New blue fluorescent and highly thermostable polyimide and poly(amide-imide)s containing triphenylamine units and (4-dimethylaminophenyl)-1,3,4-oxadiazole side groups

Article abstract of DOI:10.1016/j.dyepig.2017.09.010

A new blue fluorescent aromatic diamine, 2-(4,4′-diamino-4″-triphenylamine)-5-(4-dimethylaminophenyl)-1,3,4-oxadiazole, is synthesized in several steps. Based on this diamine four fluorescent imide-type polymers, a polyimide and three poly(amide-imide)s,

Full text of DOI:10.1016/j.dyepig.2017.09.010

Accepted Manuscript
New blue fluorescent and highly thermostable polyimide and poly(amide-imide)s
containing triphenylamine units and (4-dimethylaminophenyl)-1,3,4-oxadiazole side
groups
Corneliu Hamciuc, Elena Hamciuc, Mihaela Homocianu, Alina Nicolescu, Gabriela
Lisa
PII:
S0143-7208(17)31210-X
10.1016/j.dyepig.2017.09.010
DYPI 6234
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 27 May 2017
Revised Date: 5 September 2017
Accepted Date: 6 September 2017
Please cite this article as: Hamciuc C, Hamciuc E, Homocianu M, Nicolescu A, Lisa G, New blue
fluorescent and highly thermostable polyimide and poly(amide-imide)s containing triphenylamine units
and (4-dimethylaminophenyl)-1,3,4-oxadiazole side groups, Dyes and Pigments (2017), doi: 10.1016/
j.dyepig.2017.09.010.
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ACCEPTED MANUSCRIPT
Graphical Abstract

1
ACCEPTED MANUSCRIPT
New blue fluorescent and highly thermostable polyimide and poly(amide-imide)s containing
triphenylamine units and (4-dimethylaminophenyl)-1,3,4-oxadiazole side groups
*
1
1
1
1
2
Corneliu Hamciuc , Elena Hamciuc , Mihaela Homocianu , Alina Nicolescu , Gabriela Lisa
1
“Petru Poni” Institute of Macromolecular Chemistry, 41A Aleea Gr. Ghica Voda, 700487 Iasi,
Romania
2
“Gheorghe Asachi” Technical University of Iasi, Faculty of Chemical Engineering and
Environmental Protection, Department of Chemical Engineering, 73 D. Mangeron Street, Iasi,
Romania
Abstract: A new blue fluorescent aromatic diamine, 2-(4,4′-diamino-4″-triphenylamine)-5-(4-
dimethylaminophenyl)-1,3,4-oxadiazole, is synthesized in several steps. Based on this diamine four
fluorescent imide-type polymers, a polyimide and three poly(amide-imide)s, are prepared by
solution polycondensation reactions. The structures of the monomers and polymers are
characterized by FTIR and NMR spectroscopy. The polymers show good solubility in organic
solvents, and have high thermal stability, the decomposition temperature being above 380°C, as is
determined by TGA measurements. The thermal degradation mechanism of a polymer in an inert
atmosphere is investigated by using the coupled TG/MS/FTIR technique. The optical properties are
determined by UV-vis and fluorescence spectroscopy. The polymers exhibit strong absorption
bands in the range of 357-373 nm, and blue fluorescence in solution within the range of 423-469 nm
with low to moderate quantum fluorescence yields from 0.11 to 1.30% and Stokes shifts values of
around 77 nm. The protonation is found to affect the spectral properties of the polymers.
*
Corresponding author
Telephone and Fax: +40 - 232 217454
E-mail address: chamciuc@icmpp.ro (Corneliu Hamciuc)

2
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Keywords: polyimides; 1,3,4-oxadiazole; high thermal stability; blue fluorescence; protonation
1. Introduction
Fully aromatic polyimides are one of the most important classes of high performance polymers
used in many applications requiring polymer materials with high temperature resistance. These
polymers are characterized by an excellent combination of properties. They exhibit high thermal
and thermo-oxidative stability, good mechanical properties and low dielectric constant [1-3]. The
main disadvantage of aromatic polyimides is their infusibility and insolubility in organic solvents
which make them more difficult to be processed, thus limiting their field of applications. Much
research effort has been expended to increase the processability of these polymers, for example by
introducing flexible or bulky groups into their macromolecular chains [4, 5]. The presence of amide
groups in the polymer chains of an aromatic polyimide leads to a class of polymers, aromatic
poly(amide-imide)s, which exhibit a reasonable high thermal stability and show improved solubility
in organic solvents and lower glass transition temperatures in comparison with aromatic polyimides
of analogous chemical structure [6-8].
The incorporation of hexafluoroisopropylidene (6F) groups or dimethylsilane units produces a
disruption of the crystallinity and conjugation of aromatic polyimides. These bulky groups limit the
chain packing of the polymers and increase the free volume thus decreasing the dielectric constant.
The 6F groups improve considerably flame and oxidation resistance, optical transparency and
solubility in organic solvents and decrease the crystallinity, dielectric constant, water absorption and
color [9-12]. Also, the presence of dimethylsilane units enhances substantially the solubility in
organic solvents and maintains a high thermal stability thus improving the processability of the
resulting polymers. It was shown that the introducing of silicon linked through para positions of
phenylene rings in the main chain gives a σ-π conjugation and allows the transport of electrons [13,
14]. Another way to improve the solubility of the polyimides is the introduction in their main chain

3
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of triphenylamine groups. Such polymers exhibit special optical characteristics and hole-transport
properties and can be used in multilayer organic electroluminescent devices [15].
Much research has been directed toward studying blue light-emitting polymer materials with
emission efficiency, good thermal stability and high glass transition temperature. One approach to
develop such structures is the introduction of blue light-emitting fluorophores in the main or side
chains of the polymers. The development of thermostable polyimides having blue-fluorescence
properties for applications in light-emitting diodes is of particular interest [16]. These polymers
exhibit high glass transition temperature and good thermal and chemical stability. The presence of
1,3,4-oxadiazole rings in the macromolecular chains of the polymers improves the thermal and
thermo-oxidative stability, hydrolytic resistance and mechanical properties [17]. Due to the
electron-withdrawing character of the 1,3,4-oxadiazole ring, several oxadiazole-containing
polymers were studied for the construction of organic light-emitting diodes [18]. It is known that
the polymers with electron donor dimethylamino substituents in the para-position of the pendant
chromophoric 2,5-diphenyl-1,3,4-oxadiazole unit are promising candidates for emissive materials in
light-emitting diodes. The substituted diphenyl-1,3,4-oxadiazoles are able to transport holes as well
as electrons and show an intense fluorescence [19]. In our laboratory we have prepared poly(1,3,4-
oxadiazole-imide)s, poly(1,3,4-oxadiazole-ester-imide)s and polyazomethines derived from an
aromatic diamine 2-(4-dimethylaminophenyl)-5-(3,5-diaminophenyl)-1,3,4-oxadiazole [20-22].
Starting from another diamine, 4,4′-diamino-4″-[2-(4-phenoxy)-5-(4-dimethylaminophenyl)-1,3,4-
oxadiazole]-triphenylmethane we prepared aromatic polyamides, polyimides, poly(amide-imide)s
and polyazomethines having 2-(4-phenoxy)-5-(4-dimethylaminophenyl)-1,3,4-oxadiazole pendant
groups [23-25]. These polymers showed fluorescence in solution and in solid state. Their solutions
exhibited fluorescence in the blue region, with high quantum yield and large Stokes shift values.
Protonation with HCl as a dopant caused a significant decrease of fluorescent intensity, due to the
presence of nitrogen atoms with a free electron pair from 1,3,4-oxadiazole rings and dimethylamino
groups.

4
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Herein, as part of our continuing interest in the preparation of thermally stable polymers with
special properties for different applications, we describe the synthesis of a new aromatic diamine, 2-
(4,4′-diamino-4″-triphenylamine)-5-(4-dimethylaminophenyl)-1,3,4-oxadiazole,
containing
a
triphenylamine unit, 1,3,4-oxadiazole ring and a dimethylamino group. Based on this diamine, a
polyimide and three poly(amide-imide)s were prepared and characterized. The influence of the
polymer structure on the properties, such as solubility, glass transition temperature, thermal stability
and optical characteristics was studied. For one of the polymers a mechanism of thermal
decomposition in nitrogen was proposed.
2. Experimental
1. Materials
4
-Dimethylaminobenzohydrazide, 4-nitrobenzoyl chloride, 1-fluoro-4-nitrobenzene, 4,4′-
hexafluoroisopropylidene)diphthalic anhydride (6FDA), 4,4′-(4,4′-isopropylidenediphenyl-1,1′-
diyldioxy)dianiline, phosphorus oxychloride (POCl ) sodium hydrosulfide monohydrate, palladium
(
3
,
on activated carbon (1 wt%) were provided from Aldrich and used as received. 1-Methyl-2-
pyrrolidone (NMP) (Aldrich) was purified by stirring with NaOH and distilled from P O prior to
2
5
use. Pyridine (Aldrich) was purified by stirring with NaOH and distilled. Cesium fluoride (CsF)
also purchased from Aldrich, was dried for 6 h at 160°C before use. The synthesis of 2,2-bis[N-(4-
chloroformylphenyl)phthalimidyl]hexafluoropropane
(8)
and
2,2-bis[N-(4-
chloroformylphenyl)phthalimidyl]dimethylsilane (9) was described elsewhere [26, 27].
2
.2. Characterization
FTIR spectra were recorded on a Bruker Vertex 70 at frequencies ranging from 400 to 4000
cm by using KBr pellets. The NMR spectra were recorded on a Bruker Avance III 400
-1
1
13
spectrometer operating at 400.1 and 100.6 MHz for H and C nuclei respectively. Samples were
1
recorded with either a 5 mm multinuclear inverse detection z-gradient probe ( H spectra and all H-C
1
3
2
D experiments) or with a 5 mm four nuclei direct detection z-gradient probe ( C spectra). All the

5
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experiments were recorded using standard pulse sequences, in the version with z-gradients for 2D
spectra, as delivered by Bruker with TopSpin 2.1 PL6 spectrometer control and processing
software. Chemical shifts are reported in δ units (ppm) and were referenced to the internal
1
13
1
13
deuterated solvent for H and C chemical shifts (DMSO referenced at H: 2.51 ppm and C: 39.47
ppm). Electrospray ionization mass spectrometry (ESI-MS) was performed on an Agilent 6520
Series Accurate-Mass Q-TOF LC/MS. Data were collected and processed using MassHunter
Workstation Software Data Acquisition for 6200/6500 Series, version B.01.03. The sample was
dissolved in DMSO and diluted with methanol 1:9 (v/v), without added salt or acid prior to analysis.
The molecular weights and their distribution were determined by gel permeation chromatography
(GPC) with a PL-EMD 950 evaporative mass detector instrument. Two poly(styrene-co-
divinylbenzene) gel columns (PLgel 5 µm Mixed-D and PLgel 5 µm Mixed-C) were used as
stationary phase while N,N-dimethylformamide (DMF) was the mobile phase. The eluent flow rate
-1
was 1.0 mL min . Polystyrene standards of known molecular weight were used for calibration.
e
Differential Scanning Calorimetry (DSC) was performed on a Mettler Toledo DSC822 .
-1
Approximately 10 mg of sample were tested applying a heating rate of 10ºC min from 20 to
e
300ºC. Thermal stability was analyzed by means of a Mettler Toledo TGA-SDTA 851
derivatograph. The thermogravimetric (TG) and derivative thermogravimetric (DTG) curves were
-1
recorded in nitrogen, with a flow of 20 mL min in the temperature interval of 25-900°C and with
-1
the heating rate of 10°C min . The coupled technique TG/MS/FTIR was applied using a device that
is composed of a thermogravimetric analysis device types STA 449 F1 Jupiter (Netzsch, Germany),
coupled with a spectrophotometer type Vertex-70 FTIR (Bruker, Germany) and a mass
spectrometer QMS model 403 CAëolos (Netzsch, Germany). The analyzed sample mass ranged
-1
between 7.3 and 8.4 mg and the applied heating rate was 10°C min in the temperature range of 25-
680°C in nitrogen. Further information on the technical characteristics and operation of the
TG/MS/FTIR system is detailed in a previous paper [28]. UV-visible absorption spectra were
recorded in the 270-570 nm spectral range using an UV-visible spectrophotometer (Analytic Jena

6
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2
10 Plus) and steady state fluorescence measurements were performed on a Perkin Elmer LS 55
fluorescence spectrometer. Fluorescence spectra were recorded between 350-670 nm, by exciting
the polymer samples at the wavelength corresponding to the absorption maximum. The absolute
fluorescence quantum yields were measured with an integrating sphere on an Edinburg Instruments
-6
-1
FLS980 Spectrometer, at a concentration of 1.0×10 mol L . Both the samples and reference were
excited at the same wavelength. The Stokes shifts were calculated as the difference between the
wavenumbers corresponding to the maxima of the absorption and emission bands. All the solvents
of different polarities used for absorbance and fluorescence measurements were of spectrometric
grade. All spectral measurements were performed at room temperature.
2
2
.3. Synthesis
.3.1. N-(4-dimethylaminobenzoyl)-N′-(4-nitrobenzoyl)hydrazine (3)
4
-Dimethylaminobenzohydrazide (Aldrich) (4.475 g, 0.025 mol), NMP (35 mL) and pyridine (2
mL) were placed in a 100 mL three-necked flask equipped with mechanical stirrer, and the mixture
was stirred until complete dissolution was achieved. The solution was cooled to 0°C, and 4-
nitrobenzoyl chloride (4.637 g, 0.025 mol) was added under stirring. The flask content was kept at
0°C for 1 h and at room temperature for 6 h. The reaction mixture was poured in water while
stirring, and the resulting precipitate was filtered, washed with water and dried. Yield: 85%. FTIR
-1
(
KBr, cm ): 3252 (NH of hydrazide), 3020, 2918, 2865, 1680 (CONH), 1639 (CONH), 1605 and
1
1
510 (-C-C- aromatic), 1372 (C-N), 1343 (NO ). H NMR (CDCl , 400 MHz) δ (ppm): 3.01 (6H, s,
2
3
CH ), 6.76 (2H, d, J = 8.8 Hz, H-3), 7.82 (2H, d, J = 8.8 Hz, H-2), 8.15 (2H, d, J = 8.8 Hz, H-2’),
3
1
3
8
.38 (2H, d, J = 8.8 Hz, H-3’), 10.26 (1H, s, NH-6), 10.72 (1H, s, NH-6’). C NMR (CDCl , 100
3
MHz) δ (ppm): 39.6 (2C, CH ), 110.8 (2C, C-3), 118.6 (1C, C-1), 123.7 (2C, C-3’), 128.9 (4C, C-2
3
and C-2’), 138.4 (1C, C-1’), 149.3 (1C, C-4’), 152.5 (1C, C-4), 164.4 (1C, C-5’), 165.7 (1C, C-6).
+
+
ESI-MS: calcd. for C H N O m/z = 328.3226 [M ], found m/z = 329.2577 [M+H] .
1
6
16
4
4

7
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3
2
2' 3'
O
O
H C
4'
3
4
1
1'
5
N
NO2
5
'
H C
3
N
H
N
H
6
6'
2.3.2. 2-(4-Nitrophenyl)-5-(4′-dimethylaminophenyl)-1,3,4-oxadiazole (4)
Compound 3 (4 g) and POCl (50 mL) were introduced in a flask equipped with magnetic
3
stirrer, and refluxed for 6 h. After cooling to room temperature, the reaction mixture was poured in
an ice-water mixture, and the resulting precipitate was filtered, washed several times with water and
-1
dried. Yield: 87%. FTIR (KBr, cm ): 3025 (C-H aromatic), 2918 and 2865 (N(CH ) ), 1606 and
3
2
1
1
510 (-C-C- aromatic), 1580 and 1341 (NO stretching), 1017 and 960 (1,3,4-oxadiazole). H NMR
2
(
CDCl , 400 MHz) δ (ppm): 2.88 (6H, s, CH ), 6.56 (2H, d, J = 8.8 Hz, H-3”), 7.76 (2H, d, J = 9.2
3
3
1
3
Hz, H-2”), 8.09 (2H, d, J = 8.8 Hz, H-2’), 8.17 (2H, d, J = 8.8 Hz, H-3’). C NMR (CDCl , 100
3
MHz) δ (ppm): 39.5 (2C, CH ), 109.22 (1C, C-1”), 111.1 (2C, C-3”), 123.8 (2C, C-3’), 126.9 (2C,
3
C-2’), 128.0 (2C, C-2”), 129.3 (1C, C-1’), 148.6 (1C, C-4’), 152.2 (1C, C-4”), 161.2 (1C, C-2),
+
1
65.8 (1C, C-5). ESI-MS: calcd. for C H N O m/z = 310.3074 [M ], found m/z = 311.2457
1
6
14
4
3
+
[
M+H] .
3
" 2"
2' 3'
N N
4'
H C 4"
1"
1'
3
N
NO2
5
O
2
H C
3
2.3.3. 2-(4-Aminophenyl)-5-(4′-dimethylaminophenyl)-1,3,4-oxadiazole (5)
Compound 4 (8 g, 0.0334 mol) was dissolved in 250 mL boiling ethanol. To this boiling
solution sodium hydrosulfide monohydrate (10 g) was added within 20 min and after a half hour a
clear dark green solution was obtained. The hot ethanol solution was filtered and after cooling to
-1
room temperature a white precipitate was separated. Yield: 82%. FTIR (KBr, cm ): 3447, 3350 and
3220 (NH ), 3037 (aromatic C-H), 2915 and 2853 (N(CH ) ), 1608, 1495 (C-C aromatic), 1011 and
2 3 2
1
9
60 (1,3,4-oxadiazole). H NMR (CDCl , 400 MHz) δ (ppm): 3.05 (6H, s, CH ), 4.03 (2H, bs,
3
3
NH ), 6.75 (4H, d, J = 8.8 Hz, H-3’ and H-3”), 7.90 (2H, d, J = 8.4 Hz, H-2’), 7.95 (2H, d, J = 8.8
2
1
3
Hz, H-2”). C NMR (CDCl , 100 MHz) δ (ppm): 40.1 (2C, CH ), 111.4 (1C, C-1”), 111.6 (2C, C-
3
3

8
ACCEPTED MANUSCRIPT
3
”), 114.2 (1C, C-1’), 114.7 (2C, C-3’), 128.1 (2C, C-2”), 128.4 (2C, C-2’), 149.3 (1C, C-4’), 152.1
+
(
1C, C-4”), 163.9 (1C, C-2), 164.4 (1C, C-5). ESI-MS: calcd. for C H N O m/z = 280.3244 [M ],
1
6
16
4
+
found m/z = 281.2570 [M+H] .
2' 3'
3
" 2"
N
N
H C
4"
1"
1'
4'
3
N
NH2
5
O
2
H C
3
2.3.4. 2-(4,4′-Dinitro-4″-triphenylamine)-5-(4-dimethylaminophenyl)-1,3,4-oxadiazole (6)
Compound 5 (5.54 g, 19.79 mmol), CsF (10.52 g, 69.29 mmol), 1-fluoro-4-nitrobenzene (5.6 g, 20
mmol) and DMSO (70 mL) were added in a three necked flask. The reaction mixture was heated at
140°C under stirring and inert atmosphere for 24 h, it was cooled to room temperature and
precipitated into water. The yellow precipitate was then collected by filtration and washed with
-1
water. Yield: 69%. Mp. 235-237°C. FTIR (KBr, cm ): 3079 (aromatic C-H stretching), 2910 and
2869 (aliphatic C-H stretching), 1600 and 1504 (aromatic C-C stretching), 1580 and 1341 (NO2
1
stretching), 1008 and 954 (oxadiazole ring), 845 (C-N stretching for aromatic NO2). H NMR
(
CDCl , 400 MHz) δ (ppm): 3.07 (6H, s, CH ), 6.76 (2H, d, J = 8.8 Hz, H-3”), 7.22 (4H, d, J = 9.2
3
3
Hz, H-3*), 7.28 (2H, d, J = 8.8 Hz, H-3’), 7.97 (2H, d, J = 8.8 Hz, H-2”), 8.13 (2H, d, J = 8.4 Hz,
1
3
H-2’), 8.19 (4H, d, J = 9.2 Hz, H-2*). C NMR (CDCl , 100 MHz) δ (ppm): 40.1 (2C, CH ), 110.5
3
3
(1C, C-1”), 111.6 (2C, C-3”), 122.2 (1C. C-1’), 123.3 (4C, C-3*), 125.7 (4C, C-2*), 126.4 (2C, C-
3
1
5
’), 128.4 (2C, C-2”), 128.7 (2C, C-2’), 143.4 (2C, C-1*), 147.4 (1C, C-4’), 151.3 (2C, C-4*),
52.5 (1C, C-4”), 162.5 (1C, C-2), 165.5 (1C, C-5). ESI-MS: calcd. for C H N O m/z =
28
22
6
5
+
+
22.5115 [M ], found m/z = 523.2763 [M+H] .
NO2
4
*
3
" 2"
2' 3'
N
N
3*
H C 4"
1"
1'
4'
3
1
N
*
2*
N
5
O
2
H C
3
NO2
2.3.5. 2-(4,4′-diamino-4″-triphenylamine)-5-(4-dimethylaminophenyl)-1,3,4-oxadiazole (7)

9
ACCEPTED MANUSCRIPT
The dinitro compound 6 (9 g, 15.10 mmol), Pd/C (Pd content 1%, 0.46 g), and ethanol (200 mL)
were introduced in a three neck round-bottom flask. Hydrazine monohydrate (70 mL) was slowly
added and the reaction mixture was heated to reflux for 12 h. The hot mixture was filtered to
remove Pd/C and the solvent was evaporated. The resulting product was recrystallized from
-1
ethanol. Yield 26%. Mp. = 248-249°C. FTIR (KBr, cm ): 3456, 3350, 3220 (NH ), 3028 (C-H
2
aromatic), 2907, 2857 (C–H aliphatic), 1610, 1500 (aromatic C-C stretching), 1010, 950
1
(
oxadiazole ring). H NMR (CDCl , 400 MHz) δ (ppm): 3.05 (6H, s, CH ), 5.12 (4H, bs, NH ),
3
3
2
6.66 (4H, d, J = 8.6 Hz, H-3*), 6.75 (2H, d, J = 9.0 Hz, H-3”), 6.89 (2H, d, J = 8.8 Hz, H-3’), 7.00
1
3
(
4H, d, J = 8.6 Hz, H-2*), 7.82 (2H, d, J = 8.8 Hz, H-2’), 7.94 (2H, d, J = 8.8 Hz, H-2”). C NMR
(
CDCl , 100 MHz) δ (ppm): 40.1 (2C, CH ), 111.5 (1C, C-1”), 111.6 (2C, C-3”), 114 (1C, C-1’),
3
3
116.1 (4C, C-3*), 117.5 (2C, C-3’), 127.6 (2C, C-2’), 127.7 (4C, C-2*), 128.1 (2C, C-2”), 137.9
(
2C, C-1*), 143.5 (2C, C-4*), 151.6 (1C, C-4’), 152.1 (1C, C-4”), 163.9 (1C, C-2), 164.3 (1C, C-5).
UV-Vis (DMSO): = 364 nm. Fluorescence ( DMSO): λem = 412 nm, SS = 48 nm, QY = 8.28%.
+
+
ESI-MS: calcd. for C H N O m/z = 462.5458 [M ], found m/z = 463.3731 [M+H] .
2
8
26
6
NH2
4
*
3
" 2"
2' 3'
N
N
3*
H C 4"
1"
1'
4'
3
1
N
*
2*
N
5
O
2
H C
3
NH2
2.3.6. Synthesis of poly(amide-imide)s 10a, 10b and 10c
The poly(amide-imide)s 10a-c were synthesized by solution polycondensation reaction of
diamine 7 with diacid chlorides 8 or 9, in NMP as a solvent and in the presence of pyridine as acid
acceptor. In a typical experiment, 10a was prepared as follows: diamine 7 (0.462 g, 0.001 mol),
NMP (6 mL) and pyridine (0.2 mL) were introduced into a flask and the mixture was stirred under
nitrogen until complete dissolution. Diacid chloride 8 (0.719 g, 0.001 mol) was added and the

1
0
ACCEPTED MANUSCRIPT
reaction mixture was stirred for 10 h to yield a viscous polymer solution. The solution was diluted
to about 5% by addition of more NMP and the polymer was precipitated by pouring into methanol.
The precipitated product was filtered, washed with ethanol and water and dried under vacuum at
110°C for 10 h to give poly(amide-imide) 10a. The poly(amide-imide) 10b was prepared starting
from 7 (0.462 g, 0.001 mol) and diacid chloride 9 (0.627 g, 0.001 mol) while copolyamide 10c was
prepared from diacid chloride 8 (0.719, 0.001 mol) and a mixture of 8 (0.231 g, 0.0005 mol) and
4,4′-(4,4′-isopropylidenediphenyl-1,1′-diyldioxy)dianiline (0.205 g, 0.0005 mol).
10a
-1
FTIR (KBr, cm ): 3430 (NH stretching), 3043 (aromatic C-H), 2922, 2855 (C-H aliphatic), 1786
and 1726 (C=O of imide ring), 1671 (C=O of amide ) 1610 and 1508 (C-C aromatic) 1368 (C-N of
imide ring), 1192 and 1210 (C-F), 1017 and 961 (1,3,4-oxadiazole ring), 720 (C=O bending of
1
imide ring). H NMR (DMSO-d6, 400 MHz) δ (ppm): 3.02 (6H, s, CH ), 6.85 (2H, bs, H-2), 7.02
3
(2H, bs, H-9), 7.20 (4H, bs, H-12), 7.64 (4H, d, J = 7.2 Hz, H-18), 7.79 (2H, bs, H-23), 7.85 (6H,
bs, H-3 and H-13), 7.91 (2H, bs, H-8), 8.00 (2H, bs, H-25), 8.10 (4H, d, J = 8.4 Hz, H-17), 8.22
1
3
(
2H, bs, H-26), 10.45 (2H, bs, NH). C NMR (DMSO-d6, 100 MHz) δ (ppm): 39.7 (2C, CH ), 64.6
3
(1C, heptet, JC,F = 25 Hz, C-28), 109.9 (1C, C-4), 111.7 (2C, C-2), 114.9 (1C, C-7), 119.3 (2C, C-
9), 121.7 (4C, C-13), 123.3 (2C, q, JC,F = 287 Hz, C-29), 123.7 (2C, C-23), 124.5 (2C, C-26), 126.1
(
4C, C-12), 127.1 (4C, C-18), 127.7 (4C, C-3 and C-8), 128.3 (4C, C-17), 132.6 (2C, C-22), 132.9
2C, C-27), 134.4 (2C, C-19), 134.7 (2C, C-16), 135.9 (4C, C-14 and C-25), 137.4 (2C, C-24),
(
141.6 (2C, C-11), 150.3 (1C, C-10), 152.2 (1C, C-1), 162.8 (1C, C-6), 163.9 (1C, C-5), 164.9 (2C,
C-15), 165.7 and 165.9 (4C, C-20 and C-21). UV-Vis (DMSO): λabs = 372 nm. Fluorescence
-1
-1
(
DMSO): λem = 469 nm, SS = 92 nm, QY = 0.11%. GPC: M = 19500 g mol , M =25700 g mol ,
n
w
PDI = 1.32.

1
1
ACCEPTED MANUSCRIPT
CF
3
O
2
O
N
O
23
18
17
24
22
0
13
28
1
4
19
16
1
2
*
OC
N
2
COHN
N
*
n
2
CF3
5
H
1
5
11
1
27
2
6
O
N
10
9
8
7
6
N
N
O
5
4
3
2
1
N
H C
CH3
3
10b
-1
FTIR (KBr, cm ): 3384 (N-H stretching), 3043 (aromatic C-H), 2923, 2854 (C-H aliphatic), 1786
and 1726 (C=O of imide ring), 1671 (C=O of amide), 1608 and 1504 (C-H aromatic), 1368 (C-N of
imide ring), 1017 and 965 (1,3,4-oxadiazole ring), 1260 and 810 (Si-C stretching), 719 (C=O
1
bending of imide ring). H NMR (DMSO-d6, 400 MHz) δ (ppm): 0.80 (6H, bs, CH -Si), 3.02 (6H,
3
s, CH ), 6.85 (2H, bs, H-2), 7.02 (2H, bs, H-9), 7.20 (4H, bs, H-12), 7.63 (4H, d, J = 8.1 Hz, H-18),
3
7.85 (6H, bs, H-3 and H-13), 7.90 (2H, bs, H-8), 8.01 (2H, bs, H-26), 8.09 (4H, d, J = 8.3 Hz, H-
1
3
1
7), 8.12-8.15 (4H, m, H-23 and H-25), 10.42 (2H, bs, NH). C NMR (DMSO-d6, 100 MHz) δ
(ppm): -3.3 (2C, CH -Si), 39.7 (2C, CH ), 109.9 (1C, C-4), 111.7 (2C, C-2), 115.0 (1C, C-7), 119.3
3 3
(2C, C-9), 121.6 (4C, C-13), 122.7 (2C, C-26), 125.4 (4C, C-12), 127.0 (4C, C-18), 127.7 (4C, C-3
and C-8), 128.2 (4C, C-17), 128.4 (2C, C-23), 130.8 (2C, C-22), 132.5 (2C, C-27), 134.3 (2C, C-
1
1
6), 134.6 (2C, C-19), 135.9 (2C, C-14), 140.3 (2C, C-25), 141.5 (2C, C-11), 145.7 (2C, C-24),
50.3 (1C, C-10), 152.1 (1C, C-1), 162.8 (1C, C-6), 163.9 (1C, C-5), 164.8 (2C, C-15), 166.6 and
1
66.9 (4C, C-20 and C-21). UV-Vis (DMSO): λabs = 373 nm. Fluorescence (DMSO): λem= 423 nm,
-1
-1
SS = 50 nm, QY = 0.88%. GPC: M = 33600 g mol , M = 46100 g mol , PDI = 1.37.
n
w

1
2
ACCEPTED MANUSCRIPT
28
CH
3
O
O
N
O
2
3
18
17
2
4
22
20
19
13
14
Si
25
CH3
16
12
11
OC
N
2
COHN
15
N
*
n
*
H
1
27
2
6
O
N
10
9
8
7
6
N
N
O
5
4
3
2
1
N
H C
CH3
3
1
0c
FTIR (KBr, cm ): 3429 (N-H stretching), 3041 (C-H aromatic), 2953, 2921, 2853 (C-H aliphatic),
777, 1721 (C=O of imide ring), 1669 (C=O of amide), 1609 and 1507 (C-H aromatic), 1364 (C-N
-1
1
of imide ring), 1220 (aromatic -C-O-C-), 1209 and 1190 (C-F), 1017 and 955 (1,3,4-oxadiazole
1
ring). H NMR (DMSO-d6, 400 MHz) δ (ppm): 3.02 (6H, s, CH ), 6.62 (s), 6.71 (d, J = 7.8 Hz),
3
6
.85 (2H, d, J = 8.1 Hz), 7.04 (2H, d, J = 8.5 Hz), 7.11 (d, J = 8.4 Hz), 7.22 (4H, d, J = 7.8 Hz),
.36 (t, J = 7.7 Hz), 7.64 (4H, d, J = 7.0 Hz), 7.79 (2H, bs), 7.83-7.85 (6H, m), 7.93 (2H, d, J = 8.4
7
Hz), 8.00 (2H, bs), 8.10 (4H, d, J = 7.6 Hz), 8.22 (2H, d, J = 5.6 Hz), 10.41 (2H, bs, NH). 10.45
1
3
(
2H, bs, NH). C NMR (DMSO-d6, 100 MHz) δ (ppm): 39.7 (2C, CH ), 64.6 (1C, heptet, J = 25
3 C,F
Hz), 107.4 (CH), 109.9 (1C), 111.7 (2C), 112.0 (CH), 115.0 (1C), 119.3 (2C), 119.6 (CH), 121.6
4C), 121.9 (CH), 123.3 (2C, q, JC,F = 287 Hz), 123.7 (2C), 124.4 (2C), 126.0 (4C), 127.0 (4C),
(
1
1
27.6 (4C), 128.2 (4C), 130.9 (CH), 132.5 (2C), 132.9 (2C), 134.3 (2C), 134.6 (2C), 135.2 (C),
35.8 (4C), 137.4 (2C), 141.6 (2C), 150.3 (1C), 151.6 (C), 152.1 (1C), 158.7 (C), 162.8 (1C), 163.9
(
1C), 164.8 (2C), 165.7 and 165.9 (4C). UV-Vis (DMSO): λabs = 373 nm. Fluorescence (DMSO):
-1
-1
λem = 452 nm, SS = 79 nm, QY = 0.18%. GPC: 10c: M = 28800 g mol , M = 36100 g mol , PDI =
n
w
1.25.
2.3.7. Synthesis of polyimide 11

1
3
ACCEPTED MANUSCRIPT
Polyimide 11 was prepared by a two-step polycondensation reaction of diamine 7 with
dianhydride 6FDA. In a 100 mL three-necked flask equipped with mechanical stirrer and nitrogen-
inlet and outlet were introduced diamine 7 (0.462 g, 0.001 mol) and NMP (6 mL). The mixture was
stirred under nitrogen to the complete dissolution and 6FDA (0.444 g, 0.007 mol) was added and
stirring was continued for 12 h. Then, pyridine (3 mL) and acetic anhydride (2 mL) were added and
the resulting solution was heated at 100°C for 4 h. The flask was cooled-down to room temperature
and the solution was poured into methanol to precipitate the polymer. The solid product was
-1
filtered, washed three times with water under stirring and dried at 100°C. FTIR (KBr, cm ): 3070
(C-H aromatic), 2931, 2850 (C-H aliphatic), 1784 and 1725 (C=O of imide ring), 1612 and 1500 (-
1
C-C- aromatic), 1210 and 1192 (C-F), 720 (C=O bending of imide ring). H NMR (DMSO-d6, 400
MHz) δ (ppm): 3.02 (6H, s, CH ), 6.85 (2H, bs, H-2), 7.21 (2H, bs, H-9), 7.32 (4H, bs, H-12), 7.48
3
(4H, bs, H-13), 7.78 (2H, bs, H-18), 7.86 (2H, bs, H-3), 7.96-8.01 (4H, m, H-3 and H-20), 8.20 (2H,
1
3
bs, H-21). C NMR (DMSO-d6, 100 MHz) δ (ppm): 39.7 (2C, CH ), 64.5 (1C, heptet, J = 25
3
C,F
Hz, C-28), 109.8 (1C, C-4), 111.7 (2C, C-2), 117.2 (1C, C-7), 122.3 (2C, C-9), 123.3 (2C, q, JC,F
91 Hz, C-29), 123.5 (4C, C-18), 124.3 (2C, C-21), 125.1 (4C, C-12), 127.5 (4C, C-14), 127.7 (2C,
C-3), 127.9 (2C, C-8), 128.7 (4C, C-13), 132.6 (2C, C-17), 132.9 (2C, C-22), 135.8 (2C, C-20),
37.5 (2C, C-19), 145.7 (2C, C-11), 149.5 (1C, C-10), 152.2 (1C, C-1), 162.6 (1C, C-6), 164.2 (1C,
C-5), 165.9 and 166.0 (4C, C-15 and C-16). UV-Vis (DMSO): λabs = 369 nm. Fluorescence
=
2
1
-1
(
DMSO): λem = 417 nm, SS = 43 nm, QY = 1.30%. GPC: 11: M = 9200 g mol , M = 12400 g
n
w
-1
mol , PDI = 1.35.

1
4
ACCEPTED MANUSCRIPT
2
4
CF
3
18
O
O
N
O
1
9
17
1
5 14
3
1
12
2
3
N
*
n
*
20
11
CF3
22
16
21
O
N
1
0
9
8
7
6
N
O
N
5
4
3
2
1
N
H C
CH3
3
3. Results and discussion
3.1. Synthesis of diamine 7
A new diamine 7 was prepared through a sequence of reactions, as shown in scheme 1.
Dimethylaminobenzohydrazide reacted with 4-nitrobenzoyl chloride in NMP as solvent and
pyridine as catalyst, resulting in compound 3 containing a nitro group. This compound was treated
with POCl to give the corresponding oxadiazole nitro derivate 4. The reduction of 4 with sodium
3
hydrosulfite in ethanol afforded the amino oxadiazole derivative 5. Compound 6 was prepared
starting from 5 and 1-fluoro-4-nitrobenzene in the presence of CsF. The hydrogenation of 6 was
further performed by using hydrazine hydrate and a catalytic amount of Pd/C to obtain the diamine
7
. The structure of the compounds 3-7 was confirmed by FTIR and NMR spectroscopy.
1
13
Unambiguous assignments for the H and C chemical shifts were based on two-dimensional
1
1
1
13
homo- and heteronuclear correlations like H, H-COSY (Correlation Spectroscopy), H, C HSQC
(Heteronuclear Single Quantum Coherence) as well as HMBC (Heteronuclear Multiple Bond
Coherence). All the spectra were in good agreement with the proposed structures. In the FTIR
spectrum of 7 characteristic absorption bands appeared at 3456, 3350 and 3220 (NH asymmetric
-1
and symmetric stretching), 2954 and 2857 (C-H aliphatic), and at 1013 and 944 cm (=C-O-C=

1
5
ACCEPTED MANUSCRIPT
stretching in oxadiazole ring) confirming the presence of primary amine and dimethylamine groups,
1
and 1,3,4-oxadiazole ring (Fig. S1 of the Supplementary material). Fig. 1 represents the H NMR
spectrum of 7 with the assignment for all the protons. The protons in ortho position to the amine
groups appeared at 6.66 ppm as a doublet while the protons in ortho position to oxadiazole ring
appeared as doublet at the highest ppm values. The protons of aromatic amine groups appeared as a
singlet at 5.12 ppm.
Scheme 1
Figure 1
3.2. Synthesis and general characterization of the polymers
The poly(amide-imide)s 10a and 10b were prepared by low-temperature solution
polycondensation reaction of 7 with two diacid chlorides containing imide rings 8 and 9,
respectively. The copolyimide 10c was synthesized starting from the diacid chloride 8 and an
equimolar mixture of diamines 7 and 4,4′-(4,4′-isopropylidenediphenyl-1,1′-diyldioxy)dianiline.
The polyimide 11 was obtained in two steps; in the first step a polyamic acid was prepared by
polycondensation reaction of an equimolar amount of 7 and 6FDA, in NMP as solvent. In the
second step the poly(amic acid) was chemically cyclized in the presence of acetic anhydride and
pyridine. The chemical structure of the polymers is illustrated in Fig. 2.
Figure 2
1
The structure of the polymers was confirmed by FTIR and H NMR. In the FTIR spectra of all
the polymers characteristic absorption bands appeared at around 1780, 1720, 1360 and 720 (imide
-1
ring), at 1015 and 950 (1,3,4-oxadiazole ring) and at 2919 and 2855 cm (aliphatic C-H groups)
Fig. S2 of the Supplementary material). FTIR spectra of 10a, 10c and 11 showed characteristic
(
-1
absorption bands for 6F groups at around 1180 and 1210 cm (C-F stretching). The FTIR spectrum
-1
1
of 10b presented a specific absorption band at 810 cm (Si-C stretching). The H NMR spectra of
1
0a, 10b and 10c showed characteristic peaks of amide groups at about 10.4 ppm (see Fig. 3 for
0a).
1

1
6
ACCEPTED MANUSCRIPT
Figure 3
All the polymers were easily soluble in polar organic solvents such as NMP, DMF, N,N-
dimethylacetamide (DMAc) and DMSO. The polyimide 11 was soluble in chloroform and
tetrahydrofuran while the poly(amide-imide)s were insoluble in these solvents. The good solubility
can be explained by the presence of 6F or dimethylsilane groups in their chemical structure, which
increased the flexibility of the macromolecular chains thus enhancing the solubility. The molecular
weight was determined by GPC. The number average molecular weight (M ) values of 10a, 10b,
n
-1
1
0c and 11 were of 19500, 33600, 28800, 9200 g mol , respectively, the weight average molecular
-1
weight (M ) values were of 25700, 46100, 36100, 12400 g mol , respectively, and the
w
polydispersity index (PDI) was of 1.32,1.37, 1.25, 1.35, respectively.
3.3. Influence of the structure on the thermal stability
The thermal behavior of the polymers was investigated by DSC and TGA. The DSC
measurements did not evidence a glass transition temperature in the measurement domain. This can
be explained by a high rigidity of macromolecular chains due to the presence of 2-(4-phenoxy)-5-
(4-dimethylaminophenyl)-1,3,4-oxadiazole pendant groups which may produce steric hindrance.
The main thermogravimetric characteristics obtained from the analysis of the TG and DTG curves
are presented in Table 1. The DTG curves are comparatively shown in Fig. 4. The obtained results
reveal that polymer degradation comprised two or three stages. A significant amount of residue
resulted at 900°C, which is the temperature at which the heating process ended. If the thermal
decomposition onset temperature is taken as the thermal stability criterion, the series of thermal
stability increase is: 10b<11<10c≅ 10a.
Figure 4
Table 1
The analysis of the results shows the same thermal stability for 10a and 10c, as well as
approximately the same thermal decomposition onset temperature and approximately the same TPeak
in the first stage. In their cases, the thermal decomposition initiation probably occurred in the same

1
7
ACCEPTED MANUSCRIPT
groups which exist in both structures. A prior study [29], which applied the TG/MS/FTIR technique
to other polymers containing oxadiazole in their side chain, established that thermal decomposition
initiation occurs in the methyl groups and the oxadiazole in the side chain. The thermal
decomposition in inert atmosphere of 11 included three stages, where the second TPeak had
approximately the same value as 10a polymer and 10c copolymer. A different behavior of 10b was
found, which exhibits the lowest thermal stability when the thermal decomposition onset
temperature is considered as the thermal stability criterion. The temperature peak of approximately
5
44°C was not detected for this polymer. In order to clarify aspects related to the thermal
degradation mechanism of this polymer, the coupled TG/MS/FTIR technique in inert atmosphere
nitrogen) was used. The obtained MS spectra revealed that thermal decomposition initiation is
(
probably due to the a and b scissions in the side chains, and to the c scission in the amidic group
+
(
see scheme 2). This assumption is supported by the presence of ionic fragments m/z=15 (CH ),
3
+
2
+
m/z = 93 (C H NH ) and m/z = 103 (C H CN ) (see Fig. 5a and 5b). At temperatures higher than
6
5
6
5
540°C, the decomposition continued with the d scissions in the imide group (see scheme 2). Special
mention should be made of the ionic fragment m/z = 103 the intensity of which increased and
reached a temperature peak of approximately 580°C. It may be associated with benzonitrile
+
+
(
C H CN ) which may result, together with the ionic fragment m/z = 44 (CO ) and the fragment
6
5
2
+
m/z = 28 (CO ), from the imide group degradation (see Fig. S3 of the Supplementary material). The
+
ionic fragments m/z = 78 (C H ) and m/z = 30 (CH O ) was also identified in the MS spectra at
6
6
2
temperatures higher than 540°C (see Fig. 5c and 5d). Fig. S4 of the Supplementary material also
shows ionic current variation with temperature increase for other ionic fragments, on which we
relied when we suggested the degradation mechanism described in scheme 2, like for instance: m/z
+
+
=
18 (H O ), and also m/z = 58 (Si(CH ) ) and m/z = 128 (NCC H CN ), with lower intensity for
2 3 2 6 4
ionic current.
The degradation mechanism suggested for 10b is also supported by the FTIR analysis of the
-1
solid residue resulting after sample heating in nitrogen at a rate of 10°C min up to 540 and up to

1
8
ACCEPTED MANUSCRIPT
6
50°C. The structure of 10b was identified by FTIR spectroscopy (Fig. S5 of the Supplementary
material). In the FTIR spectra of 10b characteristic absorption bands for imide rings appeared at
-1
1
786, 1726, 1360 and 732 cm (imide rings), 1671 (amide groups), 1017 and 965 (oxadiazole ring)
-1
and 1260 and 810 cm (Si-CH ). In the case of the same polymer heated up to 540°C with the
3
-1
heating rate of 10°C min it can be observed a significant decrease of the absorption band at 1671
-1
cm , due to the partial decomposition of amide groups, and the disappearance of the absorption
-1
bands of 1017 and 965 cm , due to the decomposition of oxadiazole rings. A strong absorption
-1
band appeared at 2220 cm probably due to the formation of CN groups. In the FTIR spectrum of
the polymer heated up to 640°C the absorption bands characteristic for the imide rings at 1786,
-
1
1
726, 1360 and 732 cm were not observed. Characteristic bands can be seen at 1620 (aromatic
-1
systems), and at 1080 cm (very broad) due to the formation of Si-O-Si groups.
Scheme 2
Figure 5
Fig. 6 shows a comparison between the FTIR spectra obtained by the coupled TG/FTIR
technique for different temperatures, with a view to determining the degradation mechanism of 10b.
It can be concluded that the results were in agreement with the previous results of the MS spectra
-1
analysis. Water-specific bands ranged between 4000 and 3400 cm , CO -specific bands ranged
2
-1
-1
between 2400 and 2200 cm and between 740 and 600 cm , and benzene-specific bands ranged
-1
-1
between 1600 and 1400 cm [30]. An intense peak at approximately 3015 cm was identified,
which agrees with the literature data [31] and may be associated with the presence of CH . Intensity
4
-1
-1
peak at 1373 cm indicates the presence of benzonitrile [32], whereas the 2180 and 2108 cm peaks
may be associated with the presence of carbon monoxide [33], results which were also supported by
the MS spectra shown in Fig S3 in the Supplementary material, for the ionic fragment m/z = 28
+
-1
-1
(
CO ). A 1265 cm peak specific to amines [34] and a 1730 cm peak specific to carbonyl
compounds [35] were also identified, thus confirming the presence of ionic fragments m/z = 93
+
+
(
C H NH ) and m/z = 30 (CH O ).
6 5 2 2

1
9
ACCEPTED MANUSCRIPT
Figure 6
3
.4. Optical properties
The optical properties of the new polymers were investigated by absorption and fluorescence
spectra in different solvents, namely NMP ( = 33.0), DMF ( = 38.25), DMAc ( = 37.8) and
DMSO ( = 46.7). The absorption and fluorescence data were collected in Table 2. In all selected
ε
ε
ε
ε
solvents these compounds exhibited a strong absorption band located in the range of 357-373 nm,
attributed to the π-π* transitions resulting from the conjugation between the aromatic rings and
nitrogen atoms (see Fig. 7a). The absorption spectra of 10a with amide groups in the backbone
exhibited red shifts in all solvents (NMP (18 nm), DMF (19 nm), DMAc (10 nm) and DMSO (20
nm)) in comparison with that of corresponding polyimide 11 (see Table 2). These red shifts of the
absorption maxima are due to the specific solute-solvent interactions and indicate longer
conjugation.
On the other hand, the absorption spectra for all samples were slightly affected by changes in
the physical properties of the solvating media (the bathochromic shift caused by solvent was only
cca. 10 nm, as can be seen in Fig. 7, for compound 10a).
Figure 7
Table 2
Fig. 8 shows the fluorescence spectra of the investigated samples in various solvents. These
spectra exhibit a single emission band in all solvents, with the emission maximum centered between
407 and 473 nm in the blue region (see Fig. 8a). The emission maximum presents anomalous blue
shifts (39 and 46 nm) in DMF and DMSO solutions, respectively from 10a to 10b (see Table 2 and
Fig. 8b), due to the presence of a flexible dimethylsilane bridge that introduces a deviation from the
linearity of the chains. The copolymer 10c had an emission maximum around 451 nm that is blue
shifted in DMF and DMSO solutions in comparison with that of the corresponding poly(amide-
imide) 10a. Moreover, the hypsochromic shifts (24 nm and 13 nm) in emission maxima of 10a
were observed in DMF and DMSO compared to NMP and DMAc solvents, while for 10b some

2
0
ACCEPTED MANUSCRIPT
bathochromic shifts (17 and 33 nm) were found in DMF and DMSO compared to that of NMP and
DMAc solutions. These shifts in the fluorescence maxima are a consequence of the specific solute-
solvent interactions from the system (the reorganization of local environments due to hydrogen
bonding formation). Also, the positive solvatochromic behavior of 10b in DMF and DMSO
solutions indicates greater stabilization of the excited singlet state of the compound in these solvents
compared to NMP and DMAc solvents, while the absorption spectra are slightly affected by solvent
characteristics. In all studied solvents, 10a, 10b and 10c have the most red-shifted emission
maximum, like in absorption, compared to those of the corresponding diamine 7 and polyimide 11,
that can be due to the its longer conjugation length and to electro-affinities of 6F units which
influence the π-π* transitions (see Table 2). Also, the fluorescence bands (full width at half-
maximum of the fluorescence band, FWHM ) for 10a, 10b and 10c in all selected solvents (see
em
Table 2) are larger than that of the corresponding diamine 7 or polyimide 11, indicating that the
conjugation length is more precisely controlled (shorter conjugation) in diamine 7 and polyimide 11
[
35] and the solvents influenced easily the spectral properties of these samples. For these newly
developed polyimide and poly(amide-imde)s the Commission Internationale de L’Eclairage (CIEx,y)
coordinates were evaluated to be (7: 0.15, 0.06; 10a: 0.18, 0.10; 10b: 0.16, 0.04; 10c: 0.19, 0.10;
and 11: 0.18, 0.12) indicating blue emission.
Figure 8
For all investigated compounds, the large values of Stokes shifts (40-100 nm, see Table 2) in
each of the solvents at room temperature were estimated. The polymer 10a has larger Stokes shifts
values in DMF and DMSO solutions due to considerable media (solvent) reorganization originated
from the hydrogen bonding formation [36].
The fluorescence quantum yields (QY, %) of the polymers in dilute DMSO solution are listed
in Table 2. The highest QY value of 8.28 % was observed for diamine 7, that is much higher than
that of corresponding polyimides and poly(amide-imide)s. The polymers 10a and 10c had the

2
1
ACCEPTED MANUSCRIPT
lowest QY values of around 0.1 %. The luminescence quantum yields range from 0.11 to 8.28%,
thereby indicating a quenching effect for the compounds derived from diamine 7.
Figs. 9a and 9b display the emission spectra of poly(amide-imide) 10b and diamine 7 with an
increase of excitation wavelength from 363 to 415 nm. Fluorescence spectra displayed an emission
pattern slightly dependent on the excitation wavelength (Fig. 9a), namely it can be found that as the
excitation wavelength increased the emission band decreased in intensity and a shift to longer
wavelengths (a very small red shift) appeared. These small red shifts can be associated with a strong
correspondence between excitation energy and the vibronic structure of the emission spectra [37]
and with the existence of many binding species in the system, due to the more intense interactions
between solute and solvent [38]. Also, from Fig. 9a was observed that for 10b the spectral shifts are
followed by a slightly decrease in fluorescence band width (the full width at half-maximum of the
emission band, FWHM ), while for corresponding diamine 7 and polyimide 11 no changes in the
em
position and shape of the emission band were recorded as the excitation wavelength increased (Fig.
9b). Similar behavior was observed in all investigated compounds in selected solvents. Compared to
10a, 10b and 10c, the emission spectra of diamine 7 and polyimide 11 are less sensitive to the
excitation wavelength values.
Figure 9
The studied polymers have different numbers of nitrogen atoms which can be susceptible to
protonation. Thus, the influence of dilute HCl solution on the absorption and fluorescence spectra
of 10a in NMP solution was monitored. The changes observed in the UV-Vis spectra of 10a in
NMP solution were shown in Fig. 10a. The increase in the concentration of HCl led to the
progressive enhancement of the absorption intensities from 313 and 386 nm, respectively. These
changes in absorption intensities indicate the presence of more than one protonated species in
solution [39]. Fig. 10b shows the fluorescence response of 10a in acidic medium where a gradual
decreases in emission intensity and small blue shift (the emission maximum of the solution
containing 650 µL HCl was moved to 435 nm with respect to neutral solution) of emission band

2
2
ACCEPTED MANUSCRIPT
with a progressive increase in acid strength of the medium were observed. These changes in
emission spectral characteristics are attributed to a protonation process of the nitrogen atoms.
Figure 10
4. Conclusions
A new aromatic diamine 2-(4,4′-diamino-4″-triphenylamine)-5-(4-dimethylaminophenyl)-
,3,4-oxadiazole was synthesized and used for the preparation of a polyimide and three poly(amide
1
imide)s. The polymers were soluble in organic solvents and exhibited high thermal stability, with
decomposition temperature above 380°C. A mechanism of thermal decomposition in nitrogen of a
poly(amide-imide) was estimated by using the coupled TG/MS/FTIR techniques. The obtained
results revealed that thermal decomposition initiation is probably due to the scissions of methyl
groups and of the oxadiazole in the side chain and the amidic group in the main chain and continues
with the imide group degradation. The products eliminated during the thermal decomposition
process in nitrogen atmosphere were water, carbon dioxide, benzene, methane, benzonitrile, aniline
and carbon monoxide. The optical properties of the new diamine and polymers were studied by UV-
vis and fluorescence spectroscopy. The absorption and fluorescence maxima were observed at 357-
373 nm and 407-469 nm, respectively, depending on the structure of the compounds and the
characteristics of the solvating media. The polymers showed blue fluorescence in solution, with
low to moderate quantum fluorescence yields varying from 0.11 to 1.30%. Stokes shifts values were
around 77 nm. The emission peaks of poly(amide-imide)s were broader than those of diamine and
polyimide. Under acidic conditions the emission spectra of investigated compounds were altered.

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Figure captions
Scheme 1. Synthesis of diamine 7.
Scheme 2. The proposed thermal degradation mechanism for 10b.
1
Fig. 1. H NMR spectrum of diamine 7.
Fig. 2. Chemical structure of poly(amide-imide)s 10a, 10b, 10c, and polyimide 11.
1
Fig. 3. H NMR spectrum of 10a.
Fig. 4. DTG curves of polymers 10 and 11.
Fig. 5. Ionic current variation with temperature for the fragments: m/z = 15 (a), m/z = 103 and 93
(b), m/z = 78 (c) and m/z = 30 (d), for 10b.
Fig. 6. FTIR spectra of the volatile products evolved during thermal decomposition of 10b.
Fig. 7. UV-Vis absorption spectra for the all investigated polymers in DMF solution (a) and for
poly(amide-imide) 10a in selected solvents (b).
Fig. 8. Fluorescence spectra of all investigated samples in DMF solution (a) and of poly(amide-
imide) 10b in selected solvents (b), the CIE 1931 (X,Y) chromaticity diagram of all investigated
compounds in dilute DMSO solution (c).
Fig 9. The emission spectra for 10b in DMAc solution (a) and diamine 7 in DMF solution (b) with
an increase of excitation wavelength from 363 to 415 nm.
Fig. 10. Changes in the UV-Vis absorption (a) and emission spectra (b) of 10a upon the addition of
dilute solution of HCl.

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Scheme 1
POCl3
(
CH ) N
CONH-NH + ClOC
NO2
(CH ) N
CO N
H
N
OC
NO2
3
2
2
3 2
H
1
3
2
NH2
O N
NO2
H N
NH2
NO2
2
2
2
F
NO2
N
N
NaSH
Pd/C
N
N
N
N
O
O
N
N
O
O
N
N
N(CH3)2
N(CH3)2
4
5
N(CH3)2
6
N(CH3)2
7