2-Substituted vs 4-substituted-9,9'-spirobifluorene host materials for green and blue phosphorescent OLEDs: A structure-property relationship study

Article abstract of DOI:10.1016/j.tet.2014.05.081

Abstract We report a structure-property relationship study of four 9,9'-spirobifluorene (SBF) derivatives (4-5Pm-SBF, 2-5Pm-SBF, 4-Ph-SBF and 2-Ph-SBF), substituted with either phenyl or pyrimidine at the C2 or C4 position of the SBF core. Structural, thermal, electrochemical and photophysical properties have been examined and correlated to theoretical calculations in order to study the influence of the nature and the position of the substituent. The emission properties of 4- versus 2-substituted SBFs are noticeably different highlighting, in the excited state, the remarkable effect of substitution in ortho position of SBF. All compounds have been used as host material for green dopant in PhOLEDs with very high performances (2-5Pm-SBF: CE58 cd/A, PE35 lm/W, EQE14%). More importantly, the two 4-substituted SBFs have been used as host materials in blue PhOLEDs, displaying high performance and a decrease of VnfTH/inf for 4-5Pm-SBF due to the incorporation of the electron-withdrawing pyrimidine.

Full text of DOI:10.1016/j.tet.2014.05.081

Accepted Manuscript
2-substituted vs 4-substituted-9,9'-spirobifluorene host materials for green and blue
phosphorescent OLEDs: A Structure-Property Relationship Study
Sébastien Thiery , Céline Declairieux , Denis Tondelier , Gijun Seo , Bernard Geffroy ,
Olivier Jeannin , Rémi Métivier , Joëlle Rault-Berthelot , Cyril Poriel
PII:
S0040-4020(14)00787-X
10.1016/j.tet.2014.05.081
TET 25630
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 29 March 2014
Revised Date: 20 May 2014
Accepted Date: 21 May 2014
Please cite this article as: Thiery S, Declairieux C, Tondelier D, Seo G, Geffroy B, Jeannin O, Métivier
R, Rault-Berthelot J, Poriel C, 2-substituted vs 4-substituted-9,9'-spirobifluorene host materials for green
and blue phosphorescent OLEDs: A Structure-Property Relationship Study, Tetrahedron (2014), doi:
10.1016/j.tet.2014.05.081.
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ACCEPTED MANUSCRIPT
2
-substituted vs 4-substituted-9,9'-spirobifluorene host materials
for green and blue phosphorescent OLEDs: A Structure-Property Relationship Study
a
c
c
c
c,d
Sébastien Thiery, Céline Declairieux, Denis Tondelier, Gijun Seo, Bernard Geffroy,
a
b
*a
*a
Olivier Jeannin, Rémi Métivier, Joëlle Rault-Berthelot, Cyril Poriel
a. Université de Rennes 1-UMR CNRS 6226, "Institut des Sciences Chimiques de Rennes" MaCSE group. Bat
0C, Campus de Beaulieu, 35042 Rennes, France
1
b. PPSM, Institut d'Alembert, ENS Cachan, UMR CNRS 8531, 61 Avenue du Président Wilson, 94235 Cachan,
France
c. LPICM, Ecole Polytechnique, UMR CNRS 7647, Route de Saclay, 91128, Palaiseau
d. LICSEN, CEA Saclay, IRAMIS/NIMBE, 91191 Gif sur Yvette
Abstract
We report a structure-property relationship study of four 9,9'-spirobifluorene (SBF) derivatives (4-
5Pm-SBF, 2-5Pm-SBF, 4-Ph-SBF and 2-Ph-SBF), substituted with either phenyl or pyrimidine at
the C2 or C4 position of the SBF core. Structural, thermal, electrochemical and photophysical
properties have been examined and correlated to theoretical calculations in order to study the
influence of the nature and the position of the substituent. The emission properties of 4- vs 2-
substituted SBFs are noticeably different highlighting, in the excited state, the remarkable effect of
substitution in ortho position of SBF. All compounds have been used as host material for green
dopant in PhOLEDs with very high performances (2-5Pm-SBF: CE > 58 cd/A, PE > 35 lm/W, EQE
>
14 %). More importantly, the two 4-substituted SBFs have been used as host materials in blue
PhOLEDs, displaying high performance and a decrease of VTH for 4-5Pm-SBF due to the
incorporation of the electron-withdrawing pyrimidine.
Grpahical Abstract
N
N
N
N
Introduction
-
1 -

ACCEPTED MANUSCRIPT
In the past twenty years, the use of organic semiconducting materials for applications in “plastic
1
2,3
electronics”, such as field effect transistors (FETs), organic light emitting diodes (OLEDs), and organic
4,5
6-8
photovoltaic (OPVs), has gained fantastic interest. Particularly, OLEDs have attracted much scientific
and commercial interest because of their potential applications in organic flat-panel displays and solid-state
lighting. However, as full colour displays and white lighting require materials that emit over a broad range
of colour, the weak link of the technology remains the lack of efficient and stable blue light emitters.
Moreover, due to the triplet exciton/singlet exciton ratio of 3/1, the maximum achievable emission
quantum yield is limited to 25% for fluorescent emitters. Among the significant progress recently made,
phosphorescent organic emitting-diodes (PHOLEDs) which use heavy-metal complexes as emitters to
harvest both singlet and triplet excitons are considered as the most promising technology because,
theoretically the internal quantum efficiencies of these devices may reach 100 %. The fabrication of blue
phosphorescent devices is however still challenging because the prerequisites for designing organic host
materials are (i) a high triplet energy level (higher than E of the blue dopant), (ii) a high glass-transition
T
temperature (Tg) and (iii) matching HOMO/LUMO levels for hole and electron injection/transport. In this
context, most of host materials for blue PhOLEDs are based on carbazole, triphenylamines, phosphine
9-11
oxides or fluorene derivatives.
However, novel host materials with good thermal and morphological
stabilities to afford blue PhOLEDs with high efficiencies, stability and colour purity are still desirable. In this
context, 9,9'-spirobifluorene (SBF) based semiconductors have experienced a fantastic development during
1
2,13
14-17
the last thirty years, due to their use as chiral ligand,
as electropolymerizable building block,
as solid
18
19
20
state laser , in third-order nonlinear optics, in Metal Organic Frameworks but more importantly in
organic electronics, leading to fantastic breakthroughs in the field.
2
1-23
Thus, numbers of electron donating
and /or withdrawing functionalities have been introduced on the SBF scaffold in order to make the
21
electronic properties of the resulting dyes fitting with an application. For that purpose, electron-deficient
2
4
25
26
27
28
heterocycles such as 1,3,4-oxadiazoles, pyridine , quinoline, quinoxaline and pyridopyrazine
connected at C2 and C7 positions of SBF were reported in literature. Among those electron-deficient
heterocycles, only few examples describing the fluorene substitution by pyrimidine units (see chart 1) have
been reported to date. However, pyrimidine possesses many striking characteristics, as it is notably more
29
electron-deficient than pyridine, which has been widely studied. Thus Bryce's group has for example
30
demonstrated in 2003, that fluorene fluorophore F3 emits a pure blue emission in solution and thin films.
However the electroluminescent spectrum of F3-based OLED mainly presents the known parasite green
3
1-33
emission of dialkylfluorenes.
A similar green emission is observed on PL spectrum of the liquid crystal
34
F4. The introduction of a 9,9' Spirobifluorene unit (SBF) in TBPSF leads to improve the thermal, optical and
electronic properties and this new blue emitter has been used as host for fluorescent blue, red or green
organic dopants leading to efficient devices.
35,36
Chart 1. Literature report of fluorene substitution by pyrimidine units
-
2 -

ACCEPTED MANUSCRIPT
However, if 2-substituted SBFs have been impressively investigated for the last decades, it is far to be the
case of the three other positional isomers, that are 1-, 3- or 4-substituted SBFs. Thus, for example, 4-
37-42
substituted SBFs have only been reported in a few instances
but appears as a very appealing scaffold to
design rigid SBF-based organic host materials for PhOLEDs. In our quest for robust derivatives with high E
which can be used as host materials for green and blue phosphorescent dyes, we wish to report herein
T
43
the synthesis and the detailed study of the properties of two pyrimidine-substituted SBFs (4-5Pm-SBF and
2
-5Pm-SBF, see chart 2). Moreover, in order to give a detailed description of the influence of the pyrimidine
unit, the 2- and 4-phenyl-substituted SBFs (2-Ph-SBF and 4-Ph-SBF) have been also studied in detail (4-Ph-
44
SBF has been previously reported). Thus, after synthetic considerations, the electrochemical, thermal and
photo-physical properties will be discussed and coupled to a theoretical approach. The influence of the
nature of the substituent (pyrimidine vs phenyl) and of its position (2- vs 4-) will be notably carefully
investigated. Finally, the incorporation of these four semiconductors as host material for green and blue
PhOLEDs will be presented.
Chart 2. Molecules studied in this work
Results and discussion
The first step towards the synthesis of 4- and 2-substituted SBF was the access of the two key
platforms 4- and 2-bromo-9,9'-spirobifluorene (see structures of 4-Br-SBF and 2-Br-SBF in scheme 1). As
37,44
reported previously,
4-Br-SBF was synthesized by the mono lithium-halogen exchange of 2,2'-
dibromobiphenyl followed by the trapping of the corresponding lithiated intermediate with 9-fluorenone.
The intramolecular electrophilic ring closure of the corresponding fluorenol (not isolated), in acidic media
(
AcOH/HCl), further provides 4-Br-SBF with 75 % yield (2 steps). Finally, a subsequent Suzuki cross-coupling
between 4-Br-SBF and either 5-pyrimidine boronic acid or phenylboronic acid was performed
Pd(dppf)Cl /K CO /DMF) providing 4-5Pm-SBF or 4-Ph-SBF with significant good yields (94% and 91%
(
2
2
3
respectively). Similarly, access to 2-Br-SBF was performed by the lithium-halogen exchange of 2-
bromobiphenyl followed by the trapping of the corresponding lithiated intermediate with 2-bromo-9-
45
fluorenone. The intramolecular electrophilic ring closure of the corresponding fluorenol, in acidic media
AcOH/HCl), further provides 2-Br-SBF with 67% yield (2 steps), involved in a final Suzuki cross-coupling
(
with either 5-pyrimidine boronic acid or phenylboronic acid to lead the corresponding 2-5Pm-SBF or 2-Ph-
SBF with high yields (77% and 78% respectively).
-
3 -

ACCEPTED MANUSCRIPT
B(OH)2
(91%)
4-Ph-SBF
DMF 150°C
K2CO3 Pd(dppf)Cl2
N
Br
N
B(OH)2
4
-Br-SBF
(75%)
N
N
-5Pm-SBF
4
(94%)
B(OH)2
2
-Ph-SBF
(
DMF (150°C) or
Xylenes (135°C)
7
8
%
)
Br
K2CO3 Pd(dppf)Cl2
N
N
2-Br-SBF
N
B(OH)2
(67%)
N
2-5Pm-SBF
(77%)
Scheme 1. Synthesis of the four dyes, 4-Ph-SBF, 4-5Pm-SBF, 2-Ph-SBF and 2-5Pm-SBF
Structural Properties
Molecular structure of the four dyes was further confirmed by X-ray crystallography. The X-ray diffraction
data of single crystals of 2-Ph-SBF (Figure 1, left) and 4-Ph-SBF (Figure 1, right) reveal an asymmetric unit
44
containing two independent molecules 1 and 2. As previously reported, in 4-Ph-SBF, the angle between
the mean plane of the pendant phenyl ring and that of its attached phenyl ring of the fluorene is as large as
5
1.2° in molecule 1 and 56.6° in molecule 2.
In 2-Ph-SBF, the same angle appears to be noticeably smaller, ie 37.4° for molecule 1. Similar values have
46,47
been reported in literature for 2-substituted SBF (ca 30°)
and seems hence to be a characteristic of such
family of 2-substituted SBFs. This difference between the angle observed in 2-Ph-SBF and 4-Ph-SBF may be
at the origin of the restricted π-conjugation of the latter and will have remarkable consequences on the
electronic properties (see below). In addition, we note that the fluorene unit bearing the pendant phenyl
ring in the molecule 1 of 2-Ph-SBF is folded with a deformation of ca 7.1° between the mean planes of each
phenyl unit. However, in the case of molecule 2 of 2-Ph-SBF, we surprisingly note that the pendant phenyl
unit is almost coplanar with the fluorene unit with an angle between the mean plane of the pendant phenyl
ring and that of its attached phenyl ring of the fluorene unit as low as 4.6°. In addition and oppositely to
what was observed for molecule 1, the fluorene bearing the phenyl unit is now almost perfectly flat with
only a small deformation of 1.5° (7.1° measured in molecule 1, see above). Such structural feature appears
highly surprising and is assigned to the packing of the molecule. Indeed, numbers of short CH and CC
distances are detected in the packing diagram of 2-Ph-SBF and especially two short intermolecular CH
distances of ca 2.8 Å between the pendant phenyl ring and its close neighbours (see SI).
-
4 -

ACCEPTED MANUSCRIPT
2
-Ph-SBF
4-Ph-SBF
Molecule 1
Molecule 2
Molecule 1
Molecule 2
Figure 1. Molecular structure of the two molecules (molecule 1 and molecule 2) contained in 2-Ph-SBF (left) and 4-Ph-
44
SBF (right) single crystal asymmetric unit.
However, in the case pyrimidine based SBFs, ie 4-5Pm-SBF and 2-5Pm-SBF, we only managed to obtain
single crystals of 2-5Pm-SBF good enough for X-Ray diffraction and hence the direct comparison is not
possible. However, we are convinced that similar structural features structures occur in both 4-5Pm-SBF
and 2-5Pm-SBF. Indeed, in 2-5Pm-SBF, the angle between the mean plane of the pyrimidine plane and that
of its attached phenyl ring is recorded at 23.7° (See SI), lower than that recorded for its phenyl analogue 2-
Ph-SBF (37.4°).
Electrochemical Properties
Electrochemical properties have been investigated by cyclic voltammetry (CV) in CH Cl in oxidation
2
2
and reduction and are summarized in table 1. Pyrimidine-substituted SBF were studied in absence of Al O
2
3
as their rapid adsorption on Al O leads to a strong decrease of the intensity of the oxidation and reduction
2
3
waves.
All compounds present at least two successive oxidation waves (with maxima E and E ) before 2.2 V (figure
). Except for 2-5Pm-SBF, the oxidation is accompanied by an electropolymerization process signed on the
1
2
2
present CVs by a reduction wave at the back sweep. This polymerization process is more clearly observed
along recurrent sweeps (see CVs in SI). Compared one to another, polymerization process is highly efficient
for 2-Ph-SBF and 4-Ph-SBF and largely less efficient for 4-5Pm-SBF. Moreover, the electroactivity of the
corresponding polymers, ie Poly(2-Ph-SBF) and Poly(4-Ph-SBF) are similar with onset oxidation potentials
at ca 1.1 V vs SCE (polymers HOMO: -5.5 eV). In addition, the p-doping process reversibility of the two
polymers occurs in a large potential range between 1 and 2 V. Oppositely, Poly(4-5Pm-SBF) presents a p-
-
5 -

ACCEPTED MANUSCRIPT
doping process only occurring since 1.35 V (polymer HOMO : -5.75 eV) and appearing less intense and
reversible.
Table1. Selected electrochemical, theoretical and optical data
Electrochemical studies
Theoretical calculations
Optical
studies
1
2
b
c
el
d
theo
opt
e
E , E oxidation
peaks/
E
Reduction peak/
HOMO
(eV)
LUMO
(eV)
∆E (eV)
HOMO LUMO
∆E (eV) / E
T
∆E (eV)
red
a
E
onset (V)
(eV)
-6.16
-5.97
-6.13
-5.87
(eV)
-1.65
-1.27
-1.85
ox
a
onset (V)
4
4
2
2
-5Pm-SBF
-Ph-SBF
1.82, 2.23/
.57
1.68, 1.88/
.55
1.75, 2.00/
.56
1.60, 1.93/
.48
+ Bu NPF
-2.38/
-2.17
-2.75/
-2.45
-2.33/
-2.10
-5.97
-5.95
-5.96
-5.88
-2.23
-1.95
-2.30
-2.10
3.74
4.00
3.66
3.78
4.51/2.80
4.70/2.82
4.29/2.63
4.39/2.62
3.72
3.82
3.66
3.70
1
1
-5Pm-SBF
-Ph-SBF
1
No peak in CH
-2.3
2 2
Cl /
-1.48
1
ox
a. Measured in CH
2
Cl
2
4
6
0.2 M at 100 mV/s, b. Calculated from the onset oxidation potential Eonset , c. Calculated from the onset reduction
red
el
potential Eonset , d: ∆E = |HOMO-LUMO|, e: Calculated from the onset of the absorption spectrum in solution in cyclohexane (see spectra figure 5
left) by using ∆E = hc/λ (∆E (eV)=1237.5/λ(nm).
opt
opt
2
E
40
30
20
10
0
4 5- Pm-S BF
2 5- Pm-S BF
2
E
3
0
E
1
25
E
1
2
0
5
1
10
5
0
-
10
0
-5
.0
0.5
1.0
1.5
2.0
2.5
0.5
1.0
1.5
2.0
2.5
E(V) vs SCE
E(V) vs SCE
4-Ph-SBF
40
30
20
8
6
4
2
0
2E
2
-Ph-SBF
2
E
0
0
0
0
E
1
E
1
10
0
-
10
20
-
20
40
-
-
0.0
0.5
1.0
1.5
2.0
2.5
0.5
1.0
1.5
2.0
2.5
E(V) vs SCE
E(V) vs ECS
-
3
-3
-3
Figure 2. Cyclic voltammetry of 4-5Pm-SBF (5 × 10 M ) and 2-5Pm-SBF (2 × 10 M) (top) and of 4-Ph-SBF (5 × 10 M)
-
3
-1
and 2-Ph-SBF (5 10 M) (bottom) solutions in CH Cl + Bu NPF 0.2 M, sweep-rate 100 mV.s . Platinum disk (Ø: 1mm)
2
2
4
6
working electrode.
48
From the onset oxidation of the CVs, we determined the HOMO levels of 4-5Pm-SBF at -6.0 V
49
close to that of 4-Ph-SBF (HOMO: -5.95 eV) and of its constituting building block SBF (HOMO: -5.94 eV)
indicating that the substitution in ortho position leads to a π-conjugation interruption surely due to the
large angle observed in the X-ray structure between the pendant unit and the fluorene core. In addition, we
note that the substitution by a 5-pyrimidine or a phenyl group have both very weak effects on the HOMO
level of the 4-substituted-SBFs. Indeed, as seen in theoretical calculations, the pendant substituent is not
involved in the HOMO character of 4-substituted SBFs (Figure 3) being hence in accordance with our
electrochemical conclusions. On the other hand, HOMO levels of 2-5Pm-SBF and 2-Ph-SBF calculated from
their respective onset oxidation potentials are estimated at -5.96 eV and -5.88 eV. The highest HOMO of 2-
-
6 -

ACCEPTED MANUSCRIPT
Ph-SBF compared to that of SBF signs an extension of the π-conjugation between the fluorene and the
phenyl group in 2-Ph-SBF. This effect is however neutralized in 2-5Pm-SBF by the electron withdrawing
effect of the pyrimidine group leading to an HOMO level identical to that of SBF. Thus, in the case of 2-Ph-
SBF, the substituent is involved in the character of the HOMO (Figure 3), which is not the case for the
HOMO of 2-5Pm-SBF. Cathodic exploration in dichloromethane, reveal that all compounds are reduced at
negative potential in a non-reversible process close to the electrolytic medium reduction (see CVs in SI).
However, when studied in THF, allowing reaching a more cathodic potential range, one or two reduction
waves are observed before the reduction of the electrolytic solution (see CVs in SI). LUMO levels were
determined from the onset reduction potential in CH Cl at -2.23 ; -1.95 ; -2.30 and -2.10 eV for 4-5Pm-SBF ;
2
2
4
-Ph-SBF : 2-5Pm-SBF and 2-Ph-SBF respectively (these values are close to that measured in THF, see in SI).
The lowest LUMO level is recorded for 2-5Pm-SBF as low as -2.3 eV, 0.41 eV lower than the LUMO of SBF (-
4
4
1
.89 eV) signing the double effect of the extension of conjugation due to the substitution at the C2 of SBF
and to the electron-withdrawing effect of the electron-deficient pyrimidinium group. Thus, we note that
the pyrimidine unit is strongly involved in the LUMO character of 2-5Pm-SBF and even more strongly
involved in the case of 4-5Pm-SBF (Figure 3). Thus, the LUMO level of 4-5Pm-SBF (-2.23 eV) is shifted by
0
.07 eV compared to that of 2-5Pm-SBF. In addition, the LUMO level of 4-5Pm-SBF is shifted by 0.27 eV
compared to that of SBF, (-1.96 eV) due to the effect of the incorporation of the electron-withdrawing
pyrimidine fragment. Finally, due to the absence of π-conjugation between the phenyl and the C4-
44
fluorene, LUMO levels of 4-Ph-SBF is the highest of the present series, ie -1.96 eV, and very close to that
of SBF.
el
Finally, HOMO-LUMO gaps (∆E ) extend between 3.66 eV for 2-5Pm-SBF to 4.00 eV for 4-Ph-SBF. This trend
in HOMO-LUMO gap changes is well reproduced by theoretical calculations (figure 3) with nevertheless a
deviation of ca 0.7 eV.
Figure 3. Calculated frontier molecular orbitals by DFT of 4-5Pm-SBF ; 4-Ph-SBF : 2-5Pm-SBF and 2-Ph-SBF, after
geometry optimization at the B3LYP/6-311G+(d,p) level of theory, shown with an isovalue of 0.04 .
Geometry optimization of the four substituted dyes in the singlet and triplet states was performed using
Density Functional Theory (DFT) at the Gaussian09 B3LYP/6-311+G(d,p) level of theory. There is a clear
resemblance between the HOMO values determined by CVs and by theoretical calculations. 2-Ph-SBF is the
easiest oxidizable molecule due to the extension of conjugation between the phenyl and the 2-substituted
fluorene unit and its HOMO presents a phenyl-fluorene character, perfectly translating this extension of
conjugation. 4-5Pm-SBF is the more difficult oxidizible molecule due to the withdrawing effect of the
pyrimidine group on the fluorenyl core. However, it should be noted that 2-5Pm-SBF and 4-5Pm-SBF
presents almost identical HOMO character and HOMO energy level (-6.13 eV vs -6.16 eV resp) clearly
meaning that the position of the pyrimidine group only has a weak influence on the HOMO energy levels
and distribution. As exposed above, the more easily reduced molecule is 2-5Pm-SBF due to the double
effect of the extension of conjugation and of the electron-accepting properties of the pyrimidine unit, its
LUMO has hence a clear pyrimidine-fluorene character. In 4-5Pm-SBF, the LUMO exclusively has a
pyrimidine character and its energy level is 0.2 eV higher than that of 2-5Pm-SBF due to the absence of
-
7 -

ACCEPTED MANUSCRIPT
conjugation between the fluorene and the pyrimidine unit. This is a very important feature of the present
chemical design and clearly highlights its efficiency. Thus, in 4-substituted SBFs, the HOMO character is
almost identical with no (or weak) contribution of the substituent in accordance with our electrochemical
conclusions (see above). In addition, it must be pointed out that the LUMO+1 of 4-5Pm-SBF is very close to
its LUMO (0.01 eV) with a 4-5Pm-fluorenyl and 4,5Pm character respectively. Thus, both 2-5Pm-SBF and 4-
5
Pm-SBF have a clear fluorene/pyrimidine character in their LUMO and LUMO+1 (almost degenerated with
the LUMO which exclusively possess a pyrimidine character) respectively but present different energy
levels. This highlights the importance of the torsion angle between the fluorene and the pyrimidine, which
is surely at the origin of these different energy values. The computed triplet adiabatic S to T excitation
0
1
energies, defined as the energy difference between total energy of the molecule in their respective singlet
and triplet states, is of 2.80 and 2.82 eV for 4-5Pm-SBF and 4-Ph-SBF and of 2.63 and 2.62 eV for 2-5Pm-
44
SBF and 2-Ph-SBF respectively. These calculations predict that 4-5Pm-SBF will be, as 4-Ph-SBF, a good
candidate as host for blue and green phosphorescent dyes and both 2-5Pm-SBF and 2-Ph-SBF will be both
only adapted to green dopants.
The thermal properties of all SBF derivatives were investigated by thermogravimetric analysis (TGA) and
differential scanning calorimetry (DSC) and the results are summarized in table 2. The Td is defined as the
temperature at which the sample has lost the first 5% of mass during heating.
Table 2. Thermal properties (melting point: m.p., decomposition temperature: T , glass transition: T , crystallization
d
g
temperature: T all obtained from the tangent to the transition peak) of the four SBF dyes.
c,
4
-5Pm-SBF 4-Ph-SBF 2-5PmSBF 2-Ph-SBF
b
a
1
97-198
42
m.p.(°C)
Td (°C)
Tg (°C)
Tc (°C)
173
277
85
-
213
100-108
2
254
76
238
78
-
9
4
-
115
a: This transition appears to be not very clear, occurring on a large range. b. from reference 44
4
4
2
2
-Ph-SBF
-5Pm-SBF
-Ph-SBF
4
4
2
2
Ph-SBF
1
00
-5Pm-SBF
-Ph-SBF
-5Pm-SBF
3
2
2
1
1
0
0
.0
.5
.0
.5
.0
.5
.0
-5Pm-SBF
80
60
40
20
0
-
0.5
0
50
100
150
200
250
0
100
200
300
400
500
600
700
Temperature (°C)
Temperature (°C)
Figure 4. DSC curves from second heating cycle (Left) and TGA curves (right) of 4-Ph-SBF (black line), 4-5Pm-SBF (red
line), 2-Ph-SBF (blue line), 2-5Pm-SBF (green line)
5
% decomposition (T ) of 4-Ph-SBF (Figure 4 right, black line) and 4-5Pm-SBF (Figure 4 right, red line) respectively
d
44
occurs at 254°C and 277°C, higher than the T of SBF (234°C) showing the interest of the incorporation of
d
a pendant phenyl or pyrimidine unit at the C4 of SBF. Decomposition temperature of the 2-substituted-SBF
occurs at 242°C (2-5Pm-SBF) and 238°C (2-Ph-SBF) close to the T of SBF, clearly highlighting that the
d
substitution in position 2 only has a weak effect on the thermal stability, whereas the substitution in
position 4 leads to a more stiff structure being hence more thermally stable. Thus, we note that the
position of the substitution has a clear influence on the T . On the other hand, 4-5Pm-SBF and 4-Ph-SBF
d
respectively present melting transitions at 173 and 206°C, whereas that of 2-5Pm-SBF is detected at ca
1
97/198° (see SI). It should be noted that the fusion of 2-Ph-SBF was very surprising appearing on a wide
-
8 -

ACCEPTED MANUSCRIPT
range of temperature. The substituent also has a clear influence on the whole thermal properties as the
replacement of phenyl by pyrimidine leads to different glass transitions (T ). Thus, we note that lower Tg
g
(
Figure 4, left) are detected (recorded on the second heating cycle of DSC, Figure 4 left) for phenyl-
substituted SBF (76 and 78°C for 4-Ph-SBF and 2-Ph-SBF respectively) compared to pyrimidine-substituted
SBF (85 and 94°C for 4-5Pm-SBF and 2-5Pm-SBF respectively). The slightly higher Tg of pyrimidine-
substituted compounds compared to phenyl-substituted compounds may be the consequence of stronger
…
50
intermolecular interactions due to CH N hydrogens bonding interactions. It is important to stress that all
51
compounds present T higher than those of classical host materials for PhOLEDs such as CBP (62°C) or m-
CP (55°C). Finally, it should be mentioned that 4-5Pm-SBF, 2-5Pm-SBF and 2-Ph-SBF do no present any
g
10
cristallization phenomena,T , being hence highly promising for devices incorporation. A cristallization
c
transition was only recorded for 4-Ph-SBF but at high temperature, 115°C, during the second heating cycle
in DSC.
Photophysical studies
The UV-Vis absorption and emission spectra recorded in cyclohexane are presented figure 5. All compounds
present similar absorption bands in the range 260-315 with the same maxima at 308 nm similar to the main
37,38,44
absorption band of SBF attributed to π−π∗ transition of the fluorene unit in SBF.
2
4
4
2
2
-Ph-SBF
-5Pm-SBF
-Ph-SBF
4-Ph-SBF
4-5Pm-SBF
1
0
0
0
0
0
,0
,8
,6
,4
,2
,0
2
2
-Ph-SBF
-5Pm-SBF
-5Pm-SBF
1
0
2
60 280 300 320 340 360 380 400
3
00
350
400
450
500
Wavelength (nm)
Wavelength (nm)
Figure 5. Normalized absorption (left) and emission (right, λexc=300 nm for 4-Ph-SBF, 4-5Pm-SBF and 2-Ph-SBF and 305
-
6
nm for 2-5Pm-SBF) spectra of the four dyes recorded in cyclohexane, C=10 M.
At higher wavelength, each compound possesses its own signature with a clear supplemental absorption
peak at 320 or 319 nm for 2-5Pm-SBF or 2-Ph-SBF signing an extension of the conjugation between the
fluorene and the pyrimidine or the phenyl rings when the fluorene is substituted at C2 position. Literature
reports a λmax of 328 nm (CH Cl ) for the disubstituted analogue 2,7-di-5Pm-9,9-dihexylfluorene (compound
2
2
F2 in chart 1) clearly showing an even more important extension of π-conjugation due to the presence of
30
two pyrimidine units. It means that efficient π-conjugation occurs between fluorene and pyrimidine unit
leading to a red shift of ca 8/10 nm per pyrimidine unit. In the case of 4-substituted SBF, we note the
presence of wavelength tail between 315 and 340 nm, which appears to be larger in the case of 4-5Pm-SBF
than in the case of 4-Ph-SBF. This tail may be due to a more limited π-conjugation between the pyrimidine
or the phenyl ring and the fluorene when substituted at the C4 position. It could also reflect a minor
proportion of conformers of the molecules with a more planar structure, allowing a certain degree of π-
conjugation between the pyrimidine or phenyl rings and the fluorene moiety. As these bands at low energy
seem to be more intense for pyrimidine-based dyes than for phenyl-based dyes, one may conclude that
more efficient π-conjugation seems to occur between fluorene and pyrimidine units.
-
9 -

ACCEPTED MANUSCRIPT
opt
From the onset absorption wavelength, optical energy gap (∆E ) varying from 3.66 eV for 2-5Pm-SBF to
3
.82 eV for 4-Ph-SBF were determined (see table 1) with a variation following the same trend as that
obtained from electrochemical measurement and theoretical calculations.
The experimental UV-vis spectra of the four dyes have been compared with predicted electronic absorption
spectrum from TD-DFT calculations (see figures in SI) and compared to that of its constituting building block
SBF. From those calculations one may observe that except 4-Ph-SBF, all compounds present an additional
absorption band at a lower energy than that the main band observed in SBF (see Figures in SI). This
additional band presents an oscillator strength value as high as 0.3552 for 2-Ph-SBF and 0.1677 for 2-5Pm-
SBF, similar to that calculated for the neighbouring band (0.3346 for 2-Ph-SBF and 0.1553 for 2-5Pm-SBF),
itself calculated close to the lowest energy band of SBF. This is in accordance with the experimental
conclusions from absorption spectroscopy presented above. Looking at the detailed transitions, for 2-Ph-
SBF and 2-5Pm-SBF, the lowest energy absorption band corresponds to an HOMO-LUMO transition
involving the 2-substituted-fluorene unit (see figure 3). For 4-5Pm-SBF, the two calculated lowest energy
bands present strongly less intense oscillator strength (0.0198 and 0.0303 for excited state 1 and 2
respectively) and the more important transitions involved in these two bands correspond to (i) HOMO vs
LUMO transition (65 % in excited state 1) involving two different molecular fragments of the fluorophore
(
HOMO possessing a spirobifluorenyl character and LUMO possessing a pyrimidine character) presenting
very low orbital overlap and hence a very strong charge transfer character and (ii) HOMO vs LUMO+1
transition (58.7% in excited excited state 2) involving two fluorenyl units and hence an orbital overlap
between them (HOMO possessing
a spirobifluorenyl character and LUMO+1 possessing a
pyrimidine/fluorenyl character). Finally, calculated UV-spectrum of 4-Ph-SBF is very similar to that
calculated for SBF (see SI) and the lowest energy absorption bands with very weak oscillator strength (0.06
and 0.059 for calculated excited states 1 and 2) correspond to the HOMO vs LUMO and HOMO vs LUMO+1
transitions, corresponding mainly to fluorene-fluorene transitions.
Fluorescence spectra of the four dyes (figure 5, right) clearly show drastically different emission spectra
depending on the substitution. The first type of emission spectra recorded for the 2-substituted-SBFs
presents a well resolved emission spectra with maxima at 338/355 and 335/351 nm for 2-5Pm-SBF and 2-
49
Ph-SBF respectively, signing the extension of π-conjugation compared to SBF (λmax = 311/323 nm).
Structured emission spectrum was also reported for 2,7-di-5Pm-9,9-dihexylfluorene (compound F2 in chart
) with maxima at 361 and 378 nm due to an even more important extension of conjugation in the
1
30
disubstituted-fluorenyl core. 4-substituted SBFs presents structureless and large emission spectra centred
at 365 nm for 4-5Pm-SBF and 358 nm for 4-Ph-SBF. This surprising loss of resolution was also observed for
the rare examples of 4-substituted SBF found in literature, ie 4-diphenylphosphine oxide-SBF (λmax: 346
3
9
41
42
nm) , 4-dibenzofuran-SBF (λmax: 369 nm) and 4-dibenzothiophene-SBF (λmax: 355 nm). This feature
appears hence to be a unique characteristic of 4-substituted SBF derivatives as 2-substituted SBF analogues
(
and 9,9'dialkylfluorene as well) always present well resolved emission bands assigned to the double bond
52-55
character of the C-C bond linking the pendant substituent and the fluorene core in the excited state.
In addition, there is also an intriguing red shift observed between 4-substituted-SBF and 2-substituted-SBF
derivatives (shift of 27 nm for 5Pm-SBFs and of 23 nm for Ph-SBFs). It is clear that the position of the
substitution (C2 vs C4) is at the origin of this spectacular effect. We could assume that the C4 substitution
of phenyl or pyrimidine fragments on the fluorene do not affect dramatically the π-conjugation in the
ground state (absorption spectra are only slightly altered with a low energy tail, as described above), but
contribute to a strong planarization in the excited state leading to an impressive Stokes shift. More detailed
theoretical and spectroscopic investigations need to be conducted to unravel this critical issue.
The emission quantum yields (Φsol) were determined in cyclohexane by using standard procedures with
quinine sulphate as reference. On one hand, phenyl-substituted SBFs appear to be efficiently fluorescent
with Φsol of 0.42 and 0.87 and lifetimes of 4.20 ns and 1.56 ns for 4-Ph-SBF and 2-Ph-SBF, respectively. On
the other hand, a quenching of fluorescence is observed for pyrimidine-substituted SBFs with Φsol of 0.04
and 0.02 and lifetimes of 0.61 ns and 0.44 ns for 4-5Pm-SBF and 2-5Pm-SBF, respectively. It should be
-
10 -

ACCEPTED MANUSCRIPT
noted that in other solvents, such as THF, the quantum yields of 4-5Pm-SBF and 2-5Pm-SBF remain very
low and the solvent can hence not be responsible of these low values. It must be noted that such a
decrease of the fluorescence was not observed for previously reported compounds with pyrimidine units
35
30
such as TBPSF (Φsol=1 in solution) and F3 (Φsol=0.85 in solution) (see structures in chart 1) bearing
respectively either a 5 pyrimidine or a 2 pyrimidine unit, both being also substituted with a phenyl ring. The
presence of this phenyl ring on the pyrimidine unit appears hence to be very important and we believe
that, in our case, the absence of this phenyl ring and hence the presence of the aromatic NCHN fragment in
the 5-pyrimidine unit has a strong impact on the deactivation rates of the excited state. Indeed, pyrimidine
substituted derivatives 4-5Pm-SBF and 2-5Pm-SBF show a lower radiative rate constant k and a much
r
higher non-radiative rate constant k compared to phenyl-substituted derivatives 4-Ph-SBF and 2-Ph-SBF,
nr
as mentioned in Table 3.
Table 3. Optical properties of the four SBF dyes.
4
-5Pm-SBF
4-Ph-SBF
2-5Pm-SBF
2-Ph-SBF
λabs, solution (nm)
ε (10 , L.mol .m )
297 (0.5), 308
(0.6), 318 (sh)
297 (0.7), 308 (1.4), 296 (2.5), 308 (2.5), 297 (2.4), 308 (2.2),
4
-1
-2 a
318 (sh)
298, 311
320 (1.8)
319 (1.6)
b
λabs, thin-film (nm)
298, 311
301, 312, 326
301, 312, 329
a
λem, solution (nm)
λem, thin-film (nm)
365
372
358
363
0.42
4.20
338, 355
355, 366
0.02
335, 351
343, 359
0.87
b
a,c
Φsol
0.04
0.61
a
τ (ns)
0.44
1.56
-
1 a
7
8
7
8
k (s )
6.6×10
1.6×10
1.0×10
1.4×10
4.6×10
5.6×10
r
-
1 a
9
8
9
7
k (s )
2.2×10
8.3×10
nr
a. in cyclohexane, b. Spin-coated thin film from a solution in THF, [solution] = 10 mg/mL), c. Quantum yields in solution (Φsol) were
calculated relative to quinine sulfate (Φsol = 0.546 in H SO 1N)
2
4
From a careful inspection of the dependence of the absorption behaviour of the four dyes on solvent
polarity, we note that the absorption maximum is almost insensitive to the dielectric constant of the
environment (see Figures in SI). This indicates that the electronic and structural characteristics of the
56
ground and Franck Condon excited states do not differ much with a change in solvent polarity.
While phenyl-substituted SBFs showed minor differences of the PL spectra in various solvents (Figure 6,
top), distinct fluorescence solvatochromism was observed in pyrimidine-substituted SBF when the solvent
polarity increases from cyclohexane to ethanol (Figure 6, bottom). Indeed, both dyes are highly sensitive to
the solvent polarity with fluorescence maxima ranging from 366 and 338 nm in cyclohexane to 390 and 375
nm in ethanol for 4-5Pm-SBF and 2-5Pm-SBF respectively. This dependence of the emission wavelength on
the solvent polarity is indicative of dipole-dipole interactions between Pm-substituted SBFs and polar
solvent molecules and hence of a photoinduced intramolecular charge transfer between the donor
57
(
fluorene) and the acceptor part (pyrimidine) of the dye.
-
11 -

ACCEPTED MANUSCRIPT
Cyclohexane
Toluene
THF
Cyclohexane
Toluene
THF
1,0
1
0
0
0
0
0
,0
,8
,6
,4
,2
,0
CH Cl
DCM
EtOH
ACN
2
2
Ethanol
0
0
0
0
0
,8
,6
,4
,2
,0
CH CN
3
3
00
350
400
450
500
350
375
400
450
Wavelength (nm)
Wavelength (nm)
Cyclohexane
Toluene
THF
Cyclohexane
Toluene
THF
338
1,0
CH Cl2
2
3
66
390
1
0
0
0
0
0
,0
,8
,6
,4
,2
,0
Ethanol
CH Cl
2
2
0,8
0,6
0,4
0,2
0,0
CH CN
Ethanol
3
CH CN
3
3
25 350 375 400 425 450 475 500
3
50
400
450
500
Wavelength (nm)
Wavelength (nm)
Figure 6. Normalized PL spectra of solutions of 4-Ph-SBF (top left) and 2-Ph-SBF (top right) and of 4-5Pm-SBF (bottom
left) and 2-5Pm-SBF (bottom right) in cyclohexane, toluene, THF, CH Cl , ethanol and CH CN
2
2
3
The solid state absorption spectra of all dyes (figure 7, left) appear very similar to those in solution (figure 5
left) with only a small red shift of less than 8 nm detected and a slight increase of the lowest energy band
intensity (compared to the band at 310 nm) for the 2-substituted-SBFs. Such similarity between absorption
spectra in solution and in solid state clearly signs that there are minimal intermolecular interactions in the
ground state in thin films.
2
4
4
2
-Ph-SBF
-5Pm-SBF
-Ph-SBF
4
4
2
2
-Ph-SBF
-5Pm-SBF
-Ph-SBF
1,0
0
0
0
0
0
,8
,6
,4
,2
,0
2-5Pm-SBF
-5Pm-SBF
1
0
3
00
350
400
450
500
260 280 300 320 340 360 380 400
Wavelength (nm)
Wavelength (nm)
Figure 7. Absorption (left) and Emission (right) spectra of the four dyes recorded in solid state (spin-coated thin film
from a solution in THF, [solution] = 10 mg/mL).
Regarding the solid-state fluorescent properties (figure 7, right), except for 2-5Pm-SBF, they are almost
identical to those recorded in solution (figure 5, right) with only a small red shift ranging from 3 nm for 4-
Ph-SBF to 8 nm for 4-5Pm-SBF and 2-Ph-SBF. Solid-state fluorescent spectrum of 2-5Pm-SBF (figure 7, right,
pink line) nevertheless appears poorly resolved with two maxima recorded at 355/366 nm, red shifted by
1
7/11 nm compared to that in solution. Finally, to examine the suitability of the four dyes as host materials
for phosphorescent green and/or blue dopant, the phosphorescence of the molecules was recorded at 77 K
in a methylcyclohexane/2-methylpentane mixture (1:1), Figure 8. From those spectra, E values of the
T
molecules were calculated from the lowest phosphorescent peak of 2.75 eV for 4-5Pm-SBF and 2.56 eV for
-
12 -

ACCEPTED MANUSCRIPT
2
-Ph-SBF. Compared to the E value of 4-Ph-SBF (2.77 eV) and of SBF (2.87 eV) reported by our group
T
44
recently, we note that the E level of 4-5-Pm-SBF is sufficiently high for its use as host material for both
T
green and blue phosphorescent dyes. The E of 2-Ph-SBF (2.56 eV) and that of 2-5-Pm-SBF (2.58 eV) is
T
58
lower than that of the blue dopant FIrpic (E : 2.62 eV ) and these molecules may be used as host material
T
59
for green dopant Irppy (E : 2.42 eV ).
3
T
4
-Ph-SBF
4-5Pm-SBF
450
500
550
600
400
450
500
550
Wavelength (nm)
Wavelength (nm)
2-Ph-SBF
2-5Pm-SBF
4
50
500
550
600
450
500
550
Wavelength (nm)
Wavelength (nm)
Figure 8. Emission spectra at 77 K in a methylcyclohexane/2-methylpentane mixture (1:1) of 4-Ph-SBF ( exc
Pm-SBF (λexc= 300 nm) and 2-Ph-SBF (λexc= 250 nm) and 2-5PmSBF (λexc= 250 nm). The determination of the Et value
has been done at from the lowest phosphorescent peak (black arrow)
λ = 300 nm, 4-
5
In conclusion of the above presented photophysical and physico-chemical analysis, the position (C2 vs C4)
and the nature of the substituent (phenyl vs pyrimidine) on the SBF core leads to drastic alterations of the
resulting properties. Substitution at the C2 leads to an increase of the conjugation length and therefore to a
decrease of the singlet and triplet state energy level, while the substitution at the C4 only has a weak
influence on these two key parameters, keeping them almost identical to those of their constituting
building block SBF. This has been assigned to π-conjugation breaking induced by the large torsion angle
made by the substituents in C4. This chemical design allows hence obtaining organic semiconductors based
on
a C4-substituted SBF with high singlet and triplet state energy level with excellent
thermal/morphological properties. On the other hand, the substitution by the pyrimidine group leads to a
decrease of the LUMO level due to the pyrimidine electron affinity, which should lead in principle to a
decrease of the threshold voltage of the resulting devices. Thus, the four dyes possess the prerequisites for
their uses as host in PhOLEDs that is, a high T and Td, HOMO/LUMO levels adapted for hole and electron
g
injection/transport in the devices and E higher that of the green phosphorescent emitter Ir(ppy) (2.42
T
3
58
59
eV ) and in the case of 4-Ph-SBF and 4-5Pm-SBF for the blue phosphorescent emitter FIrpic (2.62 eV ).
-
13 -

ACCEPTED MANUSCRIPT
EML
-1.95
-2.1
-2.3
-2.3
-2.3
-2.4
LiF/Al
2.9 eV
-2.7
-
-
2.9
-
3.0
-
3.5
CuPc
NPB
TCTA
5.7 eV
TPBI
Ir(ppy)3
ITO
4.7 eV -5.2
FIrpic
-
-
5.4 eV
-
5.6
-
-5.8
-5.88
-5.95
-
5.96
-5.97
-
6.2 eV
Scheme 2. Energy level diagram of the devices.
In order to explore the potential of the present semi-conductors as host for triplet emitters, green (Ir(ppy)3)
and blue (FIrpic) PhOLEDs were fabricated. The device configuration was ITO/CuPc(10 nm)/NPB (40
nm)/TCTA (10 nm)/ EML:dopant (20 nm)/TPBi (40 nm)/LiF (1.2 nm)/Al (100 nm). ITO is used as the anode,
CuPc (copper phtalocyanine) is the hole injecting layer, NPB (N,N’-di(1-naphtyl)-N,N’-diphenyl-[1,1’-biphe-
nyl]-4,4’-diamine) is the hole-transporting layer, TCTA (4,4',4''-Tris(carbazol-9-yl)-triphenylamine) is the
electron/exciton blocking layer, TPBI (1,3,5-Tris(1-phenyl-1H-benzimidazol-2-yl)benzene) is both the
electron transporting layer and the hole blocking layer and a thin film of lithium fluoride covered with
aluminum is the cathode. Ir(PPy) and FIrpic are used as dopant for green and blue OLEDs respectively. The
3
relative energy levels of the successive layers of the devices are reported in scheme 2. Table 4 gathers
selected data obtained from the average of two experiments.
Due to their E values higher than that of Ir(ppy) , the four substituted-SBFs were used as host for Ir(ppy)
3
T
3
green dopant. Performance of the best green PhOLEDs is presented in figure 9 (left) and average
parameters are gathered in table 4. The best green PhOLED performance was obtained with 2-5Pm-SBF and
4
-5Pm-SBF host materials doped with 10% Ir(ppy) . As shown in figure 9 (left), maximum current and power
3
efficiencies of 58 cd/A and 35 lm/W are obtained respectively for the pyrimidine substituted SBF. Maximum
2
luminance as high as 30 000 cd/m is reached for these devices as shown in table 4. Phenyl substituted
dyes, 4-Ph-SBF and 2-Ph-SBF presents lower performance with EQE of 10.4% and 11.3 %, highlighting the
great interest of the incorporation of the pyrimidine unit in SBF scaffold. The threshold voltage for all
devices appears to be low and as low as 2.5 eV for 2-5Pm-SBF.
The EL spectra of the four devices based on the different host materials are identical, exclusively showing
the emission of the green dopant at 516/540 nm (figure 9 right) close to the PL emission of pure Ir(ppy)
film (509/540 nm) with no parasite emission in the range of the undoped device. This result demonstrates
3
57
an efficient energy transfer from the four SBF-derivatives to Ir(ppy) , due to their high triplet energy levels.
3
The device performance obtained with small pure hydrocarbon host molecules 4-Ph-SBF and 2-Ph-SBF are
comparable to those obtained with more complicated pure-hydrocarbon-based host materials recently
38,37,58
reported,
Performances obtained with pyrimidine-substituted SBF are even more interesting with
lowest turn-on voltages and highest EQE (close to 14%) and clearly demonstrate the interest of the
pyrimidine substitution in notably favouring the injection of electron.
-
14 -

ACCEPTED MANUSCRIPT
Table 4. Selected EL data of green and bue devices (average values calculated from two experiments).
at J= 10 mA/cm²
max
-2
Host
Guest (%)
Von (V) EQE (%)
Current
Power
efficiency
(lm/W)
L
(cd.m ) at
CIE (x ; y) at
10 mA.cm
-
2
/
efficiency
current density
-
1
-2
(
cd.A )
(mA.cm )
Green Phosphorescent OLEDs
2
-Ph-SBF
2.6
2.5
3.5
3.3
11.3
13.3
10.4
13.7
42.7
49.2
40.3
49.9
17.8
21.5
16.7
17.6
27 990 (210)
30 000 (160)
25 700 (230)
28 000 (150)
0.33 ; 0.62
0.33 ; 0.61
0.32 ; 0.62
0.34 ; 0.61
/
Ir(ppy) (10)
3
2
-5Pm-SBF
/
Ir(ppy) (9)
3
4
4
4
-Ph-SBF
/
Ir(ppy) (10)
3
4
-5Pm-SBF
/
Ir(ppy) (10)
3
Blue Phosphorescent OLEDs
4
4
4
/
-Ph-SBF
FIrPic (19)
-5Pm-SBF
FIrPic (19)
4.0
3.3
5.7
4.8
16.2
6.0
3800 (70)
2030 (50)
0.20 ; 0.44
0.20 ; 0.45
4
/
14.1
5.5
8
7
6
5
4
3
2
1
0
4
-5Pm-SBF
4-Ph-SBF
4-5Pm-SBF
2-Ph-SBF
2-5Pm-SBF
at 10mA/cm²
0
0
0
0
0
0
0
0
4-Ph-SBF
1,00
2-Ph-SBF
2-5Pm-SBF
0
0
,75
,50
0,25
0
,00
4
00
500
600
700
800
0
10
20
30
40
2
50
wavelength (nm)
Current density (mA/cm )
Figure 9. Current (empty symbol) and power efficiencies (filled symbol) versus current density of the green devices
using 4-Ph-SBF, 4-5Pm-SBF, 2-Ph-SBF and 2-5Pm-SBF doped with Ir(ppy) (10% in mass) as emitting layer (left).
3
2
Corresponding EL spectra recorded at 10 mA/cm (right).
Due to their high E values (2.77 eV for 4-Ph-SBF and 2.75 eV for 4-5Pm-SBF), higher than that of FIrpic (E :
T
T
2
.62 eV), the two 4-substituted-SBFs were used as host for this blue dopant. Characteristics of the two blue
devices are presented in figure 10. The best performance is obtained with 4-Ph-SBF with an EQE of 5.7 %, a
LE of 16.2 cd/A and a threshold voltage of 4 V while blue PhOLEDs with 4-5Pm-SBF as host reach an EQE of
2
4
.8 %, a LE of 14.1 cd/A and a threshold voltage of 3.3 V reported at a current density value of 10 mA/cm
(
Figure 10 left and Table 4). The threshold voltage of 4-5Pm-SBF is hence decreased by ca 0.7 V compared
to that of 4-Ph-SBF due to the incorporation of the pyrimidinium group in the former (which leads to a
decrease of the LUMO level and hence an easier injection of the electron in the device). This highlights the
efficiency of the chemical design investigated in this work. Both devices, reach brightness of 3800 / 2030
2
cd/m for 4-Ph-SBF / 4-5Pm-SBF based devices respectively.
EL spectra of the devices (Figure 10 right) point a main emission of the blue dopant with maxima at 473 and
5
9
5
00 nm close to the PL emission of pure FIrpic film (475/500 nm) but also, in the case of 4-PhSBF of an
additional tiny emission in the range of the undoped device (360/440 nm). This emission may be due to a
small amount of recombination in the other organic layers and especially in TCTA. CIE coordinates of 4-Ph-
SBF-based device (0.20 ; 0.44) and of 4-5Pm-SBF-based device (0.20 ; 0.45) appear nevertheless almost
identical as shown in Table 4.
-
15 -

ACCEPTED MANUSCRIPT
30
25
20
15
10
5
0
4
-5Pm-SBF
4-Ph-SBF
4-5Pm-SBF
at 10mA/cm²
4-Ph-SBF
1
0
0
0
,00
,75
,50
,25
0,00
0
10
20
30
40
2
50
400
500
600
700
800
wavelength (nm)
Current density (mA/cm )
Figure 10. Current (empty symbol) and power efficiencies (filled symbol) versus current density of the blue devices
using 4-Ph-SBF and 4-5Pm-SBF doped with FIrPic (19% in mass) as emitting layer (left). Corresponding EL spectra
2
recorded at a current density of 10 mA/cm (right).
Conclusion
In summary, four substituted SBF dyes have been synthesized and their thermal, electrochemical and
photophysical properties have been scrutinized and compared to the properties of their constituting SBF
unit. From these studies it has been demonstrated that, compare to SBF, the substitution by a phenyl unit
at the C4 position of SBF leads to weaker modification of the HOMO and LUMO levels compared to the
phenyl substitution at the C2 position, which leads to a conjugation extension and hence a decrease of the
HOMO-LUMO gap. On the other hand, the substitution by the electro-deficient pyrimidine unit compared
to the substitution by the phenyl unit leads to a significant lowering of the LUMO level. Overall, the
combination of the two effects (lowering of the HOMO through the extension of conjugation, lowering of
the LUMO through pyrimidine electro deficient effect) in 2-5Pm-SBF leads to the highest modification of
the optical energy gap (from 4.05 eV in SBF to 3.66 eV in 2-5Pm-SBF). Thus, the optical energy gap of the
four compounds is finely tuned from 4 eV for 4-Ph-SBF to 3.66 eV for 2-5Pm-SBF. In addition, the
substitution in C2 or in C4 has an impressive influence on the E . Indeed, the C2-substituted dyes have E
T
T
values at ca 2.42 eV, whereas the C4 substituted dyes have an E as high as 2.7 eV due to the π-conjugation
T
disruption. This structure properties relationship study clearly highlights how a different substitution may
lead to very different properties keeping others intact. As all compounds possess a triplet energy level
higher than 2.42 eV, they have been used as host for green dopant in PhOLEDs. Remarkable performance
has been obtained with 2-5Pm-SBF as host (CE > 58 cd/A, PE > 35 lm/W, EQE > 14 % and threshold voltage
of 2.5 V). Furthermore, the two 4-substituted SBF with triplet energy levels as high as 2.8 eV have also been
successfully used as host materials for blue PhOLEDs with high performance. The effect of the pyrimidine
substituent leads to a lowering of the threshold working voltage of the device from 4 V for 4-Ph-SBF based
blue device to 3.3 V for 4-5Pm-SBF based blue device.
Acknowledgements
S.T. and G. S. thank ANR (HOME-OLED Project n°ANR-11-BS07-020-01) for a studentship. C. D thanks ANR
(
HOME-OLED Project n°ANR-11-BS07-020-01) for a financial support as postdoctoral position. We wish to
thank the C.R.M.P.O (Centre Régional de Mesures Physiques de l'Ouest, Rennes) for high resolution mass
measurements, Service de Microanalyse-CNRS (Gif sur Yvette) for CHN analyses, CINES (Montpellier) for
computing time, the CDIFX (Rennes) for X-Ray data collection, the "Institut des Sciences Analytiques" (UMR
CNRS 5280, Villeurbanne) for TGA. Arnaud Brosseau (Cachan) is thanked for his precious assistance in
photophysical measurements. Dr Franck Camerel (Rennes) is warmly acknowledged for his help and advice
-
16 -

ACCEPTED MANUSCRIPT
in the understanding of thermal properties. Prof. Abdou Boucekkine is also warmly thanked for his help in
DFT and TD-DFT calculations.
Experimental Section
Synthesis:
All manipulations of oxygen- and moisture-sensitive materials were conducted with a standard
Schlenk technique. Commercially available reagents and solvents were used without further purification
other than those detailed below. THF was distilled from sodium/benzophenone prior to use. Light
petroleum refers to the fraction with bp 40-60°C. 2.5 M solutions of n-BuLi in hexanes or THF were
purchased from Sigma Aldrich. 2,2’-dibromobiphenyl was purchased from Fluorochem. Reactions were
stirred magnetically, unless otherwise indicated. Analytical thin layer chromatography was carried out using
aluminum backed plates coated with Merck Kieselgel 60 GF254 and visualized under UV light (at 254 and
3
2
60 nm). Chromatography was carried out using Teledyne Isco CombiFlash® Rf 400 (UV detection
00-360nm), over standard silica cartridges (Redisep® Isco, GraceResolv™ Grace or Puriflash® columns
1
13
1
Interchim). H and C NMR spectra were recorded using Bruker 300 MHz instruments ( H frequency,
corresponding C frequency: 75 MHz); chemical shifts were recorded in ppm and J values in Hz. In the
13
13
C
NMR spectra, signals corresponding to C, CH, CH or Me groups, assigned from DEPT, are noted. The
2
residual signals for the NMR solvents are: CDCl ; 7.26 ppm for the proton and 77.00 ppm for the carbon,
3
CD Cl ; 5.32 ppm for the proton and 53.80 ppm for the carbon. The following abbreviations have been used
2
2
for the NMR assignment: s for singlet, d for doublet, t for triplet and m for multiplet. High resolution mass
spectra were recorded at the Centre Régional de Mesures Physiques de l'Ouest (Rennes) on (i) Bruker
MicrO-Tof-Q II (Source: Atmospheric Pressure Chemical Ionization (APCI - direct introduction) (ASAP–
Atmospheric Solids Analysis Probe) at a temperature of 30°C - positive mode) or on (ii) Waters Q-Tof II. The
44
synthesis of 4-bromo-9,9'-spirobi[fluorene] (1) and of 4-Ph-SBF have been previously described
6
3
2
-bromo-9,9'-spirobi[fluorene] (2) 2-bromo-1,1’-biphenyl (2.16 g, 9.27 mmol, 1.15 eq) was dissolved
in dry THF (40 mL) under argon atmosphere, cooled at -78°C, and stirred during 10 minutes at this
temperature. A 2.5 M n-BuLi solution in THF (4.31 mL, 10.78 mmol, 1.34 eq) was then slowly injected via a
seringue, at -78°C. The resulting yellow mixture was stirred at the same temperature for 30 min. 2-bromo-
9
H-fluoren-9-one (2.08 g, 8.03 mmol) in dry THF (35 mL) was then added dropwise, and the mixture was
stirred for another 30 min at -78°C, and allows warming up to room temperature gradually and stirred
overnight. Saturated brine solution (10 mL) was added, and the mixture was extracted twice with ethyl
acetate (2x30 mL). The combined organic extracts were dried over anhydrous magnesium sulfate, filtered,
and concentrated under reduced pressure. Without other purification, the crude was dissolved into a
mixture of acetic acid/hydrochloric acid (50 mL/5 mL) and warmed at 70°C during 2 h under stirring. Then,
the mixture was poured into water/ice (200 mL), and the solution was neutralized with solid sodium
hydroxide until pH 7. Then the organic layer was extracted three times with dichloromethane (3x50 mL).
The combined organic extracts were dried over magnesium sulfate, filtered, and concentrated under
reduced pressure. The residue was purified by flash chromatography on silica gel (light petro-
leum/dichloromethane 95/5) to afford a colorless solid (2.14 g). [column conditions: Silica cartridge 40 g
(
2
Serlabo); solid deposit on Celite®; λdetection: (254 nm, 280 nm); light petroleum/dichloromethane (95/5) at
5 mL/min; collected fraction: 18-42 min]. Yield: 67%. mp: 168-170°C (lit. 160 °C); H NMR (300 MHz,
64 1
CD Cl ): δ 7.89 (m, 3H, ArH), 7.76 (d, J= 8.1 Hz, 1H, ArH), 7.52 (dd, J = 8.1, 1.8 Hz; 1H, ArH), 7.42 (m, 3H,
2
2
1
3
ArH), 7.15 (m, 3H, ArH), 6.87 (m, 1H, ArH), 6.71 (m, 3H, ArH); C NMR (75 MHz, CD Cl ): δ 151.5 (C), 149.1
2
2
(
1
C), 148.5 (C), 142.4 (C), 141.4 (C), 141.3 (C), 131.4 (CH), 128.8 (CH), 128.6 (CH), 128.54 (CH), 128.48 (CH),
27.6 (CH), 124.37 (CH), 124.35 (CH), 122.1 (CH), 121.8 (C), 120.8 (2xCH seen from HSQC), 66.4 (Spiro C).
General procedure for Suzuki coupling
,9'-spirobi[fluorene] brominated compound, boronic acid compound, K CO and Pd(dppf)Cl were
*
2
9
2
3
dissolved in dry DMF or xylenes. The mixture was warmed to 150°C (DMF) and 135°C (xylenes) stirred
overnight. After cooling to room temperature, saturated solution of ammonium chloride (50 mL) was ad-
*
Pd(dppf)Cl : [1,1'-Bis(diphenylphosphino)ferrocene]palladium(II) dichloride complex with dichloromethane
2
-
17 -

ACCEPTED MANUSCRIPT
ded, and organic layer was extracted three times with dichloromethane (3x30 mL) and washed with brine
(
3x30 mL). The combined organic extracts were dried over magnesium sulfate, filtered, and concentrated
under reduced pressure. The residue was purified by flash chromatography on silica gel using Teledyne Isco
CombiFlash® Rf 400. Column conditions can be found in each compounds description below.
5
-(9,9'-spirobi[fluoren]-4-yl)pyrimidine (4-5Pm-SBF). 5-(9,9'-spirobi[fluoren]-4-yl)pyrimidine was synthesi-
44
zed according to the general coupling procedure between 4-bromo-9,9'-spirobi[fluorene] (1) (0.808 g,
.045 mmol), pyrimidin-5-yl-boronic acid (0.333 g, 2.688 mmol, 1.31 eq), K CO (2.800 g, 20.260 mmol, 9.91
2
2
3
eq) and Pd(dppf)Cl (0.088 g, 0.108 mmol, 0.05 eq) in dry DMF (30 mL). The residue was purified by flash
2
chromatography on silica gel (light petroleum/ethyl acetate 85/15) to afford a colorless solid (0.759 mg,
1
2
.924 mmol) [column conditions: Silica cartridge 12 g (Serlabo); solid deposit on Celite®; λdetection: (254 nm,
80 nm); ethyl acetate in ligth petroleum (85/15) at 20 mL/min; collected fraction: 8-17 min]. Yield: 94%.
-
1
1
mp: 167°C; IR (ATR, cm ) ν = 593, 646, 723, 752, 908, 1030, 1157, 1282 1405, 1444, 1545, 3020, 3072; H
NMR (300Mhz, CD Cl ): δ 9.36 (s, 1H, ArH), 9.04 (s, 2H, ArH), 7.89 (m, 2H, ArH), 7.41 (td, J = 7.5, 1.2 Hz, 2H,
2
2
13
ArH), 7.22-7.01 (m, 7H, ArH), 6.76 (m, 3H, ArH), 6.68 (s, 1H, ArH); C NMR (75MHz, CD Cl ): δ 158.6 (CH),
2
2
1
1
1
57.4 (CH), 150.7 (C), 149.9 (C), 149.0 (C), 142.5 (C), 141.3 (C), 139.7 (C), 135.1 (C), 130.8 (C), 130.7 (CH),
28.7 (CH), 128.53 (CH), 128.48 (CH), 128.3 (CH), 128.2 (CH), 124.9 (CH), 124.7 (CH), 124.3 (CH), 123.0 (CH),
+
20.8 (CH), 66.24 (Spiro C) ; HRMS calculated for C H N 395.1542, found 395.1542 [M+H] ; Elemental
29
19
2
analysis calculated for C H N : C, 88.30 %; H, 4.60 %; N, 7.10 %. Found: C, 87.81 %; H, 4.81 %; N, 6.81 %;
2
9
18
2
4
-1
-1
λabs [nm] (ε[10 .L.mol .cm ]) = 297 (0.5), 308 (0.6).
2
-phenyl-9,9'-spirobi[fluorene] (2-Ph-SBF). 2-phenyl-9,9'-spirobi[fluorene] was synthesized according to
the general procedure between 2-bromo-9,9’-spirobi[fluorene] (2) (0.751 g, 1.901 mmol), phenylboronic
acid (0.304 g, 2.488 mmol, 1.31 eq), K CO (1.227 g, 8.883 mmol, 4.67 eq) and Pd(dppf)Cl (0.061 g, 0.076
2
3
2
mmol, 0.04 eq) in xylenes (20 mL). The residue was purified by flash chromatography on silica gel (light
petroleum/dichloromethane 9/1) to afford a colorless solid (0.581 g, 1.482 mmol), [column conditions:
Silica cartridge 24 g (Serlabo); solid deposit on Celite®; λdetection: (254 nm, 280 nm); dichloromethane in light
*
-1
petroleum (9/1) at 20 mL/min; collected fraction: 35-45 min]. Yield: 78 %.mp:100-108 IR (ATR, cm ) ν =
1
4
76, 494, 617, 634, 650, 692, 727, 748, 829, 1020, 1155, 1280, 1444, 1597, 3014, 3059; H NMR (300 MHz,
CD Cl ): δ 7.96 (dd, J = 8.0, 0.6 Hz, 1H, ArH), 7.93 – 7.88 (m, 3H, ArH), 7.66 (dd, J = 8.0, 1.7 Hz, 1H, ArH), 7.45
2
2
–
7.36 (m, 5H, ArH), 7.35 – 7.20 (m, 3H, ArH), 7.13 (td, J = 7.5, 1.1 Hz, 3H, ArH), 6.94 (dd, J = 1.7, 0.6 Hz, 1H,
13
ArH), 6.78 – 6.72 (m, 2H, ArH), 6.72 – 6.67 (m, 1H, ArH); C NMR (75 MHz, CD Cl ): δ 150.1 (C), 149.7 (C),
1
1
2
2
†
49.2 (C), 142.4 (C), 142.0 (C), 141.7 (C), 141.4 (C), 141.3 (C), 129.1 (CH), 128.40 (2xCH ), 128.38 (CH),
28.37 (CH), 127.8 (CH), 127.43 (CH), 127.38 (CH), 124.4 (CH), 124.3 (CH), 123.0 (CH), 121.0 (CH), 120.8
+
(
CH), 120.7 (CH), 66.6 (Spiro C); HRMS calculated for C H 393.1643, found 393.1646 [M+H] ; Elemental
31 21
4
-
analysis calculated for C H : C, 94.86 %; H, 5.14 %. Found: C, 94.93 %; H, 5.24 %; λ [nm] (ε[10 .L.mol
31
20
abs
1
.
-1
cm ]) = 297 (2.4), 308 (2.2), 319 (1.6).
5
-(9,9'-spirobi[fluoren]-2-yl)pyrimidine (2-5Pm-SBF). 5-(9,9'-spirobi[fluoren]-2-yl)pyrimidine was synthesi-
zed according to the general procedure between 2-bromo-9,9’-spirobi[fluorene] (2) (0.749 g, 1.897 mmol),
pyrimidin-5-yl-boronic acid (0.312 g, 2.519 mmol, 1.33 eq), K CO (1.226 g, 8.872 mmol, 4.68 eq) and
2
3
Pd(dppf)Cl (0.059 g, 0.073 mmol, 0.04 eq) in dry DMF (20 mL). The residue was purified by flash
2
chromatography on silica gel (light petroleum/ethyl acetate 8/2) to afford a colorless solid (0.5743 g, 1.456
mmol) [column conditions: Silica cartridge 24 g (Serlabo); solid deposit on Celite®; λdetection: (254 nm, 280
nm); ethyl acetate in light petroleum (8/2) at 20 mL/min; collected fraction: 34-50 min]. Yield (77 %). mp:
-
1
1
1
7
97-198°C; IR (ATR, cm ) ν = 491, 604, 619, 636, 721, 731, 750, 833, 862, 1018, 1105, 1153, 1186, 1267,
1
400, 1414, 1446, 1554, 3016, 3039, 3053; H NMR (300 MHz, CD Cl ): δ 8.94 (s, 1H, ArH), 8.67 (s, 2H, ArH),
.93 (dd, J = 7.9, 0.6 Hz, 1H, ArH), 7.87 – 7.83 (m, 1H, ArH), 7.83 – 7.79 (m, 2H, ArH), 7.56 (dd, J = 7.9, 1.7
2
2
Hz, 1H, ArH), 7.37 – 7.26 (m, 3H, ArH), 7.06 (dtd, J = 10.2, 7.5, 1.1 Hz, 3H, ArH), 6.86 (dd, J = 1.7, 0.6 Hz, 1H,
*
This transition appears to be not very clear, occurring on a large range.
In the light of the protons assignment of 2-5Pm-SBF, we believe that 2 carbons are present at 128.40 ppm.
†
-
18 -

ACCEPTED MANUSCRIPT
1
3
ArH), 6.68 – 6.60 (m, 3H, ArH); C NMR (75 MHz, CD Cl ): δ 157.8 (CH), 155.2 (CH), 150.7 (C), 149.7 (C),
2
2
1
48.8 (C), 143.2 (C), 142.4 (C), 141.4 (C), 134.53 (C), 134.45 (C), 129.0 (CH), 128.6 (CH), 128.5 (2xCH seen
from HSQC), 127.3 (CH), 124.42 (CH), 124.35 (CH), 122.9 (CH), 121.6 (CH), 121.1 (CH), 120.8 (CH), 66.6
+
4
-1
-1
(
Spiro C); HRMS calculated for C H N 395.1548, found 395.1548 [M+H] ; λ [nm] (ε[10 .L.mol .cm ]) =
29 19 2 abs
2
96 (2.5), 308 (2.5), 320 (1.8).
X-Ray :
Crystal was picked up with a cryoloop and then frozen at 150 K under a stream of dry N on a APEX
2
II Brucker AXS diffractometer for X-ray data collection (Mo Kα radiation, λ = 0.71073 Å). 4-Ph-SBF structure
44
was published previously.
-Ph-SBF (C H )); M = 784.94. APEXII, Bruker-AXS diffractometer, Mo-Kα radiation (λ = 0.71073
2
62
40
Å), T = 150(2) K; triclinic P-1 (I.T.2), a = 10.9027(4), b = 13.7902(6), c = 15.7771(5) Å, α = 102.1400(10), β =
3
-3
-1
9
7.4710(10), γ = 111.5900(10) °, V = 2099.47(14) Å .Z = 2, d = 1.242 g.cm , μ = 0.07 mm . The structure was
65
solved by direct methods using the SIR97 program, and then refined with full-matrix least-square
methods based on F (SHELXL-97) with the aid of the WINGX program. All non-hydrogen atoms were
2
66
67
refined with anisotropic atomic displacement parameters. H atoms were finally included in their calculated
2
2
positions. A final refinement on F with 9543 unique intensities and 559 parameters converged at ωR(F ) =
0
.1128 (R(F) = 0.0447) for 7649 observed reflections with I > 2σ(I).
-5Pm-SBF (C H N , C H O); M = 426.5. APEXII, Bruker-AXS diffractometer, Mo-Kα radiation (λ =
2
29
18
2
4
0
4
.71073 Å), T = 150(2) K; orthorhombic P c a b (I.T.#61), a = 8.4342(3), b = 13.6588(5), c = 38.5506(13) Å, V =
3 -3 -1
441.1(3) Å .Z = 8, d = 1.276 g.cm , μ = 0.078 mm . The structure was solved by direct methods using
2
the SIR97 program [1], and then refined with full-matrix least-square methods based on F (SHELXL-97) [2]
with the aid of the WINGX [3] program. All non-hydrogen atoms were refined with anisotropic atomic
displacement parameters. H atoms were finally included in their calculated positions. A final refinement
2
2
on F with 5055 unique intensities and 300 parameters converged at ωR(F ) = 0.1246 (R(F) = 0.0461) for
820 observed reflections with I > 2σ(I).The figures were generated with Mercury software 3.3
3
Spectroscopic studies:
Cyclohexane (analytical grade, VWR) was used without further purification. Standard 1N solution of
sulfuric acid was purcharsed from Alfa Aesar. UV-visible spectra were recorded using an UV-Visible
spectrophotometer SHIMADZU UV-1605. The energy gap was calculated from the absorption edge of the
opt
UV-vis absorption spectra in solution in cyclohexane, using the formula ΔE (eV) = hc/λ, λ being the
-
34
-19
8
-1
absorption edge (in meter). With h = 6.6x10 J.s (1eV = 1.6x10 J) and c = 3.0x10 m.s , this equation may
opt
be simplified as: ΔE (eV) = 1237.5/λ (in nm). Triplet energy level E was calculated from the maximum of
T
the first phosphorescence emission peak, and conversion in electron-volt was obtained with the previous
formula. Emission spectra were recorded with a PTI spectrofluorimeter (PTI-814 PDS, MD 5020, LPS 220B)
using a Xenon lamp. Quantum yields in solution (ø ) were calculated relative to quinine sulfate (ø = 0.546
sol
sol
in H SO 1N). ø was determined according to the following equation,
2
4
sol
where, subscripts s and r refer respectively to the sample and reference. The integrated area of the
emission peak in arbitrary units is given as T, n is the refracting index of the solvent (n = 1.426 for cyclohe-
s
xane) and A is the absorbance. Three solutions of different concentration of the substrate (A<0.1) and three
solutions of the reference (quinine sulfate) were prepared. The quinine sulfate concentration was chosen
so as the absorption of the reference and the substrate were the same at the excitation wavelength. Three
quantum yields were then calculated at this wavelength and the average value is reported. IR spectra were
recorded on a Bruker Vertex 70 using a diamond crystal MIRacle ATR (Pike). Thin films were prepared by
spin-coating 300 μL of solution of THF (10 g/L) on a sapphire plate (10 mm x 10 mm) at 2500 tr/min on a
Süss MicroTech Labspin 6.
Fluorescence intensity decays were obtained by the time-correlated single-photon counting
(
TCSPC) method with femtosecond laser excitation using a Spectra-Physics set-up composed of a Titanium
Sapphire Tsunami laser pumped by a doubled YAG laser Millennia. Light pulses at 990 nm (resp. 900 nm)
were selected by optoacoustic crystals at a repetition rate of 4 MHz, and the third harmonics at 330 nm
-
19 -

ACCEPTED MANUSCRIPT
(
resp. 300 nm) was obtained through non-linear crystals. Fluorescence photons were detected through a
monochromator by means of a Hamamatsu MCP R3809U photomultiplier. The time-to-amplitude converter
was purchased from Tennelec. The fluorescence data were analyzed by a nonlinear least-squares global
method using the Globals software package developed at the Laboratory for Fluorescence Dynamics at the
University of Illinois, Urbana-Champaign.
Electrochemical studies. Electrochemical experiments were performed under argon atmosphere 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 0.1M AgNO solution in CH CN. Ferrocene was added to the solution at the
3
3
+
end of a series of experiments. The ferrocene/ferrocenium (Fc/Fc ) couple served as internal standard. The
three electrodes cell was connected to a PAR Model 273 potentiostat/galvanostat (PAR, EG&G, USA)
monitored with the ECHEM Software. Activated Al O was added in the electrolytic solution to remove
2
3
excess moisture. 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 vs. Fc/Fc system. Following the work of
48
Jenekhe, we estimated the electron affinity (EA) or lowest unoccupied molecular orbital (LUMO) and the
ionisation potential (IP) or highest occupied molecular orbital (HOMO) from the redox data (tangent to the
red
oxidation or reduction wave). The LUMO level was calculated from: LUMO (eV)= -[E
(vs SCE) +4.4] and
onset
ox
the HOMO level from: HOMO (eV) = -[Eonset (vs SCE) + 4.4], based on an SCE energy level of 4.4 eV relative
to the vacuum. The electrochemical gap was calculated from: ΔE =|HOMO-LUMO| (in eV).
el
68 69
Theoretical modeling. Full geometry optimization with Density Functional Theory (DFT)
and Time-
Dependent Density Functional Theory (TD-DFT) calculations were performed with the hybrid Becke-3
7
0-72
73
parameter exchange
functional and the Lee-Yang-Parr non-local correlation functional (B3LYP)
74
implemented in the Gaussian 09 (Revision B.01) program suite using the 6-311G+(d,p) basis set and the
default convergence criterion implemented in the program. The figures were generated with GaussView
5
.0. The computed triplet adiabatic S to T excitation energies were calculated from the difference
0 1
between the total energy of the molecule in their respective singlet and triplet states.
Thermal analysis:
Thermal Gravimetric Analysis (TGA) was carried out by using TA SDT Q600 instrument, at the "Ecole
Nationale Supérieure de Chimie de Rennes" or at the "Institut des Sciences Analytiques" (UMR CNRS 5280)
of Villeurbanne. TGA curves were measured at 10°C/min from 0 to 600°C under an azote atmosphere.
Differential Scanning Calorimetry (DSC) was carried out by using NETZSCH DSC 200 F3 instrument equipped
with an intracooler. DSC traces were measured at 10°C/min. Two heating/cooling cycles were succesively
nd
carried out and the glass transition Tg was determined from the 2 heating cycle. Temperatures of the
different transitions given are obtained with the tangent to the transition peak.
Device fabrication and characterisation:
OLEDs based on a multilayer structure have been fabricated onto patterned ITO coated glass substrates
from XinYan Tech (thickness: 100 nm and sheet resistance: less of 20 W/m). The organic materials (from
-
6
Aldrich and Lumtec) are deposited onto the ITO anode by sublimation under high vacuum (< 10 Torr) at a
rate of 0.2 – 0.3 nm/s. The structure of the device is the following: ITO/CuPc(10 nm)/NPB (40 nm)/TCTA (10
nm)/Hosts:dopant (20 nm)/TPBi (40 nm)/LiF (1.2 nm)/Al (100 nm). In this device, ITO is used as the anode,
CuPc (copper phtalocyanine) is the hole injecting layer, NPB (N,N’-di(1-naphtyl)-N,N’-diphenyl-[1,1’-biphe-
nyl]-4,4’-diamine) is the hole-transporting layer, TCTA (4,4',4''-Tris(carbazol-9-yl)-triphenylamine) is the
electron/exciton blocking layer, TPBI (1,3,5-Tris(1-phenyl-1H-benzimidazol-2-yl)benzene) is both the
electron transporting layer and the hole blocking layer and a thin film of lithium fluoride over aluminum is
the cathode. The entire device is fabricated in the same run without breaking the vacuum. In this study, the
thicknesses of the different organic layers were kept constant for all the devices. The active area of the
devices defined by the overlap of the ITO anode and the metallic cathode was 0.3 cm². The
current-voltage-luminance (I-V-L) characteristics of the devices were measured with a regulated power
2
supply (Laboratory Power Supply EA-PS 3032-10B) combined with a multimeter and a 1 cm area silicon
calibrated photodiode (Hamamatsu). The spectral emission was recorded with a SpectraScan PR650
spectrophotometer. All the measurements were performed at room temperature and at ambient
atmosphere with no further encapsulation of devices.
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20 -

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ACCEPTED MANUSCRIPT
Supplementary Materials for
2-substituted vs 4-substituted-9,9'-spirobifluorene host materials
for green and blue phosphorescent OLEDs: A Structure-Property Relationship
Study
a
c
c
c
Sébastien Thiery, Céline Declairieux, Denis Tondelier, Gijun Seo, Bernard
*a
c,d
a
b
*a
Geffroy, Olivier Jeannin, Rémi Métivier, Joëlle Rault-Berthelot, Cyril Poriel
a. Université de Rennes 1-UMR CNRS 6226, "Institut des Sciences Chimiques de Rennes"
MaCSE group. Bat 10C, Campus de Beaulieu, 35042 Rennes, France
b. PPSM, Institut d'Alembert, ENS Cachan, UMR CNRS 8531, 61 Avenue du Président
Wilson, 94235 Cachan, France
c. LPICM, Ecole Polytechnique, UMR CNRS 7647, Route de Saclay, 91128, Palaiseau
d. LICSEN, CEA Saclay, IRAMIS/NIMBE, 91191 Gif sur Yvette
ꢀ
Summary
X-RAY DIFFRACTION............................................................................................................ 2
PHOTOPHYSICAL PROPERTIES .......................................................................................... 8
THEORETICAL MODELING................................................................................................ 16
THERMAL PROPERTIES...................................................................................................... 22
ELECTROCHEMICAL PROPERTIES .................................................................................. 25
2D NMR STUDIES ................................................................................................................. 29
COPY OF NMR SPECTRA .................................................................................................... 47
COPY OF MASS SPECTRA................................................................................................... 59
1

ACCEPTED MANUSCRIPT
X-RAY DIFFRACTION
Table 1 Crystal data and structure refinement for 2-Ph-SBF
Identification code
2-Ph-SBF
Empirical formula
Formula weight
Temperature
62 40
C H
784.94
150(2) K
Wavelength
0.71073 Å
Crystal system
Space group
Triclinic
P-1
Unit cell dimensions
a = 10.9027(4) Å = 102.1400(10)°.
b = 13.7902(6) Å = 97.4710(10)°.
c = 15.7771(5) Å  = 111.5900(10)°.
Volume
2099.47(14) Å3
Z
2
Density (calculated)
Absorption coefficient
F(000)
1.242 g/cm3
0.070 mm-1
824
Crystal size
0.26 x 0.24 x 0.09 mm3
Theta range for data collection 1.36 to 27.50°.
Index ranges
-14<=h<=13, -17<=k<=17, -20<=l<=20
Reflections collected
Independent reflections
20625
9543 [R(int) = 0.0307]
Completeness to theta = 27.50° 98.9 %
Absorption correction
Semi-empirical from equivalents
Max. and min. transmission
Refinement method
0.994 and 0.982
Full-matrix least-squares on F2
9543 / 0 / 559
Data / restraints / parameters
Goodness-of-fit on F2
1.074
Final R indices [I>2sigma(I)]
R indices (all data)
R1 = 0.0447, wR2 = 0.1128
R1 = 0.0583, wR2 = 0.1272
0.261 and -0.269 e.Å-3
Largest diff. peak and hole
2

ACCEPTED MANUSCRIPT
Table 2 Crystal data and structure refinement for 2-5Pm-SBF
Identification code
Empirical formula
Formula weight
Temperature
2-5Pm-SBF
30 22 2
C H N O
426.5
150(2) K
Wavelength
0.71073 Å
orthorhombic
P c a b
Crystal system
space group
Unit cell dimensions
a = 8.4342(3) Å, α = 90 °
b = 13.6588(5) Å, β = 90 °
c = 38.5506(13) Å, γ = 90 °
3
Volume
Z
4441.1(3) Å
8
-
3
Calculated density
Absorption coefficient
F(000)
1.276 (g.cm )
-
1
0.078 mm
1792
Crystal size
0.36 x 0.31 x 0.05 mm
1.06 to 27.46 °
-10, 9
Theta range for data collection
h_min, h_max
k_min, k_max
-17, 16
l_min, l_max
-45, 50
a
Reflections collected / unique
Reflections [I>2σ]
Completeness to theta_max
Absorption correction type
Refinement method
Data / restraints / parameters
Goodness-of-fit
21000 / 5055 [R(int) = 0.0327]
3820
0.994
multi-scan
2
Full-matrix least-squares on F
5055 / 0 / 300
1.124
c
d
Final R indices [I>2σ]
R indices (all data)
Largest diff. peak and hole
R1 = 0.0461, wR2 = 0.1246
c
d
R1 = 0.0711, wR2 = 0.1511
-
-3
0.36 and -0.315 e .Å
3

ACCEPTED MANUSCRIPT
2-Ph-SBF
2
-Ph-SBF MOLECULE 1
S 1 Top: Angle between the mean plane of the pendant phenyl ring and that of its attached phenyl
ring of the fluorene : 37.37° ; Bottom: Angle between the two mean planes of each fluorene: 7.08°
4

ACCEPTED MANUSCRIPT
2
-Ph-SBF MOLECULE 2
S 2 Angle between the mean plane of the pendant phenyl ring and that of its attached phenyl ring of
the fluorene: 4.58°
5

ACCEPTED MANUSCRIPT
S 3 Short contacts (CH and C-C, distance < (sum of rvdw-0.1) detected in crystal packing of 2-Ph-
SBF.
S 4 Short contacts (CH and C-C, distance < (sum of rvdw) detected for the 2-Ph-SBF molecule 2 (in
red above)
6

ACCEPTED MANUSCRIPT
S 5 Short contacts (CH and C-C, distance < (sum of rvdw) detected for the pendant phenyl unit of 2-
Ph-SBFmolecule 2 (in red above)
S 6 Short contacts (CH and C-C, distance < (sum of rvdw) detected for the pendant phenyl unit of 2-
Ph-SBF molecule 1 (in blue above)
7