Macromolecules
ARTICLE
Table 1. Polymer Properties and Yields
yield (%) Mn (kDa) [PDI]a soln λmaxb abs (nm) film λmaxc abs (nm) Egopt d (eV) E1/2rede (V) LUMOf (eV) HOMOg (eV)
PNDI-0Boc
PNDI-1Boc
PNDI-2Boc
PNDI-1BocL
PNDI-2BocL
87
74
76
74
93
8.8 [2.5]
4.0 [1.8]
7.2 [1.6]
4.3 [1.9]
14 [1.8]
453
380
381
467
578
471
384
382
476
576
2.31
2.19
1.94
2.37
1.96
ꢀ0.96
ꢀ0.90
ꢀ0.84
ꢀ1.20
ꢀ1.18
ꢀ3.79
ꢀ3.83
ꢀ3.90
ꢀ3.54
ꢀ3.54
ꢀ6.10
ꢀ6.02
ꢀ5.84
ꢀ5.90
ꢀ5.49
a Number-average molecular weight and polydispersity (SEC vs polystyrene standards in THF). b Solution absorption spectra (∼5 ꢁ 10ꢀ6 M CHCl3).
c Thin film absorption spectra from spin-cast CHCl3 solutions. d Optical energy gap estimated from the absorption-edge or onset of organic thin films.
e CV measurements of thin films vs Fc/Fcþ. f Estimated from LUMO = ꢀ(normalized Fc/Fcþ) ꢀ E1/2red. g Estimated from HOMO = LUMO ꢀ Eg
.
opt
t
saturated (6.4 M) sodium azide (7 mL), BuNH4Br (4.1 mg), and
dichloromethane (3.5 mL) at ꢀ5 ꢀC over 1.5 h. The biphasic mixture
was stirred for 10 min after the addition was complete. The organic
phase was separated and the aqueous phase was extracted with cold
dichloromethane (2 ꢁ 20 mL). The organic phases were combined and
washed with cold water (2 ꢁ 30 mL). The solution was then dried over
MgSO4 at 0 ꢀC and filtered over a mixture of Celite and MgSO4. The
filtrate was subsequently dried over CaH2 at 0 ꢀC for 40 min. The
mixture was filtered again through a pad of Celite and MgSO4. The light
(2 ꢁ 60 mL). The combined organics were washed with water (2 ꢁ
50 mL) and dried over Na2SO4. The solution was concentrated by
vacuum and precipitated into methanol. The precipitated polymer was
subjected to a Soxhlet extraction with acetone and methanol for 48 h to
remove low-molecular weight polymer fragments. The polymer was
redissolved in chloroform, precipitated into methanol, and dried under
reduced pressure. See Table 1 for further polymer data. PNDI-0Boc:
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orange solid (87%). H (300 MHz, CDCl3): 8.89 (br, 2H), 7.58 (br,
4H), 4.11 (br, 4H), 2.01 (m, 2H), 1.03ꢀ1.49 (m, 64H), 0.84 (m, 12H).
13C (300 MHz, CDCl3): 163ꢀ162, 147, 140, 136, 129ꢀ128, 128ꢀ125,
124ꢀ123, 45, 37ꢀ36, 32, 31, 30ꢀ29, 26, 23ꢀ22, 14. PNDI-1Boc: red
t
yellow filtrate was added to BuOH (15 mL) and heated at reflux
overnight. The cloudy-white solution was cooled to room temperature
and the solvent removed under reduced pressure to provide an off-
white solid. The residue was purified via flash chromatography using a
mixture of ethyl acetate and hexane (1:4) as eluent. 2c was isolated as
a white solid (2.4 g, 77%). 1H (300 MHz, CDCl3): δ 8.32 (d, 1H), 7.26
(d, 1H), 6.94 (dd, 1H), 6.92 (s, 1H), 1.46 (s, 9H). 13C (75 MHz,
CDCl3): δ 151.9, 137.4, 133.1, 126.6, 122.5, 122.0, 110.5, 81.6, 28.2 (3).
HRMS-FABþ (m/z): calcd for C11H13O2NBr2, 350.92947; found,
350.92859; m/z 351 (14%), 296 (39%), 251 (16%), 165 (8%), 154
(100%), 107 (32%).
Synthesis of 2. A 50 mL air-free Schlenk flask was charged with 2c
(1.1 g, 3.1 mmol) in diethyl ether (20 mL) at ꢀ78 ꢀC. 1.6 M MeLi
(2.05 mL, 3.3 mmol) was added to the solution dropwise and allowed to
stir for 10 min at ꢀ78 ꢀC. The solution was allowed to warm to 0 ꢀC.
The yellow solution was slowly transferred via cannula to a 100 mL air-
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solid (74%). H (500 MHz, CDCl3): 8.90 (br, 2H), 8.26 (br, 1H),
7.92ꢀ7.51 (br, 1H), 7.30 (br, 1H), 6.12 (br, 1H), 4.15 (br, 4H), 2.04 (m,
2H), 0.97ꢀ1.73 (m, 73H), 0.86 (m, 12H). 13C (125 MHz, CDCl3):
163ꢀ162, 153ꢀ152, 147, 144, 141, 137ꢀ134, 129ꢀ123, 81ꢀ80, 45,
37ꢀ36, 32ꢀ31, 31ꢀ29, 29ꢀ28, 27ꢀ26, 23ꢀ22, 14. PNDI-2Boc:
1
brown-red solid (76%). H (500 MHz, CDCl3): 8.91 (br, 2H), 7.99
(br, 2H), 6.03 (br, 2H), 4.16 (br, 4H), 2.03 (m, 2H), 0.99ꢀ1.61 (m,
82H), 0.85 (m, 12H). 13C (125 MHz, CDCl3): 164ꢀ160, 154ꢀ152,
144ꢀ143, 141, 139ꢀ136, 134ꢀ130, 129ꢀ123, 122ꢀ119, 81ꢀ80, 45,
37ꢀ36, 32ꢀ31, 31ꢀ29, 29ꢀ27, 27ꢀ26, 23ꢀ22, 14.
General Ladderization Treatment Generating PNDI-xBocL. Litera-
ture procedures were adapted to form the ladder polymers.74 To a
single-neck round-bottom flask, PNDI-xBoc (0.1 mmol) was dissolved
in dichloromethane (5ꢀ10 mL). Trifluoroacetic acid (3ꢀ4 mL) and
anisole (0.5 mL) were added and the mixture was heated at reflux
overnight. The reaction solution was subsequently cooled to room
temperature and the solution was carefully and slowly added to a mixed
solvent of triethylamine (10 mL) and acetone (100 mL). The precipitate
was collected by filtration and then dissolved in triethylamine (5 mL).
The solution was heated in a screw-cap vial at 80 ꢀC overnight. The
solution was then cooled to room temperature, precipitated in acetone,
and filtered. The solids were washed with acetone and dried to yield the
t
free Schlenk flask containing 1.7 M BuLi (6.08 mL, 10.3 mmol) in
diethyl ether (7 mL) at ꢀ78 ꢀC. The mixture was stirred for 4 h at
ꢀ78 ꢀC before allowing the reaction to slowly warm to 0 ꢀC. The dark
orange slurry was recooled to ꢀ78 ꢀC before adding 1 M trimethyltin
chloride (8.33 mL, 8.33 mmol). The light clear orange solution was
allowed to warm to 0 ꢀC before quenching with water (20 mL). The
organics were separated and the aqueous phase was extracted with
diethyl ether (2 ꢁ 20 mL). The organics were combined and washed
with water (2 ꢁ 30 mL) and brine (30 mL). The isolated organics were
dried over Na2SO4, filtered, and the solvent removed under reduced
pressure to produce a red-orange oil. The residue was purified via flash
chromatography by eluting through basic silica (treated with 9:1 hexane:
triethylamine) using hexane as eluent. 2 was isolated as a white crystal-
line solid (0.31 g, 19%). 1H (300 MHz, CDCl3): 7.56 (s, 1H), 7.39 (d,
1H), 7.25 (d, 1H), 6.24 (s, 1H), 1.50 (s, 9H), 0.32 (s, 9H), 0.28 (s, 9H).
13C (75 MHz, CDCl3): δ 153.93, 143.68, 142.82, 136.42, 136.03,
132.23, 130.53, 80.28, 28.44 (3), ꢀ8.55 (3), ꢀ9.49 (3). MS/EI: m/z
540 (Naþ), 504 (17%), 448 (100%), 400 (10%), 286 (15%), 165 (46%),
135 (10%).
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final ladderized polymer product. PNDI-1BocL: red solid (74%). H
(500 MHz, CDCl3): 9.74ꢀ10.50 (br, 2H), 7.83ꢀ9.53 (br, 3H),
3.79ꢀ4.52 (br, 4H), 1.88ꢀ2.52 (m, 2H), 0.95ꢀ1.79 (m, 64H), 0.84
(m, 12H). 13C (125 MHz, CDCl3): 165ꢀ160, 150ꢀ140, 138ꢀ134,
130ꢀ120, 110, 45, 37ꢀ36, 32ꢀ31, 31ꢀ29, 27ꢀ26, 23ꢀ22, 14. PNDI-
1
2BocL: violet-black solid (93%). H (500 MHz, CDCl3): 9.63ꢀ10.50
(br, 1H), 9.24 (br, 2H), 7.04ꢀ8.76 (br, 1H), 5.23 (br, 4H), 2.37 (m,
2H), 1.04ꢀ2.25 (m, 64H), 0.87 (m, 12H). 13C (125 MHz, CDCl3):
165ꢀ158, 151ꢀ146, 145ꢀ137, 135ꢀ117, 115ꢀ106, 45, 37ꢀ35,
32ꢀ31, 31ꢀ29, 29ꢀ27, 27ꢀ26, 23ꢀ22, 14.
OFET Device Fabrication. Thin film transistors were fabricated as
typical top-contact bottom-gate devices on silicon substrates. Heavily
doped p-type silicon Æ100æ substrates from Montco Silicon Technolo-
gies Inc. with a 300 nm ((5 nm) thermal oxide layer acted as common
gate, dielectric layer, and substrate. The substrates were cleaned by
sequential ultrasonication in acetone, methanol, and isopropyl alcohol
for 10 min followed by an air plasma treatment. The optimized
conditions used for obtaining the electron mobility measurements are
General Synthesis for PNDI-xBoc. To an air-free Schlenk flask,
Pd(PPh3)2Cl2 (0.005 mmol), NDIꢀBr2 (0.10 mmol), and 1,73 2, or
374 (0.10 mmol) were added within a dry glovebox and dissolved with
toluene (5 mL). The capped and sealed vessel was heated at 90 ꢀC for 4
days prior to injecting bromobenzene (0.2 mL) and stirring for 12 h. The
reaction was cooled to ambient and KF (1 g) in water (2 mL) was
injected and stirred for 2 h. The solution was extracted with chloroform
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dx.doi.org/10.1021/ma2004822 |Macromolecules 2011, 44, 4721–4728