Direct synthesis of polyaromatic chains of tribenzopentaphene copolymers through cyclodehydrogenation of their poly-tetraphenylbenzene precursors

Article abstract of DOI:10.1002/pola.28739

Three polyaromatic-based polymers are reported to contain co-monomers of trapezoidal tribenzopentaphene (TBP) polycyclic aromatic hydrocarbons. The synthetic strategy consists of initially making highly soluble tetraphenylbenzene copolymers 4a–c, followed

Full text of DOI:10.1002/pola.28739

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Direct Synthesis of Polyaromatic Chains of Tribenzopentaphene
Copolymers through Cyclodehydrogenation of Their Poly-
tetraphenylbenzene Precursors
1
Bassam Alameddine ,1 Rajamohanan Sobhana Anju ,1 Suchetha Shetty
Noorullah Baig ,1 Saleh Al-Mousawi,2 Fakhreia Al-Sagheer2
,
1Department of Mathematics and Natural Sciences, Gulf University for Science and Technology, Kuwait
2Department of Chemistry, University of Kuwait, Kuwait
Correspondence to: B. Alameddine (E-mail: alameddine.b@gust.edu.kw)
Received 6 June 2017; accepted 18 July 2017; published online 00 Month 2017
DOI: 10.1002/pola.28739
ABSTRACT: Three polyaromatic-based polymers are reported to
contain co-monomers of trapezoidal tribenzopentaphene (TBP)
polycyclic aromatic hydrocarbons. The synthetic strategy con-
sists of initially making highly soluble tetraphenylbenzene
copolymers 4a–c, followed by a cyclodehydrogenation/aromati-
zation reaction to obtain target polymers 5a–c. The polymers
were characterized by gel permeation chromatography, FT-IR,
UV-vis, emission, 1H-, and 13C-nuclear magnetic resonance
spectroscopy. The target polymers 5a–c reveal emission spec-
tra in the range of 430–480 nm; thus, qualifying them to act as
blue emitters. Investigation of the polymers optical properties
and their correlation with density functional theory calculations
suggest a distorted TBP core from planarity caused by the
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introduction of a dodecyl group at its wide edge. 2017 Wiley
Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 00,
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KEYWORDS: conjugated polymers; gel permeation chromatography
(GPC); luminescence; FT-IR; polyaromatics
As part of our research on PAHs, we have recently reported
the synthesis of several trapezoidal-like tribenzo[fg,ij,rst]pen-
taphene (TBP) derivatives bearing various aromatic side
groups either at their wide or narrow bases.58 Using a simi-
lar approach, we reveal herein the facile synthesis of long
polymer chains containing tetraphenylbenzene comonomer
units through an optimized Suzuki–Miyaura palladium-
catalyzed cross-coupling reaction condition followed by the
aromatic cyclodehydrogenation of the resulting polymers
into TBP-containing polymers.
INTRODUCTION The design of new large polycyclic aromatic
hydrocarbons (PAHs) has become a major interest because
of their remarkable contributions in numerous applications
that encompass energy storage,1–3 porous frameworks for
separation,4–8 sensors,9 lasers,10 spintronics,11 and optoelec-
tronics, among others, light emitting diodes, field-effect tran-
sistors, and photovoltaics,12–14. Prolific synthetic pathways
have been established during the first half of the 20th cen-
tury15–20 and which allowed for making PAHs with molecu-
lar structures that vary from symmetrical planar,12,21–24
contorted,25–32 to less symmetrical geometries.33–36 Recently,
extended PAHs have attracted further attention because they
offer a bottom-up approach to produce graphene ribbons,
which permits a better control over the target structures,
therefore extending the scope of potential applications.37–44
It is noteworthy that opto- and electroactive polymers
mainly consist of fused heterocyclic building blocks and their
derivatives,45–52 whereas less attention has been drawn to
poly-PAHs whose lack of effective synthesis and scarce
solubility represent the utmost challenges. Recently, more
interest has been drawn in making polyphenylenes and
triphenylene-based polymers.53–57
EXPERIMENTAL
General
All chemicals were used without further purification as pur-
chased from Aldrich, Merck, Alfa-Aesar, and Fluorochem
unless otherwise notified. All the reactions were carried out
under a protective atmosphere using dry argon. The solvents,
namely dichloromethane, chloroform, ether, hexane, metha-
nol, and tetrahydrofuran (THF) were dried, deoxygenated,
and bubbled with argon gas for 30 min. Thin layer chroma-
tography was performed on aluminum sheets coated with
silica gel 60 F254 and revealed by a UV lamp. UV-Vis spectra
Additional Supporting Information may be found in the online version of this article.
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were recorded on a VWR UV1600PC spectrophotometer.
Photoluminescence spectra were recorded on an Agilent
G9800 Cary Eclipse Fluorescence spectrophotometer. Nuclear
magnetic resonance (NMR) spectra were recorded on Bruker
BioSpin GmbH 600 MHz (1H: 600 MHz, 13C: 150 MHz) spec-
trometers using CDCl3 or CD2Cl2 as solvent and the chemical
shifts (d) are given in ppm, coupling constants (J) in Hz,
and are all referred to tetramethylsilane TMS. Relative
weight-average (Mw), number-average (Mn) molecular
ppm): d 152.31, 142.21, 141.79, 141.20, 141.01, 140.66,
139.99, 138.14, 132.26, 131.91, 131.58, 130.97, 130.73,
127.47, 127.12, 126.70, 126.32, 125.86, 121.78, 120.52,
56.12, 41.07, 34.37, 32.52, 32.09, 32.00, 30.26, 30.23, 30.15,
30.07, 29.95, 29.89, 24.43, 23.28, 23.17, 14.47, 14.34; GPC
(THF); Mw (g mol21): 60,503 Mn (g mol21): 28,411, D: 2.13.
-
FTIR (KBr, cm21): 4047, 3055, 2925, 1465, 818. UV-vis:
(THF, 1025 M), kmax [nm] 5 348, 305.
Synthesis of Polymer 4b
-
weights, and their dispersity (D 5 Mw/Mn) of the polymers
4b was prepared according to “method A’’ using 2a (100 mg,
0.14 mmol), 2,20-bithiophene-5,50-diboronic acid bis(pinacol)
ester (59 mg, 0.14 mmol), palladium (II) acetate (0.95 mg,
0.4 3 1022 mmol), Sphos (3.4 mg, 0.8 3 1022 mmol), and
K3PO4 (60 mg, 0.28 mmol) in 3.0 mL of degassed 5:1 mix-
ture of THF and water. The reaction followed by work up
yielded the desired polymer as a yellow solid (90 mg, 90%).
were recorded on Agilent gel permeation chromatography
(GPC)/SEC equipped with two columns (PL mixed-C), and
calibrated against 12 monodisperse polystyrene standards
with THF used as eluent at a flow rate of 1.0 mL min21
.
FTIR spectra were recorded on FT/IR-6300 typeA instrument
using a KBr matrix.
Synthesis
Preparation of 2a
1H NMR (600 MHz, CD2Cl2, ppm): d 7.44–7.41 (br., 4H, ArH),
7.30–7.28 (d, J 5 12Hz, 1H, ArH), 7.22–7.15 (m, 5H, ArH),
7.10–7.08 (d, J 5 12Hz, 2H, ArH), 6.95–6.83 (m, 11H, ArH),
2.53 (br., 2H, CH2), 1.22 (m, 20H, CH2), 0.85 (t, 6Hz, 3H, CH3);
13C NMR (150 MHz, CD2Cl2, ppm): d 142.74, 141.55, 140.56,
140.05, 137.49, 136.45, 132.24, 131.60, 131.25, 130.48,
129.97, 126.91, 126.57, 125.57, 125.32, 124.53, 124.21,
123.74, 33.70, 31.95, 31.32, 29.69, 29.68, 29.64, 29.49, 29.47,
29.38, 29.21, 22.70, 13.89; GPC (THF); Mw (g mol21): 38,220,
1a (650 mg, 1.12 mmol, 1 eq.) and tetradec-1-yne (261 mg,
1.35 mmol, 2.4 eq.) in dry xylene (15 mL) were refluxed
under microwave at 210 8C for 4 h in the presence of nitro-
gen. After cooling to room temperature, the solvent was
evaporated and the crude was concentrated, precipitated
using methanol, followed by Millipore filtration affording the
desired product as a white solid (790 mg, 99%).
1H NMR (600 MHz, CD2Cl2, ppm): d 7.34 (s, 1H, ArH), 7.30–
7.28 (m, 4H, ArH), 7.03–7.00 (m, 2H, ArH), 6.94–6.93 (m, 5H,
ArH), 6.89–6.87 (m, 3H, ArH), 6.83–6.82 (m, 2H, ArH), 6.78–
6.77 (m, 2H, ArH), 2.46–2.44 (t, J 5 6 Hz, 2H, CH2), 1.51–1.47
(m, 2H, CH2), 1.26–1.19 (m, 18H, CH2), 0.89–0.87 (t, J 5 6Hz,
3H, CH3). 13C NMR (150 MHz, CD2Cl2, ppm): d 141.91,
141.55, 140.80, 140.25, 139.96, 139.77, 137.91, 132.63,
131.99, 131.55, 131.02, 130.24, 127.36, 126.06, 120.70,
34.06, 32.35, 31.68, 30.08, 30.04, 29.88, 29.87, 29.77, 29.63,
23.11, 14.30. EI-MS: m/z (% int): 708.40 (Mꢀ1, 100%), (m/z
calculated for C42H44Br2 708.2).
Mn (g mol21): 17,887, D: 2.14.
-
FTIR (KBr, cm21): 4052, 3060, 2920, 1441, 789. UV-vis:
(THF, 1025 M), kmax [nm] 5 400.
Synthesis of Polymer 4c
2b (100 mg, 0.11 mmol), 9,9-dihexylfluorene-2,7-diboronic
acid (48 mg, 0.11 mmol), palladium (II) acetate (0.76 mg,
0.34 3 1022 mmol), Sphos (2.8 mg, 0.6 3 1022 mmol), and
K3PO4 (48 mg, 0.23 mmol) in 3.0 mL of degassed 5:1 mix-
ture of THF and water under argon was refluxed for 4 days.
The solvent was evaporated and the resulting mixture
extracted with chloroform (50 mL 3 3) from a saturated
aqueous solution of NaHCO3 (75 mL 3 1). The organic phase
was washed with H2O (100 mL 3 3), concentrated, and
precipitated using methanol followed by Millipore filtration.
The precipitate was washed several times with hexane and
diethyl ether to afford polymer as an off-white solid
(112 mg, 94%).
Synthesis of Polymer 4a (Method A)
A Schlenk tube was charged with 2a (100 mg, 0.14 mmol),
9,9-dihexylfluorene-2,7-diboronic acid (60 mg, 0.14 mmol),
palladium (II) acetate (0.95 mg, 0.4 3 1022 mmol), Sphos
(3.4 mg, 0.8 3 1022 mmol), and K3PO4 (60 mg, 0.28 mmol)
in 3.0 mL of degassed 5:1 mixture of THF and water. The
reaction was refluxed for 4 days under argon. The solvent
was evaporated and the resulting mixture extracted with
dichloromethane (50 mL 3 3) from a saturated aqueous
solution of NaHCO3 (75 mL 3 1). The organic phase was
washed with H2O (100 mL 3 3), concentrated, precipitated
using methanol followed by Millipore filtration. The precipi-
tate was washed several times with hexane and diethyl ether
to afford polymer as an off-white solid (100 mg, 83%).
1H NMR (600 MHz, CDCl3, ppm): d 7.58–7.50 (m, 8H, ArH),
7.29–7.24 (m, 10H, ArH), 6.76 (br., 6H, ArH), 2.44 (br., 4H,
CH2), 1.47 (br., 8H, CH2), 1.25–1.03 (m, 52H, CH2), 0.88–0.86
(t, J 5 6Hz, 6H, CH3), 0.76–0.74 (t, J 5 6Hz, 6H, CH3); 13C
NMR (150 MHz, CDCl3, ppm): d 152.31, 141.36, 141.28,
141.09, 132.16, 132.01, 131.83, 131.15, 130.97, 129.88,
129.57, 127.67, 126.66, 126.31, 121.77, 120.86, 120.52,
55.89, 41.07, 35.90, 35.86, 32.54, 32.08, 31.87, 31.81, 31.16,
30.32, 30.27, 30.09, 29.97, 29.47, 24.41, 23.28, 23.16, 14.47,
14.33. GPC (THF); Mw (g mol21): 95,711, Mn (g mol21):
1H NMR (600 MHz, CD2Cl2, ppm): d 7.80 (br., 2H, ArH),
7.62–7.51 (m., 9H, ArH), 7.31–7.22 (d, J 5 54 Hz, 4H, ArH),
7.00–6.94 (br., 10H, ArH), 2.59 (br., 2H, CH2), 2.09 (br., 2H,
CH2), 1.63–1.56 (br., 4H, CH2) 1.26–1.08 (m, 34H, CH2), 0.90
(br, 3H, CH3), 0.79 (br, 6H, CH3); 13C NMR (150 MHz, CD2Cl2,
40,141, D: 2.38. FTIR (KBr, cm21): 4049, 3022, 2925, 1457,
-
815. UV-vis: (THF, 1025 M), kmax [nm] 5 354.
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SCHEME 1 Synthesis of tetraphenyl benzene derivatives 2a–b.
Synthesis of 5a (Method B)
desired compound as a dark brown powder. FTIR (KBr,
cm21): 3054, 2919, 1457, 804. UV-vis: (THF, 1025 M), kmax
[nm] 5332, 368.
To a solution of 4a (80 mg, 0.09 mmol) in dichloromethane
(15 mL), purged with argon for 30 min, was added a
degassed solution of FeCl3 (443 mg, 2.73 mmol, 30 eq) in
MeNO2 (4 mL) over 10 min. The reaction medium was
refluxed for 6 h, where the color turned from slight yellow
to green, and finally to brown. After evaporation of DCM,
150 mL of a 1-M HCl solution were added to the residue
and the resulting green suspension was sonicated for 30 min
and filtered using Millipore. The precipitate was washed sev-
eral times with water and pentane. The precipitate was soni-
cated for 15 min in diethyl ether (5 mL), filtered, and dried
yielding 70 mg (88%) of the desired compound as a dark
brown powder.
RESULTS AND DISCUSSION
The dibrominated tetraphenylbenzene monomers 2a–b were
synthesized using a two-step reaction (Scheme 1). First, a dou-
ble Knoevenagel condensation reaction was carried out to
make 1a19 and 1b.36 The second step consisted of a [4 1 2]
Diels–Alder cycloaddition reaction where the microwave-
assisted heating of 1a with tetradec-1-yne in xylene afforded
2a in quantitative yield, whereas the reaction of 1b with
phenylvinyl sulfoxide in refluxing toluene yielded 2b in good
yield.36
FTIR (KBr, cm21): 3055, 2925, 1458, 816. UV-vis: (THF, 1025
M), kmax [nm] 5411, 337.
Polymerization of co-monomers 2a and 9,9-dihexylfluorene-
2,7-diboronic acid (3a) was carried out using the Suzuki–
Miyaura palladium catalyzed cross-coupling reaction59 with
Sphos as ligand.60 These conditions have been further opti-
mized to doubly substitute TBP and triphenylene-based
derivatives with various aromatic side groups more effi-
ciently.58 Nevertheless, the hitherto mentioned reaction
conditions yielded short polymer chains of 4a as it can be
noticed form GPC that reveal a number average molar mass
Mn ꢁ 5.5 KDa even after a prolonged 4 day reaction time
(Table 1, entry 1). Similarly, doubling the load of Pd2(dba)3
catalyst to 10 mol % and increasing the amount of solvent,
to ensure a better solubility of the reactants and their inter-
mediates, did not improve the polymerization reaction even
when the reaction time was extended to 6 days (Table 1,
entry 2). Similarly, replacing toluene with the higher boiling
Synthesis of 5b
5b was prepared according to “method B’’ using 4b (45 mg,
0.06 mmol), degassed solution of FeCl3 (306 mg, 1.89 mmol,
30 eq) in MeNO2 (3 mL) in dichloromethane (10 mL). The
reaction followed by work up afforded 40 mg (95%) of the
desired compound as a dark brown powder. FTIR (KBr,
cm21): 3055, 2909, 1431, 778. UV-vis: (THF, 1025 M), kmax
[nm] 5 304, 427, 453.
Synthesis of 5c
5c was prepared according to “method B’’ using 4c (45 mg,
0.04 mmol), degassed solution of FeCl3 (208 mg, 1.29 mmol,
30 eq) in MeNO2 (2 mL) in dichloromethane (7 mL). The
reaction followed by work up yielded 38 mg (86%) of the
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TABLE 1 Optimization of the Suzuki–Miyaura Polymerization Reactions Conditions
-
Entry
1b
Product
Catalyst (mol %)
Solvent
CM [M]a 3 1022
Mn (g/mol)
Mw (g/mol)
D
4a
Pd2(dba)3
(5)
Tol:BuOH
(1:1)
3
5400
9000
1.7
1.2
1.5
2.3
2.0
2.1
2.1
2.4
2b
3b
4c
5c
6d
7d
8d
4a
4a
4a
4a
4a
4b
4c
Pd2(dba)3
(10)
Tol: BuOH
(1:1)
1.8
1.5
2.3
4.7
5.6
5.6
5.6
4900
5900
Pd2(dba)3
(1.3)
Xylene: BuOH
(1:1)
3400
5000
Pd(pph3)4
(2)
Tol:Water
(1:1)
11,200
16,000
28,400
17,900
40,100
26,400
32,000
60,500
38,200
95,700
Pd(pph3)4
(3)
Tol:Water
(1:1)
Pd(OAc)2
(3)
THF:Water
(5:1)
Pd(OAc)2
(3)
THF:Water
(5:1)
Pd(OAc)2
(3)
THF:Water
(5:1)
a
c
With: molar concentration 2a–b in the reaction medium.
Aqueous 2N K2CO3, Aliquat
b
d
K3PO4 (1.2 eq.), S-phos (10 mol %).
K3PO4 (2 eq.), S-phos (3 mol %).
point solvent xylene yielded shorter polymer chains of 4a
with Mn ꢁ 3.4 KDa after 4 days of reaction (Table 1, entry
3). It is worthwhile to mention that starting materials and
short oligomers were detected in all the aforementioned
polymerization reactions attempts.
palladium(0), and using a 2-N aqueous solution of K2CO3,
instead of butanol and K3PO4 (Table 1, entry 4). Increasing
the molar concentration of the reactants in toluene by a fac-
tor of two has afforded longer polymer chains of 4a with Mn
ꢁ 16 KDa (Table 1, entry 5). Interestingly, polymer 4a with
a record molar mass, Mn ꢁ 28.4 KDa, was produced when
replacing Pd(0) by the more stable palladium (II) acetate
and toluene by the better solvent THF in presence of an
However, 4a was obtained in pure form with Mn ꢁ 11.2 KDa
when replacing Pd2(dba)3 by tetrakis(triphenylphosphine)
SCHEME 2 Synthetic route for 4a–c.
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ꢁ 17.9 KDa and 40.1 KDa, respectively. It is worth noting
that polymers 4a–c (Scheme 2) were isolated in very good
yields and their high purity was confirmed by GPC analysis,
1H, and 13C NMR spectroscopy (Figs. 1 and 2; Supporting
Information).
The tetraphenylbenzene moieties in polymers 4a–c were
fully aromatized into their respective TBP derivatives 5a–c
through the Scholl cyclodehydrogenation reaction using
iron(III) chloride in nitromethane61 (Scheme 3). Because of
the high molar masses of precursors 4a–c, the resulting
target polymers 5a–c are scarcely soluble in common
organic solvents, which prevented their characterization by
NMR and GPC. For this reason, cyclodehydrogenation of 4a
with shorter polymer chains (Mn ꢁ 16 KDa, Table 1, entry 5)
was carried out affording target polymer 5a. GPC analysis of
this latter depicts a molar mass Mn ꢁ 15.2 KDa, which
clearly lies within the expected range (Supporting Informa-
tion Fig. S13). It is noteworthy that the larger dispersity of
FIGURE 1 Gel permeation chromatogram of 4a.
aqueous solution of the mild base K3PO4 (Table 1, entry 6).
The same reaction conditions were used in the polymeriza-
tion of 2a with 2,20-bithiophene diboronic ester (3b) and 2b
with 9,9-dihexylfluorene-2,7-diboronic acid (3a). These two
reactions yielded polymers 4b and 4c with molar masses Mn
-
-
5a (D 5 2.8) compared with that of its precursor (D 5 2.0)
could be well explained by the stiffer polymer chains of the
former leading to a pronounced aggregation that affects the
FIGURE 2 1H NMR spectrum of 4a. [Color figure can be viewed at wileyonlinelibrary.com]
SCHEME 3 Cyclodehydrogenation reaction of polymers 4a–c.
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FIGURE 3 FT-IR of polymer 4a (blue) and polymer 5a (red). [Color figure can be viewed at wileyonlinelibrary.com]
FIGURE 4 (A) Absorbance spectra of 4a and 5a. (B) Emission spectra of 4a and 5a. (C) Absorbance spectra of 4b and 5b. (D) Emis-
sion spectra of 4b and 5b. (E) Absorbance spectra of 4c and 5c. (F) Emission spectra of 4c and 5c. All the samples were measured
using THF as solvent. [Color figure can be viewed at wileyonlinelibrary.com]
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analysis of its weight average molar mass (Mw). The struc-
tures of 5a–c were elucidated by comparing their FT-IR, UV-
visible, and emission spectra with those of their respective
precursors 4a–c.
optical properties of poly-(p-phenylenes).55 This is further
supported by the DFT calculations revealing a pseudo-planar
phenylene-bithiophene chains (Supporting Information Table
S1). Nevertheless, the long-range conjugation in 4b is dis-
rupted when the tetraphenyl benzene groups are cyclodehy-
drogenated into their more rigid TBP aromatic cores yielding
polymer 5c, and consequently, causing the observed blue shift.
The fluorescence quantum yields of 5a, 5b, and 5c in THF are
0.28, 0.23, and 0.45, respectively (absorption maxima were
used as the excitation wavelengths). It is noteworthy that the
emission spectra of polymers 5a–c further prove the efficient
aromatization of the tetraphenyl benzene precursors into their
TBP targets because all the final polymers portray emission
with peaks contours comparable with that of the doubly
substituted TBP cores.36,58
Figure 3 depicts the FT-IR absorption spectra of polymers 4a
and 5a. It could be easily noticed that the broad peak at
4047 cm21 in 4a, and which is characteristic of the carbon–
carbon free rotation in biphenyl groups56,62 has completely
disappeared in the target polymer 5a, therefore, indicating the
full aromatization of the tetraphenyl benzene groups into the
rigid TBP core. Similarly, polymer 4a reveals IR absorption sig-
nals at 3055 cm21, typical for aromatic CAH stretching vibra-
tions.41 These latter peaks become starkly attenuated in the IR
absorption spectrum of 5a indicating a decrease in the number
of CAH bonds, which is caused by the cyclodehydrogenation
reaction.
CONCLUSIONS
A versatile synthesis of copolymers containing the trapezoi-
dal tribenzopentaphene (TBP) PAH is presented. The syn-
thetic strategy consists of making soluble copolymers of
tetraphenylbenzene units through an improved Suzuki–
Miyaura cross-coupling reaction that affords polymers with
high molar masses. These latter precursors undergo a subse-
quent cyclodehydrogenation reaction to aromatize their tet-
raphenylbenzene units into the target TBP copolymers. The
optical properties of the target polymers fully corroborate
the DFT calculations suggesting a distorted TBP core from
planarity, which is induced by the presence of an alkyl group
at its wide edge (R2 position). The target polymers reveal
emission spectra in the range of 430–480 nm, thus, qualify-
ing them to act as blue emitters. The tapered structure of
TBP, which permits its functionalization at various sites quite
easily, and the straightforward synthetic method described
herein facilitate the introduction of several functional groups
into to the polymer backbone, and consequently, enable the
synthesis a wide variety of TBP-based polymers for various
optoelectronic and sensing applications.
Moreover, the IR absorption spectrum of 5a clearly shows a
reduction in the intensity of the peaks that correspond to
C@C (ꢂ1460 cm21) and CAH (600–900 cm21) bending
vibrations63 when compared with those of the precursor 4a.
Analogous FT-IR spectral changes were also observed in pol-
ymers 5b–c when compared with their respective precursors
4b–c (Supporting Information Fig. S14 and S15).
UV-Vis absorption and emission spectra of the fluorene-
tetraphenyl benzene co-polymers 4a,c and their correspond-
ing TBP containing polymers 5a,c display similar features (Fig.
4). 4a,c shows strong absorption bands at 348 nm and
354 nm, respectively. When these polymers undergo cyclode-
hydrogenation reactions, their target products 5a,c, display
red-shifted maximum absorption bands at 411 nm and
368 nm, respectively. Similarly, the emission spectra of 4a,c
exhibit strong peaks at ꢂ400 nm which undergo a ꢂ30 nm
bathochromic shift after cyclodehydrogenation into their cor-
responding polymers (5a,c), thus, revealing emission peaks at
ꢂ430 nm. It is worthwhile to note that the doubly substituted
TBP (with R1, R2 5 H) small molecule with fluorene side
groups at the same positions portrays an emission maximum
at ꢂ410 nm.58 Thus, the ꢂ20 nm red-shift observed in poly-
mers 5a,c suggests a distortion of the central aromatic core
from planarity caused by the presence of the dodecyl group at
the TBP wide edge (i.e., R2). This is further supported by the
density functional theory (DFT) calculations with B3LYP at the
6–31G* level basis set showing a contorted geometry of TBP
optimized structure when R2 is substituted by an alkyl group
(Supporting Information Table S1). On the other hand, UV-Vis
absorption spectrum of the bithiophene containing polymer
5b displays a maximum peak at 304 nm in addition to two
shoulder peaks at 427 nm and 453 nm, whereas its 4b precur-
sor reveals a maximum absorption peak at 400 nm. The emis-
sion spectrum of 5b portrays a ꢂ23 nm blue shift with respect
to that of 4b. This could be explained by the long range conju-
gation between the different aromatic groups in 4b, namely,
the terphenyl derivatives and bithiophene moieties whose
smaller size and free rotation allows for a long range planariza-
tion, and which can be compared with the structure and
ACKNOWLEDGMENTS
The work was partially supported by Kuwait Foundation for the
Advancement of Sciences (KFAS) under project code: 2013-1506-
01. The authors thank the general facilities projects GS01/01,
GS01/03, GS01/05, GS03/01, and GS03/08 at Kuwait University.
REFERENCES AND NOTES
1 F. Xu, H. Xu, X. Chen, P. D. D. Wu, Y. Wu, H. Liu, C. Gu, F.
Ruowen, D. Jiang, Angew. Chem. Int. Ed. 2015, 54, 6814.
2 F. Xu, S. Jin, H. Zhong, D. Wu, X. Yang, X. Chen, H. Wei, R.
Fu, D. Jiang, Sci. Rep. 2015, 5, 8225.
3 H. Sirringhaus, Adv. Mater. 2014, 26, 1319.
4 F. Yuan, J. Li, S. Namuangruk, N. Kungwan, J. Guo, C.
Wang, Chem. Mater. 2017, 29, 3971.
5 H. Wang, Z. Cheng, Y. Liao, J. Li, J. Weber, A. Thomas, C. F. J.
Faul, Chem. Mater. 2017, ASAP, 10.1021/acs.chemmater.7b00857.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2017, 00, 000–000
7

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
6 S. Das, P. Heasman, T. Ben, S. Qiu, Chem. Rev. 2017, 117,
1515.
35 S. Chen, P. Slattum, C. Wang, L. Zang, Chem. Rev. 2015,
115, 11967.
7 L. A. Baldwin, J. W. Crowe, D. A. Pyles, P. L. McGrier, J. Am.
Chem. Soc. 2016, 138, 15134.
36 B. Alameddine, A. H. Rice, C. Luscombe, T. A. Jenny, Chem-
istryOpen. 2015, 4, 453.
8 J. Han, X. Fan, Z.-Z. Zhuang, W.-C. Song, Z. Chang, Y.-H.
Zhang, X.-H. Bu, RSC Adv. 2015, 5, 15350.
37 W. Zeng, H. Phan, T. S. Herng, T. Y. Gopalakrishna, N.
Aratani, Z. Zeng, H. Yamada, J. Ding, J. Wu, Chem. 2017, 2, 81.
9 J. Mei, Y. Hong, J. W. Y. Lam, A. Qin, Y. Tang, B. Z. Tang,
Adv. Mater. 2014, 26, 5429.
38 C. Cheng, S. Li, A. Thomas, N. A. Kotov, R. Haag, Chem.
Rev. 2017, 117, 1826.
€
39 U. Zschieschang, H. Klauk, I. B. Mueller, A. J. Strudwick, T.
10 A. J. C. Kuehne, M. C. Gather, Chem. Rev. 2016, 116, 12823.
€
Hintermann, M. G. Schwab, A. Narita, X. Feng, K. Mullen, R. T.
Weitz, Adv. Electron. Mater. 2015, 1400010.
11 Z. Zeng, X. Shi, C. Chi, J. T. Lo, J. Casado, J. Wu, Chem.
Soc. Rev. 2015, 44, 6578.
€
€
40 F. Schlutter, T. Nishiuchi, V. Enkelmann, K. Mullen, Angew.
€
12 T. Wohrle, I. Wurzbach, J. Kirres, A. Kostidou, N.
Chem. Int. Ed. 2014, 53, 1538.
Kapernaum, J. Litterscheidt, J. C. Haenle, P. Staffeld, A. Baro,
F. Giesselmann, S. Laschat, Chem. Rev. 2016, 116, 1139.
41 A. Narita, I. A. Verzhbitskiy, W. Frederickx, K. S. Mali, S. A.
Jensen, M. R. Hansen, M. Bonn, S. D. Feyter, C. Casiraghi, X.
Feng, K. M. llen, ACS Nano. 2014, 8, 11622.
13 L. Cali, S. Kazim, M. Graetzel, S. Ahmad, Angew. Chem. Int.
Ed. 2016, 55, 2.
42 R. Denk, M. Hohage, P. Zeppenfeld, J. Cai, C. A. Pignedoli,
H. Soede, R. Fasel, X. Feng, K. Muellen, S. Wang, D. Prezzi, A.
Ferretti, A. Ruini, E. Molinari, P. Ruffieux, Nat Commum. 2014,
5, 4253.
14 Y. Zhang, L. Chen, K. Zhang, H. Wang, Y. Xiao, Chem. Eur.
J. 2014, 20, 1.
15 A. Narita, X.-Y. Wang, X. Feng, K. Muellen, Chem. Soc. Rev.
2015, 44, 6616.
43 Y.-C. Chen, D. G d. Oteyza, Z. Pedramrazi, C. Chen, F. R.
Fischer, M. F. Crommie, ACS Nano. 2013, 7, 6123.
16 Q. Zhang, H. Peng, G. Zhang, Q. Lu, J. Chang, Y. Dong, X.
Shi, J. Wei, J. Am. Chem. Soc. 2014, 136, 5057. 2
44 X. Yan, L-s. Li, J. Mat. Chem. 2011, 21, 3295.
ꢀ
17 B. Schuler, S. Collazos, L. Gross, G. Meyer, D. Perez, E.
45 J. Wang, K. Liu, L. Ma, X. Zhan, Chem. Rev. 2016, 116, 14675.
ꢀ
~
Guitian, D. Pena, Angew. Chem. Int. Ed. 2014, 126, 9150.
46 L. Zhang, B. D. Rose, Y. Liu, M. M. Nahid, E. Gann, J. Ly, W.
Zhao, S. J. Rosa, T. P. Russell, A. Facchetti, C. R. McNeill, J.-L.
Bredas, A. L. Briseno, Chem. Mater. 2016, 28, 8580.
18 H. Arslan, F. J. Uribe-Romo, B. J. Smith, W. R. Dichtel,
Chem. Sci. 2013, 4, 3973.
19 B. Alameddine, M. Schindler, S. Martin-Caba, T. Jenny, Syn-
thesis. 2012, 44, 1928.
47 J. Wolf, M. Babics, K. Wang, Q. Saleem, R.-Z. Liang, M. R.
Hansen, P. M. Beaujuge, Chem. Mater. 2016, 28, 2058.
20 T.-A. Chen, R.-S. Liu, Chem. Eur. J. 2011, 17, 8023.
48 M. J. Sung, S. Yoon, S.-K. Kwon, Y.-H. Kim, D. S. Chung,
ACS Appl. Mater. Interfaces. 2016, 8, 31172.
21 K. Hyodo, R. Toyama, H. Mori, Y. Nishihara, ACS Omega
2017, 2, 308.
49 C. B. Nielsen, S. Holliday, H.-Y. Chen, S. J. Cryer, I.
McCulloch, Acc. Chem. Res. 2015, 48, 2803.
22 B. Alameddine, O. F. Aebischer, B. Heinrich, D. Guillon, B.
Donnio, T. A. Jenny, Supramol. Chem. 2014, 26, 125.
50 S. Li, T. Yuan, G. Tu, J. Zhang, Z. Li, Polym. Chem. 2015, 6, 7436.
23 C. Wang, H. Dong, W. Hu, Y. Liu, D. Zhu, Chem. Rev. 2012,
112, 2208.
51 R. Kim, B. Kang, D. H. Sin, H. H. Choi, S.-K. Kwon, Y.-H.
Kim, K. Cho, Chem. Commun. 2015, 51, 1524.
24 C. J. Martin, B. Gil, S. D. Perera, S. M. Draper, Chem. Com-
mun. 2011, 47, 3616.
52 L. Dou, Y. Liu, Z. Hong, G. Li, Y. Yang, Chem. Rev. 2015,
115, 12633.
ꢀ
ꢀ
25 M. Martınez-Abadıa, G. Antonicelli, E. Zuccatti, A. Atxabal,
M. Melle-Franco, L. E. Hueso, A. Mateo-Alonso, Org. Lett. 2017,
19, 1718.
53 S. R. Bheemireddy, M. P. Hautzinger, T. Li, B. Lee, K. N.
Plunkett, J. Am. Chem. Soc. 2017, 139, 5801.
€
54 B. A. G. Hammer, K. Mullen, Chem. Rev. 2016, 116, 2103.
26 X. Gu, H. Li, B. Shan, Z. Liu, Q. Miao, Org. Lett. 2017, 19,
€
55 A. Abdulkarim, F. Hinkel, D. Jansch, J. Freudenberg, F. E.
2246.
€
Golling, K. Mullen, J. Am. Chem. Soc. 2016, 138, 16208.
27 K. Y. Cheung, C. K. Chan, Z. Liu, Q. Miao, Angew. Chem.
Int. Ed. 2017, Just Accepted, 10.1002/anie.201703754.
€
56 P.-I. Wang, W. Pisula, K. Mullen, D.-J. Liaw, Polym. Chem.
2016, 7, 6211.
28 R. W. Miller, S. E. Averill, S. J. V. Wyck, A. C. Whalley, J.
Org. Chem. 2016, 81, 12001.
€
57 M. Saleh, M. Baumgarten, A. Mavrinskiy, T. Schafer, K.
€
Mullen, Macromolecules 2010, 43, 137.
29 E. H. Menke, V. Lami, Y. Vaynzof, M. Mastalerz, Chem. Com-
mun. 2016, 52, 1048.
58 B. Alameddine, R. S. Anju, F. Al-Sagheer, T. A. Jenny, New
J. Chem. 2016, 40, 10363.
30 S. Ito, Y. Tokimaru, K. Nozaki, Angew. Chem. Int. Ed. 2015,
54, 1.
59 N. Miyaura, T. Yanagai, A. Suzuki, Synth. Commun. 1981,
11, 513.
31 M. Ball, Y. Zhong, Y. Wu, C. Schenck, F. Ng, M. Steigerwald,
S. Xiao, C. Nuckolls, Acc. Chem. Res. 2015, 48, 267.
60 T. E. Barder, S. D. Walker, J. R. Martinelli, S. L. Buchwald, J.
Am. Chem. Soc. 2005, 127, 4685.
32 X. Zhang, X. Jiang, K. Zhang, L. Mao, J. Luo, C. Chi, H. S.
O. Chan, J. Wu, J. Org. Chem. 2010, 75, 8069.
61 P. Kovacic, F. W. Koch, J. Org. Chem. 1963, 28, 1864.
33 J. Liu, S. Osella, J. Ma, R. Berger, D. Beljonne, D.
Schollmeyer, X. Feng, K. Mullen, J. Am. Chem. Soc. 2016, 138,
8364.
62 M. G. Schwab, A. Narita, S. Osella, Y. Hu, A. Maghsoumi, A.
Mavrinsky, W. Pisula, C. Castiglioni, M. Tommasini, D.
Beljonne, X. Feng, K. Muellen, Chem. Asian J. 2015, 10, 2134.
34 H.-W. Ip, C.-F. Ng, H.-F. Chow, D. Kuck, J. Am. Chem. Soc.
2016, 138, 13778.
63 Y.-Z. Tan, B. Yang, K. Parvez, A. Narita, S. Osella, D.
Beljonne, X. Feng, K. Muellen, Nat. Commun. 2013, 4, 2646.
8
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