Tuning the Solid State Emission of Thin Films/Microspheres Obtained from Alternating Oligo(3-octylthiophenes) and 2,6-Bis(pyrazole)pyridine Copolymers by Varying Conjugation Length and Eu3+/Tb3+ Metal Coordination

Article abstract of DOI:10.1021/acs.macromol.5b01004

A series of dialkynyl-functionalized oligo(3-octylthiophene)_m (m = 1-7 and 9, where m is the number of thiophene units) were polymerized together with 2,6-bis(pyrazole)pyridine (BPP) to get alternating copolymers (P1-P7 and P9) with the number-average molecular weights (M_n) in the range of 5.3-11 kDa. These copolymers were further self-assembled into solid microspheres. The optical emission range of these copolymers were fine-tuned from blue to red and white by changing the conjugation length of thiophene oligomers (band gap approximately from 2.1 to 1.67 eV) and coordination of metals like Eu³⁺ and Tb³⁺ in both the solution and solid states. A white color was obtained in solution, thin film, and microsphere states with CIE (Commission Internationale de l'Eclairage) coordinates close to the values of standard white color.

Full text of DOI:10.1021/acs.macromol.5b01004

Article
pubs.acs.org/Macromolecules
Tuning the Solid State Emission of Thin Films/Microspheres
Obtained from Alternating Oligo(3-octylthiophenes) and 2,6-
Bis(pyrazole)pyridine Copolymers by Varying Conjugation Length
and Eu3+/Tb3+ Metal Coordination
Yemineni S. L. V. Narayana,† Martin Baumgarten,‡ Klaus Mullen,‡ and Rajadurai Chandrasekar*,†
̈
†Functional Molecular Nano/Micro Solids Laboratory, School of Chemistry, University of Hyderabad, GachiBowli, Hyderabad
500046, India
‡Max Planck Institute for Polymer Research, Ackermannweg 10, D-55218 Mainz, Germany
S
* Supporting Information
ABSTRACT: A series of dialkynyl-functionalized oligo(3-
octylthiophene)m (m = 1−7 and 9, where m is the number of
thiophene units) were polymerized together with 2,6-
bis(pyrazole)pyridine (BPP) to get alternating copolymers
(P1−P7 and P9) with the number-average molecular weights
(Mn) in the range of 5.3−11 kDa. These copolymers were
further self-assembled into solid microspheres. The optical
emission range of these copolymers were fine-tuned from blue
to red and white by changing the conjugation length of
thiophene oligomers (band gap approximately from 2.1 to 1.67
eV) and coordination of metals like Eu3+ and Tb3+ in both the
solution and solid states. A white color was obtained in
solution, thin film, and microsphere states with CIE (Commission Internationale de l’Eclairage) coordinates close to the values of
standard white color.
emitting monomers to tune the optical emission properties,
solubility, and processability. Several research groups have also
worked on creating diverse collections of luminescent thiophene-
based conjugated copolymer structures by incorporating
transition metals into the polymer main chain.12
INTRODUCTION
■
Conjugated oligomeric and polymeric materials displaying
various color emissions are extensively used in optoelectronic
devices, including organic light-emitting diodes (OLEDs),1
organic field-effect transistors (OFETs),2 and solar cells.3 For
example, the oligomers of thiophene, widely known for their
semiconductor properties in organic electronics, are also
fluorescent (FL) compounds characterized by chemical inert-
ness, good photostability, high optical absorbance, and FL
quantum yield. Their FL emission can be easily modulated by
varying the number of thiophene rings.4 Polythiophene
derivatives are the most widely investigated conjugated polymers
because of their strong visible range absorption, high charge
carrier mobility, easy synthetic accessibility, strange electro-
optical properties, structural flexibility, and environmental
stability.4a,5 Thiophene-containing polymers are now ubiquitous
in a range of organic electronic materials such as organic solar
cells, field effect transistors (FETs), light-absorbing photoactive
layers, and hole conducting layers in plastic electronics.5 The
emission properties of the conjugated polymers can be tuned by
methods like altering the main chain molecular structure6 or the
side chain molecular structure,7 blending a luminescent polymer
with another active polymer,8 or with organic or inorganic
molecules,9 doping,10a and also by using multiple layer devices.11
These tuning methodologies were used to synthesize a range of
copolymers by combining oligo(thiophenes) and various light-
For example, Swager et al. have prepared the first conducting
polymetallorotaxanes by electrochemically polymerizing metal-
lorotaxanes, which are tetrahedral complexes containing
bithiophene−bipyridine, macrocyclic phenanthroline, and Cu2+
or Zn2+ metal ions.12a,b The same group has reported another
conducting redox-active polymers based on polythiophene−
[Ru(bipyrdine)3]n+.12c Reynolds et al. have investigated the
synthesis, metal binding (zinc, copper, nickel, and cobalt ions),
and electrochemical properties of a ligand that is a condensation
product of salicylaldehyde and 3,4-diaminothiophene deriva-
tives, and they further polymerized the α-positions of the
thiophenes metal complexes to achieve polythiophenes with
electrochromic properties.12d Further, to fine-tune the electronic
properties, both the metal center and diamine backbone of the
salen ligand were varied in a series of transition metal−
polythiophene polymers based on metal salen and 3,4-ethyl-
enedioxythiophene (EDOT).12e Pickup and co-workers have
Received: May 11, 2015
Revised: June 23, 2015
© XXXX American Chemical Society
A
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Scheme 1. Chemical Structures of Alternating Oligo(3-octylthiophenes) and 2,6-Bis(pyrazole)pyridine (BPP) Copolymers (P1−
P7 and P9) with BPP End Groups
reported bithiophene−bipyridine copolymers prepared by
electrochemical polymerization and explored an electron-rich
metal (Ru2+ and Os2+) containing poly(bithiophene-co-bithia-
zole) backbone to lower the energy of the polymer HOMO to
increase the electronic communication with the metal center.12f,g
Guillerez et al. have reported π-conjugated polymers based on
regioregular 3-(octylthiophene) tetramers alternated with either
toward optoelectronics, solar cells,10a and recently photonic
devices.10b,c
In this article, we report the syntheses, characterization, and
bottom-up self-assembly studies of a series of copolymers (P1−
P7 and P9) with diverse optical band gaps (Scheme 1). The
copolymers were prepared by reacting oligo(3-octylthiophe-
nes)m carrying dialkynyl groups (m = 1−7, 9) with metal binding
BPP units. We also discuss the optical absorption and emission
(from blue to red) properties of these copolymers and also a
method to achieve white emission by coordinating Eu3+ and Tb3+
ions to the polymers in solution, thin film, and microsphere
states. The self-assembled microspheres were thoroughly
investigated by electron, atomic force, and laser confocal
fluorescence microscopy techniques.
2,2′-bipyridine or its Ru(II) complex [Ru(bipy)3]2+.12h
A
conducting 5,5′-(2-thienyl)-2,2′-bithiazole-based polymer coor-
dinated to rhenium ion showed stable metal coordination during
oxidizing and conducting states.12i Holiday et al. have electro-
polymerized Eu3+ containing EDOT monomer to get a pure red-
emitting conducting metallopolymer.12j
In most of the reported literatures the copolymers of
oligo(thiophenes) with metal coordinating units were prepared
by electrochemical polymerization. Until now, copolymerization
of the well-known tridentate 2,6-bis(pyrazole)pyridine (BPP)
ligand with various oligo(thiophenes) has not been attempted.
BPP units are known to coordinate with diverse d- and f-block
functional metal ions to form diverse coordination geometries.
For example, BPP with Fe2+ or Zn2+ ions form octahedral
complexes exhibiting magnetic spin crossover effects and
luminescence, resepectively.13 Further BPP type ligands form
9-coordinated tricapped trigonal prismatic complexes with Eu3+
and Tb3+ ions displaying sensitized intense red and green
emissions, respectively.9a−d Therefore, copolymerization of
oligo(thiophenes) with metal chelating BPP is another strategy
to fine-tune the visible emission spectrum by coordinating
luminescent f-block metal ions into the conjugated copolymer
chains. Furthermore, incorporation of red-emitting Eu3+ and
green-emitting Tb3+ ions into metal ion binding conjugated
polymers alter the optical and electronic properties of these
materials,9,10a improving the performance of the devices at the
application level. Additionally, the bottom-up self-assembly14 of
conjugated polymers into various nano and micro scale
structures is another important emerging research area directed
RESULTS AND DISCUSSION
■
Design, Synthesis, and Characterization. 3-Octylated
thiophene and their dibromo derivatives of m1 and m2 (3 and 4)
were prepared by following the reported procedure (Scheme
2).15 Compound 1 was prepared by treatment of octylthiophene
with n-BuLi and tributyltin chloride and used without further
purification. Dibromo-m2 (4) was prepared from compound 2.
Further, 3-octylatedthiophene oligomers m3−m7 and m9 (7−
12) were synthesized in ∼60% yields by following Stille coupling
reactions of 1 with the corresponding dibromo monomers (13−
17) in the presence of a catalytic amount of [PdCl2(PPh3)2] in
THF. Compounds 7−12 were converted into their analogous
dibromo derivatives (13−18) using 2 equiv of NBS/CHCl3/
AcOH in ∼90% yields. Further dibromo derivatives of 3, 4, and
13−18 were converted into their corresponding diethynyl
products under Sonagashira cross-coupling reactions followed
by deprotection to get the key intermediates (19−26) in >99%
yields.
Metal chelating BPP derivatives 2,6-bis(4-iodo-1H-pyrazol-1-
yl)pyridine (5) and 2-(4-iodo-1H-pyrazol-1-yl)-6-(1H-pyrazol-
1-yl)pyridine (6) were also synthesized from 2,6-dibromopyr-
B
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Scheme 2. Syntheses of Diethynylated Oligo(thiophenes) (m1−m7 and m9: 19−26, Respectively) and Their Corresponding
a
Copolymers with BPP Unit (P1−P7 and P9)
a
Reagents and conditions: (a) 1 equiv of N-bromosuccinimide (NBS)/CHCl3/AcOH; (b) 2 equiv of NBS/CHCl3/AcOH; (c) Pd(PPh3)2Cl2/THF;
(d) Pd(PPh3)2Cl2/CuI/trimethylsilylacetylene/diisopropylamine/THF; (e) KOH/THF/methanol.
idine in good yields (>80%) as per our reported procedur-
e.9b−e,16 Alternating copolymers (P1−P7 and P9) were prepared
by polymerizing the ethynyl derivative of m1−m7 and m9 (19−
26) with 5 under Sonagashira cross-coupling reactions in the
presence of diisopropylamine/THF. All the copolymers were
end-capped with compound 6 under Sonogashira reaction
conditions. The molecular structures of the monomers and the
copolymers were confirmed using nuclear magnetic resonance
(NMR) measurements, mass spectrometry, and elemental
analysis. All the synthesized copolymers were soluble in organic
solvents such as chloroform (CHCl3), tetrahydrofuran (THF),
between 7.3 and 7.9 ppm were from pyrazole and pyridine
protons of main chain BPP unit of the copolymers. The peaks
around 6.6−6.4 and 8.5−8.6 ppm were from the pyrazole proton
of end-capped BPP (Figure S12). 1H NMR end group analyses of
copolymers P1−P7 and P9 showed Mn values in the range of
4.5−11.0 kDa. The obtained copolymers were further subjected
to Soxhlet extraction to remove the low molecular weight
oligomers from the copolymers. The gel permeation chromatog-
raphy (GPC) analyses of copolymers after Soxhlet purification
showed Mn in the range of 5.3−11.0 kDa (Table 1). The
copolymers P1−P7 and P9 exhibited good thermal stability up
to a temperature in the range of 270−300 °C, as proven by
thermogravimetric analysis (TGA) (Figure S9).
1
and toluene. H NMR spectra of copolymers showed aromatic
peaks of the thiophenes around 6.9−7.0 ppm. The peaks
C
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Table 1. Molecular Weight and Optical Data of Copolymers (P1−P7 and P9)
solution (CHCl3)
thin film
a
Mn by 1H NMR Mn by GPC
Mw by GPC
(kDa)
absorption λmax emission λmax
Ff
absorption λmax emission λmax
optical band
b
polymer
(kDa)
(kDa)
PDI
(nm)
(nm)
(%)
(nm)
(nm)
gap (eV)
P1
P2
P3
P4
P5
P6
P7
P9
4.5
5.6
6.4
4.5
7.5
11
5.3
6.5
6.7
6.84
7.7
11
27.6
17.1
13.4
18.9
37.5
51.7
15.2
5.21
2.62
2.01
2.75
4.90
4.70
2.11
2.16
318
390, 420, 480
31
35
30
20
40
44
50
20
331
554
560
610
618
626
635
654
674
2.10
1.82
1.78
1.73
1.71
1.70
1.69
1.67
315, 390
309, 398
309, 406
317, 413
309, 432
309, 447
308, 459
522
538
551
552
560
572
598
309, 399
309, 410
309, 415
317, 425
309, 436
309, 449
308, 477
6.5
7.2
7.3
15.7
a
b
Quinine sulfate as reference (Qref = 0.577). Estimated from the onset wavelength of optical absorption in the solid state film.
in the XYT mode. Argon ion laser (power: 280 mW) was used as an
excitation source (λ = 365 nm).
EXPERIMENTAL SECTION
■
Reagents. 2,6-Dibromopyridine, bromooctane, tributyltin chloride,
octyl bromide, 3-bromothiophene, Ni(dppp)Cl2, PdCl2(PhCN)2, AgF,
TMEDA, I2, HIO3, Pd(PPh3)4, Pd(PPh3)2Cl2, pyrazole, and deuterated
solvent CDCl3-d1 were obtained from Sigma-Aldrich. TMSA, KF,
K2CO3, LiOH, Cu(I), PPh3, and Mg metal were purchased from Avra
Synthesis, Hyderabad, India. THF, triethylamine, diisopropylamine,
dichloromethane, hexane, diethyl ether, CHCl3, and methanol solvents
were obtained from Finar Chemicals Limited, Ahmedabad, India. All
solvents were used after distillation. Methanol, EtOH, and KOH were
obtained from Merck. EDTA, MgSO4, and Na2S2O3 were purchased
from SRL Chemicals Pvt. Limited, Hyderabad. For UV−vis and
fluorescence measurements spectroscopic grade solvents were used.
Instrumental Methods. 1H and 13C NMR spectroscopic data were
recorded on a Bruker DPX 400 spectrometer with solvent proton as
internal standard (CDCl3-d1 = 7.26 ppm). LC mass spectrometry was
performed on Shimadzu LCMS-2010A mass spectrometer. IR spectra
were recorded on Nicolet 5700 FT-IR or JASCO FT/IR-5300.
Elemental analysis was recorded on a Thermo Finnigan Flash EA
1112 analyzer. The molecular weights were determined by PSS-Win
GPC (PSS) (pump: alliance GPC 2000) GPC equipped with an RI
detector using a PL gel MIXED-B column (particle size: 10 mm,
dimensions: 0.8 × 30 cm) calibrated against polystyrene standards. For
thin-layer chromatography (TLC), silica gel plates (Merck 60 F254)
were used, and compounds were visualized by irradiation with UV light.
UV−vis absorption and fluorescence spectra were recorded on a
spectrophotometer (Cary-100, Varian) and a spectrofluorometer
(Horiba, JobinYvon) respectively. For fluorescence quantum yield
measurements, solution of ligands in CHCl3 was matched optically at an
absorbing wavelength, and then the quantum yield of quinine sulfate in
0.1 M H2SO4 (Φf = 0.57, at 27 °C) was used as reference.
Characterizations of the nano/micro spheres were examined by using
a Philips XL30 ESEM scanning electron microscope (SEM) using a
beam voltage of 20 kV and a Tecnai G2 FEI F12 transmission electron
microscope (TEM) at an accelerating voltage of 200 kV. FESEM
measurements were performed on a Zeiss FESEM instrument operating
at 20 kV.
General Synthetic Procedure. Synthesis of 3-Octylthiophene
Oligomer (m3): 7. To a solution of 2,5-dibromo-3-octylthiophene 3
(1.5 g, 4.2 mmol) and tributyl(4-octylthiophen-2-yl)stannane 1 (4.318
g, 8.8 mmol) in THF (25 mL), PdCl2(PPh3)2 (59 mg, 2 mol %) was
added under a nitrogen atmosphere. The mixture was heated under
reflux for 4 h. Then the solvent from the mixture was evaporated under
reduced pressure to get pale-green color oil. The residue was purified by
column chromatography on silica gel using hexane eluent to obtain
colorless oil (1.49 g, 60%). 1H NMR (400 MHz, CDCl3-d1, 298 K) δ:
6.80−7.00 (m, 4 H), 6.77 (s, 1H), 2.70 (t, 2H), 2.59 (t, 4H), 1.63 (m,
6H), 1.27 (m, 30 H), 0.89 (t, 9 H). 13C NMR (100 MHz, CDCl3-d1, 298
K) δ: 144.1, 143.9, 143.6, 139.9, 137.4, 136.9, 135.6, 135.2, 129.8, 127.0,
126.2, 124.8, 119.89, 118.9, 118.7, 33.2, 31.9, 30.5, 30.4, 29.5, 29.4, 29.3,
28.91, 28.3, 26.8, 22.71, 14.1, 13.6. FT-IR (KBr) ν in cm−1: 2964, 2920,
2860, 1463, 1375, 1260, 1219, 1084, 1019, 827, 717. HRMS (ESI) (m/
z): (M + H)+ calcd for C36H57S3 585.3622; found 585.3620 Anal. Calcd
for C36H56S3: C, 73.91; H, 9.65. Found: C, 73.85; H, 9.76.
The above-mentioned procedure was followed for the syntheses of
oligomers m4−m7 and m9. Yields ∼60% (Scheme 2).
3-Octylthiophene Oligomer (m4): 8. 1H NMR (400 MHz, CDCl3-
d1, 298 K) δ: 6.80−7.00 (m, 6H), 6.77 (s, 2H), 2.74 (t, 4H), 2.64 (m,
4H), 1.66 (m, 8H), 1.31 (m, 40 H), 0.91 (t, 12 H). 13C NMR (100 MHz,
CDCl3-d1, 298 K) δ: 143.9, 143.6, 140.0, 137.4, 135.6, 134.6,
130.0,128.3, 127.3, 127.0, 126.3, 125.0, 124.8, 119.9, 119.7, 118.9,
118.7, 31.9, 30.7, 30.5, 30.4, 29.6, 29.4, 29.39, 29.3, 22.7, 14.1. FT-IR
(KBr) ν in cm−1: 2926, 2854, 1745, 1620, 1572, 1498, 1466, 1394, 1273,
1219, 1114, 1082, 1039, 968, 866, 792, 758, 723, 652, 611. HRMS (ESI)
(m/z): (M + H)+ calcd for C48H75S4 779.4752; found 779.4611 Anal.
Calcd for C48H74S4: C, 73.97; H, 9.57. Found: C, 73.85; H, 9.48.
3-Octylthiophene Oligomer (m5): 9. 1H NMR (400 MHz, CDCl3-
d1, 298 K) δ: 6.97−6.99 (m, 4H), 6.89 (s, 2H), 6.78 (s, 1H) 2.75 (t, 4H),
2.63 (m, 6H), 1.65 (m, 10H), 1.29 (m, 50 H), 0.94 (t, 15 H). 13C NMR
(100 MHz, CDCl3-d1, 298 K) δ: 144.1, 143.9, 143.6, 140.0, 137.3, 135.6,
134.6, 129.9, 128.2, 127.1, 126.3, 125.0, 124.8, 119.9, 119.7, 118.7, 31.9,
30.5, 30.4, 29.5, 29.4, 29.3, 29.2, 22.7, 17.2, 14.1, 13.6. FT-IR (KBr) ν in
cm−1: 2958, 2931, 2849, 1638, 1523, 1468, 1375, 1194, 832, 728. HRMS
(ESI) (m/z): (M + H)+calcd for C60H92S5 Na 995.5700; found
995.5698. Anal. Calcd for C60H92S5: C, 74.01; H, 9.52. Found: C, 74.15;
H, 9.48.
Atomic Force Microscopy Studies. Atomic force microscopy
(AFM) imaging was carried out on NT-MDT Model Solver Pro M
microscope using a class 2R laser of 650 nm wavelength having
maximum output of 1 mW. All calculations and image processing was
carried out by a software NOVA 1.0.26.1443 provided by the
manufacturer. The images were recorded in a semicontact mode using
a noncontact silicon cantilever (NSG 10) tip purchased from NT-MDT,
Moscow. The dimension of the tip is as follows: cantilever length = 95
5 μm, cantilever width 30 5 μm, and cantilever thickness = 1.52.5 μm,
resonate frequency = 140−390 kHz, force constant = 5.5−22.5 N/m,
chip size = 3.4 × 1.6 × 0.3 mm, reflective side = Au, tip height = 14−16
μm, tip curvature radius = 10 nm, and aspect ratio 3:1−5:1.
3-Octylthiophene Oligomer (m6): 10. 1H NMR (400 MHz, CDCl3-
d1, 298 K) δ: 6.89−6.99 (m, 8H), 2.75 (t, 4H), 2.63 (m, 8H), 1.66 (m,
12H), 1.29 (m, 60 H), 0.88 (t, 18 H). 13C NMR (100 MHz, CDCl3-d1,
298 K) δ: 149.5, 144.7, 142.5, 134.4, 132.3, 132.2, 132.1, 132.0, 131.9,
131.5, 129.0, 128.4, 31.7, 29.7, 29.26, 29.36, 29.31, 29.2, 29.1, 26.0, 25.9,
22.63, 14.1, 14.0. FT-IR (KBr) ν in cm−1: 2964, 2914, 2849, 1742, 1468,
1413, 1380, 1254, 1095, 1013, 871, 810, 663. HRMS (ESI) (m/z): (M +
H)+ calcd for C72H111S6 1167.7010; found 1167.7130. Anal. Calcd for
C72H110S6: C, 74.04; H, 9.49. Found: C, 74.21; H, 9.41.
Confocal Fluorescence Microscopy Studies. Confocal fluo-
rescence microscopic images and spectra were recorded on a Carl-Zeiss
laser confocal microscopy (model NL0710). The emission spectra were
recorded in XYλ scan mode, and the fluorescence images were collected
3-Octylthiophene Oligomer (m7): 11. 1H NMR (400 MHz, CDCl3-
d1, 298 K) δ: 6.92−7.03 (m, 8H), 6.80 (s, 1H), 2.80 (m, 6H), 2.66 (m,
8H), 1.71 (m, 14H), 1.39 (m, 70 H), 0.94 (t, 21H). 13C NMR (100
D
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MHz, CDCl3-d1, 298 K) δ: 143.9, 143.6, 143.2, 140.2, 139.5, 137.4,
135.6, 135.5, 134.6, 133.6, 131.0, 130.0, 128.4, 128.2, 127.1, 126.5, 126.3,
125.0, 124.8, 120.0, 119.9, 119.7, 118.7, 31.9, 30.6, 30.5, 30.4, 29.7, 29.6,
29.5, 29.4, 29.3, 28.3, 26.8, 22.7, 17.30, 14.1, 13.6. FT-IR (KBr) ν in
cm−1: 2953, 2920, 2854, 1523, 1462, 1380, 827, 728. HRMS (ESI) (m/
z): (M + H)+ calcd for C84H129S7 1361.8139; found 1361.8354. Anal.
Calcd for C84H128S7: C, 74.05; H, 9.47. Found: C, 74.12; H, 9.36.
3-Octylthiophene Oligomer (m9): 12. 1H NMR (400 MHz, CDCl3-
d1, 298 K) δ: 6.97−6.99 (m, 8H), 6.91 (m, 2H), 6.78 (s, 1H), 2.77 (m,
8H), 2.62 (m, 10H), 1.67 (m, 18H), 1.30 (m, 108 H), 0.90 (t, 27H). 13C
NMR (100 MHz, CDCl3-d1, 298 K) δ: 143.9, 143.6, 143.2, 140.2, 139.5,
137.4, 135.6, 135.5, 134.6, 133.6, 131.0, 130.0, 128.4, 128.2, 127.1, 126.5,
126.3, 125.0, 124.8, 120.0, 31.9, 30.6, 30.5, 30.4, 29.7, 29.6, 29.5, 29.4,
29.3, 28.3, 26.8, 22.7, 17.30, 14.1, 13.6. FT-IR (KBr) ν in cm−1: 2953,
2925, 2854, 1468, 1375, 1194, 827, 728. HRMS (ESI) (m/z): (M + H)+
calcd for C108H165S9 1750.0398; found 1750.0354. Anal. Calcd for
C108H164S9: C, 74.08; H, 9.44. Found: C, 74.16; H, 9.32.
CDCl3-d1, 298 K) δ: 142.9, 142.4, 140.5, 140.3, 140.1, 136.2, 135.3,
128.3, 128.2, 126.5, 126.4, 125.0, 124.4, 119.7, 108.6, 107.9, 31.9, 30.6,
30.5, 30.3, 29.7, 29.5, 29.4, 29.3, 27.9, 27.4, 27.1, 22.7, 16.4, 14.1, 13.7.
FT-IR (KBr) ν in cm−1: 2958, 2925, 2849, 1643, 1462, 1380, 1298, 1189,
1019, 821, 717. HRMS (ESI) (m/z): (M + H)+calcd for C84H127Br2S7
1517.6349; found 1517.6236. Anal. Calcd for C84H126Br2S7: C, 66.37; H,
8.35. Found: C, 66.45; H, 8.25.
2,5-Dibromo-3-octylthiophene (m9): 18. 1H NMR (400 MHz,
CDCl3-d1, 298 K) δ: 6.79−7.03 (m, 9H), 2.82 (m, 10H), 2.62 (m, 8H),
1.68 (m, 18H), 1.36 (m, 108 H), 0.96 (t, 27H). 13C NMR (100 MHz,
CDCl3-d1, 298 K) δ: 143.9, 142.4, 140.5, 140.3, 140.0, 135.4, 134.9,
134.1, 129.9, 129.2, 128.3, 126.5, 126.3, 125.0, 124.7, 119.1, 118.6, 108.7,
32.0, 30.6, 29.7, 29.6, 29.5, 29.4, 29.3, 22.8, 14.2. FT-IR(KBr) ν in cm−1:
2964, 2925, 2860, 2723, 2487, 1736, 1649, 1462, 1375, 1260, 1084,
1024, 799, 723. HRMS (ESI) (m/z): (M + H)+calcd for C108H163Br2S9
1905.8608; found 1905.8654. Anal. Calcd for C108H162Br2S9: C, 67.96;
H. Found: C, 67.86; H, 8.61.
Synthesis of 2,5-Dibromo-3-octylthiophene (m3): 13. 3-Octylth-
iophene trimer 7 (1.75 g, 2.90 mmol) and NBS (1.135 g, 6.38 mmol)
were dissolved in chloroform/glacial acetic acid (1/1, v/v (10 mL)), and
the resulting solution was vigorously stirred under reflux for 5 h under
nitrogen. The crude mixture was cooled to room temperature,
subsequently washed with saturated NaHCO3(aq) and distilled water,
and extracted with dichloromethane. The organic phase was dried over
anhydrous sodium sulfate, and the solvent from the mixture was
evaporated under reduced pressure to afford yellow oil. The product was
further purified by silica column chromatography (SiO2) with hexane as
eluent. The compound was obtained as pale-yellowish oil (2.65 g, yield
∼90%). 1H NMR (400 MHz, CDCl3-d1, 298 K) δ: 6.80−6.98 (m, 3H),
6.77 (s, 2H), 2.70 (t, 2H), 2.55 (t, 4H), 1.63 (m, 6H), 1.27 (m, 30 H),
0.89 (t, 9 H). 13C NMR (100 MHz, CDCl3-d1, 298 K) δ: 144.1, 143.9,
143.6, 139.9, 137.4, 136.9, 135.6, 135.2, 129.8, 127.0, 126.2, 124.8, 119.8,
119.9, 118.7, 33.19, 31.93, 30.55, 30.45, 29.5, 29.4, 29.3, 28.9, 28.3, 26.8,
22.7, 17.30, 14.1, 13.6. FT-IR (KBr) ν in cm−1: 2947, 2920, 2849, 1780,
1747, 1534, 1457, 1375, 1227, 1183, 1013, 821, 717. HRMS (ESI) (m/
z): (M + H)+calcd for C36H55Br2S3 741.1833; found 741.1854. Anal.
Calcd for C36H54Br2S3: C, 58.21; H, 7.33. Found: C, 58.32; H, 7.26.
The above-mentioned procedure was adopted for the syntheses of
oligomers m4−m7 and m9. Yields ∼90% (Scheme 2).
Synthesis of 2,5-Dialkyne of 3-Octylthiophenes Oligomer (m3): 21.
2,5-Dibromo-3-octylthiophene oligomer (m3) 13 (0.700 g, 1.05 mmol),
Pd(PPh3)2Cl2 (70 mg, 0.105 mmol), and CuI (10 mg, 0.05 mmol) were
taken in a clean and dry 100 mL three-neck round-bottom flask. The
flask was put under freeze−pump−thaw cycle for three times. To this,
dry THF (50 mL) and diisopropylamine (60 mL) were added.
Trimethylsilylacetylene (0.22 g, 2.32 mmol) was injected drop-by-drop
into the reaction mixture under nitrogen, and the resulting solution was
heated to 80 °C for overnight. It was then cooled to room temperature
and left stirring for an additional hour. The mixture was neutralized in an
ice bath with dilute HCl (20% in H2O, v/v, added dropwise), and the
product was extracted with portions of CH2Cl2 (3 × 20 mL). The
organic phase was collected and dried over Na2SO4, and the CH2Cl2 was
evaporated under reduced pressure. The obtained crude silyl compound
was discharged in a 250 mL two-neck round-bottom containing N2
flushed solution mixture of THF and methanol (1/1, v/v), and to this
solid KOH (2 equiv) was added and put into a N2 atmosphere. The
resultant solution was left at room temperature for 1 h stirring. The
solution was concentrated under reduced pressure, and the obtained
crude compound was purified by column chromatography (SiO2) with
hexane as an eluent. The compound was obtained as brown jelly-like
solid (0.590 g, yield ∼90%). 1H NMR (400 MHz, CDCl3-d1, 298 K) δ:
6.80−7.10 (m, 3 H), 3.56 (s, 2H), 2.70 (t, 2H), 2.59 (t, 4H), 1.63 (m,
6H), 1.27 (m, 30 H), 0.89 (t, 9 H). 13C NMR (100 MHz, CDCl3-d1, 298
K) δ: 144.5, 142.9, 141.4, 136.1, 127.3, 126.7, 125.4, 124.4, 107.8, 31.9,
31.8, 29.7, 29.6, 29.4, 29.3, 29.2, 22.6, 14.1. FT-IR (KBr) ν in cm−1:
3315, 2953, 2926, 2854, 2136, 1742, 1523, 1468, 1375, 1260, 1101,
1019, 827, 805,723, 652. HRMS (ESI) (m/z): (M + H)+calcd for
C40H57S3 633.3622; found 633.3715. Anal. Calcd for C40H56S3: C,
75.89; H, 8.92. Found: C, 75.68; H, 8.87.
2,5-Dibromo-3-octylthiophene (m4): 14. 1H NMR (400 MHz,
CDCl3-d1, 298 K) δ: 6.90−6.99 (m, 6H), 6.77 (s, 2H), 2.76 (t, 2H), 2.64
(m, 6H), 1.66 (m, 8H), 1.31 (m, 40H), 0.91 (t, 12H). 13C NMR (100
MHz, CDCl3-d1, 298 K) δ: 149.5, 140.9, 136.2, 134.9, 129.3, 126.6,
126.3, 84.3, 31.9, 30.4, 30.10, 29.5, 29.3, 29.2, 22.6, 14.0. FT-IR (KBr) ν
in cm−1: 2958, 2920, 2860, 1726, 1457, 1380, 1273, 1219, 1114, 1082,
1039, 968, 866, 792, 758, 723, 652, 611. HRMS (ESI) (m/z): (M + H)+
calcd for C48H73Br2S4 935.2962; found 935.2977. Anal. Calcd for
C48H72Br2S4: C, 61.52; H, 7.74. Found: C, 61.48; H, 7.65.
A similar procedure was adopted for syntheses of oligomers m4−m7
2,5-Dibromo-3-octylthiophene (m5): 15. 1H NMR (400 MHz,
CDCl3-d1, 298 K) δ: 6.93−7.0 (m, 3H), 6.77−6.84 (m, 2H), 2.68 (m,
4H), 2.60 (m, 6H), 1.57 (m, 10H), 1.28 (m, 50 H), 0.89 (t, 15 H). 13C
NMR (100 MHz, CDCl3-d1, 298 K) δ: 142.9, 142.4, 140.5, 136.1, 135.3,
134.9, 129.1, 128.2, 126.6, 126.4, 125.0, 124.4, 119.7, 108.6, 107.8, 31.9,
30.5, 30.3, 29.6, 29.5, 29.4, 29.2, 22.7, 14.1. FT-IR (KBr) ν in cm−1:
2953, 2926, 2854, 1742, 1523, 1468, 1375, 1260, 1101, 1019, 827, 805,
723. HRMS (ESI) (m/z): (M + H)+ calcd for C60H91Br2S5 1129.4091;
found 1129.4082. Anal. Calcd for C60H90Br2S5: C, 63.69; H, 8.02; N,
10.30. Found: C, 63.56; H, 8.15.
and m9. Yields >99% (Scheme 2).
2,5-Dialkyne of 3-Octylthiophene Oligomer (m4): 22. H NMR
1
(400 MHz, CDCl3-d1, 298 K) δ: 6.98 (s, 2H), 6.88 (s, 2H), 3.53 (s, 2H)
2.67−2.74 (m, 8H), 1.64 (m, 8H), 1.28 (m, 40H), 0.90 (t, 12H). 13C
NMR (100 MHz, CDCl3-d1, 298 K) δ: 149.5, 140.9, 136.2, 134.9, 129.3,
126.6, 126.3, 116.6, 84.3, 31.9, 30.4, 30.10, 29.5, 29.3, 29.2, 22.6, 14.1.
FT-IR (KBr) ν in cm−1: 2964, 2920, 2849, 2142, 1462, 1249, 854, 750.
HRMS (ESI) (m/z): (M + H)+calcd for C52H75S4 827.4752; found
827.4748. Anal. Calcd for C52H74S4: C, 75.48; H, 9.01; Found: C, 75.36;
H, 9.12.
1
2,5-Dibromo-3-octylthiophene (m6): 16. 1H NMR (400 MHz,
CDCl3-d1, 298 K) δ: 6.81−7.00 (m, 6H), 2.73 (t, 4H), 2.58 (m, 8H),
1.66 (m, 12H), 1.29 (m, 60 H), 0.88 (t, 18 H). 13C NMR (100 MHz,
CDCl3-d1, 298 K) δ: 149.5, 144.7, 142.5, 134.4, 132.3, 132.2, 132.1,
132.0, 131.9, 131.5, 129.0, 128.4, 31.9, 30.4, 30.10, 29.5, 29.4, 29.3, 29.2,
22.7, 22.6, 14.1. FT-IR (KBr) ν in cm−1: 2958, 2920, 2849, 1468, 1375,
1260, 866. HRMS (ESI) (m/z): (M + H)+ calcd for C72H109Br2S6
1323.5220; found 1323.5387. Anal. Calcd for C72H108Br2S6: C, 65.23; H,
8.21. Found: C, 65.36; H, 8.16.
2,5-Dialkyne of 3-Octylthiophene Oligomer (m5): 23. H NMR
(400 MHz, CDCl3-d1, 298 K) δ: 6.90−7.06 (m, 5H), 3.55 (s, 2H), 2.72
(t, 6H), 2.58 (t, 4H), 1.65 (m, 10H), 1.30 (m, 50 H), 0.90 (t, 15 H). 13C
NMR (100 MHz, CDCl3-d1, 298 K) δ: 149.5, 147.9, 144.6, 131.0, 127.0,
125.5, 124.8, 118.3, 114.4, 84.9, 84.4, 31.9, 30.3, 30.2, 30.1, 29.7, 29.5,
29.3, 29.2, 27.4, 22.6, 14.1. FT-IR (KBr) ν in cm−1: 2958, 2920, 2854,
2150, 1463, 1221, 1114, 1082, 1039, 968,866, 792, 767. HRMS (ESI)
(m/z): (M + H)+calcd for C64H93S5 1021.5881; found 1021.5821. Anal.
Calcd forC64H92S5: C, 75.23; H, 9.08; N. Found: C, 75.32; H, 9.16.
2,5-Dibromo-3-octylthiophene (m7): 17. 1H NMR (400 MHz,
CDCl3-d1, 298 K) δ: 6.78−7.00 (m, 7H), 2.77 (m, 6H), 2.59 (m, 8H),
1.65 (t, 14H), 1.32 (m, 70 H), 0.92 (t, 21H). 13C NMR (100 MHz,
2,5-Dialkyne of 3-Octylthiophene Oligomer (m6): 24. H NMR
1
(400 MHz, CDCl3-d1, 298 K) δ: 6.89−6.98 (m, 6H), 3.52 (s, 2H) 2.71−
2.73 (m, 12H), 1.62−1.66 (m, 12H), 1.29 (m, 60H), 0.99 (t, 18H). 13C
E
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Figure 1. (a, b) Effect of concentration on the absorption and emission properties of copolymer P1, respectively. (c, d) Absorption and emission spectra
of copolymers in CHCl3, respectively. (e) Emission colors of copolymers in solution state upon UV light irradiation. (f) Emission colors of copolymers
in solution state (P1−P7 and P9) in a CIE 1931 2° standard observer chromaticity diagram.
NMR (100 MHz, CDCl3-d1, 298 K) δ: 149.4, 140.9, 140.4, 136.2, 134.9,
129.3, 126.6, 126.3, 116.6, 84.3, 31.9, 30.4, 30.10, 29.5, 29.4, 29.3, 29.2,
22.7, 22.6, 14.1. FT-IR (KBr) ν in cm−1: 3309, 2953, 2925, 2854, 2098,
1654, 1462, 1375, 827, 761. HRMS (ESI) (m/z): (M + H)+ calcd for
C76H111S61215.7010; found 1215.7017. Anal. Calcd for C76H110S6: C,
75.06; H, 9.12. Found: C, 75.21; H, 9.16.
140.0, 136.2, 134.8, 134.2, 130.0, 129.5, 128.5, 126.5, 126.3, 116.6, 84.3,
31.9, 30.4, 30.10, 29.7, 29.6, 29.5, 29.4, 29.2, 28.9, 22.6, 14.0. FT-IR
(KBr) ν in cm−1: 3314, 2947, 2925, 2849, 2098, 1638, 1462, 1375, 827,
728. HRMS (ESI) (m/z): (M + H)+ calcd for C112H165S9 1798.0398;
found 1798.0239. Anal. Calcd for C112H164S9: C, 74.77; H, 9.19. Found:
C, 74.65; H, 9.08.
Synthesis of Copolymer (P1). 2,5-Diethynyl-3-octylthiophene 3
(100 mg, 0.409 mmol) 2,6-bis(4-iodo-1H-pyrazol-1-yl)pyridine 5 (185
mg, 0.400 mmol), 2-(4-iodo-1H-pyrazol-1-yl)-6-(1H-pyrazol-1-yl)-
pyridine 6 (14 mg, 0.04 mmol), THF (10.0 mL), and diisopropylamine
(20.0 mL) were added to a two-neck round-bottom flask, and the
solution was purged with nitrogen for 20 min. Afterward, the reaction
was degassed by a repeated sequence of freeze−pump−thaw cycles.
PdCl2(PPh3)2 (28 mg, 0.0409 mmol) and CuI (4.0 mg, 0.02 mmol)
were added to the reaction under nitrogen, and the mixture was stirred at
60 °C. After 16 h, a small excess of 2-(4-iodo-1H-pyrazol-1-yl)-6-(1H-
pyrazol-1-yl)pyridine 6 (14 mg, 0.04 mmol) was added and stirred for
another 6 h. The hot suspension was subsequently poured into a
saturated aqueous EDTA solution (100 mL), and the mixture was
1
2,5-Dialkyne of 3-Octylthiophene Oligomer (m7): 25. H NMR
(400 MHz, CDCl3-d1, 298 K) δ: 6.88−6.99 (m, 7H), 3.53 (s, 2H) 2.71−
2.76 (t, 10H), 2.60 (t, 4H), 1.66 (m, 14H), 1.29 (m, 70H), 0.90 (t, 21H).
13C NMR (100 MHz, CDCl3-d1, 298 K) δ: 149.4, 140.9, 140.5, 136.2,
129.3, 128.6, 128.5, 126.6, 126.3, 124.8, 116.6, 84.3, 31.9, 30.4, 30.10,
29.7, 29.5, 29.4, 29.2, 22.7, 14.1 FT-IR (KBr) ν in cm−1: 3309, 2947,
2920, 2849, 2098, 1725, 1632, 1457, 1375, 827, 717. HRMS (ESI) (m/
z): (M + H)+ calcd for C88H129S7 1409.8139; found 1409.8114. Anal.
Calcd for C88H128S7: C, 74.94; H, 9.15. Found: C, 74.82; H, 9.23.
1
2,5-Dialkyne of 3-Octylthiophene Oligomer (m9): 26. H NMR
(400 MHz, CDCl3-d1, 298 K) δ: 6.90−7.00 (m, 9H), 3.54 (s, 2H) 2.76−
2.78 (m, 14H), 2.73 (t, 4H), 1.69 (m, 18H), 1.29 (m, 90H), 0.91 (t,
27H). 13C NMR (100 MHz, CDCl3-d1, 298 K) δ: 149.4, 140.5, 140.4,
F
DOI: 10.1021/acs.macromol.5b01004
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Figure 2. (a) Emission spectra of P1 without and with metals (Tb3+, Eu3+) in CHCl3. Insets show the photographs of emission colors from P1, P1 +
Tb3+, P1 + Tb3+ + Eu3+ upon UV light irradiation. (b) Emission spectra of copolymer P1 with and without Eu3+ in CHCl3, and the insets show the
emission colors of P1 and P1 + Eu3+ upon UV light irradiation. (c) Emission spectra of mixture of P2 and P6 in CHCl3; the insets show the emission
colors of P1, P6, P1 + P6 upon UV light irradiation. (d) Emission color of copolymers P1 + Tb3+ + Eu3+ (0.29, 0.35), P1 + Eu3+ (0.33, 0.41), and (P1 +
P6) (0.30, 0.30) in solution state CIE 1931 2° Standard Observer chromaticity diagram.
stirred for 2 h. The organic layer was separated, and the aqueous layer
was extracted with CHCl3. The combined organic layers were washed
with deionized water, and the volume was minimized under reduced
pressure. The concentrated organic layer was redissolved in CHCl3 (10
mL), and MeOH (100 mL) was added dropwise to form an off-brown
precipitate. The copolymer precipitate was filtered and washed with
boiling MeOH, EtOH, hexane, and MeOH at room temperature
followed by cold CHCl3. 1H NMR (400 MHz, CDCl3-d1, 298 K) δ: 8.75
(s, 4H), 8.65 (s, 2 H), 8.59 (s, 2H), 8.0−7.64 (m, 56 H), 7.45−7.31 (m,
20 H), 7.09−7.0 (m, 10 H), 6.51 (t, 2 H, end group), 2.73 (t, 12 H), 1.65
(m, 16H), 1.40−1.28 (m, 96 H), 0.88−0.86 (m, 38 H). FT-IR (KBr) ν in
cm−1: 2920, 2848, 1599, 1582, 1511, 1462, 1391, 1193, 996, 969, 941,
804, 771, 651. Mn = 4530 by 1H NMR. From GPC data: Mn = 5.3 kDa,
Mw = 27.6 kDa, and PDI = 5.21.
ν in cm−1: 2920, 2854, 1604, 1582, 1517, 1467, 1380, 1188, 963, 947,
799. Mn = 5180 by 1H NMR. From GPC data: Mn = 6.8 kDa, Mw = 18.9
kDa, and PDI = 2.77.
P5: 1H NMR (400 MHz, CDCl3-d1, 298 K) δ: 8.90 (s, 1H), 8.76 (s, 4
H), 8.61 (s, 3H), 8.0−7.72 (m, 66 H), 7.59−7.30 (m, 28 H), 7.08−6.96
(m, 30 H), 6.54 (t, 2 H, end group), 2.80 (t, 46 H), 2.60 (t, 14 H) 1.64
(m, 116 H), 1.46−1.28 (m, 425 H), 0.90−0.88 (m, 140 H). FT-IR
(KBr) ν in cm−1: 2925, 2843, 1610, 1577, 1522, 1467, 1429, 1177, 1095,
1040, 793. Mn = 7500 by 1H NMR. From GPC data: Mn = 7.6 kDa, Mw =
37.4 kDa, and PDI = 4.9.
P6: 1H NMR (400 MHz, CDCl3-d1, 298 K) δ: 8.74 (s, 4H), 8.65 (s,
2H), 8.60 (s, 2H), 8.0−7.78 (m, 50 H), 7.59−7.40 (m, 33 H), 7.07−6.94
(m, 51 H), 6.54 (t, 2 H, end group), 2.76 (t, 74 H), 2.60 (t, 36 H) 1.64
(m, 388 H), 1.46−1.26 (m, 1270 H), 0.90−0.88 (m, 333 H). FT-IR
(KBr) ν in cm−1: 2947, 2920, 2854, 1604, 1468, 1433, 1390, 1269, 1188,
1143, 1116, 1006, 960, 947, 800. Mn = 11 000 by 1H NMR. From GPC
data: Mn = 11 000 kDa, Mw = 51.7 kDa, and PDI = 4.7.
A similar procedure was adopted for the syntheses of copolymers
P2−P7 and P9 (Scheme 2).
P2: 1H NMR (400 MHz, CDCl3-d1, 298 K) δ: 8.74 (s, 6 H), 8.65 (s,
3H), 8.58 (s, 2H), 8.0−7.67 (m, 54 H), 7.50−7.45 (m, 10 H), 7.0−6.97
(m, 16 H), 6.51 (t, 2 H, end group), 2.71 (t, 24 H), 2.50 (t, 6H) 1.69 (m,
36 H), 1.37−1.28 (m, 200 H), 0.90−0.88 (m, 64 H). FT-IR (KBr) ν in
cm−1: 2953, 2914, 2848, 1604, 1582, 1517, 1462, 1188, 996, 963, 947,
860, 799, 656. Mn = 5600 by 1H NMR. From GPC data: Mn = 6.5 kDa,
Mw = 17.1 kDa, and PDI = 2.62.
P7: 1H NMR (400 MHz, CDCl3-d1, 298 K) δ: 8.90 (s, 1H), 8.74 (s,
2H), 8.65 (s, 1H), 8.59 (s, 1H), 8.0−7.72 (m, 30 H), 7.49−7.46 (m, 22
H), 7.01−6.95 (m, 34 H), 6.53 (t, 2 H, end group), 2.78 (t, 30H), 2.55
(t, 15 H) 1.68 (m, 76 H), 1.42−1.127 (m, 338 H), 0.90−0.87 (m, 120
H). FT-IR (KBr) ν in cm−1: 2953, 2920, 2848, 1604, 1582, 1528, 1473,
1429, 1188, 958, 804, 695. Mn = 6500 by 1H NMR. From GPC data: Mn
= 7.2 kDa, Mw = 15.2 kDa, and PDI = 2.11.
P3: 1H NMR (400 MHz, CDCl3-d1, 298 K) δ: 8.74 (s, 2 H), 8.64 (s,
1H), 8.57 (s, 2H), 8.0−7.72 (m, 48 H), 7.45−7.41 (m, 26 H), 7.07−6.94
(m, 25 H), 6.57 (t, 2 H, end group), 2.75 (t, 22 H), 2.54 (t, 12H) 1.68
(m, 48 H), 1.43−1.29 (m, 268 H), 0.90−0.88 (m, 104 H). FT-IR (KBr)
ν in cm−1: 2953, 2914, 2848, 1599, 1577, 1473, 1188, 1095, 1040, 963,
941, 793. Mn = 6367 by 1H NMR. From GPC data: Mn = 6.6 kDa, Mw =
13.3 kDa, and PDI = 2.01.
P9: 1H NMR (400 MHz, CDCl3-d1, 298 K) δ: 8.76 (s, 5 H), 8.65 (s,
2H), 8.60 (s, 2H), 7.99−7.71 (m, 114 H), 7.60−7.40 (m, 95 H), 7.02−
6.94 (m, 73 H), 6.54 (t, 2H, end group), 2.78−2.31 (m, 122H), 1.93−
1.57 (m, 229 H), 1.28 (m, 511 H), 0.92−0.88 (m, 1085 H), 0.65. FT-IR
(KBr) ν in cm−1: 2922, 2851, 2216, 1604, 1581, 1496, 1469, 1433, 1390,
1269, 1188, 1143, 1116, 1006, 960, 947, 860, 798, 777, 719, 692, 653,
613, 540. From GPC data: Mn = 7.2 kDa, Mw = 15.7 kDa, and PDI =
2.16.
P4: 1H NMR (400 MHz, CDCl3-d1, 298 K) δ: 8.76 (s, 1 H), 8.67 (s,
1H), 8.61 (s, 2H), 8.0−7.72 (m, 54 H), 7.47−7.32 (m, 26 H), 7.01−6.93
(m, 30 H), 6.54 (t, 2 H, end group), 2.74 (t, 25 H), 2.56 (t, 10H) 1.69
(m, 64 H), 1.49−1.26 (m, 294 H), 0.91−0.87 (m, 104 H). FT-IR (KBr)
Optical Properties of Solution State Oligomers and Copoly-
mers in Solution and Thin Film States. The absorption and
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Figure 3. (a) Optical band gap of copolymers P1−P7 and P9. (b) Variation of maximum emission wavelengths of copolymer in solution and thin film
states.
Figure 4. (a, c) Absorption and emission spectra of copolymer thin films, respectively. Right insets show the emission colors of copolymer thin films on
quartz slide upon UV light irradiation. (b) Emission spectra of thin films of P1 and P1 + Eu3+. The insets show the emission colors of P1 and P1 + Eu3+
upon UV light irradiation. (d) Emission colors of copolymer thin films (P1−P7 and P9) and P1 + Eu3+ in a CIE 1931 2° standard observer chromaticity
diagram.
emission spectra of thiophene oligomers in solution state are presented
in Figure S1. The comparative spectral data of oligo(3-octyl thiophenes)
[m1−m7 and m9, where the numbers stand for number of thiophene
units] and copolymers P1−P7 and P9 in chloroform solution are listed
in the Tables S1 and S2. The chloroform solution of copolymer P1
showed blue emission in very diluted state (2.77 × 10−12 mol/mL)
centered at 390 and 420 nm; upon increasing the concentration to 1.21
× 10−10 mol/mL, an additional aggregation induced emission appeared
at ∼480 nm, which was further red-shifted to ∼500 nm with an increase
in intensity upon further increasing the concentration (4.77 × 10−8 mol/
mL) displaying cyan color emission. The absorption spectra did not
show any noticeable shifts upon changing the concentrations (Figure
1a). This observed concentration-dependent red-shift is due to strong
interchain interactions and excimer-like behavior which are prevalent in
copolymers with large optical band gaps17 (Figures 1b and 2b). The
optical data of copolymers are presented in Table 1. All the copolymers
(P1−P7 and P9) showed a red-shift of the absorption and emission
maxima (λmax) in their optical spectra because of the extension of π-
conjugation lengths of the copolymer upon increasing the thiophene
units from one to nine (Figure 1c,d). Correspondingly, under UV light
copolymers (P1−P7 and P9) displayed blue to orange emission in
solution state (Figure 1e), and their emission colors in the CIE 1931 2°
Standard Observer chromaticity diagrams showed x, y coordinate values
of (0.20, 0.22) for 480 nm; (0.32, 0.52) for 522 nm; (0.39, 0.50) for 538
nm; (0.46, 0.52) for 551 nm; (0.43, 0.53) for 552 nm; (0.49, 0.49) for
560 nm; (0.46, 0.51) for 572 nm; and (0.50,0.48) for 598 nm,
respectively (Figure 1f).
The BPP unit of the copolymer main chain is known to coordinate
with red-emitting Eu(tta)3 (tta = 3-thenoyltrifluoroacetonate) and
green-emitting Tb(acac)3 (acac = acetylacetonate) complexes forming
nine-coordinated structures.9a−e Taking advantage of the metal
coordinating ability of the BPP units available in the copolymer main
chain, the emission color of copolymers was tuned by coordinating
metal complexes with Eu3+ and Tb3+ ions. For example, a very dilute
solution of P1 (4.4 × 10−12 mol/mL) showed blue color emission
(Figures 1b and 2a) and to this solution (4 mL) addition a 1:1 mixture of
THF solution of Tb(acac)3 and Eu(tta)3 (0.2 mL; 4.0 × 10−15 mol/mL
and 0.2 mL; 3.99 × 10−14 mol/mL, respectively) displayed a white color
light (Figure 2a) with CIE (x, y) coordinates 0.29, 0.35 (Figure 2d). The
emission spectra of Tb3+ ion exhibited sharp emissions at 490, 547, 585,
and 620 nm due to 5D4 → 7FJ (J = 3−6) f−f transitions and Eu3+ ion
displayed peaks at 581, 594, 612, 653, 705 nm due to 5D0 → 7FJ (J = 0−
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Figure 5. (a) FESEM micrographs of copolymer spheres self-assembled from P1 (scale bar is 2 μm). (b) TEM image of P1 spheres (scale bar is 0.5 μm).
(c, d) Noncontact mode AFM image of nano/microscale spheres and their height and diameter profiles. (e) Confocal fluorescence images of copolymer
spheres (P1−P7 and P9). (f) Emission colors of nano/microspheres containing copolymers solutions (under UV−vis light excitation).
4) f−f transitions.18 The most intense emission was observed for Tb3+
ion at 547 nm, which corresponds to the 5D4 → 7FJ transition. Among
the peaks corresponding to that of Eu3+ ion, the strongest emission was
Self-Assembly Studies of Copolymers. Copolymers (P1−P7
and P9) were self-assembled in a mixture of THF/H2O (2:1) solution.
In a typical self-assembly procedure, water (1 mL) was dropwise added
to a THF solution of P1 (2 mL; 1.1 × 10−7 mol/mL), and the solution
was kept undisturbed for 15 min to stabilize the growth of particles. A
similar procedure was followed to self-assemble P2−P7 and P9.
Illumination of the THF solution of P1−P7 and P9 with laser light
displayed a fine Tyndall effect, indicating the formation of solution-
stable nano/microstructures (see Figure S10). The electron microscopy
(FE-SEM and TEM) and AFM examination of P1 revealed the
formation of nano and microspheres (Figure 5a−d). FESEM micro-
graphs displayed several aggregated nanospheres (Figure 5a). TEM
micrographs of copolymer nanospheres displayed a relatively weak
contrast as typically observed for soft organic structures (Figure 5b).
AFM cross-section analysis of spheres showed that the diameter is in the
range of ca. 700 nm−1.2 μm (Figure 5c,d). The laser confocal
fluorescence micrographs of the solid microspheres and the nano/
microsphere containing solutions exhibited FL colors corresponding to
their emission wavelengths (Figures 5e and 5f, respectively). The self-
assembly of cyan to red emitting conjugated copolymer spheres is
possibly mediated by the π−π stacking interactions of the copolymer
aromatic units, thereby increasing the close packing of the hydrophobic
octyl chains on the thiophene rings forming sphere-like structures.
To study the influence of solvent vapor annealing on the copolymer
thin films (see Figure 4a,c), the films were exposed to vapors of THF/
H2O (2:1) solution in a closed vessel up to 10 h. The optical studies of
the annealed copolymer films showed insensitivity of all the copolymer
films to annealing, except for P1, which showed ∼7 and 15 nm blue-
shifts in the absorption and emission spectra, respectively, indicating
possible alteration of the copolymer chain packing (see Figures S5 and
S6). The observed blue-shift of annealed P1 film is probably due to
ordering of copolymer film akin to copolymer organization in
microspheres via solvent diffusion, relaxing the copolymer chains
allowing their movement. Correspondingly, the AFM examination of
the film before solvent vapor annealing exhibited a clean smooth surface,
while the film after annealing showed microstructures formation on the
surface (Figure S6). The comparative optical data of copolymers in
solution, microsphere, and thin film states are presented in Table 2. The
7
observed at 612 nm (5D0 → F2) due to induced electronic dipole
transition, which clearly indicates that the chemical environment around
Eu3+ ions does not have an inversion center.19 White emission was also
achieved by mixing highly concentrated solution of cyan emitting P1 (4
mL; 1.38 × 10−11 mol/mL) (Figures 1b and 2b) with THF solution of
Eu(tta)3 (0.5 mL; 1.1 × 10−10 mol/mL). Similarly, white radiation was
also obtained by simple mixing THF solutions of blue-emitting
copolymer P1 (2 mL; 4.4 × 10−12 mol/mL) and yellow emitting
copolymer P6 (2 mL; 2.27 × 10−11 mol/mL) in 1:1 ratio (Figures 2c and
2d) corresponds to CIE (x, y) coordinates of 0.30, 0.30.
The emission spectra of spin-coated (7 mg/1 mL CHCl3)
copolymers in thin film state exhibited a strong red-shift from green
(554 nm) to orange red emission (674 nm) compared to their solutions,
owing to molecular chain ordering (Figure 4a,c, right inset).17a,20 This
shift is generally observed for many conjugated polymer systems and is
generally inferred as the formation of J-aggregates.20 Likewise, the
optical band gap of the copolymers were also decreased with increasing
number of thiophene units in the main chain of copolymers P1−P7 and
P9 from 2.1 to 1.67 eV (Table 1 and Figure 3a). The CIE plot of
emission colors of copolymers in solid thin film state showed x, y
coordinate values of (P1: 0.42, 0.48) for 554 nm; (P2: 0.51, 0.46) for
560 nm; (P3: 0.47, 0.50) for 610 nm; (P4: 0.55, 0.44) for 618 nm; (P5:
0.51, 0.47) for 626 nm; (P6: 0.57, 0.41) for 635 nm; (P7: 0.55, 0.43) for
654 nm; and (P9: 0.54, 0.45) for 674 nm, respectively (Figure 4d).
To generate white emission in the solid state, a quartz slide spin
coated (300 μL from 6.6 × 10−7 mol/mL of P1 in CHCl3) with P1 film
was dipped in a methanol solution of Eu(tta)3 (c ∼ 6.9 × 10−8 mol/mL)
for 20 min. The intensity of the Eu3+ centered red phosphorescence [5D0
→ 7FJ (J = 0−4) transitions] was controlled by the amount of complex
(P1: Eu(tta)3) formation and adjusted according to the intensity of Iblue
/
Igreen emissions to attain good quality white color with CIE (x, y)
coordinates 0.29, 0.40 (Figure 4b,d). It is interesting to observe that the
purity of the emitted white color is close to standard coordinates for pure
white color (x = 0.33, y = 0.33).
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Table 2. Comparative Optical Data of Copolymers Solutions, Microspheres Containing Solutions, Microspheres, and Thin Films
solution state
microspheres solution
microspheres
spin-coated thin film state
polymer absorption λmax (nm) emission λmax (nm) absorption λmax (nm) emission λmax (nm) emission λmax (nm) absorption λmax (nm) emission λmax (nm)
P1
P2
P3
P4
P5
P6
P7
P9
318
475
522
538
551
552
560
572
598
319
397, 417, 480
464, 497
532
331
554
560
610
618
626
635
654
674
315, 390
309, 398
309, 406
317, 413
309, 432
309, 447
308, 459
318, 392
309, 399
310, 407
314, 428
309, 439
309, 447
305, 454
531
538
552
566
583
611
633
309, 399
309, 410
309, 415
317, 425
309, 436
309, 449
308, 477
540
556
567
580
612
636
Figure 6. (a, b) Emission spectra of microspheres containing copolymer solution and laser fluorescence confocal spectra of a bunch of microspheres.
Figure 7. (a) TEM image of Eu3+ coordinated P1 spheres; inset shows their corresponding confocal fluorescence microscopic image. (b) The
corresponding EDS spectrum exhibiting Eu3+ peaks. (c) Emission spectra of Eu3+ coordinated P1 spheres displaying near white emission in comparison
with pure Eu(tta)3 (λex = 365 nm). (d) CIE 1931 2° standard observer chromaticity diagram of white emitting spheres (x = 0.30, y = 0.40).
optical property of π-conjugated copolymers in the aggregated state
differs from those in the secluded chain state. The copolymer solution
containing nano/microspheres can be treated as an intermediate state
between a solution state and solid film state. Compared to dilute
nonaggregated polymer solution state, the copolymer nano/micro
spheres solution is a mixed state containing well-dispersed copolymer
particles and dilute nonaggregated copolymer solution (dispersion
medium), whereas the copolymer chains strongly aggregate with each
other in a solid film. The copolymer solution containing nano/
microspheres can be considered as a dispersed copolymer particle
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system. As a result of aggregation, the quenching efficiency was well
pronounced in cast films, and it decreased for nano/microspheres
solutions and the effect was not observed for copolymer in dilute
solution. The emission spectra for the copolymer solution containing
micro/nanospheres (Figure 6a) and several solid microspheres (Figure
6b) were very much similar.
AUTHOR INFORMATION
Corresponding Author
*E-mail: chandrasekar100@yahoo.com; rcsc@uohyd.ernet.in
(R.C.).
■
Notes
White-Emitting Nano/Microscale Copolymer/Inorganic Hy-
brid Spheres. In order to obtain white-color-emitting spheres, the
coordination chemistry on the self-assembled solid surface approach was
followed.9b−d First, the cyan-emitting copolymer sphere were grown in
THF/H2O solution of P1, as mentioned before. Second, by injecting a
THF solution of Eu(tta)3·(H2O)3 (0.02 mL; 1.0 × 10−6 mol/mL) to the
solution containing the spheres, followed by gentle shaking, a layer of a
nine-coordinated complex9a−e was formed on the surface of the spheres.
The possible mechanism of complex formation on the spheres is the
coordination of Eu(tta)3 with the surface-exposed BPP units via
diffusion through pores. Examination of the TEM bright-field images
obtained from the metal coordinated copolymer/inorganic hybrid
spheres exhibited an apparent dark contrast due to the presence of
Eu(III) complexes compared to light contrast displayed by pure P1
spheres (Figure 7a). In addition, the energy dispersive X-ray
spectroscopy analysis (EDS) performed on the surface of a sphere
clearly confirmed the presence of Eu ions (Figure 7b). In order to verify
the appearance of cyan and white colors from P1 spheres and Eu(tta)3
coordinated P1 spheres, respectively, scanning laser confocal
fluorescence microscopy measurements were performed (Figure 5e;
see P1 and Figure 7a inset). The topographic structural data were
directly coupled with the spectroscopic properties of the specimen
(Figure 7c). For excitation Ar+ (UV: 365 nm) laser was used. As
expected, the P1 spheres displayed a cyan color due to the mixing of blue
and green (aggregation induced) FLs (Figure 5e; see P1 and Figure 1b),
whereas P1 spheres coated with Eu3+ ion showed the FL spectrum
covering the whole visible region (400−700 nm) exhibiting a significant
white light (Figure 7c). The CIE (x, y) data provided the x, y values of
0.30; 0.40 for the white-emitting spheres which are in the range of
designated coordinates for ideal white light (x = 0.33; y = 0.33) (Figure
7d).
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This study was financially supported by the Max Planck Partner
Group with University of Hyderabad Grant (MPGA POLY
0006). YSLV thanks the CSIR-New Delhi for a SRF.
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CONCLUSIONS
■
We have successfully designed, synthesized, and characterized a
series of alternating copolymers based on dialkynyl-oligo(3-
octylthiophene) and tridentate bis(pyrazol)pyridine (BPP)
ligand. The light emission of these conjugated copolymers was
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achieve soft polymer structures displaying dissimilar colors by
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ASSOCIATED CONTENT
■
S
* Supporting Information
Experimental procedures for materials characterization and
measurement, NMR spectra of monomers and polymers, and
other characterization data. The Supporting Information is
available free of charge on the ACS Publications website at DOI:
10.1021/acs.macromol.5b01004.
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DOI: 10.1021/acs.macromol.5b01004
Macromolecules XXXX, XXX, XXX−XXX