[1]Benzothieno[3,2-b]benzothiophene-Based Organic Dyes for Dye-Sensitized Solar Cells

Article abstract of DOI:10.1021/acs.joc.6b00192

Three new metal-free organic dyes with the [1]benzothieno[3,2-b]benzothiophene (BTBT) π-bridge, having the structure donor-π-acceptor (D-π-A) and labeled as 19, 20 and 21, have been designed and synthesized for application in dye-sensitized solar cells (DSSC). Once the design of the π-acceptor block was fixed, containing the BTBT as the π-bridge and the cyanoacrylic group as the electron acceptor and anchoring unit, we selected three donor units with different electron-donor capacity, in order to assemble new chromophores with high molar extinction coefficients (?), whose absorption features well reflect the good performance of the final DSSC devices. Starting with the 19 dye, which shows a molar extinction coefficient ? of over 14,000 M^-1 cm^-1 and takes into account the absorption maximun at the longer wavelength, the substitution of the BFT donor unit with the BFA yields a great enhancement of absorptivity (molar extinction coefficient ? > 42,000 M^-1 cm^-1), until reaching the higher value (? > 69,000 M^-1 cm^-1) with the BFPhz donor unit. The good general photovoltaic performances obtained with the three dyes highlight the suitable properties of electron-transport of the BTBT as the π-bridge in organic chromophore for DSSC, making this very cheap and easy to synthesize molecule particularly attractive for efficient and low-cost photovoltaic devices.

Full text of DOI:10.1021/acs.joc.6b00192

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Article
[1]Benzothieno[3,2-b]benzothiophene-Based
Organic Dyes for Dye-Sensitized Solar Cells
Agostina Lina Capodilupo, Eduardo Fabiano, Luisa De Marco, Giuseppe
Ciccarella, Giuseppe Gigli, Carmela Martinelli, and Antonio Cardone
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.6b00192 • Publication Date (Web): 17 Mar 2016
Downloaded from http://pubs.acs.org on March 17, 2016
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[1]Benzothieno[3,2-b]benzothiophene-Based Organic Dyes for Dye-Sensitized
Solar Cells
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A. L. Capodilupo,a E. Fabiano,b, L. De Marco,*c G. Ciccarella,d G. Gigli,a, C. Martinelli,e and A.
Cardone,*e
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aInstitute of Nanotechnology – NANOTEC, Italian National Council of Research – CNR, Campus
Ecotekne, Via Lecce-Monteroni, 73100, Lecce (Italy).
bIstituto Nanoscienze-CNR, Euromediterranean Center for Nanomaterial Modelling and
Technology (ECMT), Via per Arnesano 73100 Lecce, (Italy).
cCenter for Biomolecular Nanotechnologies (CBN), Fondazione Istituto Italiano di Tecnologia,
Energy Platform, Via Barsanti, 73010, Arnesano, Lecce, (Italy).
dDipartimento di Ingegneria dell'Innovazione, University of Salento, Via Monteroni, 73100, Lecce,
(Italy).
eInstitute of Chemistry of OrganoMetallic Compounds – ICCOM, Italian National Council of
Research – CNR, Via Orabona, 4, 70125, Bary, (Italy).
*Corresponding authors: Antonio Cardone, Email: cardone@ba.iccom.cnr.it: Luisa De Marco,
Email: luisa.demarco@iit.it.
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ABSTRACT. Three new metalꢀfree organic dyes with the [1]benzothieno[3,2ꢀb]benzothiophene
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5
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7
8
(BTBT)
have been designed and synthesized for application in dye sensitized solar cells (DSSC). Once fixed
the design of the ꢀacceptor block, containing the BTBT as the ꢀbridge and the cyanoacrylic group
πꢀbridge, having the structure donorꢀπꢀacceptor (DꢀπꢀA) and labelled as 19, 20 and 21,
9
π
π
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as the electron acceptor and anchoring unit, we have selected three donor units with different
electronꢀdonor capacity, in order to assemble new chromophores with high molar extinction
coefficients (ε), whose absorption features well reflect the good performance of the final DSSC
devices. Starting from the 19 dye, which show a molar extinction coefficient
1cmꢀ1, take in account the absorption maximun at the longer wavelength, the substitution of the BFT
ε
of over 14000 Mꢀ
donor unit with the BFA, yield a great enhancement of absorptivity (molar extinction coefficient
ε >
42000 Mꢀ1cmꢀ1), until to reach the higher value ( > 69000 Mꢀ1cmꢀ1) with the BFPhz donor unit.
ε
The good general photovoltaic performances obtained with the three dyes highlight the suitable
properties of electronꢀtransport of the BTBT as the ꢀbridge in organic chromophore for DSSC,
π
making this very cheap and easy to synthesize molecule, particularly attractive for efficient and
lowꢀcost photovoltaic devices.
INTRODUCTION
Since the pioneeristic work of O’Regan and Grätzel in 1991,1 dyeꢀsensitized solar cells (DSSC)
have been attracting a widespread attention both in academic world and industrial area, as the most
promising inexpensive and environmentally friendly alternative to the inorganic photovoltaic.2ꢀ6 The
efficiencies of DSSCs are strictly dependent on the nature of organic dye, photoanode, counter
electrode, electrolyte, and the intricate interactions between all these components. The organic
sensitizer plays a key role on the performance and device stability, and it is one of the most
important components to investigate, in order to gain further advance in cell efficiency. The great
research efforts allowed to reach in devices based on zinc, ruthenium complex and metalꢀfree
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organic dyes, power conversion efficiencies (PCE) of over 13%,7 10%,8 and 12%,9 respectively.
Compared to metalꢀorganic sensitizers, pure organic dyes have unique advantages such as: a) low
cost, b) nonꢀtoxicity, c) high extinction coefficients, d) flexible molecular designing, e) easy
tunability of molecular structure and then of absorption and electrochemical properties to increase
cell performance.10ꢀ13 Despite these attracting features, some drawbacks such as high recombination
losses and lower open circuit voltages (Vocs) limit the PCE in the final device.14ꢀ16 However, very
recently several reports have been published with efficiencies over 10% for metalꢀfree dyes using Iꢀ
/I3ꢀ17,18 and Co(II/III) redox shuttle,17,19ꢀ24 until to gain PCE record of 12.5% with a single sensitizer
device configuration.9 The most common and researched structural architecture of the best
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performing organic dyes is donorꢀ
moiety,25ꢀ33 while D and
πꢀbridgeꢀacceptor, DꢀπꢀA, with A being mainly the cyanoacrylic
π
being the units on which the research has been primarily focused the
chemicoꢀstructural design in order to gain improvements of photovoltaic performances. Beside high
device efficiency, the ideal sensitizer should possess other important requisites prior to consolidate
your commercial appealing, such as chemical and thermal stability, ease and lowꢀcost of the entire
synthetic methodology developed for its preparation. Since the very cheap cyanacetic acid has been
chosen as the reagent to build the acceptor unit, the design of the other two fundamental units,
donor and πꢀbridge, becomes very crucial for the global synthetic strategy. About the donor system,
the aryl amines,9,18,22,23,27 undoubtedly, resulted the best performing, and the research efforts have
been focused mainly on the strengthening of the electronꢀdonating power and on the introduction of
bulky chains to prevent aggregation and recombination processes on the TiO2. Regarding the πꢀ
bridge, it links the donor D and the acceptor A, and plays an important role by adjusting the
HOMOꢀLUMO levels and extending the absorption range.10 Moreover, the
πꢀbridge has to facilitate
the electron migration from the donor to the acceptor, so, its geometry should be preferably planar
(fused rings) rather than distorted. In fact, reports in the literature show as dyes containing fusedꢀ
rings planar structures as
π
ꢀbridge, ensure, in general, high performance.18,22,34ꢀ40 In the present
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work, we report the synthetic routes, electroꢀoptical properties and photovoltaic performances of
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three new dyes for DSSC solar cells, based on the molecular architecture Dꢀ
πꢀA and focused on the
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[1]benzothieno[3,2ꢀb]benzothiophene (BTBT) block as the ꢀbridge, with the cyanoacrylic group as
π
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the electron acceptor unit A and three different electron donor groups as the unit D. The BTBT
fusedꢀring planar system has been largely investigated for its excellent charge mobility in field
effect transistors.41ꢀ43 Are lacking, to the best of our knowledge, studies on the potentialities of this
molecule for photovoltaic applications. We thought the charge transport properties of the fusedꢀring
planar structure of BTBT, associated with a very easy and cheap synthetic access, could be very
suitable for photovoltaic purpose, especially in DSSC devices. For this aim, we selected three donor
groups with different electronꢀdonating capabilities to link the BTBT, in order to verify, through the
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cell performances, if the BTBT behaves as a general good πꢀcore in DSSC devices. The results
demonstrate the suitable ability of the BTBT structure to act as a good electronꢀtransporting bridge
in dyes for DSSC, disclosing a new interesting family of organic molecules for photovoltaic
applications.
RESULTS AND DISCUSSION
Synthesis and characterization
The synthetic general strategy followed to prepare the organic dyes is outlined in Scheme 1.
Scheme 1. Synthetic pathway to organic dyes 19, 20 and 21 by the retrosynthetic approach.
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C8H17
C8H17
C8H17
C8H17
S
S
Br
+
X
S
S
COOH
COOH
S
S
NC
NC
C8H17
C8H17
C8H17
C8H17
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C8H17
C8H17
S
S
Br
CHO
COOH
Bu3Sn
+
X
+
+
Br
NC
S
1
2
C8H17
C8H17
C8H17
C8H17
C8H17
C8H17
C8H17
C8H17
S
N
H
=
X
C8H17
C8H17
C8H17
C8H17
SnBu3
S
N
H
C8H17
C8H17
C8H17
C8H17
C8H17
C8H17
12
11
10
The intermediate 2,7ꢀdibromobenzothieno[3,2ꢀb]benzothiophene 1 was synthesized following the
literature procedure.44 The stannil derivative 2 was synthesized starting from 3ꢀmethylꢀ2ꢀ
thiophencarbaldehyde adapting a literature procedure45 (Scheme 2).
Scheme 2. Synthesis of 3-methyl-5-tributyltin-2-thiophencarbaldehyde 2.
The reagent 3ꢀmethylꢀ2ꢀthiophenecarbaldehyde was metallated by lithium Nꢀmethylpiperazide, in
situ prepared by adding butyl lithium to Nꢀmethylpiperazide. The resulting metallated derivatives
was treated before with tributyltin chloride and then with acidic aqueous solution to yield the
organotin derivative 2.
The three intermediate reagents 10, 11 and 12 were synthesized as reported in Scheme 3.
Scheme 3. Synthetic pathway to intermediate compounds 10, 11 and 12.
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Pd2dba3, P(t-Bu)3
I
NH2
+
N
H
t-BuONa, Toluene
C8H17
C8H17
C8H17
C8H17
C8H17
C8H17
C8H17
C8H17
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Br
C8H17
C8H17
C8H17
C8H17
nBuLi
Br
S
SnBu3
S
S
Bu3SnCl
THF, -78°C
PdCl2dppf, Na2CO3 2M
Toluene, reflux
C8H17
C8H17
C8H17
C8H17
8
10
O
B
2
O
C8H17
C8H17
C8H17
C8H17
C8H17
C8H17
5
Pd(PPh3)4, Na2CO3 2M
Toluene, EtOH
CF3CO2H
CH2Cl2
S
N
H
S
N O
Br
S
Br
O
S
1) Br2, AcOH (6)
N
O
N
2) (BOC)2O
DMAP, CH3CN
H
O
C8H17
C8H17
C8H17
7
C8H17
12
9
The donor building block 11 was synthesized by reacting the 2ꢀamino 9,9ꢀdioctylfluorene46 3 with
the 9,9ꢀdioctylꢀ2ꢀiodoꢀfluorene47 4 in the presence of Pd(0) and P(tꢀBu)3 as the catalytic system,
tꢀ
BuONa as a base and toluene as the solvent. The reaction mixture was refluxed overnight and the
resulting crude product was purified by column chromatography to yield the pure product 11 as a
dense brown liquid. The building blocks 10 and 12 were synthesized starting from the same
organoborane reagent 5, coupled with two different dibromoaryl reagents, the 2,3ꢀ
dibromothiophene and the dibromophenothiazine derivative 7. In the first pathway the
organoborane 5 was coupled with the 2,3ꢀdibromothiophene in the Suzuki reaction conditions,
using PdCl2dppf as the catalyst, to yield the intermediate 8, recovered as a dense light green liquid.
Compound 8 was purified by column chromatography and submitted to a stannilation reaction by
BuLi and Bu3SnCl, to yield the final compound 10, recovered as a dense green liquid. In the second
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pathway, the organoborane 5 was coupled with the dibromophenothiazine 7 in the Suzuki reaction
conditions, using Pd(PPh3)4 as the catalyst, to yield the intermediate 9. Compound 9 was purified by
column chromatography and obtained as a light brown solid. Subsequently, compound 9 was
submitted to hydrolysis of the BOC protecting group by CF3CO2H in dichloromethane, to yield,
after purification by column chromatography, the pure product 12 as a brown solid.
10
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The intermediate 7 was synthesized as reported in the literature48 in two steps, by brominating the
commercial phenothiazine with bromine in acetic acid, then reacting the resulting 3,7ꢀ
dibromphenothiazine
6
with diꢀtertꢀbutyl dicarbonate (Boc)2O, in the presence of
dimethyalmminopyridine DMAP and CH3CN as the solvent. Compound 7 was collected as a
colourless powder in an almost quantitative yield from the reaction mixture, after adding water and
filtering the resulting precipitate. The three dyes 19, 20 and 21 were synthesized as reported in
Scheme 4.
Scheme 4. Synthetic pathway to dyes 19, 20 and 21.
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The intermediates 10, 11 and 12, containing the electronꢀdonor units were then reacted with the 2,7ꢀ
dibromobenzothieno[3,2ꢀb]benzothiophene 1. The intermediate 1 was used in molar excess (2 eq.)
with respect to the donor reagents, in order to prevent the double crossꢀcoupling reaction. The
organotin reagent 10 was reacted with the dibromo BTBT 1 in the Stille crossꢀcoupling reaction, to
yield the intermediate 13, which was purified by column chromatography and obtained as a light
green solid. Subsequently, 13 was coupled in the Stille reaction conditions with the organotin
derivative 2, and then the resulting intermediate 16 was finally reacted with the cyanoacetic acid.
The dye 19 was recovered as a redꢀorange solid. The reagent 11 was reacted with the dibromo
BTBT 1 in a palladiumꢀcatalyzed amination process to yield the intermediate 14, which was
purified by column chromatography and obtained as a lightꢀgreen powder. Subsequently, 14 was
coupled in the Stille reaction conditions with the organotin 2, and the resulting intermediate 17 was
finally reacted with the cyanoacetic acid. The dye 20 was recovered as a red solid. The reagent 12
was reacted with the dibromoꢀBTBT 1 in the Stille crossꢀcoupling reaction, to yield the
intermediate 15, which was purified by column chromatography and obtained as a light green solid.
Subsequently, 15 was coupled in the Stille reaction conditions with the organotin derivative 2, and
then the resulting intermediate 18 was finally reacted with the cyanoacetic acid. The dye 21 was
recovered as a lightꢀred solid.
10
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Optical and electrochemical properties
Molar absorption spectra in solution of the three dyes are shown in Figure 1.
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120000
100000
80000
60000
40000
20000
0
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300
400
500
600
700
800
Wavelength (nm)
Figure 1. Molar absorptivity of 19, 20 and 21 in chloroform solution.
The dye 19 show a broaden absorption in the range 250ꢀ500 nm with an extinction coefficient over
10000 with a maximum value of 14190 at 453 nm. The substitution of the donor unit BFT with the
stronger electronꢀdonating arylamine unit BFA in 20 outlined a variation of the absorption profile
such as a strong enhancement of the absorption capacity. In fact, two absorption bands can be
observed in the range 300ꢀ550 nm, picked at 372 and 464 nm, with extinction coefficient of over
60000 and 42000, respectively. This improvement of the absorption properties led to an
enhancement of the photovoltaic performance, as reported below. Introducing a more complex
arylamine donor system, based on the phenothiazine molecular structure bearing two fluorene
molecules, in the 21, determined a further increase of the absorption capacity as well as a blue shift
of the absorption spectrum. Two main absorption bands can be observed in the range 250ꢀ500 nm,
picked at 320 and 420 nm, with extinction coefficients of over 100000 and 69000, respectively.
Despite the enormous increasing of the extinction coefficient in 21, its photovoltaic performances
didn’t show significant improvement, due to the blue shift of the absorption spectra.
Electrochemical properties
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To evaluate the possibility of electron injection from the excited state of the organic dyes to the
conduction band (CB) of TiO2 and the regeneration of the dyes, the redox behaviour was studied by
cyclic voltammetry (Fig. 2, Table 1).
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2
0
-2
0,0
0,3
0,6
0,9
1,2
1,5
1,8
Potential (V) vs NHE
Figure 2. Cyclic voltammograms of dyes in CH2Cl2
The first oxidation versus normal hydrogen electrode (vs. NHE), corresponding to the highest
occupied molecular orbital (HOMO) level of the dye, has been calibrated by Fc/Fc+ (0.63 V vs
.
NHE). As shown in Table 1, the HOMO levels of 19, 20 and 21 were found to be 1.22, 0.85 and
0.75 V, respectively. They are more positive than the redox potential of Iꢀ Iꢁꢀ (0.4 V vs. NHE),49
/
indicating that the oxidized dye molecules formed after electron injection into the conduction band
of TiO2 could be regenerated by the reducing species in the electrolyte solution. The energy gaps
(E0ꢀ0) between HOMO and LUMO levels calculated from onset of the absorption spectra for 19, 20
and 21 were found to be 2.38, 2.21 and 2.50 eV, respectively. The lowest unoccupied molecular
orbitals (LUMOs), has been estimated to be ꢀ1.16, ꢀ1.36 and ꢀ1.75 V, calculated from E0ꢀ0 = EHOMO
ꢀ
50
ELUMO
.
The LUMO levels of the dyes are sufficiently more negative than the conduction band
edge of TiO2 (ꢀ0.5 V vs. NHE), suggesting a sufficient driving force for electron injection from the
excited dyes to the conduction band of TiO2.51 Therefore, the electrochemical parameters suggest
these organic dyes could be efficiently used as good sensitizers in DSSCs.
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Table 1. Electrochemical data, absorption maxima and molar extinction coefficients.
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aλmax(nm)/
(M-1cm-1)
Dye
HOMO(V)
(vs. NHE)
E0-0(eV)
LUMO(V)
(vs. NHE)
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ε
453/14190
1.22
0.85
2.38
2.21
ꢀ1.16
ꢀ1.36
19
20
464/42130
372/60890
420/69800
320/108120
0.75
2.50
ꢀ1.75
21
aAbsorption maximum of the dyes measured in chloroform with a concentration ca 2
extinction coefficient at λmax. HOMO of the dyes by cyclic voltammetry in CH2Cl2, using
tetrabutylammonium hexafluorophosphate (0.1 M) as the supporting electrolyte, Ag/AgCl as the
reference electrode and Pt as the counter electrode. Scanning rate: 100 mVsꢀ1. LUMO was
calculated as the difference HOMOꢀE0ꢀ0. E0ꢀ0 was estimated from the absorption spectral onsets of
the dyes.
ꢀM. ε molar
Theoretical Study
The electronic and optical properties of the dyes were studied using density functional theory (DFT)
and timeꢀdependent (TD) DFT calculations.52ꢀ56 The TDꢀDFT results are reported in Table S1 (ESI)
and agree well with the experimental spectra. The calculations showed that in all three dyes the
lowest optically active singlet excited state has a significant chargeꢀtransfer character and is
characterized by singleꢀparticle transitions from the lowest occupied orbitals to the higher
unoccupied molecular orbital (LUMO).
A similar indication was also obtained from the isodensity plots of the frontier orbitals, reported in
Figure 3. The two indicators
Λ and ꢁ (Table S1, ESI) revealed that the charge separation upon
r57,58
excitation is the largest in 19, while it was slightly smaller for the other two dyes. This finding can
be, possibly traced back to the absence of an additional thiophene unit in 20 and 21, which is not
disturbing the electron withdrawing effect of the carboxylic acid, placed on the opposite side of the
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molecule. This same effect appears to have also a notable influence on the energy of the LUMO
orbitals, which results more stabilized in the 20 and 21 dyes with respect to 19 (LUMO energies are
ꢀ2.06, ꢀ2.01, and ꢀ1.97 eV in 19, 20, and 21, respectively). As a consequence, because the HOMO
energy is instead almost the same for the three molecules, a similar trend as for the LUMO was
observed also for the singleꢀparticle gap. Nevertheless, this is not reflecting directly in an analogous
trend for the lowestꢀlying excitation energies since all excited states, but the lowest singlet of 20,
are not fully characterized by a unique singleꢀparticle transition, but display important manyꢀbody
effects.
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Figure 3. Isodensity plots of the most relevant frontier orbitals of 19, 20 and 21.
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Photovoltaic performance
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Favourable characteristics emerge, in terms of potential photovoltaic properties, from the
characterization of 19, 20 and 21 dyes concerning in particular their light harvesting capability.
Therefore, the properties of the three dyes were tested in photoꢀelectrochemical solar cells. Due to
the high planarity of the sensitizers, favoured by the presence of the [1]benzothieno[3,2ꢀ
b]benzothiophene (BTBT) spacer, a fast intramolecular charge transfer should be expected as well
as an unfavourable πꢀπ stacking during the uptake process, which may lead to intermolecular
quenching or back transfer of the injected electrons from the TiO2 conduction band. In these cases,
the addition of chenodeoxycholic acid (CDCA) to the dyeing solutions could be useful; by
competing with the dye for the binding at the titania surface, the CDCA can in fact insert itself
between the sensitizers minimizing detrimental dye aggregation effects.59ꢀ61 Moreover, the use of a
coꢀadsorbent such as CDCA ensures a uniform coverage of the inorganic semiconductor, thereby
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–
lowering the probability of recombination between injected electrons with I3 and other acceptor
species. On the other hand, CDCA could unfavorably contend with the dyes for the attachment to
the TiO2 surface lowering the amount of sensitizers loaded on the working electrode. On these
basis, the use of chenodeoxycholic acid (CDCA) as coadsorbent has been evaluated: we prepared
0.2 mM solutions of 19, 20 and 21 dyes in THF with or without 10 mM CDCA and studied the
influence of the amount of additive on photovoltaic parameters and on the dye loading, which are
shown in Table 2. Notwithstanding the decrease in dye loading with the addition of 10 mM CDCA
the performances of the 19ꢀ, 20ꢀ and 21ꢀsensitized device were significantly improved. In particular,
the openꢀcircuit voltage (VOC) increased from 0.704 up to 0.735 V, from 0.736 to 0.765 and from
0.689 to 0.719 for 19, 20 and 21, respectively, suggesting that the detrimental recombination
processes at the TiO2/dye/electrolyte interface were partially suppressed with the use of CDCA
additive.
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Table 2. Photovoltaic parameters for DSSCs based on 19, 20 and 21 dyes.
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Dye
CDCA
(mM)
PCE
(%)
Voc
(V)
Jsc
FF
Dye
(mA/cm2)
loading
(mol/cm2)
2.9x10ꢀ7
2.4x10ꢀ7
3.0x10ꢀ7
2.4x10ꢀ7
2.8x10ꢀ7
2.2x10ꢀ7
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0
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10
0
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5.16
5.76
6.25
4.54
5.00
0.704
0.735
0.736
0.765
0.689
0.719
9.18
10.33
11.50
11.85
9.56
0.65
0.68
0.68
0.69
0.69
0.72
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20
21
10
9.67
Moreover, the shortꢀcircuit photocurrent density (JSC) augmented from 9.18 to 10.33 mA/cm2, from
11.50 to 11.85 and from 9.56 to 9.67 for 19, 20 and 21, respectively. On the whole, power
conversion efficiencies (PCE) of 5.16, 6.25 and 5.0% has been achieved with 19ꢀ, 20ꢀ and 21ꢀ
sensitized device, respectively. The IꢀV curves of DSSCs based on the three sensitizers in the
presence of 10 mM CDCA, are shown in Figure 4.
12
10
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4
20
19
21
2
0
0,0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
Voltage [V]
Figure 4. I-V curves of DSSCs fabricated with the three dyes in the presence of 10 mM
CDCA.
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Comparing the photovoltaic parameters of the three dyes in their better testing condition, we can
observe that the higher photocurrent density is related to the presence of the bisfluorenylamine
derivative (BFA) as the electronꢀdonor group, suggesting its better capability to generate electrons
and/or to be adequately regenerated by the iodine/iodide electrolyte. Further information emerge
from the analysis of the monochromatic incident photonꢀtoꢀcurrent conversion efficiencies (IPCEs)
recorded for the DSSCs (Figure 5). Notwithstanding the competitive absorption of FTOꢀglass, TiO2
and electrolyte, the IPCE spectra seem to be in agreement with the lightꢀharvesting range of
sensitizers, although the presence of large TiO2 scattering nanoparticles in the photoanode broaden
their shape. The IPCE spectra of 20 dye showed a maximun of ~60% at 500 nm, slightly higher
with respect to the ~55% obtained for the 19ꢀbased device at 450 nm and to the plateau at 50%,
ranging from 400 to 470 nm, observed for 21; this confirms the superior photovoltaic properties of
the 20 dye.
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20
10
0
350
400
450
500
550
600
650
700
750
WAVELENGTH [nm]
Figure 5. IPCEs spectra recorded for DSSCs devices fabricated with the three dyes.
The dyes of the present work show, on balance, good photovoltaic parameters, with efficiencies in
the range 4ꢀ6. Comparing these values with those reported in literature for dyes based on fusedꢀring
systems, although they are not as high as some optimized structures,18,22,23,35,39 they are
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comparable38,62ꢀ65
and sometimes competitive31,37,66ꢀ69 with others reported dyes. These
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achievements support the rationale behind the choice of the [1]benzothieno[3,2ꢀb]benzothiophene
system as a ꢀcore of dyes for DSSC.
π
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CONCLUSIONS
In summary, we have synthesized three new DꢀπꢀA dyes based on the BTBT unit as the πꢀbridge,
disclosing a new interesting class of organic dyes for DSSC. Varying the donor unit D in the
general selected structure, all dyes exhibited remarkable solarꢀtoꢀenergy conversion efficiencies
thanks to favourable lightꢀharvesting capacity and high absorptivity, highlighting the good
transporting properties of the planar BTBT unit, suitable for photovoltaic applications. With a right
choice of donor units D the optical properties can be tuned in order to adjust the absorption range
and increase the absorption capability to optimize the photovoltaic performances. Due to the high
planarity of the BTBT, the addition of CDCA additive help the efficiency of the final device by
minimizing detrimental dye aggregation effects. In fact, all dyes show better PCE value in the
presence of CDCA coadsorbent. Overall, the BTBT intermediate is very easy to synthesize and can
be prepared in very large amount, making the family of dyes based on this structure very promising
for cheap applications. Even though the performances gained with the three dyes are not high as the
best performing dyes, they are however very good and this clearly reveals an intrinsically good
potentiality of the BTBT molecular structure for DSSCs. New structures can be engineered by
selecting different donor units D and anchoring groups A, as partners of the πꢀbridge BTBT, in
order to deeper recognize the potentialities of this new class of organic dyes. Experiments are in
progress in this direction.
EXPERIMENTAL SECTION
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General Methods
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Unless otherwise noted, all reagents and solvents of ACS purity were purchased from commercial
sources and used without further purification. All reactions sensitive to air were carried out under a
nitrogen atmosphere with anhydrous solvents, distilled immediately prior to use. Toluene and THF
were distilled from sodium/benzophenone; DMF and CH3CN were distilled from 4Å molecular
sieves; CHCl3 was distilled from P2O5. Column chromatography was performed using silica gel 60,
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40ꢀ63 ꢀm. Silica gel 60 F254 aluminium sheets were used for analytical TLC. FTꢀIR spectra were
measured on a spectrophotometer using dry KBr pellets. 1H and 13C NMR spectra were recorded in
CDCl3 or (CD3)2CO or CDCl3/DMSOꢀd6 on a 500 MHz spectrometer at 500 MHz and 125.7 MHz,
respectively. The residual signals at δ = 7.24 (CDCl3) or δ = 2.05 ((CD3)2CO) or δ = 2.5
1
(CDCl3/DMSOꢀd6) ppm were used as the standard for H NMR spectra. The signals at δ = 77.0
(CDCl3) or δ = 30.83 ((CD3)2CO) ppm were used as the standard for 13CNMR spectra. MS spectra
were recorded on a mass spectrometer. Elemental analyses were done by an Elemental Analyzer.
Melting points were determined on a Gallenkamp capillary melting point apparatus. UVꢀvis spectra
of the organic compounds were recorded on a UVꢀVis spectrophotometer.
Synthesis of 3-methyl-5-(tributylstannil)thiophene-2-carbaldehyde 2. In a 250 mL threeꢀnecked
round bottom flask Nꢀmethylpiperazine (3.4 mL, 30 mmol) and anhydrous THF (60 mL) were
added under a nitrogen atmosphere. The solution was cooled to ꢀ78°C and nBuLi (2.5 M, 12 mL, 30
mmol) was added dropwise. The resulting mixture was stirred at ꢀ78°C for 30 min then a solution of
3ꢀmethylthiopheneꢀ2ꢀcarbaldehyde (3.4 g, 27 mmol) in anhydrous THF (15 mL) was added
dropwise. The mixture was stirred at ꢀ78°C for 30 min, then nBuLi (2.5 M, 12 mL) was added
dropwise, and the resulting mixture was stirred at ꢀ20°C for 5h. A solution of nBu3SnCl (8.3 mL, 30
mmol) in anhydrous THF (20 mL) was added dropwise at ꢀ78°C and the mixture was allowed to
warm at r. t. and stirred overnight. To the mixture 1N HCl (150 mL) was added at 0°C for 20 min,
then neutralized with aq. Na2CO3 solution. The mixture was extracted with hexane and the organic
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layer washed with aq 40% KF solution and dried over Na2SO4. After evaporation of the solvent
under a reduced pressure, the crude residue was purified by distillation with a kugelrohr apparatus
1
(9x10ꢀ6 torr, T = 70°C) to yield the pure product 2 (9.2 g, 82% yield) as a light yellow liquid. H
9
NMR (500 MHz, CDCl3): δ 9.98 (s, 1H), 7.00 (s, 1H), 2.56 (s, 3H), 1.59ꢀ1.52 (m, 6H), 1.33 (sext, J
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= 7.3, 6H), 1.13 (t, J = 7.3, 6H), 0.89 (t, J = 7.3, 9H) ppm. C NMR (125 MHz, CDCl3): δ 181.5,
150.4, 147.4, 142.5, 139.8, 28.8, 27.2, 13.9, 13.6, 10.9 ppm. FTꢀIR (KBr): ν 2955 (s), 2917 (s),
2870 (s), 2848 (s), 1662 (s), 1458 (m), 1415 (s), 1377 (s), 1216 (s), 1075 (m), 902 (s), 671 (s) cmꢀ1.
MS (70 eV) m/e (%): 359 ([MꢀBu]+, 94), 303 (100). 247 (65). Anal. Calcd for C18H32OSSn: C,
52.07; H, 7.77; O, 3.85; S, 7.72; Sn, 28.59. Found: C, 52.15; H, 7.81; S, 7.70.
Synthesis of 2,3-bis(9,9-dioctyl-9H-fluoren-2-yl)thiophene 8. In a 250 mL threeꢀnecked round
bottom flask, under a nitrogen atmosphere, were added 2,3ꢀdibromothiophene (0.6 g, 2.5 mmol), 2ꢀ
(9,9ꢀdioctylꢀ9Hꢀfluorenꢀ2ꢀyl)4,4,5,5ꢀtetramethylꢀ1,3,2ꢀdioxaborolane 5 (2.84 g, 5.5 mmol), Pd2dba3
(0.05 g, 0.055 mmol), AsPh3 (0.135 g, 0.44 mmol), toluene (30 mL) and EtOH (6 mL). The mixture
was degassed with a nitrogen flow for 30 min, then 2M Na2CO3 aq. (25 mL, 50 mmol) previously
degased was added and the resulting mixture was refluxed overnight. The reaction mixture was
cooled at r.t., quenched with water and extracted with CH2Cl2. The organic layer was dried over
Na2SO4 and the solvent removed under a reduced pressure. The crude residue was purified by
column chromatography using hexane as the eluent, to yield the pure product 8 (1.65 g, 77% yield)
1
as a light green dense liquid. H NMR (500 MHz, CDCl3): δ 7.71ꢀ7.66 (m, 2H), 7.61 (d, J = 7.8,
1H), 7.60 (d, J = 8.3, 1H), 7.41 (d, J = 5.2, 1H), 7.38ꢀ7.32 (m, 10H), 7.31 (d, J = 5.2, 1H), 2.00ꢀ1.78
13
(m. 8H), 1.32ꢀ0.98 (m, 40H), 0.90 (t, J = 7.3, 12H), 0.77ꢀ0.56 (m, 8H) ppm. C NMR (125 MHz,
CDCl3): δ 150.8, 150.8, 150.77, 150.76, 140.9, 140.7, 140.4, 139.8, 139.3, 138.8, 135.5, 133.2,
130.5, 128.3, 128.0, 127.1, 126.9, 126.7, 126.7, 124.0, 123.9, 123.7, 122.71, 122.69, 119.7, 119.6,
119.6, 119.5, 55.0, 54.96, 40.44, 40.38, 31.8, 30.1, 30.0, 29.4, 29.34, 29.32, 29.311, 23.78, 23.76,
22.6, 14.1 ppm. FTꢀIR (KBr): ν 2953 (s), 2925 (s), 2853 (s), 1466 (m), 1456 (m), 831 (w), 740 (s)
cmꢀ1. Anal. Calcd for C62H84S: C, 86.45; H, 9.83; S, 3.72. Found: C, 86.40; H, 9.88; S, 3.75.
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Synthesis of tert-Butyl 3,7-bis(9,9-dioctyl-9H-fluoren-2-yl)-10H-phenothiazine-10-carboxylate 9.
In a 100 mL threeꢀnecked round bottom flask, under a nitrogen atmosphere, were added tertꢀbutyl
3,7ꢀdibromoꢀ10Hꢀphenothiazineꢀ10ꢀcarboxylate 7 (0.3 g, 0.66 mmol), 2ꢀ(9,9ꢀdioctylꢀ9Hꢀfluorenꢀ2ꢀ
yl)4,4,5,5ꢀtetramethylꢀ1,3,2ꢀdioxaborolane 5 (0.77 g, 1.5 mmol), Pd(PPh3)4 (0.05 g, 0.04 mmol),
toluene (20 mL) and EtOH (5 mL). The mixture was degassed with a nitrogen flow for 30 min, then
2M Na2CO3 aq. (7.5 mL, 15 mmol) previously degased was added and the resulting mixture was
refluxed overnight. The reaction mixture was cooled at r.t., quenched with saturated aq. NH4Cl and
extracted with CH2Cl2. The organic layer was dried over Na2SO4 and the solvent removed under a
reduced pressure. The crude residue was purified by column chromatography using hexane/CH2Cl2
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(6/4) as the eluent, to yield the pure product 9 (0.6 g, 85% yield) as a light yellow dense liquid. H
NMR (500 MHz, CDCl3): δ 7.79 (d, J = 7.8, 2H), 7.75 (d, J = 7.2, 2H), 7.71 (s, 2H), 7.70 (d, J =
7.2, 2H), 7.64ꢀ7.55 (m, 6H), 7.41ꢀ7.31 (m, 6H), 2.00ꢀ1.98 (m, 8H), 1.61 (s, 9H), 1.28ꢀ1.03 (m,
40H), 0.85 (t, J = 0.9, 12H), 0.76ꢀ0.65 (bs, 8H) ppm. 13C NMR (125 MHz, CDCl3): δ 152.47,
151.45, 151.0, 140.7, 140.6, 139.9, 138.6, 137.7, 132.3, 127.2, 127.1, 126.9, 125.9, 125.8, 125.5,
122.6, 121.4, 120.0, 119.8, 82.3, 55.1, 40.1, 40.3, 31.8, 30.0, 29.18, 29.16, 28.2, 23.8, 22.6, 14.1
ppm. FTꢀIR (KBr): ν 2952 (s), 2924 (s), 2851 (s), 1717 (s), 1475 (s), 1465 (s), 1449 (s), 1392 (w),
1367 (m), 1324 (s), 1298 (m), 1251 (m), 1235 (m), 1162 (s), 1095 (w), 1048 (w), 1023 (s), 878 (w),
823 (m), 739 (s) cmꢀ1. Anal. Calcd for C75H97NO2S: C, 83.67; H, 9.08; N, 1.30; O, 2.97; S, 2.98.
Found: C, 83.75; H, 9.20; N, 1.28; S, 3.02.
Synthesis of [4,5-Bis(9,9-dioctyl-9H-fluoren-2-yl)thiophen-2-yl]tributylstannane 10. In a 100 mL
threeꢀnecked round bottom flask, under a nitrogen atmosphere, 2,3ꢀbis(9,9ꢀdioctylꢀ9Hꢀfluorenꢀ2ꢀ
yl)thiophene 8 (0.8 g, 0.9 mmol) was dissolved in anhydrous THF (30 mL). The solution was
cooled at ꢀ78°C and nBuLi (2.5 M, 0.45 mL, 1.1 mmol) was added dropwise. The resulting mixture
was stirred at ꢀ78°C for 30 min and ꢀ30°C for another 30 min. Then the reaction mixture was cooled
at ꢀ78°C and a solution of Bu3SnCl (0.36 mL, 1.1 mmol) in anhydrous THF (10 mL) was added
dropwise. The resulting mixture was allowed to warm to r.t. and stirred overnight. The reaction
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mixture was quenched with water and extracted with ethyl acetate. The organic layer was washed
with 40% aq. KF (2x20 mL), dried over Na2SO4 and the solvent removed under a reduced pressure.
The crude residue was purified by flash chromatography using hexane as the eluent, to yield the
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pure product 10 (0.9 g, 87% yield) as a light yellow liquid. H NMR (500 MHz, CDCl3): δ 7.71ꢀ
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7.65 (m, 2H), 7.62 (dd, J = 7.6, 0.8, 1H), 7.57 (dd, J = 7.8, 0.6, 1H), 7.40ꢀ7.29 (m, 11H), 1.99ꢀ1.80
(m, 8H), 1.79ꢀ1.64 (m, 6H), 1.48 (sext, J = 7.3, 6H), 1.38ꢀ0.96 (m, 55H), 0.90 (t, J = 7.3, 6H), 0.89
13
(t, J = 7.3, 6H), 0.80ꢀ0.50 (bs, 8H) ppm. C NMR (125 MHz, CDCl3): δ 150.80, 150.78, 150.72,
150.70, 145.3, 141.0, 140.8, 140.1, 141.1, 139.6, 138.8, 135.84, 135.77, 133.5, 128.1, 128.0, 126.9,
126.8, 126.67, 126.65, 123.78, 123.77, 122.68, 122.67, 119.7, 119.6, 119.5, 119.4, 55.0, 54.9, 40.5,
40.4, 31.9, 31.8, 30.09, 30.05, 29.37, 29.36, 29.35, 29.32, 29.0, 27.4, 23.80, 23.75, 22.7, 14.10,
14.09, 13.7, 11.0 ppm. FTꢀIR (KBr): ν 2955 (s), 2925 (s), 2852 (s), 1464 (m), 1456 (m), 1376 (w),
1074 (w), 1025 (w), 830 (w), 739 (s) cmꢀ1. Anal. Calcd for C74H110SSn: C, 77.26; H, 9.64; S, 2.79;
Sn, 10.32. Found: C, 77.20; H, 9.54; S, 2.84.
Synthesis of Bis(9,9-dioctyl-9H-fluoren-2-yl)amine 11. In a 100 mL threeꢀnecked round bottom
flask, under a nitrogen atmosphere, were added 9,9ꢀdioctylꢀ9Hꢀfluorenꢀ2ꢀamine 3 (0.7 g, 1.7
mmol), 2ꢀiodoꢀ9,9ꢀdioctylꢀ9H fluorene 4 (0.89 g, 1.7 mmol), Pd2dba3 (0.016 g, 0.017 mmol),
P(tBu)3 (7 mg, 0.034 mmol), tꢀBuONa (0.18 g, 1.9 mmol ) and anhydrous toluene (20 mL). The
mixture was refluxed overnight. The reaction mixture was cooled at r.t., quenched with saturated
aq. NH4Cl and extracted with CH2Cl2. The organic layer was dried over Na2SO4 and the solvent
removed under a reduced pressure. The crude residue was purified by column chromatography
using hexane/CH2Cl2 (8.5/1.5) as the eluent, to yield the pure product 11 (1.1 g, 81% yield) as a
1
light yellowꢀgreen waxy solid. H NMR (500 MHz, (CD3)2CO: δ 7.43ꢀ7.33 (bs, 1H), 7.28ꢀ7.14 (m,
4H), 6.98ꢀ6.88 (m, 4H), 6.84 (t, J = 7.4, 2H), 6.77 (t, J = 7.4, 2H), 6.62 (d, J = 8.0, 2H), 1.67ꢀ1.48
13
(m, 8H), 0.84ꢀ0.58 (m, 40H), 0.38 (t, J = 7.0, 12H), 0.35ꢀ0.15 (m, 8H) ppm. C NMR (125 MHz,
(CD3)2CO: δ 153.5, 151.6, 145.2, 143.5, 135.6, 128.6, 127.5, 124.4, 122.5, 120.4, 118.9, 112.5,
56.7, 42.4, 33.5, 31.9, 31.1, 31.0, 25.7, 24.3, 15.4 ppm. FTꢀIR (KBr): ν 3373 (s), 2955 (s), 2924 (s),
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2853 (s), 1608 (s), 1586 (s), 1491 (s), 1452 (s), 1408 (s), 1313 (m), 1272 (m), 820 (w), 738 (m) cmꢀ
1. Anal. Calcd for C58H83N: C, 87.70; H, 10.53; N, 1.76. Found: C, 87.75; H, 10.59; N, 1.69.
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9
Synthesis of 3,7-Bis(9,9-dioctyl-9H-fluoren-2-yl)-10H-phenothiazine 12. In a 100 mL threeꢀ
necked round bottom flask, a solution of tertꢀButyl 3,7ꢀbis(9,9ꢀdioctylꢀ9Hꢀfluorenꢀ2ꢀyl)ꢀ10Hꢀ
phenothiazineꢀ10ꢀcarboxylate 9 (0.56 g, 0.5 mmol), CF3CO2H (5 mL) and CH2Cl2 was stirred
overnight at r.t. The reaction mixture was quenched at 0°C in a 5% NaOH aq. solution, then
extracted with CHCl3. The organic layer was dried over Na2SO4 and the solvent removed under a
reduced pressure. The crude residue was purified by column chromatography using hexane/CH2Cl2
(7/3) as the eluent, to yield the pure product 12 (0.45 g, 92% yield) as a light brown dense liquid. 1H
NMR (500 MHz, (CD3)2CO): δ 8.09 (s, 1H), 7.81 (d, J = 8.0, 2H), 7.80ꢀ7.76 (m, 2H), 7.69 (d, J =
1.1, 2H), 7.57 (dd, J = 7.9, 1.5, 2H), 7.46ꢀ7.41 (m, 2H), 7.41ꢀ7.37 (m, 2H), 7.36ꢀ7.34 (m, 2H), 7.34ꢀ
7.29 (m, 4H), 6.83 (d, J 8.0, 2H), 2.20ꢀ2.00 (m, 8H), 1.23ꢀ0.97 (m, 40H), 0.79 (t, J = 7.2, 12H),
0.72ꢀ0.57 (m, 8H) ppm. 13C NMR (125 MHz, (CD3)2CO): δ 153.2, 152.7, 143.1, 142.8, 142.0,
140.9, 137.3, 128.9, 128.7, 128.0, 126.8, 126.5, 124.7, 122.3, 121.9, 121.5, 119.8, 116.8, 57.0, 41.9,
33.5, 31.6, 30.90, 30.86, 25.5, 24.3, 15.3 ppm. FTꢀIR (KBr): ν 3420 (s), 2924 (s), 2853 (s), 1465 (s),
1449 (s), 1297 (m), 814 (w), 740 (m) cmꢀ1. Anal. Calcd for C70H89NS: C, 86.10; H, 9.19; N, 1.43; S,
3.28. Found: C, 86.21; H, 9.18; N, 1.45; S, 3.25.
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Synthesis
bromobenzo[b]benzo[4,5]thieno[2,3-d]thiophene 13. In a 100 mL threeꢀnecked round bottom
flask, under nitrogen atmosphere, [4,5ꢀbis(9,9ꢀdioctylꢀ9Hꢀfluorenꢀ2ꢀyl)thiophenꢀ2ꢀ
yl]tributylstannane 10 (0.56 g, 0.49 mmol), 2,7ꢀdibromobenzo[b]benzo[4,5]thieno[2,3ꢀd]thiophene
1 (0.4 g, 1.0 mmol), PdCl2dppf ( 7 mg, 9.6 mol) and anhydrous toluene (20 mL) were added and
of
2-(4,5-Bis(9,9-dioctyl-9H-fluoren-2-yl)thiophene-2-yl)-7-
a
ꢀ
the resulting mixture was refluxed overnight. The reaction mixture was cooled at r.t., quenched with
saturated aq NH4Cl and extracted with ethyl acetate. The organic layer was washed with 40% aq KF
solution (2x20 mL), dried over Na2SO4 and the solvent removed under a reduced pressure. The
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crude residue was purified by column chromatography using hexane/CH2Cl2 (9/1) as the eluent, to
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yield the pure product 13 (0.38 g, 65% yield) as a light green solid. Mp 43ꢀ44 °C. H NMR (500
7
8
9
MHz, CDCl3): δ 7.63ꢀ7.57 (m, 2H), 7.54ꢀ7.49 (m, 3H), 7.42 (s, 1H), 7.39 (d, J = 8.4, 1H), 7.34 (d, J
= 1.8, 1H), 7.30ꢀ7.20 (m, 10H), 7.17 (dd, J = 8.0, 1.8, 1H), 7.04 (d, J 8.0, 1H), 1.92ꢀ1.68 (m, 8H),
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13
1.34ꢀ0.90 (m, 40H), 0.8 (t, J = 7.3, 12H), 0.68ꢀ0.40 (bs, 8H) ppm. C NMR (125 MHz, CDCl3): δ
150.99, 150.98, 150.86, 150.8, 145.5, 143.1, 141.0, 140.7, 140.4, 140.3, 139.7, 139.2, 139.1, 138.3,
137.6, 134.5, 132.2, 131.8, 130.4, 128.3, 128.2, 128.0, 127.7, 127.6, 127.3, 127.1, 126.8, 126.7,
125.6, 124.9, 123.7, 123.5, 122.76, 122.75, 122.2, 121.3, 119.8, 119.71, 119.69, 119.60, 55.1, 55.0,
49.7, 42.7, 40.4, 40.3, 31.83, 31.82, 31.6, 30.04, 29.99, 29.34, 29.33, 29.31, 29.28, 23.8, 23.7, 22.7,
22.64, 22.63, 14.12, 14.08 ppm. FTꢀIR (KBr): ν 2952 (s), 2923 (s), 2853 (s), 1606 (s), 1463 (s),
1442 (s), 1378 (m), 1306 (s), 1251 (m), 805 (s), 740 (s) cmꢀ1. Anal. Calcd for C76H89BrS3: C, 77.45;
H, 7.61; Br, 6.78; S, 8.16. Found: C, 77.29; H, 7.67; S, 8.23.
Synthesis
of
7-Bromo-N,N-bis(9,9-dioctyl-9H-fluoren-2-yl)benzo[b]benzo[4,5]thieno[2,3-
d]thiophene-2-amine 14. In a 100 mL threeꢀnecked round bottom flask, under a nitrogen
atmosphere, bis(9,9ꢀdioctylꢀ9Hꢀfluorenꢀ2ꢀyl)amine 11 (0.34 g, 0.43 mmol), 2,7ꢀ
dibromobenzo[b]benzo[4,5]thieno[2,3ꢀd]thiophene 1 (0.3 g, 0.86 mmol), Pd2dba3 (8 mg, 9.0
ꢀmol)
P( Bu)3 (4 mg, 20 mol), BuONa (41 mg, 0.43 mmol) and anhydrous toluene (20 mL) were added.
t
ꢀ
t
The resulting mixture was refluxed overnight. The reaction mixture was cooled at r.t., quenched
with saturated aq NH4Cl and extracted with ethyl acetate. The organic layer was washed with 40%
aq KF solution (2x20 mL), dried over Na2SO4 and the solvent removed under a reduced pressure.
The crude residue was purified by column chromatography using hexane/CH2Cl2 (9/1) as the eluent,
1
to yield the pure product 14 (0.38 g, 65% yield) as a light green solid. Mp 56ꢀ57 °C. H NMR (500
MHz, CDCl3): δ 8.04 (dd, J = 1.7, 0.4, 1H), 7.73 (d, J = 8.6, 1H), 7.69ꢀ7.60 (m, 6H), 7.54 (dd, J =
8.4, 1.7, 1H), 7.38ꢀ7.24 (m, 9H), 7.13 (dd, J = 8.4, 1.7, 2H), 2.06ꢀ1.78 (m, 8H), 1.34ꢀ1.02 (m, 40H),
13
0.87 (t, J = 7.1, 12H), 0.82ꢀ0.62 (m, 8H) ppm. C NMR (125 MHz, CDCl3): δ 152.2, 150.6, 146.8,
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146.5, 143.9, 143.3, 140.77, 136.76, 133.8, 132.1, 131.5, 128.2, 127.6, 126.8, 126.5, 126.4, 123.5,
122.7, 122.0, 121.8, 121.5, 120.5, 119.2, 119.17, 118.0, 117.5, 55.1, 40.3, 31.9, 30.1, 29.4, 29.3,
24.0, 22.7, 14.1 ppm. FTꢀIR (KBr): ν 2953 (s), 2914 (s), 2851 (s), 1660 (s), 1592 (s), 1488 (s), 1451
(s), 1277 (s), 1024 (s), 805 (s), 741 (s) cmꢀ1. Anal. Calcd for C72H88BrNS2: C, 77.80; H, 7.98; Br,
7.19; N, 1.26; S, 5.77. Found: C, 77.92; H, 7.85; N, 1.22; S, 5.66.
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Synthesis of 10-(7-Bromobenzo[b]benzo[4,5]thieno[2,3-d]thiophene-2-yl-3,7-bis(9,9-dioctyl-9H-
fluoren-2-yl)-10-phenothiazine 15. In a 100 mL threeꢀnecked round bottom flask, under a nitrogen
atmosphere, 3,7ꢀBis(9,9ꢀdioctylꢀ9Hꢀfluorenꢀ2ꢀyl)ꢀ10Hꢀphenothiazine 12 (0.3 g, 0.3 mmol), 2,7ꢀ
dibromobenzo[b]benzo[4,5]thieno[2,3ꢀd]thiophene 1 (0.25 g, 0.6 mmol), Pd2dba3 (8 mg, 9.0
ꢀmol)
P( Bu)3 (4 mg, 20 mol), BuONa (32 mg, 0.33 mmol) and anhydrous toluene (20 mL) were added.
t
ꢀ
t
The resulting mixture was refluxed overnight. The reaction mixture was cooled at r.t., quenched
with saturated aq. NH4Cl and extracted with ethyl acetate. The organic layer was washed with 40%
aq. KF solution (2x20 mL), dried over Na2SO4 and the solvent removed under a reduced pressure.
The crude residue was purified by column chromatography using hexane/CH2Cl2 (8.5/1.5) as the
1
eluent, to yield the pure product 15 (0.27 g, 68% yield) as a yellow grassy solid. H NMR (500
MHz, CDCl3/DMSOꢀd6): δ 8.19 (d, J = 1.6, 1H), 8.16 (d, J = 8.3, 1H), 8.07 (d, J = 1.6, 1H), 7.83 (d,
J = 8.4, 1H), 7.66 (d, J = 8.4, 2H), 7.64 (dd, J = 6.3, 1.6, 2H), 7.56 (dd, J = 8.4, 1,8, 1H), 7.51 (dd, J
= 8.4, 1.8, 1H), 7.45ꢀ7.37 (bs, 4H), 7.32 (d, J = 2.0, 2H), 7.30ꢀ7.18 (m, 6H), 7.14 (dd, J = 8.6, 2.0,
2H), 6.32 (d, J = 8.6, 2H), 2.04ꢀ1.79 (bs, 8H), 1.17ꢀ0.83 (m, 40H), 0.71 (t, J = 7.1, 12H), 0.63ꢀ0.42
(bs, 8) ppm. 13C NMR (125 MHz, CDCl3): δ 151.4, 150.9, 144.3, 143.9, 140.7, 140.3, 138.4, 134.4,
133.4, 132.6, 131.7, 128.6, 127.7, 126.74, 126.65, 125.6, 125.1, 123.6, 122.8, 122.73, 120.70,
119.9, 119.7, 119.1, 116.5, 55.1, 40.4, 31.8, 30.0, 29.21, 29.18, 23.8, 22.6, 14.1 ppm. FTꢀIR (KBr):
ν 2950 (s), 2922 (s), 2850 (s), 1465 (s), 1447 (s), 1309 (s), 807 (s), 739 (s), cmꢀ1. Anal. Calcd for
C84H94BrNS3: C, 77.98; H, 7.32; Br, 6.18; N, 1.08; S, 7.44. Found: C, 78.04; H, 7.45; N, 1.18; S,
7.56.
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Synthesis
of
5-(7-(4,5-Bis(9,9-dioctyl-9H-fluoren-2-yl)thiophene-2-
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yl)benzo[b]benzo[4,5]thieno[2,3-d]thiophene-2-yl)-3-methylthiophene-2-carbaldehyde 16. In a
100 mL threeꢀnecked round bottom flask, under a nitrogen atmosphere, 2ꢀ(4,5ꢀBis(9,9ꢀdioctylꢀ9Hꢀ
fluorenꢀ2ꢀyl)thiopheneꢀ2ꢀyl)ꢀ7ꢀbromobenzo[b]benzo[4,5]thieno[2,3ꢀd]thiophene 13 (0.2 g, 0.17
mmol), 3ꢀmethylꢀ5ꢀ(tributylstannil)thiopheneꢀ2ꢀcarbaldehyde 2 (0.085 g, 0.2 mmol), PdCl2dppf ( 3
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mg, 4 ꢀmol) and anhydrous toluene (20 mL) were added and the resulting mixture was refluxed
overnight. The reaction mixture was cooled at r.t., quenched with saturated aq. NH4Cl and extracted
with ethyl acetate. The organic layer was washed with 40% aq. KF solution (2x10 mL), dried over
Na2SO4 and the solvent removed under a reduced pressure. The crude residue was purified by
column chromatography using hexane/ethyl acetate (9/1) as the eluent, to yield the pure product 16
(0.17 g, 85% yield) as a yellowꢀorange solid. Mp 64ꢀ65 °C. Due to molecular aggregations, 13C
NMR spectrum cannot be recovered. 1H NMR (500 MHz, CDCl3): δ 9.91 (s, 1H), 8.24 (s, 1H), 8.21
(s, 1H), 7.91 (d, J = 7.8, 2H), 7.82 (dd, J = 7.8, 1.6, 1H), 7.79ꢀ7.72 (m, 2H), 7.66ꢀ7.56 (m, 4H), 7.53
(d, J = 7.8, 1H), 7.49 (d, J = 4.1, 1H), 7.35ꢀ7.26 (m, 9H), 1.96ꢀ1.73 (m, 8H), 1.36ꢀ0.92 (m, 40H),
0.83 (t, J = 7.1, 6H), 0.82 (t, J = 7.1, 6H), 0.72ꢀ0.48 (m, 8H) ppm. FTꢀIR (KBr): ν 2953 (s), 2925
(s), 2853 (s), 1662 (s), 1437 (s), 1262 (s), 1096 (s), 1060 (s), 1025 (s), 804 (s), 740 (m) cmꢀ1. Anal.
Calcd for C82H94OS4: C, 80.47; H, 7.74; O, 1.31; S, 10.48. Found: C, 80.32; H, 7.62; S, 10.53.
Synthesis
d]thiophen-2-yl)-3-methylthiophene-2-carbaldehyde 17. In a 100 mL threeꢀnecked round bottom
flask, under nitrogen atmosphere, 7ꢀBromoꢀN,Nꢀbis(9,9ꢀdioctylꢀ9Hꢀfluorenꢀ2ꢀ
yl)benzo[b]benzo[4,5]thieno[2,3ꢀd]thiopheneꢀ2ꢀamine 14, (0.2 g, 0.18 mmol), 3ꢀmethylꢀ5ꢀ
(tributylstannil)thiopheneꢀ2ꢀcarbaldehyde 2 (0.09 g, 0.2 mmol), PdCl2dppf ( 3 mg, 4 mol) and
of
5-(7-bis(9,9-dioctyl-9H-fluoren-2-yl)amino)benzo[b]benzo[4,5]thieno[2,3-
a
ꢀ
anhydrous toluene (20 mL) were added and the resulting mixture was refluxed overnight. The
reaction mixture was cooled at r.t., quenched with saturated aq. NH4Cl and extracted with ethyl
acetate. The organic layer was washed with 40% aq. KF solution (2x10 mL), dried over Na2SO4 and
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the solvent removed under a reduced pressure. The crude residue was purified by column
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chromatography using hexane/ethyl acetate (8.5/1.5) as the eluent, to yield the pure product 17
1
(0.18 g, 86% yield) as an orange solid. Mp 101ꢀ102 °C. H NMR (500 MHz, CDCl3): δ 10.04 (s,
9
1H), 8.17 (dd, J = 1.6, 0.4, 1H), 7.80 (d, J = 8.3, 1H), 7.74 (d, J = 8.7, 1H), 7.71 (dd, J = 8.3, 1.6,
1H), 8.67ꢀ8.59 (m, 5H), 7.37ꢀ7.23 (m, 10H), 7.12 (d, J = 7.4, 2H), 2.61 (s, 3H), 1.98ꢀ1.82 (m, 8H),
1.32ꢀ1.00 (m, 40H), 0.86 (t, J = 7.1, 12H), 0.80ꢀ0.64 (m, 8H) ppm. 13C NMR (125 MHz, CDCl3): δ
181.7, 152.6, 152.3, 150.6, 148.3, 142.7, 136.5, 135.1, 133.9, 129.4, 127.5, 126.8, 126.5, 123.3,
122.7, 122.0, 121.5, 121.4, 120.5, 119.3, 119.2, 55.1, 40.3, 31.8, 30.1, 29.4, 29.3, 24.0, 22.7, 14.3,
14.1 ppm. FTꢀIR (KBr): ν 2916 (s), 2848 (s), 1731 (s), 1661 (s), 1593 (s), 1451 (s), 1263 (s), 1097
(s), 1025 (s), 803 (s), 739 (s) cmꢀ1. Anal. Calcd for C78H93NOS3: C, 80.99; H, 8.10; N, 1.21; O,
1.38; S, 8.32. Found: C, 81.13; H, 8.22; N, 1.30; S, 8.42.
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Synthesis
yl)benzo[b]benzo[4,5]thieno[2,3-d]thiophen-2-yl)-3-methylthiophene-2-carbaldehyde 18. In a 100
mL threeꢀnecked round bottom flask, under nitrogen atmosphere, 10ꢀ(7ꢀ
of
5-(7-(3,7-bis(9,9-dioctyl-9H-fluoren-2-yl)-10H-phenothiazin-10-
a
bromobenzo[b]benzo[4,5]thieno[2,3ꢀd]thiopheneꢀ2ꢀylꢀ3,7ꢀbis(9,9ꢀdioctylꢀ9Hꢀfluorenꢀ2ꢀyl)ꢀ10ꢀ
phenothiazine 15 (0.21 g, 0.16 mmol), 3ꢀmethylꢀ5ꢀ(tributylstannil)thiopheneꢀ2ꢀcarbaldehyde 2
(0.08 g, 0.19 mmol), PdCl2dppf ( 3 mg, 4 ꢀmol) and anhydrous toluene (20 mL) were added. The
resulting mixture was refluxed overnight. The reaction mixture was cooled at r.t., quenched with
saturated aq. NaHCO3 and extracted with chloroform. The organic layer was washed with 40% aq.
KF solution (2x10 mL), dried over Na2SO4 and the solvent removed under a reduced pressure. The
crude residue was purified by column chromatography using hexane/CH2Cl2 (1/1) as the eluent, to
yield the pure product 18 (0.19 g, 88% yield) as an orange solid. Mp 111ꢀ112 °C. Due to molecular
1
aggregations, 13C NMR spectrum cannot be recovered. H NMR (500 MHz, CDCl3): δ 10.06 (s,
1H), 8.26 (d, J = 1.2, 2H), 7.96 (d, J = 8.4, 2H), 7.85ꢀ7.50 (bs, 6H), 7.79 (dd, J = 8.4, 1.2, 2H), 7.50ꢀ
7.00 (bs, 15H), 2.64 (s, 3H), 2.05ꢀ1.87 (m, 8H), 1.25ꢀ0.95 (m, 40H), 0.80 (t, J = 7.2, 12H), 0.70ꢀ
0.58 (bs, 8H) ppm. FTꢀIR (KBr): ν 2921 (s), 2849 (s), 1652 (s), 1465 (s), 1457 (s), 1447 (s), 1310
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(m), 811 (s), 740 (s) cmꢀ1. Anal. Calcd for C90H99NOS4: C, 80.73; H, 7.45; N, 1.05; O, 1.19; S, 9.58.
Found: C, 80.81; H, 7.49; N, 1.10; S, 9.53.
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Synthesis
of
3-(5-(7-(4,5-bis(9,9-dioctyl-9H-fluoren-2-yl)thiophen-2-
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yl)benzo[b]benzo[4,5]thieno[2,3-d]thiophen-2-yl)-3-methylthiophen-2-yl)-2-cyanoacrylic acid 19.
In a 100 mL threeꢀnecked round bottom flask, under a nitrogen atmosphere, 5ꢀ(7ꢀ(4,5ꢀbis(9,9ꢀ
dioctylꢀ9Hꢀfluorenꢀ2ꢀyl)thiopheneꢀ2ꢀyl)benzo[b]benzo[4,5]thieno[2,3ꢀd]thiopheneꢀ2ꢀyl)ꢀ3ꢀ
methylthiopheneꢀ2ꢀcarbaldehyde 16 (0.15 g, 0.12 mmol), cyanoacetic acid (17 mg, 0.2 mmol),
piperidine ( 0.1 g, 1.2 mmol) and anhydrous CHCl3 (10 mL) and CH3CN (10 mL) were added and
the resulting mixture was refluxed overnight. The reaction mixture was cooled at r.t., quenched with
water and extracted with chloroform. The organic layer was dried over anhydrous Na2SO4 and the
solvent removed under a reduced pressure. The crude residue was washed with hexane, then
dissolved in chloroform and washed with 1N aq. HCl. The organic layer was dried over anhydrous
Na2SO4 and the solvent removed at a reduced pressure, to yield the pure product 19 (0.15 g, 94%
yield) as an orange solid. Mp 45ꢀ46 °C. Due to molecular aggregations, 13C NMR spectrum cannot
be recovered. 1H NMR (500 MHz, [CD3]2CO): δ 8.46 (d, J = 1.0, 1H), 8.40 (s, 1H), 8.37 (d, J = 1.0,
1H), 8.03ꢀ7.98 (m, 2H), 7.96 (d, J = 4.0, 1H), 7.92ꢀ7.85 (m, 2H), 7.77 (d, J = 4.0, 1H), 7.71ꢀ7.65
(m, 2H), 7.64 (d, J = 7.7, 1H), 7.60 (d, J = 7.7, 1H), 7.43ꢀ7.35 (m, 4H), 7.34 (d, J = 7.7, 1H), 7.32ꢀ
7.26 (m, 4H), 1.98ꢀ1.81 (m, 8H), 1.23ꢀ0.95 (bs, 40H), 0.86 (t, J = 6.6, 12H), 0.71ꢀ0.47 (bs, 8H)
ppm. FTꢀIR (KBr): ν 3434 (s), 2955 (s), 2918 (s), 2846 (s), 1715 (m), 1582 (m), 1427 (m), 1260 (s),
1093 (s), 1021 (s), 802 (s), 738 (m) cmꢀ1. Anal. Calcd for C85H95NO2S4: C, 79.08; H, 7.42; N, 1.09,
O, 2.48; S, 9.94. Found: C, 79.21; H, 7.56; N, 1.03; S, 9.83.
Synthesis
of
3-(5-(7-(bis(9,9-dioctyl-9H-fluoren-2-yl)amino)benzo[b]benzo[4,5]thieno[2,3-
d]thiophen-2-yl)-3-methylthiophen-2-yl)-2-cyanoacrylic acid 20. In a 100 mL threeꢀnecked round
bottom flask, under a nitrogen atmosphere, 5ꢀ(7ꢀbis(9,9ꢀdioctylꢀ9Hꢀfluorenꢀ2ꢀyl)ꢀ10ꢀphenothiazinꢀ
10ꢀyl)benzo[b]benzo[4,5]thieno[2,3ꢀd]thiophenꢀ2ꢀyl)ꢀ3ꢀmethylthiopheneꢀ2ꢀcarbaldehyde 17 (0.15
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g, 0.13 mmol), cyanoacetic acid (17 mg, 0.2 mmol), piperidine ( 0.13 mL, 1.3 mmol) and
anhydrous CHCl3 (10 mL) and CH3CN (10 mL) were added and the resulting mixture was refluxed
overnight. The reaction mixture was cooled at r.t., quenched with water and extracted with
chloroform. The organic layer was dried over anhydrous Na2SO4 and the solvent removed under a
reduced pressure. The crude residue was washed with hexane, then dissolved in chloroform and
washed with 1N aq. HCl. The organic layer was dried over anhydrous Na2SO4 and the solvent
removed at a reduced pressure, to yield the pure product 20 (0.155 g, 94% yield) as a red solid. Mp
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238ꢀ239 °C. H NMR (500 MHz, (CDCl3/DMSOꢀd6): δ 8.48 (s, 1H), 8.24 (s, 1H), 7.89 (d, J = 8.3,
1H), 7.83 (d, J = 8.7, 1H), 7.80 (dd, J = 8.3, 1.5, 1H), 7.74ꢀ7.62 (m, 5H), 7.59 (d, J = 2.1, 1H), 7.33
(d, J = 7.4, 2H), 7.31ꢀ7.19 (m, 5H), 7.17 (d, J = 1.9, 2H), 7.06 (dd, J = 8.2, 1.9, 1H), 2.44 (s, 3H),
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1.92ꢀ1.75 (b, 8H), 1.30ꢀ0.90 (bs, 40H), 0.77 (t, J = 7.0, 12H), 0.69ꢀ0.48 (bs, 8H) ppm. C NMR
(125 MHz, CDCl3): δ 152.2, 150.6, 146.7, 144.1, 140.8, 136.7, 126.8, 126.4, 123.5, 122.7, 120.5,
119.2, 55.0, 53.4, 40.3, 31.8, 30.9, 30.1, 29.7, 29.4, 29.3, 24.0, 22.6, 14.1 ppm. FTꢀIR (KBr): ν 3434
(s), 2952 (s), 2923 (s), 2851 (s), 1598 (s), 1450 (s), 1388 (s), 1322 (s), 1275 (m), 740 (s) cmꢀ1. Anal.
Calcd for C81H94N2O2S3: C, 79.49; H, 7.74; N, 2.29, O, 2.61; S, 7.86. Found: C, 79.40; H, 7.78; N,
2.33; S, 7.95.
Synthesis
of
3-(5-(7-(3,7-bis(9,9-dioctyl-9H-fluoren-2-yl)-10H-phenothiazin-10-
yl)benzo[b]benzo[4,5]thieno[2,3-d]thiophen-2-yl)-3-methylthiophen-2-yl)-2-cyanoacrylic acid 21.
In a 100 mL threeꢀnecked round bottom flask, under a nitrogen atmosphere, 5ꢀ(7ꢀ(3,7ꢀbis(9,9ꢀ
dioctylꢀ9Hꢀfluorenꢀ2ꢀyl)ꢀ10Hꢀphenothiazinꢀ10ꢀyl)benzo[b]benzo[4,5]thieno[2,3ꢀd]thiophenꢀ2ꢀyl)ꢀ
3ꢀmethylthiopheneꢀ2ꢀcarbaldehyde 18 (0.17 g, 0.13 mmol), cyanoacetic acid (17 mg, 0.2 mmol),
piperidine ( 0.13 mL, 1.3 mmol) and anhydrous CHCl3 (10 mL) and CH3CN (10 mL) were added
and the resulting mixture was refluxed overnight. The reaction mixture was cooled at r.t., quenched
with water and extracted with chloroform. The organic layer was dried over anhydrous Na2SO4 and
the solvent removed under a reduced pressure. The crude residue was washed with hexane, then
dissolved in chloroform and washed with 1N aq. HCl. The organic layer was dried over anhydrous
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