Fluorescent oligomers of dibenzothiophene-S,S-dioxide derivatives: The interplay of crystal conformations and photo-physical properties

Article abstract of DOI:10.1016/j.tet.2012.04.085

Fluorescent oligomers where the backbone of dibenzothiophene-S,S-dioxide acts as the acceptor and side chains of aryl methoxy, fluorene, and arylamine act as the donors have been effectively synthesized by the palladium-catalyzed Suzuki coupling reactions, and the photo-physical properties of the compounds were investigated. From the single-crystal XRD patterns the compounds reveal a twisted conformation with an intramolecular structure and show close relationship between intramolecular or intermolecular charge transfer and their photo-physical properties. These patterns provide more comprehensive information, which is unattainable from ¹H NMR and 2D-COSY spectra. The emission spectrum in the range of 450-510 nm can be finely tuned by systematically altering the position of substitution on the donor units of side chains connected with the backbone acceptor. The fabricated devices displayed a sky blue to deep green in terms of color and performed the CIE (x,y) coordinates with values of (0.18-0.21, 0.25-0.46), respectively.

Full text of DOI:10.1016/j.tet.2012.04.085

Tetrahedron 68 (2012) 5481e5491
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Fluorescent oligomers of dibenzothiophene-S,S-dioxide derivatives: the interplay
of crystal conformations and photo-physical properties
Chung-Yi Hsu a, Mu-Tao Hsieh a, Mu-Kuo Tsai a, Yin-Ji Li a, Chien-Jung Huang b, Yan-Kuin Su c,
,
Thou-Jen Whang a
*
a Department of Chemistry, National Cheng Kung University, Tainan 70101, Taiwan
b Department of Applied Physics, National University of Kaohsiung, Kaohsiung 81154, Taiwan
c Department of Electrical Engineering, National Cheng Kung University, Tainan 70101, Taiwan
a r t i c l e i n f o
a b s t r a c t
Article history:
Fluorescent oligomers where the backbone of dibenzothiophene-S,S-dioxide acts as the acceptor and side
chains of aryl methoxy, fluorene, and arylamine act as the donors have been effectively synthesized by
the palladium-catalyzed Suzuki coupling reactions, and the photo-physical properties of the compounds
were investigated. From the single-crystal XRD patterns the compounds reveal a twisted conformation
with an intramolecular structure and show close relationship between intramolecular or intermolecular
charge transfer and their photo-physical properties. These patterns provide more comprehensive in-
formation, which is unattainable from 1H NMR and 2D-COSY spectra. The emission spectrum in the range
of 450e510 nm can be finely tuned by systematically altering the position of substitution on the donor
units of side chains connected with the backbone acceptor. The fabricated devices displayed a sky blue to
deep green in terms of color and performed the CIE (x,y) coordinates with values of (0.18e0.21,
0.25e0.46), respectively.
Received 14 March 2012
Received in revised form 22 April 2012
Accepted 23 April 2012
Available online 4 May 2012
Keywords:
Dibenzothiophene-S,S-dioxide
Crystal-lattice
Blue emitters
Molecular charge transfer
Monodisperse
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
the relentless search for superior OLEDs materials, the yearning for
emitting materials with high-energy gap that is applicable to full-
Monodisperse oligomers (
p
-conjugated oligomers) have drawn
color displays is desperate because they are indispensable com-
ponents as a solid-state exciter. However, blue emitter materials
with high efficiency and desirable Commission Internationale
much attention in recent research because of their thermal stabil-
ities and excellent chemical properties. These materials have such
applications as in sensors,1 organic photovoltaics (OPVs),2 organic
light-emitting devices (OLEDs),3 and organic field-effect transistors
(OFETs).4 Some of the well-defined conjugated materials based on
pyrene,5 phenanthrene,6 fluoranthene,7 and anthracene8 have been
developed as efficient blue emitters9 with the supra-molecular
structure of conjugated polymers.10 The latest monodisperse of-
fers many stimulating probabilities in the field of materials science
and especially as organic electronics they provide more visions into
the photo-physics of conjugated systems.10a,c
The organic light-emitting devices (OLEDs) are becoming well-
known to consumers and are finding its place in future monitor
display applications,11 in addition to full-color emitting flat panel
displays owing to the advantages of low power consumption, fast
response, and wide viewing angle. They remain great potential as
the demand for high efficiency and stabilize modulation is esca-
lating after the emitter materials have been found by Tang et.al.12 In
ꢀ
d’Enclairage (CIE) formula (y-coordinate value less than 0.15) are
still in short supply.5
A particular interest of dibenzothiophene-S,S-dioxide being as
the backbone unit in special positions and as the linking bridge to
side chains has been aroused and was synthesized by palladium-
catalyzed Suzuki coupling reactions.11b The effect of electron con-
jugation between the donor-accepting groups can be explored by
the investigation of morphologies and making the assumption that
the meta or para position conjugation has a great influence on the
intramolecular or intermolecular charge transfer (ICT) disposition
and the photoluminescence quantum yields of the excited state.
These results revealed that the ICT states can vary the emission
region of spectrum from blue to green with acceptable high emis-
sion quantum yields.5 Furthermore, the photoluminescence emitter
of dibenzothiophene-S,S-dioxide derivatives synthesized through
both appropriate copolymerization and chemical modification can
produce emitting light for the desired spectrum. The grafting of
different side chains into the backbone provides more insights into
the related conformation properties such as charge transfer in-
teractions of ground and excited states between donor and acceptor
* Corresponding author. Tel.: þ886 (6)275 7575x65356; fax: þ886 (6)274 0552;
e-mail address: twhang@mail.ncku.edu.tw (T.-J. Whang).
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2012.04.085

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C.-Y. Hsu et al. / Tetrahedron 68 (2012) 5481e5491
moieties in this family of emitters or calculated
p
-conjugation and
resonance (NMR, Bruker-AC-300FT-NMR Spectrometer), mass
charge polarization by density functional theory (DFT).9,13
spectra (MS, FAB mode-Jeol JMS-700), elemental analysis (EA,
Heraeus, Vario EL III), two-dimensional correlation spectroscopy
(2D-COSY, Bruker-AV-400-NMR Spectrometer), and single-crystal
X-ray diffraction (SC-XRD, Bruker APEXII CCD diffractometer).
Compared with 1H NMR spectra, 2D-COSY spectra is even more
straightforward and accurate in structure confirmation and exploring
bonding relationships of the compounds, but due to signal overlaps
some interference occurred when they were interpreted making it
challenging to accomplish. Therefore, to unveil further photo-physical
properties of the compounds it is imperative to obtain accurate in-
formation of structure conformations for these molecules acquired
from SC-XRD. Despite the interpretation difficulties presented by 2D-
COSY, the physical status of molecules can be illustrated more ap-
propriately from the packing conformations acquired from SC-XRD.
The main aim of our work is to develop suitable candidates of
photoluminescence emitter from the incorporating of dibenzo-
thiophene-S,S-dioxide units into oligomers. By utilizing single-
crystal X-ray diffraction (SC-XRD) to explain the photo-physical
properties of objective materials, which were influenced by the
ICT states of framework conformation constructed from the back-
bone and side chains. From the obtained relationships of confor-
mation with electron conjugation, sequence, symmetry, and
superimposition of intermolecular arrangement, and the in-
vestigated dihedral angles indicate the intramolecular backbones
have been twisted or have been constrained by their substituent
groups with the conformation of planarized ladder.10b,14
2. Results and discussion
2.1. Materials and synthesis
2.2. Two-dimensional correlation spectroscopy
With greater clarity than 1D spectrum, 2D spectrum by free
induction decay (FID) process and Fourier transform (FT) technique
can be employed to interpret the correlation between signals in 1H
spectra. The 1H environmental assignments can be achieved
through the correlations between the related signals, which are
discrete away from the diagonal. The related information between
the contour diagram and the compound structure of a 2D spectrum
for compound DBTO-MP is shown in Fig. 1a with great interest,
such as peak a correlates with peak c significantly than with peak
b and peak b correlates with peak c notably than with peak d.
Moreover, peak c is affected by peak d and peak e is less relative to
peak f. It is recognized that peak e is not showing correlation with
peak d whereas these peaks show explicit interaction in 1D spectra.
Additionally, the chemical shifts of position (1) exist both at 3.99
and 3.95 ppm and are not shown in the 2D diagram.
The appealing syntheses and symmetrical arrangements of
dibenzothiophene-S,S-dioxide derivatives outlined in Scheme 1
were readily achieved by the backbone of 2,7-diiododibenzothio-
phene. In Scheme 1, reaction (a) was first prepared by oxidation of
dibenzothiophene into S,S-dioxide derivative using hydrogen per-
oxide, acetic acid (H2O2/HOAc) at room temperature, and then re-
action (b) synthesized by twofold electrophilic iodination of
dibenzothiophene-S,S-dioxide using periodic acid, iodine (HIO4/I2)
at 80 ꢀC with a fair yield (60%). Reaction (c) using one-reactor
Suzuki coupling reaction between the side chain boronic acid and
backbone in the presence of palladium catalyst tetrakis(-
triphenylphosphine)-palladium(0) (1e3 mol %), was carried out
with a good yield (60e75%). All of the desired compounds were
confirmed by the measurements of 1H, 13C nuclear magnetic
O
O
O
O
O
S
S
O
N
O
N
O
DBTO-MP
D
BTO-PP
(c)
(c)
B(OH)2
O
O
B(OH)2
N
+
+
+
(a) HOAc, H2O2
O
S
O
S
O
O
I
S
(a)
(b)
(b) HOAc, H2SO4,
I2, H5IO6
I
(c) Pd(PPh3)4, THF,
K2CO3(aq)
+
(HO)2B
(HO)2B
(c)
(c)
O
O
S
O
O
S
DBTO-PF
DBTO-MF
Scheme 1. Synthesis processes of dibenzothiophene-S,S-dioxide derivatives, including (a) oxidation, (b) iodination, and (c) palladium catalytic Suzuki coupling reaction.

C.-Y. Hsu et al. / Tetrahedron 68 (2012) 5481e5491
5483
Fig. 1. Two-dimensional correlation spectroscopy (2D-COSY) and structures related to identified dibenzothiophene-S,S-dioxide derivatives (a) DBTO-MP, (b) DBTO-MF, (c) DBTO-PF,
and (d) DBTO-PP.
Fig. 1b exhibits the 2D spectrum of compound DBTO-MF, the
decreasing extents of correlativity are in the following order, peak
b is significantly correlated with peaks f and c and peak d is fairly
related to peak g, eventually peak i has correlations with peaks h
and j simultaneously. Even though peak a is in the vicinity of c, it
shows explicit interaction only in 1D spectra. Moreover, the
chemical shift of position (1) exists only at 1.57 ppm and is not
shown in the 2D diagram.
The 2D spectrum for compound DBTO-PF is shown in Fig.1c, the
observed correlations between peaks of symmetrical signals are
such that peak a is corresponding to peak b, both peaks d and e are
corresponding to peaks f and j simultaneously. Moreover, peak g
correlates with peak k and peak i correlates with peaks j and l
concurrently. It is worth noting that peak j is corresponding to
peaks d, e, and i simultaneously whereas showing no correlation
with peak c. Furthermore, the chemical shift of position (1) exists
only at 2.32 ppm and is not shown in the 2D diagram.
The 2D spectrum of compound DBTO-PP is shown in Fig. 1d. The
correlation contour discloses clearly that peak a is related to peak c
and peak b is related to peaks c and d simultaneously while peak e
correlates to peak f. It is recognized that peak c has no apparent
correlation with peak e while these two peaks show explicit in-
teraction in 1D spectra. However, with the integrated examination of
the signals from 1H spectra and 2D spectra the later can provide

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C.-Y. Hsu et al. / Tetrahedron 68 (2012) 5481e5491
Fig. 1. continued
additional confirmation for the assignments; therefore it is an ad-
vantageous tool to give unambiguous interpretations in this regard.
Crystallographic Data Centre (CCDC). The derivatives presented
a twisted form between backbone and side chains, and the internal
torsion (dihedral) angles of 28ꢀe33ꢀ were observed in the solid
state. The twisted configuration is accountable for the co-plane
aggregation in the solid state that may induce emitted fluores-
cence and quantum yield differences of the similar films when
comparing the efficiencies of electron conjugations with the
donoreacceptor systems.
2.3. Single-crystal X-ray analysis
As shown in Fig. 2, the single-crystal X-ray patterns of diben-
zothiophene-S,S-dioxide derivatives were analyzed by comparing
Crystallographic Information Framework (CIF) from Cambridge

C.-Y. Hsu et al. / Tetrahedron 68 (2012) 5481e5491
5485
Fig. 2. Thermal ellipsoid plots from checking crystallographic information framework (CIF) for single-crystal X-ray diffraction (SC-XRD) spectrum for (a) DBTO-MP, (b) DBTO-MF,
and (c) DBTO-PP (containing a molecule of CH2Cl2 in single crystal).
Besides, the structures of DBTO-MP (CCDC 865523), DBTO-MF
(CCDC 865522), and DBTO-PP (CCDC 865524) compounds were
confirmed further by single-crystal X-ray analyses. The principal
molecular patterns are shown in Fig. 2, while the crystallographic
data of structures are listed in Table 1. The crystal packing diagrams
and the configurations of the compounds are shown in Fig. 3. In the
crystal-lattice, these dibenzothiophene-S,S-dioxide derivatives
presented highly trustworthy information with the Final R indices
(R value less than 0.1) as 0.05, 0.06, 0.05 for DBTO-MP, DBTO-MF,
and DBTO-PP, respectively. The dihedral angles between the
backbone of dibenzothiophene-S,S-dioxide and the neighboring
side-chain groups were attained as 28ꢀ (C1eC6eC7eC8 in Fig. 2a),
30ꢀ(C22eC25eC26eC27 in Fig. 2b), and 33ꢀ(C18eC11eC2eC12 in
Fig. 2c) for DBTO-MP, DBTO-MF, and DBTO-PP, respectively.
Fig. 2a is the structure of DBTO-MP, which is verified by com-
paring CIF, the two methoxy groups on each side-chain are pointed
away from each other due to repulsion. The real structure of DBTO-
MF is shown in Fig. 2b, the result is rather incompatible in the
statement of structure with that of Ref. 9 and therefore it is required
to acquire the information SC-XRD for additional confirmation.
Moreover, to prepare the crystal-lattice of DBTO-MP and DBTO-MF
for such analyses as to what characteristics are limited to materials,
extra-pure crystal of these compounds can be produced through
sublimationecondensation process by our novel purification sys-
tem with a vertically quartz-tube evaporation device in a short
time.15 But only DBTO-PP crystals as shown in Fig. 2c were de-
veloped utilizing re-crystallization of solvent selectivity for a long
time, and it is paradoxical that two molecules of DBTO-PP hold
a solvent molecule of CH2Cl2 in the lattice. Unfortunately, the
DBTO-PF derivative was found unable to form crystal seed by these
two methods above.
DBTO-MF crystallized in the orthorhombic system and is
assigned to space group Pbcn, whereas derivatives DBTO-MP and
DBTO-PP crystallized in the monoclinic system and are assigned to
C2/c space group. Then these frameworks between backbone and
side chains assembled three-dimensional configurations along a-,
b-, and c-axis for different pattern arrangements, as shown in Fig. 3.
The view along a-axis bears resemblance to elegant crab-shape,
field cricket-shape, and traffic triangle-shape for DBTO-MP,
DBTO-MF, and DBTO-PP, respectively. When these a-axis patterns

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C.-Y. Hsu et al. / Tetrahedron 68 (2012) 5481e5491
Table 1
Crystal data and structure refinement for synthetic compounds
Identification code CCDC number
DTBO-MP(st4) CCDC 865523
DTBO-MF(st1) CCDC 865522
DTBO-PP(st5) CCDC 865524
Empirical formula
Formula weight
Temperature
C28H24O6S
488.54
C42H32O2S
600.75
C97H68N4O4S2Cl2H2
1488.59
296(2) K
296(2) K
296(2) K
ꢁ
ꢁ
ꢁ
Wavelength
0.71073 A
0.71073 A
0.71073 A
Crystal system
Space group
Unit cell dimensions
Monoclinic
C2/c
Orthorhombic
Monoclinic
C2/c
Pbcn
ꢁ
ꢁ
ꢁ
a¼31.824(3) A
a¼28.942(2) A
a¼45.633(5) A
a
¼90ꢀ
a
¼90ꢀ
a
¼90ꢀ
ꢁ
ꢁ
ꢁ
b¼7.5403(8) A
b¼8.0543(6) A
b¼8.1188(9) A
b
¼92.344(2)ꢀ
b
¼90ꢀ
b
¼99.271(2)ꢀ
ꢁ
ꢁ
ꢁ
c¼9.6839(10) A
c¼27.3731(19) A
c¼20.639(2) A
g
¼90ꢀ
g
¼90ꢀ
g
¼90ꢀ
3
3
ꢁ
3
ꢁ
ꢁ
Volume
Z
Density (calculated)
Absorption coefficient
F(000)
Crystal size
Theta range for data collection
Index ranges
Independent reflections
Data/restraints/parameters
Goodness-of-fit on F2
2321.9(4) A
4
6380.8(8) A
8
7546.4(15) A
4
1.398 Mg/m3
1.251 Mg/m3
1.310 Mg/m3
0.183 mmꢁ1
0.138 mmꢁ1
0.201 mmꢁ1
1024
2528
3104
0.2ꢂ0.067ꢂ0.009 mm3
0.4ꢂ0.1ꢂ0.037 mm3
0.08ꢂ0.04ꢂ0.006 mm3
2.56ꢀe28.26ꢀ
1.49ꢀe28.30ꢀ
0.90ꢀe28.37ꢀ
ꢁ42ꢃhꢃ41, ꢁ10ꢃkꢃ9, ꢁ12ꢃlꢃ11
2864 [R(int)¼0.0578]
2864/0/161
ꢁ38ꢃhꢃ37, ꢁ10ꢃkꢃ10, ꢁ27ꢃlꢃ36
7916 [R(int)¼0.1046]
7916/0/410
ꢁ60ꢃhꢃ56, ꢁ10ꢃkꢃ10, ꢁ27ꢃlꢃ25
9436 [R(int)¼0.0366]
9340/0/503
0.975
0.991
1.049
Final R indices [I>2
R indices (all data)
Largest diff. peak and hole
s
(I)]
R1¼0.0526, wR2¼0.1099
R1¼0.0590, wR2¼0.1124
R1¼0.0534, wR2¼0.1417
R1¼0.1142, wR2¼0.1339
R1¼0.1614, wR2¼0.1464
R1¼0.0877, wR2¼0.1674
ꢁꢁ3
ꢁꢁ3
ꢁꢁ3
0.193 and ꢁ0.292 e A
0.161 and ꢁ0.324 e A
0.485 and ꢁ0.539 e A
bisect from top to bottom, the two halves of DBTO-MP are identical
to each other, whereas one of two halves of DBTO-MF can be
overlapped with the other half after 180ꢀ rotation. The same situ-
ation happened as one of the two halves of DBTO-PP after 180ꢀ
rotation, the two halves are also indistinguishable provided that the
identities of S, Cl, and N atoms are ignored. The investigation re-
garding to the phenomenon and tropism of photo-physical prop-
erties shows the electron conjugation of DBTO-MF allows more
direct transmission than those of DBTO-MP and DBTO-PP by more
favorable structural alignment. Keeping trapping styles with crab-
shaped (DBTO-MP) and triangle-shaped (DBTO-PP) may in-
fluence the smoothness of electron transfer.
In the 2D macrostructure of the lattices by observing from c-axis, two,
four, and eight units of molecules were assembled for enantiomeric
structures for DBTO-MP, DBTO-MF, and DBTO-PP, respectively. From
a symmetrical point of view, DBTO-PP unit possesses higher sym-
metry of intermolecular conformation than the other lattice units
and in the 3D profile conformation, the section images of the com-
pounds in the same order resemble regular assembly form of z-shape
serial, spiral strip, and brick wall, respectively. For instance, more
superimposition of intermolecular interactions can be achieved from
the spiral strip form of DBTO-MF unit.
Accordingly, in the packing process of crystallization the twist-
ing conformation is the principal factor causing variation of the
related emission wavelength. Photo-physical properties such as
improving charge mobility between interplane or fluorescence
emission mechanism of a luminophore will be closely related to
molecular stacking in the solid state.20 A. Harriman et al. proposed
the potential energy diagram explaining the behavior of materials
in a fluid solvent, the rotor effect (kNR) shows a relationship with
In contrast to ordinary perception, crystal formation causes an
emission shift in wavelength and enhances the emission intensity.
Crystallographic analyses revealed that the real factors causing
greater luminescence efficiency in crystals are due to short of
powerful co-facial pep stacking and the presence of H-bondings of
the intermolecular interactions.16 Viewing along b-axis, the lattice
of DBTO-MP slants around 50ꢀ to the right and at the terminals of
the side chains the molecules display a model of enantiomorphism.
The conformation of DBTO-MF was constructed through the con-
tinuous alternating ‘V’ and ‘L’ wave-shaped coherent structure, and
the arrangement of DBTO-PP bears resemblance to sandwich shape
in which a solvent molecule was encircled by two DBTO-PP mole-
cules and the associated molecules create an oblong-shape struc-
ture by the neighboring side chains of six unit molecules.
Interestingly, the side chains of a supramolecule unit serve as
bridges and intermolecular interactions arise through them. When
both the fluorescence quantum yield (FF) and emission lifetime (sS
)
to mathematical equation [kNR¼(1ꢁFF)/ S], to describe the in-
s
teractions among emission energy gap, temperature, and dihedral
angles.21 The related effect between the dihedral angles and mo-
lecular energy states of thermal vibrations is already well-known,
as shown in configuration changes for the Schiff base derivatives
calculated by using DFT (density functional theory), which is im-
portant in explanation of correlations between the occurrence and
decay of the absorption and fluorescent state.14bed Therefore, both
the fluorescence efficiency and the emission tuning wavelength can
be interpreted by thorough investigations of the crystal confor-
mations. By comparison, fluorescence quenching in the solid state
considering the probability of H-bondings and
pep stacking in-
teractions,17 the explanation of DBTO-MP and DBTO-MF units
possessing more intermolecular arrangement sequence than DBTO-
is strongly affected from the significant molecular
pep stacking
PP lattice unit and DBTO-MF having little effect on
pe
p
stacking
interactions.20c
interactions lies in the fact that the face to face intermolecular
18
ꢁ
distance being ca. 3.329 A as shown in Fig. 3. Nevertheless, the
FTIR spectra of dibenzothiophene-S,S-dioxide derivatives, which
have been identified based on the literature data,19 showed in vir-
tual absence of intramolecular or intermolecular H-bonding.
Obviously, the structures were likely constructed from regular
alternative chiral enantiomers by viewing along c-axis of the lattices.
2.4. Physical properties, thermal characterization, and
related efficiency
The photoabsorption (UV) and photoluminescence (PL) spectra
of DBTO-MP, DBTO-MF, DBTO-PF, and DBTO-PP are shown in
Fig. 4a. The spectra exhibit the normalized intensity of absorption

C.-Y. Hsu et al. / Tetrahedron 68 (2012) 5481e5491
5487
Fig. 3. The model diagrams of molecular structures transferred from CIF taken along axes of a, b, and c, intermolecular distance and 3D profile conformation for DBTO-MP, DBTO-
MF, and DBTO-PP.

5488
C.-Y. Hsu et al. / Tetrahedron 68 (2012) 5481e5491
spectra measured in dilute dichloromethane solution (<10ꢁ4 M)
and photoluminescence (PL) spectra in thin films. Each material
(a)
possesses two principal peaks of UV absorption and one principal
Photoluminescence
DBTO-MP
DBTO-MF
DBTO-PP
peak of PL. When comparing to the differences between labs and lp
,
DBTO-PF
it is found that there are practically 100ꢄ30 nm and 200ꢄ30 nm
differences between lp and each labs for each compound.
In general, when these dibenzothiophene-S,S-dioxide de-
rivatives are excited utilizing the absorbed peak labs for charge-
transfer characterization, the PL emission will be the most effi-
cient. Upon excitation either at less than 300 nm, which is assigned
to the n/
p
*
transition of side chain molecule or at more than
transition of dibenzo-
330 nm, which is coincident to the
p
/p
*
thiophene-S,S-dioxide backbone, the emission spectra acquired are
duplicate, suggesting that excited energy can efficiently transfer
from the side chain to the dibenzothiophene-S,S-dioxide core.11b
The photo-physical properties of dibenzothiophene-S,S-dioxide
derivatives are listed in Table 2. The trait peaks of absorption wave-
length (labs), which are located at around 250 and 350 nm of ab-
sorption wavelength and is in moderate increasing order for DBTO-
MP, DBTO-MF, and DBTO-PF, while DBTO-PP exhibits 50 nm red shift,
which is risen from 350 nm for DBTO-PF to 400 nm excited wave-
length. In Table 2 these maximums correspond to the maximums of
emitted wavelength (ls) in the solvent of CH2Cl2 and the maximums of
emitted wavelength (lp) in the deposited films. Compare the PL of
DBTO-MF and DBTO-PF there is a wavelength difference of 40e50 nm
between lp and ls for both compounds, the other two compounds
exhibit a slightly wavelength difference of 10 nm. It is presumably
ascribed to the individual or integrated effects of intramolecular or
intermolecular charge transfer (ICT), solvate-chromatic effect, or the
arrangement of coplanar configuration.5,11b,13a,22
Absorbance
DBTO-MP
DBTO-PF
DBTO-MF
DBTO-PP
Wavelength (nm)
(b)
Because of these resembled structures having different side
chains connected to the dibenzothiophene-S,S-dioxide backbone,
the relatively strong emissions of these materials compared with
that of other compounds could be attributed to the favorable
donoreacceptor configuration of the material frameworks, which is
related to the extent of intermolecular stacking, intramolecular co-
planarity and p-delocalization in the films. It is worth noting that
the emission energy correlates profoundly to the related architec-
ture between backbone and side chain.
Wavelength (nm)
(c)
To examine whether the purified compounds could be poten-
tially applied for superior performance for the material of a blue
electroluminescence (EL), including DBTO-MP, DBTO-MF, DBTO-
PF, and DBTO-PP were fabricated into OLED devices. The materials
were deposited in a thermal evaporator for optoelectronic device,
which
includes
N,N0-di(1-naphthyl)-N,N0-diphenyl-benzidine
(NPB), 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), and
lithium fluoride (LiF). The typical device structure contains (a) an
indium-tin oxide (ITO) anode, (b) a hole transport layer (HTL), (c) an
emitting layer (EML), (d) a hole blocking layer (HBL), (e) an electron
transport layer (ETL), (f) an aluminum (Al) cathode, the device was
fabricated as the following sequence of indium-tin oxide ITO/NPB
(40 nm)/blue emitter (30 nm)/BCP (10 nm)/LiF (1 nm) / Al.
Each of the functional layers plays the role of an optimum
contact at the interface section at which a lower driving voltage and
the untainted color emitted from emitter layer was achieved. In this
integrated device, it was perceived that the performance of the
emitter is better because it is not likely to form exciplexes with the
hole-blocking layer. As shown in Fig. 4b and Table 2, to compare
with the PL and electroluminescence (EL) spectra, it was found
what the main peak of the PL pattern red-shifted about 10e20 nm,
which matches with the EL pattern and the full width at half
maximum (FWHM, Dup and Due) of the EL patterns displays nearly
twofold broader than those of PL. This result is related to the re-
combination of exciter photons (electrons and holes) at the in-
terface. Luminance density of 1 cd/m2 was achieved with the initial
applied voltage of 4e5 V and the EL was measured at 10 V.
Voltage (V)
Fig. 4. (a) Absorption and emission spectra. (b) Normalized spectra of photo-
luminescence and electroluminescence. (c) The plot of current densi-
tyeluminescenceevoltage (IeLeV) curves for electrical characteristics (ITO/
NPB(40 nm)/blue emitter (30 nm)/BCP(10 nm)/LiF(1 nm)/Al) for DBTO-MP, DBTO-MF,
DBTO-PF, and DBTO-PP.

C.-Y. Hsu et al. / Tetrahedron 68 (2012) 5481e5491
5489
Table 2
Related identified properties of synthesized dibenzothiophene-S,S-dioxide derivatives
Compound
Optic properties (nm)
f
(%)
Thermal properties (ꢀC)
Energy level properties (eV)
labs
ls
lp
Dup
le
Due
Tg
Tc
Tm
Td
Eg
EHOMO
ELUMO
DTBO-MP
DTBO-MF
DTBO-PF
DTBO-PP
335/245
345/270
350/235
400/295
445
417
419
502
453
465
458
508
52
60
58
65
464
484
472
524
116
112
126
105
49
82
64
17
155
116
132
110
280
233
d
308
331
353
291
370
435
506
440
3.07
3.08
3.06
2.79
ꢁ5.74
ꢁ5.72
ꢁ5.68
ꢁ5.58
ꢁ2.67
ꢁ2.64
ꢁ2.62
ꢁ2.79
d
Note: labs, trait peak of absorption wavelength; ls, maximum of emitted wavelength in the solvent of CH2Cl2; lp, maximum of emitted wavelength in the deposited film; Dup
full width at half maximum (FWHM) of photoluminescence; le, maximum of excited wavelength in the device; Due, full width at half maximum (FWHM) of electrolumi-
nescence; , calculated quantum yield by standard of quinine sulfate/1 N H2SO4; Tg, glass transfer temperature; Tc, crystallization temperature; Tm, melting temperature; Td,
,
f
decomposition temperature; Eg, calculated by the beginning wavelength of absorption; EHOMO, measured highest occupied molecular orbital of energy; ELUMO, measured
lowest non-occupied molecular orbital of energy.
To achieve narrow width emitting and improved performance
for the devices based on the derivatives of dibenzothiophene-S,S-
dioxide, it depends on the parameter settings of the evaporating
deposition configuration for emitting layers. In view of the EL ef-
ficiency of the dibenzothiophene-S,S-dioxide derivatives, that is the
ideal emission for single deposited emitting layer, DBTO-MP ex-
hibits more luminescence and current efficiency compare to other
derivatives as shown in Fig. 4c. Interestingly, the derivatives except
for DBTO-PP, which is located in CIE 1931 coordinates of (0.24,
0.46) with the occurrence of red shift due to ICT and weak electron
conjugation effects, the others are located in CIE coordinates of
(0.19, 0.25), (0.18, 0.25), and (0.21, 0.25) for DBTO-MP, DBTO-MF,
and DBTO-PF, respectively.
Table 2 shows the thermal characterization of the synthesized
dibenzothiophene-S,S-dioxide derivatives evaluated by thermogra-
vimetric analyses (TGA) and differential scan calorimetry (DSC). The
glass transition temperatures (Tg) of DBTO-MP, DBTO-MF, DBTO-PF,
and DBTO-PP were detected at 155, 116, 132, and 110 ꢀC, re-
spectively. The decomposition temperature (Td, as 5 wt % loss) of
these compounds referred to above were found by TGA analysis at
370, 435, 506, and 440 ꢀC, respectively. Among these compounds,
DBTO-MP and DBTO-PF possess excellent stability with higher Tg
and Td, respectively. The melting point (Tm) of these four compounds
in the same order shows the endothermic phase transitions occurred
at 308, 331, 353, and 291 ꢀC, respectively, which is in the similar
trend as Td. During the DSC heat-scanning process the crystallization
transition temperature (Tc), which happens after rapid cooling from
the melting state due to the exothermic transition of crystallization,
was measured at 280 ꢀC for DBTO-MP and 233 ꢀC for DBTO-MF.
Interestingly, owing to the dependent thermal properties of mate-
rials, fast exothermic transition of crystallization for DBTO-PF and
DBTO-PP was not observed, which apparently revealed the crystal-
lattice formation for these compounds are unattainable.
transfer character of the excited state and the dihedral angle of
twisted conformation of the compounds were explored. Compre-
hensively, the relationships between SC-XRD and photo-physical
properties are correlated through sequence arrangements, sym-
metry conformations, and superimposition of intermolecular in-
teractions. In the substitution reaction of the aryl methoxy side
chain by fluorene the emission exhibited slightly red-shift from sky
blue region, and for the substitution by arylamine the emission
showed red-shift further into bright green region. Furthermore, the
single-crystal X-ray pattern analyses supply more comprehensive
information than that of 1H NMR, 2D-COSY spectra, such that these
derivatives unveil the relationships between their geometries with
nonplanar molecular structures in the solid state and their photo-
physical properties. These results provide new insights into
donoreacceptor interactions in conjugated oligomers and dem-
onstrate that dibenzothiophene-S,S-dioxide is a very attractive
candidate for OLED materials.
4. Experimental section
4.1. Procedure: palladium-catalyzed Suzuki coupling
2,7-Diiododibenzothiophene (1 equiv) and the side chain bo-
ronic acid derivative 3,4-dimethoxyphenylboronic acid, 9,9-
dimethylfluoren-2-ylboronic acid, 9,9-di-tolylfluoren-2-ylboronic
acid or 4-(diphenylamino) phenylboronic acid (2.2 equiv) was
dissolved in tetra-hydrofuran (THF). The solution kept in oxygen
by bubbling dry nitrogen through it for 10 min. Tetrakis(-
triphenylphosphine)-palladium(0) or dichlorobis(triphenylphos-
phine)-palladium(II) (1e3 mol %) and sodium hydroxide or
potassium carbonate solution (2 M) were added and the solution
reflux further under nitrogen, held on heating at 80 ꢀC for 48 h in
the dark. The resulting crude was extracted into water and
dichloromethane (DCM), and then removed with water and organic
layer was dried over magnesium sulfate (MgSO4). ‘The organic
solvent was removed by the evaporating system and the derivatives
were purified through the method of column chromatography.
It should be noted that the PL quantum yield (f) was calculated
by the standard solution of quinine sulfate dissolved in 1 N H2SO4.
In the view of unit efficiency, DBTO-MF took precedence over other
materials with a yield of 82%. The estimated optical energy gap (Eg)
was evaluated through the beginning wavelength of absorption,
with 3.07, 3.08, 3.06, and 2.79 eV for DBTO-MP, DBTO-MF, DBTO-
PF, and DBTO-PP, respectively. In terms of color, only DBTO-PP
produced a sparkling olive-green, the others created a brilliant pale
blue of the emission.
4.1.1. Dibenzothiophene-S,S-dioxide. 1H NMR (300 MHz, CDCl3,
ppm)
d
7.82 (m, 4H), 7.65 (t, J¼7.6 Hz, 2H), 7.54 (t, J¼7.6 Hz, 2H). 13
C
NMR (75 MHz, CDCl3, ppm)
121.54.
d 137.53, 133.82, 131.45, 130.26, 121.98,
3. Conclusions
4.1.2. 2,7-Diiododibenzothiophene-S,S-dioxide (DBTO-I). FTIR
(n/
cmꢁ1): 3088 (w), 1458 (m), 1400 (m), 1303 (s), 1172 (s), 1068 (v),
1000 (w), 880 (w), 838 (s), 770 (v), 705 (m), 648 (w), 576 (s), 495
The novel donoreacceptoredonor oligomers of dibenzothio-
phene-S,S-dioxide derivatives, with constrained dihedral angles in
the core, have been successfully synthesized by the effective Suzuki
coupling reactions. The donor strength of the side chains was found
in the increasing order of aryl methoxyzfluorene>arylamine. The
photo-physical properties of the products have been investigated
thoroughly in this article, specifically the intramolecular charge-
(w), 428 (m). 1H NMR (300 MHz, CDCl3, ppm)
d 8.12 (s, 2H), 7.98 (d,
J¼8.0 Hz, 2H), 7.52 (d, J¼8.0 Hz, 2H). 13C NMR (75 MHz, CDCl3, ppm)
d
142.87, 138.28, 130.97, 130.16, 122.87, 95.41.
4.1.3. 2,7-Bis(3,4-(dimethoxyl)phenyl)-dibenzothiophene-S,S-dioxide
(DBTO-MP). Mp: 308 ꢀC. FTIR ( /cmꢁ1): 2800e3000 (v), 1606 (m),
n

5490
C.-Y. Hsu et al. / Tetrahedron 68 (2012) 5481e5491
1524 (s), 1474 (v), 1400 (m), 1255 (v), 1219 (s), 1175 (v), 1132 (v),
1021 (s), 890 (v), 819 (s), 765 (v), 720 (w), 638 (w), 580 (s), 520 (w),
orientation to produce 2D experiment. The diagram is profiled by
a diagonal of signals partitioned pattern into two equal halves.
There are evident symmetrical signals produced to this diagonal,
called cross signals, which indicate an interaction of the related
nuclei. Therefore, the cross signals reveal the really important
keyword of 2D spectra.
465 (m). 1H NMR (300 MHz, CDCl3, ppm)
d
¼8.02 (s, 2H), 7.83 (m,
4H), 7.20 (d, J¼8.4 Hz, 2H), 7.13 (s, 2H), 6.98 (d, J¼8.4 Hz, 2H), 3.99
(s, 6H), 3.95 (s, 6H). 13C NMR (75 MHz, CDCl3, ppm)
d
¼149.64,
149.47, 143.37, 138.55, 132.09, 131.59, 129.67, 121.77, 120.16, 119.53,
111.58, 109.92, 56.08, 55.99. C28H24O6S, MS (FABþ, m/z): 489 [Mþ].
Anal. Calcd for C: 68.84, H: 4.95, S: 6.56. Found: C: 68.84, H: 4.93, S:
6.54.
4.3. Crystal X-ray diffraction
Single-crystal X-ray data on dibenzothiophene-S,S-dioxide de-
4.1.4. 2,7-Bis(9,9-dimethyl-9H-fluoren)-dibenzothiophene-S,S-di-
rivatives were collected at 296 K, of which using the graphite
oxide (DBTO-MF). Mp: 331e336 ꢀC. FTIR (
n
/cmꢁ1): 2800e3000 (v),
monochromated Mo K
a
radiation (
l¼0.71073 A) on a Bruker APEXII
ꢁ
1742 (w), 1589 (w), 1444 (s), 1400 (m), 1299 (s), 1238 (w), 1159 (s),
1082 (w), 1068 (w), 932 (w), 880 (m), 823 (s), 780 (v), 735 (s), 705
(w), 618 (w), 570 (s), 515 (w), 428 (m). 1H NMR (300 MHz, CDCl3,
CCD diffractometer.23 The data integration and reduction were
carried out with the SAINT program.23d An analytical absorption
correction was performed in each case followed by a semiempirical
absorption correction based on the symmetrically equivalent re-
flection with the SADABS program,23b and the space group was
determined using the XPREP program.23a Based on systematic ab-
sences and intensity distribution statistics, the space groups were
determined for all of the crystals. The structures were solved using
direct methods and refinement method by full-matrix least-
squares on F2 using the SHELXS-97 program.23c In the derivatives
all non-hydrogen atoms were refined anisotropically and hydrogen
atoms were added geometrically with no refinements.
ppm)
d
8.15 (s, 2H), 7.92 (d, J¼8.0 Hz, 2H), 7.86 (d, J¼8.0 Hz, 2H),
7.81 (d, J¼7.9 Hz, 2H), 7.79e7.74 (m, 2H), 7.71 (s, 2H), 7.60 (d,
J¼7.9 Hz, 2H), 7.51e7.46 (m, 2H), 7.41e7.34 (m, 4H), 1.57 (s, 12H). 13C
NMR (75 MHz, CDCl3, ppm) d 154.66, 153.95, 143.97, 139.81, 138.65,
138.34, 137.68, 132.46, 129.95, 127.73, 127.13, 126.03, 122.69, 121.89,
121.20, 120.60, 120.56, 120.30, 47.04, 27.15. C42H32O2S, MS (FABþ, m/
z): 601[Mþ]. Anal. Calcd for C: 83.97, H: 5.36, S: 5.34. Found: C:
83.97, H: 5.35, S: 5.32.
4.1.5. 2,7-Bis(9,9-(di-p-tolyl)-2-fluorenyl)-dibenzothiophene-S,S-di-
Presently, X-ray diffraction is an analytic technique for the in-
tentness of atomic interval pattern and can identify multimode
crystal structures. Single-crystal XRD further related information can
provide detailed signals about the internal crystal-lattice of target,
not only containing unit cell size, bond angle, bond length, and
itemize of pattern ordering, but also identifying as a fingerprint in
organic compounds. Forthright associated is single crystal tasteful-
ness, where the interaction of the incident rays with the specimen
produces a diffracted ray when crystal environment satisfies with
oxide (DBTO-PF). Mp: 350e356 ꢀC. FTIR ( /cmꢁ1): 2850e3100 (v),
n
1600 (w), 1509 (s), 1449 (s), 1400 (m), 1306 (s), 1188 (w), 1166 (s),
1092 (w), 1075 (m), 1022 (w), 1000 (w), 885 (m), 823 (v), 747 (v),
655 (v), 580 (s), 498 (m), 428 (m). 1H NMR (300 MHz, CDCl3, ppm)
d
7.98 (s, 2H), 7.84e7.76 (m, 4H), 7.71 (d, J¼3.0 Hz, 2H), 7.66 (s, 2H),
7.55 (d, J¼7.8 Hz, 2H), 7.37 7.47e7.27 (m, 8H), 7.17 (d, J¼8.0 Hz, 8H),
7.08 (d, J¼8.1 Hz, 8H), 2.32 (s, 12H). 13C NMR (75 MHz, CDCl3, ppm)
d
152.78, 152.01, 143.68, 142.59, 140.68, 139.22, 138.46, 138.06,
136.40, 132.47, 129.88, 129.07, 128.18, 127.99, 127.51, 126.42, 126.17,
124.55, 121.77, 120.74, 120.47, 120.42, 65.02, 20.93. C66H48O2S, MS
(FABþ, m/z): 905[Mþ]. Anal. Calcd for C: 87.58, H: 5.35, S: 3.54.
Found: C: 87.58, H: 5.30, S: 3.56.
the Bragg’s law (n
l
¼2d sin
q). A reciprocal Fourier transform re-
lationship between unique reflections and diffraction pattern. The
deduced indices (hkl) indicate crystal’s position within a diffraction
pattern to a unit cell and a crystalline lattice in the real space.
4.1.6. 2,7-Bis(4-(diphenylamino)phenyl)-dibenzothiophene-S,S-di-
4.4. Physical properties and optical measurements
oxide (DBTO-PP). Mp: 291 ꢀC. FTIR ( /cmꢁ1): 2850e3050 (v), 1640
n
(w), 1588 (s), 1488 (m), 1443 (v), 1400 (w), 1297 (s), 1198 (w), 1158
(s), 1082 (w), 1035 (w), 898 (w), 815 (s), 754 (s), 696 (s), 647 (w),
Absorption and fluorescence spectra were recorded using an
UVeVisible spectrophotometer (Hitachi-U3010) and a lumines-
cence spectrophotometer (Hitachi-F4500), respectively. Glass
transition temperatures (Tg), crystallization temperature (Tc) and,
melting temperature (Tm) were determined with a differential
scanning calorimeter (DSC, Shimadzu DSC-60) at a heating rate of
10 ꢀC/min. Decomposition temperature (Td) was obtained from
thermogravimetric analyzer (TGA) measurements using a Perki-
nElmer TGA-7 with a heating rate of 30 ꢀC/min. Ultra-violet pho-
toelectron spectrum (UPS) measurements are reliable from Riken
Keiki AC-2, to obtain the highest occupied molecular orbital of
energy level (EHOMO). Fortunately, the lowest non-occupied mo-
lecular orbital of energy level (ELUMO) was estimated from the op-
625 (m), 585 (m), 508 (v), 428 (w). 1H NMR (300 MHz, CDCl3)
d 8.01
(s, 2H), 7.80 (m, 4H), 7.50 (d, J¼8.5 Hz, 4H), 7.30 (t, J¼7.7 Hz, 8H),
7.15 (m, 12H), 7.08 (t, J¼7.2 Hz, 4H). 13C NMR (75 MHz, CDCl3, ppm)
d
148.39, 147.26, 142.91, 138.60, 131.91, 131.69, 129.55, 129.39,
127.59, 124.88, 123.48, 123.10, 121.75, 119.85. C48H34N2O2S, MS
(FABþ, m/z): 703[Mþ]. Anal. Calcd for C: 82.02, H: 4.88, N: 3.99, S:
4.56; found: C: 82.02, H: 4.88, N: 3.98, S: 4.55.
4.2. 2D-COSY spectra
Two-dimensional correlation spectroscopy (2D-COSY) spectra
let you easily understand the connectivity of a compound by de-
ciding which protons are spinespin coupled. Indeed, 1H NMR
spectra are far too confused for exposition as most of the signals
overlap seriously. By the 2D-COSY are simplified and some extra
message is acquired, one could perform the identical assignment
between signals by detailed analysis of spinespin splitting under
a high enough resolution.
By which is yet known information from 1D spectra, the signal
acquisition of 2D spectra consists of a basic pulse sequence to re-
ceive free induction decay (FID) from evolution time and mixing
sequences when mixing sequences apply dipolar interaction or
scalar coupling mechanisms for magnetization transfer. Applying
Fourier transform (FT) technique the data display is then in both XY
tical band gap (Eg) and EHOMO, equation formula ELUMO¼EgþEHOMO
,
related to energy level message of materials.
4.5. Device fabrication and measurement
OLEDs were fabricated by vacuum deposition on ITO coated-
glass substrates and the emission area of each device was
35 mm2. The ITO substrate was then loaded into a deposition
chamber with a base pressure better than 10ꢁ6 Torr. The devices
were fabricated by evaporating organic layers onto the ITO sub-
ꢁ
strate sequentially at an evaporation rate of 1e2 A/s, except for the
ꢁ
cathode (Al) and LiF, whose deposition rates were 5 and 0.1 A/s,
respectively. EL spectra and CIE color coordinates of unpackaged

C.-Y. Hsu et al. / Tetrahedron 68 (2012) 5481e5491
5491
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Acknowledgements
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The first author is grateful to Prof. Franklin Chau-Nan Hong who
is leading Nanodevices and Nanotechnology Lab, Department of
Chemical Engineering, National Cheng Kung University for pro-
viding the photoelectron spectrometer (Model AC-2) in this study.
The authors would like to thank the National Science Council of the
Republic of China, Taiwan for financial support in this research. The
authors also appreciate Prof. Pei-Lin Wu for the interpretations of
2D-COSY spectra and Prof. Kuei-Fang Hsu, who is leading Bio-
inorganic Chemistry Lab, for the interpretations of spectra and
the use of Bruker APEXII CCD diffractometer.
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