Synthesis and properties of pyrrolo[3,2-b]pyrrole-1,4-diones (isoDPP) derivatives

Article abstract of DOI:10.1039/c4tc00427b

The synthesis of three pyrrolo[3,2-b]pyrrole-1,4-dione (isoDPP) derivatives is described, namely 1,3,4,6-tetraphenylpyrrolo[3,2-b]pyrrole-2,5(1H,4H)-dione 2, 1,4-diphenyl-3,6-di(thiophen-2-yl)pyrrolo[3,2-b]pyrrole-2,5(1H,4H)-dione 3, and 1,4-bis(4-(hexylo

Full text of DOI:10.1039/c4tc00427b

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Materials Chemistry C
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PAPER
Synthesis and properties of pyrrolo[3,2-b]pyrrole-
1,4-diones (isoDPP) derivatives†
Cite this: J. Mater. Chem. C, 2014, 2,
4276
David Gendron,a Eliot Gann,b Katherine Pattison,c Fatemeh Maasoumi,a
b
d
a
Christopher R. McNeill, Scott E. Watkins, Paul L. Burn, Benjamin J. Powellc
*
and Paul E. Shawa
The synthesis of three pyrrolo[3,2-b]pyrrole-1,4-dione (isoDPP) derivatives is described, namely 1,3,4,6-
tetraphenylpyrrolo[3,2-b]pyrrole-2,5(1H,4H)-dione 2, 1,4-diphenyl-3,6-di(thiophen-2-yl)pyrrolo[3,2-b]-
pyrrole-2,5(1H,4H)-dione 3, and 1,4-bis(4-(hexyloxy)phenyl)-3,6-di(thiophen-2-yl)pyrrolo[3,2-b]pyrrole-
2,5(1H,4H)-dione 7 in which the molecular structures differ in the aromatic ring (phenyl or thiophene)
attached to the nitrogen atom. Thin films of 2, 3, and 7 could be formed by evaporation under vacuum.
In the case of 2 and 3 GIWAXS measurements showed that the film structural ordering was similar to
that measured in single crystals. In contrast GIWAXS showed that 7 had features associated with liquid
crystalline materials. Time dependent density functional theory (TDDFT) calculations predicted that the
transition between the lowest energy singlet excitation (S1) and the ground state (S0) would be optically
forbidden due to the centrosymmetric geometries of compounds. Photophysical measurements showed
Received 4th March 2014
Accepted 1st April 2014
that the compounds were weakly luminescent, with low radiative rates in solution of order 106 sꢀ1
,
which are consistent with the TDDFT predictions. Furthermore, photoinduced absorption (PIA)
spectroscopy showed that there is a long-lived low energy state, which has been assigned as a triplet
and provides a further non-radiative decay pathway for the excited state.
DOI: 10.1039/c4tc00427b
www.rsc.org/MaterialsC
organics dyes or high electron affinity moieties as a mean to
control the properties, and in particular when used with units of
Introduction
low ionisation potential, to shi the absorption to longer
wavelengths. In recent times, several building blocks have been
investigated, including diketopyrrolopyrroles (DPP),4 iso-
indigo,5 thienopyrroledione (TPD),6 benzothiadiazole (BT),7 and
thienothiophene,8 leading to materials that have good perfor-
mance in a range of devices.
The search for new materials that can be used in optoelectronic
applications such as organic photovoltaics (OPVs),1 organic
light-emitting eld-effect transistors (LEFETs),2 or organic light-
emitting diodes (OLEDs)3 has been, and remains an important
challenge. Indeed, new materials (small molecules, dendrimers
or polymers) with tailored optical and electronic properties are
needed to better understand the interplay between molecular
and lm structure, and charge-transport and optical properties.
Understanding these structure–property relationships will ulti-
mately lead to the development and optimisation of new
materials. Thus, it is important to identify the key building
blocks for each application. In the eld of OPV one approach to
select building blocks has been to choose deeply coloured
Currently pyrrolo[3,4-c]pyrrole-1,4-dione (DPP) is one of the
most popular units used in the preparation of non-polymeric
(oen erroneously termed “small molecules”) and polymeric
materials for optoelectronic applications. In fact, the DPP unit
was rst reported by Farnum in 1974 as an undesired side
product.9 Since then, the optical, thermal, physical and elec-
tronic properties have been studied extensively in a plethora of
derivatives. For instance, excellent charge transporting proper-
ties (hole and electron mobilities of 10.5 and 3 cm2 Vꢀ1 sꢀ1
,
respectively),10 and/or high PCEs (up to 6.5%) in photovoltaic
devices11 have been observed when the DPP moiety is used as a
component within conjugated copolymers. In contrast, the
regioisomeric pyrrolo[3,2-b]pyrrole-1,4-dione (isoDPP) unit has
not attracted much attention (Fig. 1). The synthesis was
described by Langer et al.,12 but it is only recently that it has
been used as a monomer unit in conjugated polymers. The
small number of isoDPP-based copolymers that have been used
in OPVs or OFETs devices have shown promising results in
aCentre for Organic Photonics & Electronics, School of Chemistry and Molecular
Biosciences, The University of Queensland, St Lucia, QLD 4072, Australia. E-mail:
p.burn2@uq.edu.au
bDepartment of Materials Engineering, Monash University, Clayton Campus,
Wellington Road, Clayton, VIC 3800, Australia
cCentre for Organic Photonics & Electronics, School of Mathematics and Physics, The
University of Queensland, St Lucia, QLD 4072, Australia
dCSIRO Molecular Health Technologies, VIC 3169, Australia
† Electronic supplementary information (ESI) available. CCDC 975864–975866.
For ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c4tc00427b
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using an interface diffusion method, employing dichloro-
methane as the good solvent and n-hexane as the non-solvent.
Table 1 summarizes the crystallographic data of these three
compounds, and Fig. 2 shows their molecular packing. As
shown in Table 1, we note that all three isoDPP derivatives have
the same monoclinic crystal system. Moreover, compounds 2
and 3 have the same P21/n space group, whereas compound 7
has the standard P21/c space group.
From the crystal structures we see that the dihedral angles of
the two linkages, 4N and 4C, of 2, 3, and 7 (see table in Fig. 3)
are relatively large meaning that the attached phenyl and thio-
phene rings are not in the same plane as the isoDPP unit. The
phenyl rings linked to the nitrogen atom have very similar 4N
values (64–70ꢁ) for the three compounds. Substituting the
phenyl with a thiophene ring does lead to a reduced dihedral
angle at the carbon (4C from 36.5ꢁ for 2, to 24.7ꢁ and 21.2ꢁ for 3
and 7, respectively) although 4N stays the same. In other words
the phenyl rings linked on the nitrogen atoms are the dominant
factor in controlling the structure and p–p intermolecular
interactions. In contrast, when aromatic groups are attached to
the DPP moiety they lie in the same plane. In considering the
interchromophore distances the crystal structures show two
different spacings. If the isoDPP only was considered it can be
seen that for compounds 2 and 3 the inter-planar distances
Fig. 1 Molecular structures of pyrrolo[3,4-c]pyrrole-1,4-dione (DPP)
and pyrrolo[3,2-b]pyrrole-1,4-dione (isoDPP).
terms of device performance.13 However, the fundamental solid
state properties of the simple isoDPP unit have yet to be
explored in detail.
In this work we have used a systematic approach to study the
effect molecular packing has on the thermal and the optical
properties of three isoDPP model compounds. We have varied
the chemical structure by changing the aromatic groups (phenyl
to thiophene) and by adding alkoxy chains to enhance the
solubility. We have measured the single-crystal and thin-lm
structures for the compounds and have investigated the pho-
tophysical properties by steady-state and time-resolved spec-
troscopic methods.
˚
˚
(from ketone oxygen to ketone oxygen) are 5.2 A and 4.2 A,
respectively (see Fig. 3). Replacing a phenyl ring by a thiophene
ring reduces the inter-plane distance in the case of compound 3.
Results and discussion
The synthetic pathways to compounds 2, 3 and 7 are illustrated In the case of 7 the addition of an alkyloxy chain onto the phenyl
in Scheme 1. The rst step in the syntheses of 2 and 3 was the ring leads to additional disruption to the close packing of the
preparation of the oxanilide by the addition of oxalyl chloride to isoDPP units, as shown in Fig. 2(e). For compound 7, it can be
aniline in toluene.14 Aer a few minutes, a slurry was obtained, clearly seen that in the unit cell the two alkyloxy chains are
which was then directly chlorinated with phosphorous penta- intercalated between the isoDPP molecules within the same
chloride to give the bis-phenylimidoyl chloride 1. We found that plane of the unit cell. We also note that the bond angle between
intermediate 1 was not stable under ambient conditions and the CH2 and –CH3 on the alkyl chain is 90ꢁ. This unexpected
must be quickly used in the next step without purication. behaviour has also been reported for another isoDPP deriva-
Reaction of 1 with the enolate of ethyl-2-phenylacetate (formed tive,16 and as a consequence the inter-plane distance for 7 was
˚
by deprotonation with lithium di-iso-propylamide) gave much larger (10.7 A) than that measured for 2 and 3 (Fig. 3).
compound 2 in a moderate yield of 54%. Following the same However, for these three compounds the closest p–p interac-
procedure as before, but using the enolate of ethyl-2-(thiophen- tions are between the side groups. In the case of compounds 2
2-yl)acetate, resulted in the formation of compound 3 in a yield and 3 the closest p–p interactions are between the phenyl rings
˚
of 39%. Given the poor solubility of 2 and 3 we decided to attached to the nitrogens with distances of around 3.5 A and
˚
prepare a derivative that had n-hexyloxy substituents on the N- 3.7 A, respectively. In contrast, in the case of 7 the nearest
phenyl ring. To do so, we synthesised the corresponding aniline interactions are between the phenyl and thiophene units on
4 following a literature procedure,15 and then reacted this with adjacent chromophores (z3.6 A).
˚
oxalyl chloride to give 5, phosphorous pentachloride to form 6,
To determine whether the crystal structure mapped onto the
and nally ethyl-2-(thiophen-2-yl)acetate to generate compound thin lm structure we carried out grazing-incidence wide-angle
7 in a yield of 36%. Compounds 2 and 3 have low solubility in X-ray scattering (GIWAXS) measurements on vacuum evapo-
common organic solvents such as dichloromethane and tetra- rated non-annealed lms.17 Fig. 4 presents the 2D GIWAXS
hydrofuran, although they showed better solubility in boiling patterns of the vacuum evaporated lms. For the case of
N,N-dimethylformamide and 1,2-dichlorobenzene. In contrast, compounds 2 and 3 the corresponding GIWAXS patterns show
compound 7 was found to be soluble in a range of organic clear crystalline peaks indicative of a highly crystalline micro-
solvents, as expected from the addition of an alkoxy chain onto structure. In contrast, the GIWAXS pattern of compound 7
each of the two phenyl rings.
shows no crystalline peaks indicating a less ordered thin lm
To understand the solid state molecular ordering and structure. For the lm of compound 2, all the observed GIWAXS
packing of these materials, single crystals were grown. Single peaks except for the peak at 0.6 Aꢀ1 can be indexed to the single
˚
crystals for compounds 2 and 3 were successfully grown from crystal structure reported above [see Fig. 4(a)] with the relative
N,N-dimethylformamide whereas crystals of 7 were obtained intensities of the observed peaks also matching that predicted
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Scheme 1 Conditions and reagents (i) oxalyl chloride, then PCl5, toluene, D. (ii) LDA, ethyl-2-phenylacetate 1 h, THF, (acetone/dry ice bath) then
1 was added (acetone/dry ice bath) then 14 h, r.t. (iii) LDA, ethyl-2-(thiophen-2-yl)acetate 1 h, THF, (acetone/dry ice bath) then 1 was added
(acetone/dry ice bath) then 14 h, r.t. (iv) Oxalyl chloride, Et3N, THF, 2 h. (v) PCl5, toluene, 2 h, D. (vi) LDA, ethyl-2-(thiophen-2-yl)acetate 1 h, THF,
(acetone/dry ice bath) then 6 was added (acetone/dry ice bath) then 16 h, r.t.
Table 1 Crystallographic data for compounds 2, 3, and 7
In particular the 002 peak is found to be oriented along qz
indicating that this crystallographic axis is highly oriented out-
Crystal
2
3
7
of-plane (directed along the surface normal). Such an orienta-
tion corresponds to an orientation of the unit cell such that the
normal of the isoDPP cores are oriented approximately 40
degrees from surface normal, as shown sꢀch1 ematically in
Empirical formula
Molecular weight
C
30H20N2O2
C26H16N2O2S2 C38H40N2O2S2
452.55
440.46
652.87
(g molꢀ1
)
Crystal habit, color Needle, orange Needle, red
Needle, light red
Monoclinic
P21/c
5.7794(4)
13.9768(9)
20.7994(11)
90.00
96.686(6)
90.00
1668.7
˚
Fig. 4(b). The unexplained peak at q ¼ 0.6 A indicates the
Crystal system
Space group
Monoclinic
P21/n
6.2448(16)
11.883(3)
14.808(5)
90.00
100.99(3)
90.00
1078.7
2
Monoclinic
P21/n
12.2888(14)
5.8588(5)
14.7622(15)
90.00
107.799(11)
90.00
1011.97
2
presence of a minority population of molecules that exist in a
second, unknown crystal structure. Similar to compound 2, the
scattering peaks observed for compound 3 are found to match
those expected based on the single crystal structure of
compound 3. Unlike compound 2, all the peaks observed in the
GIWAXS pattern of compound 3 can be attributed to reections
expected from the single crystal structure indicating only one
crystalline form. The GIWAXS pattern of compound 3 has the
100 axis oriented largely out of plane with the 010 axis at z30
degrees from the surface normal, indicating an orientation
schematically depicted in Fig. 4(d). In this orientation, the
normal of the isoDPP cores are oriented approximately 70
˚
a (A)
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
g (ꢁ)
3
˚
V (A )
Z
2
4.21
1.299
R Factor (%)
5.68
1.356
3.44
1.485
Density (g cmꢀ3
)
by the single crystal structure. The scattering observed in degrees from surface normal. In both of these thin lms, the
Fig. 4(a) for compound 2 is also anisotropic indicating a isoDPP cores, although tilted very differently, stack in columns
preferred orientation of the molecules relative to the substrate. parallel to the substrate. The GIWAXS peaks for compound 3 are
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Fig. 2 Molecular packing observed in single crystals for (a) compound 2 unit cell viewed along a axis, (b) compound 2 unit cell viewed along b
axis, (c) compound 3 unit cell viewed from a axis, (d) compound 3 unit cell viewed along b axis, (e) compound 7 unit cell viewed from a axis, (f)
compound 7 unit cell viewed along c axis. Atoms of C, O, N and S are shown in gray, red, magenta, and yellow, respectively.
Fig. 3 Interplanar distance (a) and dihedral angles (b and c) for compounds 2, 3 and 7.
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The thermal stability of the three compounds was obtained
using Thermal Gravimetric Analysis (TGA), with the samples
ꢀ1
ꢁ
being heated at a rate of 10 C min under nitrogen (Fig. 5).
Compounds 2 and 3 were found to have Td ¼ 327 ꢁC and 350 ꢁC,
respectively (Td is the temperature at which a 5% weight loss
was observed). Hence, substituting the phenyls with thiophene
rings had only a small effect on the melting or the degradation
temperatures. Although the addition of the alkyl chain on the
phenyl ring lowered the melting point (compound 7), the
thermal stability remained high (Td ¼ 383 ꢁC). Differential
scanning calorimetry showed that the compounds did not
have glass transitions in the temperature range of 0 ꢁC to 190 ꢁC
(see ESI†).
In the next step of the study we measured the ionization
potential (IP) of the compounds using photoelectron spectros-
copy in the air (PESA) and the results are reported in Table 2. We
found that the ionization potentials of compounds 3 and 7,
bearing thiophene rings, range from ꢀ5.88 to ꢀ5.73 eV
respectively. For compound 2 the ionization potential was
outside the limits of the instrument response and hence is
greater than ꢀ6.2 eV. It is clear that with such large ionisation
potentials it would be difficult to achieve ohmic contacts for
hole injection with these simple isoDPPs. The relatively large
ionisation potentials are consistent with the fact that the
oxidation potential of a similar compound to 7 could not be
measured electrochemically due it falling outside the solvent
window.19
Density functional theory (DFT) calculations were under-
taken in order to investigate and compare the electronic struc-
tures of the compounds. Details of the results obtained from the
DFT calculations are shown in Fig. 6 and 7, and tabulated in the
Fig. 4 Thin film results (a) 2D GIWAXS pattern of compound 2, (b) ESI.† At this level of analysis a number of important similarities
schematic of crystal structure of compound 2 in a thin film, (c) 2D
GIWAXS pattern of compound 3, (d) schematic of crystal structure of
compound 3 in a thin film (e) 2D GIWAXS pattern of compound 7.
between the compounds are observed. First, there are three key
frontier orbitals in each of the compounds: the lowest unoc-
cupied molecular orbital (LUMO), highest occupied molecular
orbital (HOMO) and the HOMOꢀ1. (In compound 7 the
HOMOꢀ2 and HOMOꢀ3 are also important for a full under-
signicantly more arced than compound 2 indicating increased standing of the excitation spectrum as we will discuss below, cf.,
orientational disorder with the 100 axis of crystallites adopting Fig. 7.) The HOMOꢀ1 is important in all three compounds
a broad range of orientations about the surface normal. From
the GIWAXS pattern of compound 7 [Fig. 4(e)] there is no
evidence that the single crystal structure is adopted in the thin
lm. There is some structure in the GIWAXS pattern indicating
very short range correlations. Evidence for slightly longer range
order (albꢀe1it only over z7 repeat units) is found in the peaks at
˚
˚
q z 1.6 A corresponding to a spacing of 3.9 A consistent with
p–p stacking. This apparent p–p stacking peak is observed for
two orientations, one normal to the substrate and one at
approximately 45 degrees from normal possibly indicating two
populations. Despite the non-crystalline nature of the lm there
is orientational order throughout the lm similar to that of a
nematic phase liquid crystal.
To complete the physical characterisation of the three
isoDPP derivatives, we investigated their thermal properties.
The melting points of the compounds were relatively high
(>300 ꢁC for compounds 2 and 3, and 250 ꢁC for compound 7),
which are similar to those reported for DPP-based molecules.18 Fig. 5 TGA thermograms of compounds 2, 3 and 7.
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Table 2 Optical and electronic properties of compounds 2, 3, and 7
already suggests that the excited states of these compounds will
be more complex than the normal consideration of the simple
HOMO–LUMO energy gap.20 Turning to analyse the electron
distributions of the molecular orbitals (MOs) it can be seen that
the LUMO is primarily localized on the isoDPP core, indepen-
dent of the substituents on the nitrogen and carbon atoms. It
can also be seen that for 2 there is LUMO density on the phenyl
side groups attached to the carbon atoms and this is replicated
for the attached thiophene rings for 3 and 7. In contrast, the
HOMO and HOMOꢀ1 density is more evenly distributed over
the groups of each of the molecules independent on whether
the ring is a phenyl or thiophene, or indeed attached to a carbon
or nitrogen of the isoDPP unit. The calculated energy levels for
the HOMOs were found to follow the experimentally deter-
mined trend in the IP (see Fig. 6 and Table 2).
lmax
lem
Compound Soln,a nm Film, nm Soln,a nm Film, nm IP,b eV
2
3
7
348
412
412
373
420
415
631
653
713
645
675
698
>ꢀ6.20
ꢀ5.88
ꢀ5.73
a
b
In dichloromethane. From photoelectron spectroscopy in the air
(PESA).
To understand the nature of the excited states we performed
time-dependent DFT (TDDFT) calculations for 2, 3 and 7. The
calculated excitation spectra are reported in Fig. 8 and the
energies, oscillator strengths and characters of the ten lowest
singlet and triplet excitations are tabulated in the ESI.† In order
to understand these results it is helpful to note that all three
compounds are centrosymmetric, i.e., symmetric under inver-
sion, which maps the spatial coordinates (x, y, z) / (ꢀx, ꢀy,
ꢀz); all three molecules have Ci symmetry. Thus all of the
orbitals must be either even or odd under inversion; labelled Ag
and Au respectively. In all three molecules the LUMO is Au. In 2
and 7 the HOMO is Au and the HOMOꢀ1 is Ag, whereas these
levels cross in 3 meaning that the HOMO is Au and the
HOMOꢀ1 is Ag. In 2 and 3 the two lowest lying singlet excita-
tions, which are predominately HOMO / LUMO and HOMOꢀ1
/ LUMO (see ESI† for details), are either Ag (Au / Au) or Au
(Ag / Au). However, for 2 and 3 the HOMO and HOMOꢀ1 are
sufficiently close in energy that the relative energies of the
many-body states is determined by the degree of mixing with
higher lying molecular orbital transitions more than the relative
energies of the HOMO and HOMOꢀ1. Thus, in 2 and 3 S1 is Ag
and S2 is Au. As the electric dipole is antisymmetric (Au) under
inversion Ag transitions are dipole forbidden. Therefore the
TDDFT calculations predict that S1 is dark and S2 is the lowest
energy emissive excitation in 2 and 3. We expect this to have
clear signatures in the photophysical properties of these
molecules.
Fig. 6 Calculated frontier molecular orbital energies and Kohn–Sham
orbitals for compounds 2, 3 and 7 from DFT (ADF; B3LYP/TZP). All
orbitals are labelled as even (Ag) or odd (Au) with respect to inversion.†
In parenthesis: IP from PESA measurements (see Table 2).
In 7 the excitation spectra is somewhat more complicated.
This can be understood by comparing the DFT and TDDFT
results. Firstly, from the results plotted in Fig. 7, it is clear that
the HOMO–HOMOꢀ1 gap is substantially larger in 7 than in
either 2 or 3. Furthermore, the HOMOꢀ2 and HOMOꢀ3 are
much closer (in energy) to the HOMO for 7 than they are in
either 2 or 3. This has important consequences for the TDDFT
excitation spectra. Note that the LUMO+1 (and higher lying
virtual levels; cf. ESI†) remain at signicantly higher energies
(ꢂ2 eV) than the LUMO in all three compounds and therefore
play only minor roles in the low-energy excited states. In 2 and 3
the low-energy singlet excitations are quite pure inter-MO
Fig. 7 Calculated energies of the four highest energy occupied Kohn–
Sham molecular orbital for compounds 2, 3 and 7 from DFT (ADF;
B3LYP/TZP). All orbitals are labelled as even (Ag) or odd (Au) with
respect to inversion.
because the HOMO and HOMOꢀ1 have only a small energetic transitions due to the relatively large energy separations and
separation relative to the HOMO–LUMO gap [and indeed the symmetry constraints. But, for 7, there is strong mixing of the
typical molecular orbital (MO) gaps in these compounds]. This MO transitions, consistent with the small energy gaps. In all
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Fig. 8 (a–c) Calculated excitation spectra. The symmetry of the excitations are colour coded as indicated in the key. (d–f) Oscillator strengths of
the transitions. As the Ag and triplet transitions are optically forbidden their locations are marked by a cross.
three compounds the brightest transition is dominated by the excited state, which had a weak oscillator strength,19 and this is
transition from the highest energy Ag MO to the (Au) LUMO. In 2 consistent with our calculations. In solution compound 2 had
and 3 this is S2, which is 86% HOMOꢀ1 / LUMO in 2 and 96% an absorption peak at 353 nm while compounds 3 and 7, which
HOMO / LUMO in 3. But, in 7 the strong mixing means that contain the thiophene rings, had maxima at 415 nm. In moving
this is S5, which is HOMOꢀ1 / LUMO (52%), HOMOꢀ2 / to the solid state the peak maximum for 2 moved to 373 nm,
LUMO (29%), and HOMOꢀ4 / LUMO (15%), i.e., highly mixed. whereas for compounds 3 and 7 there was only a small change
An important consequence of this mixing is to push the in the absorption maxima, although there were signicantly
brightest excitation to relatively higher energy in 7 (compared larger oscillator strengths for the longer wavelength absorp-
with 2 and 3).
tions. The increase in intensity of the long wavelength absorp-
Therefore, with a clear theoretical framework for the optical tion tail in the solid state could be due to aggregation and/or
transitions the nal aspect of this study was an investigation of scattering affects caused by the microcrystalline structure of the
the photophysical properties of the materials. The absorbance lms in the case of 2 and 3.
and photoluminescence spectra of compounds 2, 3 and 7 in
We next studied the photoluminescence properties of the
solution and the solid-state are shown in Fig. 9, with the results materials. The solution PL spectra were all broad and feature-
summarised in Table 2. In solution all compounds show a less and there was a red shi in the peak of the PL emission in
broad absorption peak with a weak absorption tail at longer moving from 2 to 3, which is consistent with the difference
wavelengths. In previous work the low energy absorption observed in the absorption spectra. Interestingly, in spite of 3
feature was assigned to the transition of lowest lying singlet and 7 having similar absorption spectra the peak of the PL of
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Fig. 9 Normalised absorbance and photoluminescence spectra of
compounds 2, 3 and 7 in dichloromethane (solid lines) and thin films
(dashed lines).
the latter is also further red shied. In moving to the solid state
there is a slight narrowing of the PL spectra, which can be
ascribed to a decrease in conformational freedom and in the
case of 2 and 3 there is a small red shi in the PL peak. The PL
quantum yields (PLQY) in solution and the solid state showed
that all three compounds were weakly emissive (see Table 3),
which is consistent with S1 / S0 being a forbidden transition.
The PL decays of compounds 2 and 3 in solution were near
identical with lifetimes of approximately 1.6 ns (Fig. 10). In
contrast, the decay of 7 was faster than the time resolution of
our instrument. A similar compound to 7 has been previously
reported to have a lifetime of 0.45 ns in 1,2-dichlorobenzene.19
From the values of the PLQY and excited state lifetimes the
radiative and non-radiative decay rates were calculated with the
results given in Table 3. These show that compounds 2 and 3
Fig. 10 Time-resolved photoluminescence decays of compounds 2, 3
and 7 in solution (empty circles) and the solid-state (filled circles). The
PL decay of 2 was measured with excitation at 372 nm, and 3 and 7 at
441 nm.
being about an order of magnitude larger. The PL decay of
compound 2 showed a short-lived component with the same
decay lifetime as the emission in solution but also featured a
long-lived component. The long-lived component, which was
also measured at longer timescales, could be described in terms
of two decay components of 115 ns and 770 ns with equal
weighting. Long-lived decay components can arise from aggre-
gate and/or excimer emission, or indeed phosphorescence.
From the crystal structure and GIWAX measurements of 2 we
can see that the closest p–p interactions occur between the
have radiative decay rates of order 10ꢀ6 sꢀ1, which is consid-
erably slower than those reported for DPPs (z10ꢀ8 sꢀ1
)
and
21
consistent with the S1 transition having weak oscillator
strength. The PLQY and lifetime measurements were repeated
with degassed dichloromethane but there were no signicant
differences observed.
Measurements of the solid state PLQY show that both 2 and
3 were about as luminescent as they were in solution, with 7
Table 3 The optical properties of compounds 2, 3, and 7
Solution
Film
Compound
PLQY
s (ns)
kR (sꢀ1
)
kNR (sꢀ1
)
PLQY
s (ns)
kR (sꢀ1
)
kNR (sꢀ1
)
2
3
7
0.0045(5)
0.011(1)
0.00035(5)
1.54
1.66
—
2.9 ꢃ 106
6.6 ꢃ 106
—
6.4 ꢃ 108
6.0 ꢃ 108
—
0.006(1)
0.009(1)
0.003(1)
—
1.62
0.97
—
—
5.6 ꢃ 106
6.1 ꢃ 108
3.1 ꢃ 106
1.0 ꢃ 109
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Journal of Materials Chemistry C
Paper
phenyl side groups, which from our calculations have orbital measuring the change in the PIA signal with modulation of the
density, and hence is consistent with intermolecular chromo- pump frequency. The observed decrease in PIA signal (DT/T)
phore–chromophore interactions (aggregate and/or excimer with increasing frequency was tted with
ꢀ
ꢁ
emission) from the microcrystalline lm of 2. Furthermore, the
GIWAX measurement indicates that there are two crystal forms,
which is could give rise to the two distinct lifetimes. The PL
decay of 3 was found to be near identical to that measured in
solution with a lifetime of about 1.6 ns, which suggests that
intermolecular interactions in the solid state are weaker. This is
not entirely consistent with the X-ray data but may arise from
the greater orientational disorder that is observed in the
GIWAXS. The excited state lifetime of 7 in the solid state follows
a monoexponential decay with a lifetime of about 1 ns (Fig. 10),
which is longer than the decay in solution. The GIWAX
measurements on lms of 7 show that there is some short range
ordering suggesting that the increase in lifetime is at least in
part due to interchromophore interactions leading to aggregate
or excimer emission.
To better understand the radiative and non-radiative
processes we carried out photoinduced absorption (PIA) spec-
troscopy on thin lms with the spectrum plotted in Fig. 11 for 2.
In Fig. 11 it can be seen that there is a broad photoinduced
absorption signal with a peak around 2.1 eV, which could be
caused by triplet exciton or polaron absorption. A similar
feature for 3 and 7 could be partially observed – the signal
occurred at similar energies to the PL and so could not be fully
resolved. The lifetime of the excited state was determined by
DT
ꢀ
DT
T
u¼0
ꢀ
¼
(1)
T
1 þ us
where u is the modulation frequency and s is the lifetime of the
excited state. Fits to the data gave a lifetime of the excited state
absorption of 0.4 ms, which is much longer than the lifetime of
the photoluminescence signal and consistent with a triplet
state.
Drawing all the measurements together gives a clear picture
of the basic photophysics of the isoDPP compounds. In the
solution and solid state excitation is primarily to S2 in 2 and 3
and S5 in 7 as these states have the highest oscillator strengths.
In solution there is rapid relaxation via phonon coupling to S1,
which cannot relax rapidly to the ground state due to the tran-
sition being dipole forbidden. As a consequence the radiative
rate is two orders of magnitude less than the non-radiative rate.
In the solid state a similar process occurs although aggregation
opens up new channels for relaxation of the excited state.
Furthermore, we have observed intersystem crossing to the
triplet state occurs in the lms, and it would be reasonable to
expect that this also contributes to the non-radiative rate in
solution.
Conclusion
In summary, we have studied a new class of pyrrolo[3,2-b]-
pyrrole-1,4-dione (isoDPP) compounds. We have investigated
the effect of changing the aromatic ring (thiophene for phenyl)
as well as the addition of alkoxy chains, on the molecular
packing and on the optical/photophysical properties. We found
that changing to a thiophene ring had a crucial effect on the
molecular packing by reducing the 4C twisting angle and thus
slightly planarizing the overall structure. The compounds
without an alkyl chain (compounds 2 and 3) possessed poor
solubility in common organic solvents but have good thermal
stability. Finally, all the compounds are weakly uorescent in
both solution and solid state with PLQYs <1%. This present
study provides essential information about this new class of
material (isoDPP) that can be applied to the design of new
polymeric materials for applications in devices such as organic
photovoltaic cells.
Experimental
General
1H and 13C NMR spectra were recorded using a 400 or 500 MHz
Bruker spectrometer in appropriate deuterated solvents at 298
K. Chemical shis were reported as d values (ppm) relative to
the residual solvent signals [(CDCl3) 7.26 ppm; (DMF-d7) 8.02
ppm] and coupling constants are given to the nearest 0.5 Hz.
Note: the lack of solubility of compounds 2 and 3 in CDCl3 or
DMF-d7 precluded their 13C NMR spectra being measured.
UV-visible spectroscopy was performed on a Cary 5000 UV-Vis
Fig. 11 (a) Photo-induced absorption spectrum of compound 2 in the
solid state at room temperature. (b) Pump modulation dependence of
the PIA signal at 2.1 eV (circles) with a fit to the data with eqn (1) (solid
line).
4284 | J. Mater. Chem. C, 2014, 2, 4276–4288
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Journal of Materials Chemistry C
spectrophotometer as either a thin lm on quartz or as a solu- approximated by a methoxy to reduce the computational time.
tion in spectroscopic grade solvent (DCM ¼ dichloromethane, For comparison we also repeated the calculations with full
ODCB ¼ 1,2-dichlorobenzene). For compounds 2 and 3, the relaxed geometries and only small changes were found.
solvent was heated to boiling point, cooled and the absorption
Time dependent DFT (TDDFT) calculations were carried out
spectrum was measured. FT-IR spectroscopy was performed on with the Amsterdam Density Functional (ADF) 2013.01
solid samples using a Perkin-Elmer Spectrum 100 FT-IR Spec- program26 in a triple zeta plus polarization (TZP) basis of Slater
trometer with an ATR attachment. Melting points (mp) were orbitals, using a ‘small’ core and the B3LYP functional. For
measured in a glass capillary on a Buchi B-545 melting point internal consistency we used the DFT results obtained in the
apparatus and are uncorrected. Microanalyses were carried out initial stages of this calculation to report the molecular orbital
on a Carlo Erba NA 1500 Elemental Analyser. Electrospray ion- energies and wavefunctions throughout this manuscript.
isation (ESI) and electron ionization (EI) mass spectrometry was
carried out on a BRUKER HCT 3D Ion Trap mass spectrometer.
Steady-state spectroscopy
Thermogravimetric analysis (TGA) was carried out with a Per-
The photoluminescence spectra of the compounds in
kin-Elmer STA 6000 Simultaneous Thermal Analyser apparatus
ꢀ1
dichloromethane were measured with a Fluoromax 4 by exciting
the compounds at the peak absorbance. The solution PLQY
measurements were performed using the relative method with
quinine sulphate in 0.5 M H2SO4 as the standard (PLQY ¼
54.6%).27 The materials were excited at 360 nm. In the case of
compound 7 the PLQY was estimated relative to compound 3 as
the emission was signicantly lower in intensity than that of
quinine sulphate. Films were prepared by evaporation onto
fused silica substrates. Films with thicknesses of 85–120 nm
were used for the absorbance measurements, PL spectra and PL
lifetime, and lms of 150–160 nm were used for measuring the
PLQY and PIA. The PL spectra were measured with the lms
under vacuum and excited with the 442 nm output from a HeCd
laser. The emission was directed into an Acton SpectraPro 2300i
monochromator with a silicon photodiode used to measure the
PL spectrum, which was corrected for the wavelength response
of the system. The PLQY were measured using the method
described by Greenham et al.28 The lms were placed inside an
integrating sphere, the interior of which was ushed with
nitrogen, and excited with either the 325 nm (compound 2) or
442 nm (compounds 3 and 7) output of a HeCd laser with a
power of z0.2 mW incident on the lm.
ꢁ
at a heating rate of 10 C min under a nitrogen atmosphere.
Thermal decomposition values were reported as the tempera-
ture corresponding to a 5% reduction in weight (Td). Differen-
tial scanning calorimetry (DSC) was carried out with a Perkin-
Elmer Diamond Differential Scanning Calorimeter at a heating/
cooling rate of 50 ꢁC minꢀ1. X-ray crystallography (XRD) was
carried out on single crystals of compounds 2, 3 and 7 by
Professor Paul Bernhardt using an Oxford Diffraction Gemini
Ultra dual source (Mo and Cu) CCD Diffractometer. Trans-
mission optical microscopy was carried out with an Olympus
BX61 polarizing microscope. Column chromatography was
performed with Kieselgel 60 230–400 mesh silica purchased
from Merck. Thin layer chromatography (TLC) was performed
on aluminum plates coated with silica gel 60 F254. Photoelec-
tron Spectroscopy in Air (PESA) measurements were performed
using a Riken Kekei AC-2 spectrometer. For all samples a power
intensity of 5 nW was used. The spectral data for compound 2
and 3 was collected from the same batch of crystals as used for
the crystal structure determination. Prior to NMR analysis 2 and
3 in DMF-d7 were heated at reux and then allowed to cool. On
cooling a proportion of the material precipitated and the
spectrum was collected on the soluble fraction. As a conse-
quence some small baseline peaks were observed in the NMR
and the peaks quoted are for the compounds themselves.
Time-resolved photoluminescence spectroscopy
The PL decays were measured with a Fluorolog 4 with TCSPC
capability. Pulsed LEDs emitting at 372 nm (compound 2) or
441 nm (compounds 3 and 7) were used to photoexcite the
solutions and lms. Films were stored in a sealed optical
chamber in a nitrogen atmosphere for the measurements. Fits
to the data were performed following convolution with the
instrument response function (IRF), which was measured
separately with a Ludox solution.
Materials
All commercial reagents were purchased from Aldrich, Alfa
Aesar, Scharlau or Ajax Finechem and used as received unless
˚
˚
otherwise noted. Molecular sieves (4 A and 3 A) were activated
for use by heating at 200 ꢁC under vacuum (10ꢀ1 to 10ꢀ2 mbar)
for 24 h. All solvents were distilled prior to use. Tetrahydrofuran
was distilled from sodium and benzophenone under a nitrogen
atmosphere before use. (1Z,2Z)-N0,N00-Diphenyloxalimidoyl
dichloride 1,22 and 4-(n-hexyloxy)aniline 4,23 were synthesized as
described in the literature.
Photoinduced absorption spectroscopy
The 325 nm output of the HeCd laser was used as the pump
with the output from a halogen lamp via a monochromator as
the probe. A mechanical chopper was used to modulate the
Density functional calculations
Density functional calculations were performed using the pump at z180 Hz with the photoluminescence and photoin-
measured crystal structures of compounds 2, 3, and 7 with duced absorption signals detected with a silicon photodiode
proton positions determined by a geometry optimization per- coupled to a second monochromator with a phase-matched
formed using GAMESS24 using the B3LYP hybrid functional25 lock-in amplier. The lms were stored in an inert atmosphere
and the Pople 6-31G basis set. The n-hexyloxy chains have been for the duration of the measurement. The diameter of the
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Journal of Materials Chemistry C
Paper
pump beam at the sample was approximately 1 mm with a 441.2 (35%), 442.2 (6%) [M+]; C30H20N2O2 requires 440.15
power of z10 mW.
(100%), 441.16 (33%), 442.16 (6%).
Grazing-incidence wide-angle X-ray scattering (GIWAXS)
Synthesis of 1,4-diphenyl-3,6-di(thiophen-2-yl)pyrrolo[3,2-b]-
pyrrole-2,5(1H,4H)-dione (3)
Measurements were performed at the SAXS/WAXS beamline at
the Australian Synchrotron. 11 keV Photons were used with 2D
scattering patterns recorded on a Pilatus 1M detector. The
sample-to-detector distance was calibrated using a silver
behenate standard. Scattering patterns were recorded as a
function of X-ray angle of incidence, with the angle of incidence
varied from 0.05 degrees below the critical angle of the organic
lm to 0.2 degrees above the critical angle. The images reported
were taken at an angle of 0.01 degrees above the critical angle.
Data acquisition times of 3 s were used, with three 1 s exposures
taken with offset detector positions to cover gaps in the Pilatus
detector. X-ray diffraction data are expressed as function of the
scattering vector, q, that has a magnitude of (4p/l)sin(q), where
q is half the scattering angle and l is the wavelength of the
incident radiation.
n-Butyllithium (1.55 M, 1.84 cm3, 2.85 mmol) was added to a
tetrahydrofuran (2 cm3) solution of di-iso-propylamine (0.44
cm3, 3.18 mmol) cooled in an acetone/dry ice bath. Aer stir-
ring for 30 min, a tetrahydrofuran (10 cm3) solution of ethyl-2-
(thiophen-2-yl)acetate (0.40 g, 2.37 mmol) was added slowly.
The reaction mixture was then stirred for 1 h with acetone/dry
ice bath cooling. 1 (0.30 g, 1.08 mmol) in tetrahydrofuran
(6 cm3) was added dropwise to the stirred reaction mixture,
which was cooled in an acetone/dry ice bath. The solution was
allowed to warm to room temperature, and stirred for 14 h.
The mixture was poured into aqueous ammonium chloride
(5 M, 100 cm3). The addition of ether (300 cm3) resulted in the
formation of a precipitate, which was collected at the lter.
The precipitate was washed with water (200 cm3) and ether
(200 cm3). The solid was then dried under high vacuum. The
product was recrystallised twice from N,N-dimethylformamide
to afford red needles of 3 (190 mg, 39% over two steps): mp >
Synthesis of 1,3,4,6-tetraphenylpyrrolo[3,2-b]pyrrole-
2,5(1H,4H)-dione (2)
Oxalyl chloride (1.9 cm3, 22 mmol) was added to a solution of 350 ꢁC; found C, 68.6%, H, 3.6%, N, 6.4%, S, 14.0%;
aniline (4.0 g, 21 mmol) in dry toluene (32 cm3) over 10 min. A
26H16N2O2S2 requires C, 69.0%, H, 3.6%, N, 6.2%, S: 14.1%;
C
slurry formed and the mixture was stirred for 20 min at room IR nmax (neat)/cmꢀ1 1717 (CO); lmax (ODCB)/nm 415 [log(3/dm3
temperature. Then phosphorus pentachloride (9.4 g, 45 mmol) molꢀ1 cmꢀ1) (3.65)]; dH (500 MHz; DMF-d7) 6.44 (2H, dd, J ¼
was added at room temperature. The mixture was carefully 3.5 Hz, J ¼ 1.0 Hz, Th-H), 6.88 (2H, dd, J ¼ 5.0 Hz, J ¼ 3.5 Hz,
heated to reux and kept at reux until no more gas was Th-H), 7.50–7.55 (10H, m, Ph-H), 7.62 (2H, dd, J ¼ 5.0 Hz, J ¼
generated. The orange mixture was then cooled down to room 1.0 Hz, Th-H); m/z (HR-ESI) found 453.0726 (100%) 454.0783
temperature and the solvent evaporated under reduced pres- (33%), 455.0704 (13%), 456.0690 (3%) [M + H]; C26H16N2O2S2
sure. Petroleum ether (400 cm3) was added and the precipitate requires 453.0726 (100%), 453.0759 (28%), 455.0687 (9%),
ltered and discarded. The petroleum ltrate was collected and 456.0718 (4%).
the solvent removed. The resulting solid 1 (1.50 g) was used
directly (within a 3 h period) without any further purication. n-
Synthesis of N0,N00-bis(4-(hexyloxy)phenyl)oxalamide (5)
Butyllithium (1.55 M, 9.2 cm3, 14 mmol) was added to a tetra-
hydrofuran (10 cm3) solution of di-iso-propylamine (2.2 cm3, 16 Oxalyl chloride (2.15 g, 16.9 mmol) was added dropwise to a
mmol) cooled in an acetone/dry ice bath. Aer stirring for 30 stirred solution of 4 (6.87 g, 35.5 mmol) and triethylamine (4.28
minutes, a tetrahydrofuran (50 cm3) solution of ethyl-2-phe- g, 42.3 mmol) in tetrahydrofuran (120 cm3) cooled with an ice
nylacetate (2.05 g, 12 mmol) was added slowly. The reaction bath. The reaction was then allowed to warm to room temper-
mixture was then stirred for 1 h. 1 (1.5 g, 5.4 mmol) in tetra- ature with stirring over 2 h. Water (120 cm3) was added to the
hydrofuran (30 cm3) was then added dropwise to the stirred reaction mixture and the white precipitate was collected at the
reaction mixture, which was cooled in a acetone/dry ice bath. lter, washed with aqueous hydrochloric acid (1 M, 100 cm3)
The solution was allowed to warm to room temperature and and then water (200 cm3). The product was then dried in a
then stirred for 14 h. The mixture was poured into aqueous drying pistol at 50 ꢁC under high vacuum to afford a white
ammonium chloride (5 M, 300 cm3). The addition of ether powder of 5 (4.87 g, 65%): mp 218 ꢁC; found C, 71.1%, H, 6.0%,
(300 cm3) resulted in the formation of a precipitate, which was N, 8.2%; C26H36N2O4 requires C, 70.9%, H, 6.3%, N, 8.2%; IR
collected at the lter. The precipitate was washed with water nmax (solid)/cmꢀ1 3298 (NH), 1650 (CO); lmax (DCM)/nm 295
(300 cm3) and ether (300 cm3). The solid was then dried under [log(3/dm3 molꢀ1 cmꢀ1) (4.29)] 299sh (4.28), 318sh (4.17); dH
high vacuum. The product was recrystallised three times from (400 MHz; CDCl3) 0.90–0.95 (6H, m, –CH3), 1.32–1.40 (8H, m,
N,N-dimethylformamide to afford yellꢁow-orange needles of 2 –CH2–), 1.41–1.51 (4H, m, –CH2–), 1.77–1.83 (4H, m, –CH2–),
(1.25 g, 54% over two steps); mp 348 C; found: C, 81.7%, H, 3.96 (4H, t, J ¼ 6.5 Hz, –OCH2–), 6.91 and 7.57 (8H, AA0BB0, Ph-
4.6%, N, 6.3%; C30H20N2O2 requires C, 81.8%, H, 4.6%, N, 6.4%; H), 9.25 (2H, brs, N–H); dC (100 MHz; CDCl3) 14.0, 22.6, 25.7,
IR nmax (solid)/cmꢀ1 1722 (CO); lmax (ODCB)/nm 353 [log(3/dm3 29.2, 31.6, 68.3, 115.0, 121.3, 129.3, 156.8, 157.3; m/z (ESI) found
molꢀ1 cmꢀ1) (4.07)] 429sh (2.23); dH (500 MHz; DMF-d7) 7.14– 463.2567 (100%), 464.2603 (29%), 465.2680 (5%), [M + Na];
7.19 (8H, m, Ph-H), 7.23–7.27 (2H, m, Ph-H), 7.28–7.32 (4H, m,
C26H36N2O4Na requires 463.2573 (100%), 464.2606 (28%),
Ph-H), 7.33–7.36 (6H, m, Ph-H); m/z (EI) found 440.2 (100%), 465.2640 (4%).
4286 | J. Mater. Chem. C, 2014, 2, 4276–4288
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Journal of Materials Chemistry C
information or advice expressed herein is not accepted by the
Australian Government. P.E.S. is supported by an Australian
Research Council Discovery Early Career Researcher Award
(DE120101721). F.M. acknowledges The University of Queens-
land for UQ Centennial and UQ International Scholarships.
C.R.M. acknowledges support from the Australian Research
Council (FT100100275, DP130102616). This research was
undertaken in part on the SAXS/WAXS beamline at the Austra-
lian Synchrotron, Victoria, Australia.
Synthesis of 1,4-bis(4-(hexyloxy)phenyl)-3,6-di(thiophen-2-yl)-
pyrrolo[3,2-b]pyrrole-2,5(1H,4H)-dione (7)
Phosphorus pentachloride (0.90 g, 4.29 mmol) was added to a
solution of N0,N00-bis(4-(hexyloxy)phenyl)oxalamide 5 (0.90 g,
2.04 mmol) in anhydrous toluene (15 cm3) stirred at room
temperature under an argon atmosphere. The mixture was
carefully heated to reux and kept at reux until no more gas
was generated. The orange mixture was then allowed to cool to
room temperature and the solvent removed under reduced
pressure. Petroleum ether (200 cm3) was added and the
precipitate was removed by ltration and discarded. The ltrate
was collected and the solvent removed. The resulting solid of 6
(z1.80 g) was used directly (within a 3 h period) without further
purication. n-Butyllithium (1.55 M, 6.94 mL, 10.8 mmol) was
added to a tetrahydrofuran solution (10 cm3) of di-iso-propyl-
amine (1.20 g, 11.8 mmol) cooled in an acetone/dry ice bath.
Aer stirring for 30 min, a tetrahydrofuran (40 cm3) solution of
ethyl-2-(thiophen-2-yl)acetate (1.54 g, 8.98 mmol) was added
slowly with the reaction mixture being cooled in an acetone/dry
ice bath. (1Z,2Z)-N0,N00-Bis[4-(n-hexyloxy)phenyl]oxalimidoyl
dichloride 6 (1.80 g, 4.08 mmol) in tetrahydrofuran (16 cm3) was
then added dropwise to the stirred reaction mixture before it
was allowed to slowly warm to room temperature. The reaction
was stirred for a further 16 h before being poured into aqueous
ammonium chloride (5 M, 300 cm3). Diethyl ether (300 cm3) was
added to the mixture resulting in the formation of a precipitate.
The precipitate was collected at the lter, and then washed with
water (200 cm3) followed by diethyl ether (150 cm3). The solid
was then dried in an oven at 80 ꢁC for 2 h. The orange solid was
then puried by column chromatography over silica using
dichloromethane : hexane mixture (1 : 1) as the eluent to gꢁive
an orange solid of 7 (1.05 g, 36% over two steps): mp 249 C;
found C, 69.6%, H, 6.1%, N, 4.3%, S, 9.7%; C38H40N2O4S2
requires C, 69.9%, H, 6.2%, N, 4.3%, S: 9.8%; IR nmax (solid)/
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cmꢀ1 1724 (CO); lmax (ODCB)/nm 415 [log(3/dm3 molꢀ1 cmꢀ1
)
(4.39)]; dH (400 MHz; CDCl3) 0.90–0.97 (6H, m, –CH3), 1.33–1.42
(8H, m, –CH2–), 1.44–1.54 (4H, m, –CH2–), 1.77–1.87 (4H, m,
–CH2–), 3.99 (4H, t, J ¼ 6.6 Hz, –OCH2–), 6.57 (2H, dd, J ¼ 4.0 Hz,
J ¼ 1.0 Hz, Th-H), 6.80 (2H, dd, J ¼ 5.0 Hz, J ¼ 4.0 Hz, Th-H), 6.92
and 7.22 (8H, AA0BB0, Ph-H), 7.27 (2H, dd, J ¼ 5.0 Hz, J ¼ 1.0 Hz,
Th-H); dC (100 MHz; CDCl3) 14.0, 22.6, 25.7, 29.1, 31.6, 68.4,
100.4, 114.8, 126.3, 126.6, 128.2, 128.5, 129.5, 129.7, 142.5,
159.0, 170.6; m/z (ESI) found 652.2 (100%), 653.2 (54%), 654.1
(26%), 655.2 (9%) [M]; C38H40N2O4S2 requires 652.2 (100%),
653.2 (42%), 654.3 (10%), 654.2 (9%).
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