Synthesis and photovoltaic performance of dibenzofulvene-based organic sensitizers for DSSC

Article abstract of DOI:10.1016/j.tet.2016.08.006

Three novel 2D-π-A metal-free organic dyes TK 7–9 containing a dibenzofulvene (DBF) linked to two thiophene units as the π-bridge, diarylamines with and without alkoxy chains as donor groups and the cyanoacrylic acid moiety as the acceptor and anchoring group were synthesized. The new dyes TK were characterized by optical and electrochemical measurements and density functional theory calculations and were used as sensitizers in liquid dye-sensitized solar cells. The effects of alkoxy-functionalization of donor moiety and of hexyl chain insertion onto one thienyl ring of π-linker on dye properties and performances were investigated. The results discover the dye TK7, bearing two simple diphenylamine groups without alkoxy chains, exhibits the best behavior in terms of light absorption and cell performance (PCE of 7.9% and photovoltaic parameters of J_scof 17.82?mA?cm^?2, V_ocof 670?mV and FF of 0.66). Lower power conversion efficiencies of 6.3% and 6.1% were found for TK8 and TK9, respectively, as a consequence of the presence of the alkoxy chains.

Full text of DOI:10.1016/j.tet.2016.08.006

Accepted Manuscript
Synthesis and photovoltaic performance of dibenzofulvene-based organic sensitizers
for DSSC
A.L. Capodilupo, R. Giannuzzi, G.A. Corrente, L. de Marco, E. Fabiano, A. Cardone,
G. Gigli, G. Ciccarella
PII:
S0040-4020(16)30764-5
10.1016/j.tet.2016.08.006
TET 27987
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 10 May 2016
Revised Date: 11 July 2016
Accepted Date: 1 August 2016
Please cite this article as: Capodilupo AL, Giannuzzi R, Corrente GA, de Marco L, Fabiano E, Cardone
A, Gigli G, Ciccarella G, Synthesis and photovoltaic performance of dibenzofulvene-based organic
sensitizers for DSSC, Tetrahedron (2016), doi: 10.1016/j.tet.2016.08.006.
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ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Synthesis and photovoltaic performance of dibenzofulvene-based
organic sensitizers for DSSC
A. L. Capodilupo,a* R. Giannuzzi,b G. A. Corrente,a,b,c L. De Marco,a,b E. Fabiano,b,d A.
Cardone,e G. Giglia,f and G. Ciccarella.a,g*
a CNR NANOTEC - Institute of Nanotechnology c/o Campus Ecotekne, University of Salento, Via
Monteroni - 73100 Lecce. Italy.
b
Center for Biomolecular Nanotechnologies (CBN) Fondazione Istituto Italiano di Tecnologia
(IIT), Via Barsanti 1, Arnesano, 73010, Italy.
c
Dipartimento di Ingegneria dell'Innovazione, Università del Salento, Via Monteroni, 73100,
Lecce, Italy.
d
Istituto Nanoscienze–CNR, Euromediterranean Center for Nanomaterial Modelling and
Technology (ECMT), Via per Arnesano, 73100 Lecce, Italy.
e Istituto di Chimica dei Composti OrganoMetallici (ICCOM) – Consiglio Nazionale delle Ricerche
CNR, via Orabona, 4 – 720125 Bari, Italy.
f
Dipartimento di Matematica e Fisica”Ennio De Giorgi”, Università del Salento, via Monteroni,
73100, Lecce, Italy.
g Dipartimento di Scienze e Tecnologie Biologiche e Ambientali Universita' del Salento c/o Edificio
"La Stecca" via Monteroni, 73100 Lecce, Italy.
Corresponding author at CNR NANOTEC - Institute of Nanotechnology c/o Campus Ecotekne,
University
of
Salento,
Via
Monteroni
-
73100
Lecce,
Italy.
E-mail:
agostina.capodilupo@nanotec.cnr.it.
Corresponding author at Dipartimento di Scienze e Tecnologie Biologiche e Ambientali, Università
del Salento, Via Monteroni, 73100, Lecce, Italy. E-mail: giuseppe.ciccarella@nanotec.cnr.it
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ABSTRACT
Three novel 2D–π–A metal-free organic dyes TK 7–9 containing a dibenzofulvene (DBF) linked to
two thiophene units as the π-bridge, diarylamines with and without alkoxy chains as donor groups
and the cyanoacrylic acid moiety as the acceptor and anchoring group were synthesized. The new
dyes TK were characterized by optical and electrochemical measurements and density functional
theory calculations and were used as sensitizers in liquid dye-sensitized solar cells. The effects of
alkoxy-functionalization of donor moiety and of hexyl chain insertion onto one thienyl ring of π-
linker on dye properties and performances were investigated. The results discover the dye TK7,
bearing two simple diphenylamine groups without alkoxy chains, exhibits the best behavior in
terms of light absorption and cell performance (PCE of 7.9% and photovoltaic parameters of Jsc of
17.82 mA cm−2, Voc of 670 mV and FF of 0.66). Lower power conversion efficiencies of 6.3% and
6.1% were found for TK8 and TK9, respectively, as a consequence of the presence of the alkoxy
chains.
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Keywords:
Dye-sensitized solar cells
Organic dyes
Dibenzofulvene
Donor-acceptor system
Solar energy
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INTRODUCTION
In recent years, enormous attention has been paid to the research into dye-sensitized solar cells
(DSSCs).1,2 As known, the sensitizer is one of the key components of DSSCs and plays a pivotal
role in achieving higher power conversion efficiency, and plays a critical function in light
harvesting and electron injection. To date, DSSCs incorporating ruthenium based sensitizers and
zinc–porphyrin based co-sensitizers have reached high efficiency of over 11%3,4 and 12%,5,6
respectively. From a practical viewpoint, the tedious synthetic procedures, low yield of porphyrin
sensitizers and expensive ruthenium complexes represent drawbacks severely limiting for
commercial purposes. Conversely, metal-free organic dyes promise modest fabrication costs and
great flexibility in molecular tailoring and preparation.3,7,8 Moreover, metal free organic dyes show
higher molar extinction coefficients than metal complexes, and this feature leads to a much stronger
light-harvesting ability. During the past decade, a huge number of metal-free sensitizers that exceed
10% have been synthesized and evaluated in DSSC and PCE have reported.9,10 Most of the metal-
free sensitizers possess a D–π–A11-13 structure, in which D is the electron-donating moiety, π the
conjugated spacer and A the electron acceptor moiety. This push-pull structure can induce the
intramolecular charge transfer (ICT) from D to A, through the π bridge when the dye absorbs light.
This is important for light harvesting, as well as for the control of electrochemical properties. For
donors, dialkylaminophenyl groups,14-16 coumarins,17 triphenylamines,18-20 indoline,21,22
phenothiazine,23-26 carbazole,27-29 have been successfully used. The cyanoacrylic acid, as the
acceptor group, largely fulfills the need of an electron acceptor while providing the carboxylic acid
group to bind the semiconductor nanocrystalline surface. In the literature, there is a great library of
π-bridge building blocks used as a spacer between the donor and the acceptor group.30,31 Due to
their unique properties, such as coplanarity, highly ordered π-stacked structures and high charge
density, fluorene derivatives, as well as fluorenone and dibenzofulvene-based compounds, have
been widely used as π-conjugated systems to realize advanced functional materials for opto-
electronic devices, such as OFET,32,33 OLED34,35 and dye-sensitized solar cells.24,36-40
In this work, we have designed and synthesized three new metal-free organic dyes with 2D-π-A
structure (Fig. 1), labelled as TK7, TK8 and TK9. These new dyes consist of the cyanoacrylic acid
as the acceptor/anchoring group, a dibenzofulvene core linked to two thienyl rings as the π-bridge,
and the diphenylamine (TK7), bis(4-methoxyphenyl)amine (TK8) and bis(4-octyloxyphenyl)amine
(TK9) as donor moiety. The choice of the branched 2D-π-A structure was to achieve characteristics
of high electron-donating ability, reduced dyes-aggregation and charge recombination, with the aim
to gain enhanced photovoltaic performance. The functionalization of one of the two thienyl rings of
the π-linker with a hexyl chain was used as further strategy to reduce dyes-aggregation. The
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computational study was performed to investigate the basic electronic properties of the synthesized
dyes in order to compare them to the available experimental results. The dyes have been used as
sensitizers in liquid DSSC cells, studying the correlation between molecular structure and device
performance. A maximum efficiency of 7.9% has been recorded with the TK7 dye.
Fig.1 Structures of sensitizers TK7, TK8 and TK9
Results and discussion
Synthesis of materials
The synthetic routes to TK7-TK9 are detailed in Scheme 1. Compound 2 was synthesized by
reduction of compound 1 with aluminum chloride and borane tert-butylamine complex.41
Compound 3 was prepared by an ultrasound-assisted reaction starting from compound 2 and 5'-(5,5-
dimethyl-1,3-dioxan-2-yl)-3'-hexyl-2,2'-bithiophene-5-carbaldehyde 4’. The condensation reaction
was carried out in a very short time and in good yields, and the pure product was recovered by
simply precipitation and filtration. Compound 1’ was obtained by a formylation reaction following
the literature procedure,42 then it was reacted with 2,2-dimethylpropane-1,3-diol in dry toluene, in
the presence of p-toluensulfonic acid as the catalyst to give compound 2’ in good yield. Compound
3’ was obtained by the Stille reaction treating compound 2’ with tributyl(thiophen-2-yl)stannane,
using Pd2(dba)3 (dba = dibenzylideneacetone) and AsPh3 as the catalytic system. The resulting
product 3’ was underwent a formylation reaction with n-BuLi and N-formylpiperidine, at -78°C in
anhydrous THF, giving the compound 4’. Compounds 4a, 4b and 4c were obtained by reacting
21
compound 3 with 2.2 equivalents of diarylamine, in the presence of Pd(dba)2 and P(t-Bu)3, by a
Buchwald-Hartwig cross-coupling reaction (C-N amination) in a microwave reactor. Finally, TK7,
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TK8 and TK9 dyes were prepared via a Knoevenagel condensation, reacting cyanoacetic acid with
compunds 4a, 4b and 4c, respectively, in the presence of ammonium acetate, in acetic acid.
Scheme 1. Synthesis of organic dyes TK7, TK8 and TK9
Optical and electrochemical properties.
Absorption spectra of dyes TK7-9 recorded in dichloromethane are displayed in Fig. 2, and the
related data are listed in Table 1. Two distinctive bands can be observed for the dyes. The band at
longer wavelength, in the region 360−600 nm is mainly ascribed to the charge transfer (CT) from
diarylamine donor to cyanoacryclic acid acceptor. The second band, in the region 270−350 nm, is
originating from the fluorene and thiophene units, and can be attributed to π−π* transitions.43 TK7
shows two maxima absorption peaked at 304 and 422 nm, with molar extinction coefficients ε =
49000 and 33900 M-1cm-1, respectively. The sensitizers TK8 and TK9, having the bis(4-
methoxyphenyl)amine and bis(4-octyloxyphenyl)amine as donor groups, respectively, show a
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decrease of the absorption capability. In particular, TK8 shows two maxima absorption peaked at
293 nm (ε = 42500 M-1cm-1) and 416 nm (ε = 30600 M-1cm-1) while TK9 shows two maxima
absorption peaked at 270 nm (ε = 45180 M-1cm-1) and 428 nm (ε = 17500 M-1cm-1).
Fig.2 Absorption spectra of TK7, TK8 and TK9 in CH2Cl2.
Cyclic voltammetry (CV) was carried out to evaluate the electrochemical properties of the dyes.
The cyclic voltammograms are shown in Figure 3, and the relevant electrochemical data are
reported in Table 1. The estimated ground state oxidation potential versus normal hydrogen
electrode (vs NHE) corresponds to the highest occupied molecular orbital (HOMO) level of the
sensitizer. The HOMO levels of TK7-9 (Table 1) were estimated to be 0.98, 0.94, 0.93 V,
−
respectively, more positive than the redox potential of I−/I3 (0.4 V vs NHE),44 indicating that the
oxidized dyes can be effectively regenerated. The band energy gaps (E0−0) of TK7-9, were
estimated from the onset wavelength of their absorption spectra, and found to be 2.02, 1.98, and
2.00 eV, respectively. The lowest unoccupied molecular orbital (LUMO) levels of dyes were
calculated as the difference HOMO− ꢀꢁꢂꢁ and were found to be −1.04, −1.04, and −1.07 V (vs
NHE), respectively. As a result, the LUMO values are sufficiently more negative than the
conduction band edge of TiO2 (-0.5 vs NHE),45 to forecast efficient electron injection from excited
dye to the TiO2 surface.
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Fig.3 Cyclic voltammograms of TK7, TK8 and TK9.
Table 1. Absorption data, oxidation potentials, HOMO and LUMO levels, optical energy gaps
Dye
λamax (nm)(ε*103/
M-1cm-1)a (nm)
422 (33.9)
HOMO (V)b
(vs. NHE)
0.98
LUMO (V)c
(vs. NHE)
-1.04
E0-0 (eV)d
2.02
1.98
2.00
TK7
TK8
TK9
416 (30.6)
428 (17.5)
0.94
0.93
-1.04
-1.07
aAbsorption maximum in dichloromethane (~10-5 M) solution. bHOMO of dyes by cyclic voltammetry in 0.1
M TBAPF6 in CH2Cl2 solutions as supporting electrolyte, Ag/AgCl as the reference electrode, and Pt as
c
counter electrode, and calibrated against ferrocene. Scanning rate: 100 mV s−1. LUMO was calculated by
HOMO − E0−0. dE0−0 was estimated from the onset of the absorption spectrum
Theoretical approach.
In Table 2 we report the computed optical properties of the lowest lying optically active excited
states of the dyes.
Table 2 Excitation energies and absorption spectra
Dye
Excitat
ion
S1
Energ
y (eV)
2.75
Single-particle
transition
H→L (86%)
Λ
ꢀr (Å)
µz (D)
0.64
0.65
10.94
9.15
TK7
S3
3.81
H-2→L (82%)
1.81
S4
S1
S2
S3
3.87
2.58
2.95
3.58
H→L+1 (87%)
H→L (84%)
H-1→L (78%)
H-2→L (80%)
0.72
0.59
0.31
0.67
6.50
12.72
16.48
8.53
TK8
TK9
3.31
S4
S1
S2
S3
3.71
2.67
3.03
3.64
H→L+1 (86%)
H→L (83%)
H-1→L (79%)
H-2→L (80%)
0.70
0.56
0.28
0.63
8.45
6.53
16.55
9.51
3.21
S4
3.81
H→L+1 (86%)
0.65
9.27
TD-DFT excitation energies (eV), oscillator strengths, main single-particle transitions,
overlap indicator Λ, electron displacement indicator ꢀr for the lowest-lying singlet
excitations, and the component of the molecular dipole moment for the neutral dye
perpendicular to the TiO2 surface (µz, D), of TK7, TK8, and TK9.
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The excitation energies are in good agreement with the experimental spectra and allow the
identification of several singlet excitations underlying the broad absorption bands observed
experimentally. Nevertheless, in all dyes, the lowest-energy absorption peak is mainly characterized
by an excitation described by a single-particle transition from the highest occupied molecular
orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) and having a remarkable
charge-transfer character. This later feature can be recognized by inspecting the values of the
indicators Λ and ꢀr as well as looking at the shape of the relevant molecular orbitals (see Fig. 4).
Fig. 4. Isodensity plots of the most relevant frontier orbitals of TK7, TK8 and TK9.
A comparison of the results of TK7 with TK8 and TK9, shows that the presence of the alkoxy
chains in the latter enhances the charge-transfer character, also causing a slight reduction of the
excitation energy. On the other hand, the presence of a long alkyl chain in TK9 appears to have a
negligible effect on the charge-transfer character of the transition, while it seems to interfere with
the electron donating effect of the whole alkoxy group, so that the lowest singlet excitation of TK9
displays a slightly higher energy than the one of TK8. Moreover the alkoxy groups make a
contribution to the molecular dipole moments (Table 2): TK8 and TK9 show larger dipole values
aligned parallel (µz) to the carboxylate anchoring group with respect to the TK7 dye; this could
induce a band-shift (upwards) when adsorbed on the surface, thus hindering charge injection to
some extent.
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Photovoltaic devices.
Since favorable characteristics emerged from the characterization of TK7-9 dyes, concerning in
particular light harvesting capability and suitable HOMO and LUMO levels, their photovoltaic
potentialities were tested in liquid electrolyte DSSCs devices, investigating the resulting
performances by electrochemical impedance spectroscopy (EIS). The performance of solar cells
containing TK7, TK8 and TK9 and detailed photovoltaic parameters (short-circuit photocurrent
density JSC, open-circuit voltage VOC, fill factor FF and power conversion efficiency η) are reported
in Table 3.
Table 3. Photovoltaic performance of TK7, TK8 and TK9
Dye
ƞ%
FF
Voc
Jsc
Dye loading
(10-7mol/cm2)
(V)
(mA/cm2)
0.66
0.67
0.67
0.67
17.82
2.3
2.1
1.7
TK7 7.88
TK8 6.35
TK9 6.14
0.66
0.68
14.33
13.48
The higher efficiency was obtained for TK7, with a value of 7.88% and cell parameters Jsc of 17.82
mA/cm2, Voc of 0.67 and FF of 0.66. An efficiency of 6.35% was found for TK8 with cell
parameters Jsc of 14.33 mA/cm2, Voc of 0.66 and FF of 0.67, while an efficiency of 6.14% was
found for TK9 with cell parameters Jsc of 13.48 mA/cm2, Voc of 0.68 and FF of 0.67. J-V curves
of TK7-9 are reported in Fig. 5. The higher photoconversion efficiency of TK7-based device is
driven by its higher photocurrent density that is related to the molar extinction coefficients of the
sensitizers. Actually, we can observe how TK7, TK8 and TK9 dyes, having ε of 33900, 30600 and
17500 M-1cm-1, respectively, show the same trend in the Jsc values.
Further information emerges from the analysis of the monochromatic incident photon-to-current
conversion efficiencies (IPCEs) recorded for the DSSCs. Notwithstanding the competitive
absorption of FTO-glass, TiO2 and electrolyte, the IPCE spectra (Fig 6) seem to be in agreement
with the light- harvesting range of sensitizers, although the presence of large TiO2 scattering
nanoparticles in the photoanode broaden their shape. The IPCE spectra of TK7 showed a plateau at
~80% between 400 nm and 550 nm, considerably wider with respect to the spectrum observed for
TK8 and higher with respect to the response obtained for the TK9-based device. Therefore, the
IPCE spectra resulted in good accordance with the optical properties of the sensitizers and
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explained the photocurrent behavior. Furthermore, the role of the hexyl chain inserted on one of two
thienyl rings of the π-linker system could be elicited by comparing the results of the present work
with those of our previous works.36,37 In fact, the sensitizers presented here reach their better
photovoltaic performance with a lower amount of CDCA co-adsorber with respect to the dyes of
our previous works; as an example, we can observed that the best performing dye, TK7, yields
7.88% efficiency with 5mM CDCA while its hexyl-free analogous, TK3,36 achieves 7.45%
efficiency using 10 mM CDCA.
Fig. 5. J-V curves of DSSCs based on dyes TK7, TK8 and TK9
Fig. 6. IPCE spectra of DSSCs based on dyes TK7, TK8 and TK9
Electrochemical Impedance Spectroscopy Studies.
To further understand the relationship between the molecular structure and the photovoltaic
performance, we studied the charge-transfer resistance at the TiO2/dye/electrolyte interface by
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electrochemical impedance spectroscopy (EIS), carried out at different voltage bias under 1 sun
illumination. EIS spectra were analyzed through the well-known equivalent circuit proposed by
Bisquert.46 Figures 7a) e 7b) show the measured capacitance and recombination resistance plotted
versus potential drop at the sensitized electrode. Vcorr is obtained after correcting the applied
potential (Vapp) for the drop of the total series resistance Vseries (contacts, counter electrode,
47
electrolyte diffusion) collected from impedance spectroscopy data by Vcorr = Vapp - Vseries
.
The
chemical capacitance, Cꢁ, provides quantitative information about the position of the conduction
band.48
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Fig. 7. Impedance results of the DSSCs based on dyes TK7, TK8 and TK9. a) Measured
capacitance vs corrected voltage b) Charge transfer resistance vs corrected voltage c) Charge
transfer resistance represented at the equivalent CB position.
Fig. 7a shows that the chemical capacitance values are clearly shifted towards lower potentials for
TK7 dye. Assuming that neither the distribution nor the total amount of trap states changed with
dye, we may attribute the shift observed in Cµ to a displacement in the energy of the conduction
band (CB).49 The downward shift of the TiO2 CB impacts on the photovoltaic performance of the
solar cells, in particular by increasing Jsc values, thanks to a higher electron injection driving force
(see LUMO level Table 1). An additional enhancement of the photovoltaic performance could come
from the reduction of recombination between the injected electrons and the oxidized form of redox
couples. However, all the dyes show comparable values of charge transfer resistance (Fig. 7b). To
better understand the recombination resistance behaviour, the RCT was determined on the basis of a
similar number of injected electrons (i.e. at the same energy gap between the electron Fermi level
and TiO2 conduction band). The difference in charge-transfer resistance becomes more marked if
the RCT of the three devices is plotted against the voltage drop in a common equivalent conduction
band Vecb50 (Fig. 7c). In this plot, the effect of different TiO2 CB between samples is removed. This
allows an analysis of the recombination resistance on the base of an equal density of electrons n (i.e.
the same distance between the electron Fermi level and the TiO2 CB). Inspection of Fig. 7c
confirms that TK7-based devices show the highest RCT values, indicating a better suppression of
charge recombination effects. This could be related to a more favorable packing of the sensitizers at
the TiO2 surface, suggesting that the chemical structure of TK7 ensures a compact coverage of the
inorganic semiconductor, thereby lowering the probability of recombination between injected
–
electrons and I3 and other acceptor species.
Conclusions
In conclusion, we have successfully designed and synthesized three new highly efficient starburst
organic sensitizers with 2D-π-A structure (TK7, TK8 and TK9). They have the same conjugated
backbone and acceptor units and different electron donor groups. The influence of the
functionalization of the donor groups on optical, electrochemical and photovoltaic properties of
dyes was fully investigated. It was found that the dye TK7 having the simply diphenylamine group
as the electron-donor unit performed the better photovoltaic efficiencies, compared with TK8 and
TK9. The presence of alkoxy chains on the donor unit D in TK8 and TK9 induces a decreasing in
the photovoltaic performances. This suggests that the introduction of substituents in such a
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branched dye structure, although space the molecules avoiding undesirable dye-aggregation, could
lead to a less-uniform coverage of the TiO2 surface. Moreover, the presence of the hexyl chain on
one thienyl ring of π-linker plays a significant role in reducing the dye-aggregation These findings
provide more insight into structure-property relationships for organic dye, useful in addressing the
design and synthesis of new efficient structures.
EXPERIMENTAL SECTION
Materials and instrumentation.
The solvents were freshly distilled prior to use, according to standard procedures. Commercial
reagents were used as received. The microwave-assisted syntheses were performed with a CEM
Discover Labmate reactor. FT-IR spectra were measured on a Perkin-Elmer 1710
spectrophotometer using dry KBr pellets. The melting point was taken on Kleinfeld Melting Point
1
Determination Apparatus APA I. H and 13C NMR spectra were recorded on a Bruker 400 MHz
spectrometer. LC-MS spectra were acquired with an Agilent 6300 Series Ion Trap interfaced to an
Agilent 1200 HPLC, in the following general conditions: atmospheric pressure chemical ionization,
positive ions, eluent chloroform, flow rate 0.200 mL min-1, drying gas flow 5.0 L min-1, nebulizer
pressure 60 psi, drying gas temperature 350 °C, vaporizer temperature 325 °C, mass range 100–
2200 m/z. UV-Vis absorption spectra were recorded on a Varian-Cary 500 spectrophotometer.
Elemental analyses were done by a Carlo Erba CHNS-O EA1108-Elemental Analyzer.
Electrochemical characterization of dyes was carried out by cyclic voltammetry (CV) using a
AutoLab potentiostat (Methrom). A typical three-electrode cell was assembled with a glassy carbon
disk-working electrode, a Pt-wire auxiliary electrode, and an Ag/AgCl non-aqueous reference
electrode. Cyclic voltammograms were acquired at 0.1 V s-1 scan rate on 1mM dye solutions
prepared in the electrolyte solution, which consisted of 0.1M tetrabutylammonium
hexafluorophosphate (TBAPF6) in dichloromethane (CH2Cl2). All the solutions were previously
degassed with N2 and kept under a N2 atmosphere. Ferrocene was added as an internal reference for
calibration of the potential scale versus Fc+/Fc couple. Potentials referred to ferrocene were then
converted to Normal Hydrogen Electrode (NHE) by addition of 0.63 V.
Computational details.
All calculations were carried out with the TURBOMOLE51 program package using the COSMO
solvation model.52,53 Ground-state calculations and geometry optimizations were performed using
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the BLOC functional.54,55 Time-dependent calculations were carried out with the BHLYP
functional.56 In all calculations, a def2-TZVP basis set57 was employed. To quantify the charge
transfer character of each excited state two indicators were considered: the overlap indicator λ,58
which is computed as the spatial overlap between the occupied and unoccupied orbitals involved in
the excitation; the electron displacement indicator Δr,59 which measures the distance between the
ground-state and the excited-state charge distributions. We recall that small values of Λ (i.e. a
small overlap between the occupied and unoccupied orbitals) indicate a greater charge-transfer
character (when Λ = 0 an electron is completely transferred). In contrast, larger Δr values indicate
a more pronounced charge-transfer character. To study the intermolecular interactions in the dyes'
dimers we performed calculations suing the APBE-D3 functional60,61 with a def2-TZVP basis set62
and the resolution of identity approximation. 63-65
Fabrication of DSSC devices and photovoltaic measurements.
Fluorine-doped tin oxide (FTO, 15 ꢂ/sq, provided by Solaronix S.A.) glass plates were first cleaned
in a detergent solution using an ultrasonic bath for 15 min, and then rinsed with water and ethanol.
Double-layer electrodes (overall thickness 20 ꢁm) were prepared as follows: two layers of
commercial colloidal titania paste (Dyesol 18NR-T) were deposited onto the FTO glass and
gradually heated in air to obtain a ~15 ꢁm transparent nano-crystalline film. The temperature
gradient was programmed as follows: 170°C (40 min), 350°C (15 min) and 430°C (30 min). This
procedure was repeated for the scattering layer (5 µm), prepared by a Solaronix D/SP colloidal
paste. The double-layer electrode was sintered at 450°C for 30 min. The thickness of the sintered
photo-anodes were measured using a profilometer (Veeco Dektak 150 Surface Profiler). The dye
loading was performed by keeping the electrodes for 14 h and under the dark in 0.2 mM THF
solutions of TK7, TK8 and TK9 dyes, containing 5 mM of chenodeoxycholic acid (CDCA). The
counter-electrodes were prepared by sputtering a 50 nm Pt layer on a hole-drilled cleaned FTO
plate. In a typical device construction procedure, the photo-anode and the counter-electrode were
faced and assembled using a suitably cut 60 µm thick Surlyn® hot-melt gasket for sealing. The
redox electrolyte (0.1 M LiI, 0.03 M I2, 0.6 M 1-methyl-3-propylimidazolium iodide, and 0.5 M
tert-butylpyridine in dry acetonitrile) was injected into the vacuum spaces between the electrodes
through pre-drilled holes on the back of the counter electrode. The holes were sealed using Surlyn®
hot melt film and a cover glass. Photocurrent-voltage measurements were performed using a
Keithley unit (Model 2400 Source Meter). A Newport AM 1.5 Solar Simulator (Model 91160A
equipped with a 1000 W xenon arc lamp) serving as a light source. The light intensity (or radiant
power) was calibrated to 100 mW cm–2 using as reference a Si solar cell. The incident photon-to-
15

ACCEPTED MANUSCRIPT
current conversion efficiency (IPCE) was measured by the DC method, using a computer-controlled
xenon arc lamp (Newport, 140 W, 67005) coupled with a monochromator (Newport Cornerstore
260 Oriel 74125). The light intensity was measured by a calibrated silicon UV-photodetector (Oriel
71675), and the short circuit currents of DSSCs were measured by using a dual channel optical
power/energy meter, (Newport 2936-C). The surface concentrations (dye loading) of the dyes were
assessed by spectrophotometric determination as follows: double layered photoanodes (15 + 5 ꢁm,
1 cm2) were sensitized with the same solutions used for devices; then the dyes were completely
desorbed from the TiO2 surface by immersing the substrates in a 0.05 M tetrabutylammonium
hydroxide in THF solution. The evaluation of the dye concentration in the solvent, obtained by UV-
Vis measurements, allowed us to estimate the amount of the adsorbed molecules, expressed in terms
of moles of dye anchored per unit area of the photoelectrode. Electrochemical impedance
spectroscopy (EIS) was per-formed by an AUTOLAB PGSTAT 302N (Eco Chemie B.V.) in a
frequency range between 100 kHz and 10 mHz. The impedance measurements were carried out at
different voltage biases, under 1.0 sun illumination. The resulting impedance spectra were fitted by
using ZView (Scribner Associates) software.
Synthesis.
3,6-Dibromo-9H-fluoren-9-one, 1. Was synthesized following the literature procedure.66
3,6-dibromo-9H-fluorene, 2. Was synthesized following the literature procedure.37
2-(5’-((3,6-Dibromo-9H-fluoren-9-ylidene)methyl)-3-hexyl-[2,2’-bithiophen]-5-yl)-5,5-
dimethyl-1,3-dioxane, 3.
Potassium tert-butoxide (0.039 g, 0.35 mmol), compound 2 (0.056 g, 0.17 mmol) and 5'-(5,5-
dimethyl-1,3-dioxan-2-yl)-3'-hexyl-[2,2'-bithiophene]-5-carbaldehyde (3’) (0.068 g, 0.17 mmol)
were dissolved in absolute ethanol (5 mL). The reaction mixture was heated in an ultrasonic bath
for 30 min, and then the resulting precipitate was filtered off at room temperature. The pure product
was obtained as a yellow solid (80% yield). Mp: 160-162. IR (KBr, cm-1): 3431, 2953, 2920,
2848,1706, 1607, 1589, 1464, 1418, 1386, 1320, 1307, 1262, 1162, 1087, 1020, 862, 814. 1H-NMR
(400 MHz, CDCl3) δ 8.22 (d, J = 8.4 Hz, 1H), 7.82 (dd, J1 = 1.8 Hz, J2 = 1.7 Hz, 2H), 7.60 (d, J =
8.2 Hz, 2H), 7.45 (dd, J1 = 1.8 Hz, J2 = 1.8 Hz, 1H), 7.40-7.37 (m, 2H), 7.15 (d, J = 3.4 Hz, 1H),
7.01 (s, 1H), 5.61 (s, 1H), 3.79 (d, J = 11.2 Hz, 2H), 3.66 (d, J = 10.7 Hz, 2H), 2.77 (t, J = 7.8 Hz,
2H), 1.70-1.62 (m, 2H), 1.43-1.36 (m, 2H), 1.32-1.29 (m, 7H), 0.88 (t, J = 6.9 Hz, 3H), 0.82 (s,
13
3H). C-NMR (100 MHz, CDCl3) δ 141.5, 139.8, 139.3, 138.9, 138.6, 138.0, 134.7, 131.0, 130.2,
130.1, 128.0, 126.1, 125.5, 124.0, 123.1, 122.9, 122.6, 121.9, 121.3, 120.1, 97.9, 77.4, 31.5, 30.4,
16

ACCEPTED MANUSCRIPT
29.5, 29.1, 22.8, 22.4, 21.7, 13.9. MS (APCI): calcd for C34H34Br2O2S2, 698.03; found: m/z =
699.03 [M+H]+. Anal. Calcd for C34H34Br2O2S2: C, 58.46; H, 4.91; S, 9.18. Found: C, 58.49; H,
4.90; S, 9.15.
9-((5’-(5,5-Dimethyl-1,3-dioxan-2-yl)-3’-hexyl-[2,2’-bithiophen]-5-yl)methylene)-
N3,N3,N6,N6-tetraphenyl-9H-fluorene-3,6-diamine, 4a.
Compound 3 (0.100 g, 0.14 mmol), diphenylamine (0.059 g, 0.35 mmol) and sodium tert-butoxide
(0.033 g, 0.35 mmol) were added to a suspension of Pd(dba)2 (0.004 g, 0.007 mmol) and P(t-Bu)3
(0.029 mL, 0.029 mmol, 1M in toluene) in anhydrous and deoxygenated toluene (5 mL), previously
stirred under argon for 10 min. The resulting mixture was heated under a microwave irradiation at a
constant temperature of 110°C for 50 min. The solvent was removed under a reduced pressure, and
the residue was purified by column chromatography (silica gel, 50:50 hexane:CH2Cl2), to yield the
pure product 4a as an orange solid (67% yield). Mp: 164-166. IR (KBr, cm-1): 3446, 3033, 2951,
2919, 2848, 1659, 1590, 1489, 1387, 1271, 1244, 1153, 1094, 1025, 750, 694. 1H-NMR (400 MHz,
CDCl3) δ 8.18 (d, J = 8.5 Hz, 1H), 7.61(d, J = 8.4 Hz, 1H), 7.37 (s, 1H), 7.35 (dd, J1 = 3.7 Hz, J2 =
1.0 Hz, 1 H), 7.32-7.31 (m, 2H), 7.26-7.22 (m, 8H), 7.11-7.09 (m, 9H), 7.04-6.98 (m, 6H), 6.88 (dd,
J1 = 8.5 Hz, J2 = 2.2 Hz, 1H), 5.59 (s, 1H), 3.77 (d, J = 11.2 Hz, 2H), 3.65 (d, J = 10.7 Hz, 2H),
2.76-2.72 (m, 2H), 1.67-1.60 (m, 2H), 1.40-1.33 (m, 2H), 1.29-1.27 (m, 7H), 0.87-0.84 (m, 3H),
0.81 (s, 3H). 13C-NMR (100 MHz, CDCl3) δ 148.2, 147.9, 147.6, 147.4, 141.9, 139.5, 139.3, 139.2,
137.6, 135.3, 134.8, 130.9, 130.6, 129.7, 129.1, 129.0, 127.8, 126.0, 124.2, 123.9, 123.7, 122.8,
122.6, 122.4, 120.8, 115.8, 115.7, 115.0, 98.0, 77.4, 77.0, 31.5, 30.4, 30.0, 29.4, 29.1, 22.8, 22.4,
21.7, 13.9. MS (APCI): calcd for C58H54N2O2S2, 874.36; found: m/z = 875.40 [M+H]+. Anal. Calcd
for C58H54N2O2S2: C, 79.60; H, 6.22; N, 3.20; S, 7.33. Found: C, 79.62; H, 6.21; N, 3.22; S, 7.36.
9-((5'-(5,5-Dimethyl-1,3-dioxan-2-yl)-3'-hexyl-[2,2'-bithiophen]-5-yl)methylene)-N3,N3,N6,N6-
tetrakis(4-methoxyphenyl)-9H-fluorene-3,6-diamine, 4b.
Compound 3 (0.100 g, 0.14 mmol), bis(4-methoxyphenyl)amine (0.079 g, 0.35 mmol) and sodium
tert-butoxide (0.033 g, 0.35 mmol) were added to a suspension of Pd(dba)2 (0.004 g, 0.007 mmol)
and P(t-Bu)3 (0.029 mL, 0.029 mmol, 1M in toluene) in anhydrous and deoxygenated toluene (5
mL), previously stirred under argon for 10 min. The solvent was removed under a reduced pressure,
and the residue was purified by column chromatography (silica gel, 50:50 hexane:CH2Cl2) to yield
the pure product 4b as an orange solid (61% yield). Mp: 149-151. IR (KBr, cm-1): 3430, 2919,
1
2848, 1734, 1600, 1505, 1451, 1387, 1272, 1239, 1178, 1092, 1033, 825. H-NMR (400 MHz,
CDCl3) δ 8.09 (d, J = 8.6 Hz, 1H), 7.52 (d, J = 8.4 Hz, 1H), 7.30 (d, J = 3.7 Hz, 1H), 7.26 (s, 1H),
17

ACCEPTED MANUSCRIPT
7.17 (t, J = 1.6 Hz, 2H), 7.07-7.02 (m, 9H), 6.91 (s, 1H), 6.85 (dd, J1 = 8.3 Hz, J2 = 2.1, 1H), 6.83-
6.78 (m, 8H), 6.73 (dd, J1 = 8.6, J2 = 2.2, 1H), 5.59 (s, 1H), 3.80 (d, J = 2.2 Hz, 12H), 3.77-3.76 (m,
2H), 3.65 (d, J =11.1 Hz, 2H), 2.76-2.72 (m, 2H), 1.67-1.59 (m, 4H), 1.29-1.27 (m, 7H), 0.89-0.84
(m, 3H), 0.81 (s, 3H). 13C-NMR (100 MHz, CDCl3) δ 149.1, 148.8, 142.0, 141.2, 140.7, 139.8,
139.5, 139.1, 137.0, 135.1, 133.8, 130.7, 129.4, 129.2, 127.8, 126.1, 125.9, 125.6, 124.9, 123.0,
121.2, 120.6, 119.7, 114.5, 114.4, 114.0, 113.1, 112.1, 98.0, 55.3, 31.5, 30.0, 29.4, 29.1, 22.8, 22.4,
21.7, 13.9. MS (APCI): calcd for C62H62N2O6S2, 994.40; found: m/z = 995.40 [M+H]+. Anal. Calcd
for C62H62N2O6S2: C, 74.82; H, 6.28; N, 2.81; S, 6.44. Found: C, 74.83; H, 6.30; N, 2.80; S, 6.45
9-((5'-(5,5-Dimethyl-1,3-dioxan-2-yl)-3'-hexyl-[2,2'-bithiophen]-5-yl)methylene)-
N3,N3,N6,N6-tetrakis(4-(octyloxy)phenyl)-9H-fluorene-3,6-diamine, 4c.
Compound 3 (0.100 g, 0.14 mmol), compound 5’ (0.149 g, 0.35 mmol) and sodium tert-butoxide
(0.033 g, 0.35 mmol) ) were added to a suspension of Pd(dba)2 (0.004 g, 0.007 mmol) and P(t-Bu)3
(0.029 mL, 0.029 mmol, 1M in toluene) in anhydrous and deoxygenated toluene (5 mL), previously
stirred under argon for 10 min. The solvent was removed under a reduced pressure and the residue
was purified by column chromatography (silica gel, 50:50 hexane:CH2Cl2) to yield the pure product
4c as an orange solid (80% yield). Mp: 125-127. IR (KBr, cm-1): 3418, 2920, 2849, 1601, 1505,
1
1471, 1387, 1238, 1094, 1024, 824, 720. H-NMR (400 MHz, CDCl3) δ 8.08 (d, J = 5.2 Hz, 1H),
7.51 (d, J = 8.5 Hz, 1H), 7.30 (d, J = 4.7 Hz, 1H), 7.52 (s, 1H), 7.19 (t, J = 1.9 Hz, 2H), 7.06 (d, J =
3.7 Hz, 1H), 7.04-7.07 (m, 8H), 6.98 (s, 1H), 6.85 (dd, J1 = 8.4, J2 = 2.1, 1H), 6.81-6.77 (m, 8H),
6.72 (dd, J1 = 8.6, J2 = 2.2, 1H), 5.59 (s, 1H), 3.92 (t, J = 6.5, 8H), 3.77 (d, J = 11.2, 2H), 3.64 (d, J
= 11.1, 2H), 2.75-2.72 (m, 2H), 1.81-1.73 (m, 8H), 1.67-1.59 (m, 4H), 1.49-1.42 (m, 8H), 1.38-1.25
13
(m, 40H), 0.91-0.84 (m, 14H), 0.81 (s, 3H). C-NMR (100 MHz, CDCl3) δ 155.2, 154.9, 149.1,
148.8, 142.0, 141.0, 140.6, 139.8, 139.5, 139.1, 139.0, 137.0, 135.2, 133.8, 130.7, 129.4, 129.2,
127.8, 126.1, 125.9, 125.5, 115.1, 115.0, 98.0, 68.1, 68.0, 31.6, 30.4, 30.0, 29.4, 29.2, 29.1, 25.9,
2.8, 22.5, 22.3, 21.7, 13.9. MS (APCI): calcd for C90H118N2O6S2, 1386.84; found: m/z = 1385.90
[M+H]+. Anal. Calcd for C90H118N2O6S2: C, 77.88; H, 8.57; N, 2.02; S, 4.62. Found: C, 77.85; H,
8.55; N, 2.00; S, 4.65.
5-Bromo-4-hexylthiophene-2-carbaldehyde, 1’.
The compound 1’ was synthesized following the literature procedure.42
2-(5-Bromo-4-hexylthiophen-2-yl)-5,5-dimethyl-1,3-dioxane, 2’.
18

ACCEPTED MANUSCRIPT
5-Bromo-4-hexylthiophene-2-carbaldehyde (1.7 g, 6 mmol), neopentylglycol (1.3 g, 12 mmol) and
p-toluenesulfonic acid (0.60 g, 0.3 mmol) were dissolved in dry toluene (50 mL). The reaction
mixture was refluxed for 5 h and then cooled to rt. The solvent was removed under a reduced
pressure, and the residue dissolved in ethyl acetate and washed with brine. The organic layer was
dried over anhydrous sodium sulfate and the solvent evaporated under reduced pressure. The crude
residue was purified by flash chromatography on silica gel, using a mixture of 9/1 hexane/ethyl
acetate as the eluent. The pure product 2’ was obtained as a yellow oil. (95% yield). IR (KBr, cm-1):
3431, 2956, 2850, 1554, 1471, 1448, 1388, 1375, 1298, 1231, 1190, 1097, 1021, 972, 930, 922,
822, 777. 1H-NMR (400 MHz, CDCl3) δ 6.83 (s, 1H) 5.52 (s, 1H) 3.74 (d, J = 10.9 Hz, 2H) 3.61 (d,
J = 10.9 Hz, 2H) 2.51 (t, J = 7.9 Hz, 2H) 1.57-1.53 (m, 2H) 1.30-1.26 (m, 9H) 0.92-0.87 (m, 3H)
0.79 (s, 3H) 13C-NMR (100 MHz, CDCl3) δ 141.3, 140.6, 125.7, 109.4, 97.8, 77.3, 31.4, 30.0, 29.4,
29.3, 28.7, 22.7, 22.4, 21.6, 13.9. MS (APCI): calcd for C16H25BrO2S, 362.07; found: m/z = 363.1
[M+H]+. Anal. Calcd for C16H25BrO2S: C, 53.18; H, 6.97; S, 8.87. Found: C, 53.22; H, 7.01; S,
8.90.
2-(3-Hexyl-2,2'-bithiophen-5-yl)-5,5-dimethyl-1,3-dioxane, 3’.
Pd(dba)3 (0.187 g, 0.18 mmol) and AsPh3 (mg 0.110 g, 0.36 mmol) were dissolved in anhydrous
and deoxygenated toluene (40 mL). After 30 min under stirring and reflux, compound 2’ (1.3 g,
3.61 mmol) and tributyl(thiophen-2-yl)stannane (1.4 mL, 4.33 mmol) were added. The resulting
solution was refluxed overnight. The solvent was removed under a reduced pressure and the residue
was purified by column chromatography (silica gel, 95:5 hexane:CH2Cl2) to yield the pure product
3’ as a yellow oil (62% yield). IR (KBr, cm-1): 3430, 2920, 2848, 1589, 1500, 1243, 1170, 1068,
1
824. H-NMR (400 MHz, CDCl3) δ 7.30-7.29 (m, 1H) 7.09 (s, 1H) 7.06-7.04 (m, 1H) 6.98 (s, 1H)
5.59 (s, 1H) 3.77 (d, J = 11.1 Hz, 2H) 3.64 (d, J = 11.0 Hz, 2H) 2.69 (t, J = 8.3 Hz, 2H) 1.63-
1.57(m, 3H) 1.36-1.29 (m, 8H) 0.89-0.86 (m, 3H) 0.80 (s, 3H). 13C-NMR (100 MHz, CDCl3) δ
138.9, 135.9, 130.6, 127.5, 127.1, 125.9, 125.2, 98.1, 77.4, 31.5, 30.4, 30.0, 29.1, 22.8, 22.4, 21.7,
13.9. MS (APCI): calcd for C20H28O2S2, 364.15; found: m/z = 365.20 [M+H]+. Anal. Calcd for
C20H28O2S2: C, 65.89; H, 7.74; S, 17.59. Found: C, 65.91; H, 7.76; S, 17.59.
5'-(5,5-Dimethyl-1,3-dioxan-2-yl)-3'-hexyl-2,2'-bithiophene-5-carbaldehyde, 4’.
In a 25 mL round-bottomed flask, under a nitrogen atmosphere, compound 3’ (0.09 g, 0.26 mmol)
and anhydrous THF (2 mL) were added. The solution was cooled to -78 °C and then n-BuLi in
hexanes (0.12 mL, 2.5 M) was slowly added. The mixture was stirred for 1 hour and half at -78 °C,
then N-formylpiperidine (0.03 mL, 0.31 mmol) was added and the resulting mixture was allowed to
19

ACCEPTED MANUSCRIPT
warm up to room temperature and stirred overnight. The reaction mixture was poured into ice-cold
water and extracted with dichloromethane. The organic layer was dried over anhydrous sodium
sulfate. The solvent was removed under a reduced pressure and the crude residue was purified by
flash chromatography on silica gel, using a mixture 1/1 dichloromethane/hexane as the eluent, (77%
yield). IR (KBr, cm-1): 3429, 2924, 2854, 1697, 1590, 1488, 1468, 1384, 1284, 1243, 1170, 1071,
1
1026, 820, 640. H-NMR (400 MHz, CDCl3) δ 9.88 (s, 1H), 7.70 (d, J = 3.9 Hz, 1H), 7.20 (d, J =
9.9 Hz, 1H), 7.01 (s, 1H), 5.59 (s, 1H), 3.77 (d, J = 11.3 Hz, 2H), 3.65 (d, J = 10.7 Hz, 2H), 2.78-
2.74 (m, 2H), 1.67-1.60 (m, 2H), 1.41-1.34 (m, 2H), 1.30-1.26 (m, 7H), 0.88 (t, J = 6.8 Hz, 3H),
0.81 (s, 3H). 13C-NMR (100 MHz, CDCl3) δ 182.5, 146.3, 142.3, 141.4, 141.2, 136.6, 129.5, 128.2,
126.1, 97.7, 77.4, 31.4, 30.1, 30.0, 29.5, 29.0, 22.8, 22.4, 21.6, 13.9. MS (APCI): calcd for
C21H28O3S2, 392.15; found: m/z = 393.5 [M+H]+. Anal. Calcd for C21H28O3S2: C, 64.25; H, 7.19; S,
16.33. Found: C, 64.27; H, 7.17; S, 16.30.
Bis(4-(octyloxy)phenyl)amine, 5’. Was synthesized following the literature procedure.37
3-(5'-((3,6-Bis(diphenylamino)-9H-fluoren-9-ylidene)methyl)-3-hexyl-[2,2'-bithiophen]-
5-yl)-2-cyanoacrylic acid, TK7.
A mixture of 4a (0.080 g, 0.09 mmol), cyanoacetic acid (0.155 g, 1.82 mmol), acetic acid (29 mL)
and ammonium acetate (0.084 g, 1.09 mmol) was heated at 120°C for 12 h. The reaction mixture
was poured into ice-cold water, extracted with dichloromethane and washed with water. The
organic layer was dried over anhydrous sodium sulfate, the solvent removed by rotary evaporation,
and the crude residue was purified by flash chromatography on silica gel, using a mixture 10/1
dichloromethane/methanol as the eluent. The pure product TK7 was obtained as a purple solid
(75% yield). Mp: 163-165. IR (KBr, cm-1): 3430, 3032, 2917, 2848, 2214, 1588,1489, 1387, 1272,
1167, 1107, 1017, 803, 751, 695. 1H-NMR (400 MHz, DMSO-d6) δ 8.20-8.18 (m, 1H), 7.86 (d, J =
8.4 Hz, 1H), 7.75 (t, J = 4,4 Hz, 1H),7.70 (s, 1H), 7.56 (d, J = 4,0 Hz, 1H), 7.49-7.47 (m, 1H), 7.41
(dd, J1 = 10.2 Hz, J2 = 3.9 Hz, 1H), 7.32-7.18 (m, 10H), 7.08-6.89 (m, 12H), 6.81 (dd, J1 = 8.6 Hz,
J2 = 2.2 Hz, 1H), 6.64 (dd, J1 = 8.6 Hz, J2 = 2.6 Hz, 1H), 2.81-2.74 (m, 2H), 1.62-1.54 (m, 2H),
1.33-1.18 (m, 6H), 0.79-0.74 (m, 3H). 13C-NMR (100 MHz, DMSO-d6) 148.6, 148.5, 148.4, 147.5,
147.2, 147.1, 142.1, 141.1, 140.9, 140.5, 139.1, 135.9, 135.4, 132.5, 132.2, 130.6, 130.3, 130.1,
129.9, 129.8, 124.6, 124.5, 123.9, 123.8, 123.6, 123.2, 31.2, 31.1, 29.9, 28.6, 22.2, 14.2, 14.1. MS
(APCI): calcd for C56H45N3O2S2, 855.3; found: m/z = 856.1 [M+H]+. Anal. Calcd for
C56H45N3O2S2: C, 78.57; H, 5.30; N, 4.91; S, 7.49. Found: C, 78.55; H, 5.29; N, 4.91; S, 7.47.
20

ACCEPTED MANUSCRIPT
3-(5'-((3,6-Bis(bis(4-methoxyphenyl)amino)-9H-fluoren-9-ylidene)methyl)-3-hexyl-
[2,2'-bithiophen]-5-yl)-2-cyanoacrylic acid, TK8.
A mixture of 4b (0.088 g, 0.089 mmol), cyanoacetic acid (0.151 g, 0.18 mmol), acetic acid (28 mL)
and ammonium acetate (0.082 g, 1.06 mmol) was heated at 120°C for 12 h. The reaction mixture
was poured into ice-cold water, extracted with dichloromethane and washed with water. The
organic layer was dried over anhydrous sodium sulfate and the solvent was removed by rotary
evaporation. The crude residue was purified by flash chromatography on silica gel, using a mixture
10/1 dichloromethane/methanol as the eluent. The pure product TK8 was obtained as a purple solid
(70% yield). Mp: 179-181. IR (KBr, cm-1): 3431, 2920,2848, 2211, 1762, 1601, 1506, 1456, 1368,
1239, 1166, 1105, 1033, 825. 1H-NMR (400 MHz, DMSO-d6) δ 8.16 (s, 1H), 7.72 (s, 1H), 7.61 (d,
J = 8.6 Hz, 1H), 7.40 (d, J = 7.9 Hz, 1H), 7.37 (d, J = 8.1 Hz, 1H), 7.05-6.95 (m, 8H), 6.91-6.84 (m,
9H), 6.79 (d, J = 8.6 Hz, 1H), 6.68 (dd, J1 = 8.6, J2 = 2.3 Hz, 1H), 6.40 (dd, J1 = 8.7, J2 = 2.2 Hz,
1H), 3.73-3.71 (m, 7H), 3.70 (s, 5H), 2.80-2.72 (m, 2H), 2.358 (s, 2H), 1.61-1.51 (m, 2H), 1.33-
1.17 (m, 7H), 0.80-0.75 (m, 3H). 13C-NMR (100 MHz, DMSO-d6) 13C-NMR (100 MHz, DMSO) δ
169.6, 156.3, 149.7, 149.5, 141.0, 140.8, 140.5, 140.4, 140.0, 139.9, 137.3, 135.0, 128.5, 128.3,
127.9, 127.2, 127.0, 126.6, 126.2, 115.3, 115.2, 55.5, 55.4, 31.1, 29.7, 28.5, 22.2, 21.1. MS (APCI):
calcd for C60H53N3O6S2, 975.3; found: m/z = 976.5 [M+H]+. Anal. Calcd for C60H53N3O6S2: C,
73.82; H, 5.47; N, 4.30; S, 6.57. Found: C, 73.84; H, 5.46; N, 4.30; S, 6.56.
3-(5'-((3,6-Bis(bis(4-(octyloxy)phenyl)amino)-9H-fluoren-9-ylidene)methyl)-3-hexyl-
[2,2'-bithiophen]-5-yl)-2-cyanoacrylic acid, TK9.
A mixture of 4c (0.159 g, 0.115 mmol), cyanoacetic acid (0.195 g, 2.29 mmol), acetic acid (36 mL)
and ammonium acetate (0.106 g, 1.38 mmol) was heated at 120°C for 12 h. The reaction mixture
was poured into ice-cold water, extracted with dichloromethane and washed with water. The
organic layer was dried over anhydrous sodium sulfate and the solvent was removed by rotary
evaporation. The crude residue was purified by flash chromatography on silica gel, using a mixture
10/1 dichloromethane/methanol as the eluent. The pure product TK9 was obtained as a purple solid
(60% yield). Mp: 139-141. IR (KBr, cm-1): 3445, 2922, 2212, 2851, 1761, 1601, 1505, 1387, 1238,
1166, 1106, 1016, 822. 1H-NMR (400 MHz, CDCl3) δ 8.35 (s, 1H), 7.72 (s, 1H), 7.60 (d, J = 8.6
Hz, 1H), 7.42 (d, J = 3.9 Hz, 1H), 7.38 (d, J = 3.9 Hz, 1H), 7.18-7.16 (m, 1H), 7.04-6.97 (m, 8H),
6.88-6.86 (m, 1H), 6.82-6.76 (m, 10H), 6.55 (dd, J1 = 8.7 Hz, J2 = 2.4 Hz, 1H), 3.95-3.88 (m, 8H),
1.80-1.73 (m, 10H), 1.38-1.24 (m, 49H), 0.91-0.85 (m, 15H). 13C-NMR (100 MHz, CDCl3) δ 155.2,
155.1, 149.1, 141.3, 141.0, 140.6, 140.5, 126.0, 125.9, 115.1, 115.0, 77.0, 68.1, 68.0, 31.6, 31.3,
29.9, 29.2, 29.1, 28.9, 25.9, 22.5, 22.4, 13.9, 13.8. MS (APCI): calcd for C88H109N3O6S2, 1367.7;
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found: m/z = 1367.9 [M+H]+. Anal. Calcd for C88H109N3O6S2: C, 77.21; H, 8.03; N, 3.07; S, 4.68.
Found: C, 77.21; H, 8.00; N, 3.09; S, 4.64.
Acknowledgements
This research was supported by “Nanotecnologie Molecolari per la Salute dell'Uomo e
l'Ambiente_MAAT” Cod. PON02_00563_3316357. CUP: B31C12001230005, by the project
EFOR—Energia da Fonti Rinnovabili (Iniziativa CNR per il Mezzogiorno L. 191/2009 art. 2
comma 44), by PON 254/Ric. Potenziamento del “CENTRO RICERCHE PER LA SALUTE
DELL'UOMO E DELL'AMBIENTE” Cod. PONa3_00334. CUP: F81D11000210007 and and by
Regione PUGLIA (APQ Reti di Laboratorio, project “PHOEBUS” cod. 31).
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