Tuning optical and electronic properties of poly(4,4'-triphenylamine vinylene)s by post-modification reactions

Article abstract of DOI:10.1016/j.dyepig.2014.08.016

New triphenylamine-based polyarylenevinylenes with pendant phenylethynyl- and 3-pyridylethynyl substituents were synthesized by Stille polycondensation of trans-1,2-bis(tributylstannyl)ethene with two new ethynyl substituted triphenylamine monomers, i.e., N,N-bis(4-iodophenyl)-4'-(phenylethynyl) phenylamine and N,N-bis(4-iodophenyl)-4'-(3-pyridylethynyl) phenylamine. The polymers were characterized by spectral methods and cyclic voltammetry and their properties were compared with those of the unsubstituted poly(4,4'-triphenylamine vinylene). Chemical post-modifications of the polymers by tetracyanoethylene addition to the triple bond, and quaternization of pyridyl group with accent on the fine-tuning of the optical and electrochemical properties were also studied. Density functional theory calculations provide a reliable interpretation of the observed spectra and electrochemical data.

Full text of DOI:10.1016/j.dyepig.2014.08.016

Dyes and Pigments 113 (2015) 227e238
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Tuning optical and electronic properties of poly(4,4'-triphenylamine
vinylene)s by post-modification reactions
Mircea Grigoras*, Ana Maria Catargiu, Teofilia Ivan, Loredana Vacareanu, Boris Minaev,
Evgeniy Stromylo
a “P. Poni” Institute of Macromolecular Chemistry, Electroactive Polymers Department, 41A Gr. Ghica Voda Alley, Iasi 700487, Romania
b Bogdan Khmelnitsky National University, Organic Chemistry Department, bv. Shevchenko 81, Cherkasy 18031, Ukraine
a r t i c l e i n f o
a b s t r a c t
Article history:
New triphenylamine-based polyarylenevinylenes with pendant phenylethynyl- and 3-pyridylethynyl
substituents were synthesized by Stille polycondensation of trans-1,2-bis(tributylstannyl)ethene with
two new ethynyl substituted triphenylamine monomers, i.e., N,N-bis(4-iodophenyl)-4'-(phenylethynyl)
phenylamine and N,N-bis(4-iodophenyl)-4'-(3-pyridylethynyl) phenylamine. The polymers were char-
acterized by spectral methods and cyclic voltammetry and their properties were compared with those of
the unsubstituted poly(4,4'-triphenylamine vinylene). Chemical post-modifications of the polymers by
tetracyanoethylene addition to the triple bond, and quaternization of pyridyl group with accent on the
fine-tuning of the optical and electrochemical properties were also studied. Density functional theory
calculations provide a reliable interpretation of the observed spectra and electrochemical data.
© 2014 Elsevier Ltd. All rights reserved.
Received 25 May 2014
Received in revised form
18 August 2014
Accepted 18 August 2014
Available online 27 August 2014
Keywords:
Polyarylenevinylenes
Synthesis
Phenylethynyl and pyridylethynyl
substituents
Chemical modification
Tune optical and electrochemical properties
Density functional theory calculations
1. Introduction
have modified polyarylenes containing alternating fluorene and 4-
phenylethynyl substituted triphenylamine groups by DielseAlder
Poly(arylene vinylene)s (PPVs) represent a well studied class of
materials among conjugated polymers due to their interesting
scientific aspects of synthesis and very useful properties for many
optoelectronic applications [1]. The seminal work of the Cambridge
group in 1990 [2] evidenced the presence of light emitting prop-
erties in PPVs and has renewed scientific interest for this class of
polymers [3e5]. Now, the potential application of PPVs in the next
generation of full-color flat panel displays is recognized and many
researchers are interested to obtain new polymer structures with
high emission efficiency. Other interesting applications are in the
organic field effect transistors [6,7] and photovoltaic cells [8,9]. The
main routes used to tune the electro-physical properties of PPVs are
based on the use of new monomer structures or new catalytic
systems or synthesis methods. A simple and effective approach for
tuning the optoelectronic properties of conjugated polymers is
through modification of functional pendant groups with acceptor
compounds, but this method is less studied until now. Nurulla et al.
reaction of the triple bond with tetraphenylcyclopentadienone [10]
or by oxidation followed by addition of o-phenylenediamine to
obtain quinoxaline pendant units [11]. The pendant aldehyde
groups can be modified with nitrile compounds, 1,3-diethyl-2-
thiobarbituric acid or 3-dicyanovinylindan-1-one to introduce
side chain acceptor groups [12e14]. Depending on the acceptor
moieties of the side chain, the absorption spectra and energy gap
can be fine-tuned. Li et al. has modified conjugated polymers
containing carbazole and triphenylamine in the main chain by re-
action of pendant aldehyde groups with malononitrile and ethyl
cyanoacetate [15]. We have also synthesized triphenylamine-based
polyarylenes with pendant eCHO and CH2OH functions and
modified their optical properties by Knoevenagel reaction with
cyanoacetic acid or phenyl isocyanate addition [16,17]. In all cases
either a bathochromic shift of the absorption and emission peaks
was observed or new bands due to the charge-transfer complexes
formed between donor and acceptor groups. These compounds
show intramolecular charge-transfer (ICT) interactions and effi-
cient electron transfer from donor to acceptor upon photoexcita-
tion, being promising candidates for building of the dye-sensitized
and bulk heterojunction (BHJ) solar cells.
* Corresponding author.
E-mail address: grim@icmpp.ro (M. Grigoras).
http://dx.doi.org/10.1016/j.dyepig.2014.08.016
0143-7208/© 2014 Elsevier Ltd. All rights reserved.

228
M. Grigoras et al. / Dyes and Pigments 113 (2015) 227e238
Furthermore, we intend to extend this method to poly-
CV of ferrocene as the internal standard in an identical cell without
any compound in the system (E1/2 ¼ 0.40 V versus the Ag/AgCl).
Prior to the each experiment, the Bu4NClO4 solutions were deox-
ygenated by passing dry nitrogen gas for 10 min. All measurements
were performed at room temperature (25 ꢀC) under nitrogen
atmosphere.
arylenevinylenes containing triphenylamine substituted in the free
para position with phenylethynyl- and 3-pyridylethynyl groups.
The electron-rich triple bond could be post-modified by: (a) addi-
tion of tetracyanoethylene [18e26], (b) cycloaddition of tetraphe-
nylcyclopentadienone [10], (c) transformation into a quinoxaline
acceptor group [11], while pyridyl group can be (d) protonated or
quaternized with alkyl bromides [27], with final effects on the main
chain conjugation length. Routes (a) and (d) will be explored to
tune the optical and electronic properties of PPVs. So, in this paper
we report the synthesis and spectroscopic and electrochemical
characterization of poly [4,4'-(400-phenylethynyl)-triphenylamine
vinylene] and poly[4,4'-(400-3-pyridylethynyl)-triphenylamine
vinylene] obtained by Stille polycondensation. A comparative
analysis of the optical and electronic properties of parent and
chemical modified polymers will be presented and correlated using
time-dependent density functional theory (TD-DFT) calculations.
The TD-DFT analysis can provide a link between structure and NMR,
absorption and luminescence spectra of such polymers [28,29].
2.3. Monomers and polymers synthesis
The synthetic routes for triphenylamine-based monomers
starting from triphenylamine, are outlined in Scheme 1. 4,4',400-
Trisiodotriphenylamine and 4,4'-diiodotriphenylamine (1) were
obtained by iodination of triphenylamine with KI/KIO3 in acetic
acid, using known methods [30,31]. The Sonogashira coupling of
4,4',400-trisiodotriphenylamine with phenylacetylene and 3-
pyridylacetylene in the presence of catalyst [(PPh3)2PdCl2, CuI,
PPh3] using triethylamine as solvent gave monomers 2 and 3.
2.3.1. Synthesis of bis(4-iodophenyl)-phenylamine (1)
In a 250 mL two-neck round bottom flask equipped with mag-
netic stirrer, condenser and nitrogen inleteoutlet were introduced
triphenylamine (8 g, 3.2 mmol), KI (7.19 g, 4.3 mmol), and glacial
acetic acid (120 mL). The mixture was stirred in nitrogen atmo-
sphere at 85 ꢀC for 5 h and KIO3 (4.60 g, 2.15 mmol) was introduced
over 5 h. The mixture was precipitated in water and a dirty white
compound was obtained and purified by column chromatography
using ethyl acetate/hexane (1:5) as eluent. Yield: 66%,
Mp ¼ 69e70 ꢀC. 1H NMR (CDCl3, ppm): 7.50 (4H, d, J ¼ 8.8 Hz), 7.24
(2H, d, J ¼ 8.0 Hz), 7.06e7.04 (3H, d þ t), 6.82e6.80 (4H, d,
J ¼ 8.8 Hz).
2. Experimental
2.1. Materials
Triphenylamine, 3-ethynylpyridine, triethylamine, Pd(PPh3)4,
PPh3, CuI, trans-1,2-bis(tributylstannyl)ethene, all from Aldrich and
phenylacetylene (Fluka), were used as received. Other reactants
and solvents are obtained from commercial sources and used as
received or dried by known methods. Tetrabutylammonium per-
clorate ((C4H9)4NClO4) was used as supporting electrolyte in elec-
trochemical studies. All manipulations were carried out under an
inert atmosphere using the Schlenk technique.
2.3.2. Synthesis of N,N-bis(4-iodophenyl)-4'-(phenylethynyl)
phenylamine (2)
2.2. Measurements
In a 100 mL three-neck round bottom flask equipped with
magnetic stirrer, condenser and nitrogen inleteoutlet were intro-
duced phenylacetylene (0.47 mL, 4.3 mmol), PdCl2$2PPh3 (0.011 g),
CuI (0.018 g), PPh3 (0.0165 g), TEA (8 mL) and reaction mixture was
stirred at room temperature for 2 h. 4,4',400-Trisiodotriphenylamine
(2.678 g, 4.3 mmol) dissolved in TEA (5 mL) was added to the flask
and the reaction mixture was maintained 24 h at 50e60 ꢀC. The
product was separated by precipitation in water, washed with
aqueous solution 0.1 M HCl and dried. Pure yellow crystalline
compound was obtained by flash chromatography using hexane as
eluent. Yield ¼ 88.4%. Mp ¼ 74e75 ꢀC. ESI-MS ¼ 598.2 (M þ Hþ). IR
(KBr, cmꢁ1): 3043, 2210, 1634, 1574, 1505, 1313, 1265, 1177, 1058,
1002, 912, 816,753, 689. 1H NMR (CDCl3, ppm): 7.58e7.48 (6H, m),
7.4 (2H, t), 7.35e7.30 (3H, m), 7.05e6.95 (2H, m), 6.9e6.75 (4H, m).
13C NMR (CDCl3, 100.39 MHz, ppm): 146.89, 135.98, 132.84, 132.6,
131.55, 128.39, 128.17, 126.13, 123.40, 123.11, 117.55, 116.37, 89.24,
89.22.
FT-IR spectra were recorded in KBr pellets on a DIGILAB-FTS
2000 spectrometer. 1H NMR and 13C NMR spectra were recorded
at room temperature on a Bruker Avance DRX-400 spectrometer
operating respectively at 400 MHz (for 1H) and 100.39 MHz
(for 13C) as solutions in CDCl3 or DMSO-d6 and chemical shifts are
reported in ppm and referenced to TMS as internal standard or
DMSO-d5. UVeVis and fluorescence measurements were carried
out in CHCl3 solution (spectrophotometric grade) or as a film on
quartz glass, on a Specord 200 spectrophotometer and Perkin Elmer
LS 55 apparatus, respectively. The fluorescence quantum yields
were determined by the integrating sphere method using an FLS
980 spectrometer and CHCl3 as solvent upon excitation with
lex ¼ 400 nm. Differential scanning calorimetry (DSC) and ther-
mogravimetric analyses (TGA) were carried our in a TGA/DTA STA
449 F1 Netzsch (Germany) at a heating rate of 10 ꢀC/min in a ni-
trogen flow. The relative molecular weights were determined by gel
permeation chromatography (GPC) using a PL-EMD 950 Evapora-
tive Mass Detector instrument and polystyrene standards for the
calibration plot and chloroform (1 mL/min) as solvent.
2.3.3. Synthesis of N,N-bis(4-iodophenyl)-4'-(3-pyridylethynyl)
phenylamine (3)
In a 50 mL three-neck round bottom flask equipped with mag-
netic stirrer, condenser and nitrogen inleteoutlet were introduced
3-ethynylpyridine (0.165 g, 1.6 mmol), PdCl2$2PPh3 (0.056 g,
0.08 mmol), CuI (0.03 g, 0.16 mmol), PPh3 (0.04 g, 0.16 mmol),
triethylamine (15 mL) and tetrahydrofuran (5 mL). The mixture was
stirred in nitrogen atmosphere at 50e60 ꢀC for an hour after that
4,4',400-trisiodotriphenylamine (1 g, 1.6 mmol) dissolved in a
mixture of TEA (5 mL) and THF (5 mL) was added. Then the mixture
was stirred at 80 ꢀC when the solution color turned out in time from
yellow to red and some solids are deposited on the flask's walls.
After 24 h the mixture was precipitated in water, filtrated and dried.
The cyclic voltammograms (CV) were recorded using a Bio-
analytical System, PotentiostateGalvanostat (BAS 100B/W). The
electrochemical cell was equipped with three electrodes: a working
electrode (disk shape Pt electrode,
F
¼ 1.6 mm), an auxiliary
electrode (platinum wire), and a reference electrode (consisted of a
silver wire coated with AgCl). Before experiments, Pt electrode was
polished between each set of experiments with aluminium oxide
powder on a polishing cloth, and then was sonicated in a mixture of
detergent and methanol for 5 min and then rinsed with a large
amount of doubly distilled water. The reference electrode (Ag/Agþ)
was calibrated at the beginning of the experiments by running the
The pure orange compound
3 was obtained by silicagel

M. Grigoras et al. / Dyes and Pigments 113 (2015) 227e238
229
Scheme 1. Synthesis of p-ethynyl substituted diiodotriphenylamine derivatives.
chromatography using ethyl acetate/hexane (1:4 þvol/vol) as eluent.
Yield: 46.6%. Mp ¼ 80 ꢀC. ESI-MS ¼ 599.2 (M þ H ). IR (KBr, cmꢁ1):
3032, 2212, 1647, 1599, 1575, 1504, 1479, 1404, 1314, 1284, 1265,
1179, 1142, 1001, 818, 803, 700. 1H NMR (CDCl3, ppm): 8.75 (1H,
pyridyl), 8.54 (1H, d, H, pyridyl), 7.81 (1H, d, pyridyl, J ¼ 8.0 Hz), 7.57
(4H, d, J ¼ 8.8 Hz), 7.41 (2H, d, J ¼ 8.4 Hz), 7.28 (1H, t, pyridyl), 7.01
(2H, d, J ¼ 8.4 Hz), 6.85 (4H, d, J ¼ 8.8 Hz).
P2: In a 50 mL two-necked-flask were added monomer 2 (0.48 g,
0.8 mmol), trans-1,2-bis(tributylstannyl)ethene (0.47 mL,
0.8 mmol), and dry toluene (10 mL). After degassed by argon
bubbling for 15 min, the solution of Pd(PPh3)4 (9.3 mg, 0.008 mmol)
in dry toluene (2 mL) was added. The reaction mixture was
degassed again for 30 min. Then the reaction mixture was heated
and stirred to 90 ꢀC for 24 h. The mixture was precipitated in
methanol, filtrated and dried. The polymer was completely dis-
solved in chloroform and reprecipitated in methanol. Yield ¼ 70.0%.
FTIR (KBr, cmꢁ1): 3028, 2954, 2922, 2849, 2212, 1595, 1505, 1317,
1285, 1178, 1103, 1009, 960, 826, 754, 692; 1H NMR (CDCl3, ppm):
2.3.4. Synthesis of polymers
The synthesis of homopolymer P1 was previously described
[17]. Yield: 64.9%. FTIR (KBr, cmꢁ1): 3025, 2923, 1594, 1507, 1489,
1314, 1280, 1178, 1106, 958, 828, 730, 695; 1H NMR (CDCl3, ppm):
6.8e7.6 (aromatic and vinylene protons); 13C NMR (CDCl3,
6.80e7.60; 13C NMR (CDCl3, 100.39 MHz,
d, ppm): 152.13, 148.31,
146.70, 146.06, 138.42, 138.24, 132.81, 127.46, 127.07, 126.51, 124.95,
123.01, 117.43, 92,72 and 86.30 (CC triple bond).
100.39 MHz, d, ppm): 147.32, 146.77, 132.21, 129.42, 129.32, 129.12,
P3: Yield ¼ 58.1%. FTIR (KBr, cmꢁ1): 3030, 2958, 2923, 2849,
2214, 1598, 1505, 1317, 1285, 1179, 1098, 1020, 961, 804, 703; 1H
NMR (CDCl3, ppm): 5.20, 5.67, 6.80e7.80, 8.53, 8.75; 13C NMR
127.21, 126.71, 125.36, 124.65, 123.99, 123.23.
A typical procedure is described for synthesis of polymer P2
(Scheme 2).
Scheme 2. Synthesis of TPA-based PAVs by Stille coupling polymerization.

230
M. Grigoras et al. / Dyes and Pigments 113 (2015) 227e238
Table 1
Polymerization results, optical and thermal properties of polymers.
Sample
Yield (%)
Mn (PDI)
labs (nm)
Eogpt
solution (eV)
lem (nm)
FF (%)
Td5 (ꢀC)
Char yield
at 700 ꢀC (%)
Solution
Film
P1
P2
P2m
P3
P3m
64.9
70.0
74.2
58.1
79.7
4140 (1.99)
4870 (2.20)
5670 (2.12)
4580 (2.50)
5020 (2.35)
313, 357, 409
277, 403
326, 400, 514
303, 405
308, 410
2.52
2.53
2.34
2.52
2.51
460
459
461
451
453
37.9
31.6
7.2
<1
<1
363
300
76.3
79.4
374, 418 (sh)
332, 407, 525
373
290
75.2
310, 408
315, 410
(CDCl3, 100.39 MHz,
145.10, 138.24, 132.81, 127.46, 127.07, 126.90, 126.50, 124.95, 123.01,
120.76, 116.21, 92.90 and 86.64 (triple bond CC).
d
, ppm): 152.13, 148.31, 147.48, 146.70, 146.61,
stable until 150 ꢀC that means they does not participate in the Stille
polycondensation reaction carried out at 90 ꢀC. On the cooling scan
no crystallization was observed, both monomers remained in an
amorphous state. These compounds were used as monomers in
Stille coupling reaction [32,33] with trans-1,2-bis(tributylstannyl)
ethene to obtain homopolymers P2 and P3 (Scheme 2). A poly(-
arylene vinylene) containing only triphenylamine groups and
vinylene units (P1) was used as a control sample and its synthesis
was previously reported [17].
The polymers synthesized by the Stille reaction are readily sol-
uble in common organic solvents such as chloroform, dichloro-
methane, THF, DMF and toluene. Polymers were obtained in good
yields (58.1e79.7%) and reasonable molecular weights. The mo-
lecular weights of the polymers were determined by gel perme-
ation chromatography (GPC). Polymers P2 and P3 have number-
average molecular weights of 4870 g/mol and 4580 g/mol,
respectively, corresponding to degrees of polymerization of about
13e15. The polydispersity index is 2.2 and 2.5, respectively. The
polymer modification has led to a slight increase in molecular
weights (Table 1). All polymers are colored powders, P1 and P2 are
yellow solids, while P3 is a bright-red solid. Compared with parent
polymers, the modified polymers are more soluble in polar solvents
and are dark-red colored powders.
2.3.5. Chemical modification of polymers
P2m: P2 (25 mg) dissolved in CH2Cl2 (20 mL) was treated with
tetracyanoethylene (9 mg), and stirred at room temperature in
nitrogen atmosphere for 20 h. The initial yellow-greenish color of
solution turned out dark-red. After concentration, the solution was
precipitated in hexane. Yield: 74.2%. FTIR (KBr, cmꢁ1): 3034, 2959,
2923, 2222, 1593, 1504, 1325, 1285, 1182, 1010, 964, 825, 756, 696;
1H NMR (CDCl3, ppm): 7.8e6.7 (triphenylamine, phenyl and
vinylene protons).
P3m: To a solution of P3 (0.1 g) in CHCl3, (6 mL), CH3I (1 mL) was
added and the red solution was gentle refluxed in nitrogen atmo-
sphere for 3 h, cooled and precipitated in methanol to obtain a
dark-red polymer (Yield; 0.11 g, 79.7%). FTIR (KBr, cmꢁ1): 3431,
3021, 2921, 2853, 2201, 1594, 1503, 1315, 1265, 1174, 1003, 960, 816,
744, 666; 1H NMR (DMSO-d6, ppm): 9.35, 9.02, 8.71, 8.22,
7.67e6.96, 4.40 (eCH3), 3.4 and 2.5 (from solvent).
3. Results and discussion
3.1. Synthesis and characterization
The modification of polymers was carried out with tetracyano-
ethylene (TCNE) (for P2) or methyl iodide for P3 (Scheme 3). The
electron-rich acetylene function can be easily modified by the
[2þ2] cycloaddition of the strong acceptor TCNE followed by
cyclo-reversion of the adduct under mild conditions leading to a
new 1,1,4,4-tetracyano 1,3-butadiene derivative [34,35]. Tetracya-
noethylene can also react readily by electrophilic substitution with
aliphatic and aromatic amines to give tricyanovinyl compounds
[36,37]. The reaction was carried in DMF at 70 ꢀC and an excess of
TCNE. However, in our case, the presence of side product containing
1,2,2-tricyanovinyl group resulted by electrophilic substitution of
TPA is less probable because the TCNE was not used in excess and
the reactive para position of TPA is blocked by substitution with
phenylethynyl group.
Monomers used in synthesis of the functional PPVs are obtained
starting from triphenylamine, according to the reactions outlined in
Scheme 1.
Iodination of triphenylamine was carried out with KI/KIO3 in
acetic acid and depending on the molar ratios between reactants,
4,4'-diiodo- or 4,4',400-triiodo-TPA were obtained [30,31]. The
Sonogashira coupling of equimolar mixtures of tris(4-iodophenyl)
amine with phenylacetylene or 3-pyridylacetylene in presence of
Pd/Cu catalysts led to monomers 2 and 3. The structures of the
monomers 2 and 3 were proved by FT-IR, 1H NMR and MS (see
Section 2). DSC studies have evidenced only melting processes on
the first heating scan while the pendant triple bonds of 2 and 3 are
Scheme 3. Chemical modification of functional PPVs by post-reactions.

M. Grigoras et al. / Dyes and Pigments 113 (2015) 227e238
231
Infrared spectra of all polymers are shown in Fig. 1. All spectra
3.2. Thermal properties
show an absorption in the range 955e965 cmꢁ1, which is assigned
to the out of plane CeH bending vibration of the trans vinyl linkage.
For polymers P2 and P3 the presence of weak bands around
2212 cmꢁ1 and 2214 cmꢁ1, respectively, assigned to the triple bond
stretching vibration supports the formation of polymers with
pendant triple bonds. This absorption band disappears in the
spectrum of polymer P2m, being replaced by a new peak at
2222 cmꢁ1 (assigned to CN stretching vibration) indicating the
presence of nitrile linkage and confirms the addition of tetracya-
noethylene to the triple bond.
Thermal properties were investigated by thermogravimetric
analyses in the temperature range of 25e700 ꢀC (TGA) and by
differential scanning calorimetry (DSC) under nitrogen atmo-
sphere. As shown in Fig. 3 polymers exhibit good thermal stability,
the degradation onsets are at least up to 260 ꢀC. The 5% weight loss
temperatures were determined to be 363 (P1), 300 (P2), and 290 ꢀC
(P3), respectively. The char yields at 700 ꢀC were 76.3% (P1), 79.4%
(P2) and 75.2% (P3). DSC studies have evidenced a glass transition
temperature (Tg) of 182 ꢀC for P1 while for others polymers no Tg
were observed between 25 and 200 ꢀC.
1H NMR spectra of the pristine and modified polymers are
shown in Fig. 2. As it is shown in the figure the signals of the aro-
matic and trans vinylene protons appears together as a broad signal
between 6.5 and 8.0 ppm. Aromatic protons in the ortho-position to
pyridine nitrogen are downfield shifted and appear as distinct
signals at 8.75 and 8.51 ppm. Weak signals at 5.17, 5.67 and 6.6 ppm
can be assigned to the vinyl end group. For instance, 4-vinyl tri-
phenylamine shows aromatic protons as a multiplet between 6.8
and 7.2 ppm while vinyl protons are positioned as two doublets at
5.08 ppm and 5.56 ppm and a quartet at 6.60 ppm.
3.3. Optical properties
The photophysical behavior of the polymers has been studied in
dilute chloroform solution (1 ꢂ 10ꢁ5 M) or in solid state as thin
films obtained by drop-casting method from CHCl3 or DMSO (P3m).
The optical characteristics are summarized in Table 1. All absorption
spectra show structured absorption bands, each comprising two
absorption maxima in the range of 300e450 nm (Fig. 4).
The pendant triple bond is also clear evidenced by 13C NMR
spectroscopy by presence of signals between 85 and 92 ppm (see
Section 2).
The introduction of the electron-withdrawing cyano groups by
addition of TCNE to the triple bond produces an intramolecular
charge-transfer (ICT) interaction between triphenylamine unit and
the acceptor pendant group and P2m shows the absorption band
due to ICT complex at 514 nm in solution and 525 nm in solid state.
This conclusion is completely supported by quantum chemical
calculations, presented in the next chapter. The modification of P3
by cycloaddition of TCNE to triple bond is not complete, and
polymer shows IR absorptions both due to triple C^C and C^N
bonds. The pyridyl group due to its electron-withdrawing char-
acter, decreases the reactivity of triple bond versus TCNE. P3
modified with TCNE shows absorption in visible region with
maximum shifted at 594 nm due to intramolecular charge-transfer
transition. The reactivity largely depends on the electron-donating
groups substituted by the alkyne moiety, and triphenylamine
strong donor was found to afford the desired donoreacceptor
structures in a quantitative yield at room temperature.
The addition of TCNE to triple bond does not modify signifi-
cantly the form of the NMR spectrum of P2. However, adjacent
phenyl protons are shifted at lower magnetic field (at
7.97e7.67 ppm) as a result of the strong electron-withdrawing ef-
fect from the tetracyanobutadiene group. As shown in Fig. 2, after
quaternization with methyl iodide, P3m is more soluble in protic
solvents (DMSO, DMF, THF) and in NMR spectrum (in DMSO-d5) all
pyridine protons are shifted downfield and appear at 9.32 ppm,
8.94 ppm, 8.66 ppm and 8.15 ppm due to the increasing of electron-
withdrawing properties of quaternized pyridine ring.
The fluorescence quantum yields (FF) were measured for poly-
mers P1eP3 using the absolute method in which the ratio of the
number of absorbed photons of a sample and the number of
consequently emitted photons is directly measured. The all high-
diluted CHCl3 solutions were excited at 400 nm. It was noticed
that the values of fluorescence quantum yields of the sample
decrease from P1 (37.9%) to P2 (31.6%) and P3 (7.2%). The fluores-
cence quantum yield for modified polymers, P2m and P3m (excited
at 400 nm or lICT ¼ 514 nm) is very low (~1%) due to the efficient
electron transfer from donor to acceptor upon photoexcitation.
The quaternized polymer P3m shows absorption peaks at 310
and 403 nm. The absorption band assigned to the electronic pep*
transition from the aromatic rings is red shifted by about 3 nm vs
the polymer parent due to the increase of accepting properties of
pyridine by quaternization. Thin films of the polymers show similar
absorption spectra as compared with that in CHCl3 solution, with
slight red-shifted maxima while the absorption edges are shifted to
longer wavelengths relative to solution spectra (Fig. 4B). The ab-
sorption edges of these polymers are 494 nm (P1), 500 nm (P2),
534 nm (P2m), 490 nm (P3) and 537 nm (P3m), respectively. The
optical band gaps (Eg) of polymers were estimated from the ab-
sorption edge of films using the relation Eg ¼ 1240/lonset and used
to calculate energy of LUMO level.
The PL spectra of all the polymers were also recorded in chlo-
roform solution. The emission maxima are summarized in Table 1.
The maxima of emission in solution are centered at 450e460 nm.
The blue shifting of polymers P2 and P3 with respect to P1
Fig. 1. FT-IR spectra (KBr pellet) of polymers: P1, P2, P2m, P3 and P3m.

232
M. Grigoras et al. / Dyes and Pigments 113 (2015) 227e238
Fig. 2. 1H NMR spectra (CDCl3) of polymers P2, P3, P2m and P3m.
observed in UVeVis absorptions spectra can also be also seen in the
PL spectra.
Protonation of P3 by addition of HCl to the pyridyl group results
in a decrease of absorption maximum and a red shift at 408 nm
when the molar ratio [HCl]/pyridine reaches 1:1.5 due to enhancing
the electron-withdrawing capability of pyridinium moiety (Fig. 5).
B3LYP methods [38,39] using the 6e31G(d) basis set with the
GAUSSIAN 09 package [40]. The convergence criteria for geometry
optimization were
2
ꢂ
10ꢁ5 Hartree for energy and
4 ꢂ10ꢁ3 Hartree/Bohr for the force field. All the calculated vibration
frequencies are found to be real, which indicates the finding of a
true total energy minimum on the potential energy hypersurface.
The triplet excited-state geometry was also optimized for all olig-
omers in order to estimate the form and size of the exciton state
(assuming that singlet and triplet first excited states are similar in
the orbital nature). The calculated infrared frequencies were cor-
rected by scaling factor (0.96) for comparison with the observed IR
spectra. The electronic absorption spectra and triplet excited-state
energies of the studied compounds were calculated by the time-
dependent (TD) DFT method using the BMK [41] functional and
the same basis sets. The polarized continuum model (PCM) incor-
porating chloroform as a model solvent for our compounds was
used in TD-DFT calculations. The same chloroform was also used as
the solvent for the experimental measurements of the UVevis
spectra.
3.4. Theoretical analysis
3.4.1. Computation details
The ground singlet-state geometry optimization of P1, P2m and
P3m monomers, dimers and trimers was performed by the DFT/
3.4.2. Results
The calculated infrared frequencies and intensities are in a
reasonable agreement with the observed IR spectra (Fig. 1). The
triple C^C bond stretching vibrations are obtained as very weak
bands around 2212 cmꢁ1 and 2214 cmꢁ1 for all the studied oligo-
mers of P2 and P3, respectively. Even for dimers these bands
include a fine structure, which is not resolved in the observed
spectra (Fig. 1). (The calculated splitting is only 0.13 cmꢁ1 in the P2
dimer.) In contrast to observation these bands are predicted to be
more intense. A more complicated group of the close-lying IR
transitions produces a new peak in the P2m compounds near
2229e2255 cmꢁ1 which are assigned to C^N stretching vibrations
Fig. 3. TGA curves of polymers.

M. Grigoras et al. / Dyes and Pigments 113 (2015) 227e238
233
Fig. 4. Absorption spectra in solution (CHCl3) (A) and solid state (B) and emission spectra (C) in solution (CHCl3) of polymers P1, P2, P2m, P3 and P3m.
of symmetric and asymmetric types. This fine structure is slightly
resolved in the IR spectrum (Fig. 1) and explains the higher IR ab-
sorption intensity of the tetracyanobutadiene groups. All four
calculated C^N modes are split in such a way that they produce
three close-lying bands (separated by 13 cmꢁ1) and the central one
is the most intense. The central band consists of two lines of
different intensity split by only 2.4 cmꢁ1. All these fine features are
clearly seen in the IR spectrum of P2m (Fig. 1).
angle of 39ꢀ, nevertheless the photoactive molecular orbitals (MO)
are mainly delocalized in all oligomers (Fig. 6).
Based on the triphenylamine spectrum as a reference (Fig. 6a,
Table 2), absorption maxima located at around 300 nm are assigned
to
the peaks located in the range 390e410 nm can be assigned to the
* transition of the conjugated backbone (Fig. 6b, c). The ab-
pep* electronic transition from the triphenylamine unit, while
pep
sorption maxima for P1 appear at 409 nm and 313 nm (with a
shoulder at 357 nm). All these features are well reproduced in the
trimer model (Fig. 6c, Table 2). A very intense peak at 410 nm and
the shoulder are in a good agreement with the experimental
spectrum for the P1 polymer (Fig. 4, Table 1). The observed UV band
at 313 nm indicates lower intensity in agreement with calculation
(330 nm, f ¼ 0.26) as well as the far UV absorption (227 nm,
Table 2).
3.4.3. TD-DFT interpretation of the UVevisible absorption spectra
All absorption maxima in the range of 300e450 nm for com-
pounds P1, P2, P2m, P3 and P3m (Fig. 4) are assigned to
pep*
electronic transitions in conjugated phenyl rings, most of which are
non-planar to each other. As follows from geometry optimization
the rings in the triphenylamine unit are oriented by a dihedral
It is interesting to see evolution of excited states in the series of
oligomers of the P1 compound (Fig. 6, Table 2). With the increase of
the oligomer chain the first absorption band is shifted to the visible
region. This shift is very strong on going from monomer to dimer
(65 nm) and diminished drastically upon further transition to the
trimer (17 nm). For the tetramer we anticipate a negligibly small
additional shift. According to the calculated MO levels (Fig. 6c) the
orbital nature of the first band (HOMOeLUMO excitation) is the
same. This transition partly includes electron density transfer from
the pendant phenyl ring (which is not presented in LUMO) to the
backbone. From Fig. 6c one can see that the HOMOeLUMO exciton
is mostly localized on the trimer moiety. This conclusion is also
supported by our PM3 calculations of the longer oligomers
(Figs. S6eS8).
The growth of the polymer chain does not change the main
features of the HOMO and LUMO. Thus the nature of the first ab-
sorption band is the same (but the wavelength is shifted).
TD-DFT calculations show that in P2m the nature of the first
absorption band (536 nm, Table 2) is completely changed. This is
Fig. 5. Modification of UV spectrum of P3 by protonation with HCl.

234
M. Grigoras et al. / Dyes and Pigments 113 (2015) 227e238
Fig. 6. (a) P1 monomer molecule and its MOs. (b) DFT calculated MOs of P1 dimer. (c) DFT calculated MOs of P1 trimer.
the charge-transfer transition from the backbone to the tetracya-
nobutadiene groups (Fig. 7). The presence of the tetracyanobuta-
diene groups induces a new spectrum which is determined just by
this monomer feature. It will not depend much on the polymer
backbone, but mostly on the monomer characteristics. We have
calculated dimer and trimer models of P2m by the PM3 method
and this conclusion is supported to be correct.
Our TD-DFT results for the P2m monomer are in a good agree-
ment with the observed absorption spectrum in the film (Tables 1
and 2). Intensity of all absorption bands is much lower than in other
polymers. The second and third bands in P2m also demonstrate
charge-transfer nature (Fig. 7) and the total spectrum is very
different from the spectra of other species (Fig. 4).
We used two models for geometry optimization of the P3m
monomer; one in the form of the pyridyl-containing cation (Fig. 8a)
and the other e in the form of the salt (with the iodine atom coor-
dination at the nitrogen site). The former model provides quite
reasonable agreement withthe experimentalspectraupon the chain
prolongation, but the salt structure failed completely. Since we have
no any agreement for P3m with experiment for the UVevisible
spectrum we conclude that the salt model is wrong. Three highest
occupied molecular orbitals represent the lone pairs at the iodine
anion and three charge-transfer transitions are predicted in the far
visible region (the difference for the first band wavelength makes up
80 nm). In order to reproduce the observed spectrum we need to
conclude that the species dissociates in the solvent.

M. Grigoras et al. / Dyes and Pigments 113 (2015) 227e238
235
Table 2
The PL spectra are analyzed by comparison of the structural
changes in the ground singlet state and in the first excited triplet
state optimized at the DFT level. The main structural changes upon
electronic excitation are determined by displacements in the
backbone. The CeCH]CHeC motive is changed mostly into the C]
CHeCH]C structure with the corresponding deformations in the
nearest phenyl rings. This is illustrated by the P1 monomer (Figs. S2
and S3) and dimer (Figs S4 and S5) bond lengths distortion upon
S0 / T1 excitation. The largest distortions occur in the link between
two monomer moieties of the dimer.
The maxima of emission in solution are shifted to longer
wavelengths and centered at 450e460 nm (Fig. 4). The shift of
about 50 nm can be explained by a strong deformation in the
backbone. The blue shifting of polymers P2 and P3 with respect to
P1 observed in UVeVis absorption spectra are also seen and
exaggerated in the PL spectra (Table 1). This can be attributed to
additional distortions in the triple bonds upon excitation.
We anticipate that the first excited singlet and triplet states are
very close in their structure since both represent almost pure
HOMOeLUMO excitation. We have predicted the phosphorescence
0e0 transition at 475 nm for P1 monomer by the UB3LYP geometry
optimization in CHCl3 solvent and interpolated this value to 537 nm
for polymer with account of PM3 results. (We have to remind that
in Table 2 the vertical excitations calculated with the BMK func-
tional are given.) The late method also predicts that the T1 state of
polymer is slightly more localized than the S1 state. A small dif-
ference between the S1 and T1 electronic structure is represented by
a slightly larger contribution (15%) of the HOMO-1 / LUMO-1
excitation to the wave function of the T1 state in comparison with
the contribution to the S1 state (13%). See the P1 trimer, for example
(Table 2, Fig. 6c, Fig. S6).
TD-DFT calculations of the vertical excitation spectra from the ground state for the
studied molecules.
Compound
State
l
, nm E, eV
f
Assignmenta
P1_monomer
T1
S1
S2
S3
S4
454.0 2.73
e
HOMO / LUMO (95%)
328.2 3.78 0.9790 HOMO / LUMO (96%)
305.6 4.06 0.4349 HOMO / LUMO þ 1 (91%)
293.0 4.23 0.0939 HOMO / LUMO þ 2 (90%)
261.6 4.74 0.0381 HOMO / LUMO þ 4 (77%)
HOMO ꢁ 1 / LUMO þ 2 (5%)
S5
257.5 4.82 0.0330 HOMO / LUMO þ 3 (75%)
HOMO / LUMO þ 5 (8%)
P1_dimer
T1
S1
S2
561.0 2.21
e
HOMO / LUMO (95%)
393.4 3.15 2.1326 HOMO / LUMO (92%)
329.5 3.76 0.0019 HOMO ꢁ 1 / LUMO (72%)
HOMO / LUMO þ 1 (17%)
S3
S4
S5
312.4 3.97 0.9795 HOMO / LUMO þ 2 (61%)
HOMO ꢁ 1 / LUMO þ 1 (26%)
311.0 3.99 0.0413 HOMO / LUMO þ 1 (45%)
HOMO ꢁ 1 / LUMO þ 2 (24%)
296.4 4.18 0.0615 HOMO / LUMO þ 3 (65%)
HOMO ꢁ 1 / LUMO þ 4 (14%)
HOMO ꢁ 1 / LUMO þ 3 (10%)
P1_trimer
T1
S1
571.9 2.17
410.6 3.02 3.1258 HOMO / LUMO (80%)
e
HOMO / LUMO (82%)
HOMO ꢁ 1 / LUMO þ 1 (13%)
S2
S3
S4
374.7 3.31 0.4940 HOMO / LUMO þ 1 (57%)
HOMO ꢁ 1 / LUMO (35%)
330.2 3.76 0.2599 HOMO ꢁ 2 / LUMO (45%)
HOMO ꢁ 1 / LUMO þ 1 (33%)
327.1 3.79 0.1358 HOMO ꢁ 1 / LUMO (37%)
HOMO ꢁ 2 / LUMO þ 1 (25%)
HOMO / LUMO þ 1 (25%)
S5
312.9 3.96 0.7347 HOMO ꢁ 1 / LUMO þ 2 (37%)
HOMO / LUMO þ 3 (34%)
P2m
T1
S1
S2
S3
738.1 1.68
e
HOMO / LUMO (85%)
536.5 2.31 0.4633 HOMO / LUMO (95%)
418.2 2.96 0.5733 HOMO / LUMO þ 1 (93%)
352.1 3.52 0.1554 HOMO ꢁ 2 / LUMO (84%)
HOMO ꢁ 3 / LUMO (6%)
We can conclude that LUMO is more localized than HOMO in all
studied oligomers. Similar result is seen in other conjugated poly-
mers [29]. This leads to localization of the exciton in polymers.
S4
S5
346.8 3.58 0.0592 HOMO ꢁ 1 / LUMO (97%)
331.5 3.74 0.1957 HOMO ꢁ 3 / LUMO (88%)
P3m_monomer T1
482.6 2.57
e
HOMO / LUMO (89%)
3.5. Electrochemical properties
S1
S2
S3
S4
368.2 3.37 1.3322 HOMO / LUMO (90%)
325.0 3.81 0.9070 HOMO / LUMO þ 1 (95%)
295.1 4.20 0.0269 HOMO / LUMO þ 4 (90%)
275.8 4.50 0.0605 HOMO / LUMO þ 2 (93%)
HOMO ꢁ 1 / LUMO (25%)
The electrochemical properties of the parent and modified
polymers were studied in a three-electrode electrochemical cell in
deaerated acetonitrile solution containing Bu4NClO4 (0.1 M) as
electrolyte, at room temperature. The potentials were measured
against Ag/AgCl as reference electrode, using a platinum electrode
disk as the working electrode. The HOMO and LUMO energy levels
were estimated by cyclic voltammetry [42] in combination with the
optical absorption gap (Eg) and are shown in Table 3. Ferrocene was
used as internal reference and showed E1/2 at 0.40 V vs Ag/AgCl.
Using the known reference level for ferrocene, 4.8 eV below the
vacuum level, the HOMO level of the polymer was determined by
the equation [42]:
S5
268.6 4.62 0.3456 HOMO ꢁ 1 / LUMO (55%)
HOMO / LUMO þ 2 (16%)
P3m_dimer
T1
S1
S2
558.4 2.22
e
HOMO / LUMO (74%)
405.3 3.06 2.4193 HOMO / LUMO (78%)
367.5 3.37 1.2708 HOMO / LUMO þ 1 (55%)
HOMO ꢁ 1 / LUMO (30%)
S3
S4
S5
355.2 3.49 0.7344 HOMO / LUMO þ 2 (62%)
HOMO ꢁ 1 / LUMO þ 1 (23%)
331.7 3.74 0.1279 HOMO ꢁ 1 / LUMO (43%)
HOMO ꢁ 1 / LUMO þ 1 (33%)
299.7 4.14 0.0799 HOMO / LUMO þ 3 (24%)
HOMO / LUMO þ 1 (16%)
À
Á
EHOMO ¼ ꢁ 4:4 þ Eooxnset ðeVÞ:
a
The HOMO / LUMO (96%) in the last row means that this is the main contri-
bution to the first excitation band.
The LUMO energy levels were estimated using the optical band
gaps (Eg), ELUMO ¼ EHOMO þ Eogp (eV).
The first absorption band in the P3m dimer is not just a simple
HOMOeLUMO transition (Table 2), but still it includes a portion of
charge transfer from a backbone to the pendant substituents. This
explains the lower absorption intensity of P3m in comparison with
other related polymers of the relevant structure (Fig. 4).
A hypsochromic shift of the first absorption maximum and
broaden of absorption curve of the P2 (400 nm), P3 (405 nm), as
compared to P1 (409 nm) is observed in UVeVis spectra both in
solution and solid state. This behavior is attributed to higher
interchain interaction in P1 in the absence of longer pendant
substituents.
The electrochemical oxidation onsets of P2, P2m, P3 and P3m
are located at 0.89V, 0.94 V, 0.93 V and 1.03 V, respectively. The
HOMO level energies calculated are: ꢁ5.29 eV, ꢁ5.34 eV, ꢁ5.33 eV
and ꢁ5.43 eV, respectively. The HOMO levels of all polymers are
very close because polymers have the same main conjugated
backbone whereas the LUMO energy levels are between ꢁ2.81 eV
and ꢁ3.12 eV.
The modification of triple bond and the introduction of CN
groups lowered the LUMO level of P2 (ꢁ2.81 eV) at ꢁ3.02 eV
(P2m) being correlated with the introduction of dicyanovinyl
electron-withdrawing group in para position of triphenylamine

236
M. Grigoras et al. / Dyes and Pigments 113 (2015) 227e238
Fig. 7. DFT calculated MOs of P2m monomer.
moiety. For P3 the LUMO level (ꢁ2.80 eV) has decreased
at ꢁ3.12 eV (P3m), by chemical modification, the quaternized
pyridine group being spaced by triphenylamine group by ethy-
nylene linkage. Intramolecular charge-transfer interactions have
also as effect tuning of band gap in P2m and P3m. The DFT
results for the optimized geometry of the studied P1 oligomers
and for the P2m and P3m monomers are presented in Table 4.
HOMO for the P2m monomer is in a good agreement with
experiment (ꢁ5.34 eV) but P3m is
a bad model in our
simulation.
Fig. 8. (a) DFT calculated MOs of P3m monomer. (b) DFT calculated MOs of the P3m dimer.

M. Grigoras et al. / Dyes and Pigments 113 (2015) 227e238
237
Table 3
[4] Grimsdale AG, Chan KL, Martin RE, Jokisz PG, Holmes AB. Synthesis of light
emitting conjugated polymers for applications in electroluminescent devices.
Chem Rev 2009;109(3):897e1091.
[5] Mullen K, Scherf U. Organic light emitting devices: synthesis, properties and
applications. Weinheim: Wiley-VCH; 2006.
[6] Garnier F, Horowitz G, Peng XH, Fichou D. An all-organic soft thin-film tran-
sistors with very high carrier mobility. Adv Mater 1990;2(12):592e4.
[7] Peng XZ, Horowitz G, Fichou D, Garnier F. All-organic thin-film transistors
made of alpha-sexithienyl semiconducting and various polymeric insulating
layers. Appl Phys Lett 1990;57(5):2013e5.
[8] Zhan X, Zhu D. Conjugated polymers for high-efficiency organic photovoltaics.
Polym Chem 2010;1(4):409e19.
[9] Cheng YJ, Yang SH, Hsu CS. Synthesis of conjugated polymers for organic solar
cell applications. Chem Rev 2009;109(11):5868e923.
[10] Shi W, Zhen H, Luo Y, Qin H, Mi H, Awut T, et al. Pendant-decorated poly-
triphenylamine derivative: potential blue-emitting and hole-transport ma-
terial. Polym Bull 2010;64(1):53e65.
Electrochemical properties of polymers.
Egopt (eV)
E
b (V)
EHOMOc (eV)
ELUMOd (eV)
a
onset
ox
Polymer
P1
P2
P2m
P3
P3m
2.51
2.48
2.32
2.53
2.31
0.88
0.89
0.94
0.93
1.03
ꢁ5.28
ꢁ5.29
ꢁ5.34
ꢁ5.33
ꢁ5.43
ꢁ2.77
ꢁ2.81
ꢁ3.02
ꢁ2.80
ꢁ3.12
a
Optical band gap estimated from the onset wavelength of optical absorption in
the solid state film, Eogpt ¼ 1240/lonset
.
b
Onset potential of oxidation scan (vs. Ag/AgCl).
c
EHOMO ¼ ꢁ(4.8 þ Eooxnset) (eV).
d
ELUMO ¼ EHOMO þ Eogpt (eV).
[11] Shi W, Wang L, Zhen H, Zhu D, Awut T, Mi H, et al. Novel luminescent poly-
mers containing backbone triphenylamine groups and pendant quinoxaline
groups. Dyes Pigments 2009;83(1):102e10.
[12] Chen YC, Hsu CY, Ho CY, Tao YT, Lin JT. Synthesis and characterization of the
conjugated polymers tethered with dipolar side chains containing a benzo-
thiadiazole entity for bulk heterojunction solar cells. Org Electron 2013;14(9):
2290e8.
[13] Li Y, Zhou J, Wan X, Chen Y. Synthesis and properties of acceptor-donor-
acceptor molecules based on oligothiophenes with tunable and low band
gap. Tetrahedron 2009;65(27):5209e15.
[14] Stylianakis MM, Mikroyannidis JA, Dong Q, Pei J, Liu Z, Tian W. Synthesis,
photophysical and photovoltaic properties of star-shaped molecules with
triphenylamine as core and phenylethenylthiophene or dithienylethylene as
arms. Sol Energy Mater Sol Dear Mircea Cells 2009;93(11):1952e8.
[15] Zhang ZG, Yang Y, Zhang S, Min J, Zhang J, Zhang M, et al. Effect of acceptor
substituents on photophysical and photovoltaic properties of triphenylamine-
carbazole alternating copolymers. Synth Met 2011;161(13e14):1383e9.
[16] Vacareanu L, Grigoras M. Synthesis and electrochemical characterization of
new linear conjugated arylamine copolymers. High Perform Polym
2011;23(2):112e24.
Table 4
The DFT results for the optimized geometry of the studied P1 oligomers and for the
P2m and P3m monomers.
Compound
E(HOMO), eV
E(LUMO), eV
E gap
P1_monomer
P1_dimer
P1_trimer
P2m
P3m_monomer
P3m_dimer
ꢁ4.8276
ꢁ4.6469
ꢁ4.5852
ꢁ5.3781
ꢁ4.8981
ꢁ4.7536
ꢁ0.9573
ꢁ1.4547
ꢁ1.5500
ꢁ3.2648
ꢁ1.5813
ꢁ1.7122
3.8703
3.1922
3.0352
2.1133
3.3168
3.0414
HOMO for the P2m monomer is in a good agreement with experiment (ꢁ5.34 eV).
P3m is a bad model in our simulation.
4. Conclusion
[17] Ivan T, Vacareanu L, Grigoras M. Synthesis of poly(arylene vinylene)s con-
taining carbazole, triphenylamine, and phenothiazine, rings in the backbone
by cascade SuzukieHeck reactions. Int J Polym Mater 2013;62(5):270e6.
[18] Kivala M, Boudon C, Gisselbrecht JP, Seiler P, Gross M, Diederich F. Charge-
transfer chromophores by cycloaddition-retroelectrocyclization: multiva-
lent systems and cascade reactions. Angew Chem Int Ed 2007;46(33):
6357e60.
[19] Kato S, Kivala M, Schweizer WB, Boudon C, Gisselbrecht JP, Diederich F. Origin
of intense intramolecular charge-transfer interactions in nonplanar pushepull
chromophores. Chem Eur J 2009;15(35):8687e91.
[20] Shi W, Ma F, Hui Y, Mi H, Tian Y, Lei Y, et al. TCNE-decorated triphenylamine-
based conjugated polymer: click synthesis and efficient turn-on fluorescent
probing for Hg2þ. Dyes Pigments 2014;104(1):1e7.
[21] Li Y, Tsuboi K, Michinobu M. Double click synthesis and second-order non-
linearities of polystyrenes bearing donoreacceptor chromophores. Macro-
molecules 2010;43(12):5277e86.
In summary, a series of arylenevinylene polymers containing
4,4'-triphenylamine group substituted in 400 position with phenyl-
ethynyl- and 3-pyridylethynyl substituents, spaced by vinylene
linkage, were synthesized by Stille polycondensation. The absorp-
tion and emission spectra, HOMO and LUMO energy levels and gaps
energies can be fine-tuned by chemical modification of polymers
using addition of tetracyanoethylene at electron-rich triple bond or
by protonation and alkylation of pyridine ring. In both cases an
intramolecular charge-transfer complex is formed between
acceptor pendant groups and triphenylamine from conjugated
chain. The variation in the absorption and emission wavelengths
and redox properties of polymers after chemical modification
shows the possibility of fine-tuning optoelectronic properties of
arylenevinylene copolymers.
[22] Tang X, Liu W, Wu J, Lee CS, You J, Wang P. Synthesis, crystal structures, and
photophysical properties of triphenylamine-based multicyano derivatives.
J Org Chem 2010;75(5):7273e8.
[23] Lelliege A, Blanchard P, Rousseau T, Roncali J. Triphenylamine/tetracyanobu-
tadiene-based D-A-D
p-conjugated systems as molecular donors for organic
solar cells. Org Lett 2011;13(12):3098e101.
Acknowledgements
[24] Shoji T, Higashi J, Ito S, Okujima T, Yasunami M, Morita N. Synthesis of redox-
active, intramolecular charge-transfer chromophores by the [2þ2] cycload-
dition of ethynylated 2H-cyclohepta [b] furan-2-ones with tetracyano-
ethylene. Chemistry Eur J 2011;17(18):5116e29.
[25] Washino Y, Michinobu T. Application of alkyne-TCNQ addition reaction to
polymerization. Macromol Rapid Commununications 2011;32(8):644e8.
[26] Huang W, Chen H. Synthesis and characterization of a low-bandgap poly(-
arylene ethynylene) having donoreacceptor type chromophores in the side
chain. Macromolecules 2013;46(5):2032e7.
[27] Sarigiannis Y, Spiliopoulos IK. Optical and electrochemical properties of pol-
yfluorenes with pyridineetriphenylamine bipolar unit. Polym Int 2013;62(2):
196e203.
[28] Li X, Minaev B, Agren H, Tian H. Theoretical study of phosphorescence of
iridium complexes with fluorine-substituted phenylpyridine ligands. Eur J
Inorg Chem 2011;16:2517e24.
Authors (MG, AMC, TI and LV) thank to the Romanian National
Authority for Scientific Research (UEFISCDI) for financial support
(grant PN-II-ID-PCE-2011-3-0274, Contract 148/2011).
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.dyepig.2014.08.016.
[29] Justino LLG, Ramos ML, Abreu PE, Charas A, Morgado J, Scherf U, et al.
Structural and electronic properties of poly(9,9-dialkylfluorene)-based alter-
nating copolymers in solution: an NMR spectroscopy and density functional
theory study. J Phys Chem C 2013;117(35):17969e82.
[30] Sonntag M, Kreger K, Hanft D, Strohriegl P, Setayesh S, Leeuw D. Novel star-
shaped triphenylamine-based molecular glasses and their use in OFETs.
Chem Mater 2005;17(11):3031e9.
References
[1] Minaev B, Baryshnikov G, Agren H. Principles of phosphorescent organic light
emitting devices. Phys Chem Chem Phys 2014;16(5):1719e58.
[2] Burroughes JH, Bradley DDC, Brown AR, Marks RN, Mackay K, Friend RH, et al.
Light-emitting diodes based on conjugated polymers. Nature 1990;347:
539e41.
[31] Baker III TN, Doherty WP, Kelley WS, Newmeyer W, Rogers JE, Spalding RE,
et al. Electrophilic substitution reactions of triphenylamine.
1965;30(11):3714e8.
J Org Chem
[3] Akcelrud L. Electroluminescent polymers. Prog Polym Sci 2008;28(6):
875e962.

238
M. Grigoras et al. / Dyes and Pigments 113 (2015) 227e238
[32] Liang Y, Feng D, Wu Y, Tsai ST, Li G, Ray C, et al. Highly efficient solar cell
polymers developed via fine-tuning of structural and electronic properties.
J Am Chem Soc 2009;131(22):7792e9.
[33] Hou JH, Hou LJ, He C, Yang CH, Li YF. Synthesis and absorption spectra of
poly(3-(phenylenevinyl)thiophene)s with conjugated side chains. Macro-
molecules 2006;39(2):594e603.
[37] Lambert C, Gaschler W, Schmalzlin E, Meerholz K, Brauchle C. Sub-
chromophore interactions in tricyanovinyl-substituted triarylamines
combined experimental and computational study. J Chem Soc Perkin Trans
1999;2:577e87.
[38] Becke AD. Density-functional exchange-energy approximation with correct
asymptotic behavior. Phys Rev A 1988;38(6):3098e100.
e
a
[34] Kivala M, Diederich F. Acetylene-derived strong organic acceptors for planar
and nonplanar push-pull chromophores. Accounts Chem Res 2009;42(2):
235e48.
[35] Stefko M, Tzirakis MD, Breiten B, Ebert MO, Dumele O, Schweizer WB, et al.
DonoreAcceptor (DeA)-substituted polyyne chromophores: modulation of
their optoelectronic properties by varying the length of the acetylene spacer.
Chem Eur J 2013;19(38):12693e704.
[36] McKusick BC, Heckert RE, Cairns TL, Coffman DD, Mower HF.
Cyanocarbon chemistry. VI Tricyanovinylamines. J Am Chem Soc 1958;80(11):
2806e15.
[39] Lee C, Yang W, Parr RG. Development of the colle-salvetti correlation-energy
formula into a functional of the electron density. Phys Rev B 1988;37(2):785e9.
[40] Frisch MJ, Trucks GW, Schlegel HB, Scuseria GE, Robb MA, Cheeseman JR, et al.
Gaussian 09, Revision A.02. Wallingford CT: Gaussian Inc.; 2009.
[41] Boese AD, Martin JML. Development of density functionals for thermochem-
ical kinetics. J Chem Phys 2004;121(8):3405e16.
[42] Bredas JL, Silbey R, Boudreaux DS, Chance RR. Chain-length dependence of
electronic and electrochemical properties of conjugated systems: poly-
acetylene, polyphenylene, polythiophene, and polypyrrole. J Am Chem Soc
1983;105(22):6555e9.