Synthesis of carbazole-based copolymers containing carbazole-thiazolo[5,4-: D] thiazole groups with different dopants and their fluorescence and electrical conductivity applications

Article abstract of DOI:10.1039/c6ra08888k

To improve the electrical conductivity of poly(carbazole-thiazolo[5,4-d]thiazole) (p-CzTT), five different dopants, such as HCl, Fe(iii), Cu(ii), H₃BO₃, and I₂, were introduced into its framework through protonation of a nitrogen atom or by complex formation. Carbazole-thiazolo[5,4-d]thiazole (CzTT) and poly(carbazole-thiazolo[5,4-d]thiazole) (p-CzTT) were synthesized by the reactions of carbazole aldehydes and dithiooxamide. The synthesized monomer and polymer were confirmed by FT-IR, UV-vis, ¹H, ¹³C-NMR, and GPC studies. The doped polymers were examined by FT-IR spectroscopy, UV-visible absorption, fluorescence, thermogravimetric analysis (TGA), cyclic voltammetry (CV), and electrical conductivity. The optical band gap (Eoptg) of CzTT and p-CzTT were found to be 2.74 eV and 1.95 eV, respectively. The thermal stability of the polymer showed 5% weight loss at 358 °C. Based on CV analysis, the HOMO and LUMO energy levels and the electrochemical band gap (Ecvg) of p-CzTT were obtained as -5.86 eV, -3.19 eV, and 2.67 eV, respectively. The CzTT and p-CzTT exhibited fluorescence emission at 461 nm and 448 nm, respectively. Among the dopants introduced, Fe(iii)- and I₂-doped polymer showed excellent electrical conductivities of 6.8 × 10^-5 S cm^-1 and 5.9 × 10^-5 S cm^-1, respectively.

Full text of DOI:10.1039/c6ra08888k

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Synthesis of carbazole-based copolymer containing a carbazole-
thiazolo[5,4-d]thiazole groups with different dopants and their
fluorescence, electrical conductivity applications
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
Govindasamy Sathiyana, Rangasamy Thangamuthub and Pachagounder Sakthivela*
To improve the electrical conductivity of poly(carbazole-thiazolo[5,4-d]thiazole) (p-CzTT), five different dopants such as
HCl, Fe(III), Cu(II), H3BO3, and I2 were introduced into its framework through protonation of nitrogen atom or complex
formation. The carbazole-thiazolo[5,4-d]thiazole (CzTT) and poly(carbazole-thiazolo[5,4-d]thiazole) (p-CzTT) were
synthesized by the reactions of carbazole aldehydes and dithiooxamide. The synthesized monomer and polymer were
confirmed by FT-IR, UV–vis, 1H, 13C-NMR, and GPC studies. The doped polymers were examined by FT-IR spectroscopy, UV–
visible absorption, fluorescence, thermogravimetric analysis (TGA), cyclic voltammetry (CV) and electrical conductivity. The
optical band gap (Egopt) of CzTT and p-CzTT were found to be 2.74 eV and 1.95 eV, respectively. The thermal stability of
polymer showed 5% weight loss at 358 °C. Based on CV analysis, the HOMO, LUMO energy level and electrochemical band
gap (Egcv) of p-CzTT were obtained as -5.86 eV, -3.19 eV and 2.67 eV, respectively. The CzTT and p-CzTT have exhibited
fluorescence emission at 461 nm and 448 nm. Among these dopants, Fe (III) and I2 doped polymer showed excellent
electrical conductivity of 6.8×10-5 S cm-1 and 5.9×10-5 S cm-1, respectively.
semiconductor. The carbazole derivatives have deep-lying highest
occupied molecular orbital (HOMO) energy level that is attributed
1. Introduction
Conducting polymers play a vital role in the conversion of light
energy into electrical energy (solar cell) and energy storage devices
(battery, supercapacitor, and electrical double layer capacitor).1,2
Electric devices consist of organic materials which absorption of
sunlight and converts photon into electrons (solar cell) and liquid
electrolyte reactions (power tools).3-5 In particular series of organic
electronic devices, the conjugated polymers exhibit the presence of
π-electrons delocalized as the carriers for an electron moving,
character expressed. It has been found that polythiophene,
polyacetylene, polyaniline, polypyrrole, and polyphenylene
polymers cover a portion of conducting polymers.6-8
Over the past few years, π-conjugated fused ring systems have
attracted the attention of researcher due to their potential usage in
the areas of optics, electronics, and solar energy technologies.9 The
carbazole is a tricyclic fused ring system contains a single nitrogen
atom which increases the electron rich nature and hole transporting
property.10 The carbazole-based polymer and small molecules have
been considered as a motivating organic
to high open-circuit voltage (Voc). Further, it has high hole mobility
due to more preferential π-π stacking that can enhance short-circuit
current density (Jsc) and fill factor (FF) of the device. Other than
conducting properties, the carbazole-based polymers have
fluorescence, electro-optical, and hole-transporting properties.11-15
Nowadays designing of a donor–acceptor (D–A) type molecules was
found to be crucial due to their effective photoinduced
intramolecular charge-transfer characteristics between donor and
acceptor moiety. The thiazolo[5,4-d]thiazole (TTz) moiety is
commonly employed as acceptor in the system of donor-acceptor
(D-A) type polymers owing to their good electron withdrawing
properties, planar structures, and easy synthesis.16 This TTz moiety
has a rigid coplanar ring and thereby facilitates intermolecular
ordering with high charge-carrier mobility.17-19 Therefore,
introduction of thiazolo[5,4-d]thiazole moiety into electron poor
alternating copolymers may generate efficient photovoltaic
materials with both low band gap and high charge-carrier
mobility.20,21 The structural rigidity of TTz unit in fused with
coplanar ring shows low solubility in organic solvents. The solubility
of polymer can be increased by introducing alkyl side chain in the π-
conjugated fused ring system. Hence, polymers have a fused
coplanar as the main backbone with good planarity for
intermolecular packing and high charge mobility.22,23 Olgun et al.,
have reported a series of copolymer dye of thiazolo[5,4-d]thiazolo
acceptor moiety and different benzene, triphenylamine as the
donor units.24-28 They have described TTz acceptor moiety-
a.Department of Chemistry, School of Advanced Sciences, VIT University, Vellore,
Tamil Nadu, India-632 014.
b.Electrochemical Materials Science Division, CSIR-Central Electrochemical Research
Institute, Karaikudi-630 003.
† Corresponding author. E-mail: sakthivel.p@vit.ac.in and polysathi@gmail.com
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
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containing polymer showed low band gap of 1.36 eV and 2.50 eV. dopants which may form complex with N and S atoms. The effect of
The polymer and their doped polymers exhibit
a maximum dopants and their spectroscopic results are discussed.
electrical conductivity of 0.35 µS cm-1. The phenylene and
thiazolo[5,4-d]thiazoles containing compounds have been
investigated for fluorescence, electrical conductivity, and solar cell
applications. Previous reports reveal that molecules of
poly(phenylene-thiazolo[5,4-d]thiazole)26
,
thiophene-thiazolo[5,4-
d]thiazole,29 dithiophene-co-thiazolo[5,4-d]thiazole,30 and poly[{4,4-
bis(2-ethylhexyl)-4H-cyclopenta[2,1-b:3,4-b’]dithiophene-2,6-diyl}-
alt-{2,5-di(thiophen-2-yl)thiazolo-[5,4-d]thiazole-5,5’-diyl}],31 have
been used for solar cell and electrical applications.
In this work, carbazole-thiazolo[5,4-d]thiazole (CzTT) and
poly(carbazole-thiazolo[5,4-d]thiazole) (p-CzTT) were synthesized
by the reacting 9-hexyl-9H-carbazole-3-carbaldehyde (or) 9-hexyl-
9H-carbazole-3,6-dicarbaldehyde
with
dithiooxamide.
The
synthesized p-CzTT was doped with HCl, I2, Cu(II), Fe(III) and H3BO3.
The monomer (CzTT) and polymer (p-CzTT) were confirmed by 1H,
13C-NMR, and GPC. Thermal stability of the p-CzTT has been
examined by TGA. The doped and undoped forms of p-CzTT
polymer were characterized by UV-vis, FT-IR, and electrical
conductivity. The HOMO, LUMO energy levels and the band gap of
CzTT and p-CzTT were calculated by cyclic voltammetry (CV).
Scheme 1: Synthesis of CzTT and p-CzTT
2.2. GPC molecular weight and Thermal stability
The molecular weight of synthesized polymer was investigated by
GPC measurements in THF solution. From GPC, we obtained weight
average molecular weight (Mw) of 2498 g/mol and number average
molecular weight (Mn) of 2485 g/mol with n = 8 and 9. Thermal
properties of polymer (p-CzTT) was investigated by
thermogravimetric analysis (TGA) under nitrogen atmosphere at a
heating rate of 10 °C min-1 as shown in Fig. 1. TGA curve illustrates
that 5% decomposition temperature (Td) of polymer was found to
be 358 °C. The polymer has shown high thermal stability which
makes it attractive candidate for electrical and solar cell
applications.34
2. Results and discussion
2.1. Synthesis and doping of p-CzTT polymer
The
compounds
carbazole-thiazolo[5,4-d]thiazole
and
poly(carbazole-thiazolo[5,4-d]thiazole) (p-CzTT) were synthesized
from 9-hexyl-9H-carbazole-3-carbaldehyde, 9-hexyl-9H-carbazole-
3,6-dicarbaldehyde, and dithiooxamide. The outline of synthetic
procedure adopted is shown in Scheme 1. The carbazole was
alkylated by using hexyl bromide. The purpose of introducing hexyl
chain in carbazole is to reduce steric hindrance, and increase
solubility. Further, the carbazole was formylated in 3,6-poisition by
Vilsmeier–Haack formylation reaction. The obtained single and
double side aldehyde product was treated with dithiooxamide to
get monomer (CzTT) and polymer (p-CzTT). The electron rich
carbazole moiety act as p-type and the electron deficient
thiazolo[5,4-d]thiazole act as n-type material. This alternating
copolymer has more push-pull property due to the D-A type
polymer structure. The p-CzTT polymer was doped with different
dopants such as HCl, Fe(III), Cu(II), H3BO3 and I2. The possible
interaction of dopants with polymer is either partially oxidation or
reduction. These effects may enhance the electrical conductivity
and binding with metal to form a complex. This has been studied by
using cyclic voltammetry and fluorescence.
The UV-visible absorption spectrum of monomer (CzTT)
exhibited three absorption bands at λmax of 284, 326, and 403 nm.
Whereas, the polymer (p-CzTT) follow the same pattern at λmax 282,
338, 557 nm. The polymer (p-CzTT) is stable up to 356 °C as
interpreted from TGA curve. The p-CzTT shows fluorescence
emissions peak at 448 nm with the corresponding excitation at 338
nm. The undoped and doped polymers are examined for HOMO,
LUMO energy level and their band gap using CV.
In this present work, the polymer p-CzTT was doped with
different dopants like HCl, Fe(III), Cu(II), H3BO3, and I2. All the
dopants effectively react with TTz moiety to form either complex or
N-substituted bonds without any effects on carbazole moiety. The
dopants such as strong and weak acids can protonate nitrogen
atoms of TTz moiety by forming N-H bond or nitrogen-boron bonds.
Fe(III) and Cu(II) ions show a redox doping behaviour by favouring a
complex formation with TTz moiety. Iodine is also one of the redox
Figure 1. TGA curve of p-CzTT polymer
2.3. 1H-NMR spectroscopy
1H-NMR spectrum of copolymer (p-CzTT) was recorded in DMSO-d6,
and the obtained spectrum is given in Fig. 2. The p-CzTT copolymer
containing aldehyde proton (a) appeared at 10.13 ppm. The hexyl
protons (c,d,e) appears in the range of 0.5-5 ppm whereas the
carbazole protons (b,*) appears as multiplets in the range 6.5-9.5
ppm. These results confirm the chemical structure of p-CzTT
copolymer.
2 | J. Name., 2012, 00, 1-3
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between B–N after doping with H3BO3.25 The characteristic polymer
peak at 1321 cm-1 completely varied after adding dopant which
indicates the formation of new bond between dopant and
polymer.35
Figure 2. 1H-NMR spectrum of p-CzTT
2.4. FT-IR spectra of undoped and doped polymers
Synthesized and doped polymers were studied by FT-IR
spectroscopy. FT-IR spectra recorded by making the solid mixture of
polymer with dopants and the obtained spectra are shown in Fig. 3.
The obtained results are summarized in Table 1. From FT-IR spectra,
effect of various dopants were compared and confirmed the
coordination of dopants with polymer. FT-IR spectra of polymer
showed the C≡N vibration peak at 1673 cm-1 which get shifted to
low vibration frequency of 1593 cm-1 after HCl addition. This might
be due to protonation of nitrogen atoms. The peak at 1192 cm-1
indicates B–O vibration of H3BO3 doped sample. The shift of peak at
1321 cm-1 to 1379 cm-1 could be possibly due to bond formation
Figure 3. FT-IR spectra of undoped and doped form of polymer
samples
Table 1. FT-IR spectra data of undoped and doped polymers.
Samples
FT-IR absorption peak (in cm-1)
p-CzTT
773
-
-
1321
1381
1483
1483
1483
1379
1637
1548
1591
1591
1593
1643
2924
2922
2924
2924
2918
2970
3439
3361
3346
3346
3363
3184
Cu(II) doped
Fe(III) doped
I2doped
-
804
804
806
791
1236
1236
1259
1192
HCl doped
H3BO3 doped
2.5. UV–visible absorption spectroscopy
spectra of Cu(II), Fe(III) and I2 doped p-CzTT polymer recorded in
DMF solvent (0.20 g/L) are shown in Fig. 6. The concentration of
dopants are 2N (HCl), 1.81×10-4 M (Cu(II)), 1.6×10-4 M (Fe(III)),
6.18×10-4 M (H3BO3) and 1.2×10-4 M (I2) in DMF solutions. The
electron withdrawing nature of dopants causes the shift in
absorption peaks from lower to higher wavelength. Moreover, it
was observed that I2 doped polymer shows more absorbance
compared with other dopants. The monomer and polymer optical
band gaps were calculated from UV absorption edge slope and
found to be 451, 635 nm, respectively. From these results, the
optical band gap for monomer and polymer was found to be 2.74
and 1.95 eV. The doped form of polymer with HCl, Cu(II), Fe(III),
H3BO3 and I2 show the optical band gap (Egopt) of 1.92, 3.17, 2.89,
1.92 and 2.63 eV, respectively. The above mentioned values were
calculated from UV absorption edge of 645, 391, 429, 640 and 471
nm, respectively correspond to doped form of polymer with HCl,
Cu(II), Fe(III) and I2.
UV-vis absorption spectra of synthesized monomer (CzTT) and
polymer (p-CzTT) were examined in DMF solutions (1.5 × 10-5 M)
and absorption results are shown in Fig. 4. CzTT and p-CzTT showed
three maximum absorption bands at (284, 282 nm), (326, 338 nm)
and (403, 557 nm), respectively. The bands at 326 nm and 338 nm
for monomer and polymer indicate the electron transition of π-π*
for carbazole moiety. 403 nm and 557 nm bands correspond to
thiazolo[5,4-d]thiazole (S and N) group for n–σ* electron transition
for CzTT and p-CzTT, respectively. Fig. 5 illustrates UV spectra of
undoped and HCl doped copolymer in various concentrations. The
polymer showed the last band at two shoulder peak λmax
wavelength at 524 nm and 557 nm. After, HCl doping the shoulder
peak completely shift from 557 nm to 567 nm. This is due to the
interaction of HCl proton with polymer nitrogen leading to
protonation of N. UV-vis absorbance
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Figure 4. UV-visible spectra of monomer and polymer in DMF solution; Figure 5. UV-visible spectra of polymer and HCl doped polymer
for various concentration in DMF solution
shown emission peak at 448 nm and excitation peak at 338 nm. The
polymer doped with HCl, Cu(II), Fe(III), H3BO3 and I2 has shown the
excitation peaks at 341, 341, 340, 342 nm and 363 nm and emission
peak at 443, 440, 443, 441 nm and 447 nm, respectively. Further,
the FL quantum yields (ΦF) were measured by using quinine sulfate
as the reference standard. The FL quantum yields found to be 0.29
and 0.30 for CzTT and p-CzTT, respectively in DMF solutions. The
HCl, Cu(II), Fe(III), H3BO3 and I2 doped polymer shows ΦF of 0.25,
0.33, 0.36, 0.33 and 0.34, respectively. The Fe (III) and I2 doped
polymers showed more ΦF value due to the more electron
withdrawing nature of the dopant. The undoped polymer quenched
with the addition of 0.1 mL HCl increment and fluorescence
recorded until completely quenched with an equal molar ratio of
polymer and HCl. The fluorescence study was done by 0.1 mL
addition of each dopant in the polymer. The FL intensity was
observed to be continuously decreasing with the addition of dopant
up to equimolar addition. All the emission peaks are almost similar
to each other. These results conclude that the dopant-polymer
Figure 6. UV-visible spectra of undoped and Fe(III), Cu(II), I2 doped
interactions are well identified. The quenching FL intensity and red-
polymer in DMF solution
shifted emission suggest that polymer molecules have stronger π-π
interaction with dopants. The fluorescence results of doped form of
polymers reveal intermolecular interaction and enhance the charge
carrier transport properties.
2.6. Fluorescence spectroscopy
The synthesized monomer and polymer were characterized by
fluorescence (FL) spectroscopy in DMF solvent. The polymer has
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Figure 7. Fluorescence spectra of undoped and doped form of polymer
2.7. Electrochemical properties
The electrochemical behaviour of undoped and doped polymer
samples was studied by cyclic voltammetry in DMSO solutions with
0.1M [nBu4 N]+[PF6] electrolyte solution. The obtained results were
shown in Fig. 8, and the data are summarized in Table 2. The onset
oxidation potential and reduction onset potential of the undoped
polymer were observed at 1.38 eV and -1.29 eV. The HOMO and
LUMO energy levels were calculated by using equation 1 and 2. The
band gap was calculated from the energy difference between
HOMO and LUMO energy levels.
HOMO= -eV (Eoxonset - E1/2ferrocene + 4.8) . . . . . . . . . . (1)
LUMO= -eV (Eredonset - E1/2ferrocene + 4.8) . . . . . . . . . . (2)
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Figure 8. Cyclic voltammograms of undoped and doped form of polymer samples. Scan rate = 100 mV s-1.
Table 2. CV data of undoped and doped polymers.
Samples
Onset oxidation
potential (V)
0.65
Onset Reduction
potential (V)
-1.39
HOMO (eV)
LUMO (eV)
Band gap (Eg)
(eV)
CzTT
p-CzTT
HCl doped
H3BO3 doped
Cu(II)doped
Fe(III)doped
-5.11
-5.86
-4.98
-5.43
-5.07
-5.02
-5.30
-3.07
-3.19
-2.46
-3.17
-3.08
-2.88
-3.53
2.04
2.67
2.52
2.26
1.99
2.14
1.38
0.50
0.95
0.59
-1.29
-2.02
-1.91
-1.40
0.54
-1.60
I doped
0.82
-0.95
1.77
2
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2.8. SEM microscopy analysis
Figure 10. SEM images of undoped and Fe(III) doped polymer
Figure 9. HOMO and LUMO energy level diagram of doped and
The surface morphology of undoped and Fe(III) doped polymer are
investigated by scanning electron microscopy (SEM) analysis and
the images are shown in Fig. 10. The surface of undoped p-CzTT
sample appears as gel-like morphology. Porus gel network surface
covered with tumours was observed for Fe(III) doped polymer. The
appearance of tumours might be due to incorporation of Fe(III) in
the polymer. Hence, these results indicate that formation of pores
might facilitate the electron movement. The incorporation of
dopants in polymer promotes easy transportation of electrons
leading to the enhanced electric conductivity of doped polymer.
undoped polymer
In these case of doped polymers enormously changes oxidation
and reduction potential due to their ability of oxidation and
reduction behaviours. The HOMO, LUMO and the electrochemical
band gap of doped and undoped polymer are also given as an
energy level diagram in Fig. 9. The metal-doped polymer has
shown low band gap compared to acid doped polymer. The Fe(III)
doped polymer shows strong reduction potential range at -1.60 eV.
The H3BO3 and I2 doped polymer showed deep-lying HOMO energy
levels of energy band diagram. CV studies conclude that doped
form of polymer can be used in organic photovoltaic applications.
Doped forms of polymer showed lowest HOMO and LUMO energy
levels compared to undoped polymer. The polymer has shown
deep-lying HOMO energy level at -5.86 eV which enhances the
open circuit voltage of solar cells whereas the hole mobility and
band gap were still low. The doped form of polymer has shown low
band gap and lowest HOMO and LUMO energy levels. The H3BO3
and I2 doped polymer showed deep-lying HOMO energy level at -
5.43 and -5.30 eV, respectively. The Fe(III) and HCl doped polymer
have shown low-lying LUMO energy levels of -2.88 and 2.46 eV,
respectively. The Fe(III) and Cu(II) doped polymer show very close
HOMO and LUMO energy levels. Wei et al., reported that the ideal
polymer showed HOMO, LUMO energy levels and band gap at -5.4
eV, -3.9 eV and 1.5 eV respectively.36 According to ideal values, our
doped form of the polymer sample also showed HOMO and LUMO
energy levels close to the reported results due to above reason all
these doped forms of the polymer can be used as a donor in bulk
heterojunction organic solar cells (BHJ-OSCs) applications.
2.9. Powder XRD of doped and undoped polymer
The HCl, Fe(III) doped and undoped polymer samples were studied
by powder XRD. XRD patterns (Fig. 11a) shows amorphous nature
of undoped polymer used as a precursor. Fig. 11b reveals the
presence of multiple elements such as S, HCl, and H. The peaks
corresponding to these elements were confirmed by matching
with standard JCPDS data card (S: 96-901-2335, 2783; HCl: 96-101-
0389 and H: 96-901-3086, 3088), respectively. Thus, it reveals that
HCl is successfully doped with the polymer. Similarly, dual peaks
were noticed in Fig. 11c. These peaks were found to match with
standard JCPDS patterns of Fe (96-900-0667) and S (96-901-2363).
These observations prove the presence of Fe(III) in the polymer
matrix. The XRD patterns also reveal amorphous nature of polymer
samples that can be useful for electrical conductivity applications.
HCl doped polymer samples show more crystalline pattern as
compared to Fe(III) doped polymer. Due to this crystalline nature
of HCl doped polymer shown low electrical conductivity.
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folds. Similarly, the highest temperature 373K the conductivity
increase one folds to seven folds. The percentage of the
conductivity also increased with respect to the dopant which is
shown Table 3. In particularly Fe(III) doped polymer shown
maximum electrical conductivity of 6.8× 10-6 S cm-1 at 373 K.
Figure 11. XRD patterns of HCl, Fe(III) doped and undoped polymer
3.0. Electrical conductivity
The electrical conductivity of undoped and doped form of the
polymers was measured using impedance spectroscopy method,
and the obtained results are shown in Fig. 12. The conductivity was
calculated by using equation σ = (L/Rb A), where, Rb- bulk
resistance, L- thickness and A- area of the sample. The conductivity
was done at three different temperatures such as 303, 323, 373K
and the obtained data are summarized in Table 3. The conductivity
of polymer is found to increase with temperature because of
enhancement in free volume theory and segmental motion of
polymer chain which leads to improving the electrical conductivity
of polymer. It is shown in Table 3 that the conductivity values of
Figure 12. Electrical conductivity of doped and undoped polymer
Table 3. Conductivity values of undoped and doped polymers.
Samples
Conductivity (S cm-1)
303K
%
323K
%
373K
%
p-CzTT
1.30 × 10-7
1.65× 10-6
3.82× 10-6
5.82× 10-6
7.81× 10-6
9.04× 10-6
-
1.93× 10-6
4.68× 10-6
8.00× 10-6
1.34× 10-5
1.54× 10-5
1.90× 10-5
-
9.89× 10-6
1.76× 10-5
3.69× 10-5
4.92× 10-5
5.93× 10-5
6.85× 10-5
-
77
HCl doped
Cu(II) doped
H3BO3 doped
I2doped
1169
2838
4376
5907
6853
143
314
594
697
884
273
397
499
592
Fe(III) doped
doped polymer are higher than the undoped polymer with an
increase in temperature.26 This may be due to increasing the
overall mobility of electron and free volume of the polymer chains.
Since I2 and Fe(III) are more electron withdrawing group, these
dopants may enhance the electrical conductivity. The
incorporation of Fe(III) and I2 dopants can improve the electrical
properties in different ways, for example, the porous surface will
dissociate the moving of more electron.34 The HCl doped polymer
shown more crystalline nature compare to Fe(III) doped polymer
as confirmed by XRD results. The amorphous nature of polymer
shows high conductivity as it initiates the breakdown of transient
coordination bonds between charge carriers.35 Due to this, higher
electrical conductivity observed in the doped form of the
polymers. In the case of 303K, we observed electrical conductivity
increases undoped to Fe (III) doped polymers one folds to nine
4. Conclusions
In conclusion, we observed that addition of dopant to copolymer
can have observably decreased in the band gap (Egcv) and increase
the electrical conductivity of p-CzTT. The use of HCl, Cu(II), Fe(III),
H3BO3 and I2 dopants has changed their polymer HOMO, LUMO
energy levels, optical and electrochemical properties. Also, the
polymer exhibits strong FL emission peak at 448 nm and excitation
peak at 338 nm range. The Cu(II) and I2 doped polymers showed
very low bang gap of 1.99 and 1.77 eV, respectively. The maximum
electrical conductivity had shown that Fe(III) polymer it was found
that 6.8×10-5 S cm-1. The undoped and doped polymer showed
more thermal stability, deep-lying HOMO energy level, and broad
8 | J. Name., 2012, 00, 1-3
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absorption range. This result concluded that doped p-CzTT is a 5.2.2. Synthesis of 9-hexyl-9H-carbazole-3-carbaldehyde (II)
good donor material for BHJ-OSCs applications.
POCl3 (25 mL, 0.27 mole) was added drop wise to DMF (35 mL,
o
0.45 mole) for 30 min at 0 C. Compound 1a (4.00 g, 16 mmol) in
dichloromethane (20 mL) was added to the above solution at room
temperature after that increase the temperature of 90 oC and
stirred for 4 h. The reaction mixture was poured into ice-cubes and
neutralized with NaOH solution. The solution was extracted three
times with ethyl acetate and dried over anhydrous magnesium
sulphate. The excess of dichloromethane was removed by vacuum
distillation. The crude product was purified by column
chromatography (eluent: hexane/ethyl acetate- 9:1) given the
product as white colour solid compound (9-hexyl-9H-carbazole-3-
carbaldehyde (II), Yield: 68%).1H NMR (CDCl3, ppm): 10.07 (s, 1H),
8.57 (s, 1H), 8.14-8.12 (d, 1H, J=8 Hz), 8.00- 7.98 (dd, 1H, J=6.8 Hz),
7.55-7.51 (t, 1H, J=8 Hz), 7.44-7.42 (d, 2H, J=8.4 Hz), 7.33-7.30 (t,
1H, J=7.2 Hz), 4.30-4.26 (t, 2H, J=7.6 Hz), 1.90-1.82 (m, 2H), 1.31-
1.28 (m, 6H), 0.87 (m, 3H).
5. Experimental
5.1. Materials
Carbazole, 1-bromohexane, and dithiooxamide were purchased
from Sigma-Aldrich Company. Phosphoryl chloride (POCl3), dry
dimethylformamide (DMF), dichloromethane (DCM) and
chloroform (CHCl3) were obtained from SD Fine-Chem Limited.
Dimethyl sulfoxide (DMSO), methanol, HCl solution (37%),
Cu(CH3COO)2.H2O, FeCl3.6H2O, H3BO3, I2, Potassium tert-butoxide
(t-BuOK), potassium hydroxide (KOH) and sodium hydroxide
(NaOH) was purchased from AVRA Company. Other solvents were
purchased commercially as AR-grade quality and used without
further purification. Column chromatography was performed using
silica gel Merck (60-120 mesh).
5.2.3. Synthesis of 9-hexyl-9H-carbazole-3,6-dicarbaldehyde (III)
POCl3 (25 mL, 0.27 mole) was added drop wise to DMF (35 mL,
0.45 mole) for 1 h at 0 oC. Compound 1a (4.00 g, 16 mmol) in
dichloromethane (20 mL) was added to the above solution at room
temperature after that increase the temperature of 90 oC and
stirred for 24 h. The same workup procedure has been followed
according to the synthesis of compound II. The crude product was
purified by column chromatography (eluent: hexane /ethyl
acetate- 8:2) using silica gel (2.9 g, Yield: 59%).1H NMR (CDCl3,
ppm): 10.13 (s, 2H), 8.67 (s, 2H), 8.09-8.07 (d, 2H, J=8.4 Hz), 7.56-
7.54 (d, 2H, J=8.8 Hz), 4.40-4.36 (t, 2H, J=7.2 Hz), 1.93-1.89 (m, 2H),
1.38-1.34 (m, 6H), 0.86 (m, 3H).
5.2 Methods
IR Spectra was recorded using SHIMADZU Infrared
spectrophotometer (400–4000 cm-1) with resolution IV. The FT-IR
spectra were measured by using KBr pellet. 1H and 13C-NMR
spectra were obtained with Bruker 400 MHz spectrometer in CDCl3
and DMSO-d6 solvent using tetramethylsilane as an internal
standard. UV-visible absorption spectra were recorded with a
JASCO V-670 spectrophotometer at room temperature.
Fluorescence spectra were recorded using Hitachi F-7000FL
spectrometer. Thermal analyses were carried out using
SDT Q600 V8.3 Build 101 thermogravimetric analyzer (TGA). Cyclic
voltammogams were recorded with AutoLab 302 N at a scan rate
of 100 mV s-1 in 0.1
M solution of tetrabutylammonium
5.2.4. Synthesis of carbazole-thiazolo[5,4-d]thiazole (CzTT)
Compound II (0.620 g, 2.2 mmol) and dithiooxamide (0.120 g, 1
mmol) in DMF solution was heated and reflux for 5 hrs under N2
atm. After the reaction mixture was cooled to room temperature,
poured into water extracted with dichloromethane. The organic
layer was washed with water and dried over anhydrous
magnesium sulphate. The crude mixture was purified by column
chromatography (eluent: hexane/ethyl acetate- 8:2) given the
product as yellow colour solid (yield: 32%). 1H-NMR (CDCl3, ppm):
8.75 (s, 2H), 8.21-8.19 (d, 2H, J=7.6 Hz), 8.13-8.10 (dd, 2H, J=6.8
Hz), 7.53-7.50 (t, 2H, J=7.2 Hz), 7.48-7.54 (dd-4H, J=4 Hz), 7.24-7.22
(t, 2H, J=2.4 Hz) 4.35-4.32 (t, 4H, J=7.2 Hz), 1.92-1.89 (m, 4H), 1.32-
1.25 (m, 12H), 0.89 (m, 6H). 13C-NMR (CDCl3, ppm): 142.06, 141.34,
126.63, 125.59, 124.60, 123.61, 121.07, 119.90, 118.97, 109.37,
43.60, 31.80, 29.94, 27.21, 22.78, and 14.24.
tetrafluoroborate in DMSO solution. Two platinum electrodes
were used as counter and reference electrode and a glassy carbon
electrode as working electrode. Powder XRD was recorded using
PANalytical (PW3040/60) at room temperature. The morphology
study was carried out using Hitachi (S-3000H) scanning electron
microscopy (SEM). The electrical conductivity of the polymer was
studied by impedance analysis using 3250 LCR HITESTER meter in
the frequency range of 50 Hz to 5 MHz at different temperature
(303-373K).
5.2.1. Synthesis of 9-hexyl-9-H-carbazole (I)
Carbazole (3.30 g, 20 mmol), potassium hydroxide (2.96 g, 52.8
mmol) dissolved in DMF (40 mL) and then 1-bromohexane (3.30 g,
20 mmol) was added drop wise. The reaction mixture was stirred
at room temperature for 48 h. The reaction mixture was poured
into water and extracted with chloroform and dried over
anhydrous magnesium sulphate. The solvent was removed by
rotary evaporator, the residue was recrystallized in n-hexane to
afford compound 1a (4.8 g, 92%) as a white solid. 1H NMR (400
MHz, CDCl3, ppm): 8.11-8.09 (d, 2H, J=2.4 Hz), 7.46-7.42 (m, 2H),
7.42 -7.39 (d, 2H, J=8.4 Hz), 7.26-7.20 (m, 2H), 4.31-4.28 (t, 2H,
J=7.2 Hz), 1.88-1.85 (m, 2H), 1.41-1.37 (m, 6H), 0.86 (t, 3H).
5.2.5. Synthesis of poly(carbazole-thiazolo[5,4-d]thiazole) (p-
CzTT)
The compound III (0.61 g, 2 mmol) and dithiooxamide (0.20 g, 2
mmol) was mixed with ethanol and stirred at room temperature
under N2 atm. After that, 1 M sodium hydroxide solution was
added to the reaction mixture. Then, the temperature increased to
90 °C and stirred overnight, after that reaction mixture cooled to
room temperature and poured into methanol. The obtained
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precipitate was filtered, washed with cold methanol and dried in
an oven at overnight. The compound was further purified by
column chromatography (eluent: chloroform) using silica gel and
precipitated with ethanol to give the product as a brown colour
solid (yield: 68%). The compound p-CzTT was confirmed by 1H-
NMR spectroscopy it was shown in Fig. 2.
17. P. Dutta, W. Yang, S.H. Eom, and S.H. Lee, Org. Electron.,
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4199.
5.2.5. p-CzTT polymer doped with different dopants
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Zhan, J. Polym. Sci., Part A: Polym. Chem., 2011, 49, 4875.
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The p-CzTT polymer was doped with HCl, H3BO3, Cu(II), Fe(III), and
I2 using Cu(CH3 COO)2.H2O, FeCl3.6H2O, H3BO3 and I2 chemical
agents. The polymer and doped polymers have been recorded by
using FT-IR, UV-vis absorption, cyclic voltammetry (CV) and
electrical conductivity. The UV-visible spectrometer was
performed with the polymer in DMF solution. The cyclic
voltammetry measurements, FT-IR and electrical conductivity
measurements, the doping processes were carried out by mixing
and grinding in the solid phase. 15 mg of solid dopants of
Cu(CH3COO)2 .H2O, FeCl3 .6H2O, H3BO3, and I2 were added into the
each 50 mg of the p-CzTT copolymer.
Acknowledgments
This work was supported by VIT University for providing laboratory
facilities. The financial support by DST funded research project
board SERB-SB/FT/CS-185/2011.
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10 | J. Name., 2012, 00, 1-3
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Graphical abstract
Synthesis of carbazole-based copolymer containing a carbazole- thiazolo[5,4-d]thiazole groups with different
dopants and their fluorescence, electrical conductivity applications
Govindasamy Sathiyana, Rangasamy Thangamuthub and Pachagoundar Sakthivela*
HCl
NaOH