The production and characterisation of novel conducting redox-active oligomeric thin films from electrooxidised indolo[3,2,l-jk]carbazole

Article abstract of DOI:10.1002/chem.200900097

Indolo[3,2,l-jk]carbazole (IC) has been synthesised on a gram scale by flash vacuum pyrolysis. In contrast to a previous suggestion, IC is planar and it is also highly fluorescent, with a solution quantum yield of 0.41. Electro-oxidation of IC at a rotati

Full text of DOI:10.1002/chem.200900097

DOI: 10.1002/chem.200900097
The Production and Characterisation of Novel Conducting Redox-Active
Oligomeric Thin Films From Electrooxidised IndoloACHTNUTRGNEUNG[3,2,1-jk]carbazole
Stuart I. Wharton, John B. Henry, Hamish McNab,* and Andrew R. Mount*[a]
Abstract:
Indolo
[3,2,1-jk]carbazole
and spectroscopic characterisation re-
vealed the film to consist exclusively of
three redox-active (2,2’, 5,5’ and 2,5’
coupled) IC dimers with no polymeric
products. Calculations showed this cou-
pling pattern to be consistent with IC
radical-cation coupling through the ac-
cessible sites of highest unpaired elec-
tron density. The unusual combination
of a high dimer second oxidation po-
tential and a negligible dimer–dimer
coupling rate explains the lack of fur-
ther coupling. The identities of the di-
meric species were confirmed by inde-
pendent syntheses involving the
Suzuki–Miyaura coupling of IC boronic
acids as the key step. Electro-oxidation
of the IC system therefore offers a
ready route to novel conducting,
redox-active molecular films and their
redox-active, luminescent dimer con-
stituents.
(IC) has been synthesised on a gram
scale by flash vacuum pyrolysis. In con-
trast to a previous suggestion, IC is
planar and it is also highly fluorescent,
with a solution quantum yield of 0.41.
Electro-oxidation of IC at a rotating
disc electrode resulted in the passage
of steady-state currents and the repro-
ducible formation of conducting,
redox-active films with constituent spe-
cies that are also highly fluorescent.
Unusually for coupled electroactive N-
heterocyclic systems, electrochemical
Keywords: conducting materials
·
electrochemistry · luminescence ·
synthesis design · thin films
Introduction
carbazoles, isoindoles and indolocarbazoles. Carbazole[5] and
indolocarbazole[6] derivatives have been reported as efficient
hole transport materials with potential applications in organ-
ic thin-film transistors. Isoindoles are highly fluorescent and
have been investigated for light-emitting devices.[7] Poly(N-
arylcarbazol-2,7-ylene) shows blue photoemission with an
enhanced quantum yield over N-alkyl-substituted polymers
Redox-active and photoactive oligomers and polymers, pro-
duced from N-heteroaromatic monomers such as pyrroles,[1]
indoles[2] and carbazoles,[3] have received a great deal of at-
tention in recent years. Typically they display efficient lumi-
nescence and form extended p-conjugated thin-film materi-
als that show semiconducting-to-conducting electronic prop-
erties and redox activity with relatively low cost, good proc-
essability, attractive mechanical properties and the ready
tuning of properties through chemical functionalisation. This
makes them attractive for a variety of applications, including
the active film in organic electronic devices, sensors, super-
capacitors and in electroluminescent materials.[4] In particu-
lar, there has recently been much interest in the chemical
synthesis and characterisation of films formed from selected
for light-emitting diode applications.[8] Indolo
ACHTNUTRGNE[NUG 2,3-a]carba-
zole has also been investigated as a potential anion-sensing
material.[9] There is real interest in producing such systems
as molecular films as small molecules (both monomers and
oligomers) can form crystalline or homogeneous multilayers
due to their efficient packing, which should result in en-
hanced materials properties.[10] However, in reality, small-
molecule thin-film production is often problematic as oligo-
mer formation often requires specific chemical synthesis
(both monomer formation and site-specific coupling), which
can increase the complexity and cost and decrease the yield,
and there is difficulty in establishing optimum molecular or-
dering when depositing thin films from solution.[11] Although
conducting polymeric thin films such as polypyrrole can be
readily synthesised and deposited by monomer oxidation
and coupling at electrodes, the distribution of the conduct-
ing polymer chain lengths and the resulting film inhomoge-
neity and structural irreproducibility often affects the con-
[a] Dr. S. I. Wharton, J. B. Henry, Prof. H. McNab, Dr. A. R. Mount
School of Chemistry, The University of Edinburgh
The Joseph Black Building
Kingꢀs Buldings, West Mains Road, Edinburgh EH9 3JJ (UK)
Fax : (+44)131-650-6453
E-mail: a.mount@ed.ac.uk
h.mcnab@ed.ac.uk
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200900097.
5482
ꢁ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 5482 – 5490

FULL PAPER
trol and reproducibility of the performance of thin-film ma-
terials.
In this paper we report an alternative synthetic route to
would be bowl-shaped due to the strain in the central three-
ring system and the preference for nitrogen to adopt a more
trigonal pyramidal form. In this work we have obtained an
X-ray crystal structure of the picrate of IC (Figure 1), which
the N-heteroaromatic indoloACHTNUTRGNE[UNG 3,2,1-jk]carbazole (IC) mono-
mer and characterise its properties and the new thin-film
materials readily formed by its electro-oxidation. The result-
ing film formation is reproducible under controlled hydrody-
namic conditions and results in conducting redox-active
films that, unusually, consist entirely of three specific dimer
species, which, like IC, are fluorescent in solution. Such spe-
cific electrochemical IC film formation through monomer
oxidation and selective coupling demonstrates a route to
controlled thin-film formation through monomer design,
electrochemical oligomer synthesis and film deposition. A
combination of electrochemical, spectroscopic, lumines-
cence, synthetic and theoretical data are presented to identi-
fy and characterise the IC dimers formed in these films and
to give an insight into the molecular properties that under-
pin this unusual behaviour.
Figure 1. X-ray crystal structure of 4 from the IC picrate crystal showing
the crystallographic numbering scheme.
clearly shows that the molecule is in fact planar.
(CCDC 610408 contains the supplementary crystallographic
data. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.
cam.ac.uk/data_request/cif.)
Results and Discussion
Synthesis of indolo
G
E
IC forms co-crystals with picric acid in alternating planes,
which suggests that the central nitrogen atom is not basic
enough to form a picrate salt. The considerable strain im-
zole has previously been synthesised by Dunlop and
Tucker[12] by decomposition of the diazonium salt derived
from N-(2-aminophenyl)carbazole. However, we have re-
cently shown that flash vacuum pyrolysis (FVP) of 1-(2-ni-
trophenyl)indole (1) at 8758C leads to the formation of
posed by the central three-ring pyrroloACTHNUTRGNEUNG[3,2,1-hi]indole sub-
structure is accommodated almost entirely by bond length
and angular distortion of the central benzene ring and
around the central nitrogen atom. The driving force for this
system to be planar therefore outweighs the need to relieve
this serious distortion in the bond lengths and angles. This
planar configuration, as with other heteroaromatics, should
enable effective intermolecular p-stacking.
pyrroloACHTUNGTRENNUNG[3,2,1-jk]carbazole (2) via an aryl radical intermedi-
ate.[13] Application of this strategy to N-(2-nitrophenyl)car-
bazole[14] (3) readily gave IC (4) in a yield of 71% on a
gram scale, which is more than adequate for electrochemical
film production (Scheme 1). This procedure is one step
shorter than the method of Dunlop and Tucker and comple-
ments the range of substituted IC derivatives that can be
synthesised.
IC in DMF exhibits peak excitation and emission fluores-
cence wavelengths at 361 and 378 nm, respectively
(Figure 2). Its quantum yield, estimated by making a compa-
rative measurement using indole as a standard,[15] is 0.41,
which is comparable to systems such as the highly fluores-
For reference, a complete H and 13C NMR analysis of IC
was carried out (see the Supporting Information). When IC
was prepared by Dunlop and Tucker[12] it was thought that it
cent indolizinoACTHNUTRGNEUNG
[3,4,5-ab]isoindoles.[7] This makes 4 of interest
Figure 2. Steady-state excitation and emission spectra for a) IC monomer
4 at fixed emission and excitation wavelengths of 410 and 340 nm, respec-
tively and b) the dissolved film formed from IC electro-oxidation in
DMF at fixed emission and excitation wavelengths of 400 and 360 nm, re-
spectively.
Scheme 1. The FVP synthetic route to pyrrolo
indolo[3,2,1-jk]carbazole 4.
ACHTUNGERTN[NUNG 3,2,1-jk]carbazole 2 and
ACHTUNGTRENNUNG
Chem. Eur. J. 2009, 15, 5482 – 5490
ꢁ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
5483

H. McNab, A. R. Mount et al.
for fluorescence and UV light emission applications. The
fluorescence lifetime of IC was measured to be 12.7 ns.
Electro-oxidation of IC (4): Typical CVs for 1 mm IC oxida-
tion[16] (low concentration) are shown in Figure 3. The mo-
nomer oxidation peak can clearly be seen at +1.1 V; the
Figure 4. Current–time response observed at an RDE when E=+1.19 V
was applied at t=1 s. The onset of steady-state currents at each value of
W (shown in Hz) can clearly be seen.[21]
Figure 3. Cyclic voltammograms (CVs) of 1 mm IC 4 in background elec-
trolyte (MeCN/0.1m LiClO4) at a sweep rate, v=50 mVsꢀ1. The initial di-
rection of sweep is to positive potential, E, from the negative potential
limit. The cycle numbers are shown.
variation of peak height with the square root of sweep rate
(see the Supporting Information) is consistent with a solu-
tion reaction under diffusion control. The associated reduc-
tion peak near +1.0 V is clearly attenuated, increasingly
with decreasing sweep rate (see the Supporting Informa-
tion), consistent with the loss of monomer radical cation
through coupling and film formation. On repeated cycling,
peaks centred at +0.7 V (oxidation) and +0.6 V (reduction)
can be seen to grow in size; these are the redox peaks of the
conducting film.
Figure 5. Koutecky–Levich plot of iꢀ1 versus Wꢀ1/2 for IC oxidation. The
lines through the data are those calculated theoretically from Equa-
tion (1) with DIC =3.0ꢂ10ꢀ5 cm2 sꢀ1[23] and n=1.5.[24]
Electro-oxidation at higher concentrations (2.5, 5, 10, 15
and 20 mm) was also carried out at a rotating disc electrode
(RDE) with E=+1.19 V[17] at different rotation speeds, W.
In all cases, after initial surface film formation and the onset
of steady-state mass transport,[18] a reproducible steady-state
current was observed at each W (Figure 4). Large, essential-
ly steady-state currents,[19] i, were observed over several
hundred seconds, which corresponds to thick IC films of the
order of several microns;[20] this indicates the formation of
highly reproducible electronically conducting films under
hydrodynamic control. Analysis of these currents
(Figure 5[21]) showed that all the data obey the Koutecky–
Levich[22] equation [Eq. (1)],
fusion coefficient of IC, cIC is the bulk concentration of IC,
n is the kinematic viscosity of the electrolyte and i1 is the
mass-transport-independent current observed as W tends to
infinity. Equation (1) applies when first-order mass-trans-
port-dependent and -independent reactions occur in series.
Such behaviour has been seen for indoles[2b] and has been
interpreted as film growth through the mass transport of the
monomer to the electrode followed by mass-transport-inde-
pendent adsorption, oxidation and radical-cation coupling.[25]
These IC data are therefore consistent with the general cou-
pling reaction established for indoles and pyrroles
[Eq. (2)]:[1a,2b]
ꢀ
ꢀnHþ
ꢀeꢀ
nM ꢀne nM
ꢀꢀ!
ðMÞ
ðMÞþ
ð2Þ
þC
ꢀꢀꢀ!
ꢀꢀ!
n
n
!
1
i
0:6435v1=6
1
i1
¼
þ
ð1Þ
Electro-oxidation of the monomer, M, produces radical
cations which then couple and are deposited on the elec-
trode, thereby producing the redox-active surface film, (M)n,
which is then oxidised to the redox species, (M)n+, at the
electro-oxidation potential. Least-squares fitting of these
nFAcICD2=3W1=2
IC
in which n is the number of electrons for IC oxidation, F is
the Faraday constant, A is the electrode area, DIC is the dif-
5484
www.chemeurj.org
ꢁ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 5482 – 5490

Oligomeric Indolocarbazole Thin Films
FULL PAPER
data to Equation (1) gives DIC =(3.0ꢁ0.1)ꢂ10ꢀ5 cm2 sꢀ1[23]
with n=1.5[24] and i1/A=10.9ꢁ0.5 mAcmꢀ2 for the highest
concentrations (10, 15 and 20 mm). This corresponds to the
maximum coupling current density for film formation with
the rate-determining step being the surface IC coupling rate.
CVs of the films in background electrolyte show the char-
acteristic film redox peaks previously seen in Figure 3 cen-
tred at +0.7 V (see the Supporting Information) due to the
reversible redox reaction of the film [Eq. (3)], and the linear
variation of peak current with sweep rate (see the Support-
ing Information) is consistent with a film of high electronic
conduction and fast redox kinetics.
Figure 6. Electron spin density for the IC radical cation mapped onto the
electron density; blue and red regions indicate areas of the highest and
lowest electron spin density.[28]
ꢀeꢀ
þ
ꢀꢀ!
ðMÞn
ðMÞ
ð3Þ
ꢀꢀ
n
þeꢀ
the presence of three major components in an approximate
ratio of 1:2:1. The NMR analysis described in the Support-
ing Information (the 1H NMR spectrum is shown in Fig-
ure 7a and the assignments are summarised in Figure 7c)
clearly identified substructures associated with two 2-substi-
tuted ICs (as in 6 and 7) and with two 1,2,4-trisubstituted
benzenoid systems (present in both 5 and 7), consistent with
the assignments suggested by the DFT calculations. Howev-
er, some ambiguity remained regarding the exact location of
the trisubstituted aromatic substructures in the dimers, so 5–
7 were unambiguously characterised by the total syntheses
described below.
The charge calculated from each redox peak area corre-
sponds to 33ꢁ3% of the total polymerisation charge, which
indicates that n=2, that is, the film consists of electroactive
dimers formed by the covalent attachment of two monomers
with the loss of two hydrogen atoms.[26] This was confirmed
by FAB mass spectrometry as the parent ion peak was that
of this protonated dimer (m/z=481). The steady-state fluo-
rescence of the dissolved film (Figure 2b) shows a significant
redshift in emission compared with 4, consistent with dimer
formation. The emission intensity was comparable to IC, as
was the measured fluorescence lifetime of 9.5 ns, which sug-
gests dissolved dimers have comparable quantum yields to
4.[27] This, combined with their desirable redox properties,
makes these dimers of potential interest in electrolumines-
cent applications.
Synthesis of IC dimers: The key step in the synthesis of
dimers 5–7 was the formation of the biaryl unit by Suzuki–
Miyaura[30] coupling, which requires regioselective synthesis
of the bromo compounds 8 and 11 and their transformation
into boronic acids 10 and 13 via the esters 9 and 12, respec-
tively.
Chemical oxidation of IC was also carried out with exact-
ly 1 molequiv of FeCl3 in anhydrous MeCN. The precipitate
1
that formed was shown by H NMR spectroscopy and high-
resolution mass spectrometry to be the same mixture of
dimers 5–7, produced in a yield of 30% and in a similar
ratio to that formed during electro-oxidation, which suggests
that this ratio of products is fundamental and not due to the
effects of surface adsorption on the electrode.
IC dimer film characterisation: By analogy with indoles and
pyrroles[1a,2b] as coupling [Eq. (2)] involves monomer radical
cations, we argue that the most likely coupling sites are
those with the largest electron spin density, where there will
be the highest propensity for radical-coupling and bond for-
mation. DFT calculations on the IC monomer and the IC
radical cation produce a theoretical oxidation potential peak
of +1.10 V, identical to and certainly within the expected
experimental error of a few tens of millivolts[15] of the ob-
served value of +1.10 V. The calculated spin density distri-
bution in the radical cation (Figure 6) shows the highest un-
paired electron density at the 2-position, the equivalent 5-
and 11-positions as well as the equivalent 7- and 9-positions
(cf. Scheme 1). The 7- and 9-positions are sterically hindered
due to the close proximity of their hydrogen atoms; this
therefore predicts a propensity for 5,5’ (5), 2,2’ (6) and 2,5’
(7) covalently coupled dimers in the film (Figure 7b). An
HPLC analysis of the reaction mixture (Figure 8) confirmed
The bromo compound 11 was readily obtained (60%) by
FVP of 9-(4-bromo-2-nitrophenyl)carbazole (14), but this
method could not be used to prepare 8 regioselectively.
However, bromination of IC (4) with NBS in dichlorome-
thane gave a 75:25 mixture of 8 and 11 from which pure 8
was obtained in 55% yield by recrystallisation from acetic
acid.[31]
The standard method for the formation of the arylboronic
acids[32] involves halogen–metal exchange of an aromatic
bromo compound with butyllithium at ꢀ788C followed by
reaction with triisopropyl borate at room temperature. The
aryllithium species derived from both 8 and 11 proved to be
Chem. Eur. J. 2009, 15, 5482 – 5490
ꢁ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
5485

H. McNab, A. R. Mount et al.
Figure 8. HPLC trace of the dimer mixture 5+6+7 (Spherisorb S5-
ODS1 column, eluent A=H2O/MeCN (9:1)+1% NH4OAc; eluent B=
MeCN; solvent gradient: time 0 min=5% B, gradient increase in B over
30 min to 95% B, eluent mixture then maintained at this level until
55 min; detection wavelength=254 nm).
reactions described below, but full characterisation was com-
plicated by the probable presence of boroxine trimers,
which give a second signal in the 11B NMR spectra of the
boronic acids.
Compounds 5, 6 and 7 were then produced in yields of 65,
80 and 55%, respectively, by Suzuki–Miyaura coupling of
the appropriate heteroaryl bromide (8 or 11) and aryl boron
species (10 or 13) with [PdACTHNURGTNE(UNG PPh3)4] and K2CO3 in dioxane/
water (3:1).[33] These were characterised by a range of NMR
techniques (see the Supporting Information) and by high-
resolution EI mass spectrometry. HPLC analysis of these
synthetic dimers was carried out under equivalent conditions
to those used for the dissolved films (Figure 8) and showed
similar elution peaks in the order 6, 7 and 5; when a dis-
solved film sample was individually spiked with each dimer
the appropriate peak increased in intensity whilst retaining
its shape, confirming the identity of 5, 6 and 7 in the film.
NMR spiking experiments also led to an enhancement of
the appropriate 1H NMR peaks. CVs of the drop-coated
synthetic samples (see the Supporting Information) each
showed redox peaks centred near +0.7 V and the solution
fluorescence of 5, 6 and 7 (see the Supporting Information)
were each similar to one another and to the fluorescence of
the dissolved film. These data confirm that 5, 6 and 7 are
indeed the constituents of the dissolved film obtained by the
electro-oxidation of IC 4.
Figure 7. a) Typical 600 MHz 1H NMR spectrum of IC film dissolved in
[D6]acetone/[D6]DMSO. b) The dimer species present, as deduced from
this spectrum, with their labelled monomer substructures. c) Summary of
Rationale for dimer film formation: It is highly unusual for
electro-oxidation of an aromatic heterocycle to result exclu-
sively in dimer rather than polymer film formation, as found
with 4. For pyrrole[1b] the accepted mechanism is that mono-
mer electro-oxidation and radical-cation coupling produces
a series of oligomers, Mn, whose oxidation potential for radi-
cal-cation formation decreases with increasing n. At the
electrode potential required for monomer oxidation, oligo-
mer radical-cation formation and coupling then readily
occur, which leads to progressively larger oligomers and re-
1
the H and 13C NMR assignments for these dimers.[29]
very unreactive under these conditions, although the boronic
acids 10 (ca. 80%) and 13 (also ca. 80%) were both ob-
tained when 10 equiv of triisopropyl borate were used and
the reaction was carried out at 608C followed by hydroly-
sis.[32] The presence of the boronic acids 10 and 13 was con-
firmed by ESI mass spectrometry and by the cross-coupling
5486
www.chemeurj.org
ꢁ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 5482 – 5490

Oligomeric Indolocarbazole Thin Films
FULL PAPER
sults in a film with a distribution of polymer chain lengths.
For indoles,[34] electro-oxidation initially produces an asym-
metric, redox-active cyclic trimer [n=3 in Eq. (2)] that can
be further oxidised at potentials below the monomer oxida-
tion potential; these species then couple to form a polymer
of linked trimers. Figure 9 shows typical CVs of the dimer
film formed from 4 cycled to more positive potentials in
background electrolyte to induce further oxidation.
dimers are most likely formed through specific radical-
cation coupling. This opens up the prospect of exploiting the
attractive properties of 4 in thin-film materials applications.
In particular, judicious substitution at the 2- and/or 5-posi-
tions of the parent IC molecule should enable both selective
dimer production and the tuning of film characteristics (in-
cluding film composition, conductivity, homogeneity, redox
potentials and luminescence properties) for specific en-
hancement of thin-film properties. The FVP synthetic route
is readily able to produce these substituted ICs; a systematic
study of these systems will be the subject of a future publi-
cation.
Experimental Section
General methods: 1H NMR spectra were recorded on Bruker AVA600
(600 MHz), Bruker DPX360 (360 MHz) or Bruker ARX250 (250 MHz)
spectrometers. 13C NMR spectra were recorded on Bruker DPX360
(91 MHz) or Bruker ARX250 (63 MHz) spectrometers. Chemical shifts
(dH and dC) are quoted in ppm relative to tetramethylsilane. 11B NMR
spectra were recorded on a Bruker DPX360 spectrometer at 115 MHz.
Chemical shifts (dB) are quoted in in ppm relative to boron trifluoride
etherate. Mass spectra were recorded on a Kratos MS50 TC instrument
under electron impact conditions unless otherwise stated. Chemicals
were purchased from Aldrich and were used without purification. X-ray
data were collected with MoKa radiation using a Bruker Smart Apex dif-
fractometer equipped with an Oxford Cryosystems low temperature
device operating at 150K. The structure was solved using DIRDIF and
refined by least squares analysis (Saint).
Figure 9. CVs of a dimer film formed from electro-oxidised 4 in back-
ground electrolyte scanned over an extended potential range at
50 mVsꢀ1. The potential used to form these films from a solution of 4
(+1.19 V) is shown.
9-(2-Nitrophenyl)carbazole (3): Carbazole (3.0 g, 18 mmol) and 2-fluoro-
nitrobenzene (2.5 g, 18 mmol) were dissolved in DMSO (50 cm3). Caesi-
um carbonate (6.4 g, 20 mmol) was added to the solution with stirring.
The suspension was stirred for 15 h before being diluted with water
(50 cm3), when a yellow precipitate formed. The mixture was extracted
with CHCl3 (3ꢂ100 cm3) and the extract washed with water (3ꢂ100 cm3)
before being dried over MgSO4. The solvent was removed by distillation
under reduced pressure to yield 9-(2-nitrophenyl)carbazole (3; 4.9 g,
95%). M.p. 155–1568C (lit.:[12] 1568C); 1H NMR (250 MHz, CDCl3): d=
8.15–8.08 (m, 3H), 7.79 (dt, 3J=7.5, 4J=1.5 Hz, 1H), 7.68–7.58 (m, 2H),
7.36 (td, 3J=7.7, 4J=1.4 Hz, 2H), 7.27 (td, 3J=7.5 4J=1.2 Hz, 2H),
7.09 ppm (dd, 3J=7.8, 4J=1.0 Hz, 2H); 13C NMR (63 MHz, CDCl3): d=
140.62, (2 Cq), 134.14 (CH), 131.28 (CH), 131.11 (Cq), 129.03 (CH),
126.20 (2 CH), 125.83 (CH), 123.71 (2 Cq), 120.55 (2 CH), 120.48 (2 CH),
120.42 (Cq), 108.93 ppm (2 CH); MS (EI): m/z (%): 288 (100) [M]+, 241
(73), 178 (75), 121 (27), 89 (14).
As expected, the film’s redox peaks can be clearly seen
centred near +0.7 V. However, in contrast to pyrrole and
indole, further oxidation only starts to occur near the ap-
plied electrode potential of +1.19 V for monomer oxidation
and film formation, which indicates unusually high further
oxidation potentials for these dimers. There is also no evi-
dence that this further oxidation leads to significant dimer
coupling as the charges passed during this oxidation and its
associated reduction near + 1.0 V are comparable[35] and
remain stable with repeated cycling; this suggests that these
further oxidised dimers are kinetically stabilised towards
coupling. These effects combine to ensure that dimers are
exclusively formed on monomer electro-oxidation and film
formation.
9-(4-Bromo-2-nitrophenyl)carbazole (14): Carbazole (1.48 g, 8.9 mmol)
and 5-bromo-2-fluoronitrobenzene (1.67 g, 8.9 mmol) were dissolved in
DMSO (30 cm3). Caesium carbonate (3.45 g, 10.7 mmol) was added to
the solution with stirring. The suspension was stirred for 15 h before
being diluted with water (50 cm3) when an orange precipitate formed.
The mixture was extracted with CHCl3 (3ꢂ100 cm3) and the extract
washed with water (3ꢂ100 cm3) before being dried over MgSO4. The
CHCl3 layer was concentrated under reduced pressure and the residue
was pre-adsorbed onto silica for purification by dry flash chromatography
(hexane/ethyl acetate) to yield 9-(4-bromo-2-nitrophenyl)carbazole (14;
2.35 g, 72%). M.p. 151–1538C (lit.:[36] 152–1548C); 1H NMR (250 MHz,
CDCl3): d=8.22 (d, 4J=2.2 Hz, 1H), 8.03 (d, 3J=7.5 Hz, 2H), 7.84 (dd,
3J=8.5, 4J=2.3 Hz, 1H), 7.44 (d, 3J=8.5 Hz, 1H), 7.34–7.16 (m, 4H),
7.00 ppm (d, 3J=8.0 Hz, 2H); 13C NMR (63 MHz, CDCl3): d=147.38,
(Cq), 140.35 (2 Cq), 137.25 (CH), 132.56 (CH), 130.24 (Cq), 128.91 (CH),
126.33 (2 CH), 123.85 (2 Cq), 121.93 (Cq), 120.83 (2 CH), 120.54 (2 CH),
108.80 ppm (2 CH); MS (EI): m/z (%): 368 (8) [M]+, 366 (8) [M]+, 241
(10), 219 (63), 167 (100), 140 (6), 113 (21), 94 (79).
Conclusions
IndoloACHTUNGTRENNUNG[3,2,1-jk]carbazole (IC, 4) has been prepared by FVP
and fully characterised in terms of its structural, lumines-
cence and electrochemical properties. X-ray studies revealed
a planar structure capable of p-stacking and electro-oxida-
tion resulted in the reproducible, hydrodynamically con-
trolled formation of conducting films on the electrode sur-
face, which characterisation and synthesis have shown to
consist exclusively of three redox-active species, the 2,2’, 2,5’
and 5,5’ dimers, which show solution luminescence compara-
ble to IC. We have shown through computation that these
Chem. Eur. J. 2009, 15, 5482 – 5490
ꢁ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
5487

H. McNab, A. R. Mount et al.
Flash Vacuum Pyrolysis (FVP): The substrate was volatilised at low pres-
sure into a silica tube (30ꢂ2.5 cm) heated by a laboratory tube furnace.
Organic products were collected in a dry-ice/acetone cold-finger (situated
at the exit point of the furnace) and gaseous materials (consisting of NOx
byproducts from cleavage of the nitro group) were collected in a subse-
quent liquid nitrogen cooled U-tube trap (cf. ref.[13]). FVP parameters are
reported as follows: mass of substrate ma, furnace temperature Tf, inlet
temperature Ti, pressure p and sublimation/distillation time tm.
50 cm3) and dried over MgSO4. Concentration of this extract under re-
duced pressure yielded creamy white solids, the 1H NMR spectra of
which showed the correct substitution pattern for 10 and 13. However,
the 1H integrals were not consistent and the 11B NMR spectra showed
that there were two different boron species in the mixtures, which sug-
gested the presence of boroxine trimers. The boronic acids 10 and 13
were both made by following this method.
IndoloACTHUNGTERNNU[NG 3,2,1-jk]carbazole-2-boronic acid (10): Yield: 0.399 g, 80% by
1
mass, mixture 10; H NMR (360 MHz, [D6]DMSO): d=8.67 (s, 2H), 8.32
(d, 3J=7.2 Hz, 2H), 8.30 (dd, 3J=7.3, 4J=1.1 Hz, 2H), 8.22 (d, 3J=
7.2 Hz, 2H), 7.68–7.62 (m, 4H), 7.46–7.42 (m, 3H), 7.34 ppm (brs, 2H);
11B NMR (115 MHz, DMSO): d=35.63 (brs), 25.41 ppm (brs, minor);
MS (ESI): m/z (%): 283 (10B, 30) [MꢀH]ꢀ, 284 (11B, 100) [MꢀH]ꢀ; IR
(film): n˜ =3397 (OH), 1340 cmꢀ1 (B–O).
Indolo
ACHTUNGTRENNUNG
Ti =120–1608C, p=2.0ꢂ10ꢀ2 Torr, tm =190 min) produced indolo
AHCTUNGTRENNUNG
jk]carbazole 4 (1.9 g, 71%) after purification by dry flash chromatogra-
phy using hexane with an increasing gradient of ethyl acetate as eluent.
1
M.p. 155–1568C (lit.:[12] 1568C); H NMR (360 MHz, CDCl3): d=8.14 (d,
3J=7.8 Hz, 2H), 8.04 (d, 3J=7.4 Hz, 2H), 7.89 (d, 3J=8.1 Hz, 2H), 7.59
(t, 3J=7.3 Hz, 1H), 7.55 (td, 3J=7.6, 4J=1.5 Hz, 2H), 7.36 ppm (td, 3J=
7.5, 4J=1.2 Hz, 2H); 13C NMR (63 MHz, CDCl3): d=143.59 (Cq), 138.54
(2 Cq), 129.88 (2 Cq), 126.54 (2 CH), 123.01 (2 CH), 122.68 (CH), 121.53
(2 CH), 119.26 (2 CH), 118.31 (2 Cq), 112.02 ppm (2 CH); MS (EI): m/z
(%): 241 (100) [M]+, 178 (38), 121 (21), 89 (6), 57 (3).
IndoloACTHNUGRTENUNG[3,2,1-jk]carbazole-5-boronic acid (13): Yield: 0.400 g, 80% by
mass, mixture 13; 1H NMR (360 MHz, [D6]DMSO): d=8.71 (s, 1H),
8.34–8.26 (m, 5H), 8.24–8.18 (m, 3H), 8.10 (dd, 3J=8.2, 4J=1.2 Hz, 1H),
7.68–7.62 (m, 2H), 7.47–7.40 ppm (m, 2H); 11B NMR (115 MHz,
DMSO): d=34.58 (brs), 22.67 ppm (brs, minor); MS (ESI): m/z (%):283
(10B, 30) [MꢀH]ꢀ, 284 (11B, 100) [MꢀH]ꢀ; IR (film): n˜ =3419 (OH),
1340 cmꢀ1 (B–O).
5-Bromoindolo
nyl)carbazole (ma =0.594 g (1.9 mmol), Tf =8758C, Ti =160–2208C, p=
3.8ꢂ10ꢀ2 Torr, tm =40 min) gave 5-bromoindolo
[3,2,1-jk]carbazole (11;
ACHTUNGTRENNUNG[3,2,1-jk]carbazole (11): FVP of 9-(4-bromo-2-nitrophe-
Suzuki–Miyaura coupling—general method:[31] The appropriate heteroar-
yl bromide (8 or 11; 50.0 mg, 0.156 mmol) and arylboron species (10 or
13; 44.5 mg, 0.156 mmol), potassium carbonate (43 mg, 0.312 mmol) and
AHCTUNGTRENNUNG
0.312 g, 60%) after purification by dry flash chromatography using
hexane with an increasing gradient of ethyl acetate as eluent. M.p. 141–
1438C (lit.:[36] 144–1458C); 1H NMR (360 MHz, CDCl3): d=8.25 (d, 4J=
1.8 Hz, 1H), 8.14 (d, 3J=7.9 Hz, 1H), 8.06 (d, 3J=7.6 Hz, 1H), 8.00 (d,
3J=7.6 Hz, 1H), 7.86 (d, 3J=8.3 Hz, 1H), 7.76 (d, 3J=8.6 Hz, 1H), 7.65
(dd, 3J=8.3, 4J=1.8 Hz, 1H), 7.60 (t, 3J=7.6 Hz, 1H), 7.55 (td, 3J=7.9,
4J=1.4 Hz, 1H), 7.38 ppm (td, 3J=7.6, 4J=1.1 Hz, 1H); 13C NMR
(91 MHz, CDCl3): d=143.67 (Cq), 138.22, (Cq), 136.90 (Cq), 131.34 (Cq),
129.75 (Cq), 128.98 (CH), 126.67 (CH), 125.76 (CH), 123.02 (CH), 122.92
(CH), 121.81 (CH), 119.83 (CH), 119.7 (CH), 118.40 (CH), 117.06 (Cq),
114.33 (Cq), 112.88 (Cq), 111.96 ppm (CH); MS (EI): m/z (%): 321 (49)
[M]+, 319 (49) [M]+, 239 (19), 167 (100), 139 (11), 120 (21), 84 (9).
[PdACHTNUGRTNEUNG(PPh3)4] (7.2 mg, 4 mol%) were heated at reflux with stirring in 3:1
dioxane/water (10 cm3) for 4 h. The precipitate formed was filtered and
washed with water and dioxane before being dried under vacuum. The
specific purification procedure for each dimer is shown below. The
dimers prepared were insoluble in most solvents, but sparingly soluble in
DMSO/acetone mixtures and THF. All the NMR spectroscopic data
were recorded in either [D6]DMSO or [D8]THF. Each dimer was charac-
terised by 1 H, COSY, NOESY and HSQC NMR techniques. For 5 and 6,
full 13C NMR spectroscopic data were obtained by using HSQC and
HMBC techniques. The following products were obtained by this
method:
2-BromoindoloACHTUNGTRENNUNG[3,2,1-jk]carbazole (8): IndoloHCATUNGTREN[NGUN 3,2,1-jk]carbazole (4;
1.17 g, 4.8 mmol) and N-bromosuccinimide (0.86 g, 4.8 mmol) were dis-
solved in dichloromethane (50 cm3) in the absence of light. Silica gel
(10 g) was added and the mixture was left to stir for 15 h. The mixture
was filtered and the silica was washed with dichloromethane (5ꢂ50 cm3).
The combined dichloromethane fractions were washed with water (3ꢂ
50 cm3) and dried over MgSO4 before being concentrated under reduced
pressure to yield a pale-brown solid. The solid was dissolved in the mini-
mum quantity of refluxing glacial acetic acid. A small amount of solvent
was distilled under reduced pressure before cooling was allowed to occur.
A white solid precipitated and was filtered and washed with glacial acetic
5,5’-BiindoloACTHNGUETRNNU[G 3,2,1-jk]carbazole (5): The product (0.061 g, 65%) was col-
lected by filtration and washed with water and dioxane. M.p. >3608C;
1H NMR (360 MHz, [D8]THF): d=8.66 (d, 4J=1.9 Hz, 2H), 8.22 (d, 3J=
8.3 Hz, 2H), 8.21 (dm, 3J=7.2, 4J=1.1, 5J=0.7 Hz, 2H), 8.19 (d, 3J=
7.5 Hz, 2H), 8.16 (dd, 3J=7.7, 4J=1.0 Hz, 2H), 8.12 (d, 3J=7.2 Hz, 2H),
8.04 (d, 3J=7.4 Hz, 2H), 7.62 (t, 3J=7.6 Hz, 2H), 7.58 (dt, 3J=8.3, 4J=
1.4 Hz, 2H), 7.38 ppm (t, 3J=7.9 Hz, 2H); 13C NMR (91 MHz, [D8]THF,
CH resonances only): d=127.96 (2 CH), 127.28 (2 CH), 124.12 (2 CH),
124.08 (2 CH), 122.87 (2 CH), 122.85 (2 CH), 122.81 (2 CH), 122.79 (2
CH), 113.49 (2 CH), 113.47 ppm (2 CH); MS (EI): m/z (%): 480 (2) [M]+
, 190 (38), 156 (100), 128 (21) and 78 (14). HRMS (EI): m/z: calcd for
C36H20N2: 480.1627 [M]+; found: 480.1621.
acid before being dried under vacuum to yield 2-bromoindoloACHTNUTGRNEUNG[3,2,1-
jk]carbazole (8; 0.86 g, 55%). M.p. 208–2108C (lit.:[12] 205–2108C);
1H NMR (360 MHz, CDCl3): d=8.06 (s, 2H), 7.99 (d, 3J=7.8 Hz, 2H),
7.79 (d, 3J=8.1 Hz, 2H), 7.54 (td, 3J=7.9, 4J=1.1 Hz, 2H), 7.33 ppm (td,
3J=7.8, 4J=1.0 Hz, 2H); 13C NMR (63 MHz, CDCl3): d=141.65 (Cq),
138.68 (2 Cq), 128.94 (2 Cq), 127.20 (2 CH), 123.13 (2 CH), 122.07 (2
CH), 121.82 (2 CH), 119.33 (Cq), 115.54 (2 Cq), 112.07 ppm (2 CH); MS
(EI): m/z (%): 321 (99) [M]+, 319 (100) [M]+, 240 (82), 213 (14), 167
(32), 120 (7), 80 (7), 56 (23).
2,2’-BiindoloACTHNUTRGNEUG[N 3,2,1-jk]carbazole (6): The product (0.075 g, 80%) was col-
lected by filtration and washed with water and dioxane. M.p. >3608C;
1H NMR (360 MHz, [D8]THF): d=8.47 (4H, s), 8.21 (dm, 3J=8.1, 4J=
1.2, 5J=0.7 Hz, 4H), 8.04 (dm, 3J=8.3, 4J=1.1, 5J=0.7 Hz, 4H), 7.54
(ddd, 3J=8.3, 3J=7.6, 4J=1.1 Hz, 4H), 7.34 ppm (ddd, 3J=8.0, 3J=7.2,
4J=1.1 Hz, 4H); 13C NMR (91 MHz, [D8]THF): d=144.29 (2 Cq), 140.97
(2 Cq), 140.27 (4 Cq), 131.22 (4 Cq), 127.65 (4 CH), 123.90 (4 CH), 122.62
(4 CH), 121.12 (4 CH), 119.62 (4 Cq), 113.24 ppm (4 CH); MS (EI): m/z
(%): 480 (100) [M]+, 240 (61), 167 (13). HRMS (EI): m/z: calcd for
C36H20N2: 480.1627 [M]+; found: 480.1622.
IndoloACHTUNGTRENNUNG[3,2,1-jk]carbazoleboronic acids (10) and (13): Anhydrous THF
(10 cm3) was added to a dry round-bottomed flask under an atmosphere
of argon. The flask and solvent were cooled to ꢀ788C in a dry-ice/ace-
tone bath and a solution of nBuLi in hexanes (1.6m, 1 cm3, 1.94 mmol)
2,5’-BiindoloACTHNUTRGNEUG[N 3,2,1-jk]carbazole (7): The product (0.051 g, 55%) was puri-
was added.
A solution of the appropriate bromoarene (8 or 11,
fied by dry flash chromatography (hexane/ethyl acetate). M.p. 297–
3008C; 1H NMR (360 MHz, [D6]acetone/[D6]DMSO): d=8.77 (d, 4J=
1.5 Hz, 1H), 8.64 (s, 2H), 8.43–8.40 (m, 3H), 8.34–8.32 (m, 3H), 8.29 (d,
3J=8.1 Hz, 2H), 8.24 (d, 3J=7.4 Hz, 1H), 8.12 (dd, 3J=8.3, 4J=1.8 Hz,
1H), 7.72–7.66 (m, 4H), 7.48–7.44 ppm (m, 3H); 13C NMR (150 MHz,
[D6]acetone/[D6]DMSO): d=145.35 (Cq), 144.58 (Cq), 140.47 (2 Cq),
139.94 (Cq), 139.29 (Cq), 138.92 (Cq), 138.79 (Cq), 131.94 (Cq), 131.30 (2
Cq), 131.17 (Cq), 128.85 (2 CH), 128.83 (CH), 128.70 (CH), 125.05 (2
CH), 124.81 (CH), 124.76 (CH), 124.34 (CH), 123.67 (2 CH), 123.58
(CH), 121.54 (CH), 121.43 (CH), 121.21 (2 CH), 120.12 (2 Cq), 120.06
1.56 mmol) in anhydrous THF (15 cm3) was added dropwise over 30 min
at ꢀ788C through a syringe pump to form a bright-yellow solution, which
was stirred at ꢀ788C for 45 min. A solution of triisopropyl borate
(19.4 mmol) in anhydrous THF (10 cm3) was added over 30 min, stirred
for 30 min and then warmed to room temperature. The solution became
cloudy, was stirred for a further 30 min, warmed to 608C and stirred first
for 12 h and then for a further 15 h after acidification with HCl (2m).
The resulting mixture was diluted with water (5 cm3), extracted with di-
chloromethane (3ꢂ50 cm3) and the extract washed with water (2ꢂ
5488
www.chemeurj.org
ꢁ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 5482 – 5490

Oligomeric Indolocarbazole Thin Films
FULL PAPER
(Cq), 119.90 (Cq), 114.41 (CH), 114.37 (2 CH), 114.27 ppm (CH); MS
(EI): m/z (%): 480 (8) [M]+, 240 (5), 190 (78), 156 (100), 128 (26), 78
(14). HRMS (EI): m/z: calcd for C36H20N2: 480.1627 [M]+; found:
480.1622.
this suitable as a reference redox reaction.[39] Calculation of the free
energy of the reaction 4+· +In!4+In+· gives the standard reduction po-
tential of 4+·/4 relative to the indole (In) redox couple In+·/In. This can
then be converted into a calculated peak oxidation potential on any ref-
erence scale by using the experimentally measured value of the indole
peak oxidation potential if the reactants and products have similar diffu-
sion coefficients in solution.[15]
Electrochemistry: All electrochemical experiments were carried out by
using a modular potentiostat with combined waveform generator and
voltage sources (Oxford Electrodes Ltd). The platinum rotating-disc
working electrode (RDE), area 0.387 cm2, was controlled by using a rota-
tor and motor controller (Oxford Electrodes Ltd) with data collection
using in-house software written in Visual Designer (Intelligent Instru-
ments). The counter electrode was a 2 cm2 platinum gauze and the refer-
ence electrode (Bioanalytical Systems Inc.) consisted of a silver wire
dipped in a solution of AgClO4 (0.01m) in a background electrolyte of
Acknowledgements
LiClO4/MeCN (0.1m). This reference electrode has
a potential of
The authors thank Dr. Steven Magennis, Dr. Lynne A. Crawford and Dr.
Madeleine Chapman for their assistance in collecting fluorescence decay
data and in the initial synthesis and spectroscopic work, respectively. We
also thank Dr. Andy Parkin for data collection and structural analysis,
Prof. Simon Parsons for structural refinement and Dr. Ian H. Sadler for
advice on NMR spectroscopy. S.I.W. and J.B.H. thank the EPSRC and
the School of Chemistry, The University of Edinburgh, respectively, for
funding. This work has made use of the resources provided by the EaSt-
CHEM Research Computing Facility (http://www.eastchem.ac.uk/rcf).
This facility is partially supported by the eDIKT initiative (http://www.
edikt.org). The School of Chemistry is part of the EaStCHEM joint
Chemistry Research School. We also acknowledge the financial support
of the Scottish Funding Council.
+0.298 V with respect to the saturated calomel electrode and +0.542 V
with respect to the standard hydrogen electrode.[37] The electrolyte solu-
tion was thoroughly purged with nitrogen gas.
Indolo
ACHTUNGTRENNUNG
and mass spectrometry: A 20 mm solution of indoloAHCTUNGTRENNUNG
in 0.1m LiClO4/MeCN was electro-oxidised at +1.19 V using the plati-
num disc electrode rotating at 4 Hz for periods of 10 min. The film was
then reduced to its neutral redox form by stepping the potential down to
0 V and was carefully scraped off the electrode surface. This process was
repeated until about 10 mg of film was produced. The product was ana-
lysed by 1H NMR spectroscopy and was found to be a mixture of 5,5’-
biindolo
N
ACHTUNGTNER[NUNG 3,2,1-jk]carbazole (6) and
2,5’-biindolo
N
a
(600 MHz, [D6]acetone/[D6]DMSO) spectra exhibited signals and empiri-
cal integrals as follows: d=8.80 (d, 4J=1.5 Hz, 2H), 8.79 (d, 4J=1.5 Hz,
1H), 8.57 (s, 2H), 8.56 (s, 4H), 8.45–8.39 (m, 6H), 8.37–8.28 (8H, m),
8.26–8.22 (10H, m), 8.14 (dd, 3J=8.3, 4J=1.6 Hz, 2H), 8.13 (dd, 3J=8.3,
4J=1.6 Hz, 1H), 7.73–7.66 (m, 14H), 7.51–7.43 ppm (m, 10H); some vari-
ability in the chemical shifts with solvent and concentration was noted;
MS (FAB): m/z: 481 [MH]+; HRMS (FAB): m/z: calcd for C36H21N2:
481.1660 [MH]+; found: 481.1628.
[1] a) R. J. Waltman, J. Bargon, Can. J. Chem. 1986, 64, 76–95; b) S.
Sadki, P. Schottland, N. Brodie, G. Sabouraud, Chem. Soc. Rev.
2000, 29, 283–293; c) S. J. Higgins, Chem. Soc. Rev. 1997, 26, 247–
257.
[2] a) P. N. Bartlett, D. H. Dawson, J. Farrington, J. Chem. Soc. Faraday
Trans. 1992, 88, 2685–2695; b) P. Jennings, A. C. Jones, A. R.
Mount, A. D. Thomson, J. Chem. Soc. Faraday Trans. 1997, 93,
3791–3797; c) J. Xu, J. Hou, W. Zhou, G. Nie, S. Pu, S. Zhang, Spec-
trochim. Acta Part A 2006, 63, 723–728.
[3] a) S. Yapi Abe, J. C. Bernede, M. A. Delvalle, Y. Tregouet, F. Ragot,
F. R. Diaz, S. Lefrant, Synth. Met. 2002, 1261–1266; b) P. Syed Ab-
thagir, R. Saraswathi, Org. Electron. 2004, 5, 299–308.
[4] P. L. T. Boudreault, S. Wakim, N. Blouin, M. Simard, C. Tessier, Y.
Tao, M. Leclerc, J. Am. Chem. Soc. 2007, 129, 9125–9136.
[5] a) J. F. Morin, N. Drolet, Y. Tao, M. Leclerc, Chem. Mater. 2004, 16,
4619–4626; b) J. Li, F. Dierschke, J. Wu, A. C. Grimsdale, K. J.
Mullen, Mater. Chem. 2006, 16, 96–100; c) N. Drolet, J. F. Morin, N.
Leclerc, S. Wakim, Y. Tao, M. Leclerc, Adv. Funct. Mater. 2005, 15,
1671–1682.
Chemical oxidation of indolo
ACHUTGTNRNEUG[N 3,2,1-jk]carbazole (4): IndoloACHTUNGTRNE[NUGN 3,2,1-jk]car-
bazole (4; 0.064 g, 0.266 mmol) was dissolved in acetonitrile (7 cm3)
under nitrogen. Anhydrous ironACHTUNTRGNEU(GN III) chloride (0.043 g, 0.266 mmol) was
dissolved in acetonitrile (2 cm3) under nitrogen and added to this solu-
tion. A deep-purple colour appeared immediately and the solution was
stirred at room temperature under nitrogen until this colour faded. A
fine green/black suspension was formed, which was filtered and dried
under vacuum to yield a mixture of 5,5’-biindolo
2,2’-biindolo[3,2,1-jk]carbazole (6) and 2,5’-biindolo
in similar ratio to that formed electrochemically (0.019 g, 30%).
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
a
4
1H NMR (600 MHz, [D6]acetone/[D6]DMSO): d=8.81 (d, J 1.7 Hz, 2H),
8.80 (d, 4J 1.7 Hz, 1H), 8.61 (s, 2H), 8.60 (s, 4H), 8.47–8.41 (m, 6H),
8.38–8.27 (m, 8H), 8.27–8.23 (m, 10H), 8.15–8.13 (m, 3H), 7.73–7.68 (m,
14H), 7.50–7.42 ppm (m, 10H); MS (FAB): m/z: 481 [MH]+.
[6] a) S. Wakim, J. Bouchard, M. Simard, N. Drolet, Y. Tao, M. Leclerc,
Chem. Mater. 2004, 16, 4386–4388; b) Y. Li, Y. Wu, S. Gardener,
B. S. Ong, Adv. Mater. 2005, 17, 849–853; c) Y. Wu, Y. Li, S. Gar-
dener, B. S. Ong, J. Am. Chem. Soc. 2005, 127, 614–618.
[7] T. Mitsumori, M. Bendikov, O. Dautel, F. Wudl, T. Shioya, H. Sato,
Y. Sato, J. Am. Chem. Soc. 2004, 126, 16793–16803.
Fluorescence spectroscopy: Steady-state fluorescence spectra were mea-
sured by using a Jobin Yvon Spex Fluoromax spectrofluorometer (Instru-
ments S.A. group) with fused silica cuvettes. The excitation source was a
150 W continuous ozone-free xenon lamp with modified Czerny–Turner
spectrometers in both the emission and excitation positions. Datamax
data acquisition and data manipulation software were used throughout
(DataMax for Microsoft Windows, DataMax Version 2.20, 1997, Devel-
oper Instruments SA, Inc.). Time-correlated single-photon-counting
(TCSPC) experiments were performed at the Collaborative Optical Spec-
troscopy Micromanipulation and Imaging Centre (COSMIC) at The Uni-
versity of Edinburgh. All decays were measured by using an Edinburgh
Instruments TCSPC spectrometer coupled with a Hammamatsu R3809U-
50 series micro-channel plate detector. Samples were excited by using a
mode-locked Ti-sapphire laser.
[8] N. Kobayashi, R. Koguchi, M. Kijima, Macromolecules 2006, 39,
9102–9111.
[9] D. Curiel, A. Cowley, P. D. Beer, Chem. Commun. 2005, 236–238.
[10] a) A. L. Briseno, S. C. B. Mannsfeld, M. M. Ling, S. Liu, R. J. Tseng,
C. Reese, M. E. Roberts, Y. Yang, F. Wudl, Z. Bao, Nature 2006,
444, 913–917; b) A. L. Briseno, R. J. Tseng, M. M. Ling, E. H. L.
Falcao, Y. Yang, F. Wudl, Z. Bao, Adv. Mater. 2006, 18, 2320–2324.
[11] Y. Li, Y. Wu, B. S. Ong, Macromolecules 2006, 39, 6521–6527.
[12] H. G. Dunlop, S. H. Tucker, J. Chem. Soc. 1939, 1945–1956.
[13] L. A. Crawford, H. McNab, A. R. Mount, S. I. Wharton, J. Org.
Chem. 2008, 73, 6642–6646.
[14] Formed in a yield of 95% by reaction of carbazole with 2-fluoroni-
trobenzene in DMSO in the presence of caesium carbonate.
[15] Y. Wang, A. D. Stretton, M. C. McConnell, P. A. Wood, S. Parsons,
J. B. Henry, A. R. Mount, T. H. Galow, J. Am. Chem. Soc. 2007, 129,
13193–13200.
Calculations: Structures were calculated by using the Gaussian 03[38] pro-
gram at the uB3LYP/6-311+GACHTNUTRGNE(NUG d,p) level of theory with acetonitrile sol-
vation modelled by the SCRF method. It has previously been shown that
the accurate calculation of absolute values of experimental indole oxida-
tion potentials is possible to within a few tens of millivolts, which makes
Chem. Eur. J. 2009, 15, 5482 – 5490
ꢁ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
5489

H. McNab, A. R. Mount et al.
[16] All electrochemical experiments were carried out at a platinum disc
electrode (area 0.387 cm2) using MeCN/0.1m LiClO4 as the back-
ground electrolyte and Ag/Ag+ (0.01m) in the background electro-
lyte as the reference electrode unless otherwise stated.
[17] Chosen to ensure a sufficiently reactive electrode to ensure the oxi-
dation reaction is not under electrochemical control.
[18] The current at an RDE is predicted to be within 1% of the steady-
state value after a time t, with tꢂ2.1 Wꢀ1; see A. J. Bard, L. R.
Faulkner, Methods Involving Forced Convection-Hydrodynamic
Methods in Electrochemical Methods Fundamentals and Applica-
tions, 2nd ed., Wiley, New York, 2001, p. 354.
[19] In fact there was a gradual increase in current over long times. This
is consistent with two-dimensional film growth (growth laterally as
well as perpendicular to the disc electrode).
[20] The thickness can be readily estimated from the volume occupied
by each IC in the crystal structure, the charge passed during film for-
mation, the area of the electrode and by assuming 1.5 electrons are
passed during the electro-oxidation for each monomer for IC film
formation and deposition.
[21] Taking the earliest time steady-state currents, when the films were
relatively thin and the effective area for further film growth could
be made equal to the electrode area.
[22] J. Koutecky, V. G. Levich, Zh. Fiz. Khim. 1958, 32, 1565–1575.
[23] This is consistent with values found for other similar sized heteroar-
omatics.[2b]
[24] Calculated by assuming dimer products and deposition of the dimer
in the one-electron oxidised form, removing three electrons per two
monomers in the dimer [Eq. (2)].
[29] Note that the chemical shifts of the 1H NMR spectrum are suscepti-
ble to variation with slight changes in solvent ratio and sample con-
centration.
[30] N. Miyaura, A. Suzuki, Chem. Rev. 1995, 95, 2457–2483.
[31] Previous reactions of 4 with molecular bromine produced ambigu-
ous results, including the formation of mixtures of di- and monobro-
minated species.[12]
[32] C. B. de Koning, J. P. Michael, J. M. Nhalpo, R. Pathak, W. A. L. van
Otterlo, Synlett 2003, 705–707.
[33] A. V. Tsvetkov, G. V. Latyshev, N. V. Lukashev, I. P. Beletskaya, Tet-
rahedron Lett. 2002, 43, 7267–7270.
[34] J. G. Mackintosh, A. R. Mount, J. Chem. Soc. Faraday Trans. 1994,
94, 1121–1125.
[35] Trimer coupling in, for example, indoles is a subsequent chemical re-
action that leads to covalent bond formation by coupling of the fur-
ther oxidised species with the loss of two protons and the generation
of the reduced form. The associated reduction peak for the further
oxidation is therefore significantly attenuated.[34]
[36] C. Buchanan, S. H. Tucker, J. Chem. Soc. 1958, 2750–2755.
[37] V. V. Pavlishchuk, A. W. Addison, Inorg. Chim. Acta 2000, 298, 97–
102.
[38] Gaussian 03, Revision C.02, M. J. Frisch, G. W. Trucks, H. B. Schle-
gel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, J. A. Montgomer-
y, Jr., T. Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyen-
gar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N.
Rega, G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K.
Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda,
O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratchian,
J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E.
Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W.
Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P. Salvador, J. J.
Dannenberg, V. G. Zakrzewski, S. Dapprich, A. D. Daniels, M. C.
Strain, O. Farkas, D. K. Malick, A. D. Rabuck, K. Raghavachari,
J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford, J. Cio-
slowski, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaro-
mi, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng,
A. Nanayakkara, M. Challacombe, P. M. W. Gill, B. Johnson, W.
Chen, M. W. Wong, C. Gonzalez, J. A. Pople, Gaussian, Inc., Wall-
ingford, CT, 2004.
[25] The coupling of two radical cations in solution would give a second-
order dependency on concentration.
[26] The total number of electrons passed per (M)n unit in film formation
is n+1 and in the film redox reaction is 1. This gives a ratio of
redox to polymerisation charge of (n+1)ꢀ1
.
[27] The quantum yield, f, is related to the radiative (fluorescent) and
non-radiative decay rates, kR and kNR, and lifetimes, tR and tNR
,
kR
tꢀR1
byꢀ ¼
¼
The observed fluorescence lifetime is given by
and therefore for similar classes of molecules a similar fluo-
tꢀR1þtꢀ1
kR þkNR
NR
1
tꢀR1þtꢀ1
rescNeRnce lifetime indicates a similar quantum yield.
[28] The output was viewed using Jmol, an open-source Java viewer
for chemical structures in 3D (http://www.jmol.org/). Rendered
by using the Persistence of Vision Raytracer (POV-Ray) freeware
(http://www.povray.org).
[39] L. J. Kettle, S. P. Bates, A. R. Mount, Phys. Chem. Chem. Phys.
2000, 2, 195–201.
Received: January 13, 2009
Published online: April 9, 2009
5490
www.chemeurj.org
ꢁ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 5482 – 5490