Effect of end group functionalisation of small molecules featuring the fluorene-thiophene-benzothiadiazole motif as emitters in solution-processed red and orange organic light-emitting diodes

Article abstract of DOI:10.1039/C8TC02993H

A series of red fluorescent materials (compounds 1-4), which each contain the symmetric fluorene-thiophene-BT-thiophene-fluorene core, is presented along with their performance in solution-processed OLED devices. Extending the molecular conjugation throug

Full text of DOI:10.1039/C8TC02993H

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M at erials Chemistry C
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Findlay, B. Breig, C. Forbes, A. Inigo, J. Cameron, O. Kanibolotskyy and P. Skabara, J. Mater. Chem. C,
2019, DOI: 10.1039/C8TC02993H.
Volume
4
Number
1
7
January 2016 Pages 1–224
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Nguyên T. K. Thanh, Xiaodi Su et al.
Fine-tuning of gold nanorod dimensions and plasmonic properties using
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Effect of end group functionalisation of small molecules f
D
e
OI
a
: 10
t
.
u
103
r
9
i
/
n
C8TC02993H
g
the fluorene-thiophene-benzothiadiazole motif as emitters in
solution-processed red and orange organic light-emitting diodes†
a
a
b
b
b
a
V. H. K. Fell, N. J. Findlay, * B. Breig, C. Forbes, A. R. Inigo, J. Cameron, A. L.
ac
a
Kanibolotsky, P. J. Skabara *
a
WestCHEM, School of Chemistry, University of Glasgow, Joseph Black Building, University Avenue, Glasgow,
G12 8QQ, Scotland
b
WestCHEM, Department of Pure and Applied Chemistry, University of Strathclyde, 295 Cathedral Street,
Glasgow, G1 1XL, UK.
c
Institute of Physical-Organic Chemistry and Coal Chemistry, 02160 Kyiv, Ukraine
†
Supporting data are accessible from http://dx.doi.org/10.5525/gla.researchdata.622
Email: peter.skabara@glasgow.ac.uk, neil.findlay@glasgow.ac.uk
KEYWORDS: Synthesis, OLED, solution-processing, end group functionalisation, halodesilylation, structure-
property relation
Abstract
A series of red fluorescent materials (compounds 1-4), which each contain the symmetric fluorene-
thiophene-BT-thiophene-fluorene core, is presented along with their performance in solution-
processed OLED devices. Extending the molecular conjugation through end-capping with additional
fluorene units (compound 2), or through incorporation of donor functionalities (compounds 3 and 4)
improves OLED performance relative to the parent compound 1. Notably, incorporating
triphenylamine donor groups in compound 3 led to solution-processed OLED devices operating with
-2
a peak luminance of 2888 cd m and a low turn-on voltage (3.6 V).
Introduction
The development of organic light-emitting diodes (OLEDs) has grown rapidly since the first report by
1
Tang and VanSlyke three decades ago. Their potential role as key components in flat panel displays
and lighting technologies present the principal driving force behind this growth. Their role in display
technologies is particularly promising due to advantages that include efficient power conversion, a
2
3
wide viewing angle and a good coverage of the colour spectrum. Both molecular and polymeric
4
species are commonly employed as the emissive components in OLEDS. Conjugated polymers suffer
distinct disadvantages, such as poor batch-to-batch reproducibility and impurities generated during
5
their synthesis that can be challenging to remove. In contrast, small molecules (or oligomers) are
monodisperse, can be synthesised with complete reproducibility and, depending on the device
fabrication method, can be synthetically tuned to be compatible with either vacuum or solution
6
deposition techniques. Furthermore, they can be specifically synthesised to be processable from
7
, 8
polar solvents, allowing orthogonal solution-processing to be realised. Solution processing offers
advantages over more established vacuum deposition techniques, such as lower processing costs
9
and more efficient use of material, and is thus an auspicious alternative in OLED processing.
However, more effort must be made to establish solution-processed methods next to vacuum
deposition techniques in industry. To realise this, large-area processing techniques, such as ink-jet or

Journal of Materials Chemistry C
Page 2 of 16
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nozzle printing, have been developed to advance the status of solution-processed organic solar cells
DOI: 10.1039/C8TC02993H
1
0, 11
within the industry for example.
Incorporating phosphorescent heavy metal atoms as dopants within a guest network is a relatively
common method for producing red OLEDs. While the metal induces a strong spin-orbit coupling
effect and enhances the emission efficiency, such a strategy involves incorporating expensive and
1
2
finite iridium, ruthenium or europium for example. A more recent and increasingly popular
strategy utilises the effect of thermally activated delayed fluorescence (TADF) through
1
3, 14
predominantly all-aromatic organic systems.
Internal quantum efficiencies of up to 100% are
possible, but close control of the energy levels is required to enable thermal up-conversion (reverse
1
5
intersystem crossing (RISC)) from the triplet to singlet excited states to utilise the TADF effect. On
the contrary, there are fewer examples of non-doped fluorescent red OLEDs. Such materials are
often synthetically straightforward and consist of commonly available building blocks. Shimizu and
co-workers developed a series of 1,4-bis(diarylamino)-2,5-bis(4-cyanophenylethenyl)benzenes as
novel fluorophores where the emission colour could be finely-tuned by switching the substituents on
1
6
the diarylamino and cyanophenyl groups. Vacuum-processing of these materials into non-doped
OLEDs produced deep red emitting devices with external quantum efficiencies (EQE) of 1.36% and
-1
maximum current efficiency of 0.71 cd A . Promarak and co-workers reported the symmetrical
molecular emitter CAPTB, consisting of bis(3,6-di-tert-butylcarbazol-9-ylphenyl)aniline end-capping
groups attached to a di(thiophen-2-yl)benzothiadiazole fluorescent core, and its role as the emissive
1
7
layer in a solution-processed, non-doped, fluorescent OLED. Devices with luminance efficiencies of
-
1
-1
1
.53 cd A were reported, a figure which could be improved significantly to 3.97 cd A through
inclusion of the electron-injecting/hole-blocking layer dimethyl-4,7-diphenyl-1,10-phenanthroline
BCP). The same authors employed a fluorene-thiophene-BT-thiophene-fluorene core capped with
carbazole dendrimers to hinder crystallisation, resulting in OLED devices with a luminance of 4655 cd
(
-1
-1 18
m and a maximum current efficiency of 4.80 cd A . More recently, Ma and co-workers reported a
butterfly-shaped donor-acceptor molecule, PTZ-BZP, based on a phenothiazine donor core and
benzothiazole acceptor “wings”. Solution-processed NIR OLEDs offered a high EQE of 1.54% and a
maximum brightness of 780 cd m . Whilst there was no delayed fluorescence evident, ruling out
contributions from TADF for example, the authors proposed a T -S RISC “hot exciton” process as the
1
9
-2
3
1
reason behind the high performance.

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DOI: 10.1039/C8TC02993H
SiMe3
S
C6H13
C6H13
N
C6H13
C6H13
S
S
N
Me3Si
1
SiMe3
S
2
C6H13
C6H13
N
C6H13
C6H13
S
S
N
Me3Si
2
2
N
S
C6H13
C6H13
N
C6H13
C6H13
S
N
S
N
3
O
S
C6H13
C6H13
N
S
C6H13
C6H13
S
N
4
O
Figure 1: Structures of the molecular emissive species, compounds 1-4.
Previously, we reported the design, synthesis and application of novel, green emissive molecules
that, when solution-processed as the active component in OLEDs, recorded high brightness
-2 20
(
maximum luminance = 20,388 cd m ). One aspect of these molecules was their straightforward
synthesis, which was, in principle, routinely scalable and involved few synthetic steps. This is an
important factor when considering the widespread application of functional molecules in organic
devices, as lengthy, time-consuming and expensive synthetic pathways are unlikely to attract
significant commercial interest. In this work we report the synthesis, characterisation and
application of a family of molecular red emitters in solution-processed OLED devices (Figure 1). Each
target contains a common 4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole core, which is further
2
1
functionalised with monofluorene or bifluorene units to impart solubility through their alkyl chains.
2
2
Compounds 1 (which was mentioned in a Patent application in 2012 ) and 2 are terminated with a
trimethylsilyl functionality (thus enabling halodesilylation ), whilst compounds 3 and 4 are further
influenced through additional electron donating groups, consisting of triphenylamine (compound
2
3
2
4
2
5
3
) and benzofuran (compound 4) units at the terminal ends of the fluorene unit.
Results and discussion
Synthesis
The strategy for the synthesis of compounds 1 and 2 is represented in Scheme 1. The construction of
the common core unit 7 was achieved in two steps: firstly, 4,7-dibromo-2,1,3-benzothiadiazole (5),
2
6
which was synthesised according to the literature, was coupled with 2-(tributylstannyl)thiophene
2
7
under Stille conditions to form compound 6. Compound 6 was then brominated in the terminal α-
2
8
positions using N-bromosuccinimide (NBS) to form the key intermediate 7. With this in hand,
2
9
straightforward Suzuki-Miyaura couplings with the boronic acid functionalised mono- or bifluorene

Journal of Materials Chemistry C
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3
0
View Article Online
DOI: 10.1039/C8TC02993H
(
8 or 9) furnished compounds 1 and 2, respectively. Both reactions proceeded in good yield, giving
the target emissive compounds as red powders.
Br
S
S
Sn(C4H9)3
S
Br
Br
Pd[PPh3]4, DMF
NBS, CHCl3
S
S
Br
N
N
83%
N
N
87%
N
N
S
S
S
5
6
7
SiMe3
S
C6H13
C6H13
7, Pd[PPh ] ,
3 4
Ba(OH)2.H2O, THF/H2O
C6H13
C6H13
TMS
B(OH)2
N
C6H13
C6H13
S
72%
S
N
Me3Si
1
8
SiMe3
S
2
C6H13
C6H13
7, Pd[PPh3]4,
C6H13
C6H13
Ba(OH)2.H2O, THF/H2O
N
S
TMS
B(OH)2
2
6
C H
6 13
C H
13
92%
S
N
Me3Si
2
9
2
Scheme 1: Synthesis of compounds 1 and 2.
The synthesis of compounds 3 and 4 was somewhat more complex (Scheme 2). Our proposed route
3
1
involved desilylation of the terminal trimethylsilyl groups in compound 1 for bromine
functionalities (compound 10), followed by Suzuki-Miyaura coupling with the appropriately
functionalised terminal group. However, it became clear that substitution of the TMS groups of
compound 1 to bromines was challenging, with evidence of over-bromination present regardless of
*
the conditions employed as well as residual TMS groups. Alternative reaction pathways involving
3
2
iododesilylation of the TMS groups were also unsuccessful and led to the formation of by-products.
The most successful conditions involved the use of 4.4 equivalents of bromine added to a solution of
compound 1 at 0°C, followed by warming the reaction solution to room temperature overnight. This
gave almost quantitative conversion of starting material (97% conversion) with minimal evidence of
over-bromination (approximately 6%). As shown in the experimental, exchanging the TMS groups
with bromine has no impact on the melting range. The challenging nature of this bromination is in
2
0
stark contrast to our previous reports using this reaction, indicating that the presence of the
additional thiophenes are the likely cause of these complications. With compound 10 in hand, albeit
as a mixture, Suzuki-Miyaura coupling with the appropriate electron-rich terminal groups afforded
compounds 3 and 4 in yields of 63% and 34%, respectively (Scheme 2).
*
1H NMR and MALDI analysis of the isolated mixture identified peaks corresponding to the presence of TMS
groups and excess bromination. Seperation of the mixture was challenging and the next synthetic step was
undertaken without further purification.

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DOI: 10.1039/C8TC02993H
SiMe3
Br
S
S
C6H13
C6H13
6
C H
6 13
C H
13
Br2,
NaOAc,
THF
N
N
C6H13
C6H13
6
C H
6 13
C H
13
S
S
S
S
N
N
Me3Si
Br
1
10
B(OH)2
N
Pd(PPh3)4,
Ba(OH)2.H20,
THF/H2O
N
S
C6H13
C6H13
N
C6H13
C6H13
63%
S
N
N
S
3
N
O
O
B
O
O
O
O
Pd(PPh3)4,
Ba(OH)2.H20,
THF/H2O
S
C6H13
C6H13
N
34%
C6H13
C6H13
S
S
N
4
O
Scheme 2: Synthesis of compounds 3 and 4. Note that compound 10 was isolated as a mixture.
Physical characterisation
All compounds within the series show significant thermal stability, with thermal degradation only
observed at temperatures above 360°C (Table 1). Whilst extending the conjugation increased the
thermal stability in compound 2 over monofluorene analogue 1, end-capping with either TPA or
benzofuran in compounds 3 and 4 offered even enhanced stability. TPA-containing compound 3
shows the highest thermal stability with a 5% mass loss temperature of 447°C. Similarly, end-capping
significantly altered the type and temperature of the phase changes observed by differential
scanning calorimetry (see Table 1). Compounds 1 and 2 recorded glass transition temperatures of
6
7°C and 83°C, respectively. On the contrary, end-capped analogues 3 and 4 showed no transitions
at temperatures below 200°C indicating an increased suitability for device fabrication.

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DOI: 10.1039/C8TC02993H
1
1
0
0
0
0
0
.0
.8
.6
.4
.2
.0
2
3
4
3
00
350
400
450
500
550
600
650
Wavelength [nm]
1
0
0
0
0
0
.0
.8
.6
.4
.2
.0
5
50
600
650
700
750
Wavelength [nm]
Figure 2: Absorption (top) and emission (bottom) in dichloromethane solution for compounds 1-4.
Table 1: Thermal and optical properties for compounds 1-4.
λmax(abs)
λmax(em)
[nm]
E (opt)
[eV]
g
Compound
TGA [°C]a DSC [°C]b
PLQYe
c
c
d
[
nm]
1
2
3
4
361
391
447
408
67 (Tg)
83 (Tg)
369, 513
377, 515
380, 518
384, 515
620
623
626
623
2.08
2.06
2.04
2.05
19.3%
32.8%
31.1%
23.6%
241 (Tm)
224 (T )
m
a
Temperature at which 5% mass loss occurs; thermal event recorded by DSC; c recorded in dichloromethane solution
b
-5
-8
d
e
(
concentration of 10 -10 M); calculated from the onset of the longest wavelength absorbance edge; measured from a
spin-coated film on a glass substrate at a thickness of 90 nm (±10 nm).

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UV-vis absorption analysis in dichloromethane showed distinct similarities across the series, with
DOI: 10.1039/C8TC02993H
two major absorption bands and a third low intensity peak at higher energies observed for all
compounds, which is neglected in the further discussion (Figure 2). The short wavelength peaks of
higher intensity likely correspond to a π→π * transition of the excitons, while the lower energy band
represents a charge-transfer in which the excited electrons remain on the electron-withdrawing
3
3
benzothiadiazole core, while the holes are delocalised on the fluorene-thiophene moieties. Whilst
there is little difference across the series in the lower energy band, suggesting that increased
electron-donating strength has little effect on the absorption characteristics of the core, a more
pronounced bathochromic shift is observed in the higher energy band as the molecular conjugation
length is extended in compounds 2-4. Compound 4 offers the largest bathochromic shift compared
to compound 1 for the higher energy band, reflecting increased orbital overlap through the planar
benzofuran units. On the other hand, the increased donor strength of the TPA groups in compound 3
have a slightly more pronounced effect on the lower energy charge transfer band (Table 1). Similarly,
the emission spectra of compounds 4 are similar, with one broad band peaking in the range 620-626
nm. The increased donor strength of the TPA units results in the longest wavelength emission of the
series for compound 3. Solid-state PLQY values ranging from 19-31% were recorded for the series,
with compound 2 proving to be the most efficient emitter (Table 1).
Table 2: Electrochemical properties of compounds 1-4.
Oxidation
Reduction
Compound
1
HOMO [eV]a
LUMO [eV]a
Eg [eV]c
ab
ab
[
V]
[V]
+0.47/+0.42
+0.64/+0.60
+0.36/+0.32
-1.71/-1.64
-5.24
-3.13
2.12
d
-2.20(irr)
-1.69/-1.62
d
2
+0.50/+0.46
-2.02(irr)
-5.14
-5.24
-3.15
1.99
+0.88/+0.84
-2.18/-2.12
+0.47/+0.40
-1.66/1.59
3
4
+0.60/+0.54
-3.18
-3.16
2.06
2.15
-2.14/-2.05
+0.83/+0.75
+0.53/+0.48
+0.68/+0.62
-1.67/-1.61
-2.14/-2.05
-5.31
a
-4
Recorded by cyclic voltammetry of solutions of compounds 1-4 (10 M) using glassy carbon, platinum wire and Ag wire as
4 6
the working, counter and pseudo-reference electrodes, respectively, with (nBu) PF as the electrolyte in dichloromethane
-
1
+
solution (0.1 M), at a scan rate of 100 mV s . The data were referenced to the Fc/Fc redox couple, which has a HOMO of -
b
c
4
.8 eV; the peaks shown are anodic/cathodic for oxidation, and cathodic/anodic for reduction waves; calculated by
subtraction of the LUMO energy from the HOMO energy; Irr = irreversible.
d
The effect of extending the conjugation length on the electrochemical behaviour is clear when
considering compounds 1 and 2, with a slight increase of the HOMO energy and decrease of the
LUMO energy in compound 2 compared to compound 1, resulting in a slight reduction of the
electrochemical HOMO-LUMO energy gap (Table 2 and Figures S1-S4 in the SI). Introduction of
additional electron-donating groups in compounds 3 and 4 had a subtle effect on the HOMO and
LUMO energy levels. Inclusion of the TPA group in compound 3 had no evident effect on the HOMO
level compared to compound 1, despite the increase in conjugation length, but reduced the LUMO
level to -3.18 eV and the HOMO-LUMO energy gap to 2.06 eV. As observed in the UV-vis absorption
spectra, the increased orbital overlap when introducing the planar benzofuran group in compound 4
resulted in a further decrease of the HOMO level to -5.31 eV, while the LUMO level was also reduced
when compared to compound 1. However, the overall effect of introducing the benzofuran in
compound 4 was an overall widening of the electrochemical HOMO-LUMO energy gap to 2.15 eV.
Overall, the electrochemical behaviour of compounds 1-4 does not differ greatly across the series,

Journal of Materials Chemistry C
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suggesting that the common thiophene-BT-thiophene core dominates the observed characteristics
DOI: 10.1039/C8TC02993H
and that increasing the electron-donor strength within the molecule provides only subtle
manipulation of molecular energy levels. This is in contrast to similar ‘Green’ analogues that do not
contain thiophene-based π-spacer groups, as the inclusion of electron-donating functionalities have
a significant effect on the molecular energy levels.20
OLED fabrication and characterisation
3
4
The performance of an OLED is directly influenced by the thickness of the emissive layer; defining
the optimum thickness early during device optimisation is vital in order to find the balance between
3
5
a suitably thin active layer for high current, but one that is also thick enough to avoid degradation.
Compound 1 was initially chosen for concentration optimisation using the device configuration
ITO/PEDOT:PSS/compound 1/Ca (40 nm)/Al (60 nm), with compound 1 deposited by spin-coating
from toluene solution (Table 3). The impact of the turn on voltage on device performance is clear; an
increase of 2 V is observed when the thickness of compound 1 is increased. This is due to the
3
6
concurrent increase in resistance as the active layer thickness increases. This influences the overall
-1
luminance of the device as well, with a concentration of 20 mg ml affording an active layer
-2
thickness of 90 nm and the highest value for luminance (854 cd m ). Note that the turn on voltage
-2 35
was considered when the luminance reached a value of 1 cd m .
Table 3: Characteristics of OLEDs processed from solutions of varying concentrations of 1 – 4 in
toluene. Averaged data, where appropriate, is shown in parentheses.
Maximum
Current
Maximum
EQE [%]
Turn on
voltage [V]
at 1 cd m )
Concentration
-2
Compound
Luminance [cd m ]
-1
[
mg ml ]
efficiency
-2
(
-
1
[
cd A ]
1
0
2.7
390 @ 5.8 V
0.03
0.05
8
54 @ 7 V (708 @ 7
1
2
20
2.7 (2.8)a
0.10 (0.093)a 0.22 (0.19)a
a
V)
3
1
0
0
4.6
2.7
343 @ 11.4 V
719 @ 7.2
0.06
0.06
0.14
0.08
1
2
561 @ 8 V (1410 @ 8
20
2.9 (3.0)b
3.3
0.15 (0.14)b
0.16
0.25 (0.23)b
0.19
b
V)
3
1
0
0
720 @ 9.2 V
39 @ 20 V (232 @ 19
1.9 (2.2)c
0.012 (0.11)d 0.03 (0.02)d
c
V)
3
1425 @ 14 V (1238 @
0.051
(0.026)
2
3
0
0
2.1 (2.2)b
2.1 (2.3)b
2.3 (2.5)a
2.2 (2.3)b
0.08 (0.06)b
b
b
(
unfiltered)
18 V)
1
054 @ 19 V (928 @
0.040 (0.24)e 0.06 (0.05)b
b
1
9 V)
2
135 @ 8.8 V (1915 @
0.086
(0.070)
0.027
(0.022)
3
(filtered)
4
20
0.16 (0.14)a
a
a
9
V)
4
93 @ 5.5 V (421 @
1
0
0.06 (0.05)b
b
b
5
.8 V)
1
498 @ 7 V (1079 @
.7 V)b
003 @ 6.9 V (968
8.1 V)f
0.081
20
2.5 (2.9)b
2.5 (2.7)f
0.17 (0.13)a
(0.064)b
6
1
0.073
0.15 (0.15)
3
0
@
(0.071)f

Page 9 of 16
Journal of Materials Chemistry C
a
b
c
View Ar dt icle Online
DOI: 10.1039/C8TC02993H
recorded as an average over 8 devices; recorded as an average over 6 devices; recorded as an average over 5 devices;
e
recorded as an average over 3 devices (limited due to short circuits); recorded as an average over 5 devices (limited due
to short circuits); recorded as an average over 4 devices.
f
Similarly, compounds 2, 3 and 4 were found to provide optimum OLED performance when processed
-1
from solutions of 20 mg ml concentration, with maximum luminance values of 1561, 1425 and
-2
1
498 cd m respectively. The higher luminance of compounds 2 and 3 compared with compound 1
can be explained by the higher PLQY (Table 1) values for both compounds compared to the smaller
analogue. The extended conjugation present in compounds 2 and 3 recorded a solid state PLQY over
1
.5 times higher than compound 1, indicating an increased radiative recombination rate within the
material. However, the low current efficiency of compound 3 is unexpected. The main reason that
could explain this low efficiency is the roughness of the emissive material surface. Indeed, compared
to compounds 1 and 2, compound 3 was less soluble in toluene, resulting in more aggregates and a
rougher film. As such, to improve the morphology of the film, the solution of compound 3 in toluene
was filtered through a 0.45 μm PTFE filter (see SI, Figure S5). The film quality was largely improved
-2
and a uniform film was obtained, resulting in an increased luminance of 2135 cd m and a current
-1
efficiency of 0.086 cd A , as shown in Table 3. It is likely that by improving the film morphology,
fewer charges were trapped by aggregates, resulting in increased numbers reaching the
recombination zone. The higher luminance observed for compound 3 can be explained by a higher
current passing through the device, as shown in Figure 3. Additionally, at approximately 7 V for
compound 1 and approximately 8 V for compound 2 the current seems to stabilise around 1000 mA
-2
37
cm . This saturation phase is not observed in compounds 3 and 4. According to Ohm’s law, when
the voltage is increased, the current should increase proportionally, unless the resistance is changed.
For compounds 1 and 2, the resistance of the device increases and the current is limited, while for
compounds 3 and 4 no such plateau is evident (Figure 3).
Compound 4 offered comparable performance with respect to compounds 2 and 3, with a maximum
-2
luminance at 1498 cd m similar to the luminance of compound 2 whilst the efficiencies of the
OLEDs are similar to those fabricated with compound 3. However, its slightly reduced overall
performance when compared to these two extended conjugated molecules can be explained by the
reduced PLQY of compound, which could be caused by increased aggregation quenching, possibly
due to the presence of planar benzofuran units. Analysis of atomic force microscopy (AFM)
topography images (SI, figure S6) shows films containing compound 4 are the roughest and contain
the largest domain areas which could be caused by increased aggregation with respect to the other
materials.
The effect of thermal annealing on the performance of OLEDs containing compounds 1 – 4 was
studied and in general showed no improvement over untreated devices, with only compound 2
showing a small increase in performance with thermal annealing (Table S1). For all other devices the
maximum luminance and efficiencies dropped upon thermal annealing. Atomic force microscopy
images for films annealed at 80°C (SI, figure S7) show that the annealing treatment has little effect
on the overall topography with images relatively similar to those for the unannealed films (SI, figure
6
) suggesting that decreased performance with annealing is due to subtle morphological changes. In
films containing compound 2 annealing results in the root mean squared (RMS) roughness being
reduced by 0.15 nm. This small reduction in roughness may explain the improved performance with
annealing of compound 2 at temperatures below the glass transition temperature (T = 83°C),
g
despite a relatively similar topography overall.

Journal of Materials Chemistry C
Page 10 of 16
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DOI: 10.1039/C8TC02993H
red 1
red 2
2500
2000
1500
1000
red 1
red 2
red 3 filter
red 4
red 3 filter
red 4
2000
1500
1000
500
500
0
0
0
2
4
6
8
10
12
0
2
4
6
8
10
12
Voltage (V)
Voltage (V)
Figure 3: Current density and luminance vs voltage for compounds 1 – 4.
However, since the saturation phase corresponds almost exactly with the voltage at which the
maximum luminance was recorded, the peak performance of both compound 1 and compound 2 has
not yet been reached. One factor that may cause this is elevated device temperature, with an
increase in heat within the device possibly due to inefficient electron injection, particularly at an
3
8
organo-metal interface.
To resolve this, an electron-transport layer of tris(8-
3
9
hydroxyquinolinato)aluminium (Alq ) was thermally deposited on top of the emissive material.
3
Compounds 1 – 4 were investigated alongside Alq at two different thicknesses: 20 and 50 nm. For
3
each compound, inclusion of a 20 nm layer of Alq was detrimental to the maximum luminance, with
3
a drop recorded in each case, while the current efficiency was broadly unaffected. However,
inclusion of a thicker layer (50 nm) led to improved devices in every case. Notably compound 3,
-2
when filtered as before, offered a maximum luminance of 2888 cd m at a low turn on voltage of
just 3.6 V whilst devices containing compound 2 were most efficient with the highest current
-1
efficiency of 0.51 cd A and external quantum efficiency (EQE) of 0.77%. The presence of the
4
0
peripheral triphenylamino groups on compound 3 likely provides enhanced hole transport, leading
to better balanced hole and electron transport in the device compared with the other members of
the series. However, Alq layer is also contributing to the emission as devices fabricated with 50 nm
3
of Alq produced orange light.
3
Table 4: OLED characteristics for compounds 1 – 4 with varying thicknesses of Alq added, and the
3
device configuration ITO/PEDOT:PSS/ compound 1 – 4 /Alq /Ca (40 nm)/Al (60 nm). Average values
3
included in parentheses.
Maximum
Current
Maximum
EQE [%]
Alq3
Turn on [V]
-2
Material thickness
Luminance [cd m ]
-2
(
at 1 cd m )
efficiency
[
nm]
-
1
[
cd A ]
X
2.7 (2.8)a
4.2 (4.5)b
854 @ 7 V (708 @ 7 V)a
0.10 (0.093)a
0.22 (0.19)a
0.16 (0.16)b
1
2
2
5
0
0
604 @ 10 V (552 @ 10 V)b 0.10 (0.098)b
1
476 @ 12 V (1348 @ 13
5.8 (6.7)b
2.9 (3.0)c
4.2 (4.9)d
0.30 (0.28)b
0.15 (0.14)c
0.17 (0.14)d
0.28 (0.27)b
0.25 (0.23)b
0.25 (0.23)d
b
V)
c
X
1561 @ 8 V (1410 @ 8 V)
1287 @ 11 (1143 @ 10.6
2
0
d
V)

Page 11 of 16
Journal of Materials Chemistry C
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2
640 @ 13 V (2483 @ 12
5
0
6.5 (7.5)b
2.3 (2.5)a
3.8 (3.9)d
3.6 (3.8)d
2.5 (2.9)a
3.6 (3.6 )b
0.51 (0.44)b
0.086 (0.070)a
0.11 (0.10)d
DOI: 10.1039/C b8 TC02993H
0.77 (0.69)
b
V)
2
135 @ 8.8 V (1915 @ 9
X
0.16 (0.14)a
0.22 (0.21)d
0.46 (0.41)d
0.17 (0.13)a
0.17 (0.15)b
a
V)
3
1862 @ 10 V (1547 @ 10
2
5
0
0
d
(
filtered)
V)
2
888 @ 10 V (2584 @ 10
0.30 (0.26)d
d
V)
1
498 @ 7 V (1079 @ 6.7
X
0.081 (0.064)a
0.089 (0.083)b
0.16 (0.12)d
a
V)
1
1
441 @ 8.5 V (1241 @ 8.1
4
20
b
V)
572 @ 8.6 V (1457 @ 8.4
5
0
3.6 (3.6)d
0.25 (0.18)d
d
V)
a
b
c
d
recorded as an average over 8 devices; recorded as an average over 4 devices; recorded as an average over 6 devices;
3
recorded as an average over 3 devices. The best turn on voltages of each compound was recorded without using Alq .
Conclusion
Herein, a series of four linear, solution-processable red emissive molecules have been reported, all
containing a thiophene-benzothiadiazole-thiophene core. The molecules differ through the extent of
conjugation and choice of end group functionalisation, which although offering little difference in
the physical characteristics of the series, led to significant differences in OLED performance.
Compound 3, containing peripheral triphenylamine groups exhibited the highest maximum
-2
luminance of 2135 cd m in addition to a low turn on voltage of 2.3 V when used in a device
configuration of ITO/PEDOT:PSS/compound 3/Ca/Al. However, the most efficient OLED in this
configuration was produced when compound 2 was the emissive component, leading to an EQE of
0
.25%. This trend was consistent when a 50 nm layer of Alq led to increased luminance in the
3
-2
compound 3 containing device (2888 cd m ) and highest efficiency when compound 2 was used
0.77%). The dual emission of the red material and green light from Alq led to the production of
(
3
orange light. Such straightforward, readily prepared molecules could be considered as inexpensive
fluorescent orange OLEDs for tandem white light devices.
Conflicts of interest
There are no conflicts of interest to declare.
Acknowledgements
NJF, JC and AK thank the EPSRC for funding (EP/R03480X/1, EP/P02744X/2 and EP/N009908/2). We
acknowledge the EPSRC UK National Mass Spectrometry Facility (NMSF) at Swansea University for
HRMS data.
Supporting Information
The graphs for the oxidation and reduction CV cycles of compounds 1-4 are shown in the SI in
Figures S1-S4, as well as the optical microscope images in Figure S5, AFM images of unannealed films
and films annealed at 80°C in figures S6 and S7 respectively, OLED data at various annealing
1
13
temperatures of compound 1 – 4 in Table S1 and H and C NMR spectra for compounds 1 – 4 in
figures S8 – S15.

Journal of Materials Chemistry C
Page 12 of 16
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DOI: 10.1039/C8TC02993H
Experimental
General
Tetrakis(triphenylphosphine)palladium(0) (Pd(PPh
3
)
4
) was prepared41 prior to use and stored under nitrogen.
,7-Dibromobenzothiadiazole and 9,9-dihexyl-7-trimethylsilylfluoren-2-ylboronic acid and its derivative with
2
6
4
3
0
two fluorene moieties (compound 8 and 9) were synthesised according to the literature. Unless otherwise
stated, all other reagents were sourced commercially and used without further purification. Dry solvents were
obtained from a solvent purification system (SPS 400 from Innovative Technologies) using alumina as the
1
13
drying agent. H and C nuclear magnetic resonance (NMR) spectra were recorded on either a Bruker DRX 500
apparatus at 500.13 and 125.76 MHz, or a Bruker Avance DPX400 apparatus at 400.13 and 100.6 MHz.
Chemical shifts are given in ppm; all J values are in Hz. Elemental analyses were obtained on a Perkin-Elmer
2
400 analyser. Matrix assisted laser desorption ionisation-time-of-flight (MALDI-TOF) mass spectrometry were
run on a Shimadzu Axima-CFR spectrometer (mass range 1–150000 Da). Thermogravimetric analysis (TGA) was
performed using a Perkin-Elmer Thermogravimetric Analyzer TGA7 under a constant flow of argon. Differential
scanning calorimetry (DSC) was recorded on a TA Instruments DSC QC1000 under nitrogen gas. Melting points
were taken using a Stuart Scientific Melting Point apparatus. Absorption spectra were recorded on a Shimadzu
UV 2700 instrument. Atomic force microscopy studies were carried out using a Bruker Innova AFM and the
data was processed using NanoScope Analysis 1.5 program by Bruker. Photoluminescence measurements were
recorded using a Perkin-Elmer LS 50 B fluorescence spectrometer in a quartz cuvette (path length 10 mm).
Absolute PLQY measurements were performed in a calibrated integrating sphere attached to an Ocean
Optics USB2000+ spectrometer, and a Gooch & Housego double monochromater with a quartz halogen lamp.
The samples were excited at their corresponding longest absorption wavelength. Cyclic voltammetry was
recorded on a CH Instruments 660A electrochemical workstation with iR compensation at a scan rate of 100
4
2
-1
mV s using anhydrous dichloromethane as the solvent. The electrodes were glassy carbon, platinum wire and
silver wire as the working, counter and pseudo-reference electrodes, respectively. All solutions were degassed
(
Ar) and contained monomer substrates in concentrations of ca. 10-4 M, together with 0.1 M
tetrabutylammonium hexafluorophosphate as the supporting electrolyte. All measurements were referenced
against the E1/2 of the Fc/Fc+ redox couple. The HOMO (LUMO) was calculated by subtracting the half-wave
4
3
potential of oxidation (reduction) from -4.8 eV.
-1
Pre-patterned ITO slides (7 Ω sq , 15mm × 15 mm × 1.1 mm, KINTEC) were cleaned with deionised water,
acetone and isopropanol in an ultrasonic bath before treatment with UV-ozone for 2 minutes. This method has
4
4
been shown to improve the hole injection of ITO and the performance of devices in general. PEDOT:PSS
Heraeus P VP AL 4083) was spin-coated onto the pre-cleaned ITO substrates at 3000 rpm and annealed at
20°C for 20 minutes, before cooling to room temperature. These substrates were transferred into a glove box
where all the subsequent fabrications and measurements were performed. Solutions of compounds 1-4 were
(
1
-1
prepared using toluene with varying concentrations of 10, 20 and 30 mg ml . For compound 1, a solution
-1
concentration of 20 mg ml was found to be optimum and hence used to continue other characterisation
measurements such as annealing. These spin-coated films were annealed for 10 minutes at temperatures of
4
0, 60 and 80°C. After annealing these films were transferred into a thermal evaporator attached to the glove
2
box for evaporation of the electrodes. An active area of 1.5 - 4 mm was obtained by evaporation of 40 nm of
-6
calcium and 40 nm of aluminium electrodes through a shadow mask at the base pressure of 1×10 mbar. A
Dimension 3100 Atomic Force Microscope was used to analyse surfaces of these films under tapping mode.
JVL were measured inside the glove box with a light-tight box attached. A Keithley Semiconductor
Characterisation (SCS) 4200 was used to bias the OLEDs. Luminance measurements were performed by using a
Macom L203 photometer with a calibrated silicon photodetector and a photopic filter. These calibrations can
be traced back to the National Physical Laboratory, London standards. Wavelength dependent
electroluminescence spectra were measured by using an Ocean optics USB2000 + spectrometer under a lab
atmosphere.
Compound 6
4
,7-Dibromo-2,1,3-benzothiadiazole 5 (750 mg, 2.551 mmol, 1.0 eq.) and tetrakis(triphenylphosphine)
palladium(0) (590 mg, 0.510 mmol, 0.2 eq.) were charged to a reaction flask, evacuated and purged with Ar.
After anhydrous DMF (10 ml), 2-(tributylstannyl)thiophene (2.43 ml, 7.654 mmol, 3.0 eq.) and anhydrous DMF
(5 ml) were added, the mixture was heated to 120°C and stirred under Ar for 72 h. After this time, the mixture

Page 13 of 16
Journal of Materials Chemistry C
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was cooled to r.t., diluted with water (100 ml) and extracted with dichloromethane (3 x 50 ml). The combined
DOI: 10.1039/C8TC02993H
organic extracts were washed with brine (100 ml), dried (MgSO
residue. This residue was dissolved in diethyl ether (50 ml) and washed with water (4 x 80 ml) and brine (100
ml), before being dried (MgSO ) once more and concentrated under vacuum. The resulting orange powder
was purified on silica gel, eluting with 20% dichloromethane in hexane, to afford the product (6) as an orange
powder (637 mg, 83%); δ (CDCl , 500.13 MHz) 8.13 (2H, dd, J 3.5, 1.0, ArH), 7.88 (2H, s, ArH), 7.47 (2H, dd, J
.0, 1.0, ArH), 7.23-7.22 (2H, m, ArH). m.p. 120-122°C, consistent with published data.
4
) and concentrated to and orange/brown
4
H
3
4
5
5
Compound 7
Compound 6 (637 mg, 2.12 mmol, 1.0 eq.) was dissolved in chloroform (50 ml) and the reaction flask covered
in aluminium foil to ensure the mixture remained dark. N-Bromosuccinimide (831 mg, 4.67 mmol, 2.2 eq.) was
added in one portion and the mixture stirred at r.t. under Ar for 72 h. After this time, the reaction mixture was
filtered and the resultant orange solid washed with distilled water (20 ml), methanol (150 ml) and chloroform
(
4 ml). The red powder (7) was dried under vacuum overnight (842 mg, 87%); δ
H
(CDCl
3
, 400.13 MHz) 7.82 (2H,
4
6
d, J 4.4, ArH), 7.81 (2H, s, ArH), 7.17 (2H, d, J 4.0, ArH); m.p. 252-254°C, which is consistent with the literature
value.
4
7
Compound 1
Compound 7 (300 mg, 0.655 mmol, 1.0 eq.), compound 8 (1.116 g, 2.095 mmol, 3.2 eq.),
tetrakis(triphenylphospine)palladium(0) (151 mg, 0.131 mmol, 0.2 eq.) and barium hydroxide octahydrate (992
mg, 3.144 mmol, 4.8 eq.) were charged to a reaction flask, evacuated and purged with Ar (x 3). Anhydrous THF
(
25 ml) and degassed, distilled water (1.8 ml) were added and the mixture heated to reflux for 40 h. The
mixture was then cooled, diluted with water (100 ml), then extracted with dichloromethane (3 x 60 ml). The
combined organic extracts were dried (MgSO ) and concentrated under vacuum to a dark orange residue.
4
Silica gel column chromatography, eluting with 10-15% dichloromethane/hexane, afforded the product as a
dark purple residue that was dissolved in the minimum volume of hot dichloromethane and precipitated with
ice cold methanol. Further cooling in a freezer afforded a purple powder that was isolated by filtration. The
product (1) was hence isolated as deep red powder (525 mg, 72%); δ
ArH), 7.95 (2H, s, ArH), 7.76-7.68 (8H, m, ArH), 7.53-7.49 (6H, m, ArH), 2.06-2.02 (8H, m, CH
m, CH ), 0.80-0.72 (20H, m, CH , CH ), 0.34 (18H, s, CH ); δ (CDCl , 125.76 MHz) 152.7, 151.8, 150.1, 146.6,
41.2, 141.1, 139.4, 138.3, 133.0, 131.9, 128.7, 127.6, 125.8, 125.3, 124.8, 123.9, 120.2, 120.1, 119.0, 55.2,
0.2, 31.4, 29.6, 23.7, 22.5, 14.0, -0.9; m/z (MALDI-TOF) 1108.56; Anal. calculated for C70 Si : C, 75.76; H,
.99; N, 2.52 %. Found: C, 75.46; H, 7.95; N, 2.37 %; TGA: 5% mass loss at 361°C; T = 67°C, m. p. 84-86°C.
H
3
(CDCl , 500.13 MHz) 8.17 (2H, d, J 3.5,
2
), 1.16-1.09 (24H,
2
2
3
3
C
3
1
4
7
88 2
H N S
3
2
g
Compound 2
Compound 7 (141 mg, 0.308 mmol, 1.0 eq.), compound 9 (772 mg, 0.986 mmol, 3.2 eq.),
tetrakis(triphenylphospine)palladium(0) (72 mg, 0.062 mmol, 0.2 eq.) and barium hydroxide octahydrate (466
mg, 1.478 mmol, 4.8 eq.) were charged to a reaction flask, evacuated and purged with Ar (x 3). Anhydrous THF
(
15 ml) and degassed, distilled water (0.9 ml) were added and the mixture heated to reflux for 40 h. The
mixture was then cooled, diluted with water (100 ml), then extracted with dichloromethane (3 x 60 ml). The
combined organic extracts were dried (MgSO ) and concentrated under vacuum to a dark orange residue.
4
Silica gel column chromatography, eluting with 10-15% dichloromethane/hexane, afforded the product as a
dark purple residue that was dissolved in the minimum volume of hot dichloromethane and precipitated with
ice cold methanol. Further cooling in a freezer afforded a deep red powder that was isolated by filtration. The
product (2) was hence isolated as purple powder (503 mg, 92%); δ
ArH), 7.97 (2H, s, ArH), 7.82-7.71 (12H, m, ArH), 7.69-7.64 (8H, m, ArH), 7.54-7.51 (6H, m, ArH), 2.13-2.03 (16H,
m, CH ), 1.18-1.11 (48H, m, CH ), 0.80-0.75 (40H, m, CH , CH ), 0.34 (18H, s, CH ); δ (CDCl , 125.76 MHz)
52.7, 151.7, 150.2, 141.4, 140.6, 140.4, 139.8, 139.0, 132.9, 131.9, 128.7, 127.7, 126.2, 126.0, 125.8, 125.3,
24.9, 124.0, 121.5, 120.0, 119.0, 55.4, 55.1, 40.5, 40.1, 31.5, 31.4, 29.7, 29.6, 23.8, 23.7, 22.6, 22.5, 14.0, -0.8;
Si : C, 81.21; H, 8.63; N, 1.58 %. Found: C, 81.04; H,
= 83°C, m.p. 100-102°C.
H 3
(CDCl , 500.13 MHz) 8.19 (2H, d, J 4.0,
2
2
2
3
3
C
3
1
1
m/z (MALDI-TOF) 1774.15; Anal. calculated for C120
152 2
H N S
3
2
8
.41; N, 1.36 %; TGA: 5% mass loss at 391°C; T
g

Journal of Materials Chemistry C
Page 14 of 16
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DOI: 10.1039/C8TC02993H
Compound 10
Compound 1 and anhydrous sodium acetate were dried in the desiccator overnight. A 100 ml three-neck-flask,
a 25 ml two-neck-flask and a 50 ml two-neck-flask were heated in the oven overnight. The glassware was then
evacuated and refilled with nitrogen three times. The 50 ml two-neck-flask was charged with compound 1
(0.264 g, 0.2382 mmol, 1 eq) and sodium acetate (0.038 g, 0.4681 mmol, 2 eq), then again evacuated and
refilled with nitrogen (× 3). Degassed, anhydrous THF (10 ml) was then injected and the flask was protected
-1
from light by aluminium foil. After cooling to 0°C in an ice bath, bromine (0.29 ml of a 0.584 g ml solution in
dichloromethane, 1.06 mmol, 4.47 eq) was injected over 25 min. The solution was stirred at 0°C and allowed
to warm to room temperature overnight. After this time, triethylamine (0.31 ml, 0.226 g, 2.236 mmol, 9.4 eq)
was added, followed by 5% aqueous sodium thiosulfate solution (10 ml). The mixture was then poured into a
5
% sodium thiosulfate solution (90 ml), which was extracted with dichloromethane (3 × 50 ml). The solvent
was evaporated and the residue was re-precipitated into methanol. Re-precipitation into methanol, filtration
and subsequent drying resulted in isolation of a red powder that predominantly contained the required
product (246 mg consisting of 97% conversion to product and 6% overbrominated product); the product
mixture was used in the next step without further purification; δ
ArH), 7.95 (2H, s, ArH), 7.74-7.67 (4H, m, ArH), 7.64 (2H, bs, ArH), 7.57 (2H, d, J 7.4 Hz, ArH), 7.53-7.43 (6H, m,
ArH), 2.13-1.91 (8H, m, CH ), 1.20-1.00 (24H, m, CH ), 0.78 (12H, t, J 7.0 Hz, CH ), 0.73-0.59 (8H, m, CH ); m/z
MALDI-TOF) 1121.82, m.p. 84-86°C.
H 3
(CDCl , 400.13 MHz) 8.16 (2H, d, J 8.2 Hz,
2
2
3
2
(
Compound 3
Compound 10 was dried in the desiccator overnight. A 50 ml two-neck-flask, a condenser and a 100 ml three-
neck-flask were dried in the oven overnight. The condenser was attached to the 50 ml flask, and the glassware
was evacuated and refilled with nitrogen three times. The 50 ml flask was then charged with compound 10
(
0.249 g, 0.22 mmol, 1 eq), 4-(diphenylamino)phenylboronic acid (0.204 g, 0.71 mmol, 3.2 eq),
tetrakis(triphenylphosphine)palladium(0) (0.066 g, 0.057 mmol, 0.26 eq) and barium hydroxide octahydrate
0.349 g, 1.11 mmol, 5 eq), followed by evacuation and refilling with nitrogen (× 3). Then, degassed, anhydrous
(
THF (15 ml) was added, followed by addition of degassed, deionized water (2 ml). The reaction mixture was
then stirred for 44 h at 65°C. After cooling to room temperature, the mixture was poured into 150 ml
deionized water. This mixture was then extracted with dichloromethane (50 ml × 3). The solvent was
evaporated and the crude product was purified with column chromatography (petroleum ether, 40-60°C:
CHCl
3
, 7:3). Re-precipitation in methanol gave a red solid, which was then washed with acetone, resulting in
(CDCl , 400.13
isolation of the product (3) as an orange solid (0.200 g, 63%) after drying in the desiccator; δ
H
3
MHz) 8.17 (2H, d, J 3.9 Hz, ArH), 7.96 (2H, s, ArH), 7.78-7.70 (6H, m, ArH), 7.67 (2H, s, ArH), 7.61-7.53 (8H, m,
ArH), 7.51 (2H, d, J 3.9 Hz, ArH), 7.28 (8H, t, J 8.3 Hz, ArH), 7.17 (12H, t, J 8.4 Hz, ArH), 7.05 (4H, t, J 7.5 Hz, ArH),
2
1
1
2 2 2 3 C 3
.06 (8H, m, CH ), 1.19-0.98 (24H, m, CH ), 0.80-0.67 (20H, m, CH , CH ); δ (CDCl , 100.76 MHz) 152.8, 152.0,
51.8, 147.8, 147.3, 146.7, 141.0, 139.9, 139.6, 138.5, 135.7, 132.9, 129.4, 128.8, 127.9, 126.0, 125.8, 125.4,
25.0, 124.5, 124.2, 123.1 121.0, 120.2, 55.5, 40.7, 31.6, 29.8, 24.0, 22.7, 14.2; m/z (MALDI-TOF) 1450.39;
+
HRMS calculated for C100
98 4
H N S
3
: (M+H) , 1451.7032. Found: 1451.7015; TGA: 5% mass loss at 447°C; T
m
(DSC)
=
241°C; m.p. 240-242°C.
Compound 4
Compound 10 was dried in the desiccator overnight. A 50 ml two-neck-flask, a condenser and a 100 ml three-
neck-flask were heated in the oven overnight and then evacuated and refilled with nitrogen three times. The
condenser was attached to the 50 ml two-neck-flask, which was charged with compound 10 (0.292 g, 0.26
mmol, 1 eq), 2-benzofuranylboronic acid MIDA ester (0.230 g, 0.84 mmol, 3.2 eq), tetrakis
(triphenylphosphine)palladium(0) (0.069 g, 0.060 mmol, 0.23 eq) and barium hydroxide octahydrate (0.401 g,
1
.27 eq, 4.9 eq). The flask was again evacuated and refilled with nitrogen (× 3). Degassed, anhydrous THF (15
ml) and degassed, deionised water (2 ml) were injected, and the mixture was stirred at 65°C for 44 h. After
cooling to room temperature, the mixture was poured into water (200 ml) and extracted with
dichloromethane (50 ml × 3). The crude product was purified twice by column chromatography: the first
3
column used petroleum ether 40-60°C: CHCl (7:3) as eluent, while the second used petroleum ether 40-60°C:
CHCl (8:2). The product was further purified by re-precipitation in methanol. Following drying in the
3

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Journal of Materials Chemistry C
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DOI: 10.1039/C8TC02993H
desiccator, the desired product (4) was isolated as a red powder (0.105 g, 34%); δ (CDCl , 400.13 MHz) 8.17
H 3
(2H, J 3.9 Hz, ArH), 7.97 (2H, s, ArH), 7.90-7.84 (4H, m, ArH), 7.78 (2H, d, J 8.2 Hz, ArH), 7.76-7.72 (4H, m, ArH),
7
1
.69 (2H, s, ArH), 7.61 (2H, d, J 7.6 Hz, ArH), 7.58 (2H, d, J 8.1 Hz, ArH), 7.54 (2H, d, J 3.9, ArH), 7.31 (2H, td, J
†
5.2, 7.0, 1.2 Hz, ArH), 7.25 , 7.12 (2H, s, ArH), 2.10 (8H, m, CH
2 2
), 1.19-1.01 (24H, m, CH ), 0.75 (12H, J 6.97 Hz,
CH
3
), 0.68 (8H, m, CH
2
); δ
C
(CDCl
3
, 100.76 MHz) 156.7, 155.1, 152.8, 152.1, 151.8, 146.5, 141.3, 140.7, 138.6,
1
1
C
2
33.3, 129.6, 129.5, 128.8, 125.9, 125.5, 125.1, 124.3, 124.3, 124.2, 123.1, 120.9, 120.5, 120.3, 120.2, 119.3,
11.3, 101.4, 55.6, 40.6, 31.6, 29.8, 24.0, 22.6, 14.2; m/z (MALDI-TOF) 1196.15; HRMS calculated for
+
80
H
80
N
2
†
2
O S
3
: (M+H) , 1197.5455. Found: 1197.5450; TGA: 5% mass loss at 408°C; T
m
(DSC) = 224°C, m.p. 232-
34°C. integration not possible due to overlap with CDCl
3
peak. Use of CD
2
Cl
2
not suitable due to aggregation
causing broad signals.
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