Synthesis of two dihydropyrroloindoledione-based copolymers for organic electronics

Article abstract of DOI:10.1002/pola.26471

Two novel dihydropyrroloindoledione (DPID)-based copolymers have been synthesized in a two directional approach and characterized (gel permeation chromatography (GPC), ultraviolet-visible (UV-vis), cyclic voltammetry, and computational models). These planar, broad absorption copolymers show promise for use in organic electronics, with deep energy levels and low bandgaps. The two-directional Knoevenagel condensation used demonstrates the versatility of DPID as a useful yet underexploited conjugated unit.

Full text of DOI:10.1002/pola.26471

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
Synthesis of Two Dihydropyrroloindoledione-Based Copolymers for
Organic Electronics
Joseph W. Rumer,1 Sheng-Yao Dai,2 Matthew Levick,2 Laure Biniek,1 David J. Procter,2
Iain McCulloch1
1Department of Chemistry and Centre for Plastic Electronics, Imperial College London, London SW7 2AZ, United Kingdom
2School of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom
Correspondence to: J. W. Rumer (E-mail: jwrumer@imperial.ac.uk)
Received 18 October 2012; accepted 7 November 2012; published online 5 December 2012
DOI: 10.1002/pola.26471
ABSTRACT: Two novel dihydropyrroloindoledione (DPID)-based
copolymers have been synthesized in a two directional approach
and characterized (gel permeation chromatography (GPC), ultra-
violet-visible (UV–vis), cyclic voltammetry, and computational
models). These planar, broad absorption copolymers show
promise for use in organic electronics, with deep energy levels
and low bandgaps. The two-directional Knoevenagel condensa-
tion used demonstrates the versatility of DPID as a useful yet
C
V
underexploited conjugated unit. 2012 Wiley Periodicals, Inc. J.
Polym. Sci., Part A: Polym. Chem. 2013, 51, 1285–1291
KEYWORDS: conjugated polymer; copolymerization; dihydropyr-
roloindoledione; Knoevenagel condensation; organic electron-
ics; Pummerer-type cyclization; synthesis
INTRODUCTION Organic electronic materials have potential
as thin, lightweight, flexible, large-area, and crucially inexpen-
sive devices, fabricated by printing techniques.1 p-Conjugated
polymers routinely exhibit the required solubility and process-
ability2 and bulk heterojunction organic photovoltaic devices
using organic polymers as light absorbing components are now
close to 10% power conversion efficiency.3 However, the drive
for efficiency improvements and long-term stability continues.4
These are structurally related to DPP and BDP, containing the
bis-lactam molecular architecture (Fig. 1). However, the inclusion
of vinyl linkages directly flanking the acceptor core units
increases their spacing along the polymer backbone. Additionally,
the central six-membered ring in DPID is aromatic in character,
which may further enhance p–p stacking, unlike the quinoidal
nature of BDP and BDF. The synthesis, optical and electrochemi-
cal properties, and computation models are presented.
Diketopyrrolopyrrole (DPP)-based copolymers have recently
attracted much attention:5 the electron-deficient inner-core
flanked by electronically coupled electron-rich units renders
these excellent donor–acceptor n-type materials, with their pla-
narity and ability to hydrogen-bond encouraging p–p stacking.
This can lead to ambipolar charge transport6 and high perform-
ing organic solar cells.7 Likewise, the colorants benzodifura-
none8 (BDF) and benzodipyrrolidone9 (BDP)—the ‘‘stretched’’
DPP—have also been used to construct low-bandgap polymers.
The larger BDP core extends the conjugation and delocalization
of electrons, as well as altering the backbone aspect ratio, which
could further enhance p–p stacking and efficient transport.
EXPERIMENTAL
Instrumental
‘‘NMR spectra’’ were recorded on a Bruker DPX0 400 MHz
spectrometer using an internal deuterium lock at ambient
probe temperatures unless stated otherwise. Chemical shifts
(d) are quoted in ppm relative to the solvent residual peak,
with peak multiplicity (bs, broad singlet; s, singlet; d, dou-
blet; t, triplet; q, quartet; m, multiplet), integration, and cou-
pling constants (J) quoted in Hz (uncorrected) as appropri-
ate. CDCl3 was used as the solvent for all spectra unless
stated otherwise. Proton solvent residual peaks are taken as:
7.26 for CDCl3, 7.15 for C6D6, 3.34 for methanol-d4, and 2.52
for DMSO-d6; and carbon solvent residual peaks as: 77.16
for CDCl3, 128.6 for C6D6, 49.9 for methanol-d4, and 39.7 for
DMSO-d6. ‘‘Mass spectra’’ were recorded by the Imperial Col-
lege London Department of Chemistry Mass Spectrometry
Service on a Micromass Platform II or AutoSpec-Q spectro-
meter. ‘‘ultraviolet-visible (UV–vis) detection’’ was performed
using a UV-1601 Shimadzu UV–vis spectrometer. ‘‘Molecular
Recently, vinyl groups have also been incorporated into do-
nor units, also increasing their aspect ratio and reducing
steric hindrance between polymer chains. This has been
shown to result in closer packing, reducing interlamellar and
p-stacking distances.10
Here, we report two novel dihydropyrroloindoledione (DPID)-
based polymers designed for organic electronic applications.
Additional Supporting Information may be found in the online version of this article.
C
V
2012 Wiley Periodicals, Inc.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 1285–1291
1285

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
13.8 mmol, 1.2 equiv.) was added to an oven-dried round-
bottomed flask, and the flask was sealed and flushed with
nitrogen gas for 20 min. THF (110 mL) was added, and the
resulting suspension was bubbled with nitrogen gas for 15
min. Finally, iodine (2.80 g, 10.8 mmol, 1.0 equiv.) was
added, and the flask flushed again with nitrogen gas for 10
min. The flask was covered in aluminum foil and heated at
ꢀ
60 C for 18 h. The ꢂ0.1 M solution was allowed to cool to
room temperature and then used directly.
FIGURE 1 A structural comparison of various organic colorant
cores with chromophores useful for electronic applications (R
is an alkyl group).
2-Octyldodecanoic Acid
To MeCN (850 mL), H5IO6 was added (53.5 g, 0.235 mol),
and the mixture was stirred vigorously at room temperature
for 15 min. 2-Octyldodecan-1-ol (31.8 g, 0.107 mol) was
ꢀ
then added at 0 C followed by addition of pyridinium chlor-
weights’’ (number-average [Mn] and weight-average [Mw])
were recorded on an Agilent Technologies 1200 series gel per-
meation chromatography (GPC) in chlorobenzene at 80 ꢀC,
using two PL mixed B columns in series, calibrated against
narrow polydispersity polystyrene standards. ‘‘Cyclic voltam-
metry’’ (CV) was performed under an argon atmosphere in a
three-electrode electrochemical cell at a potential scan rate of
50 mVsꢁ1. Thin-films of the polymers were spin-coated (from
chlorobenzene solution, 5 mg mLꢁ1) on conducting indium tin
oxide (ITO) glass substrates and used with a platinum mesh
counter electrode, Ag/Agþ reference calibrated against ferro-
cene and nBu4NPF6 as the electrolyte in anhydrous acetonitrile
solution (0.1 M). ‘‘Microwave chemistry’’ was performed in a
Biotage initiator v.2.3. ‘‘Infrared spectra’’ were recorded using
an FTIR spectrometer as evaporated films or neat using so-
dium chloride windows. Melting points are uncorrected.
ochromate (PCC) (460 mg, 2 mol %) in MeCN (2 ꢃ 50 mL),
and the reaction mixture was stirred for overnight. The reac-
tion mixture was then diluted with ethyl acetate (EtOAc) and
washed with aq. NaHCO3 solution and brine, respectively,
dried (MgSO4), and concentrated in vacuo to give the clean
carboxylic acid (33.3 g, 99%).
1H NMR (400 MHz, CDCl3), d (ppm): 0.89 (t, J ¼ 6.8 Hz, CH3,
6H), 1.26–1.32 (m, CH2, 28H), 1.49 (m, CHCH2, 2H), 1.62 (m,
CHCH2, 2H), 2.35 (m, CH, 1H). 13C NMR (100 MHz, CDCl3), d
(ppm): 14.1 (2 ꢃ CH3), 22.68, 22.70, 27.4, 29.28, 29.36,
29.44, 29.59, 29.63, 31.88, 31.93, 32.18 (16 ꢃ CH2), 45.6
(CH), 183.2 (C¼¼O). IR (ATR): mmax (cmꢁ1): 2954, 2913, 2850,
1696, 1471, 1229, 1220, 953, 716. MS (ESþ): m/z (%): 335
(100, [MþNa]þ), 349 (80), 392 (40); HRMS (ESþ):
C20H40O2Na requires 335.2921, found 335.2917.
Experimental Procedures and Reagents
N,N’-(1,4-Phenylene)bis(2-octyldodecanamide) (2)
To a solution of 2-octyldodecanoic acid (33.3 g, 0.108 mol)
in CH2Cl2 (ꢀ200 mL) was added SOCl2 (14.0 g, 0.117 mol)
slowly at 0 C and the mixture was stirred at room tempera-
ture overnight. The mixture was concentrated in vacuo to
afford 2-octyldodecanoyl chloride which was used without
further purification (crude ¼ 35.3 g).
To a stirring solution of p-phenylenediamine (5.24 g, 48.5
mmol) and triethylamine (11.7 g, 0.116 mol) in CH2Cl2 (600
mL) was added 2-octyldodecanoyl chloride (35.3 g, 106.7
mmol) dropwise at 0 ꢀC. The resulting mixture was then
allowed to warm to room temperature and was stirred for
16 h. After this time the reaction mixture was filtered and
washed with water, followed by ethanol, and dried in vacuo
to yield the product as a poorly soluble yellow solid, which
was used without further purification (crude ¼ 35.5 g), m.p.
120–124ꢀ C (THF).
Detailed experimental procedures are described below. All sol-
vents, reagents, and other chemicals were used as received
from commercial sources, or purified using standard proce-
dures unless stated otherwise. The use of anhydrous chemi-
cals, intuitive from the reaction, infers anhydrous conditions
under an argon or nitrogen atmosphere. Glassware for inert
atmosphere reactions was oven dried and cooled under a flow
of nitrogen. All temperatures—other than room tempera-
ture—are recorded as bath temperatures of the reaction,
unless stated otherwise. Merck aluminum-backed precoated
silica gel (50 F254) plates were used for thin-layer chromatog-
raphy. Visualization was by ultraviolet light (254 nm) and/or
either potassium permanganate (VII), vanillin, iodine, or mo-
lybdate staining with heating as appropriate. Column chroma-
tography was performed on Merck silia gel (Merck 9385 Kie-
selgel 60, 230-400 mesh) under a positive air pressure using
reagent or guaranteed reagent (GR) grade solvent as received.
petroleum ether (PE) refers to petroleum spirit 60–80 ꢀC; Hex
refers to hexane. THF was freshly distilled from sodium/ben-
zophenone. For SmI2-mediated reactions, freshly distilled THF
was further deoxygenated before use by bubbling with nitro-
gen gas for 30 min. CH2Cl2 and Et3N were freshly distilled
from CaH2. All other solvents and reagents were purchased
from commercial sources and used as supplied.
1H NMR (400 MHz, CDCl3) d 0.79–1.01 (m, 12 H, 4 ꢃ CH3),
1.19–1.43 (m, 56 H, 28 ꢃ CH2), 1.44–1.58 (m, 4 H, 2 ꢃ CH2),
1.63–1.79 (m, 4 H, 2 ꢃ CH2), 2.10–2.25 (m, 2 H, 2 ꢃ CH),
7.15 (s, 2 H, 2 ꢃ NH), 7.45 (s, 4 H, 4 ꢃ ArCH). 13C NMR (101
MHz, CDCl3) d 13.98 (2 ꢃ CH3), 14.0 (2 ꢃ CH3), 22.62 (2 ꢃ
CH2), 22.64 (2 ꢃ CH2), 27.7 (4 ꢃ CH2), 29.25 (2 ꢃ CH2),
29.30 (2 ꢃ CH2), 29.47 (2 ꢃ CH2) 29.52 (2 ꢃ CH2), 29.59 (2
ꢃ CH2), 29.62 (2 ꢃ CH2), 29.8 (4 ꢃ CH2), 31.86 (2 ꢃ CH2),
31.91 (2 ꢃ CH2), 33.2 (4 ꢃ CH2), 49.1 (2 ꢃ CH), 120.8 (4 ꢃ
Samarium diiodide was prepared by a modification of the
procedure of Imamoto and Ono.11 Samarium powder (2.00g,
1286
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 1285–1291

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
ArCH), 134.3 (2 ꢃ ArC), 174.4 (C¼¼O). IR (ATR): mmax cmꢁ1
:
of DMSO (0.61 g, 7.76 mmol) in CH2Cl2 (5 mL) dropwise via
cannula, the resulting solution was then stirred for 30 min
before a solution of 4 (1.52 g, 1.94 mmol) in CH2Cl2 (7.4
mL) was added dropwise. The solution was stirred for a fur-
ther 1 h, then NEt3 (1.96 g, 19.4 mmol) was added at ꢁ78
3282 (NH), 2953, 2918, 2849, 1650 (C¼¼O), 1536, 1518. MS
(EIþ): m/z (%): 697 (100, [M]þ), 402 (70); HRMS (ESþ):
C46H84O2N2 requires 696.6527, found 696.6506.
N1,N4-Bis(2-octyldodecyl)benzene-1,4-diamine (3)
ꢀ
ꢀC, and the solution allowed to warm to 20 C. The resulting
To a stirring solution of 2 (35.5 g, 51.0 mmol) in THF (500 mL)
was added LiAlH4 (7.74 g, 0.204 mol). The mixture was reflux
suspension was then stirred for a further 1.5 h. CH2Cl2 (75
mL) and a saturated aqueous solution of NaHCO3 (100 mL)
were then added, and the organic layer was separated and
washed with a saturated aqueous solution of NaHCO3 (2 ꢃ
100 mL), dried with MgSO4 and concentrated in vacuo to
yield the intermediate glyoxamide as a green oil, which was
used immediately without further purification.
ꢀ
for 72 h before quenched by 15-N NaOH solution at 0 C. The
salt was filtered from the mixture and the mixture was washed
by ether for two times. The combined organic fractions were
dried (MgSO4) and concentrated in vacuo afford the unstable
product as brown oil (32.3 g, 99% for three steps).
1H NMR (500 MHz, C6D6), d (ppm): 0.93 (t, J ¼ 6.9 Hz, CH3,
12H), 1.30–1.36 (m, CH2, 64H), 1.57 (m, CH, 2H), 2.98 (d, J
¼ 6.3 Hz, NCH2, 4H), 6.62 (s, ArH, 4H). 13C NMR (125 MHz,
C6D6), d (ppm): 14.8 (4 ꢃ CH3), 23.5, 27.6, 30.22, 30.57,
32.73, 32.99, 38.7 (32 ꢃ CH), 49.6 (2 ꢃ NCH2), 115.3 (4 ꢃ
ArCH), 141.9 (2 ꢃ ArC). IR (ATR): mmax (cmꢁ1): 2920, 2851,
1516, 1464, 1239. MS m/z (ESþ): 669 ([Mþ]100%). HRMS
(ESþ): C46H89N2 requires 669.7021, found 669.7032.
To a solution of the glyoxamide in CH2Cl2 (20 mL) was added
thiophenol (1.68 g, 3.49 mmol). The resulting solution was
stirred for 15 h at 20 ꢀC. TFAA (4.67 mL, 34.9 mmol) was
then added, the solution stirred for 1 h, then BF3.OEt2 (2.42
mL, 19.4 mmol) was added. After 2 h, the solution was cooled
ꢀ
to 0 C and carefully quenched with a saturated aqueous solu-
tion of NaHCO3 (100 mL), then washed with a saturated aque-
ous solution of NaHCO3 (3 ꢃ 25 mL), dried with MgSO4, and
concentrated in vacuo to yield 5 as a deep red oil (crude ¼
1.73 g), which was used without further purification.
N,N’-(1,4-Phenylene)bis(2-hydroxy-N-(2-octyldodecyl)aceta-
mide) (4)
1H NMR (400 MHz, CDCl3), d (ppm): 0.92 (m, CH3, 12H),
1.33 (m, CH2, 64H), 1.77 (m, CH, 2H), 3.48 (m, NCH2, 4H),
4.61 (s, CHS, 2H, one diastereoisomer), 4.63 (s, CHS, 2H, one
diastereoisomer), 6.74 (s, ArH, 2H), 7.26 (m, ArH, 4H), 7.33
(m, ArH, 2H), 7.46 (m, ArH, 4H). 13C NMR (100 MHz, CDCl3),
d (ppm): 14.0 (4 ꢃ CH3), 22.5, 26.1, 29.2, 31.8 (32 ꢃ CH2),
36.0 (2 ꢃ CH), 44.8 (2 ꢃ NCH2), 49.3 (2 ꢃ CHS), 106.3 (2 ꢃ
ArCH), 126.6 (2 ꢃ ArC), 128.6 (2 ꢃ ArCH), 131.1 (2 ꢃ ArC),
133.9 (2 ꢃ ArCH), 139.1 (2 ꢃ ArC), 173.4 (2 ꢃ C¼¼O). IR
(ATR): mmax (cmꢁ1): 2922, 2852, 1699, 1470, 1346, 1159,
872, 738, 689, 649. MS m/z (ESþ): 964 (100%, Mþ). HRMS
(ESþ): C62H95N2O2S2 requires 963.6840, found 963.6825.
To a stirring solution of 3 (32.3 g, 48.3 mmol) and triethyl-
amine (10.8 g, 0.106 mol) in CH2Cl2 (480 mL) was addꢀed ace-
toxyacetyl chloride (14.5 g, 0.106 mol) dropwise at 0 C. The
resulting mixture was then allowed to warm to room tempera-
ture and was stirred for 16 h. After this time, a saturated aque-
ous solution of NaHCO3 was added, and the aqueous layer was
washed with 2 ꢃ CH2Cl2, and the combined organic fractions
were dried (MgSO4) and concentrated in vacuo to yield inter-
mediate acetoxy amide as a pale yellow solid (crude ¼ 47.1 g),
which was used without further purification.
To a solution of intermediate acetoxy amide (47.1 g, 48.3
mmol) and K2CO3 (65.0 g, 0.48 mol) in MeOH/H2O (9:1, 300
mL) and THF (300 mL) was stirred for 18 h at room tem-
perature. K2CO3 was then filtered and washed by EtOAc. H2O
was then added, and the organic layer was separated and
washed with brine, dried (MgSO4), and concentrated in
vacuo to give the crude product. Purification by flash column
chromatography on silica gel eluting with 30% EtOAc in hex-
ane gave 4 (31.3 g, 83% for two steps) as pale yellow oil.
1,5-Bis(2-octyldodecyl)-5,7-dihydro-1H,3H-pyrrolo
[2,3-f]indole-2,6-dione (6)
To a stirred solution of 5 (1.73 g, 1.80 mmol) in THF (30
mL) was added SmI2 (89.8 mL of a 0.1 M solution in THF,
5.0 equiv.) at room temperature. After 14 h, the reaction
mixture was opened to air and aqueous saturated NaHCO3
(250 mL) was added. The aqueous layer was extracted with
EtOAc for three times, the organic layer was dried (Mg2SO4)
and concentrated in vacuo. Purification by column chroma-
tography using 10% EtOAc in petroleum ether as eluant
gave 6 (738 mg, 51% for three steps) as a deep green oil.
1H NMR (400 MHz, CDCl3), d (ppm): 0.85 (t, J ¼ 7.3 Hz, CH3,
12H), 1.17–1.28 (m, CH2, 64H), 1.44 (m, CH, 2H), 3.68 (d, J ¼
7.3 Hz, NCH2, 4H), 3.86 (s, (C¼¼O)CH2, 4H), 7.22 (s, ArCH, 4H).
13C NMR (100 MHz, CDCl3), d (ppm): 14.0 (4 ꢃ CH3), 22.5, 26.1,
29.24, 29.16, 29.21, 29.53, 29.84, 30.96, 31.74, 31.79, 35.9 (32
ꢃ CH2), 53.2 (2 ꢃ CH), 60.5 (2 ꢃ (C¼¼O)CH2), 129.4 (4 ꢃ
ArCH), 140.1 (2 ꢃ ArC), 171.7 (2 ꢃ C¼¼O). IR (ATR): mmax
(cmꢁ1): 2921, 2852, 1657, 1509, 1458, 1383, 1289, 1093. MS
m/z (ESþ): 808 ([MþNaþ] 100%). HRMS (ESþ): C50H93N2O4
requires 785.7130, found 785.7125.
1H NMR (400 MHz, CDCl3), d (ppm): 0.84 (t, J ¼ 7.1 Hz, CH3,
12H), 1.21–1.36 (m, CH2, 64H), 1.82 (m, CH, 2H), 3.52 (d, J
¼ 7.6 Hz, NCH2, 4H), 3.55 (s, (C¼¼O)CH2, 4H), 6.71 (s, ArH,
2H). 13C NMR (100 MHz, CDCl3), d (ppm): 14.0 (4 ꢃ CH3),
22. 5, 26.3, 29.15, 29.88, 31.7 (32 ꢃ CH2), 35.9 (2 ꢃ NCH2),
36.1 (2 ꢃ CH), 44.5 (2 ꢃ (C¼¼O)CH2), 105.7 (2 ꢃ ArCH),
123.6 (2 ꢃ ArC), 139.9 (2 ꢃArCN), 174.5 (2 ꢃ C¼¼O). IR
(ATR): mmax (cmꢁ1): 2920, 2852, 1702 (C¼¼O), 1473, 1376,
1344, 1160, 1125. MS(ESþ): 772 ([MþNa]þ, 100%). HRMS
(ESþ): C50H88N2O2Na requires 771.6729, found 771.6739.
1,5-Bis(2-octyldodecyl)-3,7-bis-phenylsulfanyl-5,7-
dihydro-1H,3H-pyrrolo[2,3-f]indole-2,6-dione (5)
To a stirred solution of oxalyl chloride (0.54 g, 4.26 mmol)
in CH2Cl2 (5 mL) at ꢁ78ꢀC under N2 was added a solution
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 1285–1291
1287

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
44.9 (2 ꢃ NCH2), 100.1 (2 ꢃ C¼¼CH), 122.5 (2 ꢃ CBr), 123.4
(2 ꢃ ArC), 124.8 (2 ꢃ C¼¼CH), 127.3 (2 ꢃ ArCH), 130.4 (2 ꢃ
BrC¼¼CH), 137.8 (2 ꢃ SC¼¼CH), 138.4 (2 ꢃ SC¼¼CH), 140.2
(ArCN), 166.9 (2 ꢃ C¼¼O). IR (ATR): mmax (cmꢁ1): 2920,
2850, 1684, 1604, 1478, 1414, 1381, 1121, 785, 662. MS
(MALDI-Dithranol): 1095 ([M]þ, 100%).
Poly-(3Z)-(7Z)-1,5-bis(2-octyldodecyl)-3,7-bis-
[(5-thiophen-2-yl)-5,7-dihydro-1H,3H-pyrrolo
[2,3-f]indole-2,6-dione-phenyl (P1)
[PDPIDDT-P: Poly-dihyropyrroloindoledionedithiophenyl-phenyl]. A
microwave vial was charged with M1 (76 mg, 0.07 mmol), 1,4-
benzenediboronic acid bis(pinacol) ester (37 mg, 0.09 mmol), 5
mol % of tris(dibenzylideneacetone)dipalladium, and 10 mol %
of triphenylphosphine and sealed. A degassed solution of Ali-
quat 336 (two drops) in toluene (1.5 mL) was then added, fol-
lowed by a degassed aqueous solution (0.3 mL) of potassium
phosphate tribasic (63 mg, 0.30 mmol), and the mixture
refluxed with vigorous stirring for 3 days at 115 ꢀC. The crude
polymer was precipitated in methanol and then purified by
Soxhlet extraction with acetone, hexane, and chloroform.
Remaining palladium residues were removed by vigorously stir-
ring the latter fraction with aqueous sodium diethyldithiocarba-
SCHEME 1 Synthesis of the DPID monomer M1.
ꢀ
(3Z)-(7Z)-1,5-Bis(2-octyldodecyl)-3,7-bis-[(5-bromothio-
phen-2-yl)-5,7-dihydro-1H,3H-pyrrolo[2,3-f]indole-2,6-
dione (M1)
mate for 3 h at 55 C. The organic phase was then separated,
washed (water), concentrated in vacuo, and again precipitated
in methanol, filtered off, and dried under high vacuum to afford
the title compound as a dark purple solid (26 mg, 37% yield).
Mn ¼ 106 kDa, Mw ¼ 186 kDa, PDI ¼ 1.75.
To a solution of 6 (97.6 mg, 0.13 mmol) in THF (2 mL) was
added 2-thiophene-carboxaldehyde (54.8 mg, 0.29 mmol),
pyridine (41 mg, 0.52 mmol), and Ti(OiPr)4 (222 mg, 0.78
mmol). The reaction mixture was stirred in room tempera-
ture for 3 h. Then it was diluted with ethyl acetate (25 mL),
washed with water (25 mL), aqueous NaHCO3 (25 mL), and
brine (25 mL), dried with MgSO4, and concentrated in vacuo
to give the crude product. Purification by flash column chro-
matography on silica gel eluting with 30% CH2Cl2 in hexane
gave M1 (93.7 mg, 66%) as a black solid.
Poly-(3Z)-(7Z)-1,5-bis(2-octyldodecyl)-3,7-bis-
[(5-thiophen-2-yl)-5,7-dihydro-1H,3H-pyrrolo
[2,3-f]indole-2,6-dione-thiophene (P2)
[PDPIDDT-T:
Poly-dihyropyrroloindoledionedithiophenyl-thiop
hene]. A microwave vial was charged with M1 (98 mg, 0.09
mmol), 2,5-bis(trimethylstannyl)thiophene (37 mg, 0.09 mmol),
2.2 mol % of tris(dibenzylideneacetone)dipalladium, and 8.8
mol % of tri(o-tolyl)phosphine. The vial was then sealed, chloro-
benzene added, the mixture degassed and submitted to the
microwave reactor for: 3 min at each of 100, 120, 140, and 160
ꢀC and finally 50 min at 180 ꢀC. The crude polymer was precipi-
tated in methanol and then purified by Soxhlet extraction with
acetone, hexane, and chloroform. Remaining palladium residues
were removed by vigorously stirring the latter fraction with
1H NMR (400 MHz, C6D6), d (ppm): 0.92 (t, J ¼ 6.6 Hz, CH3,
12H), 1.27–1.47 (m, CH2, 64H), 2.10 (m, CH, 2H), 3.77 (d, J
¼ 7.3 Hz, NCH2, 4H), 6.73 (d, J ¼ 4.0 Hz, BrC¼¼CH, 2H), 6.86
(s, C¼¼CH, 2H), 6.89 (d, J ¼ 4.3 Hz, SC¼¼CH, 2H), 7.31 (s,
ArCH, 2H). 13C NMR (100 MHz, CDCl3), d (ppm): 14.8 (4 ꢃ
CH3), 23.5, 27.2, 30.21, 30.9, 32.7 (32 ꢃ CH2), 37.3 (2 ꢃ CH),
FIGURE 2 Determination of M1 configuration by NOE and proton NMR analysis.
1288
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 1285–1291

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
SCHEME 2 Synthesis of DPID polymers P1 and P2.
aqueous sodium diethyldithiocarbamate for 3 h at 55 ꢀC. The or-
ganic phase was then separated, washed (water), concentrated
in vacuo and again precipitated in methanol, filtered off, and
dried under high vacuum to afford the title compound as a dark
purple solid (52 mg, 57% yield). Mn ¼ 25 kDa, Mw ¼ 41 kDa,
PDI ¼ 1.60.
ton on the center ring and the Hc proton on the thiophene
for the Z-isomer, confirming the stereochemistry present.
Meanwhile in the E-isomer, the Hb vinyl proton is shifted
downfield due to the deshielding effect of the carbonyl group
(Fig. 2).18 The Z isomer is desired as this facilitates a plana-
rizing sulfur–oxygen interaction believed to result from a 3-
center-4-electron interaction between a lone pair of electrons
on the oxygen atom and a r*
orbital leading to a weak
SAC
unsymmetrical hypervalent bond.19
RESULTS AND DISCUSSION
The DPID tricycle 6 was synthesized as depicted in Scheme 1.
p-Phenylenediamine 1 underwent two-directional acylation
with 2-octyldodecanoyl chloride to give the diamide 2 and
subsequent reduction to give the corresponding diamine 3 in
good yield. Reaction with acetoxyacetyl chloride followed by
ester hydrolysis proceeds in good yield to give the 1,4-bis(hy-
droxyacetamide) 4. Swern oxidation affords the 1,4-bis(glyoxa-
mide), which then undergoes a two-directional Pummerer-
type12 cyclization as previously developed by Procter et al.13
to close the intermediate tricycle 5. Reductive cleavage of the
sulfanyl groups by samarium iodide14,15 completes the DPID
core (6). The use of a bulky thiophenol in the Pummerer-type
cyclization gave predominantly (>5:1) the linear isomer
shown (5), presumably due to unfavorable steric interactions
involved in forming the alternative ‘‘bent’’ isomer.
The synthesis of the polymers is shown in Scheme 2. The
phenyl copolymer P1 was synthesized under standard
Suzuki coupling conditions in a toluene/water solvent sys-
tem, whereas the thiophene copolymer P2 was synthesized
under standard microwave Stille coupling conditions in
chlorobenzene. The polymers were purified by precipitation
from methanol followed by Soxhlet extraction using acetone,
hexane, and finally chloroform. The latter fraction was then
heated and vigorously stirred with aqueous sodium diethyl-
dithiocarbamate to remove residual catalytic metal impur-
ities. Lower molecular-weight oligomers were readily
removed in the acetone and hexane fractions, giving a partic-
ularly high number-average molecular weight for P1 and a
satisfactory value for P2 (Mn ¼ 106 and 25 kDa for P1 and
P2, respectively) with moderate polydispersity indexes
(PDIs) (Table 1).
The ‘‘linear’’ DPID tricycle 6 was then subjected to a two-
directional Knoevenagel condensation with 5-bromo-2-thio-
phenecarboxaldehyde. Use of the coordinating Lewis acid
titanium(IV) iso-propoxide promotes the reaction forming
the Z isomer.16 Separation by column chromatography thus
afforded the monomer M1 almost exclusively in its expected
cis (Z) configuration, as a waxy black solid17 (Fig. 2). A nu-
clear Overhauser effect experiment reveals a through-space
interaction between the vinyl proton Hb and both the Ha pro-
Optical absorption spectra of the DPID monomer M1 and
polymers P1 and P2 are shown in Figure 3 and key proper-
ties summarized in Table 1. While the monomer displays
absorption maxima below 450 nm, both polymers display a
maxima above 600 nm due to extended conjugation. The
red-shift in solution (ꢂ25 nm) from P1 to P2 can be attrib-
uted to the difference of comonomer from phenyl to the more
TABLE 1 Properties of DPID Polymers P1 and P2
abs
kmax
Energy Levels
(eV)b
(nm)
onset
onset
Solutionc
Filmd
EHOMO
ELUMO
Mn
Mw
Eox
Ered
(kDa)a
(kDa)a
PDIa
1.7
Eg
(eV)
(eV vs. Fc/Fcþ)
(eV vs. Fc/Fcþ)
opt
Compounds
P1
106
186
630
655
635
655
1.68
0.66
ꢁ0.91
ꢁ0.85
ꢁ5.47
ꢁ5.47
ꢁ3.89
ꢁ3.95
P2
25
41
1.6
1.57
0.67
a
c
Determined by GPC using polystyrene standards and PhCl as the elu-
Solutions in dilute PhCl.
Thin-films spin-coated from ꢂ5 mg mLꢁ1 PhCl solutions on glass
d
˚
ent at 80 C.
b
onset
Calculated using the equations EHOMO ¼ ꢁ Eox
(vs. Fc/Fcþ) – 4.8 eV,
substrates.
onset
ELUMO ¼ ꢁ Ered
(vs. Fc/Fcþ) þ 4.8 eV.20
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 1285–1291
1289

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
mated from the oxidation onset, are both –5.47 eV. The low-
est unoccupied molecular orbital (LUMO) energy levels of P1
and P2, estimated from the reduction onset, are ꢁ3.89 and
ꢁ3.95 eV, respectively. Such deep energy levels are compara-
ble to those of BDP-based polymers, showing stronger elec-
tron affinities and lower electron densities than typical DPP-
based polymers. These deep HOMO energy levels could lead
to a high open-circuit voltage (Voc) in devices and may indi-
cate good air stability.
The difference in bandgap (ꢂ0.1 eV) between P1 and P2 is
related to a lower P2 LUMO level, as found by CV. This might
be due to the reduced P2 dihedral angle (between the DPID
cores and flanking vinyl groups) allowing a more planar con-
jugated backbone.21
Figure 5 displays the optimized structures of P1 and P2,
their HOMO and LUMO energy distributions and their calcu-
lated bandgaps and dihedral angles (at the B3LYP/6-31G*
level, for N-methyl-substituted polymers, modeled as tet-
ramers only shown in part). While both polymers are almost
fully planar, P2 shows less torsional twisting (consistently a
0ꢀ dihedral angle) between the DPID core and the flanking
vinyl groups. This supports the notion that the slight twist-
ing of P1 induces a bandgap ꢂ0.1 eV wider than more pla-
nar P2. Interestingly, for both polymers the HOMO and
LUMO are both delocalized along the polymer chain, as
opposed to being localized on the donor and acceptor parts,
FIGURE 3 Normalized UV–vis absorption spectra of M1 and
polymers P1 and P2; dilute solutions are in chlorobenzene; and
thin-films spin-coated from ꢂ5 mg mLꢁ1 chlorobenzene solu-
tions on glass substrates.
electron rich and more planarizing thiophene unit. The red-
shift (ꢂ20 nm in the onset of absorption) on going from solu-
tion to film is not very strong, presumably due to aggregation
in the solutions from intermolecular interactions such as
solid-state packing effects, which may be beneficial for charge
transport. In addition, P1 and P2 both display a particularly
broad absorption, which may be favorable for light absorption
and subsequent charge generation in heterojunction solar
cells. The low optical bandgaps show DPIDs should be effec-
tive units for constructing low-bandgap polymers.
Electrochemical behavior is summarized in Table 1 and
shown in Figure 4. The polymers were investigated by cyclic
voltammetry (CV) in a three-electrode electrochemical cell
with an ITO working electrode, Ag/Agþ reference electrode
and Pt counter electrode. Bu4NPF6 in acetonitrile solution
(0.1 M) was used as the electrolyte. Thin-films of the poly-
mers were spin-coated (from chlorobenzene solution, 5 mg
mLꢁ1) on ITO conducting glass substrates. The potentials
were calibrated using the ferrocene/ferrocenium redox cou-
ple (Fc/Fcþ).
Both polymers show irreversible reduction at negative
potential and pseudoreversible oxidation at positive scan.
The highest occupied molecular orbital (HOMO) levels, esti-
FIGURE 5 Segments of energy minimized structures (B3LYP/6-
31G*) of P1 and P2 tetramers with N-methyl substitution show-
ing calculated dihedral angles, with visualization of the HOMO
(bottom) and LUMO (top) energy distributions and calculated
bandgap beneath each structure.
FIGURE 4 Cyclic voltammograms of P1 and P2 (thin-films spin-
coated from chlorobenzene solution [5 mg mLꢁ1] on conduct-
ing indium tin oxide [ITO] glass substrates.
1290
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 1285–1291

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
Soc. 2012, 134, 16532–16535; (f) X. Guo, M. Zhang, L. Huo, C.
Cui, Y. Wu, J. Hou, Y. Li, Macromolecules 2012, 45, 6930–6937.
respectively. This large delocalization could facilitate
enhanced ambipolar transport.
6 J. D. Fan, J. Seifter, B. Lim, R. Hufschmid, A. J. Heeger, F.
Wudl, J. Am. Chem. Soc. 2011, 133, 20799–20807.
CONCLUSIONS
7 W. Li, W. S. C. Roelofs, M. M. Wienk, R. A. J. Janssen,
J. Am. Chem. Soc. 2012, 134, 13787–13795.
In summary, two novel DPID-based copolymers were
designed and synthesized by a completely two-directional
pathway. Both polymers show broad, long wavelength absorp-
tion and deep energy levels. PDPIDDT-P [P1] and PDPIDDT-T
[P2] are characterized by UV–vis absorption spectroscopy,
electrochemical oxidation and reduction (CV) and computa-
tional modeling. The broad absorption profile and planar
backbone of PDPIDDT-T [P2] makes it a promising donor poly-
mer for both organic transistors and solar cells.
8 K. Zhang, B. Tieke, Macromolecules 2011, 44, 4596–4599.
9 C. Weibin, J. Yuen, F. Wudl, Macromolecules 2011, 44,
7869–7873.
10 H. Chen, Y. Guo, G. Yu, Y. Zhao, J. Zhang, D. Gao, H. Liu,
Y. Liu, Adv. Mater. 2012, 24, 4618–4622.
11 T. Imamoto, M. Ono, Chem. Lett. 1987, 501.
12 L. H. S. Smith, S. C. Coote, H. F. Sneddon, D. J. Procter,
Angew. Chem. Int. Ed. 2010, 49, 5832.
The investigation of organic photovoltaic devices and organic
field-effect transistors, both with varied aromatics flanking
the DPID core, varied comonomers, and linear alkyl chains
for transistor applications22 will be of interest. Work in this
direction is in progress and will be reported in due course.
13 (a) M. Miller, W. Tsang, A. Merritt, D. J. Procter, Chem.
Commun. 2007, 498–500; (b) C. Ovens, N. G. Martin, D. J.
Procter, Org. Lett. 2008, 10, 1441; (c) M. Miller, J. C. Vogel, W.
Tsang, A. Merritt, D. J. Procter, Org. Biomol. Chem. 2009, 7,
589–2597; (d) L. H. S Smith, T. T. Nguyen, H. F. Sneddon, D. J.
Procter, Chem. Commun. 2011, 47, 10821.
14 (a) D. J. Procter, R. A. Flowers, II, T. Skrydstrup, Organic
Synthesis Using Samarium Diiodide: A Practical Guide; Cam-
bridge, UK: RSC Publishing, 2009; (b) K. L. Turner, T. M. Baker,
S. Islam, D. J. Procter, M. Stefaniak, Org. Lett. 2006, 8, 329; (c)
L. A. McAllister, K. L. Turner, S. Brand, M. Stefaniak, D. J.
Procter, J. Org. Chem. 2006, 71, 6497; (d) L. A. McAllister, R. A.
McCormick, K. M. James, S. Brand, N. Willetts, D. J. Procter,
Chem. Eur J. 2007, 13, 1032; (e) K. M. James, N. Willetts, D. J.
Procter, Org. Lett. 2008, 10, 1203; (f) S. C. Coote, S. Quenum,
D. Procter, J. Org. Biomol. Chem. 2011, 9, 5104.
ACKNOWLEDGMENTS
This work was carried out under EPSRC grant EP/G037515/1
and with funding from the University of Manchester.
REFERENCES AND NOTES
1 (a) M. Pagliaro, G. Palmisano, R. Ciriminna, Flexible Solar
Cells; Wiley-VCH: Weinheim, 2008; (b) H. Zhou, L. Yang, W.
You, Macromolecules 2012, 45, 607–632; (c) A. Facchetti, Chem.
Mater. 2011, 23, 733–758; (d) P. M. Beaujuge, J. M. J. Frechet,
J. Am. Chem. Soc. 2011, 133, 20009–20029. (e) H. Yan, Z. H.
15 S. C. Coote, R. A. Flowers, II, T. Skrydstrup, D. J. Procter, In
Organic Synthesis Using Samarium Diiodide. Encyclopedia of
Radicals in Chemistry, Biology and Materials; C. Chatgilialoglu,
A. Studer, Eds.; Wiley-VCH: Weinheim, 2011; pp 849–900.
ꢀ
€
Chen, Y. Zheng, C. Newman, J. R. Quinn, F. Dotz, M. Kastler,
A. Facchetti, Nature 2009, 457, 679–686.
16 (a) L. Sun, N. Tran, F. Tang, H. App, P. Hirth, G. McMahon,
C. Tang, J. Med. Chem. 1998, 41, 2588–2603; (b) B. A. Robi-
chaud, K. G. Liu, Tett. Lett. 2011, 52, 6935–6938; (b) A. Mille-
maggi, R. J. K Taylor, Eur. J. Org. Chem. 2010, 41, 4527–4547.
2 Handbook of Conducting Polymers, 3rd ed.; T. A. Skotheim,
J. R. Reynolds, Eds.; CRC Press: Boca Raton, Florida, USA,
2007.
3 (a) H. Zhicai, C. Zhong, S. Su, M. Xu, H. Wu, Y. Cao, Nat. Pho-
ton. 2012, 6, 591–595; (b) R. F. Service, Science 2011, 332, 293.
17 L. Sun, N. Tran, F. Tang, H. App, P. Hirth, G. McMahon, C.
Tang, J. Med. Chem. 1998, 41, 2588–2603.
4 M. Jørgensen, K. Norrman, S. A. Gevorgyan, T. Tromholt, B.
Andreasen, F. C. Krebs, Adv. Mater. 2012, 24, 580–612.
18 Y. Lai, L. Ma, W. Huang, X. Yu, Y. Zhang, H. Ji, J. Tian, Bio-
org. Med. Chem. Lett. 2010, 20, 7349–7353.
5 (a) Z. Chen, M. J. Lee, R. S. Ashraf, Y. Gu, S. Albert-Seifried,
M. Meedom Nielsen, B. Schroeder, T. D. Anthopoulos, M. Hee-
ney, I. McCulloch, H. Sirringhaus, Adv. Mater. 2012, 24,
647–652; (b) H. Bronstein, Z. Chen, R. S. Ashraf, W. Zhang, J.
Du, J. R. Durrant, P. Shakya Tuladhar, K. Song, S. E. Watkins,
Y. Geerts, M. M. Wienk, R. A. Janssen, T. Anthopoulos, H. Sir-
ringhaus, M. Heeney, I. McCulloch, J. Am. Chem. Soc. 2011,
133, 3272–3275; (c) X. Zhang, L. J. Richter, D. M. DeLong-
champ, R. J. Kline, M. R. Hammond, I. McCulloch, M. Heeney,
R. S. Ashraf, J. N. Smith, T. Anthopoulos, B. Schroeder, Y. H.
Geerts, D. A. Fischer, M. F. Toney, J. Am. Chem. Soc. 2011,
133, 15073–15084; (d)A. T. Yiu, P. M. Beaujuge, O. P. Lee, C. H.
ꢀ
ꢀ
19 C. Rethore, A. Madalan, M. Fourmigue, E. Canadell, E. B.
ꢀ
Lopes, M. Almeida, R. Clerac, N. Avarvari, New J. Chem. 2007,
31, 1468–1483.
20 C. M. Cardona, W. Li, A. E. Kaifer, D. Stockdale, G. C. Bazan,
Adv. Mater. 2011, 23, 2367–2371.
21 (a) H. Bronstein, D. S. Leem, R. Hamilton, P. Woebkenberg,
S. King, W. Zhang, R. S. Ashraf, M. Heeney, T. Anthopoulos, J.
de Mello, I. McCulloch, Macromolecules 2011, 44, 6649–6652;
(b) R. S. Ashraf, A. J. Kronemeijer, D. James, H. Sirringhaus, I.
McCulloch, Chem. Commun. 2012, 48, 3939–3941.
22 W. Zhang, J. Smith, S. E. Watkins, R. Gysel, M. McGehee,
A. Salleo, J. Kirkpatrick, R. S. Ashraf, T. Anthopoulos, M.
Heeney, I. McCulloch, J. Am. Chem. Soc. 2010, 132,
11437–11439.
ꢀ
Woo, M. F. Toney, J. M. J. Frechet, J. Am. Chem. Soc. 2012,
134, 2180–2185; (e) C. Kanimozhi, N. Yaacobi-Gross, K. W.
Chou, A. Amassian, T. D. Anthopoulos, S. Patil, J. Am. Chem.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2013, 51, 1285–1291
1291