Dispirofluorene-indenofluorene derivatives as new building blocks for blue organic electroluminescent devices and electroactive polymers

Article abstract of DOI:10.1002/chem.200701036

A series of new dispiro[fluorenc-9′,6.9″.12-indeno[1,2b] fluorenes] (DSF-IFs) has been synthesised. These new building blocks for blue-light-emitting devices and electroactive polymers combine indenofluorene (IF) and spirobifluorene (SBF) properties. We report here our synthetic investigations towards these new structures and their thermal, structural, photophysical and electrochemical properties. These properties have been compared to those of IF and SBF. We also report the anodic oxidation of DSF-IFs that leads to the formation of non-soluble transparent three-dimensional polymers. The structural and electrochemical behaviour of these polymers has been studied. The first application of these building blocks as new blue-light-emitting materials in organic light-emitting diodes (OLED) is also reported.

Full text of DOI:10.1002/chem.200701036

FULL PAPER
DOI: 10.1002/chem.200701036
Dispirofluorene–Indenofluorene Derivatives as NewBuilding Blocks for
Blue Organic Electroluminescent Devices and Electroactive Polymers
Cyril Poriel,*[a] Jing-Jing Liang,[a] Jolle Rault-Berthelot,*[a] FrØdØric Barri›re,[a]
Nicolas Cocherel,[a] Alexandra M. Z. Slawin,[c] David Horhant,[a] Morgane Virboul,[a]
Gilles Alcaraz,[a, d] Nathalie Audebrand,[a] Laurence Vignau,*[b] Nolwenn Huby,[b]
Guillaume Wantz,[b] and Lionel Hirsch[b]
Abstract: A series of new dispiro[fluor-
ene-9’,6,9’’,12-indeno[1,2b]fluorenes]
(DSF-IFs) has been synthesised. These
new building blocks for blue-light-emit-
ting devices and electroactive polymers
combine indenofluorene (IF) and
electrochemical properties. These prop-
erties have been compared to those of
IF and SBF. We also report the anodic
oxidation of DSF-IFs that leads to the
formation of non-soluble transparent
three-dimensional polymers. The struc-
tural and electrochemical behaviour of
these polymers has been studied. The
first application of these building
blocks as new blue-light-emitting mate-
rials in organic light-emitting diodes
(OLED) is also reported.
AHCTREUNG
Keywords: cyclic voltammetry · dis-
pirofluorene–indenofluorene · fluo-
rescence · light-emitting diodes ·
polymers
ACHTREUNGspirobifluorene (SBF) properties. We
report here our synthetic investigations
towards these new structures and their
thermal, structural, photophysical and
Introduction
promising applications in flat-panel displays that could re-
place cathode-ray tubes or liquid-crystal displays.[1] The abil-
ity to mass produce thin, efficient, bright displays from or-
ganic polymers and small molecules that can supplant
modern liquid-crystal technology depends almost entirely on
the ability to create new materials that can undergo efficient
electroluminescence in a wide range of wavelengths. In
terms of revenue, 2005 and 2006 have been the break-
through years for the OLED technology in small- and
medium-size displays. However, its market penetration is ex-
pected to remain modest in 2007.[2] This mainly arises from
the rather short lifetime of organic materials despite the
recent years improvements. Indeed, a number of approaches
have been tried for producing full-colour displays, for exam-
ple, in fabricating red, green and blue pixels. However, the
shorter lifetime of the blue-emitting materials is still one the
main problem in OLED technology.[2] In this context, the
quest for a material, for example, polymers[3–17] or small
molecules,[18–46] with stable blue emission within an electrolu-
minescent device continues to hold the attention of number
of research groups. It is of course not an easy task to find a
small molecule that not only possesses a very large band
gap, a large quantum yield in the solid state and that is also
stable to the harsh OLED environment. Fluorene (F) deriv-
atives have been the most studied materials for blue emis-
During the last two decades, organic light-emitting diodes
(OLEDs) have attracted considerable interest owing to their
[a] Dr. C. Poriel, J.-J. Liang, Dr. J. Rault-Berthelot, Dr. F. Barri›re,
N. Cocherel, Dr. D. Horhant, M. Virboul, Dr. G. Alcaraz,
Dr. N. Audebrand
UMR CNRS 6226 “Sciences Chimiques de Rennes”
UniversitØ de Rennes 1, Bat 10C, Campus de Beaulieu
35042 Rennes cedex (France)
Fax : (+33)223-236732
E-mail: cyril.poriel@univ-rennes1.fr
joelle.rault-berthelot@univ-rennes1.fr
[b] Dr. L. Vignau, Dr. N. Huby, Dr. G. Wantz, Dr. L. Hirsch
UMR CNRS 5218 UniversitØ de Bordeaux
ENSCPB, 16 Avenue Pey-Berland, 33607 Pessac cedex (France)
Fax : (+33)540-006631
E-mail: l.vignau@enscpb.fr
[c] Prof. A. M. Z. Slawin
School of Chemistry, University of StAndrews
St Andrews, Fife KY16 9ST (UK)
[d] Dr. G. Alcaraz
Laboratoire de Chimie de Coordination (LCC)
UPR CNRS 8241, Equipe A. O. C., 205 route de Narbonne
31077 Toulouse Cedex 04 (France)
Supporting information for this article is available on the WWW
under http://www.chemeurj.org/ or from the author.
Chem. Eur. J. 2007, 13, 10055 – 10069
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10055

sion, and this has led to many publications and patents.
However, up to now, this has failed to produce an efficient,
cheap and robust blue-light emitters.[2,33] Since the electronic
and optical characteristics of the rigid F arise from its planar
biphenyl moieties, the structurally related compound, inden-
ofluorene (IF), with a planar, longer conjugated p-terphenyl
moieties has been suggested as a promising building block.
Indeed, its incorporation into polymer or oligomer back-
bones instead of F units has recently led to a strong en-
hancement of OLED properties.[3,6,25,47–50] Moreover, it is
known that spiro-linked molecules such as spirobifluorene
(SBF)[51] exhibit greater morphological stability and more
intense fluorescence, without any significant change in their
absorption and fluorescence spectra compared to the non-
spiro-linked parent compounds.[28] Another highly important
characteristic, which holds for most of SBF compounds, is
that they do not exhibit any emission bands beyond 500 nm.
Such parasite emission bands are usually found in polyfluor-
enes after annealing and are usually assigned to chain de-
Results and Discussion
Synthesis of DSF-IF derivatives
Retrosynthetic analysis: SBF can be considered as the join-
ing of two fluorene units through a shared spiro carbon.
First described by Clarkson and Gomberg in 1930,[54] it was
readily obtained in a two-step synthesis from 2-iodobiphenyl
and fluorenone through a metal–halogen exchange reac-
tion.[55–58] As DSF-IF can be considered as the joining of two
SBF moieties through a shared phenyl ring, it seemed rea-
sonable to adopt a similar strategy. Our retrosynthetic ap-
proach, based on a double lithium–halogen exchange reac-
tion, is presented in Scheme 1 and involved 2,2’’-di-
ene units.[16] We thus
fects arising to partial oxidation of fluorACHTREUNG
decided to desiGn a new family of chromophores that com-
bine the IF and F properties within a single molecule
through a spiro linkage. This new family of molecules has
been called dispirofluorene–indenofluorene (DSF-IF).[52]
The molecular design adopted in these molecules preserve
Scheme 1. Retrosynthetic analysis of DSF-IF.
AHCTREiUNG odo[1,1’;4’,1’’]terphenyl (2,2’’-DITP) as the key starting ma-
terial. It should be noted that dihalogenated-p-terphenyls
are not readily accessible and the target 2,2’’-diio-
do[1,1’;4’,1’’]terphenyl has only been reported once so far.[59]
Synthesis of 2,2’’-DITP: As it was crucial in our strategy to
develop an efficient synthesis of 2,2’’-DITP at the multigram
scale, two approaches were developed, both starting from
commercially available 2-iodoaniline (Scheme 2, routes 1
and 2). To avoid long and sophisticated multistep syntheses,
the first method we developed involved original arylboronic
acids bearing a triazene moiety in the ortho position readily
convertible into iodide (Scheme 2, route 1).[52,53] 2-Iodoani-
line (1) was diazotised by conventional means[60] and reacted
in situ with pyrrolidine under basic conditions. The resulting
o-iodoaryltriazene 2 was then converted into the corre-
sponding boronic acid 3 by a lithiation/borylation sequence
involving n-butyllithium and trimethylborate followed by
hydrolytic workup. Suzuki–Miyaura coupling[61] of o-triaze-
nylboronic acid 3 with p-diiodobenzene (conditions: [PdCl2-
the p conjugation of the IF, which plays a prominent role in
the electronic, electrochemical and photophysical proper-
ties; the introduction of the spiro configuration[51] gives the
molecules a highly rigid structure.
In this work, as a development to our preliminary note,[53]
we first report our synthetic investigations and a new
straightforward route to the diiodoterphenyl as key building
block in the synthesis of DSF-IFs. The thermal, structural,
photophysical and electrochemical properties of these mole-
cules will be discussed, together with their first application
in electroluminescent devices. In addition, these versatile
molecules also have the potential to form polymers by elec-
trochemical oxidation leading to transparent electroactive
deposits with interesting electrochromic properties. The
structural and electrochemical behaviours of these polymers
will be also developed.
ACHTREUNG
AHCTREUNG
AHCTREUNG
route 2), we decided to explore the protection of the amino
group of the starting material 1, to avoid any solubility and
reactivity issues in the subsequent Suzuki–Miyaura cross
coupling. The tert-Butylcarbamoyl (Boc) group was chosen
as a protecting group (it is one of the most useful known
protecting groups for amines).[62] The use of the non-nucleo-
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Electroluminescent Devices
FULL PAPER
is simple, can be performed
under mild conditions, is highly
adaptable, and is efficient for
the preparation of 2,2’’-DITP at
the multigram scale.
Synthesis of substituted 2,2’’-
DITPs—2,2’’-DITP
A
and
2,2’’-DITP(oct)2: Two other ter-
AHCTREUNG
phenyl derivatives substituted
with isopropyl (2,2’’-DITP-
AHCTREUNG
AHCTREUNG
tions of the biphenyl linkage
were prepared by following
route 1 as previously report-
ed.[53] However, as routes 1 and
2 involved the same para-alkyl-
substituted starting iodoaniline
Scheme 2. Synthesis of 2,2’’-DITP a) 1. NaNO2, AcOH/HCl, 08C; 2. C4H9N/KOH, H2O, 0 8C (95%); b) 1.
nBuLi, Et2O, ꢀ788C; 2. B(OMe)3, ꢀ788C!RT; 3. H2O/NH4Cl (77%); c) 1,4-C6H4I2, K2CO3, [PdCl2(MeCN)2],
tBu3P, dioxane/H2O, 80 8C (89%); d) MeI, 1208C (64%); e) 1. NaHMDS, THF, RT; 2. Boc2O (84%); f) 1,4-
C6H4(B(OH)2)2, [PdCl2(dppf)], Na2CO3, DMF/H2O, 90 8C (91%); g) TFA, CH2Cl2, 08C!RT (99%); h) 1.
NaNO2, H2O/HCl, 08C; 2. KI/H2O, 0 8C!608C (63%).
it was evident that route
2
might also be used (Scheme 3).
philic,
strong
base
sodium
hexamethyldisilazane
(NaHMDS)[63] prior the addition of the di-tert-butyldicar-
bonate (Boc2O) leads cleanly to the corresponding tert-
butyl-carbamoylated derivative 5. Reaction of 5 with 1,4-
phenylenebisboronic acid under Suzuki–Miyaura cross-cou-
pling conditions with [PdIICl
2ACHTRE(UNG dppf)]/CH2Cl2 (dppf=1,1’-
bis(diphenylphosphino)ferrocene) as the catalyst and
sodium carbonate as the base in a mixture of N,N-dimethyl-
formamide and water (3:1) led to the terphenyl 6 in good
yield.[64] Deprotection of the amino groups was performed
under acidic conditions and diamino derivative 7 was quan-
titatively obtained. Although the conversion of the 2-amino-
biphenyl in 2-iodobiphenyl is an easy and high-yielding reac-
tion,[65] it was more difficult in our case to perform the Sand-
meyer reaction with two free amine units instead of one.
Indeed, only a few examples are reported in the literature
for the concomitant conversion of two amino groups into
iodine through a double Sandmeyer reaction. These reac-
tions remain unclear and are difficult to reproduce; the re-
sulting diiodides are mostly obtained in low yields.[4,59,66–68]
The target 2,2’’-DITP was obtained in 63% yield by using a
tenfold excess of KI as described by Holmes and co-work-
ers.[9] In the solid state (Figure 1), the two iodophenyl rings
Scheme 3. Synthesis of substituted 2,2’’-DITP(iPr)2 and 2,2’’-DITP(oct)2.
Synthesis of DSF-IFs: With the three terphenyl 2,2’’-DITPs
in hand, the lithium–iodine exchange with n-butyllithium in
THF at low temperature followed by quenching with fluor-
AHCTREeUNG none gave the corresponding diols 8–10, which were finally
heated to reflux in acidic conditions to yield the correspond-
ing DSF-IFs (Scheme 4).[53]
The moderate yields obtained in the lithium–halogen ex-
change reaction may be partially explained by the systemat-
ic formation of a byproduct identified by single-crystal X-
ray diffraction as the monofluorenol 11 (Figure 2). This phe-
nomenon has already been observed by Huang and co-
workers in investigations of related compounds.[69] Depend-
ing on the conditions, this monocoupling derivative may be
formed in moderate (20%) to high yield (50%).
Physicochemical properties of DSF-IF derivatives: As DSF-
IFs combine 9,9’-SBF and IF frameworks, it was of great in-
terest to compare their physicochemical properties with
these two constituent building blocks. 9,9’-SBF was prepared
according to literature procedures.[65,70,71] IF was prepared in
a four step synthesis, by a modified Wang procedure (see
details in the Supporting Information).[72]
Figure 1. Crystal structure from single-crystal X-ray data of 2,2’’-DITP.
of 2,2’’-DITP lie on each side of the central phenyl ring (in
trans positions to one another) with angles of around 548.
This second sequence (Scheme 2, route 2) was satisfactori-
ly performed with an overall yield of 48%. This new route
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C. Poriel, J. Rault-Berthelot, L. Vignau et al.
Thermal properties of DSF-IF
derivatives: Thermal properties
were examined using thermog-
ravimetric (TGA) and differen-
tial scanning calorimetry (DSC)
analyses. The glass transition
(Tg), melting transition (Tm),
crystallisation (Tc) and decom-
position (Td) temperatures are
summarised in Table 1. The Td
Scheme 4. Synthesis of DSF-IFs.
Structural properties: The DSF-
IFs are dispiro molecules with a
linear antarafacial geometry.[69]
Single crystals of DSF-IFACTHRE(UNG iPr)2
were obtained by slow diffusion
of hexane into a solution of the
sample in CDCl3 and were ana-
lysed by X-ray diffraction in
order to elucidate its molecular
structure and bulk-packing
characteristics (Figures 3 and
4).
The angles between the plane
of indenofluorenyl moieties
(through the central phenyl
ring) and that of fluorenyl moi-
eties (through the central cyclo-
pentane ring) are 89.3 and 898,
which indicates that the fluo-
rene rings are almost perfectly
Figure 2. Crystal
structure
from single-crystal X-ray data
of the byproduct 11 (hydrogen
atoms have been omitted for
clarity).
orthogonally linked through the spiro carbon. It also indi-
cates that no additional deformation on these dispiro com-
pounds is observed when comparing with a simple spirobi-
fluorene X-ray structure.[57,73,74] The indenofluorenyl moiety
is almost perfectly flat with only two distortions on each
side, probably caused by the two isopropyl substituents.
As indicated in the crystal packing diagram of DSF-IF-
Figure 4. Crystal packing diagram of DSF-IF(iPr)2. Top: along the c
stacking axis. Bottom: along the a stacking axis. The co-crystallised sol-
vent (CDCl3) and the hydrogen atoms have been omitted for clarity.
ACHTREUNG(iPr)2 presented in Figure 4, the fluorene rings lie on each
side and in the top and bottom faces of the indenofluorene
plane efficiently suppressing any interchromophore interac-
tions. The plane-to-plane distance between two indenofluor-
ene moieties was calculated to be 5.43 Š. These structural
features may reduce the excimer formation in solid film as
already observed for similar structures.[75,76]
is defined as the temperature at which 5% loss occurs
during heating.[51] As shown by the TGA curves presented
in Figure 5a, the three DSF-IF were highly stable as they
only started to decompose around 3608C for DSF-IF and
DSF-IFACHTER(UNG oct)2 and around 3808C for DSF-IFACHRTE(UGN iPr)2. For com-
Figure 3. Crystal structure from single-crystal X-ray data of DSF-IF(iPr)2 (hydrogen atoms have been omitted for clarity).
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Electroluminescent Devices
FULL PAPER
Table 1. Thermal properties of the DSF-IFs, IF and SBF [8C].[a]
[b]
[c]
[e]
Td
Tg
Tc[d]
Tm
DSF-IF
DSF-IF(iPr)2
DSF-IF(oct)2
IF
355
382
366
200
204
n.o.
n.o.
88
n.d.
n.d.
n.o.
n.o.
156
n.d.
n.d.
n.o.
n.o.
237
n.o.
204
SBF
[a] n.d.: not determined, n.o.: not observed. [b] Td: decomposition tem-
perature (5% loss). [c] Tg: glass transition temperature, determined by
DSC in second heating cycle. [d] Tc: crystallisation transition tempera-
ture, determined by DSC in second heating cycle. [e] Tm: melting point,
determined by DSC in first heating cycle and melting point apparatus.
parison, SBF[51] and IF,[3,48,77] which have been widely used
as efficient building blocks within materials for OLEDs,
both start to decompose around 2008C. Thus, the higher
thermal stability of the new di-spiro DSF-IFs building
blocks appears to be promising for incorporation as central
core of polymers or oligomers. This stability may be due to
the presence of their rigid spiro-fused orthogonal bifluorene
linkages, as such spiro-configuration benefit has already
been described in the literature.[78–81]
Figure 5b–d show the DSC heating curves of the three
DSF-IFs. In the case of DSF-IFACTHRE(UNG oct)2 (Figure 5d) an endo-
thermic peak at 2378C corresponding to the melting transi-
tion (Tm) appeared during the first run. After cooling the
sample down, a glass transition temperature Tg around 888C
was observed during the second run. Further heating above
the Tg resulted in the appearance of an exothermic peak
(1568C) due to crystallisation and finally the melting transi-
tion again. A completely different behaviour was observed
in the cases of DSF-IF (Figure 5b) and DSF-IFCAHTRE(UNG iPr)2 (Fig-
ure 5c). From room temperature to 3008C no significant
phase transition (including Tg) was detected neither for
DSF-IF nor for DSF-IFACHTRE(UGN iPr)2. This phenomenon has been
already observed for similar bulky structures such as spiro-
fluorene–anthracene derivatives.[3] Such thermal behaviour
is of importance to improve the lifetime of OLEDs.[2] Thus,
in term of thermal properties, DSF-IF and DSF-IF
promising for practical use in OLEDs.
ACHTREU(NG iPr)2 are
Electrochemical properties of DSF-IF derivatives—anodic
behaviour: DSF-IF oxidation (Figure 6A and B) occurs
along two processes which have maxima at E1 (1.47 V) and
E2 (1.95 V). The E1 and E2 potential values are similar for
DSF-IFACHTREUNG(oct)2 and DSF-IFCAHTRE(UGN iPr)2 (Table 2). This shows that
the presence of alkyl groups on the indenofluorenyl moieties
of DSF-IFs has only a weak influence on the oxidation po-
tential. The donor inductive effect leads to an E1 shift of
ꢀ30 mV for octyl and ꢀ100 mV for isopropyl groups. For
the three DSF-IFs, the intensities of E1 and E2 waves are in
a ratio of 1:4 electrons. This may correspond to a first one-
electron oxidation at E1 followed by a four-electron oxida-
tion at E2. It should be noted that only the E1 wave is rever-
sible (Figure 6A). Figure 6C and E present the CVs record-
ed along IF and 9,9’-SBF oxidation in a similar potential
range. The anodic oxidation of IF and 9,9’-SBF occurs in
Figure 5. Thermal analysis of DSF-IFs. a) TGA curves for DSF-IF (g);
DSF-IF(iPr)2 (c) and DSF-IF(oct)2 (b). DSC curves, first run (b)
and second run (c) for b) DSF-IF; c) DSF-IF(iPr)2 and d) DSF-
IF(oct)2.
two waves with maxima E1 at 1.31 and 1.69 V and E2 at 1.81
and 1.86 V, respectively. For IF the potential shift between
E1 and E2 is around 0.5 V whereas for 9,9’-SBF the shift be-
tween the two peaks is only 0.17 V. The intensity ratio of E1
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C. Poriel, J. Rault-Berthelot, L. Vignau et al.
Electrochemical properties of DSF-IF derivatives—cathodic
behaviour: The cathodic behaviour of DSF-IFCAHTRE(UNG oct)2 is pre-
sented in Figure 7 together with the reduction of IF, F and
9,9’-SBF. In DMF, the DSF-IFs present a reversible reduc-
tion wave around ꢀ2.4 V (see E1 values reported in
Table 2). As expected, the inductive donor effect of the
alkyl groups in DSF-IFACTHER(NGU oct)2 and DSF-IFCAHRTE(UGN iPr)2 leads to a
shift of E1 towards more negative potentials relative to
DSF-IF.
Figure 6. Cyclic voltammetry in presence of A),B) DSF-IF (3”10ꢀ3 m);
C),D) IF (2”10ꢀ3 m); E),F), 9,9’-SBF (5”10ꢀ3 m) in CH2Cl2 (Bu4NPF6
0.2m) for DSF-IF and 9,9’-SBF and in CH3CN+CH2Cl2 (v/v) (Bu4NPF6
0.1m) for IF; working electrode: Pt disk diameter 1 mm; sweep-rate
100 mVsꢀ1. The potential limit was 0.4–2.4 V in A; 0.4–1.7 V in B; 0.2–
2.3 V in C; 0.3–1.5 V in D; 0.8–2.24 V in E; 0.37–1.7 V in F. The current
scale S is equal to 2 in D, 4 in B, 8 in A and C and 16 in E and F.
Table 2. Electrochemical data for DSF-IFs, IF, SBF and F.
Oxidation potential
[V] vs. SCE[a]
Reduction potential
[V] vs. SCE[a]
ox
red
E1
E2
E
E1
E
onset
onset
DSF-IF
1.47
1.44
1.37
1.31
1.69
1.62
1.95
1.99
1.95
1.81
1.86
–
1.36
1.30
1.26
1.22
1.54
1.48
ꢀ2.32
ꢀ2.48
ꢀ2.48
ꢀ2.55
ꢀ2.73
ꢀ2.87
ꢀ2.23
ꢀ2.35
ꢀ2.33
ꢀ2.41
ꢀ2.58
ꢀ2.71
DSF-IF(oct)2
DSF-IF(iPr)2
IF
SBF[82,83]
F[82,83]
[a] Obtained from CVs recorded in CH2Cl2 +Bu4NPF6 (0.2m) in oxida-
tion and in DMF+Bu4NPF6 (0.1m) in reduction.
Figure 7. Cyclic voltammetry of DSF-IF(oct)2 (5.78”10ꢀ4 m), IF (2.91”
10ꢀ3 m), F (6.32”10ꢀ3 m) and 9,9’-SBF (2.4”10ꢀ3 m) in DMF (Bu4NPF6
0.1m), working electrode: Pt disk diameter 1 mm, sweep-rate 100 mVsꢀ1
.
The potential limit was ꢀ0.58 V to ꢀ2.6 V for DSF-IF(oct)2; ꢀ2.72 V for
IF; ꢀ3.1 for F and ꢀ2.94 V for 9,9’-SBF. The current scale S is equal to
0.4 (c) and 0.8 (a) for DSF-IF(oct)2; 4 for IF and 9,9’-SBF and 8
for F.
and E2 waves is 1:3 for IF and 1:1 for 9,9’-SBF. Figure 6D
and F show that the wave E1 is reversible in the case of IF
and irreversible for 9,9’-SBF. As already observed for DSF-
IFs, iterative cycles in the E1 potential range of IF do not
show any modification of the CV nor of the electrode sur-
face. For 9,9’-SBF, iterative cycles leads to a slow electrode-
position process.[82,83] Finally, a comparison of the first oxida-
tion peak of IF with the one of DSF-IF shows that IF is
more easily oxidised than the indenofluorenyl unit in DSF-
IF. The positive shift of 0.16 V from IF to DSF-IF oxidation
may result from the electron-withdrawing effect of the
spiro-linked fluorenyl units rendering the indenofluorenyl
part of DSF-IF more difficult to oxidise. This might be seen
as a proof of the spiroconjugation already described from a
theoretical point of view in the literature.[84–91] All these ob-
servations lead us to conclude that the oxidation of DSF-IF
compounds occur first through a one-electron oxidation of
the indenofluorenyl part of the molecule (E1) followed by
the oxidation of the spiro-linked fluorenyl units (E2).
IF reduction (E1 =ꢀ2.55 V) is slightly more difficult than
that of DSF-IFs one. As already observed in the oxidation
process, the spiro-linked fluorenyl groups have an electron-
withdrawing effect on the indenofluorenyl part of the mole-
cules through the spiro carbon atoms. DSF-IFs exhibit a
second, quasi-reversible, reduction wave at more negative
potentials close to the F and 9,9’-SBF reduction potentials
(see the broken line of DSF-IFACHTER(UNG oct)2 reduction). This second
reduction wave leads to the reduction of the spiro-linked
fluorenyl units of the DSFIFs.
Theoretical calculations[92] are consistent with the electro-
chemical measurements pointing to an indeno-based pri-
mary oxidation and reduction in DSF-IFs, as shown by the
calculated nature of the frontier molecular orbitals of DSF-
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Electroluminescent Devices
FULL PAPER
IF in Figure 8. Indeed, we note the indenofluorenyl charac-
ter of the HOMO and LUMO and the spirofluorenyl char-
acter of the two pairs of quasi-degenerate LUMO+1,
LUMO+2 and HOMOꢀ1, HOMOꢀ2.
with only a small deviation (0.2 eV or less). These values are
also qualitatively consistent with the theoretical values ob-
tained with DFT calculations: although the HOMOs and es-
pecially the LUMOs energies are overestimated by the DFT
method (ca. 0.1–0.4 and 0.9–1 eV respectively), the experi-
mental trend in the frontier molecular orbital energy and as-
sociated band gap is well reproduced theoretically. The
DSF-IFs band gap appears to be wide (3.5/3.6 eV) with a
HOMO level around ꢀ5.7 eV and the LUMO level around
ꢀ2.1 eV. SBF and F have a larger band gap (larger than
4 eV) with a deeper HOMO and a higher LUMO. As a con-
sequence, the DSF-IFs compounds are interesting in this re-
spect, for electroluminescent devices, since their energy
level better fit the cathode and anode work function (see
Figure 13 in a later section).
Anodic electrodeposition—synthesis of electroactive poly-
mers: The first oxidation of DSF-IFs involves the indeno-
fluorenyl part of the molecules in a one-electron process
(vide supra), whereas the second oxidation occurs on the
two spiro-linked fluorenyl units. This second process occurs
in a potential range slightly more positive than the oxidation
potential of SBF and F oxidation (Table 2). These two com-
pounds are known to undergo electropolymerisation pro-
cesses[82,83,97–99] and DSF-IFs present the same behaviour.
Indeed, recurrent sweeps between 0.5 and E2 lead to gradual
modification of the CVs and to the modification of the elec-
trode surface by an insoluble transparent deposit. The de-
posits derived from DSF-IFs are three-dimensional com-
pounds with high electrochemical stability and interesting
electrochromic behaviour (see Figure 9).
Figure 8. Sketch of DSF-IF frontier molecular orbitals from Gaussian03
B3LYP/6–31G* calculations.[92–94]
Electrochemical and optical band gap: Following the work
of Jenekhe,[95] we did an experimental estimation of the
electron affinity (EA) or lowest unoccupied molecular orbi-
tal (LUMO) and of the ionisation potential (IP) or highest
occupied molecular orbital (HOMO) from the redox data
(Table 3). The LUMO level was calculated from: LUMO
Oxidation on transparent ITO-glass electrodes, allowed
the observation of the intense blue DSF-IF radical cations
generated at E1 and the pink radical cations generated at E2.
The observation of these colourations allows us to assert
that DSF-IF polymerisation occurs in good yield as one ob-
served no diffusion of coloured species in solution at the vi-
cinity of the electrode along the electrodeposition process.
Upon reduction at 0.5 V, the deposit became instantaneously
transparent.
red
(eV)=ꢀ[E
(vs SCE)+4.4] and the HOMO level from:
onset
ox
HOMO (eV)=ꢀ[E
(vs SCE)+4.4], based on an SCE
onset
energy level of 4.4 eV relative to the vacuum. The electro-
chemical gap DEel obtained as E ꢀE
(in eV) was also
ox
onset
red
onset
compared to the optical band gap calculated from the ab-
sorption edge of the UV/Vis absorption spectra using the
formula DEopt (eV)=hc/l.
The calculated band gaps from electrochemical data of
DSF-IFs are consistent with the measured optical band gaps
Coulometric measurements recorded along DSF-IF oxida-
tion (see details in the Support-
ing Information) show that the
Table 3. Molecular frontier orbital energy and HOMO/LUMO gaps of DSF-IFs, IF, SBF and F from electro-
chemical, optical and theoretical data.
p-doping level, called m in this
work, of the spiro-linked fluo-
rene units is between 0.7 and 1
electron. This value is equiva-
lent to the one of poly(9,9’-
SBF) but higher than the one
poly(F), that is, 0.3 electrons.
The three poly(DSF-IFs)
present a similar electrochemi-
cal behaviour in terms of onset
oxidation potential, potential
range of stability and p-doping
level. This shows that the sub-
stitution of the indenofluorenyl
HOMO
[eV][a]
LUMO
[eV][b]
HOMO
[eV][c]
LUMO
[eV][c]
DEel
DEopt
DEcalc
[eV][d]
[eV][e]
[eV][f]
from redox data
from calculations
DSF-IF
DSF-IF(oct)2
DSF-IF(iPr)2
IF
SBF
F
ꢀ5.76
ꢀ5.70
ꢀ5.66
ꢀ5.62
ꢀ5.94
ꢀ5.88
ꢀ2.17
ꢀ2.05
ꢀ2.07
ꢀ1.99
ꢀ1.82
ꢀ1.69
ꢀ5.41
–
ꢀ5.35
ꢀ5.43
ꢀ5.69
ꢀ5.81
ꢀ1.23
–
ꢀ1.19
ꢀ1.13
ꢀ0.84
ꢀ0.77
3.59
3.65
3.59
3.63
4.12
4.19
3.51
3.47
3.44
3.61
3.91
3.97
4.18
–
4.16
4.30
4.85
5.04
[a] Calculated from the onset oxidation potential. [b] Calculated from the onset reduction potential. [c] Gauss-
ian 03 B3LYP/6–31G* calculation:[92,94] a SCRF solvation model[96]was applied to the optimised geometry of
each model using dichloromethane and acetonitrile for the determination of the HOMO and LUMO energy
ox
onset
red
onset
respectively. [d] Calculated as DEel =E ꢀE . [e] Calculated from the absorption edge of the absorption
spectrum using DEopt =hc/l. [ f]DEcalc =jHOMOꢀLUMOj from theoretical calculations.
Chem. Eur. J. 2007, 13, 10055 – 10069
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C. Poriel, J. Rault-Berthelot, L. Vignau et al.
part of the molecule by an alkyl group does not influence
the p-doping process of the polyfluorenyl chains. Figure 9B–
D present the anodic behaviour of poly(DSF-IF) deposits.
units is between 1 and 1.7. The higher m’ values, relative to
the m values, are due to the higher potential reached along
the p-doping process. The m’ values show the high-energy
storage potential of the poly(DSF-IF).
Electrochromic properties of these polymers were ob-
served when switching their oxidation state from their neu-
tral to their p-doped level. The deposit changes colour from
transparent to purple with a short switching time and a good
stability of the switch measured along chronoamperometric
exploration. As the current keeps more than 95% of its ini-
tial value (after 1000 cycles), these polymers possess highly
interesting electrochromic properties.[100]
In terms of mechanism, and keeping in mind the electro-
AHCTREpUNG olymerisation process of F and 9,9’-SBF already described
in literature,[99] we expected that the polymerisation of DSF-
IF begins by the one-electron oxidation of the indenofluor-
enyl part of the molecule at E1, followed by the oxidation of
the spiro-linked fluorenyl units at E2. The cation radical of
these units are quickly involved in dimerisation processes.
Figure 9. Cyclic voltammetry in CH2Cl2 (Bu4NPF6 0.2m). A) DSF-IF (3”
10ꢀ3 m), ten sweeps between 0.5 and 2.22 V, working electrode: Pt disk di-
ameter 1 mm. B)–D) working electrode: Pt disk diameter 1 mm modified
by a deposit of poly(DSF-IF). For B, the electrodeposition was per-
formed along the CVs recorded in A; for C and D the electrodeposition
was performed by oxidation of a 3”10ꢀ3 m solution of DSF-IF in CH2Cl2
(Bu4NPF6 0.2m) at fixed potential: 1.9 V for C and 2.3 V for D with Qt,
the amount of charge for the formation, equal to 2”10ꢀ4 C. The potential
limit was 0.24 to 2.1 V in B and 0.5 to 2.1 V in C and D. The current
scale S is equal to 40 in A and B and to 16 in C and D. Sweep-rate:
ꢀ
The formation of the C C bond leads to new dihydrodimer–
dications that lose protons to form the final dimers. The
electrogenerated dimers are easier to oxidise than the start-
ing ACHTREmUNG onomer and give new dimer radical cations at the level
of the monomer oxidation potential. Then, these dimer radi-
cal cations will repeat the coupling step to form trimers, tet-
ramers and so forth. The reduction of the deposit at 0.5 V
lead to the charge neutralisation and the formation of the
neutral poly(DSF-IFs) (Scheme 5). This scheme, which is an
100 mVsꢀ1
.
In B, the deposit was obtained
along the CVs recorded Fig-
ure 9A. The onset oxidation po-
tential of the deposit is at
0.94 V, negatively shifted of
420 mV when compared to the
ox
onset
E
of DSF-IF signing an ex-
tension of the conjugation
length in the polymer. The de-
posit is electrochemically stable
(reversibility of the p-doping
process higher than 95%) in a
Scheme 5. Schematic representation of DSF-IFs electrodeposition.
rather large potential range (up
to more than 2 V). CVs report-
ed Figure 9C,D were recorded
for thin deposits of poly(DSF-IF) prepared at different po-
tentials (E=1.9 and 2.3 V, see the Supporting Information).
For the deposit prepared at the lowest potential (Figure 9C),
the first wave is associated with the oxidation of the indeno-
fluorenyl part of the polymer and is followed by three other
waves that might be attributed to the different oxidation
levels of the polyfluorenyl chains. For the deposit prepared
at higher potential (Figure 9D), the oxidation of the indeno-
fluorenyl part appears as a shoulder before the two oxida-
tion waves of the polyfluorenyl chains. Coulometric meas-
urements were also performed along poly(DSF-IF) p-doping
process between 0.5 and 2.1 V and show that the p-doping
level, called m’ in this work, of the spiro-linked fluorene
ideal representation of the polymer network, is however in-
formative as it shows that the aromatic polyfluorenyl chains
are well organised in parallel wires, with no evident inter-
chain communication between one another due to the in-
denofluorenyl groups.
Optical properties of DSF-IF derivatives
UV/Vis absorption spectra of the DSF-IFs: The UV/Vis ab-
sorption of DSF-IFs were first studied and compared with
the UV/Vis absorption of F, SBF and IF (Table 4, Figure 10,
top). For solubility purposes, these compounds were all stud-
ied in solution in CH2Cl2. F and SBF have similar absorption
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Electroluminescent Devices
FULL PAPER
Table 4. Photophysical properties
UV/Vis absorption spectra of
the polymers: Poly(DSF-IF)
spectrum exhibits a large ab-
sorption band between 300 and
350 nm due the more extended
conjugation than in the DSF-IF
monomer (Figure 10, bottom).
Such a large band was also ob-
served as the main absorption
band in poly(SBF).[82,83] We also
observed two sharp peaks at
lAbs [nm][a]
lExc [nm]
lEm [nm][a,b]
fsol [%][c]
DSF-IF
DSF-IF(iPr)2
DSF-IF(oct)2
IF
231, 254, 300, 311, 330, 337, 345
344
348
348
334
309
347, 356, 366
351, 359, 370
351, 359, 370
339, 347, 356
312, 323
62
66
66
61
20
231, 254, 300, 311, 333, 340, 348
228, 254, 301, 312, 334, 341, 349
228, 235, 289, 302, 319, 328, 334
229, 252, 297, 309
SBF
[a] Measured in dichloromethane. [b] Measured in cyclohexane for all compounds except for IF (decalin).
[c] The relative quantum yield was measured with reference to quinine sulphate in 1n H2SO4 (f=0.546).
312 and 346 nm. These absorptions fit well with those of
DSF-IF (Figure 10, top) and confirm the presence of DSF-
IF patterns in the polymeric network.
Emission spectra: The photoluminescence of DSF-IFs was
studied in cyclohexane and compared with SBF and IF in
order to evaluate the efficiency of these molecules as key
structures for further OLED applications (Figure 11 and
Figure 11. Emission spectra: 6”10ꢀ7 m solutions of DSF-IF (g), DSF-
IF(iPr)2 (d) DSF-IF(oct)2 (c) in cyclohexane, IF (a) in decalin.
Table 4). The central building block IF exhibits two main
emissions (lexc =334 nm) with maxima at 339 and 356 nm
(Figure 11). DSF-IF after excitation at 344 nm shows two
similar emissions at 347 and 366 nm. This 10 nm shift, al-
ready observed in the UV/Vis absorption (Figure 10, top)
may be attributed to the interaction between the F rings and
the central IF ring through the spiro-carbon. DSF-IF(iPr)2
and DSF-IF(oct)2 exhibit the same behaviour with emission
at 351 and 370 nm. The small Stokes shift observed for
DSF-IFs is consistent with the rigidity observed in the solid
state structure. fsol was determined by using standard proce-
dures with quinine sulphate dihydrate as reference.[72] IF ex-
hibits a quantum yield of 61%, slightly lower than the re-
sults reported by Wang.[72] The three DSF-IFs appear to be
highly efficiently fluorescent with high quantum yields of
around 65%.
Figure 10. Top: UV/Vis spectra of DSF-IF (a), F (g), SBF (c)
and IF (d) in solution in CH2Cl2 (10ꢀ5 m). Bottom: UV/Vis spectra of
DSF-IF in solution in CH2Cl2 (c), poly-DSF-IF deposited on an ITO
electrode plunged in CH2Cl2 (a).
spectra, displaying two sharp bands (290 and 301 for F, 297
and 309 nm for SBF) in addition to a broad one around
250–265 nm. The electronic spectra of DSF-IFs present ab-
sorption bands around 230, 254, 300, 310 as for F and SBF
and three additional bands around 330–335, 335–340 and
345–350 nm. For DSF-IF we precisely observed these three
bands at 330, 337 and 345 nm, which are in accordance with
the absorption bands of IF at 319, 328 and 334 nm,[72] but
bathochromically shifted by about 10 nm. This shift may be
assigned to the influence of the spiro-linked F rings on the
IF moieties. This effect may arise from the interactions be-
tween the two orthogonally linked p systems, that is, spiro-
conjugation, as already observed with CV.
Organic light-emitting diodes (OLEDs) using DSF-IFs as
the emitting layer: As the DSF-IF core may be interesting
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C. Poriel, J. Rault-Berthelot, L. Vignau et al.
as a new building block for electroluminescent devices, it
seemed of great interest to study its behaviour in OLEDs.
DSF-IF, DSF-IF(iPr)2 and DSF-IF(oct)2 exhibited similar
electroluminescence properties therefore only results on
DSF-IF(iPr)2 are presented. Basic OLED structures with
ITO as the anode, poly(3,4-ethylene dioxythiophene) doped
with poly(styrene sulfonate): PEDOT/PSS as the hole inject-
ing layer (HIL), DSF-IF(iPr)2 as the emitting layer (EML)
and Ca as the cathode were first fabricated and character-
ised (Figure 12a). The associated band energy diagram of
Figure 13. Electroluminescence spectrum of ITO/PEDOT/DSF-IF(iPr)2/
Ca device with the corresponding colour placed on the CIE 1964 chroma-
ticity diagram.
Figure 12. a),b) Structures of the investigated OLEDs. HIL, HTL and
EML correspond to the hole-injecting layer, the hole-transport layer and
the emitting layer, respectively. c),d) Schematic representation (before
contact) of the energetic structure associated with the investigated devi-
ces.
(Figure 14, bottom), which is promising for single-layer blue
OLEDs.
To improve the performances of the DSF-IF(iPr)2-based
OLEDs a hole transport layer (HTL), N,N’-diphenyl-N,N’-
bis(3-methylphenyl)-[1,1’-biphenyl]-4,4’-diamine (TPD) was
inserted between the anode and the emitting layer (Fig-
ure 12b and d).[101] The HOMO energy level of TPD lies be-
tween those of PEDOT and DSF-IF(iPr)2. This should result
in an easier hole injection into the DSF-IF(iPr)2 layer. How-
ever the comparison of the voltage–luminance characteris-
tics of the OLEDs with and without TPD (Figure 15) reveal
poorer performances of the TPD/DSF-IF(iPr)2-based device
both in terms of luminance and efficiency. The TPD-based
OLEDs reach a maximum efficiency of 0.4 CdAꢀ1 versus
0.9 CdAꢀ1 for the single-layer DSF-IF(iPr)2-only device
(vide supra). Furthermore the threshold voltage is slightly
increased. This can be due to the additional TPD layer,
which causes a global increase of the organic layer thickness
and results in a higher turn-on voltage. Moreover, the
LUMO level of TPD (ꢀ2.5 eV) lies below that of DSF-
IF(iPr)2 (ꢀ2.1 eV). As a consequence, when electrons are in-
jected into the DSF-IF(iPr)2 layer they are not confined
within that layer as there is no energetic barrier to cross at
the DSF-IF(iPr)2/TPD interface. The use of an electron
that structure is presented in Figure 12c. The LUMO of
DSF-IF(iPr)2 is very low (ꢀ2.1 eV), therefore a cathode
with a low work function needs to be used in order to
enable charge injection into the DSF-IF(iPr)2 layer. Calcium
seemed the most appropriate available metal for that pur-
pose with a work function of ꢀ2.9 eV. LiF/Al was also
tested but resulted in lower efficiency OLEDs.
The normalised electroluminescence spectrum recorded
for ITO/PEDOT/DSF-IF(iPr)2/Ca devices (Figure 13) exhib-
its two main emission peaks in the blue region at 399 and
416 nm. Two other contributions are found at 483 and
587 nm. The chromatic coordinates calculated from the elec-
troluminescence spectrum in the CIE 1964 chromaticity dia-
gram are (0.21; 0.16). These coordinates correspond to a
blue colour as can be seen on Figure 13.
Current-density–voltage–luminance characteristics of the
ITO/PEDOT/DSF-IF(iPr)2/Ca OLEDs are presented in
Figure 14 (top). The turn on voltage appears around 7 V.
The luminance of the device reaches 200 Cdmꢀ2 at 15 V and
for a current density of 22 mAcmꢀ2. In terms of efficiency,
the devices reach 0.9 CdAꢀ1 and 0.19 LmWꢀ1 at 200 Cdmꢀ2
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Electroluminescent Devices
FULL PAPER
blocking layer with a LUMO level significantly above
ꢀ2.1 eV would improve the confinement of electrons. Simi-
larly, holes are not confined within the DSFIF(iPr)2 layer.
Therefore, some charge carriers (electrons and holes) can
cross the emitting layer without radiative recombination.
This causes a decrease of efficiency.
To enhance injection electrons and block holes, Alq3 is
often inserted between the emitting layer and the cathode.
A ITO/PEDOT/TPD/DSF-IF(iPr)2/Alq3/Ca device has been
made but its electroluminescence spectra showed a contribu-
tion of Alq3. Indeed, the LUMO level of Alq3 (ꢀ3.1 eV)
lies below that of DSF-IF(iPr)2 (ꢀ2.1 eV) as well as below
the work-function of Ca (ꢀ2.9 eV). It means that electrons
are confined in the Alq3 layer instead of in the emitting
layer. Moreover, as the HOMO level of Alq3 (ꢀ5.6 eV) lies
slightly above that of DSF-IF(iPr)2 (ꢀ5.7 eV), no hole
blocking effect can be observed. This confirms that Alq3 is
not a suitable material to enhance both electron injection
and hole-blocking processes in those systems. Similarly, Wu
and co-workers did not observe any hole blocking in PPV
derivatives.[102] The use of a electron and/or hole-blocking
layers able to confine charge carriers in the DSF-IF(iPr)2
layer appears essential for multilayer devices.
Figure 14. Top: I-V-L characteristics. Bottom: luminous and energetic ef-
ficiencies of an ITO/PEDOT/DSF-IF(iPr)2 (30 nm)/Ca OLED.
Conclusion
In summary we have synthesised a series of new lumino-
phores combining one indenofluorenyl unit and two spiro-
linked fluorenyl units. These molecules, called DSF-IFs,
have been prepared by short efficient syntheses through a
key di-iodinated terphenyl intermediate (2,2’’-DITP). We
believe this intermediate might be of great interest for the
elaboration of other dispiro compounds for organic opto-
AHCTREeUNG lectronics. Their electrochemical behaviour has been stud-
ied and compared to their constituent building blocks, that
is, IF and SBF, to evaluate their HOMO/LUMO levels and
to understand their electronic properties. These results have
been confirmed by DFT calculations. The thermal and pho-
tophysical properties of DSF-IFs have been estimated and
appeared to be promising for OLED applications. These
versatile molecules may be also polymerised through the
fluorene cores, and lead to electroactive three-dimensional
materials with interesting optical and electrochromic proper-
ties. The preliminary studies carried out on DSF-IFs for the
OLED application led to interesting and promising proper-
ties for blue emitters. Indeed, DSF-IF(iPr)2 exhibits good
performances when used in a single-layer device. The effi-
ciencies could even be further increased with the use of
charge-blocking layers. Further optimisations of the devices
are currently in progress and will be reported in due course.
Experimental Section
Figure 15. Top: Luminance–voltage characteristics. Bottom: luminous ef-
ficiency of OLEDs with the following structures: ITO/PEDOT/DSF-
IF(iPr)2 (30 nm)/Ca and ITO/PEDOT/TPD (20 nm)DSF-IF(iPr)2
(30 nm)/Ca.
General: Commercially available reagents and solvents were used with-
out further purification other than those detailed below. Dichloro-
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10065

C. Poriel, J. Rault-Berthelot, L. Vignau et al.
A
was allowed to stir at room temperature for 4 h and was then cooled to
08C and carefully neutralised (pHꢁ7–8) with a saturated aqueous solu-
tion of sodium hydrogencarbonate. The resulting mixture was extracted
with dichloromethane (3”50 mL). The organic layer was dried (MgSO4)
and evaporated in vacuo to give compound 7 (1.1 g, 99%) as a colourless
solid. M.p. 2128C (dichloromethane/hexane); 1H NMR (300 MHz;
CDCl3): d=7.55 (s, 4H; ArH), 7.21–7.15 (m, 4H; ArH), 6.88–6.78 (m,
4H; ArH), 3.42 ppm (brs, 4H; NH); 13C NMR (75 MHz; CDCl3): d=
143.5 (C), 138.3 (C), 130.4 (CH), 129.4 (CH), 128.5 (CH), 137.1 (C),
118.7 (CH), 115.6 ppm (CH); HRMS (EI): m/z calcd for C18H16N2:
260.13135 [M]+; found: 260.1327.
hexane was distilled from sodium/benzophenone. Light petroleum refers
to the fraction with b.p. 40–608C.
Synthesis: Reactions were stirred magnetically, unless otherwise indicat-
ed. Analytical thin-layer chromatography was carried out using alumini-
um-backed plates coated with Merck Kieselgel 60 GF254 and visualised
under UV light (at 254 and/or 360 nm). Chromatography was carried out
with silica 60 A CC 40–63 mm (SDS). 1H and 13C NMR spectra were re-
corded on Bruker 200 and 300 MHz instruments (1H frequencies, corre-
sponding 13C frequencies are 50 and 75 MHz); chemical shifts were re-
corded in ppm and J values in Hz. In the 13C NMR spectra, signals corre-
sponding to CH, CH2 or Me groups, assigned from DEPT, are noted; all
others are C. The residual signals for the NMR solvents are: CDCl3;
7.26 ppm for the proton and 77.00 ppm for the carbon, CD3OD;
3.31 ppm for the proton and 49.05 ppm for the carbon, (CD3)2SO;
2.50 ppm for the proton and 39.43 ppm for the carbon. The following ab-
breviations have been used for the NMR assignment: s for singlet, d for
doublet, t for triplet, q for quintet and m for multiplet. “br” abbreviation
means that the signal is broad. High-resolution mass spectra were record-
ed at the CRMPO (Rennes). Substituted 2,2’’-DITPs and the correspond-
ing DSF-IFs were prepared according literature procedures.[53] 9,9’-SBF
was prepared according literature procedures.[65,70,71] IF was prepared in a
four-step synthesis by a modified Wang procedure (see details in Sup-
porting Information).[72]
2,2’’-Diiodo-[1,1’:4’,1’’]terphenyl (2,2’’-DITP): Sodium nitrite (1.8 g,
26.1 mmol) dissolved in water (72 mL) and cooled at 08C was added se-
quentially over 15 min to
a stirred solution of compound 7 (2.7 g,
10.4 mmol) suspended in water (135 mL) containing concentrated hydro-
chloric acid (38 mL) at 08C. The clear yellow solution was stirred for 1 h
at 08C (solution 1). In a separate vessel, a solution of potassium iodide
(17.4 g, 104.8 mmol) in water (190 mL) was cooled to 08C (solution 2).
Solution 1 was added to solution 2 over 10 min at 08C and the dark red
solution was stirred for a further 1 h at 08C. The ice bath was removed
and the mixture was stirred at room temperature for 2 h and then heated
to 608C for a further 2.5 h. The resulting mixture was stirred at room
temperature overnight and extracted with dichloromethane (5”100 mL).
The organic layers were washed with water, dried (MgSO4) and the sol-
vent was removed in vacuo. The red crude product was purified by
column chromatography on silica gel eluting first with light petroleum
and second with dichloromethane/light petroleum (1:9). After removal of
the solvents, crystallisation (light petroleum) afforded compound 2,2’’-
DITP (3.0 g, 63%) as a colourless solid. M.p. 1568C (light petroleum)
(lit. [59]; m.p. 158.98C (ethanol)); 1H NMR (300 MHz; CDCl3): d=7.98
(d, J=7.5 Hz, 2H; ArH), 7.42–7.39 (m, 8H; ArH), 7.08–7.03 ppm (m,
2H; ArH); 13C NMR (75 MHz; CDCl3): d=146.2 (C), 143.3 (C), 139.6
(2-Iodophenyl)carbamic acid tert-butyl ester (5): Sodium bis(trimethyl-
ACHTREUNGsilyl)amide (8.2 mL, 16.4 mmol) was added dropwise to a stirred solution
of 1 (1.8 g, 8.2 mmol) in dry THF (7.5 mL) at room temperature under
an argon atmosphere. After 25 min, di-tert-butyldicarbonate (1.9 g,
8.2 mmol) was added over 5 min by syringe. The reaction mixture was
stirred at room temperature for 2 h. Water (50 mL) was then added, and
the resulting mixture was extracted with dichloromethane (3”50 mL).
The organic layer was washed with a saturated aqueous solution of
sodium chloride (50 mL), dried (MgSO4), and evaporated in vacuo. Pu-
rification by column chromatography on silica gel eluting with ethyl ace-
tate/light petroleum (1:9) gave compound 5 (2.2 g, 84%) as a yellow/
(CH), 130.1 (CH), 128.84 (CH), 128.81 (CH), 128.1 (CH), 98.5 ppm
ACHTREUNG(C-
I); IR (KBr): n˜ =3060, 3038, 1929, 1911, 1800, 1583, 1555, 1458, 1424,
1391, 1250, 1005, 999 cmꢀ1
; HRMS (EI): m/z calcd for C18H12I2:
481.90285 [M]+; found: 481.9027; elemental analysis calcd (%) for
orange oil. H NMR (300 MHz; CDCl3): d=8.04 (dd, J=7.5, 1.5 Hz, 1H;
C18H12I2: C 44.8, H 2.5; found: C 44.4, H 2.5.
ArH), 7.74 (dd, J=7.5, 1.5 Hz, 1H; ArH), 7.31 (td, J=7.5, 1.5 Hz, 1H;
ArH), 6.82 (s, 1H; NH), 6.76 (td, J=7.5, 1.5 Hz, 1H; ArH), 1.54 ppm (s,
9H; Me); 13C NMR (75 MHz; CDCl3): d=152.5 (C=O), 138.8 (CH),
138.77 (C), 129.1 (CH), 124.6 (CH), 120.1 (CH), 88.7 (C-I), 81 (C),
28.3 ppm (CH3); HRMS (EI): m/z calcd for C11H14INO2: 319.00693 [M]+;
found: 319.0038.
9-[1,1’:4’,1’’]Terphenyl-2’’-yl-9H-fluoren-9-ol (11): Mono alcohol deriva-
tive 11 was obtained as a byproduct during the coupling of the 9-fluor-
AHCTREUNG
enone and 2,2’’-DITP. M.p. 123.58C; 1H NMR (300 MHz; CDCl3) d=
8.51 (d, J=7.5 Hz, 1H; ArH), 7.64–7.11 (m, 15H; ArH), 6.97 (d, J=
7.5 Hz, 1H; ArH), 6.81 (d, J=8.3 Hz, 2H; ArH), 6.06 (d, J=8.3 Hz, 2H;
ArH), 2.46 ppm (brs, 1H; OH); 13C NMR (75 MHz; CDCl3): d=150.6,
148.8, 141.5, 141.4, 141.3, 140.6, 140.3, 140.1, 139.6, 139.4, 137.8, 131.0,
129.2, 128.8, 128.7, 127.9, 127.2, 126.9, 126.3, 124.9, 124.4, 123.5, 120.0,
119.9, 82.41 ppm; HRMS (EI): m/z calcd for C31H22O: 410.16707 [M]+;
found: 410.1691.
2,2’’-Di-tert-butylbiscarbamate[1,1’:4’,1’’] terphenyl (6): Sodium carbonate
(3.3 g, 31.5 mmol) dissolved in water (7 mL) was added to a solution of
tert-butyl (2-iodophenyl)carbamate 5 (2.7 g, 8.5 mmol), 1,4-phenylene bis-
boronic acid (0.5 g, 3.2 mmol) and 1,1’-bis(diphenylphosphino)ferrocene
palladium(II)dichloride dichloromethane complex (0.1 g, 0.1 mmol) in
DMF (22 mL) at room temperature. The Schlenk tube was degassed, and
the mixture was allowed to stir at 908C for 12 h under an argon atmos-
phere. The reaction mixture was then quenched with water (100 mL) and
extracted with ethyl acetate (4”50 mL). The combined organic layers
were washed with a saturated aqueous solution of sodium hydrogencar-
bonate (50 mL), dried (MgSO4) and evaporated in vacuo. Purification by
column chromatography on silica gel eluting with ethyl acetate/light pe-
troleum (1:10) afforded compound 6 (1.3 g, 91%) as a colourless solid.
M.p. 140–1428C (acetonitrile); 1H NMR (300 MHz; CDCl3): d=8.10 (d,
J=8.3 Hz, 2H; ArH), 7.50 (s, 4H; ArH), 7.37 (td, J=8.3, 1.5 Hz, 2H;
ArH), 7.26 (dd, J=8.3, 1.5 Hz, 2H; ArH), 7.14 (td, J=8.3, 1.5 Hz, 2H;
ArH), 6.57 (s, 2H; NH), 1.48 ppm (s, 18H; Me); 13C NMR (75 MHz;
CDCl3): d=152.9 (C=O), 137.9 (C), 135.2 (C), 131 (C), 130.3 (CH), 129.9
(CH), 128.6 (CH), 123.4 (CH), 120.4 (CH), 80.6 (C), 28.3 ppm (Me); IR
(KBr): n˜ =3250 (NH), 3028, 2978, 2931, 2870, 2815, 2761, 2715, 2284,
2205, 1930, 1915, 1700 (CO), 1581, 1529, 1476, 1448, 1391, 1366, 1304,
1289, 1245, 1164, 1040, 1036, 1007 cmꢀ1; HRMS (EI): m/z calcd for
C28H32N2O4·CO2C4H8: 360.18378 [MꢀCO2C4H8]+; found: 360.1861.
Spectroscopic studies: UV/Vis spectra were recorded using a UV/Visible
spectrophotometer UVIKON XL Biotech. The optical band gap was cal-
culated from the absorption edge of the UV/Vis absorption spectra by
using the formula DEopt (eV)=hc/l in which l is the absorption edge (in
m). With h=6.6262”10ꢀ34Js (1 eV=1.602”10ꢀ19 J) and c=2.99”
108 msꢀ1, this equation may be simplified as: DEopt (eV)=1237.5/l (l in
nm). Photoluminescence spectra were recorded at room temperature
with a PTI spectrofluorimeter (PTI-814 PDS, MD 5020, LPS 220B) using
a xenon lamp. Quantum yields (fsol) were calculated relative to quinine
sulfate (fsol =0.546 in H2SO4 1n) using standard procedures.[72] fsol was
determined according to the following Equation (1), in which subscripts s
and r refer to the sample and reference, respectively. The integrated area
of the emission peak in arbitrary units is given as T, n is the refracting
index of the solvent (ns =1.42662 for cyclohexane and 1.469 for decalin;
nr =1.3325) and A is the absorbance. The emission spectra of DSF-IF,
DSF-IF(iPr)2, DSF-IF(oct)2, SBF and F were recorded in solution in cy-
clohexane and IF in solution in decalin. IR spectra were recorded on a
BIORAD IRFTS175C.
ꢀ
ꢁ
1,1’:4’,1’’-Terphenyl-2,2’’-diamine (7): Trifluoroacetic acid (17.0 mL,
229.0 mmol) was added to a solution of compound 6 (1.8 g, 3.9 mmol) in
dichloromethane (200 mL) at room temperature. The reaction mixture
2
Ts Ar ns
Tr As nr
ð1Þ
ꢀsol ¼ ꢀref  100 Â
10066
www.chemeurj.org
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2007, 13, 10055 – 10069

Electroluminescent Devices
FULL PAPER
Thermal analysis: Thermogravimetric analyses (TGA) were performed
with a Rigaku Thermoflex instrument under a nitrogen atmosphere.
TGA measurements were carried out between 40 and 6008C with a heat-
ing rate of 408Chꢀ1 for IF and SBF and 58Cminꢀ1 for DSF-IFs. DSC
measurements were carried out on a DSC 2010 TA instrument between
50 to 3508C at a rate of 108Cminꢀ1 for DSF-IFs and at a rate of
408Cminꢀ1 for SBF and IF. Melting points were determined by using an
electrothermal melting-point apparatus or by DSC.
through a shadow mask. The OLEDs were then stored and characterised
under inert atmosphere in a nitrogen glove box ([O2] and [H2O]<
1 ppm). Contacts on ITO and Ca were taken using a probe (Karl Suss
PM5). Current–voltage–luminance (I-V-L) curves were recorded using a
Keithley 4200 SCS. Light emission was collected using a calibrated pho-
todiode. Electroluminescence spectra were measured with a CCD spec-
trometer (Ocean Optics HR 2000).
Electrochemical studies: All electrochemical experiments were per-
formed using a Pt disk electrode (diameter 1 mm), the counter electrode
was a vitreous carbon rod and the reference electrode was a silver wire
in a solution of AgNO3 in CH3CN (0.1m). Ferrocene was added to the
electrolyte solution at the end of a series of experiments. The ferrocene/
ferrocenium (Fc/Fc+) couple served as internal standard and all reported
potentials were referenced to its reversible formal potential. All solvents
were purchased from SDS with less than 100 ppm of water and stored
under Argon. Activated Al2O3 was added in the electrolytic solution to
remove excess moisture. The three-electrode cell was connected to a
PAR Model 173 potentiostat monitored with a PAR Model 175 signal
generator and a PAR Model 179 signal coulometer. The cyclic voltamme-
try traces (CVs) were recorded on an XY SEFRAM-type TGM 164. For
a further comparison of the electrochemical and optical properties, all
potentials are referred to the SCE electrode that was calibrated at
ꢀ0.405 V versus Fc/Fc+ system in CH2Cl2. The peak potentials are given
with an error of ꢂ20 mV corresponding to 1 mm on the XY-Sefram re-
cording table. Chemicals for electrochemistry: acetonitrile with less than
5% of water (ref. SDS 00610S21) and dichloromethane with less than
100 ppm of water (ref. SDS 02910E21) were used without purification.
Tetrabutylammonium hexafluorophosphate from FLUKA was used with-
out purification. Aluminum oxide was obtained from Wolm, activated
by heating at 3008C under vacuum for 12 h and used at once under
argon pressure.
Acknowledgements
The authors would like to thank the CINES (Centre Informatique Na-
tional delꢁEnseignement SupØrieur, Montpellier) for awarding of comput-
ing time, the C.R.M.P.O (Centre RØgional de Mesure Physique delꢁOu-
est) for high-resolution mass measurements and for CHN analysis. We
also thank Dr. Muriel Hissler for helpful discussions and her help in
fluorACTHREeUNG scence measurements and Stephanie Fryars for technical assistance.
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X-ray structure determination: Crystal data and structure refinements for
2,2’DITP: C18H12I2, Mr 482.08, crystal size 0.1”0.1”0.1 mm, colourless
prism, orthorhombic, space group Pbca, T=93(2) K, a=11.2215(18), b=
8.0151(12), c=16.796(3) Š, V=1510.7(4) Š3, Z=4, 1calcd =2.120 Mgmꢀ3
,
m(MoKa)=4.150 mmꢀ1, 8697 measured reflections, 1315 independent re-
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served reflections [I>2s(I)]. Crystal data and structure refinements for
11: C31H22O, Mr 410.49, crystal size 0.1”0.1”0.01 mm, colourless platelet,
orthorhombic, space group Pbca, T=173(2) K, a=14.901(2), b=
8.2947(12), c=35.765(5) Š, V=4420.6(11) Š3, Z=8, 1calcd =1.234 Mgmꢀ3
,
m (CuKa)=0.562 mmꢀ1, 19222 measured reflections, 1707 independent re-
flections (Rint)=(0.1798), final R1=0.0780, wR2=0.1832 for 1233 ob-
served reflections [I>2s(I)]. Crystal data and structure refinements for
DSF-IF(iPr)2: C31H22O, Mr 410.49, crystal size 0.18”0.18”0.1 mm, colour-
less prism, monoclinic, space group P21, T=93(2) K, a=9.7998(7), b=
14.8143(11),
c=15.1839(12) Š,
V=2111.6(3) Š3,
Z=2,
1calcd =
1.380 Mgmꢀ3, m(MoKa)=0.444 mmꢀ1, 13187 measured reflections, 5575
independent reflections (Rint)=(0.0153), final R1=0.0236, wR2=0.0623
for 5556 observed reflections [I>2s(I)]. CCDC 653146, 653147 and
653148 contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cambridge Crystal-
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