Imine-bridged planar poly(phenylenethiophene)s and polythiophenes

Article abstract of DOI:10.1021/ja964223u

Synthetic routes to soluble planar poly(phenylenethiophene)s and polythiophenes are described. The main polymer backbones are synthesized via Pd(0)-catalyzed couplings of the electron-rich N,N'-(bis-tert-butoxycarbonyl)-3,4-diamino-2,5-bis(tri-n- butylsta

Full text of DOI:10.1021/ja964223u

9624
J. Am. Chem. Soc. 1997, 119, 9624-9631
Imine-Bridged Planar Poly(phenylenethiophene)s and
Polythiophenes
Qing T. Zhang and James M. Tour*
Contribution from the Department of Chemistry and Biochemistry, UniVersity of South Carolina,
Columbia, South Carolina 29208
ReceiVed December 9, 1996X
Abstract: Synthetic routes to soluble planar poly(phenylenethiophene)s and polythiophenes are described. The main
polymer backbones are synthesized via Pd(0)-catalyzed couplings of the electron-rich N,N′-(bis-tert-butoxycarbonyl)-
3,4-diamino-2,5-bis(tri-n-butylstannyl)thiophene with electron-deficient aryldibromodiones. The prebridged polymers
have bathochromically shifted absorptions due to donor/acceptor interactions between the consecutive repeat units.
Upon exposure of the polymers to trifluoroacetic acid or titanium tetrachloride, imine bridges are formed that force
the consecutive units into planarity. The bridging units are sp2-hybridized, thus allowing for greater electron
delocalization between the consecutive aryl units. The syntheses of model trimeric systems were conducted to provide
further data for assessing the optical properties of the polymers. Protonation of the imine moieties causes bathochromic
shifts of >100 nm in several cases. The effect is explained by an intramolecular charge transfer. Thus these
arrangements of planar structures with imine bridges serve as optically based proton sensors with spectral shift
differences far-exceeding those of nonplanar imine-containing polymers.
Introduction
minimize optical bandgaps in conjugated materials is to combine
intramolecular CT with the maximization of conjugation via
planarization.
The optoelectronic properties of conjugated polymers vary
significantly based upon the degree of extended conjugation
between their consecutive repeat units. We and others have
sought to maximize extended π-conjugation in poly(p-phen-
ylene)s (PPPs) by forming covalent linkages between the
consecutive repeat units.1 This results in a lowering of the
optical bandgaps or an increase of the bandwidths in the
polymers. Although polythiophenes have been studied exten-
sively due to the ease with which they can be functionalized,
to our knowledge, there are no reports of ladder polymers based
on polythiophenes. The overwhelming majority of conjugated
ladder polymers are based upon PPP backbones.1 There have
been proposals that ladder polymers with backbones that are
thiophene-based would exhibit unusually low optical bandgaps
due to the relative stabilities of their quinoidal forms,1m but no
experimental studies have been conducted. Here we describe
syntheses and optical investigations on planar poly(phenylene-
thiophene)s and a planar polythiophene. Novel optoelectronic
properties in polymers with significant charge transfer (CT)
character in their backbones,2 coupled with the growing interest
in developing polymer-based sensors,3 have promoted us to
explore the utility of these thiophene-containing planar polymers
and their oligomeric analogues for proton-induced intrachain
CT-based variations. We found that a unique method to
Monomer Preparation
The monomers for the desired planar polymers were readily
prepared. Thiophene was selectively brominated at the 2,5-
positions and then nitrated. Reduction of the nitro moieties with
concomitant dehalogenation4 followed by tert-butoxycarbonyl
(Boc) protection and stannylation yielded the requisite thiophene
monomer 1 (eq 1). Although the LDA treatment followed by
quenching with chlorotrimethylsilane afforded the analogous bis-
(silane) in 98% yield, the bis(stannane) 1 was unstable during
(2) (a) Yamamoto, T.; Zhou, Z.-h.; Kanbara, T.; Shimura, M.; Kizu, K.;
Maruyama, T.; Nakamura, Y.; Fukuda, T.; Lee, B.-L.; Ooba, N.; Tomaru,
S.; Kurihara, T.; Kaino, T.; Kubota, K.; Sasaki, S. J. Am. Chem. Soc. 1996,
118, 10389. (b) Ferraris, J. P.; Bravo, A.; Kim, W.; Hrncir, D. C. J. Chem.
Soc., Chem. Commun. 1994, 991. (c) Karikomi, M.; Kitamura, C.; Tanak,
S.; Yamashita, Y. J. Am. Chem. Soc. 1995, 117, 6791. (d) Havinga, E. E.;
Ten Hoeve, W.; Wynberg, H. Polym. Bull. 1992, 29, 119.
(3) (a) Marsella, M. J.; Swager, T. M. J. Am. Chem. Soc. 1993, 115,
12214. (b) McCullough, R. D.; Williams, S. P. J. Am. Chem. Soc. 1993,
115, 11608. (c) Brockmann, T. W.; Tour, J. M. J. Am. Chem. Soc. 1995,
117, 4437. (d) McCullough, R. D.; Williams, S. P. Chem. Mater. 1995, 7,
2001. (e) Jenekhe, S. A.; Osaheni, J. A. Macromolecules 1992, 25, 5828.
(f) Tarkka, R. M.; Zhang, X.; Jenekhe, S. A. J. Am. Chem. Soc. 1996, 118,
9438. (g) van Mullekom, H. A. M.; Vekemans, J. A. J. M.; Meijer E. W.
Chem. Commun. 1996, 2163. (h) Delnoye, D. A. P.; Sijbesma, R. P.;
Vekemans, J. A. J. M.; Meijer, E. W. J. Am. Chem. Soc. 1996, 118, 8717.
(4) (a) Mozingo, R.; Harris, S. A.; Wolf, D. E.; Hoffhine, C. E., Jr.;
Easton, N. R.; Folkers, K. J. Am. Chem. Soc. 1945, 67, 2092. (b) Galvez,
C.; Garcia, F.; Garcia, J.; Soldevila, J. J. Heterocycl. Chem. 1986, 23, 1103.
X Abstract published in AdVance ACS Abstracts, October 1, 1997.
(1) (a) Overberger, C. G.; Moore, J. A. AdV. Polym. Sci. 1970, 7, 113.
(b) Schlu¨ter, A.-D. AdV. Mater. 1991, 3, 282. (c) Yu, L.; Chen, M. Dalton,
L. R. Chem. Mater. 1990, 2, 649. (d) Hong, S. Y.; Kertesz, M.; Lee, Y. S.;
Kim, O.-K. Chem. Mater. 1992, 4, 378. (e) Godt, A.; Schlu¨ter, A.-D. AdV.
Mater. 1991, 3, 497. (f) Yu. L.; Dalton, L. R. Macromolecules 1990, 23,
3439. (g) Scherf, U.; Mu¨llen, K. Synthesis 1992, 23. (h) Lamba, J. J. S.;
Tour, J. M. J. Am. Chem. Soc. 1994, 116, 11723. (i) Schlu¨ter, A.-D.;
Schlicke, B. Synlett 1996, 425. (j) Kertesz, M.; Hong, S. Y. Macromolecules
1992, 25, 5424. (k) Kintzel, O.; Mu¨nch, W.; Schlu¨ter, A.-D.; Godt, A. J.
Org. Chem. 1996, 61, 7304. (l) Scherf, U.; Mu¨llen, K. AdV. Polym. Sci.
1995, 123, 1. (m) Roncali, J. Chem. ReV. 1997, 1733. (n) Dai, Y.; Katz, T.
J.; Nichols, D. A. Angew. Chem., Int. Ed. Engl. 1996, 35, 2109. (o) Nuckolls,
C.; Katz, T. J. Castellanos, L. J. Am. Chem. Soc. 1996, 118, 3767. (p)
Goldfinger, M. B.; Swager, T. M. J. Am. Chem. Soc. 1994, 116, 7895. (q)
Handbook of Conducting Polymers; Skotheim, T. J., Ed.; Dekker: New
York, 1986.
S0002-7863(96)04223-0 CCC: $14.00 © 1997 American Chemical Society

Planar Poly(phenylenethiophene)s and Polythiophenes
J. Am. Chem. Soc., Vol. 119, No. 41, 1997 9625
chromatographic purification and even amine-washed silica gel
caused significant decomposition of 1. Hence a low isolated
yield of 1 was obtained in our efforts to ensure purities necessary
for the subsequent step-growth polymerizations. Diketone 21p
was prepared from 2,4-dibromoterephthaloyl chloride1h as
described previously, while the complementary compounds 3
(67%) and 4 (63%) were easily prepared by AlCl3-promoted
Scheme 1
Friedel-Crafts acylation of n-butylbenzene or 1-phenyloctane,
respectively, with 2,4-dibromoterephthaloyl chloride. Tetra-
bromination of thiophene followed by selective 2,5-debromi-
nation afforded 3,4-dibromothiophene. Cyano-substitution,
hydrolysis and bromination at the 2,5-positions afforded the
dicarboxylic acid 5.5 Bis(acid chloride) formation and treatment
with n-butylbenzene yielded the diketone monomer 6 (eq 2).
Polymerization Reactions
The modified Stille polymerizations6 were carried out with
a Pd(0) catalyst and triphenylarsine as the supporting ligand.
Triphenylphosphine gave lower molecular weight polymers,
probably due to phosphine aryl transfer reactions.6 Addition
of CuI as a cocatalyst lowered the molecular weights for the
poly(phenylenethiophene)s while CuI addition increased the
molecular weights for the polythiophenes. The reason for the
catalysis differences in the two polymer systems is unclear. Use
of higher polymerization temperatures resulted in the loss of
some of the Boc residues and darkening of the material. The
polymerizations are shown in Scheme 1. All the polymers were
analyzed prior to planarization by size exclusion chromatography
(SEC) in THF relative to polystyrene (PS) standards. Since
SEC is a measure of the hydrodynamic volume and not the
molecular weight, significant yet consistent errors in Mn and
Mw usually result when comparing rigid rod polymers to the
flexible coils of PS standards.7 The errors in this Mn range are
generally off by a factor of 1.5-2. Therefore, the values
recorded here are given simply as a reference. The trifluoro-
acetic acid (TFA) or TiCl4-induced8 Boc removal and Schiff
base formation products are also shown in Scheme 1. Notice
that the imine formation strategy provides an efficient method
for the planarization between the consecutive repeat units, since
we can avoid the arduous task of introducing new atoms along
a rigid rod backbone from exogenous reagents; all the needed
atoms are present in the monomers.
Analyses of the Polymers
The protons on the backbone benzenoid moieties shifted from
ca. 7.3 ppm in 7-9 to ca. 9.8 ppm in 10-12 upon planarization;
a trend consistent with earlier studies on ladder PPPs.1p There
were only trace amounts of remaining ketone signatures present
in the FTIR spectra, likely due to the end groups, and remaining
Boc residues were often undetected by NMR and FTIR analyses.
Since the imine formation was reversible under the acidic
conditions, any intermolecular Schiff base formation could have
equilibrated back to the more stable six-membered imine ring.
Furthermore, intermolecular Schiff base formation is unlikely
to have been obtained in the final polymers since that would
have resulted in a cross-linked insoluble network.
(5) (a) Gronowitz, S. Acta Chem. Scand. 1959, 13, 1045. (b) MacDowell,
D. W. H.; Wisowaty, J. C. J. Org. Chem. 1972, 37, 1712. (c) Pomerantz,
M.; Yang, H.; Cheng, Y. Macromolecules 1995, 28, 5706.
(6) (a) Bao, Z.; Chan, W. K.; Yu, L. J. Am. Chem. Soc. 1995, 117, 12426.
(b) Stille, J. K. Angew. Chem., Int. Ed. Engl. 1986, 25, 508. (c) Farina, V.
Pure Appl. Chem. 1996, 68, 73. (d) Farina, V.; Krishnan, B. J. Am. Chem.
Soc. 1991, 113, 9585.
(7) This effect in molecular weight differences was determined using
rigid rod oligomers of precisely known length and constitution to generate
a calibration curve versus polystyrene in THF by SEC. See: (a) Tour, J.
M. Chem. ReV. 1996, 96, 537.
The optical spectra for the poly(phenylenethiophene)s 7-9
were recorded in CH2Cl2 (Figure 1). See Table 1 for a complete
listing of the optical data. Compounds 7-9 had larger than
(8) (a) Boone, H. W.; Hall, H. K., Jr. Macromolecules 1996, 29, 5835.
(b) Weingarten, H.; Chupp, J. P.; Whiye, W. A. J. Org. Chem. 1967, 32,
3246.

9626 J. Am. Chem. Soc., Vol. 119, No. 41, 1997
Zhang and Tour
Figure 1. Optical spectra of 7 (s), 8 (- ‚ -), 9 (- - -), and 13 (‚‚‚)
Figure 2. Optical spectra of 10 (- ‚ -), 11 (‚‚‚), and 14 (s) in TFA/
CH2Cl2 (1:2). The spectrum for 12 is nearly identical to the spectrum
of 11.
in CH2Cl2.
Table 1. Optical Data for the Polymers and Their Corresponding
Trimers
increase in λmax (Figures 1 and 2, and Table 1) was noticed
which could be indicative of the greater electron delocalization
in the planar form. However, there are two factors that must
be considered. First, 13 has an unusually large λmax value when
compared to typical fully substituted polythiophenes. Highly
regiochemically pure 3-substituted polythiophenes have λmax
values of 450-460 nm in solution,10 while 3,4-disubstituted
polythiophenes generally have λmax < 300 nm due to the
unavoidable 3-3′ (head-to-head) interactions.11 In the case of
13, the large λmax value is likely due to the donor/acceptor
alternating arrangement which induces intramolecular CT as
described above.2,9 Second, in 14, molecular modeling12
confirms that there is severe buttressing of the two aryl moieties
at the adjacent imine-carbon positions which causes a twisting
of the planar backbone. Recording of the optical spectra of 14
in TFA/CH2Cl2 (1:2) resulted in a bathochromic shift over that
recorded in CH2Cl2 albeit smaller than the shifts observed in
the poly(phenylenethiophene)s (Table 1). This could be the
result of a proton-induced enhancement of the intramolecular
CT.2a
λmax
(CH2Cl2),
(nm)a
λmax
emissmax
emissmax
(TFA/CH2Cl2, (CH2Cl2), (TFA/CH2Cl2,
compd
1:2), (nm)a
(nm)
1:2), (nm)
7
8
9
372
c
c
c
479
503
509
b
c
c
c
375 (sh)
375 (sh)
b
10
11
12
13
14
19
20
21
22
23
25
463
477
477
no emission
no emission
no emission
c
b
b
b
b
378 (sh)
412, 439
332, 352
356
c
523
450
393
416
495, 526
515, 551
380 (sh)
423
no emission no emission
413
487
514
475
476
470
431
457
558
588
435, 464
451
436
425, 449
325, 345 (sh)
358
a No absorptions of <310 nm are listed here. The italic values are
the more intense of the two listed. b The polymers were not soluble in
CH2Cl2. c Addition of TFA would result in loss of the Boc group.
expected values of λmax when compared to less sterically
encumbered poly[(dialkylphenylene)thiophene]s which have
λmax values of ca. 340 nm.6a In 7-9, the thiophene moieties
are electron rich and the phenylene units are electron deficient,
thus inducing an alternating donor/acceptor repeat unit config-
uration which establishes significant intramolecular charge
transfer (CT) character between the consecutive polymer repeat
units, resulting in an increase in the absorbance maxima (Figure
1).2,9 Though a direct comparison was sought of the optical
spectral properties of 7-9 versus 10-12 in identical solvents,
the planar polymers 10-12 required TFA/CH2Cl2 (1:2) mixtures
for their dissolution. Any use of acid for recording the optical
spectra of 7-9 would have caused loss of the Boc moieties
and planarization. Attempts to cast films of 10-12 from TFA/
CH2Cl2 (1:2) followed by removal of the solvent in vacuo did
not permit salt removal as indicated by FTIR studies.2a Interest-
ingly, the planar polymers 10-12 had significantly longer
wavelength absorptions (Figure 2) by ca. 100 nm relative to
their nonplanar precursors 7-9. This could be a function of
the enhanced π-conjugation upon planarization, or simply a
solvent-induced difference (aprotic for 7-9 and strongly acidic
for 10-12). Due to the solubility differences of the planarized
and nonplanarized forms of the poly(phenylenethiophene)s, a
more precise explanation awaits an oligomeric study in which
common solvents can be used (vide infra).
With all of the ladder polymers, the nitrogen lone pair remains
orthogonal to the polymer backbone, hence it is no longer able
to add electron density to the polymer backbone by a resonance
effect. Thus the donor portion is not as strong a donor in the
planar polymer as it is in the nonplanar polymer. Though the
carbonyl portion of the acceptor moiety is lost upon planariza-
tion, the imine remains an electron-withdrawing group in the
cyclized material. The imine units in the ladder polymer are
fixed in near planarity with the conjugated polymer backbone,
thereby increasing their electron-accepting ability. Hence
planarization has a dual effect on the donor/acceptor properties.
Interestingly, even though 10-12 had thiophene units that were
forced into a nearly 180° relationship between the 2,5-bonds
(148° being the optimal bond angle in an unperturbed
thiophene),13 the linear arrangements permitted a greater degree
(9) (e) Zhang, Q. T.; Tour, J. M. J. Am. Chem. Soc. 1997, 119, 5065.
(10) (a) McCullough, R. D.; Lowe, R. D.; Jayaraman, M.; Anderson, D.
L. J. Org. Chem. 1993, 58, 904. (b) Chen, T.-A.; Wu, X.; Rieke, R. D. J.
Am. Chem. Soc. 1995, 117, 233.
(11) Kankre, J.; Lukkari, J.; Pasanen, P.; Sillapa¨a¨, R.; Laine, H.; Harmaa,
K. Macromolecules 1994, 27, 4327.
(12) Molecular modeling was performed using a Silicon Graphics Power
Indigo2 employing MacroModel 4.5 for both structure drawing and
minimization. Minimization was done on a tetramer containing four
thiophene units and three imine brides using a MM2* force field. The energy
calculation was minimized over a large number of iterations to convergence
at a local minimum nearest in energy to the drawn starting compound’s
initial energy.
In the case of the polythiophenes 13 and 14, CH2Cl2 could
be used to dissolve both the preplanar (13) and planar (14)
forms. Upon the conversion of 13 to 14 (Scheme 1, eq 4), an
(13) Phillips, R. W.; Sheares, V. V.; Samuliski, E. T.; DeSimone, J. M.
Polym. Prepr. (Am. Chem. Soc., DiV. Polym. Chem.) 1994, 35 (1), 367.

Planar Poly(phenylenethiophene)s and Polythiophenes
J. Am. Chem. Soc., Vol. 119, No. 41, 1997 9627
Scheme 2
Figure 3. Optical spectra of 21 in CH2Cl2 (-‚‚‚), 21 in TFA/CH2Cl2
(1:2) (- ‚ -), 22 in CH2Cl2 (s), and 22 (‚‚‚) in TFA/CH2Cl2 (1:2).
Aqueous workup afforded the aldehyde which was oxidized to
the carboxylic acid,15 converted to the acid chloride, and
subjected to Friedel-Crafts acylation conditions to afford 24.
The couplings were achieved using the same conditions that
afforded the corresponding polymers.
The optical spectra of the trimeric (phenylenethiophene)s 19-
22 showed unexpected and remarkable features. The optical
absorption maxima underwent enormous bathochromic shifts
when recorded in TFA/CH2Cl2 (1:2) versus CH2Cl2 (Table 1).
The protic system is likely increasing the intramolecular CT
by making the iminium-bearing units more electron deficient.
Moreover, these spectra were recorded at varying concentrations
to confirm that the charge transfer is likely intramolecular (or
inter-repeat unit)2a and not intermolecular; there was no change
in λmax upon dilution. The high degree of conjugation in the
planar systems is further suggested since the affect of CT
separation between the protonated and nonprotonated forms is
far greater than the differences noted in nonplanarized polymers.2a
Using these simple trimeric models, it is obvious that a direct
comparison of the optical data for 7-9 in CH2Cl2 versus 10-
12 in TFA/CH2Cl2 is not be possible since the charge separation
in the protonated cases greatly lowers the optical bandgaps. A
common solvent must be utilized.
While the optical absorption maxima of the trimers 19 and
20 were considerably smaller than the absorption maxima of
polymers 10-12, the absorption maxima of 21 and 22 are large
relative to the corresponding absorptions of the polymers (all
using TFA/CH2Cl2 (1:2), Table 1, Figures 2 and 3). The optical
absorption maximum of the polymers 10-12 reside between
the values for the complementary trimers 19/20 and 21/22. It is
unclear why the complementary pairs 19/20 and 21/22 exhibit
such large (ca. 100-130 nm) optical absorption differences
regardless of their protonated or unprotonated states. In 21/
22, the acceptor units are polarized in opposite directions while
they are pointing in the same direction in 19/20. Thus greater
CT separation is likely in 21/22 with a concomitant bathochro-
mic shift. In polymers 10-12, the intramolecular CT separation
can follow both opposing and similar directions, resulting in
optical absorptions that reside between the values for the
complementary trimer pairs.
of π-conjugation, as evidenced by the optical absorption
maxima, than the curved and distorted backbone configuration
(due to aryl buttressing) in 14.
Emission signals with very large Stokes shifts (ca. 100-130
nm) were apparent for the preplanar polymers 7-9 and 13 in
CH2Cl2. Since highly delocalized systems can undergo exci-
ton-exciton annihilation, it is not surprising that the corre-
sponding planar polymers 10-12 and 14 showed no emission
signals (Table 1). Conversely, this could be an effect of the
azine functionality.
Synthesis of Model Trimers and Their Optical Analyses
To more precisely assess the degree of extended conjugation
or intrachain CT interactions in the in the polymers, it was
necessary to prepare systems that could be dissolved in a
common solvent system. Using reactions similar to those
described above, the syntheses of model trimers were conducted
as shown in Scheme 2. 17 was prepared by lithium-halogen
exchange of 3-bromothiophene followed by carboxylation. Acid
chloride formation, conversion to the acyl azide, and Curtius
rearrangement with tert-butyl alcohol capture yielded the Boc-
protected amine. Finally, Boc-directed 2-position lithiation and
quenching with the chlorostannane afforded the desired 17.14
Thiophene-3-carbaldehyde was protected as its acetal which
directed 2-position lithiation and subsequent bromination.
The problem of comparing polymer 14 to trimers 23 and 25
is exacerbated since 14 and 23 have the aryl buttressing problem
(leading to backbone twisting) while 25 does not. Nevertheless,
polymer 14 has a longer wavelength maximum than either of
the complementary trimeric forms.
To further explore this protonation effect on planar oligomers,
we reinvestigated two planar trimeric phenylenes that were
(14) Bjo¨rk, P.; Aakermann, T.; Hornfeldt, A.-B.; Gronowitz, S. J.
Heterocycl. Chem. 1995, 32, 751.
(15) (a) Fournari, P.; Guilard, R.; Person, M. Bull. Soc. Chim. Fr. 1967,
4115. (b) Campaigne, E.; LeSuer, W. M. J. Am. Chem. Soc. 1949, 71, 333.

9628 J. Am. Chem. Soc., Vol. 119, No. 41, 1997
Zhang and Tour
models for the planar PPPs (26-28) that we synthesized
previously.1h The planar PPPs were not soluble without TFA
being present, however, the oligomeric versions were previously
studied only in CH2Cl2. The CT bands in 26-28 are assigned
to 514, 516, and 549 nm bands, respectively, since these bands
are not present in typical nonheteroatom-containing ladder
PPPs.1,2a In this case, polymers 26-28 have longer absorption
maxima than either of the two complementary trimers 29/30.
Notice, as with the previous planar trimers, there is an enormous
optical difference when 29 or 30 are subjected to acidic versus
neutral conditions. Thus planarization greatly affects the amount
Experimental Section
General. Unless otherwise noted, all operations were carried out
under a dry, oxygen-free nitrogen atmosphere. Molecular weight
analyses were performed using two 30 × 75 cm Burdick and Jackson
GPC columns (105 Å, 10 µm and 500 Å, 5 µm) eluting with THF at
60 °C (flow rate 1.0 mL/min). Molecular weight results were based
on five polystyrene standards (Mw ) 435 500, 96 000, 22 000, 5050,
and 580 with a correlation coefficient >0.9998) purchased from
Polymer Laboratories Ltd. Combustion analyses were obtained from
Atlantic Microlab, Inc., P.O. Box 2288, Norcross, GA 30091. Capillary
GC analyses were obtained using an Alltech model 932525 (25 m ×
0.25 mm, 0.2 µm film of AT-1 stationary phase) capillary GC column.
Alkyllithium reagents were obtained from Aldrich Chemical Co. Inc.
or FMC. Reagent grade diethyl ether and tetrahydrofuran (THF) were
distilled under nitrogen from sodium benzophenone ketyl. Reagent
grade benzene and dichloromethane were distilled over calcium hydride.
Bulk grade hexane was distilled prior to use. Gravity column
chromatography, silica gel plugs, and flash chromatography were carried
out using 230-400 mesh silica gel from EM Science. Thin-layer
chromatography was performed using glass plates precoated with silica
gel 60 F254 with a layer thickness of 0.25 mm purchased from EM
Science. Unless otherwise noted, all monomers for the polymerizations
were >99.5% pure, and all other nonpolymeric materials were >96%
pure as judged by NMR, GC, or combustion analyses. The absorption
and emission spectral data are listed in Table 1, while the molecular
weight data are listed in Scheme 1.
N,N′-Bis(tert-butoxycarbonyl)-3,4-diamino-2,5-bis(tri-n-butyl-
stannyl)thiophene (1). A solution of n-butyllithium (44.30 mL, 70.0
mmol, 1.58 M in hexane) was slowly added to diisopropylamine (8.46
mL, 60.0 mmol) in ether (50 mL) at -78 °C. The solution was warmed
to room temperature, then cooled to 0 °C with an ice bath. A solution
of N,N′-bis(tert-butoxycarbonyl)-3,4-diaminothiophene4b (3.14 g, 10
mmol) in THF (10.0 mL) was added, and the mixture was warmed to
room temperature for 10 min. After the mixture was recooled to 0 °C,
chlorotributylstannane (6.52 mL, 22.0 mmol) was added. The yellow
mixture was stirred for 3 h. A saturated sodium chloride solution (50
mL) was added, the organic layer was separated off, and the aqueous
layer was extracted with dichloromethane (3×). The combined organic
layers were dried over anhydrous sodium sulfate and filtered. Tri-
ethylamine (30 mL) was added to the filtrate, and the resulting solution
was stirred overnight. The solvent was evaporated in vacuo, and the
residue was purified by flash chromatography with hexane on treated
silica gel (washed with triethylamine, then hexane). The product was
collected as the first fraction. The solvent was removed in vacuo to
give 2.94 g (37%) of the title compound. FTIR (KBr): 3278, 2957,
2926, 2872, 1717, 1506, 1392, 1376, 1246, 1162, 1065, 1018, 876,
of CT possible when we compare these to nonplanarized imine-
containing CT polymers,2a thereby indicating that the propensity
for extended conjugation in the ladder systems permits an
optimization of intramolecular CT.
Conductivity Studies
As a test case, we studied the conductivity characteristics on
pressed pellets of polymer 11 in their neutral and HCl-protonated
forms. Four-point probe measurements indicated that both
forms had conductivity values of <10-7 Ω‚cm-1, thus making
these insulators. Iodine doping of the neutral material gave no
enhancement of the conductivity. Due to the presence of the
electron deficient pyridyl system in the ladder polymers,
p-doping becomes more difficult than in typical polythiophenes,
a phenomenon that we have observed previously in the planar
PPPs such as 27.1h
771 cm-1
.
1H NMR (400 MHz, CDCl3): δ 6.37 (s, 2 H), 1.51 (m, 12
H), 1.47 (s, 18 H), 1.33 (sext, J ) 7.4 Hz, 12 H), 1.10 (m, 12 H), 0.88
(t, J ) 7.3 Hz, 18 H). 13C NMR (100 MHz, CDCl3): δ 155.0, 138.6,
136.2, 82.4, 29.4, 28.7, 27.7, 14.0, 11.2. LRΜS (positive ion APCI)
calcd relative isotopic intensities for C38H74N2O4SSn2 (M+): 888.4
(13%), 890.4 (41%), 891.3 (82%), 893.3 (100%), 895.4 (80%), 896.4
(49%), 899.4 (19%). Found: 887.6 (12%), 889.5 (41%), 891.5 (76%),
893.5 (100%), 895.5 (81%), 896.5 (42%), 897.5 (25%). Anal. Calcd
for C38H74N2O4SSn2: C, 51.14; H, 8.35; N, 3.14. Found: C, 51.20;
H, 8.37; N, 3.07.
Conclusion
We have described routes to soluble planar poly(phenylene-
thiophene)s and polythiophenes by using Pd-catalyzed coupling
routes followed by Schiff base formations to force the consecu-
tive repeat units into near planarity. Bond deformations that
are caused by pendant group interactions can adversely affect
the conjugation. Intramolecular CT profoundly decreases the
optical bandgap in the planarized systems, especially when the
CT effect is enhanced by protonation of the imine units; shifts
in the optical absorption maxima of 100 nm can be observed
upon protonation. The effect of intramolecular CT can even
be observed with small oligomeric ladder systems which
provides a further motivation to study these simple small
conjugated structures. Therefore, coupling of intramolecular
CT with maximization of conjugation via planarization is a
unique method to minimize optical bandgaps in conjugated
materials.
Compound 3. A solution of dibromoterephthaloyl chloride1h (2.00
g, 5.97 mmol) in dichloromethane was added slowly to a suspension
of aluminum chloride (3.18 g, 23.90 mmol) in dry dichloromethane
(15 mL) maintained at 0 °C. The mixture was allowed to stir at 0 °C
for 10 min. n-Butylbenzene (4.01 g, 29.85 mmol) was slowly added.
The mixture was stirred for 30 min and was then poured onto ice.
Dichloromethane (50 mL) was added, and the mixture was shaken
vigorously. The layers were separated, and the aqueous layer was
extracted with dichloromethane (3×). The combined organic portions
were washed with a saturated sodium bicarbonate solution (50 mL)
and water, then dried over magnesium sulfate. The residue, which
remained after the solvent was evaporated, was purified by flash
chromatography on silica gel with ethyl acetate:hexane (1:10) to give
2.2 g (67%) of the title compound. FTIR (KBr): 2926, 2857, 1669,
1604, 1460, 1416, 1384, 1344, 1248, 1184, 1152, 1060, 934, 881, 841,
752, 666. 1H NMR (400 MHz, CDCl3): δ 7.74 (d, J ) 8.20 Hz, 4 H),

Planar Poly(phenylenethiophene)s and Polythiophenes
J. Am. Chem. Soc., Vol. 119, No. 41, 1997 9629
7.56 (s, 2 H), 7.26 (d, J ) 8.20 Hz, 4 H), 2.68 (t, J ) 7.80 Hz, 4 H),
1.62 (p, J ) 7.40 Hz, 4 H), 1.35 (sext, J ) 7.40 Hz, 4 H), 0.92 (t, J )
7.40 Hz, 6 H) ppm. 13C NMR (100 MHz, CDCl3): δ 193.33, 150.53,
143.35, 132.90, 130.48, 129.00, 118.43, 35.87, 33.11, 22.11, 13.89.
Anal. Calcd for C28H28Br2O2: C, 60.45; H, 5.07. Found: C, 60.32;
H, 5.14. HRMS calcd for C28H28Br2O2: 554.0456. Found: 554.0461.
Compound 4.1h This compound was synthesized in the same
manner as described for compound 3. Used were 2,5-dibromotereph-
thaloyl chloride1h (3.00 g, 8.31 mmol) and 1-phenyloctane (3.95 g, 20.78
mmol). The yield was 3.50 g (63%). Spectral properties were identical
to those reported earlier1h though the synthesis was different.
AsPh3 (0.0061 g, 0.02 mmol) were used. The yield was 0.29 g (69%).
FTIR (KBr): 3423, 3359, 2959, 2931, 2871, 2860, 1730, 1665, 1605,
1506, 1455, 1384, 1368, 1280, 1244, 1171, 943, 854, 771. 1H NMR
(400 MHz, CDCl3): δ 7.62 7.50 (br d, J ) 8.35 4 H), 7.40-7.22 (br
s, 2 H), 7.20-6.90 (br s, 4 H), 2.80-2.30 (br s, 4 H), 1.60-1.02 (m,
26 H), 1.00-0.80 (br t, J ) 7.90 Hz, 6 H). 13C NMR (100 MHz,
CDCl3): δ 195.96, 153.09, 149.21, 140.95, 133.95, 132.00, 130.54,
129.47, 128.32, 80.15, 35.69, 33.04, 28.10, 22.29, 13.83. Anal. Calcd
for (C42H48N2O6S)n: C, 71.16; H, 6.82; N, 3.95. Found: C, 71.23; H,
6.80; N, 3.89.
Polymer 9. N,N′-Bis(tert-butoxycarbonyl)-3,4-diamino-2,5-bis(tri-
n-butylstannyl)thiophene (0.4374 g, 0.4900 mmol), 4 (0.3340 g, 0.5000
mmol), dry THF (5.0 mL), Pd2(dba)3 (0.0092 g, 0.0100 mmol), and
AsPh3 (0.0061 g, 0.0200 mmol) were used. The yield was 0.276 g
(67%). FTIR (KBr): 3356, 2928, 2856, 1728, 1664, 1605, 1493, 1385,
1245, 1161, 933, 767. 1H NMR (400 MHz, CDCl3): δ 7.70-7.50 (br
d, J ) 8.35 Hz, 4 H), 7.40-7.22 (br s, 2 H), 7.20-6.80 (br s, 4 H),
2.80-2.30 (br s, 4 H), 1.70-1.02 (m, 42 H), 0.90-0.80 (br t, J )
7.40 Hz, 6 H). 13C NMR (100 MHz, CDCl3): δ 195.78, 153.03, 149.25,
140.90, 133.96, 130.55, 129.46, 128.26, 80.12, 36.03, 31.87, 30.97,
29.37, 29.21, 28.11, 22.66, 14.09. Anal. Calcd for (C50H64N2O6S)n:
C, 73.14; H, 7.86. N, 3.41. Found: C, 73.13; H, 7.89; N, 3.34.
General Schiff Base Formation Procedure for Polymers 10, 11,
and 12. Under nitrogen, trifluoroacetic acid (1.5 mL) was added to
the Boc-protected polymer in methylene chloride (1.5 mL) at room
temperature. The brown solution was stirred at room temperature for
12 h, then poured into a solution of aqueous sodium hydroxide (10
mL, 3 M). The mixture was stirred at room temperature for 2 h, then
heated to evaporate the methylene chloride. The resulting solid was
collected by filtration and was washed with water, methylene chloride,
and ether. To this solid in a screw cap tube was added triethylamine,
and the mixture was heated 80 °C for 12 h. The mixture was allowed
to cool to room temperature, then the solid was collected by filtration
and washed with water, ether, and methylene chloride. The solid was
dried in vacuo to give the title compound.
Polymer 10. This compound was synthesized as described in the
general procedures. Polymer 7 (0.1302 g, 0.1666 mmol) was used as
the starting material. The yield was 0.0874 g (91%). FTIR (KBr):
3149, 2923, 2851, 1569, 1451, 1385, 1205, 1154, 872, 662. 1H NMR
(300 MHz, TFA-d/CDCl3 (1:1)): δ 9.9 (br s, 2 H), 4.19 (br s, 4 H),
2.22 (br, 4 H), 1.80 (br, 4 H), 1.62-1.10 (br, 32 H), 0.90 (br, 6 H).
Anal. Calcd for (C36H52N2S)n: C, 79.36; H, 9.62; N, 5.14. Found:
C, 76.81; H, 9.43; N, 5.02.16
Polymer 11. This compound was synthesized as described in the
general procedures. Polymer 8 (0.6190 g, 0.8731 mmol) was used as
the starting material. The yield was 0.3983 g (97%). FTIR (KBr):
3139, 2913, 2851, 1610, 1554, 1451, 1385, 1236, 841, 651. 1H NMR
(300 MHz, TFA-d/CDCl3 (1:1)): δ 9.78 (br s, 2 H), 8.10 (br m, 4 H),
7.78 (br m, 4 H), 3.05-2.80 (br, 4 H), 1.68-1.40 (br, 4 H), 1.20-
0.90 (br, 6 H). Anal. Calcd for (C32H28N2S)n: C, 81.32; H, 5.97; N,
5.93. Found: C, 78.33; H, 5.79; N, 5.60.16
2,5-Dibromothiophene-3,4-dicarboxylic Acid (5). Thiophene-3,4-
dicarboxylic acid5b (0.50 g, 2.91 mmol) and glacial acetic acid (5 mL)
were added to a 10 mL flask with a stirring bar. Bromine (0.90 mL,
17.4 mmol) was added dropwise. The mixture was stirred overnight.
Aqueous sodium bisulfate solution was added until the reddish color
disappeared. The mixture was filtered, and a gray solid was obtained.
The crude product was recrystallized from water to give 0.96 g (80%)
of the title compound. IR (KBr): 3300-2600, 1697, 1465, 1377, 1247,
912, 687 cm-1
.
1H NMR (400 MHz, DMSO): δ 13.6 (br s). 13C NMR
(100 MHz, CDCl3) δ 163.0, 135.6, 114.9.
2,5-Dibromothiophene-3,4-dicarboxylic Acid Chloride. Oxalyl
chloride (1.06 mL, 12.1 mmol) was slowly added to 2,5-dibro-
mothiophene-3,4-dicarboxylic acid (1.00 g, 3.03 mmol) and DMF (1
drop) in benzene (50 mL). The mixture was heated to reflux for 1 h,
then cooled to room temperature. The volatiles were removed in vacuo,
affording 1.19 g (100%) of the title compound. IR (KBr): 1755, 1414,
1356, 1145, 992, 949, 716, 673 cm-1 13C NMR (100 MHz, CDCl3):
.
δ 160.2, 136.4, 118.8. HRMS calcd for C6Br2Cl2O2S: 363.7363.
Found: 363.7361. No MS peak for the cyclic anhydride (C6Br2O2S)
at 311.9 amu was observed.
Compound 6. This compound was synthesized in the same manner
as described for compound 3. Used were 2,5-dibromothiophene 3,4-
diacid chloride (0.50 g, 1.49 mmol) and n-butylbenzene (1.15 mL, 7.45
mmol). The yield was 0.23 g (35%). IR (KBr): 2954, 2862, 1662,
1600, 1436, 1380, 1251, 1174, 995, 841, 769, 626. 1H NMR (400
MHz, CDCl3): δ 7.59 (d, J ) 8.3 Hz, 4 H), 7.19 (d, J ) 8.3 Hz, 4 H),
2.61 (t, J ) 7.8 Hz, 4 H), 1.57 (p, J ) 7.3 Hz, 4 H), 1.31 (sext, J )
7.3 Hz, 4 H), 0.91 (t, J ) 7.3 Hz, 6 H). 13C NMR (100 MHz, CDCl3):
δ 189.2, 149.8, 142.0, 134.0, 130.0, 128.6, 113.7, 35.8, 33.1, 22.3, 13.9.
Anal. Calcd for C26H26Br2O2S: C, 55.54; H, 4.66. Found: C, 55.61;
H, 4.67. HRMS calcd for C26H26Br2O2S: 560.0020. Found: 560.0005.
General Polymerization Procedure for Polymers 7, 8, 9, and 13.
In a drybox, the diketone monomer (0.50 mmol) and N,N′-bis(tert-
butoxycarbonyl)-3,4-diamino-2,5-bis(tri-n-butylstannyl)thiophene (0.49
mmol) were dissolved in dry THF (5.0 mL) in a screw cap tube. Pd2-
(dba)3 (2 mol %) and AsPh3 (4 mol %) were added to the solution.
The tube was capped and heated to 80 °C for 72 h. The dark mixture
was cooled, poured into a solution of KF (10 mL, 1.00 M), and stirred
for 30 min. The insoluble white solid was removed by filtration. The
organic layer was separated, dried over sodium sulfate, and evaporated
to dryness. Acetone (5.0 mL) was added to dissolve the residue. The
solution was added slowly to hexane (200 mL). The precipitate was
collected by filtration, redissolved in acetone, and precipitated with
hexane again. The polymer was collected by filtration and then dried
under vacuum.
Polymer 7. N,N′-Bis(tert-butoxycarbonyl)-3,4-diamino-2,5-bis(tri-
n-butylstannyl)thiophene (0.4374 g, 0.4900 mmol), 2 (0.314 g, 0.5000
mmol), dry THF (5.0 mL), Pd2(dba)3 (0.0092 g, 0.0100 mmol), and
AsPh3 (0.0061 g, 0.0200 mmol) were used. The yield was 0.20 g
(51%). FTIR (KBr): 3415, 3374, 3149, 2923, 2851, 1723, 1697, 1497,
1456, 1385, 1246, 1164, 1077, 1005, 872, 769, 605. 1H NMR (400
MHz, CDCl3): δ 7.61-7.52 (br s, 2 H), 6.91-6.70 (br s, 2 H), 2.70
(br s, 4 H), 1.70-1.50 (m, 4 H), 1.38 (m, 18 H), 1.30 (br s, 36 H),
0.89 (t, J ) 7.0 Hz, 6 H). 13C NMR (75 MHz, CDCl3): δ 204.91,
153.27, 142.54, 130.97, 130.12, 129.20, 124.82, 124.60, 80.82, 42.07,
31.92, 29.71, 29.68, 29.61, 29.55, 29.37, 29.30, 28.31, 28.12, 24.47,
22.69, 14.12. Anal. Calcd for (C46H72N2O6S)n: C, 70.73; H, 9.29; N,
3.59. Found: C, 70.84; H, 9.36; N, 3.52.
Polymer 12. This compound was synthesized as described in
general procedures. Polymer 9 (0.2547 g, 0.3101 mmol) was used as
the starting material. The yield was 0.1687 g (93%). FTIR (KBr):
3139, 2913, 2841, 1549, 1456, 1380, 1236, 887, 836, 646. 1H NMR
(300 MHz, TFA-d/CDCl3 (1:1)): δ 9.78 (br s, 2 H), 8.10 (br, 4 H),
7.82 (br, 4 H), 3.10 (br, 4 H), 1.94 (br, 4 H), 1.80-1.30 (br, 20 H),
0.98 (br, 6 H). Anal. Calcd for (C40H44N2S)n: C, 82.15; H, 7.58; N,
4.79. Found: C, 80.43; H, 7.61; N, 4.53.16
Polymer 13. N,N′-Bis(tert-butoxycarbonyl)-3,4-diamino-2,5-bis(tri-
n-butylstannyl)thiophene (0.4374 g, 0.4900 mmol), 6 (0.2810 g, 0.5000
mmol), THF (5.0 mL), Pd2(dba)3 (0.0092 g, 0.0100 mmol), and AsPh3
(0.0061 g, 0.0200 mmol) were used. The yield was 0.2810 g (70%).
FTIR (KBr): 3426, 3159, 2964, 2923, 2862, 1723, 1656, 1605, 1497,
1385, 1241, 1164, 1000, 872, 841, 764, 615. 1H NMR (400 MHz,
(16) It is common to obtain low carbon values in combustion analyses
of highly unsaturated polymers based on arene structures. This is due to
incomplete combustion with remaining carbon residues. In most cases, the
H and N values remain reasonably accurate. See ref 1h and (a) Chimil, K.;
Scherf, U. Makromol. Chem., Rapid Commun. 1993, 14, 217. (b) Wallow,
T. I.; Novak, B. M. J. Am. Chem. Soc. 1991, 113, 7411. (c) Stephens, E.
B.; Tour, J. M. Macromolecules 1993, 26, 2420.
Polymer 8. N,N′-Bis(tert-butoxycarbonyl)-3,4-diamino-2,5-bis(tri-
n-butylstannyl)thiophene (0.4374 g, 0.4900 mmol), 3 (0.278 g, 0.5000
mmol), dry THF (5.0 mL), Pd2(dba)3 (0.0092 g, 0.0100 mmol), and

9630 J. Am. Chem. Soc., Vol. 119, No. 41, 1997
Zhang and Tour
CDCl3): δ 8.00-7.02 (br d, J ) 8.3 Hz, 4 H), 7.02-6.80 (m, 4 H),
2.60-2.30 (m, 4 H), 1.70-1.10 (m, 26 H), 1.00-0.80 (m, 6 H) ppm.
13C NMR (75 MHz, CDCl3): δ 192.00, 153.07, 148.86, 140.00, 134.81,
132.15, 131.51, 129.78, 128.43, 128.08, 80.63, 35.59, 33.06, 28.28,
22.16, 13.87. Anal. Calcd for (C40H46N2O6S2)n: C, 67.20; H, 6.49;
N, 3.92. Found: C, 65.94; H, 6.41; N, 3.75.
General Procedure for Schiff Base Formation on the Trimers.
Under nitrogen, titanium tetrachloride (1.0 M in methylene chloride)
was added slowly to a solution of the nonplanar trimer in methylene
chloride. The mixture was stirred at room temperature for 3 h, then
poured into water. The mixture was extracted with dichloromethane
(3×). The combined organic layer was washed with aqueous potassium
carbonate (2.0 M) and water, then dried over magnesium sulfate and
filtered. The solvent was removed in Vacuo to give desired the desired
products.
Trimer 19. 1 (0.4374 g, 0.49 mmol), 151h (0.2411 g, 1.0 mmol),
Pd2(dba)3 (0.0092 g, 0.0100 mmol), AsPh3 (0.0062 g, 0.0200 mmol),
and THF (5 mL) were used to afford the nonplanar trimer which was
used directly for the next step with titanium tetrachloride (2.0 mL, 1.0
M in CH2Cl2). The total yield for two steps was 0.1913 g (67%). IR
(KBr): 3117, 2953, 2862, 1549, 1380, 749, 672. 1H NMR (300 MHz,
CDCl3): δ 8.29 (d, J ) 8.3 Hz, 2 H), 8.13 (d, J ) 7.6 Hz, 2 H), 7.75
(t, J ) 8.2 Hz, 2 H), 7.62 (t, J ) 8.2 Hz, 2 H), 3.55 (t, J ) 7.2 Hz, 4
H), 2.00 (p, J ) 7.8 Hz, 4 H), 1.60 (sext, J ) 7.4 Hz, 4 H), 1.01 (t, J
) 7.3 Hz, 6 H). 13C NMR (75 MHz, CDCl3): δ 162.1, 145.0, 132.2,
130.5, 128.3, 127.2, 127.2, 125.6, 123.7, 36.1, 32.7, 23.3, 14.1. HRMS
calcd for C26H26N2S: 398.1817. Found: 398.1804.
The Nonplanar Trimer Leading to 20. 1 (0.8748 g, 0.98 mmol),
16 (0.6345 g, 2.00 mmol), Pd2(dba)3 (0.0184 g, 0.02 mmol), AsPh3
(0.0124 g, 0.04 mmol), and THF (5 mL) were used to afford 0.80 g
(92%). IR (KBr): 3333, 2964, 2923, 2862, 1728, 1708, 1605, 1523,
1487, 1456, 1385, 1287, 1246, 1159, 928, 754, 692. 1H NMR (400
MHz, CDCl3): δ 7.58 (d, J ) 8.2 Hz, 4 H), 7.47-7.39 (m , 6 H), 7.30
(d, J ) 7.6 Hz, 2 H), 7.11 (d, J ) 7.5 Hz, 4 H), 6.95 (br s, 2 H), 2.59
(t, J ) 7.8 Hz, 4 H), 1.56 (p, J ) 7.6 Hz, 4 H), 1.45-1.22 (m, 22 H),
0.88 (t, J ) 7.3 Hz, 6 H). 13C NMR (75 MHz, CDCl3): δ 197.9,
153.3, 148.7, 139.8, 134.7, 131.6, 130.4, 130.1, 130.0, 128.7, 128.4,
128.2, 127.7, 122.5, 79.9, 35.8, 33.2, 28.1, 22.4, 13.9. HRMS calcd
for C48H54N2O6S: 786.3703. Found: 786.3682.
Trimer 20. The above nonplanar trimer (0.5642 g, 0.7169 mmol)
in methylene chloride (2.0 mL) and titanium tetrachloride (4.0 mL,
1.0 M in methylene chloride) were used. The yield was 0.3762 g (93%).
IR (KBr): 3159, 3036, 2944, 2913, 2851, 1610, 1539, 1380, 1303,
1010, 841, 774, 754, 677, 656. 1H NMR (300 MHz, CDCl3): δ 8.24
(2 overlapping d, app t, J ) 8.0 Hz, 4 H), 7.80 (t, J ) 7.2 Hz, 2 H),
7.73 (d, J ) 7.6 Hz, 4 H), 7.56 (dd, J ) 8.0, 7.1 Hz, 2 H), 7.31 (d, J
) 7.2 Hz, 4 H), 2.71 (t, J ) 7.8 Hz, 4 H), 1.65 (p, J ) 7.8 Hz, 4 H),
1.39 (sext, J ) 7.2, 4 H), 0.96 (t, J ) 7.2 Hz, 6 H). 13C NMR (75
MHz, CDCl3) δ 160.2, 145.2, 143.3, 137.0, 132.4, 130.7, 130.4, 129.4,
128.8, 128.2, 127.0, 125.6, 123.2, 35.6, 33.7, 22.4, 14.1. HRMS calcd
for C38H37N2S: 550.2443. Found: 550.2443.
Polymer 14. Under nitrogen, titanium tetrachloride (1.0 mL, 1.0
M in methylene chloride) was added slowly to a solution of polymer
13 (0.0376 g, 0.051 mmol) in methylene chloride (1.0 mL). The
mixture was stirred at room temperature for 12 h, then poured into
water (10 mL). The mixture was extracted with methylene chloride
(3×). The combined organic layers were dried over magnesium sulfate
and filtered. The solvent was removed in vacuo. The crude material
was added to triethylamine (2.0 mL) in a screw cap tube and was heated
80 °C for 12 h. The mixture was allowed to cool to room temperature,
then the solid was collected by filtration and washed with water. The
product was dried in vacuo to give 0.0224 g (91%) of the title
compound. FTIR (KBr): 2933, 2864, 1663, 1607, 1485, 1396, 1220,
838, 760, 624. 1H NMR (300 MHz, TFA-d/CDCl3 (1:1)): δ 7.30-
7.00 (br, 8 H), 2.80-2.50 (br, 4 H), 1.70 (br, 4 H), 1.50 (br, 4 H), 1.10
(br, 6 H). Anal. Calcd for (C32H28N2S)n: C, 75.28; H, 5.47; N, 5.85.
Found: C, 71.79; H, 5.57; N, 5.33.16
2-Bromo-4′-(n-butyl)benzophenone (16). This compound was
synthesized in the same manner as described for compound 3. Used
were 2-bromobenzoic acid chloride1h (2.18 g, 9.95 mmol), aluminum
chloride (1.99 g, 14.93 mmol), and n-butylbenzene (1.86 mL, 11.94
mmol) to afford 2.70 g (86%). IR (KBr): 3046, 2949, 2862, 1667,
1595, 1467, 1426, 1302, 1282, 928, 749. 1H NMR (400 MHz,
CDCl3): δ 7.70 (d, J ) 8.0 Hz, 2 H), 7.62 (d, J ) 7.9 Hz, 1 H), 7.39-
7.30 (m , 3 H), 7.24 (d, J ) 8.0 Hz, 2 H), 2.66 (t, J ) 7.3 Hz, 2 H),
1.60 (p, J ) 7.3 Hz, 2 H), 1.35 (sext, J ) 7.3 Hz, 2 H), 0.91 (t, J )
7.3 Hz, 3 H). 13C NMR (75 MHz, CDCl3): δ 195.7, 149.7, 141.0,
133.8, 133.1, 131.0, 130.4, 128.9, 128.7, 127.1, 119.5, 85.8, 33.2, 22.4,
13.9. HRMS calcd for C17H17BrO: 316.0463. Found: 316.0465.
N-(tert-Butoxycarbonyl)-3-amino-2-(tri-n-butylstannyl)thio-
phene (17). A solution of n-butyllithium (23.74 mL, 36.08 mmol, 1.52
M in hexane) was slowly added to diisopropylamine (4.73 mL, 36.08
mmol) in ether (50 mL) at -78 °C. The solution was warmed to room
temperature then cooled to 0 °C with an ice bath. A solution of N-(tert-
butoxycarbonyl)-3-aminothiophene14 (3.59 g, 18.04 mmol) in ether (10.0
mL) was added, and the mixture was warmed to room temperature for
10 min. After the mixture was recooled to 0 °C, chlorotributylstannane
(6.46 mL, 19.84 mmol) was added. The yellow mixture was stirred
for 1 h. A saturated sodium chloride solution (50 mL) was added, the
organic layer was separated off, and the aqueous layer was extracted
with dichloromethane (3×). The combined organic layers were dried
over anhydrous sodium sulfate and filtered. Triethylamine (30 mL)
was added to the filtrate, and the resulting solution was stirred overnight.
The solvent was evaporated in vacuo, and the residue was purified by
flash chromatography with hexane on treated silica gel (washed with
triethylamine, then hexane). The solvent was removed in vacuo to
give 7.19 g (82%) of the title compound. FTIR (KBr): 3436, 3333,
2954, 2913, 2851, 1713, 1544, 1513, 1462, 1364, 1246, 1146, 1056,
867, 713. 1H NMR (400 MHz, CDCl3): δ 7.49 (d, J ) 4.9 Hz, 1 H),
7.36 (br s, 1 H), 6.32 (br s, 1 H), 1.56 (q, J ) 8.1 Hz, 6 H), 1.49 (s,
9 H), 1.38 (sext, J ) 7.2 Hz, 6 H), 1.12 (t, J ) 8.0 Hz, 6 H), 0.89 (t,
J ) 7.3 Hz, 9 H). 13C NMR (75 MHz, CDCl3): δ 153.5, 142.9, 130.7,
124.1, 122.0, 80.1, 29.0, 28.4, 27.3, 13.7, 11.0. Anal. Calcd for C21-
H39NO2SSn: C, 51.65; H, 8.05; N, 2.87. Found: C, 51.71; H, 7.99;
N, 2.94.
Trimer 21. 3 (0.1005 g, 0.25 mmol), 17 (0.2393 g, 0.49 mmol),
Pd2(dba)3 (0.0046 g, 0.005 mmol), AsPh3 (0.0031 g, 0.01 mmol), and
THF (3 mL) were used to form the nonplanar trimer which was used
directly for the next step with titanium tetrachloride (1.0 mL, 1.0 M in
CH2Cl2). The total yield for two steps was 0.0691 g (70%). IR
(KBr): 3118, 3067, 2944, 2862, 1564, 1456, 1380, 1277, 682, 697. 1H
NMR (300 MHz, CDCl3): δ 8.91 (s, 2 H), 7.71 (d, J ) 5.2 Hz, 2 H),
7.64 (d, J ) 5.2 Hz, 2 H), 3.51 (t, J ) 7.8 Hz, 4 H), 2.00 (p, J ) 7.8
Hz, 4 H), 1.39 (sext, J ) 7.4, 4 H), 1.05 (t, J ) 7.4 Hz, 6 H). 13C
NMR (75 MHz, CDCl3): δ 161.4, 129.3, 126.8, 126.0, 124.8, 121.8,
35.6, 31.9, 23.0, 14.1. HRMS calcd for C24H24N2S2: 404.1381.
Found: 404.1384.
Nonplanar Trimer Leading to 22. 181h (0.2000 g, 0.3598 mmol),
17 (0.3443 g, 0.7052 mmol), Pd2(dba)3 (0.0066 g, 0.0072 mmol), AsPh3
(0.0044 g, 0.0144 mmol), and THF (5 mL) were used. The yield was
0.260 g (89%). IR (KBr): 3426, 3109, 2959, 2924, 2857, 1729, 1667,
General Procedure for Pd-Catalyzed Couplings to Prepare the
Trimers. In a drybox, the diketone and the stannane were dissolved
in dry THF in a screw cap tube. Pd2(dba)3 (2 mol %) and AsPh3 (4
mol %) were added to the solution. The tube was capped, removed
from the drybox and heated to 80 °C for 12 h. The dark mixture was
cooled, poured into a solution of KF (10 mL, 1.00 M), and stirred for
30 min. The precipitate was filtered and redissolved in acetone. The
insoluble white solid was removed by filtration. The acetone solution
was dried over sodium sulfate, filtered, and evaporated to dryness. In
some cases, the product was purified by a flash chromatograph on silica
gel with ethyl acetate:hexane (1:10) to give the desired compounds.
1600, 1571, 1467, 1421, 1383, 1237, 1154, 945, 879.
1H NMR (400
MHz, CDCl3): δ 7.64 (d, J ) 8.1, 4 H), 7.52 (s, 2 H), 7.35 (br s, 2 H),
7.17 (d, J ) 8.1 Hz, 4 H), 7.09 (d, J ) 5.5 Hz, 2 H), 6.80 (br s, 2 H),
2.61 (t, J ) 7.6 Hz, 4 H), 1.56 (p, J ) 7.4 Hz, 4 H), 1.47 (s, 18 H),
1.32 (sext, J ) 7.4 Hz, 4 H), 0.90 (t, J ) 7.4 Hz, 6 H). 13C NMR (75
MHz, CDCl3): δ 196.3, 152.8, 149.8, 142.2, 134.4, 133.8, 132.2, 130.9,
130.2, 129.8, 128.8, 128.6, 125.0, 80.6, 35.8, 33.1, 28.3, 22.3, 13.9.
HRMS calcd for C46H52N2O6S2: 792.3267. Found: 792.3270.
Trimer 22. The above nonplanar trimer (0.0664 g, 0.0837 mmol)
in methylene chloride (2.0 mL) and titanium tetrachloride (1.0 mL,
1.0 M in methylene chloride) were used. The yield was 0.0451 g (97%).

Planar Poly(phenylenethiophene)s and Polythiophenes
J. Am. Chem. Soc., Vol. 119, No. 41, 1997 9631
IR (KBr): 3108, 2920, 2912, 2851, 1610, 1554, 1380, 1292, 826, 733,
667. 1H NMR (300 MHz, TFA-d): δ 9.60 (s, 2 H), 8.18 (br d, 2 H),
7.92 (d, J ) 8.2 Hz, 6 H), 7.73 (d, J ) 8.2 Hz, 4 H), 2.92 (t, J ) 7.5
Hz, 4 H), 1.80 (p, J ) 7.5 Hz, 4 H), 1.50 (sext, J ) 7.5 Hz, 4 H), 1.01
(t, J ) 7.2 Hz, 6 H). HRMS calcd for C36H32N2S2: 556.2007.
Found: 556.1995.
Nonplanar Trimer Leading to 23. 6 (0.5620 g, 1.00 mmol), 17
(0.9571 g, 1.96 mmol), Pd2(dba)3 (0.0183 g, 0.02 mmol) AsPh3 (0.0122
g, 0.04 mmol), and THF (5 mL) were used. The yield was 0.693 g
(88%). IR (KBr): 3313, 3118, 2964, 2923, 2862, 1723, 1656, 1569,
1477, 1385, 1236, 1159, 1067, 759, 636. 1H NMR (300 MHz,
CDCl3): δ 7.68 (br s, 2 H), 7.41 (br overlapping d, J ) 5.5-8.2 Hz,
6 H), 7.21 (d, J ) 5.5 Hz, 2 H), 6.97 (d, J ) 8.32 Hz, 4 H), 2.52 (t,
J ) 7.51 Hz, 4 H), 1.52-1.43 (m, 22 H), 1.24 (sext, J ) 7.5 Hz, 4 H),
0.87 (t, J ) 7.3 Hz, 6 H). 13C NMR (75 MHz, CDCl3): δ 191.7,
152.7, 149.2, 140.5, 136.8, 136.6, 134.6, 129.6, 128.2, 126.6, 123.6,
113.7, 80.7, 35.6, 33.0, 28.4, 22.1, 13.9. HRMS calcd for C44H50-
N2O6S3: 798.2831. Found: 798.2811.
Timer 23. The above nonplanar trimer (0.1801 g, 0.2254 mmol),
methylene chloride (2.0 mL) and titanium tetrachloride (1.0 mL, 1.0
M in methylene chloride) were used. The yield was 0.120 g (95%).
IR (KBr): 3087, 2923, 2851, 1610, 1544, 1508, 1462, 1354, 1108,
810, 667. 1H NMR (300 MHz, CDCl3): δ 7.72 (d, J ) 5.4 Hz, 2 H),
7.65 (d, J ) 5.4 Hz, 2 H), 6.99 (d, J ) 8.0 Hz, 4 H), 6.83 (d, J ) 8.0
Hz, 4 H), 2.52 (t, J ) 7.5 Hz, 4 H), 1.60 (p, J ) 7.8 Hz, 4 H), 1.39
(sext, J ) 7.3 Hz, 4 H), 0.97 (t, J ) 7.3 Hz, 6 H). 13C NMR (75
MHz, CDCl3): δ 155.3, 153.2, 142.4, 141.5, 139.5, 129.1, 128.5, 127.9,
126.0, 125.4, 124.6, 35.5, 33.5, 22.5, 14.1. HRMS calcd for
C34H30N2S3: 562.1571. Found: 562.1559.
CDCl3): δ 7.52 (d, J ) 5.9 Hz, 1 H), 7.28 (d, J ) 5.9 Hz, 1 H). 13C
NMR (75 MHz, CDCl3): δ 159.7, 133.8, 131.6, 126.3, 123.5.
Compound 24. This compound was synthesized in the same manner
as described for compound 3. Used were 2-bromothiophene-3-
carboxylic acid chloride (4.87 g, 21.59 mmol), aluminum chloride (3.60
g, 26.90 mmol), and n-butylbenzene (6.8 mL, 43.6 mmol). The yield
was 5.46 g (78%). IR (KBr): 3097, 2933, 2862, 1651, 1600, 1508,
1400, 1256, 1169, 990, 882, 841. 1H NMR (400 MHz, CDCl3): δ
7.75 (d, J ) 8.3 Hz, 2 H), 7.27 (m, 3 H), 7.08 (d, J ) 5.7 , 1 H), 2.67
(t, J ) 7.5 Hz, 2 H), 1.60 (p, J ) 7.3 Hz, 2 H), 1.38 (sext, J ) 7.3 Hz,
2 H), 0.91 (t, J ) 7.3 Hz, 3 H). 13C NMR (75 MHz, CDCl3): δ 190.4,
149.2, 139.7, 134.8, 130.2, 129.4, 128.6, 126.2, 116.1, 35.8, 33.2, 22.4,
13.9. HRMS calcd for C15H15BrOS: 322.0227. Found: 322.0015.
Trimer 25. N,N′-Bis(tert-butoxycarbonyl)-3,4-diamino-2,5-bis(tri-
n-butylstannyl)thiophene (0.8182 g, 0.92 mmol), 24 (0.6047 g, 1.9
mmol), Pd2(dba)3 (0.0183 g, 0.02 mmol), AsPh3 (0.0123 g, 0.04 mmol),
and THF (5 mL) were used. General procedure for Schiff base
formation was directly carried out on the product. The total yield for
two steps was 0.32 g (62%). IR (KBr): 3108, 3026, 2913, 2851, 1523,
1456, 1385, 1313, 1159, 1062, 831, 703. 1H NMR (300 MHz,
CDCl3): δ 7.90 (d, J ) 8.1 Hz, 4 H), 7.70 (d, J ) 5.4 Hz, 2 H), 7.47
(d, J ) 5.4 Hz, 2 H), 7.32 (d, J ) 8.1 Hz, 4 H), 2.71 (t, J ) 7.5 Hz,
4 H), 1.40 (p, J ) 7.4 Hz, 4 H), 1.60 (sext, J ) 7.4, 4 H), 0.96 (t, J )
7.3 Hz, 6 H). 13C NMR (75 MHz, CDCl3): δ 154.5, 145.7, 143.8,
142.4, 137.3, 132.9, 129.8, 128.52, 125.7, 125.5, 125.2, 35.6, 33.6,
22.4, 14.0. HRMS calcd for C34H30N2S3: 562.1571. Found: 562.1587.
Acknowledgment. Support came from the Office of Naval
Research and the National Science Foundation (DMR-9158315).
We thank FMC for a gift of alkyllithium reagents.
2-Bromothiophene-3-carboxylic Acid Chloride. Oxalyl chloride
(3.1 mL, 35.4 mmol) was slowly added to 2-bromothiophene-3-
carboxylic acid15 (4.88 g, 23.6 mmol) and DMF (1 drop) in benzene
(50 mL). The mixture was heated to reflux for 1 h, then cooled to
room temperature. The volatiles were removed in vacuo, affording
5.06 g (95%) of the title compound. IR (KBr): 3108, 1759, 1703,
1
Supporting Information Available: FTIR and H NMR
spectra for 7-14, 19-23, and 25 (28 pages). See any current
masthead page for ordering and Internet access instructions.
1492, 1390, 1210, 995, 836, 728, 677, 641 cm-1
.
1H NMR (400 MHz,
JA964223U