Delineating poly(aniline) redox chemistry by using tailored oligo(aryleneamine)s: Towards oligo(aniline)-based organic semiconductors with tunable optoelectronic properties

Article abstract of DOI:10.1002/chem.201101697

The simple and elegant Buchwald-Hartwig cross-coupling reaction has been used to synthesise a designed range of new aniline-based tetramers in one step, and without the need for protecting groups. Variation of the central aromatic ring has provided the opportunity to carefully tune the optoelectronic properties in this series, thus enabling a structure-activity relationship study by using a range of photophysical and electrochemical techniques. As a result, the long-proposed sequences of electron-electron (EE) and electron-chemical (EC) processes that support the complex redox and proton-transfer reactions involved in the well-known switching of redox states of poly- and oligo(aniline)s are revealed here for the first time. We also present the initial results from time-dependent DFT calculations to clarify the optoelectronic behaviour of these oligomers. The dc-conductivity measurements of conducting thin films of this series, doped with the prototypical poly(aniline) protonating agent d,l-camphor-10-sulfonic acid (CSA), externally plasticised with triphenyl phosphate (TPP), and processed from m-cresol (MC) solutions, are also presented. Aniline black, blue, orange and red! The Buchwald-Hartwig cross-coupling reaction is used to synthesise a range of new aniline-based tetramers with carefully tunable optoelectronic properties (see figure; EB=emeraldine base; PANI=poly(aniline)). The long-proposed sequences of electron-electron and electron-chemical processes that support the complex redox and proton-transfer reactions involved in the switching of redox states of poly- and oligo(aniline)s are revealed for the first time. Copyright

Full text of DOI:10.1002/chem.201101697

DOI: 10.1002/chem.201101697
Delineating PolyACTHNUTRGNEUNG(Aniline) Redox Chemistry by Using Tailored
Oligo(Aryleneamine)s: Towards OligoACTHNUTRGNEUNG(Aniline)-Based Organic
Semiconductors with Tunable Optoelectronic Properties
Zhecheng Shao,[a] Patrice Rannou,[b] Saꢀd Sadki,[b] Natalie Fey,[a] David M. Lindsay,[c] and
Charl F. J. Faul*[a]
Abstract: The simple and elegant
Buchwald–Hartwig cross-coupling reac-
tion has been used to synthesise a de-
signed range of new aniline-based tet-
ramers in one step, and without the
need for protecting groups. Variation
of the central aromatic ring has provid-
ed the opportunity to carefully tune
the optoelectronic properties in this
series, thus enabling a structure–activi-
ty relationship study by using a range
of photophysical and electrochemical
techniques. As a result, the long-pro-
posed sequences of electron-electron
(EE) and electron-chemical (EC) pro-
cesses that support the complex redox
and proton-transfer reactions involved
in the well-known switching of redox
also present the initial results from
time-dependent DFT calculations to
clarify the optoelectronic behaviour of
these oligomers. The dc-conductivity
measurements of conducting thin films
of this series, doped with the prototypi-
states of poly- and oligoACHTUNTRGNEUNG(aniline)s are
revealed here for the first time. We
cal polyACTHUGNETRNNU(G aniline) protonating agent d,l-
camphor-10-sulfonic acid (CSA), exter-
nally plasticised with triphenyl phos-
phate (TPP), and processed from m-
cresol (MC) solutions, are also present-
ed.
Keywords: amination · conducting
materials · optoelectronic proper-
ties · semiconductors · structure–ac-
tivity relationships
Introduction
ature. It was only from 1984 onwards that the simultaneous,
seminal contributions of MacDiarmid et al. and Geniꢀs et al.
The chemistry of aniline has played an important role in the
history of modern synthetic chemistry,[1] especially during
the first half of the 19th century.[2] Aniline has a long and
rich scientific and technological history,[1] first as a dyestuff
(i.e., so-called aniline black[3]) and, more recently, as the
basis for molecular-[4] and macromolecular-based[5] function-
al organic materials. Yet, despite being one of the most stud-
ied classes of conducting organic materials to date, its recent
scientific development has been surprisingly erratic. Follow-
ing the discovery of conducting polymers in 1977,[6] the elec-
triggered a revival of research into conducting poly-
AHCTUNGTRENNUNG
(aniline).[8] Eventually, the discovery of the counterion-in-
duced solution processability[9] and the truly metallic behav-
iour of d,l-camphor-10-sulfonic acid (CSA) doped poly-
AHCTUNGTRENNUNG
(aniline)[10] brought this solution-processable synthetic
metal, showing an impressive room temperature dc conduc-
tivity up to approximately 1000 ScmÀ1, to the pinnacle of
the field of conducting polymers.[11]
Interestingly, even as far back as the early 1900s, Green
and Woodhead had tentatively discussed the various redox
states observed in the family of aniline-black dyes based on
trochemical synthesis of polyACTHNUTRGENUGN(aniline) was first reported in
1980,[7] with surprisingly little immediate impact in the liter-
octa
theses of defined, phenyl-capped tetra
TANI)[13] and octa(aniline) (Ph/Ph OANI)[14] were only pub-
(aniline) model compounds.[12] However, the first syn-
ACHTUNGTRENNUNG
AHCTUNGTREG(NNUN aniline) (Ph/Ph
AHCTUNGTRENNUNG
[a] Dr. Z. Shao, Dr. N. Fey, Dr. C. F. J. Faul
School of Chemistry, University of Bristol
Bristol BS8 1TS (UK)
lished in 1968 and 1986, respectively. These reports provided
the opportunity to study these soluble oligomers as models
of their polymeric analogue by using the so-called oligomer
approach.[15] After these initial studies, many papers were
Fax : (+44)0117-925-1295
E-mail: charl.faul@bris.ac.uk
published on the use of these oligoACHTUNTRGNEUNG(aniline)s as molecular
[b] Dr. P. Rannou, Prof. S. Sadki
nanowires,[16] and in functional hybrid inorganic/organic and
carbon nanotube/organic materials,[17] rod–coil oligomers
and copolymers.[18] Several new synthetic routes have been
UMR5819-SPrAM (CEA/CNRS/Univ. J. FOURIER)
Institut Nanosciences & Cryogꢁnie (INAC), CEA-Grenoble
17, Rue des Martyrs, 38054 Grenoble Cedex 9 (France)
[c] Dr. D. M. Lindsay
developed for oligoACTHNUTRGNEUNG(aniline)s, but very little progress has
WestCHEM, School of Chemistry, University of Glasgow
Joseph Black Building, University Avenue
Glasgow G12 8QQ (United Kingdom)
been made in expanding the molecular engineering possibili-
ties for designing new aniline-based organic (semi)conduc-
tors with tunable optoelectronic properties.[4b] This is espe-
cially true when compared to the recent activities in novel
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201101697.
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FULL PAPER
oligomer conjugates,[19] as well as the successful develop-
ment of other p-conjugated systems[15] (e.g., oligo(2,5-thie-
nylene)s[20] and oligo(1,4-phenylene vinylene)s), which are
fuelling the rapid development of the field of organic optoe-
lectronics[21] and its associated devices (e.g., light-emitting
diodes (LEDs), lasers, solar cells and field-effect transistors
(FETs)).
The palladium-catalysed amination of aryl halides and
aryl pseudo halides, developed by Buchwald and Hartwig,[22]
is an attractive strategy for the synthesis of aniline oligo-
mers. Indeed, soon after the initial reports of this reaction,
Buchwald demonstrated its applicability in the controlled
iterative synthesis of terminally functionalised oligo-
egy. Focusing on Ph/Ph TANI, and choosing to examine the
effect of varying the nature of the central ring, has allowed
us to take advantage of the symmetrical molecular architec-
ture of this species to produce a novel range of derivatives
with a modified central aromatic core. We have used pre-
liminary time-dependent density functional theory (TD-
DFT) calculations to assign the observed transitions in UV/
Vis spectra of the representative aniline tetramer 2 in differ-
ent oxidation states. Furthermore, we show how electro-
chemical studies have allowed us to observe the discrete oxi-
dation and reduction steps that result in the conversion of
these TANI derivatives from their fully reduced to fully oxi-
dised states. Finally, a preliminary discussion of the electron-
ic transport properties of this series of oligo(aryleneamine)s
is reported on the basis of four probe dc-conductivity meas-
urements performed on CSA-doped TANI thin films pro-
cessed from m-cresol (MC) solutions.
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
pared, bearing a range of functional groups at the termini,
and their electronic properties were studied. In a similar ap-
proach, Hartwig demonstrated the utility of the amination
in constructing triarylamines, by synthesising hexadecamers
of N-p-anisyl-functionalised m-aniline.[24] Both Cu- and Pd-
catalysed aminations have been used by Blackstock et al. to
construct dendritic poly(arylamine)s with interesting redox
chemistry.[25]
Results and Discussion
To initiate our studies, we designed the Ph/Ph TANI deriva-
tives 3–6, which could be readily synthesised by Buchwald–
Hartwig amination[26] of the corresponding dihalide with two
equivalents of N-phenyl-1,4-phenylenediamine (Scheme 1).
The resulting facile, one-step method (without the use of
protecting groups[26d]) delivers Ph/Ph TANI 2 and a series of
Herein, we report our studies on the effects of introducing
modifications into the p-conjugated backbone of Ph/Ph
TANI by using the Buchwald–Hartwig cross-coupling strat-
Scheme 1. Synthesis of Ph/NH2 TANI 1, Ph/Ph TANI 2 and the related novel derivates 3–6 in their leucoemeraldine base (LEB) state. Reaction condi-
tions: [Pd(dba)2] (dba=dibenzylideneacetone; 6 mol%), rac-2,2ꢃ–bis(diphenylphosphino)–1,1ꢃ–binaphthyl (BINAP; 9 mol%) (a–c, e), 2-dicyclohexyl-
phosphino-2’,4’,6’-triisopropylbiphenyl (X-Phos; 9 mol%) (d), sodium tert-butoxide, toluene, 1108C, 24 h; f) iron(III) chloride, HCl.
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
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C. F. J. Faul et al.
related derivatives 3–6 in the fully reduced LEB state. Ph/
Ph TANI 2 was accessed by the cross-coupling of two equiv-
alents of N-phenyl-1,4-phenylenediamine with 1,4-dibromo-
benzene. Variation of the dibromoaromatic centrepiece al-
lowed for rapid access to the novel derivatives 3–6 in their
LEB states (Scheme 1). In order to fully compare the data
obtained from this new series of aniline-based oligomers
with previously published data for the parent tetraACTHNUTRGNEUG(N aniline),
Ph/NH2 TANI (1) was synthesised by using a slight modifi-
cation of a known oxidative coupling route.[27]
Derivatives 3, 4 and 6 (Scheme 1) were synthesised in uni-
formly high yield by using similar Buchwald–Hartwig condi-
tions as for the synthesis of 2. For the synthesis of 5, howev-
er, X-Phos[28] was employed instead of rac-BINAP, as the
use of the latter ligand afforded only a low yield of 5, along
with the mono-aminated species as the major product. This
is possibly due to inefficient oxidative addition of the cata-
lyst to the electron-rich 9-dianilino-10-bromoanthracene in-
termediate for the second coupling (the only other report-
ed[29] bis-amination of 9,10-dibromoanthracene also employs
a bulky, electron-rich ligand: tris(tert-butyl)phosphine). The
TANI series 2–6, obtained directly in the LEB oxidation
1
state, was characterised by H, 13C and 2D NMR spectrosco-
py, FTIR spectroscopy, high-resolution mass spectrometry
and elemental analysis. Purity was furthermore confirmed
by size exclusion chromatography (SEC; see Figure 1 and
Table S1 in the Supporting Information). The corresponding
EB states were obtained quantitatively upon treatment of
2–6 (in their pure LEB states) with an equimolar amount of
ammonium persulfate in hydrochloric acid (2m), followed
by treatment with an excess of ammonium hydroxide (2m)
(see the Supporting Information).
Our synthetic strategy provides ample opportunity to ex-
plore the molecular architecture of TANI, and, specifically,
the influence of the size and nature of the central p-conju-
gated unit on the optoelectronic properties of this series of
Ph/Ph TANIs. With oligomers 1–6 in hand, we were able to
investigate and compare the effect of carefully designed and
controlled changes of the molecular architecture on the
properties of each derivative, and hence, initiate enquiries
that will provide insight into the structure–function–proper-
Figure 1. a) SEC elugrams of the TANI derivatives 1–6 in their EB states
recorded from solutions in THF (ꢀ0.1 mgmLÀ1) with UV/Vis detection
located at 355 nm and b) the corresponding chemical structures of the
emeraldine base (EB) states of 1–6.
For 1EB and 2EB the two absorption maxima (l1max and
l2max) have previously been assigned to p–p* and n–p* tran-
sitions, respectively, based on theoretical[30,31] and experi-
ty relationship within oligoACTHNUGRTENUNG(aniline)s.
As expected, the designed changes in molecular architec-
ture had a significant impact on the optoelectronic proper-
ties of the TANI series (as was immediately evident from
the dramatic differences in the colours observed for the
LEB and EB states of 1–6 in both the solid state and in so-
lution, see Figure S1a–c in the Supporting Information).
The UV/Vis spectrum of 2EB demonstrates that addition
of a phenyl capping group onto 1EB induces bathochromic
shifts of both l1max (by ꢀ10 nm) and l2max (by ꢀ6 nm). As
highlighted in Figure 2, our molecular engineering approach
to the central p-conjugated units in the rest of the series
now allows for large and tunable modifications of the elec-
tronic structure of the different TANIs, resulting in batho-
chromic shifts of up to 24 nm and hypsochromic shifts of up
to 90 nm for the first and second transitions, respectively.
mental[32–34] studies of poly
recent work[35] on oligo
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
tually a further p–p* transition. We have used TD-DFT cal-
culations at the B3LYP/6-31G* level in a PCM solvation
field for tetrahydrofuran on Ph/Ph TANI 2 in its LEB and
EB oxidation states to assign the observed transitions (see
Computational Details). Table 1 shows the calculated key
transitions (oscillator strengths f >0.1); comparison with
our experimental data shows an overestimation of calculated
transition energies, also observed for transition metal com-
plexes.[36] Although quantitatively unreliable, this approach
nonetheless facilitates the interpretation of transitions and
Figure 3 shows the main contributing orbitals.
The calculations confirm that both bands of the EB state
resonance forms considered have mainly p–p* character,
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Organic Semiconductors with Tunable Optoelectronic Properties
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Figure 2. a) Steady-state (THF) solution UV/Vis absorption spectra of
TANIs 1–6 in their EB states. Inset: Colours of the visible (400–750 nm)
part of the spectrum. For the corresponding chemical structures of
TANIs 1EB–6EB see Figure 1b.
Table 1. Low-energy singlet transitions for 2 as obtained from TD-DFT
calculations.
TANI
Transition
f[a]
Assignment ([%])
[eV] ([nm])
2LEB
2EB[b]
3.45 (360)
3.64ACHTUNGTRENNUNG(341)
1.84 (674)
3.62 (342)
1.66
0.32
1.45
1.00
117–118 (90)
117–119 (88)
116–117 (80)
110–117 (45)
114–117 (18)
116–117 (86)
115–117 (83)
109–117 (46)
116–118 (18)
113–117 (16)
2EB2[b]
1.75 (709)
2.43 (510)
3.64 (341)
0.86
0.34
0.92
[a] f is the oscillator strength. [b] Resonance forms of 2EB with deproto-
nation of two nitrogen atoms around the core (2EB) and on one side of
the core (2EB2, +1.4 kcalmolÀ1 above 2EB), see Figure 3 for structures.
with some nitrogen lone pair character contributing to the
transition around 300 nm (l1). Some of the EB orbitals have
charge-transfer character, which is not captured well by the
DFT approach used here,[37] and thus hampers quantitative
predictions. A more complete discussion of the calculated
structures, predicted transitions and the impact of conforma-
tional change can be found in the Supporting Information,
along with a brief discussion of known TD-DFT issues when
calculating charge-transfer bands. We are currently evaluat-
ing a range of DFT approaches with the aim of achieving
improved agreement with experimental data, and will report
calculation results for the full series of compounds described
here in due course.
The combination of this newly developed series of materi-
als and ongoing in-depth TD-DFT studies of the whole
series has presented further opportunities to carefully tune
the architecture of the different materials architectures and
thus, their properties for novel optoelectronic applications.
Figure 3. Orbitals contributing strongly (>40 %) to the transitions sum-
marised in Table 1 as calculated by DFT.
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C. F. J. Faul et al.
In order to compare this library of molecularly engi-
neered, aniline-based organic semiconductors with the well-
known electrochemical behaviour of oligo- and poly-
EE process to reach its conducting state (the so-called emer-
aldine salt (ES) state). Interconversion to the electronically
insulating PNGB state can be accomplished through two EC
steps during which both electron and proton transfer occur,
as shown in Scheme 2 (see Figures S3 and S4 in the Support-
ing Information for the full series).
ACHTUNGTRENNUNG
(aniline)s,[38] cyclic voltammetry (CV) and differential
pulsed voltammetry (DPV) investigations were carried
out.[39] To provide insight into the results obtained, we will
focus our discussion on the DPV measurements, as this pro-
vided a wealth of high quality data, which has not been seen
to date for such electroactive species. Tables 2 and 3 summa-
rise the data discussed below.
Initial examination of the DPV results shows three, and in
some cases even four, reversible-to-quasi-reversible well-de-
fined peaks. These peaks are tentatively associated with a
sequence of electron-electron (EE) and electron-chemical
(EC: i.e., electron and proton transfers) mechanism-coupled
reactions,[39] and is found for the whole TANI series 1–6 (see
Figures S2–S4 in the Supporting Information for all DPV
data). This remarkable set of results, never reported before
Until now, no study has been published where the se-
quence of these four electrochemical processes has been un-
ambiguously identified for oligoACHTUNGTRNEUNG
(aniline)s.[40] To the best of
our knowledge, our DPV-based electrochemical characteri-
sation is the first experimental confirmation of such EE and
EC processes[39] for para-coupled aniline-based organic
(semi)conductors.
Further to this interesting electrochemical data, the inser-
tion of appropriately selected, p-conjugated, central blocks
within the molecular structure of these oligo(arylenea-
mine)s/(aryleneimine)s (see Scheme 1 and Figure S3 in the
Supporting Information) now provides a route to a tunable
modulation of the optoelectronic properties of aniline-based
organic semiconductors. This is highlighted in Table 2,
where the four apparent standard redox potentials E8x,ox.
(with x=1–4) are listed for the investigated series of TANI
1–6, with the data organised according to the ease of oxida-
tion. Closer inspection of Table 2 shows that the experimen-
tal E81,ox and E82,ox values connected to the EE electrochem-
ical process experienced by TANI 5, 2, 3 and 1 are in agree-
ment with the respective ability
for either poly- or oligoACHTUNTGRNEUNG(aniline)s, can be rationalised by dis-
cussing the electrochemical behaviour of 2 as an example.
The starting point for our discussions is based on the well-
established existence[12] of three distinct oxidation states:
leucoemeraldine base (100% reduced), emeraldine base
(50% oxidised/reduced), and pernigraline base (PNGB,
100% oxidised), as depicted in Scheme 2. Starting from its
electronically insulating LEB state, 2 can experience one
of their p-conjugated central
blocks to allow for extension of
their p-conjugated systems. It is
only in the cases of 4 and 6 that
the fourth apparent standard
redox potentials (E84,ox) could
not be determined, even after
extensive investigations. We
propose that the arguments
used to explain the features of
the fourth DPV peak of 2 (see
above) also hold true for 4 and
6.
Indeed, as exemplified in the
representative case of 2, four
separate DPV peaks are ob-
served during the reduction
scan, at À267, À65, 121 and
427 mV, and three separate
DPV peaks are observed during
the oxidation scan, at À247,
À56 and 131 mV (Figure 4b
and a, respectively). The low in-
tensity of the fourth DPV peak
observed during the oxidation
scan (and associated with the
fully oxidised PNGB state of 2)
Scheme 2. Chemical structure of TANI 2 in its LEB, EB and PNGB redox states and tentative sequence of EC
and EE mechanism-coupled reactions supporting the electrochemical behaviour observed during the DPV
can be rationalised by the high
reactivity of 2PNGB (which im-
mediately reacts with minute
C
characterisation of 2. Note that to maintain electroneutrality of 2, each generated radical cation ( +) requires
a corresponding anion (AÀ).
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Organic Semiconductors with Tunable Optoelectronic Properties
FULL PAPER
Table 2. DPV data of 1–6 collected during an oxidation scan[a] and classi-
fied according to the ease of oxidation of their p-conjugated central
blocks (see Figures S2 and S3 in the Supporting Information).
TANI
Oxidation [mV]
derivative
E81,ox.
E82,ox.
E83,ox.
E84,ox.
5
2
3
1
4
6
À317
À267
À121
À35
À25
26
À170
À65
96
0
121
323
217
427
625
816
161
111 and 222
126
473
[b]
449 and 565
500
–
[b]
–
ACTHNUTRGNEUNG
[a] All potentials are versus Fc+/Fc [E8(Fc+/Fc)=0.425 vs. saturated calo-
mel electrode (SCE)]. [b] Not observed.
amounts of reducing agent) and its short lifetime under our
DPV conditions (i.e., with a scan rate of 10 mVsÀ1 and in
the presence of diphenyl phosphate (DPP) as a proton
source).[38]
Remarkably, within this series of TANIs, we repeatedly
observed splitting of the signals for the E82,ox. and E83,ox. elec-
trochemical processes into two DPV peaks for derivative 4.
Although a definitive conclusion awaits further detailed
TD-DFT and spectroelectrochemical investigations, we ten-
tatively attribute these phenomena to the plausible co-exis-
tence of two isomeric forms (obtained only after the second
step of the EE and the first EC electrochemical processes,
respectively), showing different apparent standard redox po-
tentials.
Table 3 summarises the four apparent standard redox po-
tentials E8x,red. (with x=1–4) for the series 1–6. With respect
to the previous discussions (vide supra) regarding the EE
and the two EC processes experienced during the oxidation
of 1–6, the four observed reduction steps of these aniline-
based organic semiconductors are less obviously connected
with their molecular structure, especially when considering
the cases of 1, 3 and 4. In contrast, fully consistent redox be-
haviour emerged when considering the EE electrochemical
behaviour of 5, 2 and 6. Indeed, comparison of Tables 2
(compare values for E81,ox and E82,ox) and 3 (compare values
for E83,red and E84,red) show the following expected clear sym-
metrical trend with respect to the ease of oxidation versus
the ease of reduction: 5>2@6 versus 6@2>5.
Finally, we also prepared d,l-camphor-10-sulfonic acid
doped thin films (thickness of ꢀ20 mm) of our TANI series
cast on polypropylene substrates from m-cresol solutions.
This combination of dopant and processing solvent is a
widely used benchmark combination for the generation of
high-performance PANI-based materials showing dc conduc-
tivity in the range of 100—1000 ScmÀ1.[9,10] Moreover, in
order to ensure good mechanical and electrical quality con-
ducting thin films over the 1 cm2 measured area character-
ised by the 4-probe method in the Van der Pauw configura-
tion,[41,42] we also added (e.g., 25 wt% with respect to the
TANI derivatives in their EB states) an external plasticiser
(triphenyl phosphate (TPP)).[43]
Figure 4. Differential pulse voltammograms of 2 during a) oxidation and
b) reduction scans. See the Supporting Information for experimental con-
ditions (dotted line arrows are guidelines only).
Table 3. DPV data of 1–6 collected during a reduction scan[a] (See Figur-
es S2 and S4 in the Supporting Information). For ease of comparison the
compounds are listed here in the same order as in Table 2.
TANI
Reduction (mV)
derivative
E81,red.
E82,red.
E83,red.
E84,red.
[b]
5
2
3
1
4
6
–
–
À237
À247
65
À105
À56
235
317
203
211
131
513
503
313
[b]
À142
À61
70
[b]
À195
À36
–
[b]
65
453
–
[a] All potentials are versus Fc+/Fc [E8
A
observed.
Table 4 summarises the dc-conductivity values obtained
for the plasticised and doped TANI thin films. Irrespective
of the chemical structures of the TANI derivatives 1–4, the
dc-conductivity values all fall within the 10À2 ScmÀ1 range.
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C. F. J. Faul et al.
Table 4. Dc conductivity sdc of CSA-doped and TPP-plasticised thin
films of the TANI series, measured by using a temperature-controlled
custom-built 4-probe measuring station in ambient air at 295 K.
have been obtained for CSA-doped and plasticised support-
ed thin films processed from m-cresol solutions.
A number of projects are currently under investigation in
our laboratories, including finding optimal conditions for the
processing and preparation of thin films for dc-conductivity
measurements, method evaluation and expansion of the TD-
DFT investigations to include the whole TANI series (thus
also providing calculated HOMO–LUMO gap levels), de-
tailed spectroelectrochemical characterisation and investiga-
tions into higher oligomeric series.[15,21] Medium-term goals
include the use of their (semi)conducting forms as active
semiconducting layers[44] and/or as organic electrodes[45] in
organic optoelectronic devices[20,21] and high selectivity gas
sensors.
TANI derivative
sdc [mScmÀ1
]
1EB
2EB
3EB
4EB
5EB
6EB
N
(TPP)25wt%
16
12
37
14
[a]
–
[b]
–
[a] 5EB decomposed to produce white crystals under treatment with
acid. This is currently under further investigation. [b] It was not possible
to produce high quality continuous films from 6EB under these process-
ing conditions.
Although this dc-conductivity level is four to five orders of
magnitude lower than that obtained for the highest conduct-
ing PANIACHTUNGTRENNUNG
(CSA)0.5 thin films obtained so far,[9,10] it falls
Experimental Section
within the range to be expected for bulk oligomer systems
(e.g., insoluble and infusible HCl-doped TANI,[4b,17d] acid-
surfactant-doped TANI films[4a] and HCl-doped octaanili-
ne[4b,14] (OANI) powders in the form of pressed pellets).
Considering the fact that a significant amount (e.g., up to
All reagents and solvents were purchased from Aldrich, and appropriate-
ly purified, if necessary. Unless otherwise noted, all of the reactions were
carried out under a nitrogen atmosphere and in dry solvents. 1H NMR
and 13C NMR spectra were recorded on a JEOL Lambda 300, Eclipse
400 or Varian VNMRS500 spectrometers in [D6]DMSO solutions. Chemi-
cal shifts of 1H and 13C NMR signals are quoted relative to internal
standards; Me4Si (d=0.00 ppm) and [D6]DMSO (d=39.5 ppm) for 1H
and 13C spectra, respectively, and expressed by chemical shifts in ppm,
multiplicity, coupling constant and relative intensity. Coupling constants
ꢀ18 wt% in the case of 1EB
ACHTUNTGRENNUG(CSA) CHTUGNTNERN(NUG TPP)25wt%) of the ex-
0.5A
ternally plasticised and doped TANIAHCTUGNTRE(NNUNG CSA)0.5 thin films con-
sist of the insulating TPP external plasticiser, one can ex-
trapolate a renormalised higher intrinsic dc-conductivity
level for our doped TANI thin films. Although the obtained
values are still lower than recently reported for HCl-doped
TANI self-assembled single nanostructures,[17b] we are en-
couraged that our approach provides materials with conduc-
tivities on par with standard prepared materials. The elec-
tronic transport features shown by these readily accessible
tetraaniline derivatives can therefore be considered as
promising for the development of new generations of high
dc conductivity and molecularly engineered oligo- and poly-
are reported in Hertz and refer to 3J
ACTHNUTRGNEU(GN H,H) couplings unless otherwise
stated. High resolution EI and CI mass spectra were recorded on a VG
Autospec 3-sector spectrometer at 70 eV. Mass spectra were recorded on
an Applied Biosystems 4700 Proteomics Analyser MALDI-TOF mass
spectrometer. Elemental analyses were carried out on a Euro Vector
Euro EA 3000 in the Microanalytical Laboratory at the University of
Bristol. Infrared spectroscopy was carried out on a Perkin–Elmer Spectra
100 FTIR spectrometer. Steady-state solution (THF) UV/Vis absorption
spectra were recorded in situ during analytical size exclusion chromatog-
raphy analyses by using the diode array detector (DAD) of a Hewlett–
Packard 1100 Chemstation equipped with a 300*7.5 mm Polymer labs
PLgel Mixed-D 5 mm/104 ꢄ column, a diode array (DA) detector and a
refractive index (RI) detector. The column temperature and the flow rate
were fixed to 408C and 1 mLminÀ1, respectively. The calibration curve
was built by using 10 polystyrene (PS) narrow standards (S-M2-10* kit
from Polymer Labs). Two runs of 20 mL injection of about 0.1 mgmLÀ1
HPLC grade THF solution were typically analysed for each sample with
an UV/Vis detection located at 355 nm. Cyclic voltammetry and differen-
tial pulse voltammetry (DPV) experiments were carried out in a one-
compartment electrolytic cell containing a 0.1m tetrabutylammonium
perchlorate (NBu4ClO4)/acetonitrile electrolytic solution. The potentio-
stat used was an Autolab PGSTAT302, interfaced to a PC computer. The
working electrode was a platinum disk (0.785 mm2 area). A platinum
wire was used as the counter electrode and silver wire as a pseudo-refer-
ence electrode. The reference was calibrated after each experiment
against the ferrocinium/ferrocene couple (E8Fc+/Fc =0.43 V vs. the Ag/
AgCl reference) as recommended by IUPAC.S1 See the Supporting Infor-
mation for full details on NMR and other analyses. The electronic trans-
port properties (i.e., dc conductivity sdc [ScmÀ1]) of the CSA-doped[9,10]
and TPP-plasticised[43] TANI thin films (thickness of ꢀ20 mm) cast on
polypropylene (PP) substrates was measured by using a temperature-con-
trolled custom-built 4-probe measuring station operating in the Van der
Pauw configuration.[41,42] Measurements on 1 cm2 supported thin films
were performed in ambient air at 295 K. Film thickness was determined
by recording SEM images of cross sections of cast films on a JEOL JSM
5600LV SEM.
ACHTUNGTRENNUNG
Conclusion
In conclusion, we have presented a practical, one-pot syn-
thetic route for the production of a range of new electroac-
tive oligoACHTUNGTRENNUNG(aniline) materials. Facile exchange of the central
phenyl core of the parent Ph/Ph TANI 2 produces a range
of new materials where optoelectronic properties can now
be tuned. This synthetic route will enable access to a variety
of new molecular and macromolecular architectures and ma-
terials with designed optoelectronic properties in the area of
oligo(aryleneamine)s- and oligo(aryleneamine)s-based alter-
nated or (multi)block copolymers. We have also used TD-
DFT calculations to clarify the nature of the optical transi-
tions observed for the parent TANI 2. In addition, we have
experimentally unravelled for the first time proof of sequen-
ces of electron-electron- and electron-chemical-coupled pro-
cesses, that have long been proposed but never observed. Fi-
nally, promising dc-conductivity levels of about 10À2 ScmÀ1
Representative experimental procedures for 2 and 3 are given below. For
the synthesis of compounds 1 and 4–6, see the Supporting Information.
12518
www.chemeurj.org
ꢂ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 12512 – 12521

Organic Semiconductors with Tunable Optoelectronic Properties
FULL PAPER
N1,N1’-(1,4-Phenylene)-bis(N4-phenylbenzene-1,4-diamine) (2LEB):
Schlenk tube was charged with N-phenyl-1,4-phenylenediamine
(483.6 mg, 2.63 mmol, 2.1 equiv), [Pd(dba)2] (43.1 mg, 0.08 mmol,
A
sulting deep green precipitate was collected by centrifugation and treated
with acetone (200 mL) and ammonium hydroxide (50 mL, 2m), with stir-
ring, for 30 min. After removal of acetone under reduced pressure, the
residue was filtered to afford the product, in the emeraldine base state
3EB, as a metallic-purple powder (240 mg, 98%). MALDI-MS: m/z (%):
AHCTUNGTRENNUNG
6 mol%), rac-BINAP (70.1 mg, 0.11 mmol, 9 mol%), 1,4-dibromoben-
zene (294.9 mg, 1.25 mmol, 1 equiv) and sodium tert-butoxide (360.4 mg,
3.75 mmol, 3 equiv) and placed under an atmosphere of nitrogen. Anhy-
drous toluene (40 mL) was added and the reaction mixture was heated
under stirring to 1108C. After 24 h, TLC analysis indicated complete con-
sumption of the starting dibromide. The reaction mixture was cooled to
room temperature and phenylhydrazine (675.9 mg, 6.25 mmol, 5 equiv)
was added (to prevent oxidation of the product). The solvent was then
removed under reduced pressure. The remaining solid was suspended in
a mixture of ethanol (100 mL) and deionised water (20 mL). After stir-
ring for 1 h, the precipitate was separated by centrifugation and washed
with ethanol until complete removal of any remaining starting dianiline
was achieved, as monitored by TLC analysis, to afford the product, in the
leucoemeraldine base state 2LEB, as a white powder (461 mg, 83%).
M.p. 250.1–250.98C; 1H NMR (500 MHz, [D6]DMSO, 258C): d=7.74 (s,
2H), 7.58 (s, 2H), 7.14 (dd, J=7.6 Hz, J=8.2 Hz, 4H), 6.99 (d, J=
8.9 Hz, 4H), 6.95 (s, 4H), 6.93 (d, J=8.9 Hz, 4H), 6.90 (d, J=7.6 Hz,
4H), 6.67 ppm (tt, J=7.3, 4J=1.1 Hz, 2H); 13C NMR (75 MHz,
[D6]DMSO, 258C) d=146.1, 139.5, 137.6, 135.2, 129.6, 121.3, 119.1, 118.4,
117.7, 115.1 ppm; IR (neat): n˜ =3390, 1597, 1511, 1492, 1444, 1300, 1217,
1106, 866, 813, 742, 691 cmÀ1; MALDI-MS: m/z (%): 442.2161; elemental
490.2144; elemental analysis calcd (%) for C34H26N4·ACTHUNGTRNEUNG(H2O)0.3 (496.0): C
81.44, H 5.47, N 11.17; found: C 81.31, H 5.84, N 11.01.
Computational Details
All calculations were performed by using Gaussian 03 (Revision C.02)[46]
and the popular B3LYP density functional[47] with the all-electron 6-31G*
basis set for all atoms (5d functions). Geometries were optimised in the
gas phase at this level of theory, whereas TD-DFT calculations[48] for the
first 20 singlet transitions were performed with a tetrahydrofuran (e=
7.58) continuum solvation field, by using the default polarisable continu-
um model PCM[49] as implemented in G03 with radii from the UFF force
field (explicit hydrogen atoms). To avoid problems with cavity generation
and slow convergence, solvated calculations were run without symmetry,
and some scrf solvation parameters were changed from their default set-
tings (ofac=0.8, rmin=0.5).
analysis calcd (%) for C30H26N4·ACTHUNTRGNEUGN(H2O)0.3 (447.9): C 80.44, H 5.99, N
12.51; found: C 80.28, H 6.21, N 12.24. A solution of ammonium persul-
fate (114.1 mg, 0.5 mmol, 1 equiv) in hydrochloric acid (20 mL, 2m) was
added dropwise to a solution of 2LEB (221.3 mg, 0.5 mmol, 1 equiv) in
DMF (50 mL) under stirring for 30 min. The resulting solution was
poured into deionised water (250 mL) and stirred for 15 min. The result-
ing deep green precipitate was collected by centrifugation and treated
with acetone (200 mL) and ammonium hydroxide (50 mL, 2m), with stir-
ring, for 30 min. After removal of acetone under reduced pressure, the
residue was filtered to afford the product, in the emeraldine base state
Acknowledgements
Z.S., C.F.J.F and D.M.L. thank the School of Chemistry, University of
Bristol for financial support. D.M.L. and N.F. thank the EPSRC for the
award of Advanced Research Fellowship [GR/S52100/02 (D.M.L.), EP/
E059376/1 (N.F.)]. Prof. A. Pron and Prof. A. J. Orr-Ewing are thanked
for helpful discussions.
2EB, as
a
purple powder (213 mg, 97%). MALDI-MS: m/z (%):
4 A(H2O)0.3 (445.9): C
440.1993; elemental analysis calcd (%) for C30H24N ·CTHNUGTRENNUNG
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80.80, H 5.56, N 12.56; found: C 80.92, H 6.09, N 12.52.
N1,N1’-(Naphthalene-1,4-diyl)-bis(N4-phenylbenzene-1,4-diamine)
(3LEB): A Schlenk tube was charged with N-phenyl-1,4-phenylenedia-
mine (483.6 mg, 2.63 mmol, 2.1 equiv), [PdACTHNUTRGNEUNG(dba)2] (43.1 mg, 0.08 mmol,
6 mol%), rac-BINAP (70.1 mg, 0.11 mmol, 9 mol%), 1,4-dibromonaph-
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was heated under stirring to 1108C. After 24 h, TLC analysis indicated
complete consumption of the starting dibromide. The reaction mixture
was cooled to room temperature and phenylhydrazine (675.9 mg,
6.25 mmol, 5 equiv) was added (to prevent oxidation of the product). The
solvent was then removed under reduced pressure. The remaining solid
was suspended in a mixture of iso-propanol (100 mL) and deionised
water (20 mL). After stirring for 1 h, the precipitate was separated by
centrifugation and washed with iso-propanol until complete removal of
any remaining starting dianiline was achieved, as monitored by TLC
analysis, to afford the product, in the leucoemeraldine base state 3LEB,
as a yellow-green powder (517 mg, 84%). M.p. 159.7–162.18C; 1H NMR
(500 MHz, [D6]DMSO, 258C): d=8.15 (AA’XX’, 2H), 7.75 (s, 2H), 7.74
(s, 2H), 7.49 (AA’XX’, 2H), 7.15 (s, 2H), 7.14 (dd, J=7.3, 4J=1.2 Hz,
4H), 6.98 (d, J=8.9 Hz, 4H), 6.90 (dd, J=7.6, 4J=1.2 Hz, 4H), 6.89 (d,
J=8.9 Hz, 4H), 6.67 ppm (tt, J=7.3, 4J=1.1 Hz, 2H); 13C NMR
(100 MHz, [D6]DMSO, 258C): d=146.1, 140.8, 135.4, 135.1, 129.6, 129.1,
125.7, 123.9, 121.2, 118.4, 118.4, 116.2, 115.1 ppm; IR (neat): n˜ =3391,
3364, 1596, 1508, 1480, 1454, 1424, 1399, 1378, 1295, 1259, 1233, 818, 754,
694 cmÀ1; MALDI-MS: m/z (%): 492.2312; elemental analysis calcd (%)
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Received: June 3, 2011
Published online: September 16, 2011
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