatography in
cyclohexane to obtain the final product as white crystals (Yield: 65%).
1H NMR (400 MHz, CD2Cl2):
2H).
δ
(ppm) 8.02 (d, J = 8.3 Hz, 2H); 7.72 (s, 2H); 7.33 (d, J = 8.3 Hz,
13C NMR (101 MHz, CD2Cl2):
δ (ppm) 141.96, 123.26, 122.55, 122.45, 119.94, 114.84.
9-Heptadecanyl-2,7-dibromocarbazole (9): 2,7-dibromo-9-H-carbazole (4 g, 12 mmol) and
potassium hydroxide (0.84 g, 17.8 mmol) were solubilized in dry DMSO (40 mL). The reaction
mixture was heated at 80°C for one hour before adding dropwise a solution of 9-Heptadecane p-
toluenesulfonate (6.4 g, 15.6 mmol) in 60 mL of dry DMSO. After cooling down at room
temperature, the reaction mixture was poured into 300 mL of water and extracted three times
with 100 mL of diethylether, dried over magnesium sulfate and the solvent was removed under
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vacuum. The white powder was purified by flash chromatography in cyclohexane to afford white
crystals (yield: 90%)
1H NMR (400 MHz, CDCl3):
δ (ppm) 7.5 (s, 2H); 7.27 (s, 2H); 7.12 (m, 2H), 4.48 (tt, J = 10.1,
5.1 Hz, 1H); 2.20 (m, 2H); 1.83 (m, 2H) 1.32 – 1.02 (m, 28H); 0.83 (t, J = 7.0 Hz, 6H).
13C NMR (100 MHz, CDCl3):
δ
(ppm) 125.61; 125.23; 120.43; 118.54; 111.70, 108.87, 56.43;
33.85; 31.89; 29.53; 29.43; 29.30; 26.94; 22.73; 14.20.
HRMS (EI+, m/z) [M]+ calculated (%) for C29H41Br2N: 561.16057, found 561.16261
9-Heptadecanyl-2,7-diformylcarbazole (10): 9-Heptadecanyl-2,7-dibromocarbazole (3 g, 5.3
mmol) was solubilized in 130 mL of dry THF and was cooled at -78 °C. Then 16 mL (25.6
mmol) of a solution of n-butyl lithium was added dropwise. The reaction mixture was then
heated up at 0°C for 1 hour and cooled down again at -78°C. Then 6 mL of DMF was added and
the reaction was mixed during 4 hours at room temperature. The reaction mixture was then
poured into 100 mL of cold and lightly acid water, filtered and washed with water. The crude
yellow solid was then purified by flash chromatography two times, first in toluene and a second
time in a mixture of heptane and ethyl acetate (80/20) to afford a yellow powder (yield: 82%).
1H NMR (400 MHz, CDCl3):
δ (ppm) 10.17 (s, 2H); 8.25 (s, 2H); 8.00 (d, J = 48.1 Hz, 2H); 7.72
(d, J = 8.0 Hz, 2H), 4.68 (tt, J = 10.2, 5.1 Hz, 1H); 2.25 (m, 2H); 1.92 (m, 2H) 1.26-1.09 (m,
28H); 0.80 (t, J = 7.0 Hz, 6H).
13C NMR (101 MHz, CDCl3):
δ (ppm) 192.56; 121.28; 113.32; 112.66; 103.47; 57.28; 33.94;
31.83; 29.40; 29.38; 29.19; 26.94; 22.69; 14.16.
= 2916, 2844, 1689, 1570, 1460, 1444, 1223, 1166, 992, 856, 803, 731 cm-1.
FT-IR (ATR):
ν
HRMS (EI+, m/z) [M]+ calculated (%) for C31H43NO2: 461.32938, found 461.32967
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9-Heptadecanyl-2,7-diazidocarbazole (11): 9-Heptadecanyl-2,7-dibromocarbazole (4.00 g, 7.1
mmol), sodium azide (1.85 g, 28.5 mmol), copper iodide (0.28 g, 1.47 mmol), and sodium
ascorbate (0.144 g, 0.77 mmol) were solubilized in 40 mL of toluene. DMF (0.240 mL, 2.23
mmol) was added with 12 mL of a mixture of ethanol (8.5 mL) with water (3.5 mL) and was
heated at 110°C for 20 hours. The reaction was then allowed to cool down at room temperature,
poured into 50 mL of water and extracted 3 times with 50 mL of ethyl acetate, dried over
magnesium sulfate and the residual solvent was removed under vacuum. The orange powder was
purified by flash chromatography (cyclohexane/ethyl acetate 9:1) to afford an orange solid
(yield: 65%).
1H NMR (400 MHz, CDCl3):
δ (ppm) 7.98 (t, J = 9.1 Hz, 2H); 7.12 (s, 2H), 6.95 (b, 2H); 4.41
(tt, J = 10.0, 4.9 Hz, 1H); 2.20 (m, 2H); 1.89 (m, 2H); 1.13 (m, 24H); 0.75 (t, J = 7.0 Hz, 6H).
13C NMR (101 MHz, CDCl3):
δ
(ppm) 143.47; 139.95; 137.86; 137.22; 130.52; 130.06; 121.24;
121.05; 119.90; 110.67; 102.20; 99.58; 56.95; 33.60; 31.87; 29.44; 29.41; 29.26; 26.86; 22.73;
14.18.
FT-IR (ATR): ν
= 2100 cm-1 (C-N3 asymetric stretch)
HRMS (EI+, m/z) [M]+ calculated (%) for C29H41N7: 487.34234, found 487.34247
9-Heptadecanyl-2,7-diaminocarbazole (12): In a 100 mL flame dried flask, 9-Heptadecanyl-
2,7-diazidocarbazole (3 g, 6.15 mmol) was solubilized in 40 mL of THF. Then 3.88 mL (15.7
mmol) of tributylphosphine was added and the system was mixed for 3 hours at room
temperature. Then 15 mL of water were added and the reaction was mixed for 20 more hours.
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The reaction mixture was then directly dried under vacuum and the orange oil purified by flash
chromatography in toluene to give a pink powder (yield: 85%).
1H NMR (400 MHz, CD2Cl2):
δ (ppm) 7.63 (m 2H); 6.67 (d, J = 71.8 Hz, 2H); 6.48 (s, 2H); 4.31
(m, 1H); 3.72 (s, 4H); 2.18 (m, 2H); 1.86 (m, 2H); 1.41-0.92 (m, 24H); 0.85 (t, J = 7.0 Hz, 6H).
13C NMR (101 MHz, CD2Cl2):
δ
(ppm) 144.68; 144.07; 143.89; 140.93; 119.87; 119.66; 108.08;
97.75; 94.97; 56.48; 33.72; 32.19; 29.87; 29.79; 29.61; 27.30; 23.00; 14.22.
FT-IR (ATR): = 2954, 2923, 2852, 1598, 1521, 1495, 1465, 1354, 1305, 1173, 1097, 1020, 895,
ν
816, 766, 720, 662, 575, 554 cm-1.
HRMS (EI+, m/z) [M]+ calculated (%) for C29H45N3: 435.36135, found 435.36093
2,3-dihydrothieno[3,4-b][1,4]dioxine-5,7-dicarbaldehyde (13):
A
solution of 3,4-
ethylenedioxythiophene (1 g, 6.89 mmol) in dry THF (30 mL) was cooled to -78°C under argon
and treated with 1.6 M solution of n-BuLi (9.5 mL). The temperature was slowly raised to 0 °C
and the mixture was stirred at the same temperature for 20 minutes. The reaction mixture was
cooled again to -78°C and treated with dry DMF (2 mL, 26 mmol). The resulting mixture was
then stirred at room temperature for 2 hours and poured into crushed ice containing HCl. The
white precipitate was filtered, washed with water, and dried.
1H NMR (400 MHz, CDCl3):
13C NMR (101 MHz, CDCl3):
δ
(ppm) 10.04 (s, 2H), 4.44 (s, 4H);
(ppm) 181.09, 147.31, 124.30, 65.30.
δ
HRMS (EI+, m/z) [M]+ calculated (%) for C8H7O4S: 199.00650, found 199.00686
General procedure for polyazomethine synthesis
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For the synthesis of polyazomethines, about 100 mg of diformylcarbazole and
diaminocarbazole derivatives were dissolved in toluene (2 mL) in stoichiometric amount. Silica
(3 mg) was then added and the reaction mixture was heated at 130°C under µ-wave irradiation
during 4 hours, the power being automatically adapted to maintain a constant temperature. The
crude product was filtered and silica was washed with chloroform to recover the polymer. The
crude polymer was then purified via a Soxhlet extractor with methanol and then chloroform. All
polymers are named depending of the position of the linkage on the carbazole subunits, and
synthesized starting from carbazoles bearing the two nitrogens of the azomethine linkage. For
example, the (2,7-3,6 Cbz) was synthesized from 2,7-diaminocarbazole and 3,6-
diformylcarbazole.
For the statistic co-polymers, the 2,7-diaminocarbazole 12 (1 equivalent) was dissolved in
toluene in presence of 2,7-diformylcarbazole 10 and EDOT dialdehyde 13 with a different ratio
of the different dialdehyde. However, the total amount of aldehyde functions was kept equal to
the amount of amino functions (for example, 1 eq of diamino carbazole 12 was reacted in
presence of 0.25 equivalent of 10 and 0.75 equivalent of the EDOT 13). Throughout the paper,
we refer to these polymers as “2,7-EDOT-%”: for instance, in the previous example, the
synthesized polymer corresponds to 2,7-EDOT-75.
Poly(2,7-diimino-N-dodecylcarbazole-alt-2,7-N-dodecylcarbazole) (2,7-2,7Cbz)
1H NMR (400 MHz, CDCl3):
δ (ppm) 9.00 – 6.55 (m, 14H), 4.75 (s, 1H), 4.59 (s, 1H), 2.36 (s,
4H), 1.98 (s, 4H), 1.48-0.91 (m, 48H), 0.81 (m, 12H).
FT-IR (ATR):
ν= 3411 (N-H stretch), 2913 (CH2 asymmetric stretch), 2858 (CH2 symmetric
stretch), 1691 (CH=O stretch), 1590 (CH=N stretch), 1458 (C=C stretch) cm-1
14

ACCEPTED MANUSCRIPT
Poly(2,7-diimino-N-dodecylcarbazole-alt-3,6-N-dodecylcarbazole) (2,7-3,6Cbz)
1H NMR (400 MHz, CDCl3):
4H), 1.99 (s, 4H), 1.37-0.92 (m, 48H), 0.92 (m, 12H).
FT-IR (ATR): = 3370 (N-H stretch), 2925 (CH2 asymmetric stretch), 2850 (CH2 symmetric
δ (ppm) 8.69-6.51 (m, 14H), 4.65 (s, 1H), 4.37 (s, 1H), 2.36 (s,
ν
stretch), 1690 (CH=O stretch), 1590 (CH=N stretch), 1470 (C=C stretch) cm-1
Poly(3,6-diimino-N-dodecylcarbazole-alt-2,7-N-dodecylcarbazole) (3,6-2,7Cbz)
1H NMR (400 MHz, CDCl3):
4H), 1.99 (s, 4H), 1.37-0.92 (m, 48H), 0.92 (m, 12H).
FT-IR (ATR): = 341 (N-H stretch), 2923 (CH2 asymmetric stretch), 2849 (CH2 symmetric
δ (ppm) 8.69-6.51 (m, 14H), 4.65 (s, 1H), 4.37 (s, 1H), 2.36 (s,
ν
stretch), 1688 (CH=O stretch), 1610 (CH=N stretch), 1463 (C=C stretch) cm-1
Poly(3,6-diimino-N-dodecylcarbazole-alt-3,6-N-dodecylcarbazole) (3,6-3,6Cbz)
1H NMR (400 MHz, CDCl3):
(s, 4H), 1.35-0.92 (m, 48H), 0.83 (m, 12H).
FT-IR (ATR): = 3393 (N-H stretch), 2931 (CH2 asymmetric stretch), 2848 (CH2 symmetric
δ (ppm) 9.00–7.20 (m, 14H), 4.72-4.53 (m, 2H), 2.34 (s, 4H), 1.98
ν
stretch), 1694 (CH=O stretch), 1582 (CH=N stretch), 1458 (C=C stretch) cm-1
Poly(2,7-diimino-N-dodecylcarbazole-alt-2,7-N-dodecylcarbazole-ran-2,7-diimino-N-
dodecylcarbazole-alt-3,4-ethylenedioxythiophene) (2,7-EDOT-“EDOT percentage”)
15

ACCEPTED MANUSCRIPT
1
The H NMR and FT-IR signals can slightly shift depending of the amount of EDOT inserted.
1
For H NMR the only difference between them is the integration of the four EDOT protons
around 4.45 ppm. For the (2,7-EDOT-50):
1H NMR (400 MHz, CDCl3):
1H), 4.44 (s, 3H), 2.32 (m, 2H), 2.96 (m, 3H), 1.36-1.00 (m, 24H), 0.83 (t, 6H).
FT-IR (ATR): = 2917 (CH2 asymmetric stretch), 2852 (CH2 symmetric stretch), 1697 (CH=O
δ (ppm) 8.79 (s, 2H) 9.05-7.30 (m, 6H), 7.23-6.52 (m, 2H), 4.57 (s,
ν
stretch), 1575 (CH=N stretch), 1459 (C=C stretch) cm-1
Results and discussion
Synthesis of carbazole monomers
In order to tune the opto-electronic features of carbazole-based polyazomethines, four
carbazole monomers were designed, differing from each other in the position of reactive groups
towards the formation of azomethine linkages. Two di-amino and two di-formaldehyde
functionalized carbazoles were thus substituted in 3,6 and 2,7 positions. The general procedure is
shown in Scheme 1. Both 3,6 di-substituted carbazoles were synthesized from the alkylated
carbazole 1 which in turn was obtained in one alkylation step from the commercial carbazole.
The alkylation step ensures the solubility of the final polymer. The success of alkylation was
confirmed by NMR, where the disappearance of the aromatic protons on the carbazole nitrogen
at 10.59 ppm and the appearance of all protons on the alkyl chain was observed. The alkyl chain
3 used for this purpose had to be synthesized in two steps via a Grignard reagent, through the
synthesis of the alcohol derivative 2. It is noteworthy that a broadening of aromatic signals was
only observed on NMR spectra when alkylation was achieved with branched moieties and not
with linear alkyl chains, as already reported in literature as atropoisomeric behaviour. [38,39] For
16

ACCEPTED MANUSCRIPT
instance, in the case of NOESY NMR spectrum of 2,7-diformylcarbazole 10 a spatial interaction
between aromatic protons at 8 ppm and those from the alkyl chain around 1 and 2 ppm can be
observed. All the signals on the horizontal line at 10.17 ppm show the interactions between the
aldehyde proton and aromatics ones (see SI). The alkylated carbazole 1 can either be involved in
a Vilsmeier-Haack reaction in presence of DMF and POCl3 to afford the 3,6-diformylcarbazole 4
with a yield of 65% or a nitration in the so-called Menke conditions in presence of copper nitrate
in order to give the 3,6-dinitrocarbazole 5.[40] Its reduction, using palladium on charcoal and
hydrazine, gave the desired 3,6-diaminocarbazole 6 via the formation of an hydroxylamine
during the reaction.[41,42] The purity and structure of these two monomers were proven with
various techniques. For both monomers the measured mass is coherent with the theoretical one.
1
13
The structure and purity were confirmed by ATR-FTIR, H and C NMR experiments (see SI,
Figures S3, S4 and S8). The two 2,7 substituted carbazole derivatives 10 and 12, the diformyl
and diaminocarbazole respectively, were synthesized from the 2,7-dibromo-9H-carbazole 8. The
synthesis was carried out in two steps, starting with the nitration of the dibromo-biphenyl in
presence of nitric acid in acetic acid to give the nitrated compound 7 followed by a Cadogan
cyclization.[43,44] The compound was then alkylated using the previously synthesized chain 3 in
presence of potassium hydroxide. Finally, the 2,7-diformylcarbazole 10 was obtained after a
nucleophilic substitution with butyl lithium and DMF. The 2,7-diaminocarbazole 12 was
synthesized in two uncommon steps. Indeed, the previously synthesized 2,7-dibromocarbazole 8
was subjected to an azidation reaction using sodium azide and copper iodide (Ullman reaction)
giving rise to the diazido compound 11.[45] In this reaction, the dimethylethylenediamine is used
as a ligand and sodium ascorbate is used to stabilise the copper.[46] The presence of azide
17

ACCEPTED MANUSCRIPT
functions was confirmed via ATR-FTIR, where the strong band at 2120 cm-1 corresponding to
H
N
C8H17
C8H17
N
Et3N
Me3N-HCl
C8H17
C8H17
C8H17
C8H17
O
H2 H2
Mg
H3C
C
C
Br
+
HO
TsO
Et2O
6
CH2Cl2
r.t. 2H
KOH
DMSO
H
O
r.t. overnight
2
3
1
4
1
5
6
C8H17
C8H17
H
NO2
N
N
3
Br
HNO3, H2SO4
Acetic Acid
POEt3
Br
Br
Br
Br
Br
Br
KOH
DMSO
Br
7
8
9
10
9
11
12
the azide stretching deformation is observed (see SI, Figure S16).
Scheme 1: Synthesis of carbazole monomers; the 3,6-diformylcarbazole (4), the 3,6-
diaminocarbazole (6), the 2,7-diformylcarbazole (10) and the 2,7-diaminocarbazole (12).
Then, the 2,7 diaminocarbazole 12 was prepared via the reduction of azido groups thanks to a
Staudinger reaction in presence of tributylphosphine.[47] The purity and structure of products
1
were assessed by NMR amongst other analyses (see SI). For both 10 and 12 monomers, the H
NMR spectra showed a shift of aromatic signals due to the substitution of bromine with amino
and formyl moieties. Besides, the appearance of the formyl signal at 10.11 ppm and the broad
signal corresponding to the amino functions at 3.79 ppm for the diformyl and diaminocarbazole
respectively confirmed the structure.
18

ACCEPTED MANUSCRIPT
O
O
S
O
H
S
1) n-Buli, -78°C, THF
2) DMF, -78°C
H
O
O
O
13
Scheme 2: Synthesis of the EDOT dialdehyde derivative 13.
Scheme 3: Synthesis of carbazole-based polyazomethines.
Finally, the EDOT dialdehyde 13 was synthesized using butyl lithium and DMF in one step
using commercial EDOT following the same protocol as for the 2,7 diformylcarbazole (Scheme
2). Once again the purity was confirmed via classical spectroscopy techniques (see SI, Figures
S19 and S20).
Synthesis of carbazole-based polyazomethines
All the polymers were synthesized following the same method (Scheme 3). Stoichiometric
amounts of diamino- and diformyl-carbazole monomers were allowed to react in toluene for four
hours at 130°C. Microwave radiations were preferred to the conventional dean-stark apparatus in
order to speed up the polymerization reaction. Indeed, polymers with similar size and dispersity
have been obtained after one day with the conventional dean-stark apparatus and only in four
hours under microwave irradiation. Silica gel was added in the reaction media as a desiccant
agent, in order to shift the equilibrium toward the formation of the polymer. The formation of the
azomethine linkages was particularly confirmed by ATR-FTIR spectroscopy where the
19

ACCEPTED MANUSCRIPT
disappearance of amino and formyl signals, respectively at 1600 cm-1 and 1700 cm-1, along with
the appearance of a signal at 1650 cm-1 corresponding to the azomethine -C=N- stretching were
1
observed. By H NMR, the signal corresponding to the -CH=N- bond was observed around 8.8
ppm, for each polymer (See SI, Figure S21).
1,5
2,7-2,7Cbz
3,6-2,7Cbz
3,6-3,6Cbz
2,7-3,6Cbz
0,0
1
0
300
400
500
600
700
800
Wavelength (nm)
Figure 1: Absorption (top) and emission (bottom) spectra of the fully carbazole-based
polyazomethines in chloroform at a concentration of 5.10-4 g.L-1
Table 1 : Molecular weight, thermal and optical properties of carbazole based polyazomethines
Absorptiond
Emissiond
b
c
ꢐꢐꢐꢐa
ꢎꢏ
ꢐꢐꢐꢐꢐa
ꢎꢑ
Td
Tg
Ða
a
ꢐꢐꢐꢐꢐ
ꢒꢓn
Polymer
sol
film
sol
g.mol-1
g.mol-1
λmax
λmax
λmax
°C
°C
Φfe
nm
nm
nm
2,7-2,7
Cbz
3600
3650
3500
3700
10500
13700
10050
11700
2.9
3.7
2.9
3.2
4 (6)
4 (6)
4 (6)
4 (6)
451
430
430
436
98
91
272-428
270-436
267-402
265-420
405-540
0.03
0.02
0.03
2,7-3,6
Cbz
270-400
267-416
405-570
405-580
3,6-2,7
Cbz
112
93
3,6-3,6
264-310-360
263-315-362 405-455-565 0.04
20

ACCEPTED MANUSCRIPT
Cbz
aMeasured by SEC in CHCl3 at 30 °C, relative to PS standards. Values between brackets have
b
been estimated by mass spectrometry FD-TOF. Degradation temperature obtained by TGA
c
under N2 at 10 °C min−1. Glass transition temperature obtained by DSC under He at 20 °C
d
min−1. Maximum of absorption and emission measured in CHCl3 solutions (5.10-4 g.L−1) and
e
spin-coated on quartz. Fluorescence quantum yield, measured in solution using an integration
sphere.
Molecular weights of compounds were evaluated by SEC and are reported in Table 1. All
polycarbazole azomethines have a similar size (confirmed by mass spectrometry and NMR, see
SI), from 3500 to 3700 g.mol-1 with dispersity between 2.0 and 3.0 which is quite coherent with
a condensation reaction mechanism. These results have been obtained on raw polymers,
extraction with Soxhlet apparatus tends to eliminate smaller oligomers and consequently narrows
the distribution. It is noteworthy that the shape of chromatograms is also in agreement with a
polycondensation process showing a series of oligomers. Similar results were obtained in the
presence of most commonly used desiccants such as magnesium sulfate or lithium chloride even
though they have been reported to have an impact on the preparation of higher molecular weight
polyazomethines.[23] The thermogravimetric (TGA) and differential scanning calorimetry
(DSC) analyses showed good thermal stability with decomposition temperatures ranging from
430 to 450 °C, as well as glass transition temperatures ranging from 93 to 112 °C. As commonly
observed in the case of alternated π-conjugated polymers, such materials appear amorphous.
Oligomer conformation
Although the study of bulk and thin film morphologies of the synthesized oligomers goes
beyond the scope of this article, theoretical calculations can provide some hints of the possible
structure of the chains, and in particular if linearity (crystallinity) is favoured with respect to
21

ACCEPTED MANUSCRIPT
more folded (amorphous) structures. Still focusing on dimers, the conformational analysis
revealed that 512 main conformers can exist, essentially depending on the rotation about the C-
N=R and R-C=N single bonds (see supporting information). Each conformer was optimized and
its energy employed in the Boltzmann-weighted calculation of the average end-to-end distance,
whose histogram is reported in Figure 2, together with a graphical representation of the most
stable conformer for sake of illustration (even if in all the cases there are dozens of conformers
contributing to the average distribution). Overall the rather irregular structure of the oligomers
and the existence of several stable conformers do not seem favour crystallinity, in accord with
the experimental observation; however, there exists striking differences between the different
structures: while (2,7-2,7 Cbz) is mostly elongated, and hence probably prone to the formation of
π-stacked domains, (2,7-3,6), (3,6-2,7) and (2,7-EDOT) are more likely to assume bent
conformations with average end-to-end distances about 25% shorter than (2,7-2,7). Quite
surprisingly, the (3,6-3,6) stands out from the others, because it tends to form folded structure
with intrachain non-bonded contacts that might be interesting for enhancing the number of
charge transport pathways in organic electronics applications.
22

ACCEPTED MANUSCRIPT
Figure 2: Left: Boltzmann weighted distribution of end-to-end distances for the five dimers.
Right: molecular structure of the minimum energy dimers. The corresponding average end-to-
end distances are 38.9, 28.5, 26.2 9.6, and 28.6 Å, respectively.
Optical characterizations and evaluation of electronic delocalization
As shown in Figure 1, polyazomethines with 2,7-carbazole linkages showed higher absorption
coefficient as compared to 3,6- derivatives (at similar concentrations). Moreover, maximum of
absorption was red shifted from 359 nm to 426 nm, suggesting an increase of the delocalization
or of conjugation length. Besides, all polymers showed broad emission spectra along with rather
low fluorescence quantum efficiency values as compared to literature, albeit these yields could
be increased by lowering the temperature or doping the polymers by protonation (e.g. with 2,2,2-
trifluoroethanoic acid).[24,26,48] Turning to the calculation on dimers, we observe that the
23

ACCEPTED MANUSCRIPT
maximum absorption wavelengths in Tables 2 are consistent with the experimental data in Table
1. Although we do not expect an exact match of the results because the calculated value depends
strongly both on the number of monomers and on the choice of the functional,[49,50] this
agreement strengthens the validity of the computational results. Absorption spectra were
calculated only for the most stable dimer conformers out of 512 for each species, but we verified
that the frontier orbital energies in gas phase exhibit negligible variations (less than 50 meV)
upon conformational change. As a consequence, we predict a very weak direct correlation
between optical or electrochemical gap and chain conformation; still less direct correlations are
possible due to conformer-dependent intermolecular interactions and packing.
To investigate the differences between these apparently very similar polymers, we computed
two delocalization indexes, the bond length and the bond order alternation (BLA and BOA), and
monitored as well the average length of the C=N and N-C bonds.[51–53] In a perfectly resonant
polymer all the bonds of the same type along the backbone (C-C and C-N in our case) should
have identical length, and the indicators in Table 2 measure the deviation from this ideal
situation. Both BLA and BOA identify the 2,7-2,7 as the most conjugated one, even if looking at
the C=N and N-C bond lengths is hard to spot a difference between the polymers. This is
somewhat surprising as only for 2,7-2,7 it is possible to write a full quinoid resonant structure,
while for polymers with the 3,6 unit, on the basis of the resonant structure one would expect a
break of the conjugation.[54] The BOA seems to better capture this effect with respect to the
purely geometrical BLA parameter, and clearly indicates a higher delocalization for 2,7-2,7.
Table 2 : Electronic and structural properties for dimers as calculated with density functional
theory at PBE0/def2-TZVP/def2-SVP level. The absorption spectrum and its λmax were obtained
24

ACCEPTED MANUSCRIPT
by adding Gaussian distributions with standard deviation of 0.15 eV centered at the excited state
energies obtained with the Tamm-Dancoff Approximation. BLA and BOA stands for bond
length and bond order alternation, respectively.
S0-S1
HOMO LUMO
H-L
(eV)
λmax
(nm)
N=C
(Å)
C-N
(Å)
Dimer
BLA
(Å)
BOA
(eV)
-5.50
-5.36
-5.39
-5.16
-5.26
(eV)
-2.17
-1.76
-2.02
-1.51
-2.23
(eV)
2.82
(2,7-2,7
Cbz)2
3.33
438
1.2738 1.3953 0.0492
1.2739 1.3946 0.0521
1.2746 1.3977 0.0501
1.2741 1.3970 0.0546
1.2774 1.3928 0.0553
0.3104
0.3251
0.3369
0.3635
0.3438
(2,7-3,6
Cbz)2
3.60
3.37
3.65
3.03
3.07
2.88
3.09
2.59
402
430
356
479
(3,6-2,7
Cbz)2
(3,6-3,6
Cbz)2
(2,7-
EDOT)2
Synthesis of random copolyazomethines composed of 3,4-ethylenedioxythiophene
(EDOT) and 2,7-carbazole (2,7-Cbz) subunits
In order to tune the properties of such polymers, copolymers random copolymers were
synthesized introducing EDOT moieties in the chain, calculations showing a decrease of the
electronic gap with EDOT insertion. Copolymerization reactions were carried out in toluene
solution between 2,7-diaminocarbazole 12 and either EDOT bisaldehyde 13 or a mixture of
bisaldehyde, i.e. 2,7-diformylcarbazole 10 plus different ratio of EDOT bisaldehyde 13 from 25
mol% to 75 mol%, by keeping stoichiometric amounts of aldehyde vs amine functions (see
scheme 4). For instance, the copolymer 2,7-EDOT-25 was prepared from one equivalent of 2,7-
diamino carbazole 12 and 0.75 equivalent of 2,7-diformyl carbazole 10 plus 0.25 equivalent of
EDOT bisaldehyde 13.
25

ACCEPTED MANUSCRIPT
Scheme 4: Polyazomethine copolymer integrating EDOT and carbazole units.
Molecular, thermal and optical characteristics of copolymers are gathered in Table 3.
Table 3: Molecular weight, thermal and optical properties of polyazomethines containing EDOT
Absorption
Emission
Polymer
ꢐꢐꢐꢐ
ꢎꢏ
ꢐꢐꢐꢐꢐ
ꢎꢑ
ꢐꢐꢐꢐꢐ
ꢒꢓn
Td
Tg
(Theoretical
dialdehyde
EDOT
Φf
Ð
sol
sol
g.mol-1 g.mol-1
/°C
/°C
λmax
λmax
film
percentage)
/nm
/nm
365
2,7-2,7Cbz
(0%)
3600
3150
10500
9600
2.9
3.0
4 (x=4)
451 101
393 114
272-428
0.03
0.04
2,7-EDOT-
25
4 (x=3, y=1)
272-426
272-450
265-482
262-483
367
367
370
380
(25%)
2,7-EDOT-
50
4200
2500
2400
10100
7950
4900
2.4
3.2
2.0
6 (x=3, y=3)
4 (x=1,y=3)
4 (y=4)
371
391
382
89
0.06
0.08
0.06
(50%)
2,7-EDOT-
75
/
/
(75%)
2,7-EDOT-
100
(100%)
26

ACCEPTED MANUSCRIPT
aMeasured by SEC in CHCl3 at 30 °C, relative to PS standards and by mass spectrometry
MALDI-TOF. bObtained by TGA under N2 at 10 °C min−1. cObtained by DSC under He at 20 °C
d
e
min−1. Measured in CHCl3 solutions (5.10-4 g l−1) and spin-coated on quartz. Measured in
solution in an integration sphere.
The EDOT insertion does not seem to have any impact on the decomposition temperature but
slightly increase the molecular weight with insertion of 50% EDOT. The red shift of the
absorption peak observed with the increase in EDOT content (see Figure 3) can be attributed to
the diminution of the band gap, as confirmed by calculation data along with electrochemical
results (see Tables 2 & 4). Besides, the lower absorption signals as observed in Figure 3 upon
insertion of EDOT subunits can be explained by a lower molar attenuation coefficient in the case
of EDOT as compared to carbazole subunits, respectively 7050 L.mol-1.cm-1 and 32000 L.mol-
1.cm-1 at 255 nm.[55,56]
Table 4 : Electrochemical properties of the polyazomethinesa
HOMO
(eV)
LUMO
(eV)
Polymer
GAP (eV)
- 5.22
- 5.40
- 5.41
- 5.50
- 5.31
- 5.52
- 5.35
- 2.30
- 2.22
- 2.21
- 2.45
- 2.70
- 3.09
- 3.05
2.92
3.18
3.20
3.05
2.61
2.45
2.30
2.7-2.7 Cbz
2.7-3.6 Cbz
3.6-3.6 Cbz
3.6-2.7 Cbz
2.7-Edot-25
2.7-Edot-50
2.7-Edot-75
2.7-Edot-
100
- 5.20
- 3.09
2.11
aCalculated from the onset of the oxidation peak (Eonsetox) and reduction peak (Eonsetred).
27

ACCEPTED MANUSCRIPT
0%(2,7-2,7Cbz)
25%
50%
75%
100%
0,5
0,0
1
0
200 300 400 500 600 700 800 900
Wavelength (nm)
Figure 3: Absorption (top) and emission (bottom) spectra of polyazomethines containing
different ratio of EDOT moiety
Electrochemical properties
Electrochemical features (see Table 4) were estimated by cyclic voltammetry. HOMO and
LUMO energy levels were estimated according to the equations: EHOMO(eV) = -(EOx) (V) + 4.4 -
0.03 and ELUMO(eV) = -(ERed) (V) + 4.4 + 0.22, where 0.03 eV corresponds to the energetic
position of the potential E1/2 for the ferrocene/ferrocenium (Fc/Fc+) redox couple, estimated from
a ferrocene solution in chloroform using saturated calomel electrode as reference.[57,58] The
electrochemical band gap was thus estimated in the range from 2.11 to 3.18 eV. In fact, these
results are in accord with the repeating units catenation and the electronic delocalization, in
particular in the case of 2,7-carbazole subunits that showed lower band gap values. Moreover,
alternation of electron-withdrawing and -donating subunits also leads to a decrease of the optical
gap, as confirmed by the red-shift observed on absorption spectra of such polymers.
28

ACCEPTED MANUSCRIPT
Conclusions
In this work, we successfully synthesized original
π-conjugated copolyazomethines. Their
synthesis by itself combines different advantages: it can be performed without metallic-based
catalyst, avoiding the need of stringent purifications, and can even been carried out with solid
silica as desiccant, which subsequently can be simply removed by filtration. Furthermore, the
polymerizations could be performed under microwave irradiation which is faster and eco-
friendlier as compared to more conventional heating process. Different diamino and diformyl
carbazole monomers have been synthesized, and we particularly investigated the impact of
carbazole catenation within the polyazomethine backbone leaning towards 2,7-carbazole
preferred linkages. Integration of EDOT subunits allows obtaining polymers with higher
molecular weight and a red shift of their absorption with respect of carbazole-based
polyazomethines, showing promise for such low band-gap materials. The latter are currently
investigated in optoelectronic devices, such as OFET and OPV (see preliminary data in
supporting information). The integration of different co-monomers in the polymer chain is also
under consideration.
ASSOCIATED CONTENT
Supporting Information
.
The following files are available free of charge.
Figure S1 to S20: 1H, 13C, 1H-13C HSQC NMR, ATR-FTIR spectra of synthesized monomers.
Figure S21 to S33: 1H-13C HSQC NMR, ATR-FTIR spectra of synthesized polymers.
29