Bis[bis-(4-alkoxyphenyl)amino] derivatives of dithienylethene, bithiophene, dithienothiophene and dithienopyrrole: Palladium-catalysed synthesis and highly delocalised radical cations

Article abstract of DOI:10.1002/chem.200700668

Five diamines with thiophene-based bridges-(E)-1,2-bis-{5-[bis(4- butoxyphenyl)amino]-2-thienyljethylene (1), 5,5′-bis[bis(4-methoxyphenyl) amino]-2,2′-bithiophene (2), 2,6-bis[bis(4-butoxyphenyl)amino]dithieno[3, 2-b:2′,3′-d]thiophene (3), N-(4-tert-butylphenyl)-2,6-bis[bis(4- methoxyphenyl)amino]dithieno[3,2-b:2′,3′-d]pyrrole (4a) and N-tert-butyl-2,6-bis[bis(4-methoxyphenyl)amino]dithieno[3,2-b:2′, 3′-d]pyrrole (4b)-have been synthesised. The syntheses make use of the palladium(0)-catalysed coupling of brominated thiophene species with diarylamines, in some cases accelerated by microwave irradiation. The molecules all undergo facile oxidation, 4b being the most readily oxidised at about -0.4 V versus ferrocenium/ferrocene, and solutions of the corresponding radical cations were generated by addition of tris(4-bromophenyl)aminium hexachloroantimonate to the neutral species. The near-IR spectra of the radical cations show absorptions characteristic of symmetrical delocalised species (that is, class III mixed-valence species); analysis of these absorptions in the framework of Hush theory indicates strong coupling between the two amine redox centres, stronger than that observed in species with phenylenebased bridging groups of comparable length. The strong coupling can be attributed to high-lying orbitais of the thiophene-based bridging units. ESR spectroscopy indicates that the coupling constant to the amino nitrogen atoms is somewhat reduced relative to that in a stilbene-bridged analogue. The neutral species and the corresponding radical cations have been studied with the aid of density functional theory and time-dependent density functional theory. The DFT-calculated ESR parameters are in good agreement with experiment, while calculated spin densities suggest increased bridge character to the oxidation in these species relative to that in comparable species with phenylene-based bridges.

Full text of DOI:10.1002/chem.200700668

FULL PAPER
DOI: 10.1002/chem.200700668
BisACHTREUNG[bis-(4-alkoxyphenyl)amino] Derivatives of Dithienylethene, Bithiophene,
Dithienothiophene and Dithienopyrrole: Palladium-Catalysed Synthesis and
Highly Delocalised Radical Cations
Susan A. Odom, Kelly Lancaster, Luca Beverina, Kelly M. Lefler, Natalie J. Thompson,
Veaceslav Coropceanu, Jean-Luc BrØdas, Seth R. Marder, and Stephen Barlow*[a]
Abstract: Five diamines with thio-
phene-based bridges—(E)-1,2-bis-
{5-[bis(4-butoxyphenyl)amino]-2-thie-
nyl}ethylene (1), 5,5’-bis[bis(4-methoxy-
phenyl)amino]-2,2’-bithiophene (2),
2,6-bis[bis(4-butoxyphenyl)amino]di-
thieno[3,2-b:2’,3’-d]thiophene (3), N-(4-
tert-butylphenyl)-2,6-bis[bis(4-methoxy-
phenyl)amino]dithieno[3,2-b:2’,3’-d]pyr-
role (4a) and N-tert-butyl-2,6-bis[bis(4-
methoxyphenyl)amino]dithieno[3,2-
b:2’,3’-d]pyrrole (4b)—have been syn-
thesised. The syntheses make use of
the palladium(0)-catalysed coupling of
brominated thiophene species with dia-
rylamines, in some cases accelerated by
microwave irradiation. The molecules
all undergo facile oxidation, 4b being
the most readily oxidised at about
ꢀ0.4 V versus ferrocenium/ferrocene,
and solutions of the corresponding rad-
ical cations were generated by addition
of tris(4-bromophenyl)aminium hexa-
chloroantimonate to the neutral spe-
cies. The near-IRspectra of the radical
cations show absorptions characteristic
of symmetrical delocalised species
(that is, class III mixed-valence spe-
cies); analysis of these absorptions in
the framework of Hush theory indi-
cates strong coupling between the two
amine redox centres, stronger than that
observed in species with phenylene-
based bridging groups of comparable
length. The strong coupling can be at-
tributed to high-lying orbitals of the
thiophene-based bridging units. ESR
spectroscopy indicates that the cou-
pling constant to the amino nitrogen
atoms is somewhat reduced relative to
that in a stilbene-bridged analogue.
The neutral species and the corre-
sponding radical cations have been
studied with the aid of density func-
tional theory and time-dependent den-
sity functional theory. The DFT-calcu-
lated ESRparameters are in good
agreement with experiment, while cal-
culated spin densities suggest increased
bridge character to the oxidation in
these species relative to that in compa-
rable species with phenylene-based
bridges.
ACHTREUNG
AHCTREUNG
ACHTREUNG
ACHTREUNG
AHCTREUNG
AHCTREUNG
AHCTREUNG
Keywords: amination
·
electron
spin resonance · mixed-valent com-
pounds · oxidation · radicals
Introduction
The radical cations are mixed-valence (MV) compounds
and typically show NIRintervalence charge-transfer (IVCT)
bands; this terminology reflects the fact that in a valence-lo-
calised cation—that is, in a MV compound belonging to
Robin and Dayꢀs class II[1]—the transition is related to elec-
tron-transfer from one redox site to the other, although the
terminology is also commonly applied to delocalised (class
III MV) systems, since the adiabatic states involved can be
considered as arising from the same diabatic surfaces. IVCT
absorptions have been analysed in the framework of
Marcus–Hush theory[2] for radical cations of species in
which diarylamino groups are linked by bridging groups
based variously on benzene and other arenes,[3–5] biphenyl
and other oligophenylenes,[3,6–8] phenylene-ethynylene,[3,9]
Compounds containing two or more diarylamino redox
groups have recently attracted attention as systems for
studying electronic coupling and delocalisation.
[a] S. A. Odom, K. Lancaster, Dr. L. Beverina, K. M. Lefler,
N. J. Thompson, Dr. V. Coropceanu, Prof. J.-L. BrØdas,
Prof. S. R. Marder, Dr. S. Barlow
School of Chemistry and Biochemistry and
Center for Organic Photonics and Electronics
Georgia Institute of Technology, Atlanta, GA 30332-0400 (USA)
Fax : (+1)404-894-5909
E-mail: stephen.barlow@chemistry.gatech.edu
phenylene-ethenylene,[10,11]
cyclophanes,[12]
organoplati-
Supporting information for this article is available on the WWW
under http://www.chemeurj.org/ or from the author.
num[13] and phosphonium[14] moieties.
Chem. Eur. J. 2007, 13, 9637 – 9646
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9637

Although the NIRspectra of the radical cations of 5,5 ’-
bis(diphenylamino)
[2,2’]bithiophene[15] (IVb+, see below)
Results and Discussion
ACHTREUNG
and of 5,5’’-bis[4-(bis-4-tolylamino)phenyl][2,2’;5’,2]terthio-
Synthesis: Our syntheses of compounds 1–4 (Schemes 1 and
2; see Supporting Information for full details) make exten-
sive use of palladium-catalysed aminations. Bis(4-butoxy-
phenyl)amine (5), an intermediate common to the synthesis
of both 1 and 3, was obtained from 1-bromo-4-butoxyben-
zene and 4-butoxyaniline under coupling conditions similar
to those reported for the synthesis of bis(4-methoxyphenyl)-
amine.[24] With conventional heating the reaction was com-
plete after 1 hour; the product was obtained in good yield
after recrystallisation (73% versus the yield of 89% report-
ed for bis(4-methoxyphenyl)amine after 3 h heating[24]). We
also carried out the synthesis of 5 with single-mode micro-
wave irradiation; however, this offered no particular advant-
age over conventional heating, giving a slightly lower yield
and only a slightly reduced reaction time.
phene[16] have been reported, and the radical cations of bis-
ACHTREUNG[bis-(4-methoxyphenyl)amino]oligothiophenes have been
studied computationally,[17] we are not aware of a detailed
experimental investigation from the standpoint of mixed va-
lency of a bis(diarylamino) system with a thiophene-based
bridge.[18] Here we investigate the extent to which the lower
ionisation potential of thiophene versus benzene (8.9 eV[19]
versus 9.24 eV[20]) can lead to more effective mediation of
coupling between two diarylamino groups in radical cation
species with thienylene-based bridges than in analogous spe-
cies with phenylene-based bridges; increased coupling has
previously been found for bis(diarylamino) derivatives in
which phenylene units of bridging groups are replaced by
donor-substituted phenylene groups.[9] Stronger donor–ac-
ceptor coupling in thienylene-bridged dipolar chromophores
than in phenylene analogues—as shown, for example, in
first hyperpolarisability data[21]—has been attributed to the
reduced aromatic character of thiophene; this may also po-
tentially play a role in MV species. Somewhat reduced steric
hindrance in the thiophene-based species may also lead to
better p overlap between nitrogen- and bridge-based orbi-
tals than in the phenylene analogues.[22]
Although 2-(diarylamino)-3,4-diarylthiophenes have also
been obtained from reactions that involve cyclisation to
form the thiophene ring and utilise diarylamide or thioa-
mide starting materials,[25] most published syntheses of 2-(di-
arylamino)thiophene derivatives have involved coupling of a
diarylamine with a 2-halothiophene. Diphenylamine has
been coupled with 2-halothiophenes, in the presence of a
[26,27]
palladium source (Pd
A
or [Pd2dba3] {dba=diben-
Specifically, we report the synthesis and spectra of new
bis(diarylamino) systems with thiophene-containing bridges:
zylideneacetone}[26]) in conjunction with PtBu3 (36–78%
from 2-bromothiophene[26–28]), or by use of CuI-mediated
modified Ulmann conditions (40% yield from 2-iodothio-
phene).[29] Various other diarylamines including bis(4-alkoxy-
phenyl)amines have been coupled with a,a’-dibromooligo-
thiophenes and with 1,3-bis(5-bromothien-2-yl)benzo[c]thio-
(E)-1,2-bis{5-
ACHTREUNG[bis(4-butoxyphenyl)amino]-2-thienyl}ethylene
(1), 2,6-bis[bis(4-methoxyphenyl)amino]-2,2’-bithiophene (2),
ACHTREUNG
phene in moderate yields in the presence either of Pd-
[30]
ACHRTE(UNG OAc)2/PtBu3 or of [PdACHRTE(UGN dppf)Cl2]/dppf {dppf=1,1’-bis(di-
phenylphosphino)ferrocene}[31] as catalysts.
Initially we attempted the coupling of 5 with 2-bromothio-
phene in the presence of Pd2dba3/dppf as the catalyst but
observed no evidence for the formation of 5-[bis(4-butoxy-
phenyl)amino]thiophene (6); however, we successfully ob-
tained 6 after changing the catalyst to Pd2dba3/PtBu3. We
carried out the reaction both with conventional heating and
with a microwave reactor; after a few attempts at optimisa-
tion of the conditions we found that microwave heating
could produce the desired product 6 in higher yields (95%)
than conventional heating (73%) and that fewer byproducts
were obtained under microwave conditions, which facilitated
chromatographic isolation of the desired product (an oil).
Consequently, we used microwave irradiation as the heating
source for many of our subsequent reactions with 2-bromo-
thiophene derivatives.[32] From 6, 5-[bis-(4-butoxyphenyl)-
2,6-bis
phene (3), N-(4-tert-butylphenyl)-2,6-bis
phenyl)amino]dithieno[3,2-b:2’,3’-d]pyrrole (4a) and N-tert-
butyl-2,6-bis[bis(4-methoxyphenyl)amino]dithieno[3,2-b:2’,3’-
ACHTREUNG
AHCTREUNG
ACHTREUNG
ACHTREUNG
d]pyrrole (4b).[23] We show that analysis of the NIRspectra
of the corresponding radical cations in the framework of
Hush theory[2] gives couplings in thienylene-based systems
about 1.5 to 1.8 times greater than in phenylene-based ana-
logues. Finally, we report the ESRspectra of the radical cat-
ions, which show well resolved hyperfine coupling; in combi-
nation with DFT calculations, these couplings give insight
into the spin distribution in the radical cations and indicate
that the increased effective coupling in the thienylene-based
systems is accompanied by increased bridge character to the
oxidation.
AHCTREaUNG mino]-2-formylthiophene (7) was readily obtained in good
yield under Vilsmeier conditions, affording the pure product
in 71% yield. Compound 7 can also be synthesised directly
through the coupling of 5 with 2-bromo-5-formylthiophene
in the presence of a Pd2dba3/PtBu3 catalyst; however, we
found that the desired aldehyde 7 was accompanied by a sig-
nificant amount of the decarbonylated product 6. Com-
9638
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Chem. Eur. J. 2007, 13, 9637 – 9646

Highly Delocalised Radical Cations
FULL PAPER
pound 7 was reductively coupled under McMurry conditions
to give the target 1 in moderate yield.
In addition to its role as an intermediate in the synthesis
of 1, 7 is also of interest as a potential p-donor for dipolar
chromophores, such as those used for electrooptic applica-
priate amine with 3,3’-dibromo-2,2’-bithiophene; we were
unable to obtain this product using conditions previously re-
ported for n-alkylamines,[42] but obtained 9b in good yield
when PtBu3 was used in place of BINAP {BINAP=2,2’-bis
(diphenylphosphino)-1,1’-binaphthalene}.
Treatment of 9a and 9b with
N-bromosuccinimide in CHCl3/
AcOH gave 10a and 10b, re-
spectively, which, to the best of
our knowledge, are the first re-
ported examples of 2,6-dibro-
mo-dithieno[3,2-b:2’,3’-d]pyr-
roles. It is worth noting that
while the reaction was success-
ful for N-aryl and N-tert-butyl
species, analogues of 10a and
10b with n-alkyl N-substitution
decomposed under these condi-
tions with no dibromo deriva-
tive isolable; presumably the
presence of the CH group a to
N
in the n-alkyl derivatives
Scheme 1. Synthesis of compounds 1 and 3 (Ar=4-nBuOC6H4).
plays a role in these decomposi-
tions. Chromophores incorporating diarylamino-based
donors generally show superior thermal and photochemical
stability to their dialkylamino analogues;[33,34] calculations
suggest that bis(4-alkoxyphenyl)amino-based donors show
p-donor strength comparable to that of dialkylamino-based
analogues,[35] and experimental[21] and theoretical[35] work
suggests that the presence of the thienylene ring should lead
to stronger donor–acceptor coupling than in phenylene ana-
logues.
Compound 3 was obtained in good yield as a glassy solid
from the microwave-assisted palladium-catalysed coupling
of 5 with 2,6-dibromodithieno[3,2-b:2’,3’-d]thiophene (8),[36]
which was prepared by bromination of the parent dithie-
no[3,2-b:2’,3’-d]thiophene[37] with N-bromosuccinimide in
CHCl3/AcOH. The same reagents were used to synthesise
the previously reported compound 2[30] from 5,5’-dibromo-
2,2’-bithiophene and bis(4-methoxyphenyl)amine in higher
yield (76% versus 27%) than previously reported with use
Scheme 2. Synthesis of bis(diarylamino)dithienopyrroles 4a and 4b
(Ar’=MeOC6H4; R=4-tBuC6H4 for 4a, 9a and 10a; R=4-tBu for 4b,
9b and 10b).
tions. Compounds 10a and 10b were converted into 4a and
4b, respectively, with the same catalyst system that was used
to form 2 and 3.
of PdACHTREUNG(OAc)2/PtBu3.
N-Aryldithieno[3,2-b:2’,3’-d]pyrroles have previously been
obtained by coupling of 3-bromothiophene with anilines to
produce N,N-bis(3-thienyl)anilines, followed by bromination
and copper-mediated coupling,[38] or by the palladium-cata-
lysed coupling of 3,3’-dibromo-2,2’-bithiophene[39] with ani-
lines (35% over 50 h for aniline).[40,41] We chose the second
route as the intermediate 3,3’-dibromo-2,2’-bithiophene can
also be used for the synthesis of other N-substituted dithie-
no[3,2-b:2’,3’-d]pyrrole derivatives; by using an increased re-
action temperature (reflux rather than 808C) we were able
to obtain high yields of the N-(4-tert-butylphenyl) derivative
9a in one hour. The N-tert-butyl derivative 9b was also syn-
thesised by the palladium-catalysed coupling of the appro-
Electronic spectra of the neutral species: The UV/visible
spectra of the neutral species 1, 2, 3 and 4a (4b has a very
similar spectrum to 4a) are compared in Figure 1. The data
for the lowest-energy transitions are summarised in Table 1
including transition dipole moments mge, which were ob-
tained, in Debye, from integration of the spectra according
to Equation (1), where n˜ and e(n˜) are in cmꢀ1 and mꢀ1 cmꢀ1,
respectively.
sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
R
sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
Z
~
eð~nÞd~n
eðnÞ
ð1Þ
~
mge ¼ 0:09584
dn ꢁ 0:09584
~
n
~
nmax
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9639

S. Barlow et al.
nitrogen
p
orbitals). The
HOMO orbital, in particular,
has significant bridge-based
contributions from the local
HOMO of the bridge, out of
phase with those from the dia-
rylamine-based orbitals. The
LUMO in each case is princi-
pally bridge-based, resembling
the LUMO of the isolated
bridging moiety. The calculated
energies compare well with the
Figure 1. UV/visible absorption spectra for 1, 2, 3, and 4a in dichloromethane.
experimental data, although
they are systematically underes-
timated by about 2000 cmꢀ1 (this corresponds to less than
10% of the actual transition energy). The lowest-energy
transitions are seen for compound 1, which is consistent
with the expected effect of extending conjugation with a vi-
nylene moiety. Compounds 3 and 4a show very similar tran-
sition energies, which are blue-shifted relative to that of 2;
this is presumably partly attributable to the destabilising
contributions to the LUMOs of 3 and 4a from the central
heteroatoms of the bridges. Both theory and experiment
show larger transition dipole moments in the species with
Table 1. Absorption maxima, absorptivities and transition dipole mo-
ments for the lowest-energy absorptions of the neutral compounds 1, 2,
3, 4a and I in dichloromethane with TD-DFT gas-phase values[a] in ital-
ics.
Compound
n˜max [cmꢀ1
]
emax [mꢀ1 cmꢀ1
]
mge [D]
1
2
3
4a
I
22600
24600
25800
26200
25100[b]
20500
22400
23800
24300
23100
41400
25800
32100
34100
54900[b]
8.58
6.57
7.31
7.62
11.9
9.03
8.79
8.31
12.2
10.0[b]
[a] Computed with TD-DFT at the B3LYP/6-31G
from ref. [10].
ACHTRE(UNG d,p) level. [b] Data
Data for the previously report-
ed (E)-4,4’-bisACHTREUNG[bis(4-methoxy-
phenyl)amino]stilbene (I, see
below)[10] are also included for
comparison. Table 1 also in-
cludes absorption maxima and
transition dipole moments ob-
tained by use of time-depen-
dent density functional theory
(TD-DFT) for gas-phase 1, 2,
3, 4a and I (nBu and tBu
groups replaced by Me).
The TD-DFT calculations
(see Supporting Information
for details) show that the
lowest-energy transition for
each system is predominately a
direct HOMO to LUMO exci-
tation. The molecular orbitals
involved in the transition are
shown for each molecule in
Figure 2, along with the
HOMOꢀ1, which is important
in the spectra of the radical
cations (see below). In each
case
the
HOMO
and
HOMOꢀ1 are of opposite
parity and can be regarded as
in- or out-of-phase linear com-
binations of two diarylamine-
based orbitals (dominated by
Figure 2. HOMOꢀ1, HOMO and LUMO for 1, 2, 3 and 4a according to DFT calculations at the B3LYP/6-
31G(d,p) level.
AHCTREUNG
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Highly Delocalised Radical Cations
FULL PAPER
Table 2. Redox potentials for bisACHTREUNG
more extended conjugation—the vinylene-bridged com-
pounds 1 and I—than in 2, 3 and 4a, which is consistent
with polarisation of the transition along the long axis be-
tween the two amine groups.
+/0
versus FeCp2
[PF6]ꢀ.
CH2Cl2
CH3CN
+/0
2+/+
+/0
2+/+
1
1
1
1
1
1
DE =
2
Compound
E =
E =
DE =
E =
E =
2
2
2
2
2
[a]
1
ꢀ0.23
ꢀ0.20
ꢀ0.19
ꢀ0.40
ꢀ0.43
+0.08
+0.09
ꢀ0.15
ꢀ0.14
ꢀ0.04
+0.13
ꢀ0.08
ꢀ0.10
+0.22
+0.31
+0.34
0.09
0.16
0.32
0.32
0.33
0.14
0.22
0.49
ꢀ0.22[a]
Electrochemistry: Cyclic voltammograms of 1–4 (Figure 3,
Table 2) indicate that the five compounds each show two
facile reversible oxidations. The table also includes redox
2[b,c]
3
ꢀ0.14
ꢀ0.19
ꢀ0.31
ꢀ0.37
–
ꢀ0.02
+0.03
ꢀ0.07
ꢀ0.15
–
0.12
0.22
0.24
0.22
–
4a
4b
potentials of related bisACHTRE[UGN bis(4-methoxyphenyl)amino] ana-
I[d]
logues with hydrocarbon bridges,[3,11,30] indicating 1–4 to be
rather more readily oxidised than analogues with 1,4-phen-
ylene, biphenyl-4,4’-diyl, or (E)-stilbene-4,4’-diyl bridges.[43]
The dithienopyrrole-based bridges result in the most elec-
tron-rich compounds, which are about 0.2 V more readily
oxidised than their dithienothiophene-bridged analogue,
which is consistent with the ionisation potentials of the
simple pyrrole (8.2 eV) and thiophene (8.9 eV) heterocy-
cles,[19] with the N-alkyl derivative 4b being slightly more
electron-rich than its N-aryl analogue 4a.
IIa[e]
IIIa[e]
–
–
–
–
–
–
[a] Separation not resolvable. [b] Values for 2 in MeCN/0.1m [nBu4N]+
[PF6]ꢀ reported in ref. [30] are similar. [c] Potentials for IVa, IVb and
longer Ph-terminated species in PhCN/0.1m [nBu4N]
+A[PF6]ꢀ are reported
AHCTREUNG
CTHREUNG
in ref. [15]. [d] Data from ref. [10]. [e] Data from ref. [3].
rather large compared to many of the other species included
in the table, indicating that the corresponding radical cations
are relatively stable to disproportionation.
Electronic spectra of the monocations 1+–4+: The radical
cations of 1–4 were generated in dichloromethane solution
by addition of an excess of the diamine to a solution of
tris(4-bromophenyl)aminium hexachloroantimonate (see
Supporting Information for details) as previously described
for other diamines.[10,11,13] Figure 4 shows the Vis/NIRspec-
tra of the resulting solutions, with the exception of that of
4b+ (shown in Supporting Information), which is essentially
identical to that of 4a+. The insensitivity of the spectra of
4a+ and 4b+ to the substituent on the pyrrole nitrogen is
consistent with the lack of pyrrole nitrogen contributions to
the relevant orbitals (see Figure 2). Cations 1+–4+ show in-
tense absorption bands in the NIRregion; these are similar
in terms of energy, absorptivity, and lineshape to the inter-
valence charge-transfer (IVCT) absorptions previously ob-
served for other strongly coupled bis(diarylamino) MV cat-
ions, data for some examples of which are also included in
Table 3. Firstly, the observed bandwidths at half height
Figure 3. Cyclic voltammograms of 1, 2, 3, 4a and 4b (CH2Cl2, 0.1m
[nBu4N] CHTREUNG )
+A[PF6]ꢀ, 50 mVsꢀ1 with Cp2Co+/0 as an internal reference
(ꢀ1320 mV versus FeCp2+/0).
The separations between the first and second redox po-
1
tentials (DE = ) for all five compounds are greater in the less
2
polar solvent, which is consistent with the predictions of the
dielectric continuum model for the electrostatic contribution
[44]
1
1
to DE = . Although DE = values have often been used as
2
2
measures of the electronic coupling (V) between the diabat-
ic states in the MV species, it has been shown that they pro-
vide a very poor guide and must be used with extreme cau-
1
(n˜ = [obs]) are narrower than the width predicted for a class II
2
MV species by Equation (2) (which is written for the case in
tion;[45] indeed, the values of DE = in Table 2 show no clear
which both n˜ = [Hush] and n˜max are in cmꢀ1).
1
1
2
2
relation with the spectroscopic estimates of V given for 1+–
4a+, I+, IIa+ and IIIa+ in Table 3 (see below). However, it
pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
ð2Þ
~
~
n= ½HushŠ
1
¼
ð2310 Â nmax
Þ
1
2
is worth noting that the DE = values for 3, 4a and 4b are
2
Chem. Eur. J. 2007, 13, 9637 – 9646
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9641

S. Barlow et al.
1
structures in that both n˜ = [obs]
2
1
and n˜ = [high] are well below
2
1
n˜ = [Hush]
, the bands are the
2
broadest of the species under
1
consideration
(n˜ = [obs]
over
2
600 cmꢀ1 greater than for the
next broadest—that of 3+) and
are considerably less asymmet-
1
1
ric as gauged by n˜ = [high]/n˜ = [low]
2
2
(compare the values of 1.34
and 0.95 for 3+ and 4a+, re-
spectively). Thus, the charac-
teristics of the low-energy NIR
absorptions strongly support
the assignment of 1+–4+ to
Class III, along with the previ-
ously studied I+.
Figure 4. Visible/NIRspectra of monocations 1+–4a+ in dichloromethane. The onsets of strong absorption at
high energy (at ꢁ20000 for 1+ and ꢁ23000 cmꢀ1 for 2+, 3+ and 4a+) correspond to absorption by the excess
neutral diamines present; the absorptivity scale applies only to the lower energy absorptions attributable to
the radical cations.
Secondly, for 1+, 2+ and 3+ the bands are strongly asymmet-
ric; following Lambert and Nçll, the asymmetry is quanti-
The DFT results for the 1+, 2+, 3+, 4a+ and I+ radical
cations also suggest that all these systems should be assigned
to class III. While use of DFT often affords overdelocalised
structures and, therefore, may suggest a symmetric class III
structure for a class II species, it has previously been found
to give good agreement with structural and spectroscopic
features when applied to species shown experimentally to
belong to class III.[4,6,11] The DFT results show that 1–4 un-
dergo similar geometric changes to I on oxidation (see Sup-
1
1
1
fied in Table 3 by the ratio n˜ = [high]/n˜ = [low], where n˜ = [high] and
2
2
2
1
n˜ = [low] are defined as twice the bandwidths on the high- and
2
low-energy sides of the absorption maximum, respectively.
1
1
The values of n˜ = [high] approach the Hush limit (n˜ = [Hush]). In
2
2
organic MV radical cations these spectral characteristics
were originally interpreted in terms of a cut-off on the low-
energy side of the band due to the thermal population of
the electron-transfer barrier top;[3,46,47] according to this
model, this situation is predicted for any system belonging
to Robin and Dayꢀs class II[1] (valence-localised) but lying
very close to the borderline with class III (delocalised): that
is, with a low barrier to intramolecular electron transfer.
Subsequent work suggested that these lineshapes could also
arise from coupling of the electron transfer in class III and
class II/class III borderline systems to symmetric vibra-
tions.[48] A number of other bis(diarylamino) MV cations
have been found to exhibit similar lineshapes; crystallo-
graphic and vibrational studies[4,6,11] and variable-tempera-
ture measurements of the IVCT band shapes[49] support the
latter of the two interpretations. Although the NIRabsorp-
tions of 4a+ and 4b+ are also consistent with delocalised
ꢀ
porting Information for details): the N Cbridge bonds contract
(N Cbridge bonds being shorter in 1–4 and 1+–4+ than in I
ꢀ
+
ꢀ
and I , respectively), the N Caryl bonds lengthen, the bridge
bond-length pattern shifts towards, but not fully to, a semi-
quinoidal limit, the nonplanar bridges (those of 1, 2, and I)
planarise, and the angle between the planes defined by the
bridging groups and by the amine N atoms and the attached
C atoms decreases (more dramatically and giving a smaller
final angle in 1+–4+ than in I+). The TD-DFT transition en-
ergies and transition dipole moments are included in
Table 3. The calculated energies are slightly overestimated
for the ethylene-bridged species 1+ and I+ and slightly un-
derestimated for 2+ and for the fused-ring species 3+ and
4a+, with the variation in n˜max between compounds being
well reproduced; this further
supports our assignment of the
Table 3. Parameters from the low-energy NIRabsorptions of 1+, 2+, 3+, 4a+ and other symmetric bis
ACHTREUNG
cations to class III. The transi-
tion dipole moments are gen-
erally less well reproduced by
TD-DFT calculations than in
the case of the corresponding
neutral species.
According to DFT calcula-
tions, the molecular orbitals of
the radical cations very closely
resemble those of the corre-
sponding neutral species, with
the semi-occupied orbitals of
the radical ions corresponding
to the HOMOs of the neutral
species (Figure 2). In the no-
koxyphenyl)amino] radical cations in CH2Cl2 or, for IIa+ and IIIa+, CH2Cl2/0.1mm [nBu4N]+A
CHTREUNG
values from TD-DFT calculations[a] in italics.
[b]
[e]
n˜max [cmꢀ1
]
emax
[mꢀ1 cmꢀ1
/
mge [D]
V[Eq. (3)]
V[Eq. (4)]
1
1
n˜ = [obs] n˜ = [Hush]
1
n˜ = [high]
1
n˜ = [high]/
2
2
2
2
[c]
[d]
]
[cmꢀ1
]
[cmꢀ1
]
[cmꢀ1
]
[cmꢀ1
]
1
n˜ = [low]
1
n˜ = [Hush]
2
2
1+
2+
3+
8750
10100
10500
9480
10020
10300
11600
6980
56500
47900
57100
49000
39300[f]
2720
3338
3640
4260
4500
4830
4920
5370
3750
3830
4650
1.37
1.17
1.34
0.95
0.70
0.75
0.85
0.77
13.0
12.3
14.0
12.3
9.3
2150
2820
3400
3480
1400
4375
5050
5250
6270
3020
3180
4675
9.6
10.4
9.7
4a+ 12500
I+
6080[f]
2760[f]
3170[g]
3640[g]
1.40[f] 0.86
1.45[g] 0.98
1.76[g] 0.99
13.5[f] 15.5
IIa+
IIIa+
6360[g] 6920[h] 28000[g]
9350[g] 9250[h] 22700[g]
11.6[g] 14.5[h] 1550
9.17[g] 10.1[h] 3240
[a] B3LYP/6-31GACHTREUNG(d,p) level. [b] Calculated using Equation (2). [c] Ratio of bandwidth on high-energy side to
that on low-energy side. [d] Ratio of twice the band on the high-energy side to the bandwidth from Equa-
tion (2). [e] Estimated from Equation (3) using the experimentally determined values of n˜max and mge and the
geometric N–N distance. [f] Data taken from refs. [10,11]. [g] Data from ref. [3]. [h] TD-DFT values from
ref. [48].
9642
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Chem. Eur. J. 2007, 13, 9637 – 9646

Highly Delocalised Radical Cations
FULL PAPER
menclature of the neutral molecules, the TD-DFT results in-
dicate that the lowest-energy transition of the radical cations
is predominantly HOMOꢀ1 to HOMO in nature, with
other configurations playing a slightly more important role
in the more extended species. Thus, the transition is between
combinations of diarylamino-based orbitals (dominated by
amine nitrogen p orbitals) with opposite parity, this orbital
picture closely resembling that previously reported for other
delocalised bis(diarylamino) radical cations,[4,6,15–17,50] and
thus suggesting that the lowest energy bands of 1+–4+ have
significant IVCT character.
along with values from Equation (4). According to either es-
timate, 1+, 2+, 3+ and 4a+ all show rather large couplings,
as would be anticipated from the electron-rich character of
the thiophene-containing bridges. Comparison of the dithie-
nylethylene derivative with the stilbene species, 1+ and I+,
or of the bithiophene and biphenyl species, 2+ and IIa+, re-
spectively, shows that replacement of phenylene with thieny-
lene groups leads to increased coupling. The coupling sug-
gested by Equation (4) in the dithienopyrrole-bridged spe-
cies 4a+ is the strongest yet reported for a bis
phenyl)amino] MV species, including IIIa+ (a stronger cou-
ACHTRE[UNG bis(4-alkoxy-
The electronic structure calculations also provide some in-
sight into the differences in experimentally observed band
shapes. The relaxation energy associated with the lowest ex-
cited state of the radical cations was estimated by the sym-
metry-constraint approach.[48] The relaxation energies were
estimated by DFT to be 2873 cmꢀ1, 3480 cmꢀ1, 3331 cmꢀ1
and 3943 cmꢀ1 for 1+, 2+, 3+ and 4a+, respectively, and thus
follow the trend seen in the experimentally measured values
pling of V
[Eq. (4)] =5790 cmꢀ1 is obtained for the 1,4-
bis(diphenylamino)benzene radical cation IIIb+,[4] emphasis-
ing that the relative electron-richness of the bridge and the
end groups is important, while
a value of V[Eq. (4)] =
ꢁ5550 cmꢀ1 for IVb+ can be deduced from the published
spectrum[15]). For all the compounds in Table 3 the couplings
estimated according to Equation (3) are significantly smaller
than those obtained from Equation (4). This discrepancy is
at least partly attributable to the N–N separation being
greater than the true diabatic electron-transfer distance;
that is, the redox centres cannot be regarded as centred on
the N atoms, but are displaced somewhat into the bridge.
Assuming the validity of Equations (3) and (4),[51] the appro-
priate values of R would have to be approximately half to
two-thirds of the geometric N–N separation. In view of the
reduced diabatic electron-transfer distances in all these spe-
cies, it is interesting to ask to what extent these species can
still be regarded as diamino MV species, rather than being
“bridge-oxidised” species. To obtain information pertinent
to this question, we turn next to examine the electron-spin
resonance (ESR) spectra of the monocations.
of n˜ = [obs] (2720, 3338, 3640, and 4260 cmꢀ1, respectively).
1
2
Therefore, the increase in bandwidth on going from 3+ to
4a+ could be related to a significant (about 600 cmꢀ1) in-
crease in the corresponding relaxation energy. Usually,
larger relaxation energies result in a more symmetric (Gaus-
sian-like) band shape; this is consistent with the broader,
more symmetric, lineshape of the IVCT of 4a+ relative to
that of 3+.
Electronic coupling: According to Hush theory,[2] the elec-
tronic coupling (V) between two redox centres can be ob-
tained from the transition dipole moment (mge) and the ab-
sorption maximum (n˜max) of the IVCT band of the MV spe-
cies according to Equation (3) in which e is the electronic
charge and R is the diabatic electron-transfer distance; that
is, the distance between donor and acceptor in the absence
of any electronic coupling.
Electron-spin resonance of monocations: Room tempera-
ture X-band ESRspectra were acquired for the same
CH2Cl2 solutions of 1+–4+ as used for measurement of the
Vis/NIRspectra; the spectra show more resolvable coupling
than the spectra of bis(diarylamino) MV species that we
have previously reported.[10,11,13] The spectra are shown in
Figure 5 (as in the case of the optical spectra, the ESRspec-
trum of 4b+ is shown only in the Supporting Information,
due to its close similarity to that of 4a+). The spectra are
reminiscent of those of the radical cations of bis(diphenyl-
~
V ¼ mgenmax=ðeRÞ
ð3Þ
In the case of Class III MV systems, the coupling can also
be obtained directly from the IVCT maximum by using
Equation (4).
AHCTREUNG
amino)-terminated oligothiophenes such as IVa+ and IVb+,
~
V ¼ nmax=2
ð4Þ
in which coupling constants to the I=1 14N and the I=1= 1H
2
of the bridging ligand are of comparable magnitude.[15]
Estimates of V from Equation (3), obtained by assuming R
Figure 5 shows the spectra, along with the previously report-
to be the geometric N–N separation, are given in Table 3,
Figure 5. Experimentally observed X-band ESRspectra (lower, solid line) of I+ and 1+–4+ in dichloromethane with simulations (upper, dotted lines)
used to obtain coupling constants.
Chem. Eur. J. 2007, 13, 9637 – 9646
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www.chemeurj.org
9643

S. Barlow et al.
ed spectrum of I+,[11] and spectra simulated using
WinSim.[52,53] In all cases, the spectra are centred at g=
2.004, a typical value for triarylamine radical cations.[54] In
all cases the spectra were fitted by assuming coupling to two
equivalent 14N nuclei, to varying numbers of pairs of 1H
nuclei, and the to the pyrrole 14N of 4a+ (i.e., with the cat-
ions assumed to be symmetrical, at least on a timescale of
>10ꢀ7 s).[55] The coupling constants obtained from the simu-
lations are given in Table 4; values obtained from DFT cal-
consistent with the bridge character of the oxidation increas-
ing in the order I+ < 3+ < 2+ < 4a+ < 1+. DFT-calculat-
ed spin densities (see Table 5) are consistent with this pic-
ture. Even in I+ there is considerably more spin density on
the stilbene bridge than on the terminal aryl groups, which
is consistent with the shift of the diabatic states into the
bridge suggested by the NIRdata (see above) and with the
appearance of the partially occupied orbital (corresponding
to the HOMO of the neutral species shown in Figure 2). In
the thiophene-containing radi-
cal cations the spin density on
Table 4. Experimentally observed and theoretical (italics) ESRhyperfine coupling constants (G) for some bis-
ACHTREUNG
[bis(4-alkoxyphenyl)amino] radical cations.[a]
the bridge is increased at the
expense of that on N and that
on the terminal aryl groups,
with the bridge character in-
creasing in the same order as
deduced from the values of
AN. Nevertheless, the calcula-
tions indicate that the amino
nitrogen atoms bear greater
spin density than any of the
other atoms, suggesting that,
although the bridge character
of the oxidation is increased in
1+–4+ relative to that in ana-
1+ 2+
3+
4a+
I+
AN(a)
2.68
2.00
2.28
1.90
–
2.91
ꢀ1.90
ꢀ2.09
ꢀ1.79
–
3.20
2.70
2.20
–
3.32
ꢀ2.51
ꢀ2.15
–
3.44
2.15
–
–
–
3.43
3.17
1.24
–
–
1.61
3.15, 3.18
3.80[c]
3.65
[b]
[d]
AH(a)
ꢀ1.85
ꢀ1.17, ꢀ1.20
ꢀ0.76, ꢀ0.82[e]
ꢀ0.26, ꢀ0.30[e]
ꢀ1.48
[b]
[b]
[f]
[d]
[d]
AH(b)
AH(c)
–
–
–
–
–
AN(b)
–
–
ꢀ1.22
–
–
[a] Isotropic Fermi contact couplings calculated at the open-shell B3LYP/6-31GACHTRE(UGN d,p) DFT level with both sign
and magnitude; experimental values are moduli (jAj). [b] H(a), H(b) and H(c) are defined in Scheme 3.
[c] We have previously reported[11] a somewhat larger value for this coupling constant by inspection of the ex-
perimentally measured spectrum; however, the spectra are better simulated with the present value. [d] Not re-
solvable in the experimentally measured spectrum. [e] The two values given are H(a), H(a’) or H(b), H(b’).
[f] This nitrogen is that in the pyrrole ring of 4a+.
culations, also given in the table, are in good agreement
with the experimental data, and allow us to assign the re-
solvable 1H coupling, as indicated in Table 4 and in
Scheme 3. Moreover, the good agreement between experi-
mentally measured and DFT-calculated coupling constants
suggests that DFT describes the spin distribution in the radi-
cal cations well and, therefore, suggests that we are justified
in using DFT spin densities as a means of assessing the
degree to which the oxidation can be regarded as amine-
based (see below).
logues such as I+, the species with thiophene-based bridges
can still be regarded as having significant MV diamine char-
acter.
Table 5. DFT-calculated spin densities for different portions of the radi-
cal cations 1+, 2+, 3+, 4a+ and I+.
1+
2+
3+
4a+
I+
terminal aryl
amino N atoms
bridging group
0.12
0.25
0.63
0.15
0.28
0.57
0.17
0.29
0.54
0.13
0.27
0.60
0.27
0.31
0.42
A value of AN =8.97 G has been reported for [(4-
MeOC6H4)3N]+ in MeCN;[56] thus, a notional class III (or
rapidly exchanging) MV system consisting of two such
redox centres would be expected to show AN = ꢁ4.5 G. The
experimentally measured (and calculated) AN values are
lower, decreasing in the order I+ > 3+ > 2+ > 4a+ > 1+,
suggesting that the total spin density for the two 14N atoms
is reduced relative to that in [(4-MeOC6H4)3N]+, which is
Conclusions
Bis(4-alkoxyphenyl)amines can be coupled to bromothio-
phene and related derivatives in good yield under palladi-
um-catalysed conditions; at least in some cases microwave
irradiation leads to improved yields and fewer side reac-
tions. Five bisACTHER[NGU bis(4-alkoxyphenyl)ACHRTEaUGN mino] species with thio-
phene-based bridges have been synthesised. The ease of oxi-
dation of these materials suggests that compounds of this
type may have applications as hole-injection materials in or-
ganic light-emitting diodes, while the 5-[bis-(4-butoxyphenyl)-
amino]-2-formylthiophene intermediate used in the synthe-
sis of one of these compounds has potential utility as a
potent p-donor for incorporation into stable electrooptic
chromophores. The radical cations of the bisACHTREU[NG bis(4-alkoxy-
phenyl)amino] compounds have been generated; their NIR
spectra are indicative of strong coupling between the two
redox centres, stronger than that observed in species with
phenylene-based bridging groups of comparable length. This
can be largely attributed to high-lying orbitals of the thio-
Scheme 3. Labelling scheme for 1H and 14N nuclei for which coupling
constants are given in Table 4.
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Chem. Eur. J. 2007, 13, 9637 – 9646

Highly Delocalised Radical Cations
FULL PAPER
[21] L.-T. Cheng, W. Tam, S. R. Marder, A. E. Stiegman, G. Rikken, C.
W. Spangler, J. Phys. Chem. 1991, 95, 10643.
phene-based bridging units (steric factors may also contrib-
ute); indeed, ESRspectroscopy and quantum chemical cal-
culations indicate increased spin density on the bridging
groups than in comparable species with phenylene-based
bridges, with a concomitant reduction in spin density on the
amino nitrogen centres. However, the observed ESRcou-
pling constants, the calculated spin densities and the calcu-
lated radical cation structures demonstrate that the amine
nitrogen atoms still play a dominant role in the oxidation
process; that is, that these cations can still be regarded as
MV compounds, albeit with an appreciable bridge-based
character.
[22] For a more extreme case in which steric hindrance has an influence
on the electronic coupling (and where steric and ionisation potential
effects are in opposition, rather than working in concert), see: C.
Lambert, C. Risko, V. Coropceanu, J. Schelter, S. Amthor, N. E.
Gruhn, J. C. Durivage, J. L. BrØdas, J. Am. Chem. Soc. 2005, 127,
8508.
[23] A few other (E)-1,2-bis[5-(diarylamino)-2-thienyl]ethylene deriva-
tives with less strongly electron-donating terminal aryl groups than
those of 1, along with some analogous dialkylamino species, have
been reported in patents (M. Kuroda, N. Koshio, Japanese Patent
03109555, 1991; M. Kuroda, M. Amano, N. Koshio, Japanese Patent
05094877, 1993) as potential photoconductors and hole-injection ma-
terials for organic light-emitting diodes. 1-{Bis[2-(diphenylamino)di-
thieno[3,2-b:2’,3’-d]thiophene-6-yl]amino}perylene is, to the best of
our knowledge, the only bisACHTRE(UGN amino)dithienothiophene to have been
reported; this compound also appeared in a patent as a luminescent
material (H. Tanaka, M. Kanno, T. Yagi, Y. Toba, Japanese Patent
2003129043, 2003).
Acknowledgements
This work was supported in part by the National Science Foundation
(STC Program, Agreement DMR-0120968; CRIF Program, Agreement
CHE-0443564; graduate research fellowship for S.A.O) and by the US
Army Research Laboratory and the US Army Research Office (contract
50372-CH-MUR). We also thank S. Jones for helpful discussions.
[24] D. A. Pratt, F. A. Di Labio, L. Valgimigli, G. F. Pedulli, K. U.
Ingold, J. Am. Chem. Soc. 2002, 124, 11085.
[25] a) O. Zeika, H. Hartmann, Synthesis 2004, 3, 377; b) H. Hartmann,
P. Gerstner, D. Rohde, Org. Lett., 2001, 11, 1673.
[26] M. W. Hooper, M. Utsunomiya, J. F. Hartwig, J. Org. Chem. 2003,
68, 2861.
[27] K. R. Ogawa, S. D. Rothstein, S. C. Rasmussen, J. Org. Chem. 2001,
66, 9067.
[28] M. Watanabe, T. Yamamoto, M. Nishiyama, Chem. Commun. 2000,
2, 133.
[29] P. V. Bedworth, Y. Cai, A. Jen, S. R. Marder, J. Org. Chem. 1996, 61,
2242.
[1] M. B. Robin, P. Day, Adv. Inorg. Chem. Radiochem. 1967, 9, 247.
[2] N. S. Hush, Prog. Inorg. Chem. 1967, 8, 391.
[3] C. Lambert, G. Nçll, J. Am. Chem. Soc. 1999, 121, 8434.
[4] A. V. Szeghalmi, M. Erdmann, V. Engel, M. Schmitt, S. Amthor, V.
Kriegisch, G. Nçll, R. Stahl, C. Lambert, D. Leusser, D. Stalke, M.
Zabel, J. Popp, J. Am. Chem. Soc. 2004, 126, 7834.
[30] P. Gerstner, D. Rohde, H. Hartmann, Synthesis 2002, 2487.
[31] R. Kisselev, M. Thelakkat, Chem. Commun. 2002, 1530.
[32] Microwave irradiation was not used in the synthesis of the dithieno-
pyrroles 9a and 9b since we found (in unpublished experiments
with other anilines) that microwave heating was accompanied by
formation of a significant amount of a byproduct and that, in any
case, conventional heating times were relatively short. As 4a, 4b,
10a and 10b are unstable to air under the reaction conditions, and
as it was more practical to achieve rigorously deoxygenated condi-
tions with conventional heating, we also did not use the microwave
reactor for the synthesis of 4a and 4b; in any case the conventional-
ly heated reaction was complete in 30–40 min.
[33] C. R. Moylan, R. J. Twieg, V. Y. Lee, S. A. Swanson, K. M. Better-
ton, R. D. Miller, J. Am. Chem. Soc. 1993, 115, 12599.
[34] S. Ermer, S. M. Lovejoy, D. S. Leung, H. Warren, C. R. Moylan, R. J.
Twieg, Chem. Mater. 1997, 9, 1437.
[35] O. Kwon, S. Barlow, S. A. Odom, L. Beverina, N. J. Thompson, E.
Zojer, J. L. BrØdas, S. R. Marder, J. Phys. Chem. A 2005, 109, 9346.
[36] P. Li, B. Ahrens, N. Feeder, P. R. Raithby, S. J. Teat, M. S. Khan,
Dalton Trans. 2005, 5, 874.
[5] G. Nçll, M. Avola, J. Phys. Org. Chem. 2006, 19, 238.
[6] P. J. Low, M. A. J. Paterson, H. Puschmann, A. E. Goeta, J. A. K.
Howard, C. Lambert, J. C. Cherryman, D. R. Tackley, S. Leeming, B.
Brown, Chem. Eur. J. 2004, 10, 83.
[7] J. Bonvoisin, J.-P. Launay, M. Van der Auweraer, F. C. De Schryver,
J. Phys. Chem. 1994, 98, 5052.
[8] J. Bonvoisin, J.-P. Launay, W. Verbouwe, M. Van der Auweraer, F. C.
De Schyver, J. Phys. Chem. 1996, 100, 17079.
[9] C. Lambert, S. Amthor, J. Schelter, J. Phys. Chem. A 2004, 108,
6474.
[10] S. Barlow, C. Risko, S.-J. Chung, N. M. Tucker, V. Coropceanu, S. C.
Jones, Z. Levi, J. L. BrØdas, S. R. Marder, J. Am. Chem. Soc. 2005,
127, 16900.
[11] S. Barlow, C. Risko, V. Coropceanu, N. M. Tucker, S. C. Jones, Z.
Levi, V. N. Khrustalev, M. Y. Antipin, T. L. Kinnibrugh, T. Timofee-
va, S. R. Marder, J. L. BrØdas, Chem. Commun. 2005, 764.
[12] S. Amthor, C. Lambert, J. Phys. Chem. A 2006, 110, 1177.
[13] S. C. Jones, V. Coropceanu, S. Barlow, T. Kinnibrugh, T. Timofeeva,
J. L. BrØdas, S. R. Marder, J. Am. Chem. Soc. 2004, 126, 11782.
[14] C. Lambert, G. Nçll, F. Hampel, J. Phys. Chem. A 2001, 105, 7751.
[15] D. Rohde, L. Dunsch, A. Tabet, H. Hartmann, J. Fabian, J. Phys.
Chem. A 2006, 110, 8223.
[16] J. Casado, M. C. Ruiz Delgado, Y. Shirota, V. Hernꢂndez, J. T. Lꢃpez
Navarrete, J. Phys. Chem. B 2003, 107, 2637.
[17] J. C. Lacroix, K. I. Chane-Ching, F. Maquꢄre, F. Maurel, J. Am.
Chem. Soc. 2006, 128, 7264.
[37] J. Frey, A. D. Bond, A. B. Holmes, Chem. Commun. 2002, 2424.
[38] K. Ogawa, S. Rasmussen, J. Org. Chem. 2003, 68, 2921.
[39] E. Khor, S. C. Ng, H. C. Hwee, S. Chai, Heterocycles 1991, 32, 1805.
[40] K. Nozaki, K. Takahashi, K. Nakano, T. Hiyama, H.-Z. Tang, M.
Fujiki, S. Yamaguchi, K. Tamao, Angew. Chem. 2003, 115, 2051;
Angew. Chem. Int. Ed. 2003, 42, 2051.
[41] For analogous palladium-catalysed syntheses of carbazoles from
2,2’-dihalobiphenyls or 2,2’-bis(trifluoromethansulfonato)biphenyls
see ref. [40] and A. Kuwahara, K. Nakano, K. Nozaki, J. Org. Chem.
2005, 70, 413.
[42] G. Koeckelberghs, L. D. Cremer, W. Vanormelingen, W. Dehaen, T.
Verbiest, A. Persoons, C. Samyn, Tetrahedron 2005, 61, 687.
[18] We have also reported that the dication of (E,E)-2,5-bis{4-
ACHTRE[UGN bis(4-me-
thoxyphenyl)amino]styryl}-3,4-dibutoxythiophene is singlet (S.
a
Zheng, S. Barlow, C. Risko, T. L. Kinnibrugh, V. N. Khrustalev, S. C.
Jones, M. Yu. Antipin, N. M. Tucker, T. V. Timofeeva, V. Coropcea-
nu, J. L. BrØdas, S. R. Marder, J. Am. Chem. Soc. 2006, 128, 1812)
whereas its 1,4-benzene-bridged analogue is paramagnetic (ref. [10]),
thus demonstrating greater coupling between the two radical centres
in the thiophene-bridged example.
[43] The redox potential of 1,3-bis
yl]benzo[c]thiophene is reported to be ꢀ0.21 V versus FeCp2
THF/0.1m [nBu4N]
+A[PF6]ꢀ (see ref. [31]). For direct comparison
ACHTRE[UNG 5-bis(4-methoxyphenyl)aminothien-2-
+/0
in
CTHREUNG
[19] J. A. Sell, A. Kuppermann, Chem. Phys. Lett. 1979, 61, 355.
[20] L. ꢅsbrink, E. Lindholm, O. Edqvist, Chem. Phys. Lett. 1970, 5,
1609.
with 1–4, we synthesised the n-butoxy analogue of that compound
(see Supporting Information) and found it to undergo reversible oxi-
Chem. Eur. J. 2007, 13, 9637 – 9646
ꢁ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
9645

S. Barlow et al.
+/0
dation at ꢀ0.28 V versus FeCp2
in CH2Cl2/0.1m [nBu4N]
[PF6]ꢀ
C. H. Londergan, J. C. Salsman, B. J. Lear, C. P. Kubiak, Chem.
Phys. 2006, 324, 57). The use of Equation (3) has also recently been
questioned (S. F. Nelsen, M. N. Weaver, Y. Luo, J. V. Lockard, J. I.
Zink, Chem. Phys., 2006, 324, 195).
(no separation between first and second oxidation processes was dis-
cernable). Thus, this species is slightly more easily oxidised than 1–
3, presumably due to the gain in aromaticity of the benzo ring of the
bridging group on oxidation.
[52] D. R. Duling, J. Magn. Reson. Ser. B 1994, 104, 105.
[53] http://epr.niehs.nih.gov/pest.html.
[54] S. Bamberger, D. Hellwinkel, F. A. Neugebauer, Chem. Ber. 1975,
108, 2416.
[44] S. Ferrere, C. M. Elliott, Inorg. Chem. 1995, 34, 5818.
[45] F. Barriere, N. Camire, W. E. Geiger, U. T. Mueller-Westerhoff, R.
Sanders, J. Am. Chem. Soc. 2002, 124, 7262.
[46] S. F. Nelsen, Chem. Eur. J. 2000, 6, 581.
[55] The ESRspectra of class II MV systems can suggest delocalisation
if the rate of intramolecular electron transfer is sufficiently fast; for
example, the ESRspectrum of a tolane-bridged bis(diarylamine)
radical cation, IRand vis-NIRdata for which indicate belongs to
class II, shows equivalent coupling to both nitrogen centres
(ref. [11]).
[47] Definitively localised class II bis(diarylamino) MV systems show
more-or-less symmetrical Gaussian IVCT bands that have widths in
excess of that predicted by Equation (2). For examples see
refs. [3,7,8,10–14].
[48] V. Coropceanu, M. Malagoli, J. M. AndrØ, J. L. BrØdas, J. Am.
Chem. Soc. 2002, 124, 10519.
[56] E. T. Seo, R. F. Nelson, J. M. Fritsch, L. S. Marcoux, D. W. Leedy,
R. N. Adams, J. Am. Chem. Soc. 1966, 88, 3498.
[49] V. Coropceanu, C. Lambert, G. Nçll, J. L. BrØdas, Chem. Phys. Lett.
2003, 373, 153.
[50] V. Coropceanu, M. Malagoli, J. M. Andre, J. L. Bredas, J. Chem.
Phys. 2001, 115, 10409.
[51] In addition, it has been suggested that Equation (2) may not be ap-
plicable in the case of strongly coupled systems (for example, see:
Received: May 3, 2007
Revised: June 26, 2007
Published online: September 11, 2007
9646
www.chemeurj.org
ꢁ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2007, 13, 9637 – 9646