A versatile approach for creating hybrid semiconducting polymer-fullerene architectures for organic electronics

Article abstract of DOI:10.1039/c4ta00741g

A novel methodology, through which fullerenes are effectively introduced directly onto semiconducting species, is presented herein. Electron accepting perfluorophenyl-quinolines either as small molecules, as homopolymers, or as random copolymers with regioregular poly(3-alkyl thiophene), have been synthesized and further employed for the preparation of hybrid materials with C₆₀ or PCBM. More specifically, via this route one of the fluorine atoms of the perfluorophenyl ring is transformed into an azide that undergoes [3+2]-cycloaddition onto the fullerene's surface, producing 1,6-azo bridged carbon nanostructure-organic semiconducting hybrids. This journal is the Partner Organisations 2014.

Full text of DOI:10.1039/c4ta00741g

Journal of
Materials Chemistry A
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PAPER
A versatile approach for creating hybrid
semiconducting polymer–fullerene architectures
for organic electronics†
Cite this: J. Mater. Chem. A, 2014, 2,
8110
a
a
ab
*
Sofia Kakogianni, Souzana N. Kourkouli, Aikaterini K. Andreopoulou
ab
*
and Joannis K. Kallitsis
A novel methodology, through which fullerenes are effectively introduced directly onto semiconducting
species, is presented herein. Electron accepting perfluorophenyl-quinolines either as small molecules, as
homopolymers, or as random copolymers with regioregular poly(3-alkyl thiophene), have been
synthesized and further employed for the preparation of hybrid materials with C60 or PCBM. More
specifically, via this route one of the fluorine atoms of the perfluorophenyl ring is transformed into an
azide that undergoes [3+2]-cycloaddition onto the fullerene's surface, producing 1,6-azo bridged carbon
nanostructure–organic semiconducting hybrids.
Received 11th February 2014
Accepted 11th March 2014
DOI: 10.1039/c4ta00741g
www.rsc.org/MaterialsA
of the polymeric and the hybrid molecules proved the potential
of these molecules as electron acceptors in OPVs. However, it is
Introduction
well known that polymeric and even small organic electron
acceptors greatly suffer from low charge carrier mobility. For
that reason we have already prepared hybrid structures by
functionalizing single wall carbon nanotubes (SWCNTs) with
different quinoline species bearing electron accepting groups.31
The combination of SWCNTs with semiconducting polymers
offers an attractive route to reinforce the macromolecular
compounds as well as to introduce novel electronic properties
based on electronic interactions and/or morphological alter-
ations between the two constituents. And also this method
suffers from the limited SWCNT content allowed into the
photovoltaic active layer. Thus, an ideal solution would be to
couple the processability and good electron accepting proper-
ties of peruorophenyl-quinolines with the even greater elec-
tron accepting and transporting properties of fullerenes, and
also ensure the applicability of the nal hybrid materials in the
active layer of an OPV.
As already mentioned, the idea to connect semiconducting
polymeric species onto carbon nanostructures, like CNTs or
fullerenes, has been demonstrated by various research groups.
However, in all cases a non-conjugated connecting bridge has
been employed for the organic part xation onto the carbon
nanostructure's surface.11,12,32–34 Instead, a conjugated inter-
connecting part through the direct attachment of the semi-
conductor onto the carbon nanostructure could enhance
electronic interactions between the two counterparts possibly
creating novel hybrid systems with unique integrated properties.
Working in this direction we employed an efficient meth-
odology for the attachment of fullerene species onto per-
uorophenyl-quinolines, either polymeric or monomeric ones,
using one of the uorine atoms of the peruorophenyl ring
Efficient bulk heterojunction (BHJ) organic photovoltaic (OPV)
solar cells comprised of bicontinuous, nanophase separated
active layers that remain stable over time and environmental
conditions are of utmost importance for their commercializa-
tion.1–3 Parameters such as the chemical structure of the donor
and the acceptor, the conditions for mixing and depositing the
active layer as well as post-deposition treatment and device
architecture have been exhaustively investigated.4–13 Numerous
new and “exotic” materials have appeared over time with
continuous enhancement of the OPV performance.14–16 Never-
theless, the still most commonly employed system, especially
when it comes to large area devices, remains the rr-poly(3-hexyl-
thiophene) and [6,6]-phenyl C61-butyric acid methyl ester
binary mixture (P3HT–PCBM). The introduction of a hybrid
compatibilizer, bearing both an electron donating polymer and
electron accepting fullerene units, has been effective at
enhancing the stability of this blend but in almost every case,
compatibilizers require multiple and laborious post-polymeri-
zation synthesis steps.17–29
Recently, we reported our efforts towards the development of
polymeric or hybrid electron acceptors based on the per-
uorophenyl-quinoline entity.30 The optoelectronic properties
aDepartment of Chemistry, University of Patras, University Campus, Rio-Patras,
GR26504, Greece. E-mail: andreopo@upatras.gr; j.kallitsis@upatras.gr; Fax: +30
2610997122; Tel: +30 2610962652
bFoundation for Research and Technology Hellas/Institute of Chemical Engineering
Sciences (FORTH/ICE-HT), Platani Str., Patras, GR26504, Greece
† Electronic supplementary information (ESI) available: Synthesis procedures,
schemes and characterization of new materials via GPC, FTIR, TGA, UV-Vis and
PL. See DOI: 10.1039/c4ta00741g
8110 | J. Mater. Chem. A, 2014, 2, 8110–8117
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which can be easily transformed into an azide. This undergoes
[3+2]-cycloaddition with fullerene species in a simple and
straightforward reaction,35–39 producing 1,6-azo bridged
fullerene based hybrids. Through this route polymeric as well as
small molecule peruorophenyl-quinoline C60 hybrids were
created. Taking this a step further, we developed electron
donor–acceptor copolymers comprising rr-poly(3-alkyl-thio-
phene) and poly(peruorophenyl-quinoline) blocks. On the
peruorophenyl rings of the quinoline block we then attached
fullerene units, either C60 or PCBM ones.40 These hybrid mate-
rials are designed so as to be used as compatibilisers of typical
P3HT:PCBM blends in BHJ OPVs. Work in this direction is
currently under way.
Synthesis procedures
The synthesis procedures for dodecyloxy-biphenyl-boronic acid,
Ph-5FQ, C12(Ph)2-5FQ, Ph-5FQ-N3, C12(Ph)2-5FQ-N3 and P5FQ-
N3 are given in the ESI.†
Synthesis of the phenyl-peruorophenylquinoline C60
hybrid, Ph-5FQ-N-C60. A 100 mL round bottom ask equipped
with a reux condenser and a magnetic stirrer was degassed
(amed under vacuum) and lled with argon. Ph-5FQ-N3 (0.50 g,
1.06 mmol), C60 (0.80 g, 1.11 mmol) and 40 mL 1,2-dichlo-
benzene (o-DCB) were added and the system was degassed and
ushed with argon again. The reaction mixture was stirred at
ꢁ
140 C for 48 h. Aer evaporation of the solvent, the solid was
dissolved in toluene, ltered to remove any undissolved resid-
uals and chromatographed through silica gel loaded with
petroleum ether using petroleum ether, petroleum ether-
: toluene 1 : 1 and 1 : 2 mixtures, and nally toluene. The
second fraction contained the desired Ph-5FQ-N-C60 hybrid
material, which was rotary evaporated and the solid was dried
under vacuum at 50 ꢁC overnight, yield 60%. 13C NMR (dC;
CS2 : CDCl3 1 : 3; Me4Si): 149.51, 148.26, 147.35, 145.55, 145.45,
145.36, 145.24, 144.72, 144.55, 144.34, 144.11, 144.04, 143.31,
143.23, 143.15, 142.89, 142.32, 142.23, 141.22, 140.56, 140.52,
140.34, 137.57, 130.83, 129.87, 129.73, 129.08, 128.94, 128.91,
Experimental
Materials
Fullerene, carbon 60, 99.5% was purchased from SES
research. [60]PCBM 99% was purchased from Solenne b.v.
Tetrahydrofuran was purchased from Aldrich and was
distilled with benzophenone and metallic sodium [THF(dry)].
N,N-Dimethylformamide, purchased from Aldrich, was dried
over CaH2 and distilled under reduced pressure [DMF(dry)].
All other solvents and reagents were purchased from Aldrich,
Alfa Aesar or Across and were used without further purica-
tion unless otherwise stated. Bromo phenyl peruoroquino-
127.98, 127.59, 127.01, 126.29, 123.72, 123.58, 115.81, 80.60. 15
N
(dN; CS2 : CDCl3 1 : 3): 311.15, 378.85. 19F NMR (dF; CS2 : CDCl3
1 : 3): ꢀ147.70, ꢀ163.95.
line
(Br-5FQ),30
peruorophenyl-vinylphenyl-quinoline
Synthesis of the dodecyloxy-biphenyl-peruorophenylquino-
line C60 hybrid, C12(Ph)2-5FQ-N-C60. A 100 mL round bottom
ask equipped with a reux condenser and a magnetic stirrer
was degassed (amed under vacuum) and lled with argon.
C12(Ph)2-5FQ-N3 (182.71 mg, 0.25 mmol), C60 (180.16 mg, 0.25
mmol) and 25 mL toluene were added and the system was
degassed and ushed with argon again. The reaction mixture
(5FQ),30 polymeric peruorophenylquinoline (P5FQ),30 2-
vinyl terminated regioregular poly(3-octylthiophene)41 and 4-
bromo-40-acetoxy biphenyl42 were synthesized according to
the reported procedures.
Instruments and measurements
ꢁ
was stirred at 110 C for 48 h. Aer evaporation of the solvent,
1H, 13C, 19F, 15N and 2D NMR (HMBC) spectra were recorded on
Bruker Advance DPX 400.13, 100.6 and 376.5 MHz spectrome-
ters, respectively, with CDCl3 as solvent containing TMS as
internal standard. Gel permeation chromatography (GPC)
measurements were carried out using a Polymer Lab chroma-
tographer equipped with two PLgel 5 mm mixed columns and a
UV detector using CHCl3 as eluent with a ow rate of 1 mL
minꢀ1 at 25 ꢁC and polystyrene standards. Sonication was done
on a Bransonic (Branson), ultrasonic cleaner 2510 model.
Thermogravimetric analysis (TGA) was carried out on ꢂ8 mg
samples contained in alumina crucibles in a Labsys TM TG
apparatus of Setaram under nitrogen and at a heating rate of
ꢁ
the solid was stirred in n-hexane for 2 days at 40 C in order to
remove most of the unreacted C60. Column chromatography
using silica gel was performed in order to remove any remaining
traces of C60, using petroleum ether–toluene gradient mixtures,
providing pure C12(Ph)2-5FQ-N-C60 as the second fraction. The
obtained solid was dried under vacuum at 50 ꢁC overnight, yield
55%. 13C NMR (dC; CS2 : CDCl3 1 : 3; Me4Si): 158.99, 149.20,
148.33, 147.05, 145.57, 145.47, 145.40, 145.24, 144.86, 144.74,
144.59, 144.38, 144.14, 144.09, 143.35, 143.26, 143.19, 142.91,
142.36, 142.27, 141.26, 140.58, 140.55, 140.07, 138.36, 137.73,
132.64, 131.15, 129.81, 129.56, 129.11, 129.03, 128.93, 128.09,
127.92, 127.32, 126.27, 123.63, 123.22, 114.97, 80.65, 68.03,
32.43, 30.22, 30.18, 30.15, 30.07, 29.90, 29.83, 29.79, 26.63, 23.36,
14.67. 15N (dN; CS2 : CDCl3 1 : 3): 311.02, 373.5. 19F NMR
(dF; CS2 : CDCl3 1 : 3): ꢀ161.80, ꢀ145.90.
10 C minꢀ1. UV-Vis spectra were recorded using a Hitachi U-
ꢁ
1800 spectrophotometer. Continuous wave photoluminescence
was measured on a Perkin Elmer LS45B spectrouorometer. FT-
IR spectra were recorded on a Perkin-Elmer 16PC FTIR spec-
trometer. Transmission electron microscopy (TEM) measure-
ments were performed on a JEOL JEM2100 operating at 200 kV.
Sample preparation for TEM examination involved the prepa-
ration of dilute solutions of the samples in THF or o-DCB and
ltration through a 0.45 mm lter. A drop of the solution was
placed on 3 mm carbon coated copper grids (Electron Micros-
copy Sciences) and the samples were dried in air for 2 days.
Synthesis of the poly(peruorophenyl-quinoline) C60 hybrid,
P5FQ-N-C60. A 50 mL round bottom ask equipped with a reux
condenser and a magnetic stirrer was degassed (amed under
vacuum) and lled with argon. P5FQ-N3 (0.22 g, 0.43 mmol), C60
(0.30 g, 0.43 mmol) and 20 mL o-DCB were added and the
system was degassed and ushed with argon again. The reac-
tion mixture was stirred at 140 ꢁC for 48 h. Aer evaporation of
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the solvent, the solid was stirred in n-hexane for 2 days at 40 ꢁC and a magnetic stirrer was degassed (amed under vacuum)
ꢁ
and in toluene for another 2 days at 40 C in order to remove and lled with argon. P3OT-(P5FQ-N3) (70.00 mg), PCBM (65.00
unreacted C60 traces, ltered and the obtained solid was dried mg, 0.07 mmol), and 20 mL o-DCB were added and the system
under vacuum at 50 ꢁC overnight, yield 60%. Unfortunately, the was degassed and ushed with argon again. The reaction
low solubility of this hybrid and the strong coupling of the mixture was sonicated for 20 min and then was stirred at 140 ꢁC
carbon to uorine atoms of the uorinated phenyl ring did not for 72 h. Aer evaporation of the solvent, the solid was stirred in
allow its successful NMR characterization.
n-hexane at 40 ꢁC for 3 days with a view to remove any traces of
Synthesis of the random copolymer regioregular-poly(3- unreacted PCBM. The mixture was ltered and the solid was
octylthiophene)-r-poly(peruorophenylquinoline), P3OT-P5FQ. washed with n-hexane, toluene several times and nally with
A 10 mL round ask equipped with a reux condenser and a n-hexane. TLC of the hybrid copolymer on silica gel plates using
magnetic stirrer was degassed and lled with argon. Vinyl-5FQ toluene as eluent was used to conrm the absence of free PCBM
(250.00 mg, 0.53 mmol), vinyl terminated rr-P3OT (25.00 mg, in the nal hybrid. The obtained solid was dried under vacuum
0.13 mmol), azobisisobutyronitrile (AIBN) (8.70 mg, 0.05 at 50 ꢁC overnight affording 105.80 mg. 1H NMR (dH; CDCl3;
mmol), 3 mL THF(dry) and 2 mL o-DCB were added and the Me4Si): 8.4–8.0 (broad, 3H-P5FQ), 7.92 (d, 2H-PCBM), 7.8–7.2
ask was degassed and ushed with argon again. The reaction (broad, 8H-P5FQ), 7.57–7.53 (m, 2H-PCBM), 7.48 (d, 1H-PCBM),
mixture was stirred at 110 ꢁC for 72 h. The mixture was 6.98 (s, 1H-P3OT), 3.68 (s, 3H-PCBM), 2.93–2.89 (m, 2H-PCBM),
precipitated into methanol and aer ltration the obtained 2.79 (t, 2H-P3OT), 2.55–2.51 (t, 2H-PCBM), 2.23–2.15 (m, 2H-
solid was washed with diethyl ether and EtOAc. The solid was PCBM), 1.68 (m, 2H-P3OT), 1.5–1.2 (broad, 6H-P3OT), 0.88
dried under vacuum at 40 C overnight affording 130.00 mg of (broad, 3H-P3OT). 13C NMR (dC; CDCl3; Me4Si): 173.46, 148.83,
ꢁ
the nal copolymer. 1H NMR (dH; CDCl3; Me4Si): 8.40–7.70 148.36, 147.83, 145.87, 145.21, 145.17, 145.09, 145.06, 144.81,
(broad, 3H-P5FQ), 7.70–7.00 (broad, 8H-P5FQ), 6.98 (s, 1H- 144.68, 144.64, 144.53, 144.44, 144.03, 143.78, 143.14, 143.02,
P3OT), 6.95–6.3 (broad, 2H-P5FQ), 2.80 (t, 2H-P3OT), 1.69 (m, 142.95, 142.25, 142.20, 142.15, 141.01, 140.80, 138.05, 137.59,
2H-P3OT), 1.47–1.20 (two broad, 6H-P3OT), 0.87 (t, 3H-P3OT). 136.75, 134.55, 132.62, 132.11, 130.55, 128.45, 128.26, 127.72,
13C NMR (dC; CDCl3; Me4Si): 150.72, 146.08, 139.80, 136.71, 119.73, 79.89, 51.87, 51.66, 33.89, 33.69, 31.91, 30.7, 29.55,
133.74, 130.55, 130.54, 129.43, 129.41, 128.74, 128.59, 127.4, 29.46, 29.30, 22.68, 22.39, 14.13. 15N NMR (dN; CDCl3): 234.32,
127.15, 126.45, 126.10, 117.29, 115.42, 31.92, 30.55, 29.57, 209.97. 19F NMR (dF; CDCl3): ꢀ152.50, ꢀ110.78.
29.47, 29.32, 22.70, 14.12. 19F NMR (dF; CDCl3): ꢀ161.58,
ꢀ153.27, ꢀ142.58. 15N NMR (dN; CDCl3): 234.76.
Results and discussion
Table S1† presents the various copolymers prepared along
with their molecular characteristics from GPC analyses.
Synthesis of the copolymer P3OT-(P5FQ-N3). A 50 mL round
bottom ask with a reux condenser and a magnetic stirrer was
degassed and lled with argon. Copolymer P3OT-P5FQ (100.00
mg, 0.15 mmol), NaN3 (36.80 mg, 0.59 mmol), 4 mL THF(dry)
and 6 mL DMF(dry) were stirred at 40 ꢁC for 24 h under argon.
In this work the previously reported peruorophenyl-vinyl-
phenylquinoline monomer and its homopolymer (P5FQ)27 as
well as the newly synthesized small monomolecular phenyl-
(Ph-5FQ) and dodecyloxybiphenyl-(C12(Ph)2-5FQ) substituted
peruorophenyl-quinolines (Schemes S1 and S3,† respectively)
were employed for the initial screening and the optimization of
The reaction mixture was precipitated into a mixture of deion-
the reaction conditions for the development of the hybrid
ized water–methanol (1 : 1). Aer ltration the solid was
fullerene based materials. Additionally, the electron donating–
washed with deionized water three times and dried under
ꢁ
vacuum at 30 C overnight affording the nal azide in quanti-
tative yield. For P3OT-(P5FQ-N3) ATIR spectroscopy was used for
the conrmation of the successful azide introduction.
Synthesis of the hybrid copolymer P3OT-(P5FQ-N-C60). A 50
mL round bottom ask equipped with a reux condenser and a
magnetic stirrer was degassed (amed under vacuum) and lled
with argon. P3OT-(P5FQ-N3) (80.00 mg), C60 (40.00 mg, 0.06
mmol), and 10 mL o-DCB were added and the system was
degassed and ushed with argon again. The reaction mixture
ꢁ
was stirred at 140 C for 72 h. Aer evaporation of the solvent,
the solid was stirred in n-hexane and then in toluene each for 3
ꢁ
days at 40 C in order to remove traces of unreacted C60. The
mixture was ltered and the obtained solid was dried under
vacuum at 50 ꢁC overnight affording 100.00 mg. Due to the low
solubility of this hybrid material in CDCl3 NMR spectroscopy
evaluation was not successful even aer the addition of CS2 to
improve the solubility of the fullerene part.
Synthesis of the hybrid copolymer P3OT-(P5FQ-N-PCBM). A
50 mL round bottom ask equipped with a reux condenser Scheme 1 Synthesis of C60 based hybrids.
8112 | J. Mater. Chem. A, 2014, 2, 8110–8117
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vinylic peruorophenylquinoline monomer27 (Scheme S5, Table
S1†). Scheme
1 presents the general reaction sequence
employed for the preparation of peruoroquinoline-C60
hybrids.
The polymeric, copolymeric and small organic molecules
carrying the peruorphenyl ring were converted to azides and
then reacted with C60 providing the nal C60-based hybrids
(Schemes S1, S3, S4 and S6†). A systematic NMR investigation
of the C60-based small molecular hybrids was performed.
In all C60 hybrid cases, no alterations in their 1H NMR
spectra were observed in comparison to the initial organic
counterpart. As an example the 1H,13C-2D HMBC (Hetero-
nuclear Multiple Bond Correlation) NMR spectrum of Ph-
5FQ-N-C60 in the CDCl3–CS2 3 : 1 mixture is presented in
Fig. 1 through which the quinoline carbon peaks can be
distinguished from those of C60. In the 13C-NMR spectrum,
the appearance of the substituted fullerene peaks at the
region 141–146 ppm demonstrates the attachment of C60
onto the quinoline moieties. Specically, 16 well resolved
resonances are detected as is expected for [6,6]-closed azir-
idinofullerene structures.35,43–45 Moreover, in Fig. S3† the 13C
NMR spectra of Ph-5FQ-N-C60 and C12(Ph)2-5FQ-N-C60 are
directly compared to the initial Ph-5FQ and C12(Ph)2-5FQ,
respectively, showing the distinct alteration of the hybrids'
13C NMR spectra. The peak at about 80.6 ppm observed in the
spectra of the hybrids is attributed to the bridgehead carbon
atom.35,43–45
Fig. 1 1H, 13C-HMBC 2D NMR spectra of Ph-5FQ-N-C60 in the
CDCl3–CS2 3 : 1 mixture.
electron accepting random copolymer P3OT-P5FQ was prepared
through free radical polymerization (FRP) of the allyl-termi-
nated rr-poly(3-octyl thiophene) macromonomer34 and the
Fig. 2 Synthesis route toward rr-poly(3-octyl thiophene)-co-[poly(perfluorphenyl-quinoline)-PCBM] hybrids and 1H NMR spectra of the P3OT-
P5FQ(iii) copolymer and the P3OT-(P5FQ-N-PCBM) hybrid, both in CDCl3.
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reveal a spot due to free PCBM, other than a diffuse broad spot
at the base owing to the copolymeric hybrid.
Additional evidence of the successful introduction of the
fullerene derivatives to the organic materials is provided
through infrared spectroscopy, Fig. 3a, and thermogravimetric
analyses, Fig. 3b.
The FTIR spectra of P3OT-P5FQ are a sum of the respective
individual blocks (Fig. S9†). As evident in Fig. 3a the P3OT-
(P5FQ-N3) copolymer shows an intense peak at 2124 cmꢀ1
attributed to the azide functionality, which disappears
completely aer its cycloaddition to PCBM. The nal hybrid
P3OT-(P5FQ-N-PCBM) exhibits the 524, 572 and 1429 cmꢀ1
peaks assigned to fullerene and the characteristic peak of the
C]O group at 1740 cmꢀ1. For all the C60 bearing molecules
FTIR spectroscopy also revealed the disappearance of the azide
peak and intense ones at 524 and 572 cmꢀ1 due to the attach-
ment of the C60 units. Even though the 1427 cmꢀ1 peak of C60
was overlapped from the quinoline peaks, the one at 1180 cmꢀ1
was clearly identied (Fig. S1, S2 and S4†).
TGA analysis of the P3OT-P5FQ copolymer and its C60 and
PCBM hybrids, Fig. 3b, revealed the anticipated higher carbon
residue of the hybrid materials compared to the initial copol-
ymer. For the P3OT-(P5FQ-N-C60) hybrid at 800 ꢁC, a 79.5%
residue was obtained while for P3OT-(P5FQ-N-PCBM), a 78%
one was obtained compared to the 49% residue of the P3OT-
P5FQ copolymer.
The PL spectra in solution aer excitation at the quinolines'
absorption maxima, ꢂ340 and ꢂ440 nm, showed luminescence
peaks owing to the P5FQ segments. For all the C60 hybrids of
Scheme 1, the UV-Vis and PL spectra in solution and the lm
form are presented in Fig. S6–S8.† Noticeably, one common
feature which dominates the photoluminescence in the lm
form of all hybrid cases, monomeric, polymeric, or copolymeric
ones, is the quenching of the quinoline's luminescence aer the
attachment of the fullerene derivatives, as can be seen in Fig. 4.
Fig. 3 (a) FT-IR spectra and (b) TGA thermograms of the P3OT-P5FQ
copolymer, its C60 and PCBM hybrid analogues and of the neat
fullerene derivatives.
The same synthesis procedure for the development of C60
The optical properties in the lm form of P3OT-(P5FQ-N-C60)
based hybrid electron accepting or electron-donating–electron- and P3OT-(P5FQ-N-PCBM) are depicted in Fig. 5 in comparison
accepting materials was also employed for the insertion of
PCBM ([6,6]-phenyl-C61-butyric acid methyl ester) moieties
along the poly(peruorophenylquinoline) block of the random
copolymer P3OT-P5FQ. Fig. 2 analytically depicts the reaction
conditions for the preparation of the P3OT-(P5FQ-N-PCBM)
1
copolymeric hybrid along with a direct comparison of the H
NMR spectra of the initial P3OT-P5FQ(iii) random copolymer
and its respective PCBM hybrid. The initial P3OT-P5FQ(iii)
copolymer presented 50% contents for the P3OT and the P5FQ
blocks, respectively. Peak integration at 3.67 ppm, owing to the
CH3O protons of PCBM and at 2.8 ppm due to the CH2 protons
neighboring the thiophene ring, and by keeping the ratio of
P3OT to P5FQ as in the initial copolymer, provides a 25%
content of PCBM in the hybrid copolymer, 37% for P3OT and
38% for P5FQ. Since the copolymer was exhaustively cleaned
with n-hexane at 40 ꢁC and then with toluene and no azide
functionalities could be detected from FTIR, as explained
below, we can conclude with certainty that no free PCBM
remained in the nal hybrid copolymer. Moreover, TLC per-
Fig. 4 PL spectra, excitation at 340 nm, of Ph5FQ, C12(Ph)25FQ and
P5FQ and their respective hybrids with C60, in a film form cast from
formed in typical silica gel plates using toluene as eluent did not THF solutions.
8114 | J. Mater. Chem. A, 2014, 2, 8110–8117
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Fig. 5 (a) UV-Vis and (b) PL spectra, excitation at 520 nm, of the P3OT-P5FQ copolymer, its C60 and PCBM hybrids and of the net P3OT and
P5FQ counterparts, in a film form cast from THF solutions.
Fig. 6 TEM images of unstained P3OT-(P5FQ-N-PCBM) (a) using THF and (b) using o-DCB; (c) P3OT-PF5FQ using o-DCB (scale bar 100 nm).
The insets in (a)–(c) show higher magnifications with the scale bar corresponding to 20 nm; (d) the TEM image of a P3OT-P5FQ/PCBM blend and
of the net PCBM (inset, 20 nm scale bar), both using o-DCB.
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to the initial electron donor–acceptor copolymer P3OT-P5FQ during the NMR experiments. This research has been co-
and to the neat P3OT and P5FQ polymers. The inset shows the nanced by the program Nanorganic – 09SYN-42-722 of the
absorption of the fullerene derivatives also in the lm form. The GSRT of the Greek Ministry of Education and by the “ARISTEIA”
UV-Vis spectra of the hybrids are a sum of their net counter- Action of the “Operational Programme Education and Lifelong
parts' individual spectrum. The PL spectra of the hybrid mate- Learning” co-funded by the European Social Fund (ESF) and
rials aer excitation at 520 nm, corresponding to the P3OT's National Resources, through the project "Design and Develop-
absorption maximum, showed the characteristic photo- ment of New Electron Acceptor Polymeric and Hybrid Materials
luminescence peaks of the poly(thiophene) segments. The and their Application in Organic Photovoltaics – DENEA 2780.
optical properties of these hybrid copolymers in THF solutions
(Fig. S10–S13†) also showed the coexistence of P3OT, P5FQ and
the fullerene derivative.
References
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electron microscopy (TEM), Fig. 6. Fig. 6a and b present the
TEM images of the hybrid copolymer with PCBM using THF and
o-DCB, respectively, without any thermal treatment of the
samples. Fig. 6c shows the TEM images of the net P3OT-P5FQ
copolymer using o-DCB, while it should be noted here that lms
obtained from THF solutions showed exactly the same
morphology. The insets depict higher magnications with the
scale bars corresponding to 20 nm. Uniform lms were
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hybrid. The morphology of the blend (Fig. 6d), in contrast to
that of the hybrid copolymer, showed clear PCBM aggregates as
well as crystallites similar to those obtained from net PCBM cast
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