End-group telechelic oligo- and polythiophenes by "click" reactions: Synthesis and analysis via LC-ESI-TOF MS

Article abstract of DOI:10.1021/ma1016727

End-group-modified poly(3-hexylthiophenes) (P3HT) with complex hydrogen-bonding moieties have been prepared starting from telechelic alkyne-functionalized P3HT via a copper(I) catalyzed azide/alkyne "click" reaction. The final polymers are projected to ar

Full text of DOI:10.1021/ma1016727

8436 Macromolecules 2010, 43, 8436–8446
DOI: 10.1021/ma1016727
End-Group Telechelic Oligo- and Polythiophenes by “Click” Reactions:
Synthesis and Analysis via LC-ESI-TOF MS
Claudia Enders, Susanne Tanner, and Wolfgang H. Binder*
Chair of Macromolecular Chemistry, Institute of Chemistry, Division of Technical and
Macromolecular Chemistry, Faculty of Natural Sciences II (Chemistry and Physics),
Martin-Luther University Halle-Wittenberg, Von-Danckelmann-Platz 4, D-06120 Halle, Germany
Received July 25, 2010; Revised Manuscript Received August 27, 2010
ABSTRACT: End-group-modified poly(3-hexylthiophenes) (P3HT) with complex hydrogen-bonding moieties
have been prepared starting from telechelic alkyne-functionalized P3HT via a copper(I) catalyzed azide/alkyne
“click” reaction. The final polymers are projected to arrange into pseudoblock copolymers consisting of
alternating donor/acceptor polymers for application in solar cell materials. Starting from a bromine-telechelic
P3HT (Mn=2000 g/mol; Mw/Mn=1.2) prepared via the McCullough method followed by additional
bromination reaction yielding telechelic P3HTs with (80% Br/Br; 20% H/Br) end groups, the respective
R,ω-(trimethylsilyl)ethynyl-P3HTs were prepared via Sonogashira coupling reactions. Analysis of the end groups
of the alkynyl-telechelic P3HT species was achieved by use of LC-ESI-TOF methods for the first time, proving the
formation of ∼59% (ethynyl/ethynyl) and ∼40% (ethynyl/H) species within the R,ω-(trimethylsilyl)ethynyl-
P3HTs, with only minor amounts (∼1%) of the respective (H/H)-modified species. Additionally, MALDI
methods were used for a qualitative assessment. Subsequent azide/alkyne “click” reaction with either 1-(6-
azidohexyl)thymine or 5-((4-azidobenzoyl)amino)-N,N0-(6-(octanoylamino)pyridin-2-yl)isophthalamide using
CuI, CuBr(PPh3)3, or CuI P(OEt)3 as catalyst yielded the final products with attached hydrogen bonds as
3
judged by LC-ESI-TOF methods. The described method opens an access toward supramolecular P3HT polymers
with hydrogen-bonding moieties.
Introduction
One of the first successful end-group functionalizations of
P3HT was reported by Janssen et al.31 transforming the bromine
The performance of polymeric organic semiconductors has been
studied intensely via the concept of the bulk-heterojunction solar
cells,1,2 often relying on supramolecular ordering concepts of
oligomeric and polymeric building blocks.3-10 Mostly poly-
(3-hexylthiophene)s (P3HT) or p-phenylenevinylene(s) have been
used due to their favorable optoelectronic properties, good solu-
bility, and solution processability. As these polymers are also
envisioned as a replacement for silicon-based organic field effect
transistors (OFETs), a wide range of structural variations has been
studied, many of them addressing the molecular ordering of P3HT
polymers in the solid state.11 Therefore, synthetic approaches
toward defined side-chain and end-group-functionalized regiore-
gular P3HTs have been studied extensively,12-33 most of them on
the basis of the Grignard metathesis method (GRIM).34-36 Being
based on a Kumada-type coupling reaction,15 this chain-growth
polycondensation reaction yields P3HT polymers with (Br/H) end
groups, if the conventional initiation via, for example, 2-bromo-
5-chloromagnesio-3-hexylthiophene together with 2-bromo-
3-hexyl-5-iodothiophene as monomer and Ni(dppp)Cl2 (dppp =
propane-1,3-diylbis(diphenylphosphine) as catalyst are used.
GRIM polymerization by direct addition of functionalized
Grignard reagents (R0MgX) or initiation with functionalized
nickel-aryl complexes can yield end-group-functionalized P3HT
polymers as either monocapped (R0) or dicapped macromolecules
(R0/R0), often as a mixture with unfunctionalized, fully hydro-
genated (H/H) polymers, or the respective starting polymers
containing (Br/H or Br/Br) end groups. Mechanistically, these
mixtures are generated by incomplete coupling reactions, or via
chain transfer and subsequent Br/Mg exchange.15
end groups of P3HT into 5-(trimethylsilyl)-2-thienyl end groups by
adding Grignard reagents and a fresh amount of the Ni(dppp)Cl2
catalyst to the polymerization reaction of P3HT. Another, similar
method by Liu et al.30 furnished the respective OH-substituted
P3HT polymers by reaction with THP-protected-thienyl-zinc
compounds. Subsequently, many authors12,15-17,21,23,24,26,30,31
have extended this method using a wide variety of different
Grignard reagents for quenching the GRIM polymerization,
proving the (often mixed) end groups by 1H NMR and
MALDI-TOF MS. If alkynyl end groups12,26 are introduced,
subsequent azide/alkyne “click” reactions can be used to
obtain triazole end-group-funtionalized polymers in a mixture
with nonfunctionalized (Br/H; H/H) polymers.12,13,16 Addition-
ally, P3HT-containing block copolymers can be prepared, for
example, yielding P3HT-PS, P3HT-PMMA, or P3HT-PLA block
copolymers.18,19,21,24 The direct use of nickel-based initiators12,33
(R0-Ni(PPh3)2Br) yielded (siloxyphenyl)- or TMS-alkynyl-phenyl-
capped P3HTs as a mixture of several isomeric compounds,
either with the desired (R0/H; R0/Br) end groups or with capped
species with the end groups of the respective starting materials
(Br/Br; Br/H; H/H).12
The present publication aims at the synthesis of functionalized
P3HTs with hydrogen-bonding moieties to study ordered supra-
molecular P3HT polymers for solar cell applications (Scheme 1).
Our synthetic concept is based on a GRIM polymerization with
successive end-group functionalization via azide/alkyne “click”
chemistry and Sonogashira reaction, thus allowing us to achieve
an indirect functionalization of the respective P3HTs with a
multitude of hydrogen-bonding moieties in a modular fashion.
An important issue concerns the subsequent characterization and
*Corresponding author. E-mail: wolfgang.binder@chemie.uni-halle.de.
pubs.acs.org/Macromolecules
Published on Web 09/21/2010
r 2010 American Chemical Society

Article
Macromolecules, Vol. 43, No. 20, 2010 8437
Scheme 1. Structures of Oligo- and Polythiophenes Obtained after Azide/Alkyne “Click” Reaction
quantification of the individually functionalized P3HT polymers by
LC-ESI-TOF methods and additional mass spectrometric methods,
such as MALDI mass spectrometry. Especially LC-ESI-TOF
methods are intensively investigated as, surprisingly, this method
has not been used for the analysis of P3HTs up to now.
diode array detector and a Nova Pak C18 column by Waters
˚
(60 A, 4 μm, dimension 3.9 ꢀ 150 mm), which are temperate at
25 °C. The HPLC run for 1-(3-hexylthymine)-4-(5-(5-(1-(1-(3-
hexylthymine)-1H-1,2,3-triazol-4-yl)thiophen-2-yl)thiophen-2-
yl)thiophen-2-yl)-1H-1,2,3-triazole (1a) was performed with a
MeOH-MeCN gradient of 25:75 to 99:1 in 30 min and detected
at a wavelength of 200 nm. The sample was prepared as follows
1 mg/1 mL in MeCN:MeOH (1:1), afterward 5 μL of this sample
solution was injected for one measurement. The chromato-
graphic separation of all P3HTs was done with a MeCN-THF
gradient of 90:10 to 20:80 in 70 min and detected at 400 nm using
a sample concentration of 5 mg/1 mL in THF and an injection
volume of 5 or 10 μL. The MS measurement was supported by a
postcolumn injection of MeOH (300 μL/h). Afterward the
LC-MS data were analyzed using DataAnalysis 4.0. The device
specific mass accuracy of these recorded spectra is 10 ppm. For a
rough quantification we sum up the MS trace area of a single
species and divided it through the sum of whole analyzed MS
trace area (100%) to yield a percentage. If we detected more than
one species, we calculated the ratio between them, through a
sum up of the intensities of the isotopic pattern of one single
polymer species. The MALDI-TOF MS measurements were
obtained on an autoflex smartbeam III by Bruker Daltonics.
The instrument is equipped with a pulsed N2 laser (337 nm, 0 ns
pulse) and a time-delayed extracted ion source. MALDI spectra
were recorded using the positive-ion linear (LP) and the reflector
(RP) modus. The accelerating voltage was 20 kV, and the low
mass gate was 400.0 m/z. For the calibration of the MALDI
spectra PEG 2000 standard (polymer source Inc.) was used with
DCTB and LiTFA in the ratio 100:10:1. Polymer samples were
prepared by combining the matrix and the analyte in a 100:10
ratio. For the polymer with bromine end groups terthiophene
was used as matrix; furthermore dithranol after the Sonogashira
reaction and DCTB after “click” reaction were applied. The
cationization salt solution of 20 mg/mL AgTFA in THF was
added to some samples in a 100:1 ratio of matrix: salt.
Experimental Section
Materials. Tetrahydrofuran (THF) was predried over KOH
and freshly distilled over Na and benzophenone. Triethylamine
was predried by refluxing over KOH and finally freshly distilled
over CaH2. All reagents like tert-butylmagnesium chloride (2 M
in ether), (trimethylsilyl)acetylene, tetrakis(acetonitrile)copper(I)
hexafluorophosphate, copper(I) iodide, bromotris(triphenylphos-
phine)copper(I), tetra-n-butylammonium fluoride (1 M in THF),
[1,3-bis(diphenylphosphino)propane]nickel(II) chloride (Ni(dppp)-
Cl2), and bis(triphenylphosphino)palladium(II) dichloride (PdCl2-
(PPh3)2) were purchased from Sigma Aldrich and used without
further purification. The copper catalyst CuII P(OEt)3 was synthe-
30
sized according to the literature,37 also 5,5 -bis((trimethylsilyl)-
ethynyl)-2,20:50,200-terthiophene (5) and 5,500-diethynyl-2,20:50,200-
terthiophene (6) were synthesized on the basis of the literature.38-40
The synthesis of 1-(6-azidohexyl)thymine (7a) and 5-((4-azido-
benzoyl)amino)-N,N0-(6-(octanoylamino)pyridin-2-yl)isophthal-
amide (7b) was done according to the literature.41-44 Tetra-
hydrofuran (THF), methanol, and acetonitrile with HPLC
grade were purchased from Sigma Aldrich. The MALDI-TOF
matrices, dithranol, trans-3-indoleacrylic acid (IAA), trans-
2-[3-(4-tert-butylphenyl)-2-methyl-2-propenylidene]malononitrile
(DCTB), and the salt sodium trifluoroacetate (NaTFA), were
purchased from Sigma Aldrich. Terthiophene used as the MALDI
matrix was synthesized according to the literature.40
Measurements. 1H NMR (400 MHz) and 13C NMR (100 MHz)
spectra were recorded on a Gemini 2000 FT-NMR spectrometer.
For data interpretation of spectra MestRecC 4.7.0.0 was used. All
chemical shifts (δ) are given in parts per million (ppm) relative to
Me4Si (TMS); coupling constants (J) are given in Hertz. All NMR
samples were dissolved in CDCl3 or DMSO-d6, unless otherwise
stated. Number-average molecular weights (Mn) and molecular
weight distribution were measured by a Viscotek GPCmax
VE2001 gel-permeation chromatography (GPC) unit with THF as
eluent in a flow rate of 1 mL/min and an injection volume of 100 μL
using a refractive index detector (VE 3580 RI, Viscotek) and
a column set HHR-HGuardþGMHHR-N (Viscotek, mixed bed).
An external calibration was made with polystyrene standard
(1050-115 000 g/mol).
Microwave irradiation supported reactions were performed
on a Discover LabMate by CEM Mikrowellen. For these
reactions 10 mL vials with an IntelliVent snap-on cap sytem
were used.
Synthesis. Poly(3-hexylthiophene) (9)23. In a well dried
three-necked flask 2,5-dibromo-3-hexylthiophene (8) (326 mg,
1 mmol) was dissolved in 5 mL of freshly distilled dry THF, and
the mixture was stirred under an atmosphere of argon. tert-
Butylmagnesium chloride (0.5 mL, 1 mmol) was added via a
syringe, and the mixture was stirred for 2 h at room temperature.
Subsequently, a suspension of Ni(dppp)Cl2 (45.2 mg, 0.083
mmol) in 1 mL of dry THF was added in one portion. The
mixture was stirred for 10 min at room temperature, and 400 μL
of a 1 M Br2/THF solution was added under an atmosphere of
The LC-ESI-TOF (electrospray-ionization time-of-flight)
measurements were performed with a microTOF II focus
(Bruker Daltonics) equipped with an ESI source and combined
with an Elite LaChrom HPLC by Hitachi/VWR setup with a

8438 Macromolecules, Vol. 43, No. 20, 2010
Enders et al.
argon. The reaction mixture was stirred for an additional 5 min
and then poured to 100 mL of methanol to precipitate the
polymer. After centrifugation, the polymer was dried under
high vacuum (yield = 105 mg, 32%). 1H NMR (CDCl3, J (Hz),
400 MHz): δH 6.95 (m, 1H), 2.75 (m, 2H), 1.59 (m, 2H), 1.32 (m,
6H), 0.88 (m, 3H). GPC: Mn = 2000 g/mol, Mw/Mn = 1.20.
R,ω-(Trimethylsilyl)ethynyl-P3HT (10). Poly(3-hexylthiophene)
(9) (30 mg, 0.015 mmol), PdCl2(PPh3)3 (5.2 mg, 7.45 ꢀ10-3
mmol), CuI (1.4 mg, 7.45ꢀ10-3 mmol), and (trimethylsilyl)-
acetylene (41 μL, 0.3 mmol) were dissolved in 4 mL of dry
triethylamine, and the solution was sealed in a 10 mL vial with a
IntelliVent snap-on cap. The reaction mixture was stirred at 90 °C
for 2.5 h in a cavity resonator (15 W). After cooling to room
temperature the mixture was poured in 150 mL of chloroform. The
organic phase was washed with 50 mL of NH4Cl solution and 50
mL of brine. After drying over Na2SO4, the solvent was evaporated
to dryness. The product was dried under high vacuum (yield = 32
mg, 95%). 1H NMR (CDCl3, J (Hz), 400 MHz): δH 6.96 (s, 12H),
2.79 (m, 24H), 1.60 (m, 24H), 1.32 (m, 72H), 0.90 (m, 36H), 0.25
(s, 9H), 0,06 (s, 18H). GPC: Mn = 2200 g/mol, Mw/Mn = 1.09.
Semitelechelic Thymine-Capped P3HT 2 via “Click” Reaction.
R,ω-(Trimethylsilyl)ethynyl-P3HT 10 (17 mg, 11.2 ꢀ 10-3mmol)
was dissolved in 3 mL of dry THF in a 10 mL vial with a IntelliVent
snap-on cap and degassed by argon. Tetra-n-butylammonium
fluoride (34 μL, 0.034 mmol) was added and stirred at room
temperature for 10 min. Subsequently 1-(6-azidohexyl)thymine
(7 mg, 0.028 mmol) 7a,45 copper(I) iodide (10.4 mg, 11.2 ꢀ
10-3mmol), diisopropylethylamine (5 μL), and 0.1 mL of
2-propanol/H2O (1:1) were added to this solution and stirred at
120 °C for 1.5 h in cavity resonator (300 W). The reaction mixture
was poured in 50 mL of chloroform and washed with 30 mL of
NH4Cl solution and 30 mL of brine. The organic phase was dried
over Na2SO4, and the solvent was evaporated to dryness. Finally,
the product was dried under high vacuum (yield = 29.3 mg, 92%).
1H NMR (CDCl3, J (Hz), 400 MHz): δH 6.96 (s, 22H), 2.79 (m,
44H), 1.60 (m, 44H), 1.32 (m, 132H), 0.90 (m, 66H). GPC: Mn =
3100 g/mol, Mw/Mn = 1.33.
and the solvent was evaporated to dryness. The product was dried
under high vacuum (yield = 69 mg, 89%). 1H NMR (DMSO-d6,
J (Hz), 400 MHz): δ = 11.1 (s, 2H, -NH thymine), 8.5 (s, 2H,
dCH- triazole), 7.4 (s, 2H, arom. H thiophene), 7.3 (m, 6H, 4H
3
arom.H thiophene þ 2H CHd thymine), 4.3 (t, 4H, J(H,H) =
6.64, CH2- triazol), 3.3 (t, 4H, 3J(H,H) = 7.06, CH2- thymine),
1.8 (m, 4H, -CH2-), 1.7 (s, 6H, -CH3 thymine), 1.5 (m, 4H,
-CH2-),1.3(m, 8H, -CH2-).13CNMR(CDCl3,100MHz):δ=
163.8, 150.5, 140.9, 140.8, 134.8, 134.4, 132.1, 124.7, 124.6, 124.5,
120.5, 108.1, 49.4, 46.9, 29.3, 28.2, 25.4, 25.1, 11.8.
Hamilton-Receptor Capped Terthiophene (1b). 5,50-Bis((tri-
methylsilyl)ethynyl)-2,20:50,200-terthiophene (20 mg, 0.045 mmol)
(5) was dissolved in 2 mL of dry THF in a 10 mL vial with a
IntelliVent snap-on cap, and the solution was degassed by argon.
Tetra-n-butylammonium fluoride (91 μL, 0.091 mmol) was added,
and the mixture was stirred at room temperature under an argon
atmosphere for 30 min. Subsequently, 5-((4-azidobenzoyl)amino)-
N,N0-(6-(octanoylamino)pyridin-2-yl)isophthalamide (69 mg, 0.091
mmol) (7b),41,42,44 bromotris(triphenylphosphine)copper(I) (7.6
mg, 8.2 ꢀ 10-3 mmol), diisopropylethylamine (40 μL), and 0.1
mL of 2-propanol/H2O (1:1) were added to this solution, and the
resulting mixture was stirred at 90 °C for 20 min in a cavity resonator
(100 W). The reaction mixture was poured into chloroform and
washed with 50 mL of NH4Cl solution and with 50 mL of brine. The
crude product was purified by column chromatography (CHCl3/
MeOH, 10:0.3). The product was dried on high vacuum (yield = 20
mg, 24%). 1H NMR (DMSO-d6, J (Hz), 400 MHz): δ = 10.8 (s,
2H, -NH), 10.42 (s, 4H, -NH), 10.34 (s, 4H, -NH), 9.41 (s, 2H,
dCH- triazole), 8.20 (m, 4H, arom. H thiophene), 8.04 (s, 2H,
arom. H thiophene), 8.31 (m, 6H, arom. H), 8.59 (m, 8H, arom. H),
7.56 (m, 12H, arom. H), 2.4 (m, 4H, -CH2), 1.58 (m, 4H, -CH2-),
1.17 (m, 18H, -CH2-), 0.85 (m, 12H, -CH3). 13C NMR (CDCl3,
100 MHz): δ = 172.7, 165.6, 151.04, 150.5, 140.5, 135.2, 133.6,
132.7, 132.5, 132.5, 131.9, 131.9, 130.1, 129.9, 129.2, 129.1, 36.6, 31.6,
29.0, 28.9, 25.4, 22.5, 14.4.
Results and Discussion
Semitelechelic Hamilton-Capped P3HT 3 via “Click” Reac-
tion. R,ω-(Trimethylsilyl)ethynyl-P3HT (10) (18 mg, 8.2 ꢀ
10-3mmol) was dissolved in 3 mL of dry THF in a 10 mL vial
with a IntelliVent snap-on cap, and the solution was degassed by
argon. Tetra-n-butylammonium fluoride (25 μL, 0.025 mmol)
was added, and the mixture was stirred at room temperature
for 10 min. Subsequently, 5-((4-azidobenzoyl)amino)-N,N0-(6-
(octanoylamino)pyridin-2-yl)isophthalamide (15.6 mg, 0.021
mmol) (7b),41,42,44 bromotris(triphenylphosphine)copper(I)
(7.6 mg, 8.2 ꢀ 10-3mmol), diisopropylethylamine (5 μL), and
0.1 mL of 2-propanol/H2O (1:1) were added to this solution, and
the resulting mixture was stirred at 90 °C for 1.5 h in a cavity
resonator (100 W). The reaction mixture was poured to 50 mL of
chloroform and washed with 30 mL of NH4Cl solution and with
30 mL of brine. The organic phase was dried over Na2SO4 and
the solvent was evaporated to dryness. Finally, the product was
dissolved in a small amount THF and precipitated in methanol,
the precipitate was dried under high vacuum (yield = 14 mg,
Our current approach toward functionalized P3HT polymers
with pendant hydrogen bonds is based on (a) the synthesis of
bromine-capped P3HT via the GRIM method and (b) the
subsequent transformation into alkynyl-capped P3HT via Sono-
gashira-type reactions followed by (c) the azide/alkyne “click”
reaction46-51 to attach the respective hydrogen-bonding moi-
eties. An important aspect of this work also concerns the exact
analysis of the expected polymer mixtures by LC-ESI-TOF and
also MALDI methods, which are generated by the inherent side
reactions during the GRIM polymerization. As LC methods
allow a rough quantification of individual oligomeric and poly-
meric species, this method was favored over the often used
MALDI methods, which especially in the case of polar end
groups lead to highly large errors in (semi)quantification of
individual polymeric compounds.
Model Reactions on Oligo(thiophene)s. As a starting point,
the synthetic approach was probed on the unsubstituted
terthiophene 4 to check the quality of the synthetic pathway
and, additionally, get a reference compound for further
spectroscopic and chromatographic investigations. Thus
(see Scheme 2) we synthesized terthiophene as a central
building unit via Kumada cross coupling reaction starting
from the mono- and bivalent bromine thiophene. To intro-
duce alkynyl end groups, we use the efficient Pd-catalyzed
Sonogashira reaction based on the bromine-capped terthio-
phene 439 to yield the bicapped (trimethylsilyl)ethynyl
terthiophene 5 in 63%. As the deprotected compound 6
proved unstable in air and under light (formation of a brown
insoluble precipitate), no further workup procedures of the
alkynyl-bicapped terthiophene 6 were done, and we directly
proceeded with the functionalization via a copper-catalyzed
1
62%). H NMR (CDCl3, J (Hz), 400 MHz): δH 6.96 (s, 21H),
2.79 (m, 42H), 1.60 (m, 42H), 1.32 (m, 126H), 0.90 (m, 63H).
GPC: Mn = 3300 g/mol, Mw/Mn = 1.17.
1-(3-Hexylthymine)-4-(5-(5-(1-(1-(3-hexylthymine)-1H-1,2,3-tria-
zol-4-yl)thiophen-2-yl)thiophen-2-yl)thiophen-2-yl)-1H-1,2,3-triazole
(1a). 5,500-Diethynyl-2,20:50,200-terthiophene (30 mg, 0.101 mmol)
(6), 1-(6-azidohexyl)thymine (56 mg, 0.222 mmol) (7a),45 tetrakis-
(acetonitrile)copper(I) hexafluorophosphate (3.7 mg, 0.01 mmol),
and diisopropylethylamine (40 μL) were dissolved in 2 mL of
acetonitrile under an inert gas atmosphere. The reaction mixture
was degassed, and additionally a freeze-thaw cycle was done three
times to remove oxygen. The suspension was stirred for 16 h at
50 °C. Afterwards the solvent was evaporated and the residue was
poured into chloroform and washed with 50 mL of NH4Cl solution
and with 50 mL of brine. The organic phase was dried over Na2SO4,

Article
Macromolecules, Vol. 43, No. 20, 2010 8439
Scheme 2. Functionalization of Bivalent Bromine Terthiophene (4) via Sonogashira and Subsequent “Click” Reactiona
a (a) (Trimethylsilyl)acetylene, Pd(PPh3)2Cl2, CuII, diisopropylamine, 75 °C, 15 h (yield 63%). (b) K2CO3, MeOH, RT, 20 h (yield 92%).
(c) CuIPF6(CH3CN)4, R0-N3 (7), diisopropylethylamine, CH3CN, 50 °C, 16 h (yield: 1a = 89% 1b = 24%).
Scheme 3. Polymerization of 2,5-Dibromo-3-hexylthiophene (8) via GRIM Reaction and the Postfunctionalization via Sonogashira and Subsequent
“Click” Reactiona
a (a) tert-Butylmagnesium chloride, THF, Ni(dppp)Cl2 (yield = 32%; GPC Mn = 2000 g/mol, Mw/Mn = 1.20). (b) (Trimethylsilyl)acetylene,
Pd(PPh3)2Cl2, CuII, triethylamine, 90 °C, microwave 15 W (yield = 95%; GPC Mn = 2200 g/mol, Mw/Mn = 1.09). (c) TBAF, THF, RT, 10 min,
Cu(I)-cat, R0-N3 (7), diisopropylethylamine, THF, 120/90 °C, 300/100 W, 0.5-1.5 h (yield: 2 = 92%, 3 = 62%).
1,3-dipolar cycloaddition reaction to generate the bicapped
terthiophene 1a in a yield of 89%. The purity of the product
was established by NMR spectroscopy and LC-ESI-TOF
mass spectrometry (see Supporting Information, Figures S3
and S4). In a similar manner, other hydrogen-bonding
moieties such as those depicted in Scheme 2 were attached
to the terthiophene unit, yielding the respective functional-
ized terthiophene 1b in yields of up to 24%.
NMR spectroscopy, both MALDI-mass spectrometry and
ESI-TOF methods were applied, as reported previously.55
According to ESI-TOF and MALDI-TOF mass spectro-
metry (see Figure 1) a mixture of Br/Br-capped 9a and Br/H
capped poly(3-hexylthiophene) 9b were generated. As both
methods did not allow a direct quantification of the indivi-
dual species in the direct measurement modes, LC-ESI-TOF
methods were probed before further synthetic steps were
undertaken.
Polymer Synthesis and Analysis via Mass Spectrometry.
The cross coupling of 3-substituted thiophene monomers via
organomagnesium52 or organozinc compounds53 yields re-
gioregular poly(3-hexylthiophene) (HT-P3HT) in over 98%
efficiency, as described via GRIM polymerization by
McCullough and co-workers.54 Thus our synthetic approach
is similar to the one developed for the terthiophene 4, relying
on a series of Sonogashira reactions followed by the attach-
ment of the hydrogen-bonding moieties via the azide/alkyne
“click” reaction. We therefore started from 2,5-dibromo-3-
hexylthiophene (8) obtaining regioregular poly(3-hexylthio-
phene) 9 (see Scheme 3). To achieve a more defined end-
group pattern, conventional GRIM polymerization was
conducted with/without a quenching reaction using Br2/
THF solution to favor the introduction of bromine end
groups (H/Br; Br/Br) into the polymer at the end-group
positions. As the analysis of the respective polymeric mixture
(Mn = 2020 g/mol; Mw/Mn = 1.2) cannot be achieved by
The LC-ESI-TOF measurements of the poly(3-hexylthio-
phene) (9) were probed using conditions reported before by
Langeveld-Voss et. al.31 who used LC methods in junction
with MALDI-TOF analysis of 5-(trimethylsilyl)-2-thienyl
end-capped P3HTs. However, the measurements needed an
additional optimization of the ESI-TOF measurements be-
cause of the difficult ionization of poly(3-hexylthiophene)
with increasing chain length. As a first step to probe the
optimal molecular weight for ionization via ESI, we there-
fore prepared P3HTs (9) with different molecular weights
ranging from 4 ꢀ 103 to 1 ꢀ 104 g/mol (see Supporting
Information, Table S1, Figures S5-S8) and measured them
via ESI-TOF MS using direct injection in the presence of
silver acetate or methanol to achieve an optimal ionization.
The experiments showed that polymers with higher molecu-
lar weights ((6-9) ꢀ 103 g/mol) are not desorbed well despite
additional postcolumn injection of silver solution and

8440 Macromolecules, Vol. 43, No. 20, 2010
Enders et al.
Figure 1. (a) ESI-TOF mass spectra (direct injection) and (b) MALDI-TOF mass spectra of the poly(3-hexylthiophenes) 9, demonstrating the
respective Br/Br (9a) and Br/H species (9b). (c) Isotopic pattern of P3HT6(Br/Br)-9a (M = C60H84S6Br2, Mcalc = 1154.33 g/mol) as [M]þ• adduct.
(d) Isotopic pattern of P3HT11(Br/Br)-9a (M = C60H84S6Br2, Mcalc = 1154.33 g/mol) as [M þ NH4]þ adduct. (e) Isotopic pattern of P3HT6(Br/H)-9b
(M = C60H85S6Br, Mcalc = 1076.42 g/mol) as [M]þ• adduct. (f) Isotopic pattern of P3HT11(Br/H)-9b (M = C90H127S9Br, Mcalc = 1574.66 g/mol) as
[M þ Li]þ adduct. (g) Isotopic pattern of P3HT9(Br/H)-9b (M = C90H127S9Br, Mcalc = 1574.66 g/mol) as [M þ NH4]þ adduct.
methanol as solvent. Thus polymer series with defined end-
group structures of H/H, H/Br, and Br/Br could be identified
with a molecular weight of <4000 g/mol, showing a maximum
of desorption in the mass range of 1800 m/z. Therefore, P3HT
with a molecular weight of ∼2000 g/mol displayed a satisfying
ionization and also excellent HPLC separation for an optimal
analysis of the end-group structure. Thus the directly prepared
polymers were purified by repeated precipitations into methanol
being then subjected to GPC measurements (Mn = 2000 g/mol;
Mw/Mn=1.15-1.20) and LC-ESI-TOF or MALDI-TOF mass
spectrometry.
The LC measurements of 9 (see Figure 2) yielded an excellent
separation of the low-molecular weight species (n = 5-18),
also revealing species with different end-groups (n = 5-13)
when a gradient of THF and acetonitrile was used. However, at
chain lengths above n = 13, no separation of the individual end-
group-modified species could be achieved. Thus each separated
peak represents a poly(3-hexylthiophene) (P3HTn) with a spe-
cific repeating unit (n) and an end-group structure either (Br/H)
or (Br/Br), which could be proven by analysis of the respective
ESI-TOF mass spectra and the subsequent comparison of
measured and simulated isotopic pattern (see Figure 2b/2c).
To achieve an idea about the amounts of the individual species
9a and 9b, a rough quantification via integration of the respec-
tive peak areas in the MS trace was achieved. This results in a
composition of ∼80% Br/Br 9a and 20% Br/H 9b as end
groups, if Br2/THF (0.4 equiv, 1 M solution) was used at the
end of the GRIM reaction. In contrast, a conventional GRIM
reaction without the final addition of Br2/THF after the poly-
merization reaction yielded a polymer with ∼10% H/H, 40%
monovalent (Br/H), and 50% bivalent (Br/Br) end-group
species.
Additionally, we analyzed polymers 9 with MALDI-TOF
mass spectrometry to compare the two different techniques
(desorption and ionization) according to an ideal analysis of
the end-group functionalization on P3HT. The MALDI
spectra in Figure 1b show four different main series, which
could be identified as P3HT with Br/Br and Br/H end groups
as radical cation and NH4þ adduct. It should be mentioned
that many authors23,26,55 have investigated their end-group
compositions on P3HT often via MALDI-TOF measure-
ments and reported about quantification values that were
not explained and verified. Normally, MALDI measure-
ments cannot be quantified directly as selective ionization
may take place leading to strong deviation of the peak
intensities from the actually present amounts. Therefore, in
recent years a method for a (semi)quantitative relationship
between different end-group polymer species and their de-
sorption has been developed by us56 and others,57-59 which is
based on the addition of a defined polymer as internal
standard with similar or equal molecular properties to one
of the polymer species in the analyzed mixture. We examined
a mixture of P3HT-9 (H/Br, Br/Br) and pure P3HT-11 (H/H
as internal standard) against desorption of the different end-
group species to yield a correction factor based on the
individual sensitivity of end-group species (see Supporting
Information, Tables S2-S4).
According to the semiquantification methods we calcu-
lated the total signal intensity It from the sum of intensities of
one isotopic pattern (one polymer end-group species) multi-
plied with their repeating unit (eq 1).
X
It ¼
IS nunit
3
ð1Þ

Article
Macromolecules, Vol. 43, No. 20, 2010 8441
Figure 2. (a) HPLC chromatogram of P3HT-9 at 400 nm with different fractions. Two fractions were picked out and simulated. (b) Isotopic pattern of
P3HT7(Br/Br)-9a (M = C70H98S7Br2, Mcalc = 1320.41 g/mol) as [M]þ• adduct. (c) Isotopic pattern of P3HT8(Br/H)-9b (M = C80H113S8Br1, Mcalc
=
1408.58 g/mol) as [M]þ• adduct.
where ΣIS is the summed up intensity of a single isotopic
pattern, nunit is the number of repeating unit, and It is the
total signal intensity of polymer with one specific end group.
A plot of these signal intensities versus weight ratio of the
polymer mixture with the internal standard results in two
different correction factors (see Supporting Information,
Figures S10 and S11). The first analysis of the MALDI
spectra results in an end-group composition of 4% H/H,
53% H/Br, and 43% Br/Br end-group species without an
intensity correction. Therefore, we corrected the ratio of H/
H to H/Br with the factor 7.4 to yield 77.0% of H/Br species,
also the ratio between H/H to Br/Br was corrected with a
factor of 2.6 to get 22.2% of Br/Br species. The intensity
correction yielded a new end-group composition of 0.8% H/
H, 77.0% H/Br, and 22.2% Br/Br polymer species. It now
shows a significantly different end-group distribution in the
polymer backbone in comparison to the ESI-TOF measure-
ments (20% H/Br, 80% Br/Br). Thus obviously polymers
with H/Br end group are overestimated in the MALDI
methods due to their preferred desorption.
Table 1. Sonogashira Reaction of P3HT (9) Synthesized via GRIM
Polymerization with an Expected Molecular Weight of 2000 g/mol
(GPC: Mn = 2020 g/mol, Mw/Mn = 1.2)a
reaction conditions
reaction
mol %b
microwave
entry power (W)
time
(min)
10a 10b 10c 9a
9b
11
56
12
1
1d
2
0
15
3 days
30
150
30
30
150
30
0.2 22.2
1.1c 20.5c
8c 41c
29
10
40
3
4
15
25
59
44
49
43
40
44
14.4 40
1.2c
5
6
35
35
43
47
52
43
9
10
8
12
100
7
100
100
100
8e
9
30
360
a ESI-TOF MS: end-group distribution Br/Br = 80%, H/Br = 20%.
b End-group distribution determined via ESI-TOF MS. c Incomplete
reaction determined via ESI-TOF MS. d Reaction carried out in diiso-
propylamine at 75 °C for 3 days. e Solvent mixture of diethylamine and
DMF in a ratio of 2: 1.
Sonogashira Reactions. As now the different species of the
poly(3-hexylthiophenes) 9a and 9b were analyzed, successive
Sonogashira reactions were probed for the attachment of
the terminal acetylene moiety (Eth) by reaction with TMS-
acetylene. We tested the reaction condition on the model com-
pound terthiophene using triethylamine as solvent and base and
Cu(I) iodide and PdCl2(PPh3)3 as the catalytic system.38 Reac-
tion conditions probed included reactions without cocatalyst
CuII to avoid Glaser-type homocoupling reactions of the
alkynes,60 lower reaction temperature,61 or the use of micro-
wave irradiation.62 Table 1 shows the efficiency of the Pd/
Cu(I)-catalyzed Sonogashira reaction on end-functionalized
P3HT (Br/Br and Br/H end groups). When the reaction was
probed with high temperature (75 °C) for 3 days an incom-
plete reaction (entry 1) was observed, showing a large amount
of unreacted starting materials. To increase the conversion,
we chose microwave radiation, with different irradiation
powers; in a second step, reaction time and different bases
were probed.
Again, the efficiency of the Sonogashira reaction onto
P3HT (9) was investigated by LC-ESI-TOF MS analysis
under the different reaction conditions using microwave
irradiation (Figure 3). Thus the individual species with
ethynyl moieties (Eth/H; H/H) with increasing chain length
(n = 8-12) could be separated via the used LC method.
Three different polymer end-group species could be identi-
fied in a series of two different HPLC peaks (see Figure 3). At
low retention time (27-32 min) an almost complete separa-
tion is observed for the polymer species P3HTn(Eth/H) 10b
and P3HTn(H/H) 11, which at higher retention times (35-40
min) merge into one single peak in the LC. Additionally,

8442 Macromolecules, Vol. 43, No. 20, 2010
Enders et al.
Figure 3. (a) HPLC chromatogram of P3HT-10 (entry 3 in Table 1) at 400 nm with different fractions, two fractions were picked out and simulated.
(b) Isotopic pattern of P3HT7(Eth/Br)-10b (M = C75H107S7SiBr, Mcalc = 1338.54 g/mol) as [M]þ• adduct. (c) Isotopic pattern of P3HT8(Eth/H)-10b
(M = C85H122S8Si, Mcalc = 1426.71 g/mol) as [M]þ• adduct. (d) Isotopic pattern of P3HT7(Eth/Eth)-10c (M = C80H116S7Si2, Mcalc = 1356.57 g/mol)
as [M]þ• adduct. (e) Isotopic pattern of P3HT8(H/H)-11 (M = C80H114S8, Mcalc = 1330.58 g/mol) as [M]þ• adduct.
a polymer with the end group P3HTn(Eth/Eth) 10c is sepa-
rated at low retention times, which subsequently merges with
the two other two peaks at higher retention times (43-
50 min). Therefore, all species with chain lengths n<12
could be separated by LC. Table 1 shows the quantitative
data obtained by integration of the respective LC or mass
peaks. In the case of overlapping LC peaks, the correspond-
ing mass traces were analyzed quantitatively by taking the
appropriate fraction under the LC peak, corresponding to
the fraction of the respective species in the mass analysis.
With increasing microwave radiation starting with 15, 25, up
to 100 W (see Table 1; entries 2, 4, and 6) and equal reaction
time, the amount of bivalent (Eth/Eth) 9c and also mono-
valent (H/Eth) 10b end-capped P3HT increased signifi-
cantly. At longer reaction time of 150 min using a constant
microwave power of 15 W (Table 1, entry 3) we recognized an
increasing amount of bivalent P3HT (Eth/Eth) species 10c.
In the case of 35 W and 2.5 h the amount of monovalent (Br/
Eth) (10a) decreased and that of the monovalent (H/Eth)
species (10b) increased. To prove the limits of the Sonoga-
shira reaction via microwave irradiation, we chose a high
power (100 W) and a long reaction time (360 min), which
indicated a complete formation of P3HTn(H,H) 11. We
assumed that the Pd catalyst in the Sonogashira reaction
together with the microwave irradiation induced the genera-
tion of protonated species (H/H).63,64
diethylamine and DMF. Further investigation via MALDI-
TOF MS (Figure 4, entry 3) showed similar species as in the
ESI-TOF measurements ionized as the respective radical
cation. Preferably radical cations of P3HT have been formed
during the ESI-TOF but also MALDI-TOF analysis and can
be explained due to their high affinity to donate electrons.
Similar to our previous (semi-)quantification (Supporting
Information, Tables S4, S5, Figures S12, S13) of the MALDI
spectra, a distribution of the end groups in a ratio of 38%
Eth/Eth 10c, 50% Eth/H 10b, and 12% H/H 11 species was
observed. These different end-group species were corrected
with a factor of 79.2 for polymers with Eth/Eth and with 18.9
for polymers with Eth/H end groups, yielding a new ratio of
69.7% Eth/Eth 10c, 30.0% Eth/H 10b, and 0.3% H/H 11,
which again shows a deviation from the values obtained via
LC-ESI-TOF measurements.
Azide/Alkyne “Click” Reactions. In recent years the azide/
alkyne “click” reaction was intensively investigated as a tool
for the synthesis of block copolymers and their end-group
functionalization reactions.65-67 As a last step, therefore, the
synthesized alkyne-modified P3HTs 10 were subjected to
azide/alkyne “click” reactions to attach the hydrogen-bond-
ing moieties via the respective azides 7a,b. Results for the
“click” reaction of 10 with the thymine (7a) and “Hamilton-
receptor” (7b) functionalized azides are shown in Table 2,
using the quantification of the complex reaction mixture by
LC-ESI-TOF methods.
Analysis of P3HT-10 via LC-ESI-TOF. The best results
were obtained with a reduced microwave power of 15 W and
a reaction time of approximately 2.5 h, resulting in a ratio of
59% bivalent 10c and 40% monovalent 10b polymer (entry
3). Additionally, we could identify 1% of the polymer 11
(P3HT-H/H) in the mixture. Influence of base or solvent is
negligible according to experiments shown in entries 7 and 8,
probing the exchange of triethylamine against a mixture of
Table 2 summarizes the results of the azide/alkyne “click”
experiments with the azide compounds (7a,b) under various
reaction conditions. The products of each reaction were
analyzed by LC-ESI-TOF mass spectrometry, yielding in-
formation on the product distribution in the mixture. The
first reactions were conducted with azide compound 7a
on the alkyne-modified P3HT (10) with different copper(I)

Article
Macromolecules, Vol. 43, No. 20, 2010 8443
Figure 4. (a) MALDI-TOF MS spectra of P3HT-10 (entry 3 in Table1) in the linear positive modus with three different series. (b) Isotopic pattern of
P3HT9(Eth/H)-10b (M = C95H136S9Si, Mcalc = 1592.78 g/mol) as [M]þ• adduct. (c) Isotopic pattern of P3HT9(Eth/Eth)-10c (M = C100H144S9Si2,
Mcalc = 1688.83 g/mol) as [M]þ• adduct. (d) Isotopic pattern of P3HT10(H/H)-11 (M = C100H142S10, Mcalc = 1662.83 g/mol) as [M]þ• adduct.
Table 2. Azide/Alkyne “Click” Reaction of Acetylene-Functionalized P3HT 10 (GPC: Mn = 2200 g/mol, Mw/Mn = 1.1)a
reaction conditions
mol %c
entry
R0N3
Cu(I) species
microwave power (W)
temp (°C)
time (min)
monovalent
bivalent
11
10bb
yieldd (%)
1
2
3
4
6
7
8
9
7a
7a
7a
7b
7b
7b
7b
7b
CuBr(PPh3)3
CuI
CuI P(OEt)3
CuBr(PPh3)3
CuBr(PPh3)3
CuBr(PPh3)3
CuI
300
300
300
100
100
100
100
100
120
120
120
90
90
90
90
90
60
30
60
90
90
60
2b (42%)
2b (18%)
2b (64%)
3b (92%)
3b (92%)
3b (84%)
3b (2.2%)
3b (9%)
2c (5%)
2c (82%)
2c (0%)
3c (0%)
3c (0%)
3c (0%)
3c (6.3%)
3c (0%)
51
0
36
8
2
81
92
87
e
3
8
e
16
92
91
62
55
76
90
90
CuI P(OEt)3
3
a ESI-TOF MS: end-group distribution Eth/Eth (10c) ∼59%, Eth/H (10b) ∼40%, H/H (11) ∼1%) with the azides 7a, 7b under microwave irradiation.
b Incomplete reaction because of incomplete deprotection of TMS group, determined via ESI-TOF MS. c End-group distribution determined via
ESI-TOF MS. d Isolated yield. e Sample yield not determined.
catalysts using microwave irradiation. It should be noted
that the “click” reaction did not proceed without the use of
microwave irradiation. The best results for the “click” reac-
tion were achieved with copper(I) iodide generating mono-
and bis-telechelic thymine-functionalized polymer 2 in a
ratio of 2b = 18% and 2c = 82% (Table 2, entry 2). In
comparison to the reaction with CuBr(PPh3)3 (entry 1) no
starting material and no P3HT(H/H) 11 was observed. The
“click” reaction with the Hamilton receptor azide 7b in the
presence of CuBr(PPh3)3 surprisingly results exclusively in
the formation of the monotelechelic P3HT-3b in amounts
of ∼84%. In contrast, the use of copper(I) iodide catalyst
(entry 8) leads the formation of mono- and bis-telechelic
P3HT-3 (3b/3c = 1: 3) with a surprisingly a large fraction of
(H/H)-telechlic P3HT 11 as side product. We assume that
the mismatch of the product distribution (3b/3c = 84/0)
together with the formation of 11 in a significant amount
hints at a reversible Sonogashira reaction forming the re-
spective hydrogenated species discussed before.
Figure 5 displays HPLC chromatograms of P3HT 2 with
the observed and simulated isotopic patterns of the identified
species. The LC separation of P3HT-2 shows a series of
peaks starting at low retention time (22-45 min), where a
mixture of P3HT (H/Thy) 2b, P3HT (Thy/Thy) 2c, and

8444 Macromolecules, Vol. 43, No. 20, 2010
Enders et al.
Figure 5. (a) HPLC chromatogram of P3HT-2 (entry 1 in Table 2) at 400 nm wþith different fractions. (b) Measured and simulated isotopic pattern of
P3HT8(H/Thy)-2b (M = C93H130S8N5O2, Mcalc = 1605.81 g/mol) as [M þ Na] adduct. (c) Measured and simulated isotopic pattern of P3HT8(Thy/
Thy)-2c (M = C106H148S8N10O4, Mcalc = 1880.94 g/mol) as [M þNa]þ adduct.
Figure 6. (a) HPLC chromatogram of P3HT-3 (entry 4 in Table 2) at 400 nm withþdifferent fractions. (b) Measured and simulated isotopic pattern of
P3HT8(H/Ham)-3b (M = C123H161S8N10O5, Mcalc = 2115.05 g/mol) as [M þ H] and [M þ Na]þ adduct.

Article
Macromolecules, Vol. 43, No. 20, 2010 8445
P3HT (H/H) 11 could be identified and simulated as the
respective sodium adducts. In contrast to the alkyne-telechelic
P3HTs (10), which were detected as radical cations by ESI-
TOF mass spectrometry, the P3HTs 2 and 3 modified with
H-bonding moieties were identified as sodium adducts that
can be explained by the preferred complexation via the
H-bonding interactions.
The chromatographic separation of the Hamilton receptor
end-capped P3HT 3b, and the measured and simulated mass
peaks, are displayed in Figure 6. Two different end-group
species, P3HT-3b (H/Ham) and P3HT-11 (H/H), could be
separated starting with the more polar clicked P3HT. The
first P3HT-H/Ham species could be detected with a repeat-
ing unit of 7 and ending with 12 where an overlap with the
second polymer species of H/H was observed at a retention
time of 37 min. The final P3HTs 2 and 3 were additionally
investigated via MALDI-TOF MS, revealing that P3HT
(H/H) (11) is desorbed preferentially in comparison to
the “click” products 2 and 3 (see Supporting Information,
Figures S14 and S15).
Acknowledgment. Grants from the DFG INST 271/249-1,
INST 271/247-1, and INST 271/248-1 are gratefully acknowledged.
Supporting Information Available: Detailed information for
the synthesis of the azide compound 7b and the copper catalyst
CuII P(OEt)3 and their NMR data, as well as NMR data of
3
bifunctionalized terthiophene (4, 5, and 1a); HPLC-ESI-TOF
and MALDI-TOF MS spectra for thymine-functionalized
terthiophene 1a with the simulation of the isotopic pattern;
ESI-TOF MS spectra (direct infusion) of P3HT with different
molecular weights (9700, 8300, 6000, and 4700 g/mol); assign-
ment of ESI- and MALDI-TOF MS peaks of P3HT with
different end-group species according to the represented figures,
MALDI-TOF spectra of P3HT 3a and 2a with IAA/NaTFA
and different matrices; plots for desorption sensitivity analysis
of MALDI signal intensity ratio versus weight ratio for P3HT-
9/P3HT 11 and P3HT-10/P3HT 11. This material is available
free of charge via the Internet at http://pubs.acs.org.
References and Notes
Depending on the H-bonding moiety we therefore could
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the azide compound 7a and 7b a mono- or telechelic P3HT
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in contrast, copper(I)iodide leads to the favored telechelic
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Whereas MALDI qualitatively yields the same results, LC-
ESI-TOF methods are better suited for the separation and
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We have described a synthetic strategy toward poly(3-hexyl-
thiophenes) (P3HTs) with hydrogen-bonding moieties at their
chain end, which is based on a combination of a Sonogashira
reaction witha subsequent azide/alkyne“click”reaction to attach
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