(3E,7E)-3,7-Bis(2-oxoindolin-3-ylidene)-5,7-dihydropyrrolo[2,3-f]indole-2,6(1H,3H)-Dione based polymers for ambipolar organic thin film transistors

Article abstract of DOI:10.1039/c5cc01021g

A novel acceptor, (3E,7E)-3,7-bis(2-oxoindolin-3-ylidene)-5,7-dihydropyrrolo[2,3-f]indole-2,6(1H,3H)-dione, was reported. Donor-acceptor (D-A) polymer semiconductors using this new building block showed high ambipolar charge transport performance with hol

Full text of DOI:10.1039/c5cc01021g

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(3E,7E)-3,7-Bis(2-oxoindolin-3-ylidene)-5,7-
dihydropyrrolo[2,3-f]indole-2,6(1H,3H)-dione based
polymers for ambipolar organic thin film transistors
Cite this: DOI: 10.1039/x0xx00000x
Received 00th January 2012,
Accepted 00th January 2012
DOI: 10.1039/x0xx00000x
Yinghui He, Chang Guo, Bin Sun, Jesse Quinn and Yuning Li*
www.rsc.org/
A novel acceptor, (3
dihydropyrrolo[2,3-
Donor-acceptor (D-A) polymer semiconductors using this
new building block showed high ambipolar charge transport
performance with hole and electron mobilities up to 0.19 and
0.09 cm2 V-1 s-1, respectively, in thin film transistors.
E
,7
E
)-3,7-bis(2-oxoindolin-3-ylidene)-5,7-
,3 )-dione, was reported.
We started our study by conducting computational simulations on
two model compounds: IBDFꢀMe (see ESI) and IBDPꢀMe (Fig. 1b).
The simulation results showed that IBDPꢀMe has a very small
dihedral angle (~10°) between an indolinꢀ2ꢀone unit and the 5,7ꢀ
dihydropyrrolo[2,3ꢀf]indoleꢀ2,6ꢀ(1H,3H)ꢀdione core, which is
comparable to that of IBDFꢀMe (~8°). As for the frontier orbitals,
the highest occupied molecular orbital (HOMO)/the lowest
unoccupied molecular orbitals (LUMO) energy levels were predicted
to be ꢀ6.11 eV/ꢀ3.78 eV and ꢀ5.52 eV/ꢀ3.44 eV for IBDFꢀMe and
IBDPꢀMe, respectively, suggesting that IBDP is a weaker acceptor
than IBDF.
f
]indole-2,6(1
H H
Polymer semiconductors are useful materials for lowꢀcost organic
electronics such as organic thin film transistors (OTFTs)1,2 and
organic photovoltaics (OPVs)3,4 due mainly to their excellent
solution processability and mechanical robustness. In recent years, a
number of donorꢀacceptor (DꢀA) πꢀconjugated polymers have
demonstrated high mobility in OTFTs.5–7 In these highꢀperformance
DꢀA polymers, the intermolecular DꢀA interaction of the donor and
acceptor building blocks could shorten the πꢀπ stacking distance and
thus improve the interchain charge transport. Intensified research
effort has been devoted to the development of novel electron donor
and acceptor building blocks in order to enhance the charge carrier
The syntheses of the IBDP monomer (7) and polymers (P1 and P2)
are outlined in Scheme 1. First, pꢀphenylenediamine was N,N’ꢀ
dialkylated with dodecyl bromide in ethanol to form 1, which was
used to prepare 4 following a similar synthetic route reported
previously.16 Compound 6 was synthesized using a modified
literature
method.17
Specifically,
6ꢀbromoꢀ1ꢀ(2ꢀ
decyltetradecyl)indolineꢀ2,3ꢀdione was first chlorinated with PCl5 to
give the intermediate 5, which was reduced with zinc to form 6.
Condensation of 4 with two equivalents of 6 in refluxing acetic acid
in the presence of a catalytic amount of HCl afforded monomer 7.
mobility for
a
wider range of application of polymer
semiconductors.8,9 Recently our group reported an novel acceptor
building block, (3E,7E)ꢀ3,7ꢀbis(2ꢀoxoindolinꢀ3ꢀylidene)benzo[1,2ꢀ
b:4,5ꢀb’]difuranꢀ2,6(3H,7H)ꢀdione (IBDF, Fig 1a)10, which has been
used for DꢀA polymers for OTFTs.10–15 Owing to the strong electron
withdrawing capability of IBDF, IBDFꢀbased DꢀA polymers showed
excellent nꢀtype and ambipolar charge transport performance with
high electron mobility up to 1.74 cm2 Vꢀ1 sꢀ1.12
In this study, we designed and synthesized a novel acceptor
building block, namely (3E,7E)ꢀ3,7ꢀbis(2ꢀoxoindolinꢀ3ꢀylidene)ꢀ5,7ꢀ
dihydropyrrolo[2,3ꢀf]indoleꢀ2,6(1H,3H)ꢀdione (IBDP, Fig 1a),
which is a structural analogue to IBDF, where the lactones in the
IBDF core are replaced with lactams in the IBDP core. Previously it
was found that the IBDFꢀbased polymers required giant substituents
such as 4ꢀoctadecyldocosyl (containing 40 carbon atoms) to render
polymers soluble in commonly used solvents such as chloroform.10,12
Unfortunately, precursors to such large substituents are not readily
available. This makes the optimization of IBDFꢀbased polymers
difficult. The newly designed IBDP core allows for substitution at
four nitrogen atoms, potentially enabling solubilisation of the IBDPꢀ
based polymers with more easily accessible shorter substituents. We
synthesized an IBDP compound (7 in Scheme 1) with readily
available dodecyl and 2ꢀdecyltetradecyl substituents and used this
IBDP unit as an acceptor and bithiophene or (E)ꢀ1,2ꢀdi(thiophenꢀ2ꢀ
yl)ethane as a donor to form two DꢀA polymers (P1 and P2). Both
polymers showed high ambipolar charge transport performance.
Fig. 1 (a) Structure of IBDF and IBDP; (b) Structure of IBDPꢀMe, its
optimized geometry, LUMO and HOMO distribution through computational
calculation.
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Scheme 1 Synthetic route to the IBDP monomer and polymers: i) Ethanol/reflux.; ii) CH2Cl2/Et3N/0 °C to r.t., THF/MeOH/H2O/K2CO3/r.t.; iii)
CH2Cl2/oxalyl chloride/DMSO/Et3N/ꢀ78 °C to r.t., CH2Cl2/thiophenol/TFAA/BF3 Et2O/r.t.; iv) THF/H2O/ammonium cerium nitrate/r.t.; v)
•
Toluene/PCl5/r.t.; vi) AcOH/Zn/r.t.; vii) AcOH/HCl/reflux; viii) Chlorobenzene/P(oꢀtolyl)3/Pd2(dba)3/120 °C.
Two IBDPꢀbased polymers P1 and P2 were synthesized via the dual band absorption, wherein the low energy band can be attributed
Stille coupling polymerization of 6 with 5,5'ꢀbis(trimethylstannyl)ꢀ to the internal charge transfer (ICT) transition and the high energy
2,2'ꢀbithiophene and (E)ꢀ1,2ꢀbis(5ꢀ(trimethylstannyl)thiophenꢀ2ꢀ band is originated from the πꢀπ* transition.18,19 In solution, the
yl)ethene, respectively. The crude polymers were purified by Soxhlet maximum absorption wavelengths (λmax) are 699 nm for P1 and 711
extraction successively using acetone and hexanes to remove the nm for P2. The λmax of the P1 film remained at 699 nm, but a
oligomers and other impurities. Finally the polymers were dissolved prominent shoulder at 822 nm appeared, indicating the more
in chloroform to afford P1 and P2 in yields of 82% and 98%, extended conjugation of the polymer chains in the solid state.
respectively. Both polymers have very good solubility in several Interestingly, P2 showed a blueꢀshift in absorption from solution
common solvents such as chloroform, toluene, chlorobenzene, and (711 nm) to the film (698 nm), which might be induced by the Hꢀ
1,2ꢀdichlorobenzene at room temperature. The molecular weights of aggregationꢀtype interchain packing in the solid state.20,21 The
these polymers were measured by gelꢀpermeation chromatography optical band gaps of the polymer films are calculated to be 1.23 eV
(GPC) at 80°C with chlorobenzene as eluent and polystyrene as for P1 and 1.22 eV for P2 using the absorption onsets. Cyclic
standards. The number average molecular weight (Mn) and the voltammetry (CV) was used to reveal electrochemical property of
polydispersity index (PDI) were determined to be 128 kDa and 2.89 the polymers (ESI). By using the oxidative onset potentials, HOMO
for P1 and 158 kDa and 1.59 for P2. The thermal stability of the levels were calculated to be ꢀ5.60 eV and ꢀ5.71 eV for P1 and P2,
polymers was characterized by thermogravimetric analysis (TGA). A respectively. LUMO levels were calculated from the reduction onset
5% weight loss was observed at 384 °C for P1 and 380 °C for P2, potentials to be ꢀ3.71 eV and ꢀ3.70 eV for P1 and P2, respectively.
indicating good thermal stability of both polymers (ESI).
The band gaps obtained from the CV (P1: 1.89 eV; P2: 2.01 eV) are
The UVꢀVisꢀIR absorption spectra of the polymers in solution and larger than their optical band gaps, which might be due to the large
in thin film are shown in Fig. 2. Both polymers exhibited typical exciton binding energy that can be as high as ~0.4ꢀ1.0 eV.22,23
P1 and P2 were evaluated as channel semiconductors in bottomꢀ
gate,
bottomꢀcontact
OTFT
devices
fabricated
on
dodecyltrichlorosilane (DDTS) modified SiO2/Si wafer substrates.
Both polymers showed ambipolar charge transport behaviour (see
detailed device data in ESI). For devices based on P1, the best
performance with hole mobility of 0.19 cm2 Vꢀ1 sꢀ1 and electron
mobility of 0.088 cm2 Vꢀ1 sꢀ1 was achieved for the 150 °Cꢀannealed
films (Fig. 3). Annealing at a higher temperature of 200 °C led to a
slight increase in the electron mobility (up to 0.089 cm2 Vꢀ1 sꢀ1), but
a significant drop in the hole mobility (0.057 cm2 Vꢀ1 sꢀ1). For
devices based on P2, the best overall performance with hole/electron
mobilities of 0.10 cm2 Vꢀ1 sꢀ1/ 0.075 cm2 Vꢀ1 sꢀ1 was obtained for the
200 °Cꢀannealed polymer films (ESI). Annealing at a higher
temperature of 250 °C did not further improve the device
performance. We noticed that P1 and P2 showed lower charge
transport performance than some of the IBDF based polymers.12,15
One possible reason for their lower mobility is that an optimal side
chain combination is not reached in these polymers. P1 and P2
Fig. 2 The UVꢀVisꢀIR absorption spectra in solution (chloroform) and in thin
film.
2 | J. Name., 2012, 00, 1-3
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In conclusion, a novel electronꢀaccepting building block,
IBDP, is designed, synthesized, and incorporated into D–A
polymers. Two IBDPꢀbased polymers showed good solution
processability and exhibited a high ambipolar semiconductor
performance in OTFTs with hole mobility up to 0.19 cm2 Vꢀ1 sꢀ1
and electron mobility up to 0.09 cm2 Vꢀ1 sꢀ1. Our preliminary
results demonstrated that IBDP is a promising electron acceptor
building block for polymer semiconductors.
140
120
100
80
VG
VG
-120
-100
-80
-60
-40
-20
0
0 V
0 V
20 V
40 V
60 V
80 V
100 V
-20 V
-40 V
-60 V
-80 V
-100 V
60
40
20
0
Notes and references
-100 -80 -60 -40 -20
0
20
40
60
80 100
VDS (V)
Department of Chemical Engineering and Waterloo Institute for
Nanotechnology (WIN), 200 University Ave W, Waterloo, Ontario, N2L
3G1, Canada.
1E-3
1E-4
1E-5
1E-6
0.016
0.012
0.008
0.004
0.000
VDS = -100V
VDS = 100V
E-mail: yuning.li@uwaterloo.ca; Fax: +1 519-888-4347;
Tel: +1 519-888-4567 ext. 31105
Electronic Supplementary Information (ESI) available: detailed
procedures for the synthesis and device fabrication, and additional data.
See DOI: 10.1039/c000000x/
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side chains on IBDP. However, the excessively strong side chain
interaction in the solid state might hinder the πꢀπ stacking of the
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13.
use of branched side chains with a larger spacer between the
branching point and the backbone such as 4ꢀdecylhexadecyl or four
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14.
transport performance.
Transmission Xꢀray diffraction (XRD) measurement was
15.
performed on polymer flakes of both polymers. P1 and P2 showed
intense primary diffraction peaks at 2θ = 3.26° and 3.51°, which
correspond to the interlayer lamellar dꢀspacing of 2.71 nm and 2.52
nm, respectively. The weak diffraction peak at 2θ = 25.04° for P1 is
originated from the πꢀ π stacking distance of polymer chains, which
was calculated to be 0.355 nm. No noticeable πꢀ π stacking peak was
observed for P2, which might explain the lower performance
observed for P2 than that of P1. The presence of four long side
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carrier mobility of these IBDP polymers compared to the IBDF 20.
21.
polymers as discussed previously. The surface morphology of P1
and P2 thin films spinꢀcoated on dodecyltrichlorosilane (DDTS)
modified SiO2/Si wafer substrates was examined by atomic force
microscopy (AFM). P1 thin films showed fibreꢀlike domains, which
grew slightly as the annealing temperature increased from 100°C to
150°C and remained similar at an annealing temperature of 200°C.
In general, P2 thin films showed poorly defined domains compared
to P1 films, indicative of the less ordered chain packing of P2.
22.
23.
24.
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