Using the nitro group to induce p-stacking in terthiophenes

Article abstract of DOI:10.1139/V09-165

A new synthetic route to mononitrated oligothiophenes is described, as well as the preparation of halogenated derivatives (Br, I) thereof. An unusual deep red colour is observed and explained, with the aid of DFT calculations, as arising from a significant quinoidal contribution to the molecular structure. The crystal structures of two compounds, H(C₄H₂S) ₃NO₂ and Br(C₄H₂S) ₃NO₂, are presented. Both compounds have planar sheets held together by intermolecular short contacts (hydrogen bonds and, for the latter, NO₂...Br interactions); the sheets do not directly superimpose, so the effect of the π-stacking is not maximized. Solid-state fluorescence and extended-Hueckel band-structure calculations are also presented for these materials.

Full text of DOI:10.1139/V09-165

309
Using the nitro group to induce p-stacking in
terthiophenes
Wendy A. Sears, Craig D. MacKinnon, Robert C. Mawhinney, Lauren C. Sinnemaki,
Matthew J. Johnson, A. John Winter, and Craig M. Robertson
Abstract: A new synthetic route to mononitrated oligothiophenes is described, as well as the preparation of halogenated
derivatives (Br, I) thereof. An unusual deep red colour is observed and explained, with the aid of DFT calculations, as
arising from a significant quinoidal contribution to the molecular structure. The crystal structures of two compounds,
H(C4H2S)3NO2 and Br(C4H2S)3NO2, are presented. Both compounds have planar sheets held together by intermolecular
short contacts (hydrogen bonds and, for the latter, NO2ÁÁÁBr interactions); the sheets do not directly superimpose, so the ef-
fect of the p-stacking is not maximized. Solid-state fluorescence and extended-Hu¨ckel band-structure calculations are also
presented for these materials.
Key words: oligothiophene, organic semiconductor, crystal structure, band structure, nitro-substitution.
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Resume : On decrit une nouvelle methode generale de synthese des oligothiophenes mononitres ainsi que la preparation
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de leurs derives bromes et iodes. On a observe une couleur rouge fonce inhabituelle et, en se basant sur des calculs de la
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theorie de la fonctionnelle de la densite (TFD), on suggere qu’elle resulte d’une importante contribution quinonoıdale a la
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structure moleculaire. On a determine les structures cristallines des deux composes H(C4H2S)3NO2 et Br(C4H2S)3NO2. Les
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deux composes se presentent sous la forme de feuillets plans maintenus en place par des contacts intermoleculaires courts
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(liaisons hydrogenes et, dans le deuxieme cas, interactions NO2ÁÁÁBr); les feuillets ne sont pas directement superposes et il
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en resulte que l’effet de superposition p n’est pas maximise. On rapporte aussi les resultats obtenus pour la fluorescence a
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l’etat solide de ces materiaux ainsi que les calculs etendus de Hu¨ckel de leur structure de bande.
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Mots-cles : oligothiophene, semiconducteur organique, structure cristalline, structure de bande, substitution par un groupe
nitro.
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[Traduit par la Redaction]
substituted with both an electronic acceptor and an elec-
tronic donor will contain an internal charge-transfer elec-
tronic transition that can be exploited for non-linear optical
devices6,7 or as light-emitting diode dyes.8 These electronic
consequences are well-documented; far less is known of the
structural consequences. Perfluorination9 and a,u-cyano-
substitution,10,11 for example, both lead to a greater degree
of p-stacking in the single-crystal structure, which is fortu-
nately a beneficial outcome as p-stacking has been shown
to increase mobility in standard device configurations.12,13
The nitro group is a typical example of a strong electron-
withdrawing group that has been attached to molecular ma-
terials.14–17 While the resultant materials have been well-
studied electronically, structural investigations into the con-
sequences of nitro substitution are sparse. Therefore, we
have undertaken the synthesis and crystal growth of structur-
ally simple nitro-substituted oligothiophenes. We chose to
limit ourselves to mono-nitrated derivatives because these
species are of greater synthetic interest, potentially allowing
Introduction
Organic materials are carbon-based small molecules or
polymers with interesting electronic properties. Two of the
most studied organic semiconductors are the oligothio-
phenes1–3 and the acenes.4 The promise of organic materials
is held in the ability of the compounds to undergo ‘‘tuning’’
of the electronic structures through molecular substitution.
Thus, an overwhelming variety of oligomers have been
made, from dendrimers to polymers to molecules substituted
at every position.
Unsubstituted organic semiconductors are mostly p-type
(where the charge is carried by positive charges, or holes).
Attachment of electron-withdrawing groups can convert
them to n-type conductors (negative charge carriers), e.g.,
dihexylsexithiophene is p-type while bis(perfluorohexyl)sex-
ithiophene is n-type.5 The lowering of the frontier orbitals
upon attachment also increases environmental stability be-
cause reactivity with oxygen in the air is reduced. Molecules
Received 28 August 2009. Accepted 28 October 2009. Published on the NRC Research Press Web site at canjchem.nrc.ca on 4 March
2010.
W.A. Sears, C.D. MacKinnon,1 R.C. Mawhinney, L.C. Sinnemaki, M.J. Johnson, and A.J. Winter. Department of Chemistry,
Lakehead University, 955 Oliver Road, Thunder Bay, ON P7B 5E1, Canada.
C.M. Robertson.2 Department of Chemistry, University of Waterloo, Waterloo, ON N2L 3G1, Canada.
1Corresponding author (e-mail: craig.mackinnon@lakeheadu.ca).
2Present address: Department of Chemistry, University Science Laboratories, South Road, Durham DH1 3LE, United Kingdom.
Can. J. Chem. 88: 309–317 (2010)
doi:10.1139/V09-165
Published by NRC Research Press

310
Can. J. Chem. Vol. 88, 2010
Scheme 1.
subsequent substitution to generate more complex mole-
cules. The use of the letter ‘‘T’’ as an abbreviation for the
2,5-disubstituted thienyl ring is common in the oligothio-
phene literature (see Scheme 1). Using this abbreviation, we
report herein the synthesis of several XTnNO2 species,
where X = H, Br, or I, and n = 2 (bithiophene) and 3 (ter-
thiophene). We also present the crystal structures of
HT3NO2 and BrT3NO2.
Results and discussion
Synthesis
The compounds HT3NO2 and BrT3NO2 have been previ-
ously reported, but experimental details are scanty.18 Fur-
ther, we found the reported conditions to be excessively
harsh, resulting in loss of regiochemical control, multiple ni-
trations, or oxidation of the thiophene ring.19 Therefore, we
report a new, milder synthesis of these species. We also re-
port synthesis of the new species BrT2NO2 and IT3NO2,
which can be made the same way (although synthesis of
BrT2NO2 by the route T2 ? BrT2H ? BrT2NO2 proved to
have higher yield and purity). The reaction Scheme summa-
rizes the syntheses. Nitration using nitric acid in acetic an-
hydride gave the best results, allowing us to heavily favour
nitration at one (and only one) of the a-sites on H2T2 and
H2T3. Unfortunately, this could not be extended to longer
oligomers (the lack of solubility of T4, for example, required
heating the nitration step, leading to inseparable mixtures of
regioisomers). Suzuki coupling20–22 of HT2B(OH)2 and
BrT2NO2 seemed to be a reasonable alternate route, but the
low solubility of the product HT4NO2 prevented purification
by recrystallization or chromatography. Sublimation af-
forded some material but it was always accompanied by a
significant amount of H2T4 and unidentified decomposition
product(s) (probably due to polymerization). The insolubility
of HT4NO2 also prevented the regioselective synthesis of
halogenated derivatives. Stille coupling23–26 was even less
useful because it had the same problems as the Suzuki
method, with the additional difficulty of stannyl contamina-
tion.
ized in Table 1. It is obvious from these data that the nitro
group has an effect on lMAX that is larger than it should be
based on a simple particle-in-a-box argument, i.e., the NO2
group should extend the molecule by only two bonds, the
same as the nitrile group. Instead, the lMAX of HT3NO2 is
closest to that of H2T5 (extending the conjugation by eight
bonds). We conclude that the NO2 substituent helps rigidify
the backbone by introducing a quinoidal resonance structure
1Q to the molecule. This restricts the free rotation (it has a
very small energy barrier35,36) about the C5–C2’ and the
C5’–C2’ (ring–ring) bonds in the aromatic form 1A. This ro-
tation disrupts the extended conjugation of the oligomer and
shortens the lMAX, so the restricted rotation in 1Q increases
the effective average conjugation length. Addition of a sec-
ond nitro group (e.g., compound 2) does not have the same
effect, presumably because the quinoidalization has already
occurred with the first NO2 group.
For verification, we turned to DFT calculations. If the res-
onance form 1Q is significant, it should lead to a greater de-
gree of p-bonding between C2 and C3 than is present in the
aromatic form 1A. The bonds C1–C2 and C3–C4 should
also lengthen. The results are shown in Table 2, along with
experimental bond lengths from crystal structures when
available (HT3NO2 and BrT3NO2 are reported below for the
first time, while the other species have been previously re-
ported). Unfortunately, the ratio derived from the crystal
structures is unconvincing, partly due to the fact that the ra-
tio (C2–C3/C1–C2) can vary widely due to crystal packing
effects, and partly because the errors in the calculated ratios
are within the statistical errors arising from the atomic
ESDs. The computational results are more convincing, and
may anyway be more representative of the structure in solu-
tion (i.e., in the absence of packing effects). For the com-
puted structures, the C2–C3 bond decreases in length by
Spectroscopic and computational studies
˚
0.012 A on changing from an H to an NO2. The C1–C2
bond lengths also increase slightly, verifying that the reso-
nance structure 1Q does, in fact, have some influence on
the structure of these molecules.
This change is essentially identical no matter what is hap-
pening at the other end of the molecule (independent of R2).
This is somewhat counterintuitive because the quinoidal
form 1Q should be stabilized by lone pairs on R2, which
could occur when R2 = Br but not when R2 = H. We would
conclude that the nitro group is such a strong electron-with-
drawing substituent that a donor group at the other end is
The most striking characteristic of the nitro-substituted
terthiophenes is their deep red colour, in contrast to the pale
yellow of unsubstituted H2T3. We10,27 and others18,28–30 have
reported the UV–vis and fluorescence spectra in solution of
a variety of oligothiophenes; some of the data are summar-
Published by NRC Research Press

Sears et al.
311
Table 1. Absorption and fluorescence data for XTnNO2 compounds. Solutions of CH2Cl2 were used, lMAX values are reported in nm
units. Literature values are in brackets.
Compound
H2T3
H2T4
UV–vis absorption
[354]
[390]
417 [418, C6H6]29
Fluorescence (solution)a
428, 420 [411, 433]
440, 465 [454, 484]
496, 516 [482, 514, dioxane]30
504
581 [610]
581 [590]
585
Fluorescence (solid)a
HOMO–LUMO gapb
480, 505, 455 [471, 455, 505]32 318
528, 552 [555, 526]33
669
575c
643
669
670
H2T5
BrT2NO2
HT3NO2
BrT3NO2
IT3NO2
Compound 2
BrT3CN
401
332
379
383
[440]
[430]
442
[444]31
381
426
438
Note: Literature values are also in CH2Cl2 from ref. 18, unless otherwise stated.
aItalicized peaks are shoulders, peaks are listed in order of decreasing intensity.
bUsing the PBE0/6–311++G(2df,pd) basis set, energy converted to equivalent wavelength in nm.
cTransition overlaps with a Raman scattering peak, which might alter the lMAX slightly.
Table 2. Selected bond lengths for H2T3, HT3NO2, BrT3NO2, compound 2, and T3CN2; calculated values are at the PBE0/6–
˚
311++G(2df,pd) level, distances in A.
Compound
H2T3
C1–C2
C2–C3
C3–C4
C4–C5
Ratioa
Crystal structureb
1.374(13)
1.359(13)
1.385(12)
1.3282(14)
[1.375 (avg)]
1.362
1.458(12)
1.412(13)
1.431(11)
1.407(13)
[1.427 (avg)]
1.412
1.422(11)
1.398(12)
1.426(11)
1.442(11)
[1.422 (avg)]
1.373
1.450(12)
1.439(13)
1.460(13)
1.447(12)
[1.449 (avg)]
1.442
1.038
1.032
1.040
Calculated
Calculatedc,d
1.368
1.423
1.380
1.457
HT3NO2
BrT3NO2
Crystal structure
Calculated
1.354(3)
1.366
1.405(2)
1.400
1.369(2)
1.382
1.450(2)
1.437
1.038
1.025
Crystal structure
Calculated
Calculatedc,d
1.391(9)
1.366
1.373
1.404(9)
1.400
1.409
1.371(10)
1.382
1.392
1.464(9)
1.437
1.450
1.009
1.025
1.026
Compound 2
T3(CN)2
Crystal structuree 31
1.363(3)
1.359(3)
[1.361 (avg)]
1.373
1.404(3)
1.402(3)
[1.403 (avg)]
1.410
1.377(3)
1.379(3)
[1.378 (avg)]
1.391
1.461(3)
1.451(3)
[1.456 (avg)]
1.452
1.031
1.027
Calculatedc
Crystal structuref 10
1.367(15)
1.362(14)
1.302(17)
1.350(16)
1.341(16)
[1.344 (avg)]
1.389(16)
1.424(13)
1.376(16)
1.417(14)
1.384(14)
[1.398 (avg)]
1.367(15)
1.370(14)
1.345(16)
1.346(14)
1.353(15)
[1.356 (avg)]
1.461(14)
1.362(14)
1.447(14)
1.450(14)
1.469(14)
[1.438 (avg)]
1.040
aThe ratio of the bond lengths (C2–C3)/(C1–C2).
bThere are two crystallographically independent H2T3 molecules, neither of which have C2v symmetry.
cAt the B3LYP/631G** level, from ref. 34.
dCalculated for the mononitrated equivalent of 2 (H or Br in place of one NO2).
eThe molecule does not have C2v symmetry in the crystal structure.
fThere are 2.5 molecules in the asymmetric unit.
essentially irrelevant (or, put another way, the far thiophene
ring acts as the donor group).
Because of its low solubility, conversion from HT3NO2 to
BrT3NO2 required heating and a long reaction time, which
created a mixture of brominated products. Purification by re-
peated recrystallization did not fully separate these substan-
ces, so consequently a small amount of disubstituted
material remained, which was modeled using partial occu-
pancies as shown in Fig. 1 (the atoms labeled ‘‘H/Br2’’ and
‘‘H/Br3’’ are the partially occupied sites). Repeated sublima-
tion of the product did lead to pure BrT3NO2 by combustion
Solid-state structures
Since we wished to determine the solid-state influence of
the nitro group, crystals of both HT3NO2 and BrT3NO2 were
grown, the former by sublimation and the latter from solu-
tion. The pertinent refinement data are given in Table 3. Un-
fortunately, the crystals for BrT3NO2 were of low quality.
Published by NRC Research Press

312
Can. J. Chem. Vol. 88, 2010
Table 3. Crystallographic refinement information for HT3NO2 and BrT3NO2.
Compound
HT3NO2
C12H7NO2S3
293.37
BrT3NO2
C12H6BrNO2S3
476.53
Empirical formula
Formula weight
Crystal system
Space group
Triclinic
Triclinic
ꢀꢀ
ꢀꢀ
P1
P1
˚
a (A)
6.3225(3)
7.6385(4)
13.2640(6)
74.5191(10)
83.4360(10)
87.3150(10)
613.20(5)
2
7.3587(6)
7.8832(7)
13.7617(12)
97.595(2)
96.644(2)
113.5590(10)
712.77(11)
2
˚
b (A)
˚
c (A)
a (8)
b (8)
g (8)
3
˚
V (A )
Formula units (Z)
rcalcd. (g cm–3)
m (Mo Ka) (mm–1)
Crystal dimensions (mm)
F(000)
1.589
0.595
2.222
7.063
0.40 Â 0.24 Â 0.14
0.22 Â 0.08 Â 0.04
300
457
q range (8)
3.21 < q < 26.50
7285
2532
0.0315
0.0881
2.98 < q < 25.99
8090
2795
0.0537
0.1084
1.276
Reflections collected
Unique reflections
R1 [I > 2s(I)]
wR2 (all data)
Goodness of fit on F2
1.051
Fig. 1. Crystal structure of BrT3NO2. Top left: molecule showing atom numbering and thermal ellipsoids. Top right: two coplanar molecules
showing the lack of face-to-face p-stacking between layers. Bottom: the two-dimensional sheet forcing coplanarity on the molecules, show-
ing the short OÁÁÁBr contacts and hydrogen bonds.
analysis. However, we were unable to obtain even low-
quality single crystals of purified BrT3NO2. Fortunately, the
gross structure does give the necessary information on
atomic connectivities, and it shows the molecules forming
ribbons held together by the halo-nitro supramolecular syn-
thon.37,38 Contact between the bromo and one oxygen on
the nitro (as opposed to both oxygens equally) is typical.39
The ribbons stack cofacially, but they are offset so that the
p-systems overlap very little. Interestingly, rings 1 (C1–C4)
and 2 (C5–C8) are mutually syn, while rings 2 and 3 (C9–
C12) are anti to each other. While the syn orientation is
less common, it is not unheard of (in fact, compound 2 also
has mutually syn rings in its crystal structure31).
Figure 2 shows the crystal structure of HT3NO2. In this
case, sublimation led to good-quality crystals. The mole-
cules line up in head-to-tail ribbons joined by hydrogen
bonds between each nitro oxygen and an aromatic hydrogen.
There is also a cross-ribbon hydrogen bond, generating a
two-dimensional sheet. These sheets stack in the third di-
mension, leading to p-stacks, the favored orientation for
maximizing carrier mobility in molecular semiconductors.
The p-stacking is not fully optimized, however, as consecu-
tive ribbons run in opposite directions in the centrosymmet-
ric space group.
Even though the p-stacking is not optimal in either struc-
ture, there are clearly intermolecular interactions that give
Published by NRC Research Press

Sears et al.
313
Fig. 2. Crystal structure of HT3NO2. Top left: molecule showing atom numbering scheme and thermal ellipsoids. Top right: side view of the
p-stack; the top and bottom molecules have one S pointing at the viewer while the middle molecule has two, demonstrating the alternation
in the sense of the stacking. Bottom: two-dimensional sheets held together with hydrogen bonds.
rise to intermolecular interactions between molecules in the
solid state. The normalized fluorescence spectra for H2T3
and HT3NO2 (in both CH2Cl2 solution and powder solid)
are shown in Fig. 3. The lMAX for all the solid-state data
were presented in Table 1, along with the solution data. The
lMAX increases significantly for the solids compared with
the solutions, demonstrating that the solid-state optical band
gap is smaller than the molecular HOMO–LUMO gap.
The electrostatic hydrogen bonds connecting the mole-
cules in the solid state do not contribute to the formation of
an extended three-dimensional electronic structure. This is
verified by Extended Hu¨ckel band structure calculations on
RT3NO2 (R = H, Br), the results of which are shown in
Fig. 4, along with the same calculation on H2T3, using the
literature crystal structure;35 numerical data are given in Ta-
ble 4. The bandwidths are narrow, with little dispersion
along any of the reciprocal space axes. In triclinic space
groups, in which all these structures crystallize, the direc-
tions X, Y, and Z do not correspond to the real-space axes
a, b, and c; however, this does not affect the gross conclu-
sion that the dispersion is small. The band gap is signifi-
cantly lower in the nitro-substituted species than in the
unsubstituted molecule, but this is a reflection of the change
in the energies of the HOMO and LUMO not a reflection of
an increase in the bandwidths. The bandwidths are much
Fig. 3. Normalized solution and powder fluorescence spectra for
H2T3 and HT3NO2.
nance structure. The solid-state crystal structure consists of
two-dimensional planes of molecules held together by hy-
drogen bonds. Although the sheets do not superimpose, there
is some p-stacking between the sheets. Bromination and io-
dination of this molecule is possible, and the BrT3NO2 mol-
ecule also has a p-sheet crystal structure, with hydrogen
bonds and NO2ÁÁÁBr contacts. In this case, there is little p-
interaction between the sheets. Neither solid has large dis-
persion in the band structure, but the bandwidths are similar
to unsubstituted H2T3, so longer nitrated oligomers may
have more electronically useful band structures. The band
gap is significantly smaller in nitro-substituted species, but
this is simply a reflection of the smaller HOMO–LUMO
gap. These results suggest that the nitro group is a good can-
didate for inducing p-stacking in oligothiophenes.
41
narrower than those published for H2T6 but are comparable
to H2T3, so longer nitro-substituted oligomers may have sig-
nificantly larger bandwidths.
Conclusions
The attachment of one nitro group to a terthiophene
oligomer is possible by using the relatively mild conditions
of nitric acid in acetic anhydride. The resultant product,
HT3NO2 has an unusually small HOMO–LUMO energy
gap, which we attribute to the effect of the quinoidal reso-
Experimental
Materials
Starting reagents were purchased from Aldrich and used
Published by NRC Research Press

314
Can. J. Chem. Vol. 88, 2010
Fig. 4. Extended-Hu¨ckel band structures of H2T3, HT3NO2, and BrT3NO2. The dashed line is the Fermi level.
Table 4. Band structures of selected oligothiophenes.
Compound
H2T3
Band gap
2.08
0.92
0.60
2.24
Valence bandwidth
Conduction bandwidth
0.11
0.048
0.023
0.44
Reference
This worka
This work
This work
40
0.013
0.083
0.016
0.52
HT3NO2
BrT3NO2
b
H2T4
H2T6
1.94
0.79
0.52
41
aThe band structure calculation is new to this work, using the literature crystal structure (ref. 35).
bThe crystal structure contains sites with partial Br occupancy; the band structure calculation has assumed 100% H for those sites.
without purification, except N-bromosuccinimide (NBS),
which was recrystallized from water. Solvents were pur-
chased from Anachemia or Caledon and purified prior to
use: dichloromethane, diethyl ether, and tetrahydrofuran
(THF) by passage through an alumina column under N2;
alcohols by distillation from magnesium under N2.
Oligothiophenes 2,2’-bithiophene (H2T2); 2,2’:5’,2@-terthio-
phene (H2T3); 2,2’:5’,2@:5@,2@’-quaterthiophene (H2T4); and
2,2’:5’,2@:5@,2@’:5@’,2@@-quinquethiophene (H2T5) were synthe-
sized by Grignard couplings of thienylmagnesium bromide
(HTMgBr) to 2-bromothiophene (BrTH); 2,5-dibromothiophene
(Br2T); 5,5’-dibromo-2,2’-bithiophene (Br2T2); and 5,5’-di-
bromo-2,2’:5’,2@-terthiophene (Br2T3), respectively, using
the Kumada coupling catalyst (Ni(dppp)Cl2) [1,3-bis(diphe-
spectrometer, while UV–vis absorption spectra were re-
corded on a PerkinElmer Lambda 11 UV–vis spectrometer;
both were recorded as CH2Cl2 solutions. Combustion analy-
ses were performed on a CEC (SCP) 240-XA Analyzer.
Gradient vacuum sublimations and crystal growth for X-ray
crystallography were performed on an Applied Test Systems
model 3210 split tube furnace attached to a series 2404
three-zone temperature control system. Melting points were
recorded on an Electrothermal 9100 apparatus and are un-
corrected. Mass spectra were recorded on a Micromass VG
Autospec electron impact mass spectrometer at Lakehead
University or on a Bruker Reflex III laser desorption/ioniza-
tion time-of-flight mass spectrometer at the Mass Spectrom-
etry Facility in the Advanced Analysis Centre at the
University of Guelph.
nylphosphino)propane]dichloronickel(II).42 The method of
43
¨
Bauerle was used for monobromination to create 5-bromo-
2,2’-bithiophene (BrT2H), and for all dibrominations. 5-Bromo-
2,2’:5’,2@-terthiophene-5’-carbonitrile (BrT3CN) was prepared
by the literature route.10 All reactions were performed under
an atmosphere of N2 (using Schlenk conditions).
X-ray crystallography
Single-crystal data were collected using the Smart Apex
CCD (Bruker) equipped with an area detector utilizing
˚
graphite-monochromated Mo Ka radiation (l = 0.71073 A).
The data were corrected for Lorentz and polarization effects.
Absorption corrections were based on fitting a function to
the empirical transmission surface as sampled by multiple
equivalent measurements of numerous reflections using the
scale function of the APEX II software. The space groups
for all compounds were determined on the basis of the sys-
tematic absences using symmetry and space group of the
APEX II package. Structure solution and refinement using
the SHELXTL package of APEX II were successful in the
chosen centrosymmetric space groups. The structure solution
Instruments
FTIR spectra were recorded as nujol mulls on a Nicolet
380 FTIR spectrometer; vibrational frequencies are reported
as wavenumbers (cm–1), with an experimental resolution of
4 cm–1. NMR spectra were recorded on a Varian Unity In-
ova 500 at room temperature in CDCl3 or DMSO-d6 solu-
tions, referenced to TMS added to the sample or to the
residual protonated solvent peak. Fluorescence measure-
ments were taken on a PerkinElmer LS50B luminescence
Published by NRC Research Press

Sears et al.
315
via direct method led to the identification of the heavy
atoms and the refinement on F2 using least-square method
resulted in good R values. Full details of the structures have
been deposited with the Cambridge Crystallographic Data
Centre (see Supplementary data for details).
trum m/z: 373 (M+, 100%), 327 ([M – NO2]+, 27%), 283
([M – SCNO2]+, 73%), 145 (33%). Anal. calcd. for
C12H6BrNO2S3: C 38.72, H 1.62, N 3.76; found: C 38.57,
H 1.94, N 3.84%. Crystals suitable for X-ray crystallogra-
phy were prepared by repeatedly recrystallizing the crude,
i. e., isolating and redissolving material in toluene; this had
the effect of concentrating the multibrominated byproducts,
giving the structure as discussed in the text.
Computational details
Calculations used the PBE0 hybrid functional44–46 and the
large basis set 6–311++G(2df, pd)47,48 as implemented in the
Gaussian 03 package.49
Synthesis of 5-iodo-5’-nitro-2,2’:5’,2@-terthiophene (IT3NO2)
To a solution of 3.19 g (11 mmol) HT3NO2 in 250 mL of
DMF was added portionwise (in the dark) 2.48 g (11 mmol)
of NIS. The mixture was then stirred overnight, followed by
precipitation upon addition of water, giving 2.7 g (64%) of
red-orange material. This material was purified by sublima-
Synthesis of 5-bromo-5’-nitro-2,2’-bithiophene (BrT2NO2)
Although this compound was often made in the method
outlined in the Scheme 1, we found that the following
method gave a higher-purity product. In 25 mL of acetic an-
hydride, 4.79 g (20 mmol) of BrT2 was dissolved, and the
mixture was cooled to 0 8C. To this solution (maintaining
0 8C) was added dropwise with stirring a mixture of 1.50 g
(24 mmol) of nitric acid in 20 mL of acetic anhydride. The
resultant mustard-yellow solution was quenched with satu-
rated sodium bicarbonate and extracted into dichlorome-
thane. Rotary evaporation followed by recrystallization
(from ethanol) and sublimation (two times) yielded 1.45 g
1
tion in vacuo. Mp 232–233 8C. H NMR (CDCl3) d (ppm):
7.86 (d, JAB 4.5 Hz, 1 H), 7.26 (d, JAB 3.0 Hz, 1 H), 7.20 (d,
JAB 4.0 Hz, 1 H), 7.09 (d, JAB 4.0 Hz, 1 H), 7.07 (d, JAB
4.0 Hz, 1 H), 6.91 (d, JAB 4.0 Hz, 1 H). Mass spectrum m/
z: 419 (M+, 100%), 373 ([M – NO2]+, 23%), 329 (40%), 293
([M – I]+, 11%). Anal. calcd. for C12H6INO2S3: C 34.38, H
1.44, N 3.34; found: C 34.50, H 1.65, N 3.11%.
1
(25.6%) of analytically pure material. Mp 190–193 8C. H
Supplementary data
NMR (DMSO-d6) d (ppm): 8.12 (d, JAB 4.0 Hz, 1 H), 7.56
(d, JAB 4.0 Hz, 1 H), 7.45 (d, JAB 4.0 Hz, 1H), 7.36 (d, JAB
4.0 Hz, 1 H). Mass spectrum m/z: 291 (M+, 98%), 261 ([M –
NO]+, 26%), 245 ([M – NO2]+, 23%), 201 ([M – SCNO2]+,
100%). Anal. calcd. for C8H4BrNO2S2: C 33.12, H 1.38, N
4.83; found: C 32.75, H 1.62, N 4.51%.
Supplementary data for this article (computational data,
including optimized geometries, orbital energies, and verti-
cal excitation energies on the series R1TnR2 (n = 1–3; R1 =
H or Br, R2 = H or NO2) and experimental information on
the synthesis of XT4NO2 (X = H, Br)) are available on the
journal Web site (http://canjchem.nrc.ca) or may be pur-
chased from the Depository of Unpublished Data, Document
Delivery, CISTI, National Research Council Canada, Ot-
tawa, ON K1A 0R6, Canada. DUD 5327. For more informa-
tion on obtaining material, refer to http://cisti-icist.nrc-cnrc.
gc.ca/eng/ibp/cisti/collection/unpublished-data.html. CCDCs
739773 (HT3NO2) and 739774 (BrT3NO2) contain the X-ray
data in CIF format for this manuscript. These data can be
obtained, free of charge, via http://www.ccdc.cam.ac.uk/
conts/retrieving.html (Or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax +44 1223 336033; or deposit@ccdc.cam.ac.uk).
Synthesis of 5-nitro-2,2’:5’,2@-terthiophene (HT3NO2)
In 100 mL of acetic anhydride, 8.75 g (35 mmol) of H2T3
was dissolved, and the mixture was warmed until the oligo-
thiophene dissolved. To this solution was added dropwise
with stirring 2.75 g (44 mmol) of nitric acid. The dark-col-
oured solution was quenched with saturated sodium bicar-
bonate, at which time a dark-red precipitate formed. The
solid was suction-filtered and washed with toluene and hex-
anes to give 3.19 g (31%) of an orange powder. Gradient
sublimation in a tube furnace (95–70 8C) afforded analyti-
cally pure red crystals suitable for X-ray crystallography.
Rotary evaporation followed by recrystallization (from etha-
nol) and sublimation (two times) yielded 1.45 g (25.6%) of
analytically pure material. Mp 157–160 8C. 1H NMR
(DMSO-d6) d (ppm): 8.12 (d, JAB 4.5 Hz, 1 H), 7.69 (d, JAB
4.0 Hz, 1 H), 7.63 (d, JAB 6.0 Hz, 1H), 7.46 (d, JAB 4.5 Hz,
2 H), 7.41 (d, JAB 4.0 Hz, 1 H), 7.15 (dd, JAB = JAC 4.5 Hz,
1 H). Mass spectrum m/z: 293 (M+, 100%), 247 ([M –
NO2]+, 25%), 203 (87%). Anal. calcd. for C12H7NO2S3: C
49.13, H 2.40, N 4.77; found: C 49.14, H 2.46, N 4.77%.
Acknowledgments
Funding for this research was primarily supplied by the
Research Corporation (Cottrell College Science Award) and
by Lakehead University. RCM would also like to thank
SHARCNET for computational facilities. LCS was partially
supported by the Natural Sciences and Engineering Research
Council of Canada (NSERC) USRA Award. Thanks to Prof.
William Sears in the Department of Physics at Lakehead
University and to Dr. Abdeljalil Assoud in the Department
of Chemistry at the University of Waterloo for some helpful
discussions.
Synthesis of 5-bromo-5’-nitro-2,2’:5’,2@-terthiophene
(BrT3NO2)
In 100 mL of DMF was dissolved 0.78 g (2.7 mmol)
HT3NO2. While stirring in the dark, 1.84 g (10 mmol) was
added portionwise over the course of 2 h, after which the
solution was stirred overnight. Crude material precipitated
upon addition of water. The red solid was recrystallized
from toluene and repeatedly sublimed (120–90 8C) to ob-
tain analytically pure material. Mp 172–175 8C. Mass spec-
References
(1) Fichou, D. Handbook of Oligo- and Polythiophenes; Wiley-
VCH: Weinheim, 1999.
(2) Barbarella, G.; Melucci, M.; Sotgiu, G. Adv. Mater. 2005, 17
(13), 1581. doi:10.1002/adma.200402020.
Published by NRC Research Press

316
Can. J. Chem. Vol. 88, 2010
¨
¨
(3) Mishra, A.; Ma, C.-Q.; Bauerle, P. Chem. Rev. 2009, 109
(3), 1141. doi:10.1021/cr8004229.
Landfester, K.; Moller, M. Eur. J. Org. Chem. 2007, 2007
(34), 5686. doi:10.1002/ejoc.200700566.
(4) Anthony, J. E. Chem. Rev. 2006, 106 (12), 5028. doi:10.
1021/cr050966z. PMID:17165682.
(5) Facchetti, A.; Deng, Y.; Wang, A.; Koide, Y.; Sirringhaus,
(27) Sears, W. A.; Sears, W. M.; MacKinnon, C. D. Synth. Met.
2008, 158 (1-2), 50. doi:10.1016/j.synthmet.2007.12.002.
(28) Nakayama, J.; Konishi, T.; Murabayashi, S.; Hoshino, M.
Heterocycles 1987, 26 (7), 1793. doi:10.3987/R-1987-07-
1793.
H.; Marks, T. J.; Friend, R. H. Angew. Chem. Int. Ed. 2000,
39
(24),
4547.
doi:10.1002/1521-3773(20001215)
39:24<4547::AID-ANIE4547>3.0.CO;2-J.
(6) Rao, V. P.; Wong, K. Y.; Jen, A. K.-Y.; Drost, K. J. Chem.
(29) Sease, J. W.; Zechmeister, L. J. Am. Chem. Soc. 1947, 69
(2), 270. doi:10.1021/ja01194a031.
Mater. 1994, 6 (12), 2210. doi:10.1021/cm00048a004.
(30) Becker, R. S.; de Melo, J. S.; Mac¸anita, A. L.; Elisei, F. J.
Phys. Chem. 1996, 100 (48), 18683. doi:10.1021/jp960852e.
(31) Pappenfus, T. M.; Raff, J. D.; Hukkanen, E. J.; Burney, J.
R.; Casado, J.; Drew, S. M.; Miller, L. L.; Mann, K. R. J.
Org. Chem. 2002, 67 (17), 6015. doi:10.1021/jo025572b.
PMID:12182637.
´ ˆ
(7) Zhang, J. X.; Dubois, P.; Jerome, R. J. Chem. Soc., Perkin
Trans. 2 1997, (6): 1209. doi:10.1039/a606547c.
(8) Koumura, N.; Wang, Z.-S.; Mori, S.; Miyashita, M.; Suzuki,
E.; Hara, K. J. Am. Chem. Soc. 2006, 128 (44), 14256.
doi:10.1021/ja0645640. PMID:17076489.
(9) Sakamoto, Y.; Komatsu, S.; Suzuki, T. J. Am. Chem. Soc.
2001, 123 (19), 4643. doi:10.1021/ja015712j. PMID:
11457268.
(10) Barclay, T. M.; Cordes, A. W.; MacKinnon, C. D.; Oakley,
R. T.; Reed, R. W. Chem. Mater. 1997, 9 (4), 981. doi:10.
1021/cm960545l.
(32) Choi, Y.; Tepavcevic, S.; Xu, Z.; Hanley, L. Chem. Mater.
2004, 16 (10), 1924. doi:10.1021/cm0353052.
(33) Hopmeier, M.; Gebauer, W.; Oestreich, M.; Sokolowski, M.;
Umbach, E.; Mahrt, R. F. Chem. Phys. Lett. 1999, 314 (1-2),
9. doi:10.1016/S0009-2614(99)01116-1.
(34) Casado, J.; Pappenfus, T. M.; Miller, L. L.; Mann, K. R.;
´ ´ ´
Ortı, E.; Viruela, P. M.; Pou-Amerigo, R.; Hernandez, V.;
(11) MacKinnon, C. D.; Parent, S. L. M.; Mawhinney, R. C.; As-
soud, A.; Robertson, C. M. CrystEngComm 2009, 11 (1),
160. doi:10.1039/b810479d.
(12) Gao, X.; Wu, W.; Liu, Y.; Qiu, W.; Sun, X.; Yu, G.; Zhua,
D. Chem. Commun. (Camb.) 2006, (26): 2750. doi:10.1039/
b603632e. PMID:17009451.
´
Lopez Navarrete, J. T. J. Am. Chem. Soc. 2003, 125 (9),
2524. doi:10.1021/ja027835p. PMID:12603140.
(35) Van Bolhuis, F.; Wynberg, H.; Havinga, E. E.; Meijer, E.
W.; Staring, E. G. J. Synth. Met. 1989, 30 (3), 381. doi:10.
1016/0379-6779(89)90661-9.
(13) Ando, S.; Murakami, R.; Nishida, J.; Tada, H.; Inoue, Y.;
Tokito, S.; Yamashita, Y. J. Am. Chem. Soc. 2005, 127
(43), 14996. doi:10.1021/ja055686f. PMID:16248617.
(14) Prakash, M.; Radhakrishnan, T. P. Chem. Mater. 2006, 18
(13), 2943. doi:10.1021/cm052607q.
(15) Caruso, U.; Diana, R.; Fort, A.; Panunzi, B.; Roviello, A.
Macromol. Symp. 2006, 234 (1), 87. doi:10.1002/masy.
200650212.
(36) Telesca, R.; Bolink, H.; Yunoki, S.; Hadziioannou, G.; Van
Duijnen, P. T.; Snijders, J. G.; Jonkman, H. T.; Sawatzky,
G. A. Phys. Rev. B 2001, 63 (15),o. 155112. doi:10.1103/
PhysRevB.63.155112.
(37) Kruszynski, R.; Czestkowski, W. Acta Crystallogr. 2002,
E58, o481.
´
(38) Wagner, P.; Swierczek, K.; Kubicki, M. Acta Crystallogr.
2007, C63, o445.
(16) George, S.; Nangia, A.; Lam, C.-K.; Mak, T. C. W.; Nicoud,
J.-F. Chem. Commun. (Camb.) 2004, (10): 1202. doi:10.
1039/b402050b. PMID:15136838.
(39) Thaimattam, R.; Sharma, C. V. K.; Clearfield, A.; Desiraju,
G. R. Cryst. Growth Des. 2001, 1 (2), 103. doi:10.1021/
cg010286z.
(17) Feng, K.; De Boni, L.; Misoguti, L.; Mendonc¸a, C. R.; Mea-
dor, M.; Hsu, F.-L.; Bu, X. R. Chem. Commun. (Camb.)
2004, (10): 1178. doi:10.1039/b402019g. PMID:15136827.
(18) Garcia, P.; Pernaut, J. M.; Hapiot, P.; Wintgens, V.; Valat,
P.; Garnier, F.; Delabouglise, D. J. Phys. Chem. 1993, 97
(2), 513. doi:10.1021/j100104a040.
(19) Soucy-Breau, C.; MacEachern, A.; Leitch, L. C.; Arnason,
T.; Morand, P. J. Heterocycl. Chem. 1991, 28 (2), 411.
doi:10.1002/jhet.5570280239.
(40) Siegrist, T.; Kloc, C.; Laudise, R. A.; Katz, H. E.; Haddon,
R. C. Adv. Mater. 1998, 10 (5), 379. doi:10.1002/(SICI)
1521-4095(199803)10:5<379::AID-ADMA379>3.0.CO;2-A.
(41) Siegrist, T.; Fleming, R. M.; Haddon, R. C.; Laudise, R. A.;
Lovinger, A. J.; Katz, H. E.; Bridenbaugh, P.; Davis, D. D.
J. Mater. Res. 1995, 10 (9), 2170. doi:10.1557/JMR.1995.
2170.
(42) Tamao, K.; Kodama, S.; Nakajima, I.; Kumada, M. Tetrahe-
dron 1982, 38 (22), 3347. doi:10.1016/0040-4020(82)80117-8.
¨
¨
¨
(20) Oh-e, T.; Miyaura, N.; Suzuki, A. J. Org. Chem. 1993, 58,
2201. doi:10.1021/jo00060a041.
(43) Bauerle, P.; Wurthner, F.; Gotz, G.; Effenberger, F. Synth-
esis 1993, 1993 (11), 1099. doi:10.1055/s-1993-26009.
(44) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev. Lett.
1996, 77 (18), 3865. doi:10.1103/PhysRevLett.77.3865.
PMID:10062328.
(21) Chisaka, J.; Lu, M.; Nagamatsu, S.; Chikamatsu, M.;
Yoshida, Y.; Goto, M.; Azumi, R.; Yamashita, M.; Yase, K.
Chem. Mater. 2007, 19 (10), 2694. doi:10.1021/cm0701658.
(22) Lightowler, S.; Hird, M. Chem. Mater. 2005, 17 (22), 5538.
doi:10.1021/cm0512068.
(45) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. Rev. Lett.
1997, 78 (7), 1396. doi:10.1103/PhysRevLett.78.1396.
(46) Perdew, J. P.; Ernzerhof, M.; Burke, K. J. Chem. Phys.
1996, 105 (22), 9982. doi:10.1063/1.472933.
(23) Milstein, D.; Stille, J. K. J. Am. Chem. Soc. 1978, 100 (11),
3636. doi:10.1021/ja00479a077.
(24) Jousselme, B.; Blanchard, P.; Levillain, E.; Delaunay, J.; Al-
lain, M.; Richomme, P.; Rondeau, D.; Gallego-Planas, N.;
Roncali, J. J. Am. Chem. Soc. 2003, 125 (5), 1363. doi:10.
1021/ja026819p. PMID:12553839.
(47) Hehre, W. J.; Ditchfield, R.; Pople, J. A. J. Chem. Phys.
1972, 56 (5), 2257. doi:10.1063/1.1677527.
(48) Francl, M. M.; Pietro, W. J.; Hehre, W. J.; Binkley, J. S.;
Gordon, M. S.; Defrees, D. J.; Pople, J. A. J. Chem. Phys.
1982, 77 (7), 3654. doi:10.1063/1.444267.
´
(25) Liu, J.; Tanaka, T.; Sivula, K.; Alivisatos, A. P.; Frechet, J.
(49) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G.
E.; Robb, M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Mon-
tgomery, J. A.; Stratmann, R. E.; Burant, J. C.; Dapprich, S.;
M. J. J. Am. Chem. Soc. 2004, 126 (21), 6550. doi:10.1021/
ja0489184. PMID:15161272.
(26) Ellinger, S.; Kreyes, A.; Ziener, U.; Hoffmann-Richter, C.;
Published by NRC Research Press

Sears et al.
Millam, J. M.; Daniels, A. D.; Kudin, K. N.; Strain, M. C.;
317
G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.;
Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng,
C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.;
Johnson, B.; Chen, W.; Wong, M. W.; Andres, J. L.; Gonza-
lez, C.; Head-Gordon, M.; Replogle, E. S.; Pople, J. A.
Gaussian 03, Revision E.01 ed.; Gaussian Inc.: Wallingford,
CT, 2004.
Farkas, O.; Tomasi, J.; Barone, V.; Cossi, M.; Cammi, R.;
Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.; Och-
terski, J. W.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Moro-
kuma, K.; Salvador, P.; Dannenberg, J. J.; Malick, D. K.;
Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Cio-
slowski, J.; Ortiz, J. V.; Baboul, A. G.; Stefanov, B. B.; Liu,
Published by NRC Research Press