Preparation and Characterization of poly(Azomethines) Containing Ether and Methylene Bridges: Photophysical, Electrochemical, Conductivity and Thermal Properties

Article abstract of DOI:10.1007/s10895-016-1966-1

In this paper, a series of polyazomethines (PAZs) were prepared using dihydroxy substituted Schiff bases and 1,4-diiodobenzene. Also, different group effect such as methylene carbon and etheric oxygen bridges on photophysical, electrochemical, conductivit

Full text of DOI:10.1007/s10895-016-1966-1

J Fluoresc
DOI 10.1007/s10895-016-1966-1
ORIGINAL ARTICLE
Preparation and Characterization of poly(Azomethines)
Containing Ether and Methylene Bridges: Photophysical,
Electrochemical, Conductivity and Thermal Properties
1
1
İsmet Kaya & Tahsin Yılmaz
Received: 31 July 2016 /Accepted: 19 October 2016
Springer Science+Business Media New York 2016
#
. .
Keywords Poly(azomethines) Photophysical properties
Abstract In this paper, a series of polyazomethines (PAZs)
.
.
.
were prepared using dihydroxy substituted Schiff bases and
Thermal stability Cyclic voltammetry Band gap SEM
1
,4-diiodobenzene. Also, different group effect such as meth-
ylene carbon and etheric oxygen bridges on photophysical,
electrochemical, conductivity and thermal properties were
clarified. The new polymeric materials structures were con-
Introduction
1
firmed by means of H–NMR, FT-IR and UV-vis measure-
ments. The molecular weight distributions of polymers were
determined with gel permeation chromatography (GPC) mea-
surements. Photophysical behaviors of polymers were ex-
plored by UV-vis absorption and fluorescence measurements.
TGA-DTA and DSC techniques have been used for the ther-
mal characterization of the PAZs. Thermal data and fluores-
cence measurements showed that etheric oxygen bridge con-
taining polymers have a bit higher char and emission intensity
than the methylene carbon bridge carrying polymers.
According to TG analysis, Ton values of P-2MPDP, P-2-
OPDP, P-4-MPDP and P-4-OPDP were found as 210, 250,
The design and synthesis of new conjugated polymers (CPs)
have attracted much interest in recent years owing to their
versatile properties such as thermal stability [1], optical [2],
photoluminescence [3, 4], semi-conductivity, etc. [5]. Due to
these unique properties, they have found applications in poly-
mer light-emitting diodes (PLEDs) [6, 7], photovoltaic cells
[8, 9], transistors [10], and molecular electronics [11]. Up to
now, several types of conjugated oligomers or polymers have
been reported by many researchers [12–15].
Among the CPs, polyazomethines (PAZs) or polymeric
Schiff bases have received much attention owing to their
advantageous properties such good heat resistance, me-
chanical strength, liquid crystalline, semi-conductivity
and optical and electrical properties [16–19]. However,
due to the main-chain rigidity and strong intermolecular
interactions, the aromatic polyazomethines exhibit low sol-
2
49 and 233 °C, respectively. The HOMO-LUMO energy
levels, electrochemical (E’ ) and optical (E ) band gaps were
g
g
calculated from cyclic voltammetry (CV) and UV-vis mea-
surements, respectively. The electrochemical (E ′) band gaps
g
values of P-2MPDP, P-2-OPDP, P-4-MPDP and P-4-OPDP
were calculated as 2.68, 2.32, 2.34 and 2.07, respectively.
Additionally, four-point probe technique was used to measure
solid state electrical conductivities of both doped and undoped
states of the PAZs.
ubility in organic solvents and high T values which seri-
g
ously limit their processability and therefore their applica-
bility [20, 21]. Numerous techniques have been used to
improve the solubility of PAZs. One of the most effective
approaches to enhance the solubility is the insertion of
flexible linkages into the polymer backbone [22–24].
Physical and chemical characteristics of polyazomethines
have been changed by modification of the polymer struc-
ture with minor variations in the polymer composition, as
seen in previous studies [25–27].
*
İsmet Kaya
kayaismet@hotmail.com
1
Polymer Synthesis and Analysis Laboratory, Department of
Chemistry, Çanakkale Onsekiz Mart University,
Therefore, the main purpose of this study is to synthesize
four new different polyazomethines and investigate the effect of
1
7020 Çanakkale, Turkey

J Fluoresc
Scheme 1 Synthesis of Schiff bases
structural differences on their photophysical, electrochemical
and thermal properties in addition to conductivity properties.
Technologies Gladi ATR sampling accessory within the wave-
lengths of 4000–400 cm . NMR spectra were obtained on
−1
Bruker 400 MHz spectrometer by using DMSO-d as a sol-
6
vent. Tetramethylsilane was used as internal standard. The
number average molecular weight (M ), weight average mo-
n
Experimental
lecular weight (M ) and polydispersity index (PDI) were de-
w
termined by Gel Permeation Chromatography-Light
Scattering (GPC-LS) device by Malvern Viscotek GPC Dual
Materials and Characterization
2
70 max. For GPC investigations a medium 300 × 8.00 mm
All chemicals were supplied from analytical grade and used as
received without any further purification. The UV–Vis mea-
surements were performed using Analytikjena Specord 210
Plus spectrophotometer. A PerkinElmer FT-IR/FIR spectrom-
eter frontier system was used to determine the chemical struc-
ture of the monomers and polymers. Measurements were per-
formed in solid powder form at room temperature using PIKE
Dual column Light Scattering Detector (LS) and a refractive
index detector (RID) were used to analyze the products at
55 °C. Also, LiBr (40 mM) was added to the DMF mobile
phase to dissociate molecular aggregates of polymer during
GPC analysis.
Photopysical Measurements
The UV–vis measurements were performed using Analytikjena
Specord 210 Plus spectrophotometer in DMSO solution at
2
5 °C. The fluorescence spectra were measured using a
Shimadzu RF-5301PC spectrometer. Photoluminescence (PL)
spectra were obtained in DMF solutions and slit width adjusted
as 3 nm for all measurements.
Electrochemical Measurements
CHI 660C Electrochemical Analyzer at a potential scan rate of
20 mV/s was used to generate cyclic voltammograms. All
measurements were taken in 0.1 M TBAPF in CH CN elec-
6
3
trolyte solution under an argon atmosphere.
Conductivity Measurements
The electrical conductivities were determined via four-point
probe technique using a Keithley 2400 Electrometer. Iodine
doping of PAZs was performed in solid state by exposing the
polymer pellets with iodine vapor.
Scheme 2 Synthesis of P-2-MPDP and P-2-OPDP

J Fluoresc
Scheme 3 Synthesis of
P-4-MPDP and P-4-OPDP
Thermal Measurements
phenylenenitrilomethylylidene)]diphenol (2-OPDP),
,4′-[methylenebis(4,1-phenylenenitrilomethylylidene)]diphenol
4
TG/DTA analyses were made in Perkin-Elmer Diamond
( 4 - M P D P ) , a n d 4 , 4 ′ - [ o x y b i s ( 4 , 1 -
phenylenenitrilomethylylidene)]diphenol (4-OPDP) were syn-
thesized by the condensation reaction of diamines (DAs) (4,4′-
diaminodiphenylmethane or 4,4′-oxydianiline) with hydroxy
benzaldehydes (2-hydroxybenzaldehyde or 4-
hydroxybenzaldehyde). The reactions were performed as in the
literature (Scheme 1) [10] and all of the Schiff bases were ob-
tained yellow colored powder. The yields of 2-MPDP, 2-OPDP,
Thermal Analysis system between 20 and 1000 °C (in N ,
2
−1
heating rate 10 °C min ). DSC curves of PAZs were obtained
from heating the samples from 50 to 450 °C under N purging
2
at 10 °C min− by a PerkinElmer Pyris Sapphire.
1
Morphological Measurements
4
-MPDP, and 4-OPDP were found as 93, 92, 89 and 91 %,
SEM images of PAZs were recorded using a Jeol JSM-7100F
Schottky instrument in a powder form. PAZ polymers were
prepared by sprinkling on double-sided adhesive tape
mounted on an aluminum stub and then they coated with a
thin gold/palladium film by a sputter coater.
respectively.
Synthesis of the Poly(Azomethines)
Poly(azomethines) (PAZs) were shortened as P-2-MPDP,
P-2-OPDP, P-4-MPDP, and P-4-OPDP and they synthe-
sized according to the reactions presented in Schemes 2
and 3. The reactions were carried out using the proce-
dures described in the literature [23, 28] and P-2-MPDP
Synthesis of the Schiff Bases
2,2′-[methylenebis(4,1-phenylenenitrilomethylylidene)]diphenol
(
2 - M P D P ) , 2 , 2 ′ - [ o x y b i s ( 4 , 1 -
Table 1 Solubility behavior of the compounds
Compounds
DMSO
DMF
THF
CHCl
3
Ethanol
Acetone
3
CH CN
Toluene
Ethyl acetate
n-hexane
2
2
4
4
-MPDP
-OPDP
-MPDP
-OPDP
●
●
●
●
●
●
■
■
●
●
●
●
●
●
■
■
●
●
●
●
■
■
■
■
●
▲
▲
▲
▲
▲
▲
▲
▲
▲
▲
●
▲
▲
▲
▲
▲
▲
▲
▲
▲
▲
▲
▲
▲
▲
▲
▲
▲
▲
▲
▲
▲
▲
▲
▲
▲
▲
▲
▲
▲
▲
▲
▲
●
▲
▲
▲
▲
▲
▲
●
P-2-MPDP
P-2-OPDP
P-4-MPDP
P-4-OPDP
▲
▲
▲
▲
●
soluble, ■ partially soluble, ▲ insoluble

J Fluoresc
Fig. 1 FT-IR spectra of
monomers (a) 2-MPDP
(a), 2-OPDP (b), 4-MPDP (c),
and 4-OPDP (d) and polymers
(
(
b) P-2-MPDP (e), P-2-OPDP
f ), P-4-MPDP (g), and
P-4-OPDP (h)
and P-2-OPDP were yellow colored powder while P-4-
MPDP, and P-4-OPDP obtained dark-brown colored
powder. Yield: 71, 70, 66, and 65 % for P-2-MPDP,
P-2-OPDP, P-4-MPDP, and P-4-OPDP, respectively.
compounds were soluble in DMSO, THF, and DMF but insol-
uble in CH CN, toluene, ethyl acetate, and n-hexane. 4-MPDP
3
and 4-OPDP were soluble in acetone whereas the others are
insoluble. These results showed that the synthesized PAZs have
high solubility in polar organic solvents due to methylene car-
bon and etheric oxygen bridges in polymer chain [29].
Results and Discussion
Figure 1 and Table 2 showed the FT-IR spectra and spectral
data of all of the synthesized compounds. According to Fig. 1
and Table 2, disappearance of carbonyl band of aldehyde com-
pounds and a new strong sharp band that appears between
1608 and 1622 cm region is attributed to the ν(C = N) band,
confirming the formation of the SBs. As can be seen FT-IR
Solubility and Characterization
−1
The results of the solvent solubility test were summarized in
Table 1. As can be seen in Table 1, all of the synthesized
Table 2 FT-IR spectral data of
the compounds
−1
Compounds Functional groups (cm )
–OH Aromatic–CH Aliphatic–CH Imine–CH = N– Aromatic–C = C– –C-O-C–
2
2
4
4
-MPDP
-OPDP
-MPDP
-OPDP
3211 3055
3210 3051
3190 3040
3190 3058
3340 3055
3327 3055
3337 3028
3230 3043
2943–2923
1615
1614
1608
1622
1615
1617
1615
1605
1596,1568, 1496
1569, 1490, 1455
1576, 1517, 1445
1600, 1587, 1496
1574, 1489
–
–
1260
–
2989
–
1243
1282
1218
1280
1236
P-2-MPDP
P-2-OPDP
P-4-MPDP
P-4-OPDP
2907
–
1571, 1497, 1459
1591, 1512
2914
–
1578, 1496

J Fluoresc
355 cm− which could be ascribed to the terminal hydroxyl
1
3
(
−OH) groups. Also, the presence of –C-O-C– bond was
−1
proved by the band at 1218–1282 cm , while –CH = N–
groups manifested by the strong absorption band at 1605–
1
−
1
617 cm . Aromatic –CH, aliphatic –CH and aromatic –
C = C– stretching bands were appeared between 3028 and
−
1
−1
−1
3
055 cm , 2907–2989 cm and 1445–1600 cm
,
respectively.
1
Figure 2 illustrates H–NMR spectra of 4-MPDP and
P-4-MPDP. Also, H–NMR spectral data of all of the syn-
1
thesized compounds were given in Table 3. As can be
seen in Table 3, the resonance of the hydroxyl (−OH),
azomethine (−CH = N) and aromatic protons of SBs was
appeared in the range of 10.15 to 13.19, 8.46 to 8.97 and
6
.90 to 7.78 ppm, respectively. Similarly, the resonance
peaks of the terminal hydroxyl (−OH), azomethine
−CH = N) and aromatic protons of PAZs were observed
(
around 10.13–13.24, 8.45–9.00 and 6.46–7.97 ppm, re-
spectively. Aliphatic –CH protons were appeared between
3
.48 and 4.04 ppm for both SBs and PAZs. The above
information illustrated that SBs and PAZs have the ex-
pected chemical structures [24, 29].
Gel Permeation Chromatography
The Mn, Mw, and PDI values of the polymers were calculated
via GPC technique and results were given in Table 4.
According to the GPC results, the M values of P-2-MPDP,
n
P-2-OPDP, P-4-MPDP, and P-4-OPDP were calculated as
8130, 9760, 14,570 and 15,600 Da, respectively. Also, PDI
values of P-2-MPDP, P-2-OPDP, P-4-MPDP, and P-4-OPDP
were determined as 1.08, 1.09, 1.08 and 1.07, respectively.
According to average molecular weight, repeated units of
P-2-MPDP, P-2-OPDP, P-4-MPDP, and P-4-OPDP were
found as nearly 17–18, 20–22, 30–33 and 32–35, respectively.
These obtained average molecular weight values were
1
Fig. 2 H–NMR spectra of 4-MPDP (a) andP-4-MPDP (b)
data, FT-IR spectra of the SBs showed the broad peaks in the
−1
region of 3190–3211 cm , which could be ascribed to the
hydroxyl (−OH) stretching vibrations. In the FT-IR spectral
data of polyazomethines, the peaks appear between 3227 and
1
Table 3 H–NMR spectral data
of the compounds
Compounds Spectral data (δ ppm)
2
-MPDP
13.19 (s, −OH), 8.97 (s,–CH = N–), between 7.38 and 6.96 ppm (Aromatic region), 4.04
Aliphatic region).
(
2
-OPDP
-MPDP
13.05 (s, −OH), 8.97 (s, −CH = N–), between 7.65 and 6.97 ppm (Aromatic region).
10.13 (−OH), 8.46 (s, −CH = N–), between 7.77 and 6.90 ppm (Aromatic region), 3.96
4
(
Aliphatic region).
4
-OPDP
10.15 (−OH), 8.48 (s, −CH = N–), between 7.78 and 6.90 ppm (Aromatic region).
13.24 (−OH), 8.97 (s, −CH = N–), between 7.97 and 6.51 ppm (Aromatic region), 3.48
P-2-MPDP
(
Aliphatic region).
P-2-OPDP
P-4-MPDP
13.13 (−OH), 9.00 (s,–CH = N–), between 7.67 and 7.00 ppm (Aromatic region).
10.13 (−OH), 8.45 (s, −CH = N–), between 7.97 and 6.46 ppm (Aromatic region), 3.91
(
Aliphatic region).
P-4-OPDP
10.13 (−OH), 8.51 (s, −CH = N–), between 7.97 and 6.54 ppm (Aromatic region)

J Fluoresc
Table 4 The Mn, Mw, PDI, and
values of the PAZs
Compounds Total
Molecular weight distributions
Fraction I
%
Fraction II
M
w
M
n
PDI
M
w
M
n
PDI
%
M
w
M
n
PDI
%
P-2-MPDP
P-2-OPDP
P-4-MPDP
P-4-OPDP
8740
8130 1.08
11,300
10,500
1.08 68
1.08 55
1.06 65
1.06 82
3300
3600
5400
4300
3100 1.07 32
3100 1.16 45
4300 1.26 35
3300 1.30 18
10,640
9760 1.09 16,400 15,200
15,740 14,570 1.08 21,300 20,100
16,680 15,600 1.07 19,400 18,300
consistent with results in the literature [30]. The M values of
values while PAZs have between 2.77 and 3.13 eV E values.
n
g
polyazomethine ethers (P-2 and P-4) containing different sub-
These results indicated that PAZs have a bit lower E values
g
−
1
stituent groups had been found as 17,500 g mol and
than their Schiff bases due to their polyconjugated structures.
The photoluminescence (PL) behaviors of the synthesized
compounds were studied in DMF solution. Figure 4 shows fluo-
rescence spectra all of the synthesized compounds. The fluores-
cence data of the synthesized compounds were also given in
Table 6. These results showed that P-4-OPDP has the highest
fluorescence wavelength and intensity while P-2-MPDP has the
lowest. These results showed that compounds that etheric oxy-
gen bridge containing PAZs have higher fluorescence wave-
length and intensities than the methylene carbon bridge carrying
PAZs. These could be probably the interaction of polarity and
dielectric constants of solvents with the structure of the polymers.
−1
1
8,700 g mol , respectively [29].
Photophysical Properties
UV-visible absorbance and fluorescence measurements were
performed to investigate the photophysical behaviors of the
synthesized compounds. The absorption spectra of the synthe-
sized compounds were shown in Fig. 3. The first absorption
band in the range 200 to 320 nm was ascribed to the π → π∗
transition of the aromatic rings. The second band between 320
∗
and 400 nm was ascribed to the π → π transition of the
azomethine group [31]. As seen in Fig. 3, a red shift occurs
at the absorption edges of the synthesized PAZs as compared
to their corresponding SBs. This was because of conjugated
Stokes shift (ΔλST) is the difference between positions of
the band maxima of emission and excitation spectra of the
same electronic transition. This knowledge offers significant
structure of the PAZs. The optical band gaps (E ) all of the
g
compounds were determined as in previous study [32]. The
conformational differences between ground state (S
first excited state (S ). If the ΔλST value is too small, the
emission and excitation spectra will overlap more. Then the
0
) and the
calculated E values were also summarized in Table 5. As can
1
g
be seen in Table 5, SBs have in the range 2.95 to 3.15 eV Eg
Fig. 3 UV-vis absorption spectra
of the produced compounds

J Fluoresc
Table 5 CV analysis results
Compounds
CV
UV-vis
a
b
c
d
HOMO (eV)
LUMO (eV)
E’
g
(eV)
E
g
(eV)
λonset (nm)
2
-MPDP
-OPDP
-MPDP
-OPDP
-5.81
-5.80
-5.58
-5.53
-5.37
-5.41
-5.39
-5.41
-3.29
-2.89
-3.16
-2.54
-2.69
-3.09
-3.05
-3.34
2.52
2.91
2.42
2.99
2.68
2.32
2.34
2.07
3.06
3.15
2.97
2.95
3.04
3.13
2.84
2.77
405
394
418
421
408
397
438
448
2
4
4
P-2-MPDP
P-2-OPDP
P-4-MPDP
P-4-OPDP
a
b
c
d
Highest occupied molecular orbital
Lowest unoccupied molecular orbital
Electrochemical band gap
Optical band gap
emitting light will be self-absorbed and the photoluminescence
efficiency will diminish [33]. ΔλST values are listed in Table 6.
ΔλST values of 2-MPDP, 2-OPDP, 4-MPDP, and 4-OPDP are
calculated as 129, 83, 59, and 64, respectively. Similarly, ΔλST
values of P-2-MPDP, P-2-OPDP, P-4-MPDP, and P-4-OPDP
are 80, 58, 60, and 7, respectively. According to Stokes shift
values, the synthesized compounds (except for 2-MPDP)
could be used for the fabrication of fluorescence sensor due
to quite high Stokes shift value [32].
solution. The HOMO-LUMO energy levels and electrochem-
ical band gaps (E’ ) of the SBs and PAZs were calculated by
g
À
Á
À
Á
onset
ox
onset
red
using the oxidation onset E
values, as shown below.
and reduction onset E
À
Á
onset
ox
EHOMO ¼ − E
þ 4:39
ð1Þ
À
Á
onset
red
ELUMO ¼ − E
þ 4:39
ð2Þ
ð3Þ
0
Eg ¼ ELUMO−EHOMO
Electrochemical Properties
Electrochemical oxidation/reduction behavior of the SBs and
The electrochemical data of the synthesized compounds
are summarized in Table 5. The oxidation peaks in cyclic
PAZs was checked by cyclic voltammetry (CV) in CH CN
3
Fig. 4 Fluorescence spectra of
the compounds

J Fluoresc
Table 6 Fluorescence data of the compounds
a
b
c
d
e
f
g
Compounds
λ
Ex
λ
Em
λ
max (Ex)
λ
max (Em)
I
Ex
IEm ΔλST
2
2
4
4
-MPDP
-OPDP
-MPDP
-OPDP
390 520 392
410 530 450
400 485 427
430 490 428
521
533
486
492
530
505
562
580
26 25
46 38
129
83
210 120 59
46 45
63 61
64
80
P-2-MPDP 460 530 450
P-2-OPDP 440 505 447
P-4-MPDP 500 560 502
P-4-OPDP 560 580 573
221 217 58
349 349 60
870 907
7
Fig. 6 TGA curves of the compounds
a
Excitation wavelength for emission
Emission wavelength for excitation
b
electrical conductivity as a function of the doping time. It
revealed that the initial rise in conductivity is sharp and satu-
ration occurs within 96 h if doping is carried out at room
temperature. The increase in conductivity was due to the for-
mation of charge transfer complex by iodine with nitrogen
atom and aromatic π-electron cloud of the polymer chain
c
Maximum emission wavelength
Maximum excitation wavelength
d
e
Maximum excitation intensity
Maximum emission intensity
f
g
Stokes shift
[34]. At the un-doped states of the polymers P-2-OPDP has
the highest electrical conductivity, while P-4-MPDP has the
lowest. The maximal (or saturated) conductivity values of the
voltammograms probably correspond to the oxidation of
hydroxyl groups to form phenoxy radicals. The reduction
peaks were presumably owing to the reduction of the
azomethine linkages via protonation of azomethine nitro-
gen, as indicated in previous studies [22, 29]. As seen in
−9
−9
−9
PAZs was found to be 2.9 × 10 , 8.3 × 10 , 5.0 × 10 ,
−8
−1
1
.0 × 10 S cm for P-2-MPDP, P-2-OPDP, P-4-MPDP
and P-4-OPDP on saturation, respectively. It was seen in dop-
ing state conductivities of PAZs that the maximal conductivity
was increased with doping by iodine for P-4-OPDP.
Consequently, owing to high rate of conductivity increase
with doping P-4-OPDP could be used as a gas sensing mate-
rial against electro-acceptor gases like iodine.
Table 5, the (E’ ) values of the synthesized PAZs were
g
smaller than that of their corresponding SBs. This was a
consequence of the polyconjugated structures of the PAZs,
which increase HOMO and decrease LUMO energy levels,
resulting in lower electrochemical band gaps.
Conductivity Properties
Thermal Analysis
Electrical conductivities of the powdered PAZs were deter-
mined on pressed pellets by using four probes connected with
The thermal analyses of the synthesized compounds were per-
formed using TGA-DTA and DSC under nitrogen atmo-
sphere. The TGA and DTG curves of the synthesized com-
pounds were shown in Figs. 6 and 7, respectively. Thermal
decomposition data of the compounds were also summarized
in Table 7. Table 7 indicated that 2-MPDP has the highest
onset temperature (T ). The T (°C) and char content (%)
Keithley 2400 electrometer. For this purpose, the pressed
2
PAZs (up to 1700 kg/cm ) were exposed to I vapors for
2
9
6 h at room temperature. Figure 5 showed variation of the
on
on
-7
0
1
-
0
8
1
-9
0
1
P-2-MPDP
P-2-OPDP
P-4-MPDP
P-4-OPDP
-
0
10
1
-11
10
0
24
48
DopingTime (h)
72
96
Fig. 5 Electrical conductivity changes of the PAZs versus doping time
Fig. 7 DTG curves of the compounds

J Fluoresc
Table 7 TG-DTG and DSC data of the compounds
TGA
DSC
a
b
c
d
e
f
g
Compounds
Ton (°C)
WmaxT (°C)
T20 (°C)
T50 (°C)
Char (%)
Tg (°C)
ΔCp (J/g K)
2
2
4
4
-MPDP
-OPDP
-MPDP
-OPDP
338
346
261
116
210
250
249
233
369
374
353
359
422
158
365
385
430
397
372
371
525
376
892
790
–
13
3
-
-
-
-
-
-
236,541
0
-
158, 299, 434
260, 412, 497
269, 391, 491
266, 425, 523
271, 489
26
45
48
53
55
-
P-2-MPDP
P-2-OPDP
P-4-MPDP
P-4-OPDP
197
86
211
186
0.046
0.032
0.098
0.110
–
a
The onset temperature
b
c
d
e
f
Maximum weight temperature
The temperature of 20 % weight loss
The temperature of 50 % weight loss
Char residue at 1000 °C
Glass transition temperature
Specific heat capacity
g
were 338 and 13 for 2-MPDP; 346 and 3 for 2-OPDP; 261 and
for 4-MPDP; 116 and 26 for 4-OPDP; 210 and 45 for P-2-
MPDP; 250 and 48 for P-2-OPDP; 249 and 53 for P-4-MPDP;
33 and 55 for P-4-OPDP, respectively. According to the TGA
polymer derivatives. Additionally, the char (%) of the PAZs
was higher than their Schiff bases. The presence of rigid aro-
matic groups hinders intermolecular interactions between
polymer chains and thereby reduces thermal stability at the
beginning of the process, but at elevated temperatures poly-
mers exhibited enhanced stability. These results were consis-
tent with the results of our previous study [22]. Thermal prop-
erties of the compounds indicated that etheric oxygen bridge
containing PAZs (48 and 55 %) have a bit higher char than the
carrying methylene carbon bridge (45 and 53 %) in the
structure.
0
2
results, the Ton values of the SBs were higher than their
The glass transition temperatures (Tg) of the PAZs were
determined from DSC measurements and the results given in
Table 7. The Tg was taken as the midpoint of the change in
slope of the baseline in DSC curve. The Tg values of PAZs
were changed between 86 and 211 °C. The results showed that
the PAZs derived from 4-hydroxybenzaldehyde (P-4-MPDP
and P-4-OPDP) have higher the glass transition temperatures
than the PAZs derived from 2-hydroxybenzaldehyde (P-2-
MPDP and P-2-OPDP). Variations in the Tg values were at-
tributed to the differences in the chain structure and molecular
weight of the PAZs [27, 29, 32]. As a result, the synthesized
PAZs has quite high thermal stability.
Morphological Properties
SEM technique was carried out to investigate surface morphol-
ogy of the PAZs (100 μm and 10 μm). Figure 8 displays SEM
photographs of PAZs at different magnifications. As seen in
the SEM images, P-2-OPDP was showed a sponge-like view
with porous structure (Fig. 8a). On the other hand, P-4-MPDP
Fig. 8 SEM images of P-2-OPDP (a, b), P-4-MPDP (c, d) and P-4-
OPDP (e, f)

J Fluoresc
7.
8.
9.
Hestand NJ, Spano FC (2014) The effect of chain bending on the
photophysical properties of conjugated polymers. J Phys Chem B
and P-4-OPDP have different particle sizes and consist of
semi-crystalline particles (Fig. 8d and f). This difference was
ascribable to the structural variations of the polymers.
118:8352–8363
Hriz K, Jaballah N, Fave JL, Majdoub M (2015) New anthracene-
based semi-conducting polymer analogue of poly(phenylene sulfide):
synthesis and photophysical properties. Opt Mater 46:401–408
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Synthesis and fluorescence study of conjugated polymers based on
Conclusion
2
,4,6-triphenylpyridine moieties. New J Chem 40:6281–6288
1
0. Kamacı M, Kaya I (2016) New low-band gap polyurethanes contain-
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and morphological properties. J Taiwan Inst Chem E 59:536–546
Poly(azomethines) (PAZs) were synthesized via polycon-
densation reactions of the dihydroxy substituted Schiff
bases with 1,4-diiodobenzene and different group effect
on some physical properties clarified. It was observed
that the synthesized PAZs were found to have high sol-
ubility in polar organic solvents like DMSO and DMF.
Photophysical behaviors of PAZs were investigated using
UV-vis and PL spectroscopy. P-4-OPDP has higher emis-
sion intensity when compared the others. Also, etheric
oxygen bridge containing PAZs have higher fluorescence
intensity than the methylene carbon bridge carrying
PAZs. All of the PAZs emit almost the same color
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Brumbac M (2009) Organic/organic′ heterojunctions: organic light
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(
blue–green) in DMF solution. Thermal data results indi-
1
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and etheric oxygen bridges in the polymer structure and
molecular weight of the PAZs were effected the thermal
stabilities. Ton values of the PAZs were determined in the
range 210 to 250 °C. Additionally, the obtained results
from thermal analysis were observed a similar tendency
with fluorescence intensity. Consequently, the fine
photophysical and thermal characteristics of PAZs could
make these polymers interesting materials for thermally
stable light-emitting materials.
1
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