Organic sensitizers bearing a trialkylsilyl ether group for liquid dye sensitized solar cells

Article abstract of DOI:10.1016/j.dyepig.2015.07.026

In this work we present the synthesis, optical characterization and performance of five metal-free sensitizers for dye-sensitized solar cells (DSSC). All dyes include, for the first time, a trialkylsilyl ether group in the π-conjugated bridge (a thiophene

Full text of DOI:10.1016/j.dyepig.2015.07.026

Accepted Manuscript
Organic sensitizers bearing a trialkylsilylether group for liquid dye sensitized solar
cells
Raquel Pérez-Tejada, Natalia Martínez de Baroja, Santiago Franco, Laia Pellejà,
Jesús Orduna, Raquel Andreu, Javier Garín
PII:
S0143-7208(15)00294-6
10.1016/j.dyepig.2015.07.026
DYPI 4866
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 8 June 2015
Revised Date: 16 July 2015
Accepted Date: 22 July 2015
Please cite this article as: Pérez-Tejada R, Martínez de Baroja N, Franco S, Pellejà L, Orduna J, Andreu
R, Garín J, Organic sensitizers bearing a trialkylsilylether group for liquid dye sensitized solar cells, Dyes
and Pigments (2015), doi: 10.1016/j.dyepig.2015.07.026.
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ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Organic sensitizers bearing a trialkylsilylether group for liquid dye sensitized
solar cells
a
a
a*
b*
a
Raquel Pérez-Tejada , Natalia Martínez de Baroja , Santiago Franco , Laia Pellejà , Jesús Orduna ,
a
a
Raquel Andreu , Javier Garín
a
Departamento de Química Orgánica - Instituto de Ciencia de Materiales de Aragón (ICMA), Universidad de Zaragoza - CSIC,
E-50009 Zaragoza, Spain
Institute of Chemical Research of Catalonia (ICIQ), Avda Països Catalans 16, Tarragona E-43007 Spain
b
*
Corresponding author. Tel.: +34 976762283; E-mail address: sfranco@unizar.es (S. Franco)
Abstract
In this work we present the synthesis, optical characterization and performance of five metal-free
sensitizers for dye-sensitized solar cells (DSSC). All dyes include, for the first time, a trialkylsilyl ether
group in the π-conjugated bridge (a thiophene ring). The influence of different donor unities, like
-
triarylamine (TPA), 4H-pyranylidene and dithiafulvene have been evaluated in DSSC with a liquid I /I
3
electrolyte, obtaining the best results with the 4H-pyranylidene moiety. The size and the position of the
bulky group have a great importance in the efficiency of the final devices.
In order to explain the recombination processes and electron life-time, charge extraction (CE) and
transient photovoltaic (TPV) experiments have been carried out.
1
.
Introduction
Solar energy offers a clean, well-spread and inexhaustible energy source. Although the market is
dominated by silicon-based photovoltaic devices, in recent years the interest on alternatives more
environment-friendly has increased, specially focused on reducing mass during cell manufacture processes
and the thickness of the final device.
1
, 2
3, 4
Organic Photovoltaic Cells (OPVs)
and particularly Dye Sensitized Solar Cells (DSSCs) constitute
an interesting alternative due to their low manufacturing cost, flexibility of molecular design, light-weight
and great aesthetic features, like color and transparency. The key element in a DSSC device is probably the
sensitizer dye and over the last years, thousands of new dyes have been investigated. The most efficient
5
organic sensitizers are based on Donor-π spacer-acceptor (D-π-A) structures, a type of push-pull systems
which lead to effective photoinduced intramolecular charge-transfer (ICT). In these systems small variations
in the different parts of the molecule (mostly in the donor and the π-bridge) may result in significant changes
in the photovoltaic properties. Triphenylamine (TPA)-based metal free organic dyes are one of the most
6
, 7
common donor groups in DSSCs,
as it presents several advantages, like a non-planar structure, which
suppresses the formation of aggregates. Furthermore, the physical properties can be easily modulated by
8
-13
14-17
introduction of bulky or donor groups.
dithiafulvene
Recently, proaromatic systems like 4H-pyranylidene
and
1
8-20
have been introduced as alternative and efficient donor unities in DSSCs, but no studies
comparing their properties have been reported.
When designing a new sensitizer, one important factor to take into account is related to the minimization
2
1,
of aggregates by π-π stacking. This may be performed by using additives, such as deoxycholic acid (DCA)
22
12, 23-26
or by the introduction of bulky groups both, in the donor or in the π-bridge.
However, it is relatively
difficult to synthesize dyes with bulky chains in the conjugated spacer, requiring tedious and multiple
reaction steps.

ACCEPTED MANUSCRIPT
2
7, 28
Silicon-based dyes have been very promising for DSSCs due to its photo and thermal stability.
Examples of organic sensitizers bearing a dithienosilole (DTS) as a π-linker have been reported with high
2
9-34
efficiencies.
However, to the best of our knowledge, organic dyes featuring a trialkylsilyl ether
(
R R R SiO−) were never used to preclude the π-aggregation on the TiO in DSSCs. This popular protecting
1
2
3
2
3
5
group can be easily introduced from alcohols and the overall size and the stability depends on the nature of
the R , R or R . Moreover, the silylether group greatly enhances the solubility of the sensitizer that
1
2
3
facilitates its adsorption on the TiO surface.
2
In the present work, a series of five new metal-free organic sensitizers for DSSCs with a trialkylsilyloxy
group have been designed, synthesized and characterized. In order to evaluate the donor influence on the
photovoltaic properties a TPA and two proaromatic donor unities (4H-pyranylidene and dithiafulvene) have
been used (Figure 1).
tBu
CH3
Si
NC
H C
3
O
COOH
S
D
D:
S
S
N
O
4
H-Pyr
1,3-DT
TPA
Fig 1. Molecular structures of TBDMS organic sensitizers
The influence of the size and the relative position on the heterocyclic linker of two bulky groups,
tert-butyldimethyl (TBDMS) or tert-butyldiphenyl silylether (TBDPS) are also studied (Figure 2). Finally,
the photophysical properties, molecular orbital calculations and the performance of DSSCs based on these
organic dyes are reported.
Fig. 2. Molecular structures of 4H-pyranylidene organic sensitizers
2
.
Experimental section
2.1. General information
Infrared measurements were carried out in KBr or neat using a Perkin-Elmer Fourier Transform Infrared
600 spectrometer. Melting points were obtained on a Gallenkamp apparatus in open capillaries and are
uncorrected. H- and C-NMR spectra were recorded on a Bruker ARX300 or a Bruker AV400 at 300 or
1
1
13

ACCEPTED MANUSCRIPT
4
00 MHz and 75 or 100 MHz respectively; δ values are given in ppm (relative to TMS) and J values in Hz.
1
1
The apparent resonance multiplicity is described as s (singlet), d (doublet), and m (multiplet). H- H COSY
1
13
and H- C-HSQC experiments were recorded on a Bruker ARX300 or a Bruker AV400 at 300 or 400 MHz
in order to establish peaks assignment and spatial relationships. Electrospray mass spectra were recorded on
a Bruker Microtof-Q spectrometer; accurate mass measurements were achieved using sodium formate as
external reference. UV-Visible spectra were recorded with an UV-Vis UNICAM UV4 spectrophotometer.
Pulse differential voltammetry measurements were performed with a µ-Autolab type III potentiostat using a
glassy carbon working electrode, Pt counter electrode, and Ag/AgCl reference electrode. The experiments
-1
were carried out under argon in CH Cl , with Bu NPF as supporting electrolyte (0.1 mol L ). Scan rate was
2
2
4
6
-1
-1
0
.01V s , modulation amplitude 0.025V and modulation time 0.05 s .
2
.2. Synthesis
4-((tert-butyldimethylsilyloxy)methyl)-5-((2,6-diphenyl-4H-pyran-4-ylidene)methyl)thiophene-2-
carbaldehyde (7)
A solution of 2,6-diphenyl-(4H-pyran-4ylidene)-diphenylphosphine oxide 5 (680 mg, 1.56 mmol) in
anhydrous THF (12 ml) was prepared, purged with argon and cooled to −78ºC. To this solution, n-BuLi (1.6
M in hexanes) (1.2 mL, 2.08 mmol) was added dropwise and the resulting mixture was stirred for 15 min.
Then 3-((tert-butyldimethylsilyloxy)methyl)thiophene-2-carbaldehyde 4 (472 mg; 1.84 mmol) in anhydrous
THF (5 mL) was added dropwise and the mixture was warmed to 0 ºC for 3 hours (TLC monitoring using
1
0% EtOAc in hexanes). Saturated NH Cl solution was added to quench the reaction and the solvent was
4
evaporated under reduced pressure. The organic layer was extracted with EtOAc (2 × 25 mL) and dried over
anhydrous MgSO . After the removal of the solvent, the residue was dissolved in EtOAc/hexanes (3/97) and
4
filtered over silica gel to give the crude tert-butyl((2-((2,6-diphenyl-4H-pyran-4-ylidene)methyl)thiophen-3-
yl)methoxy)dimethylsilane 6 as an intermediate. Then, a solution of 2,2,6,6-tetramethylpiperidine (0.27 mg,
t
1
.58 mmol) in THF (8.4 mL) was prepared, purged with argon and cooled to −78 ºC. To this solution, BuLi
(
1.7 M in pentane) (1.01 mL, 1.71 mmol) was added dropwise and the resulting mixture was stirred for 1h
and then a solution of 6 (676.0 mg, 1.41 mmol) in THF (33.6 mL) was added. The resulting mixture was
stirred for an additional hour, DMF (0.28 mL, 3.70 mmol) was added dropwise and the mixture was warmed
to −30 ºC. The reaction was quenched by the addition of saturated NH Cl solution and the solvent was
4
evaporated under reduced pressure. The organic layer was extracted with EtOAc (2 × 20 mL) and dried over
anhydrous MgSO . After the removal of the solvent, the aldehyde 7 was purified by silica gel column
4
chromatography (6% EtOAc in hexanes). Yield: red oil (583.0 mg, 1.16 mmol; 82%).
-1
1
IR (neat): cm 1648 (C=O), 1573 (C=C). H NMR (400 MHz, CDCl ): δ (ppm) 9.81 (s, 1H), 7.90−7.76
3
(
m, 4H), 7.69 (s, 1H), 7.55−7.43 (m, 6H), 7.29 (d, J = 2.0 Hz, 1H), 6.55 (d, J = 2.0 Hz, 1H), 6.07 (s, 1H),
13
4
1
2
.75 (s, 2H), 0.96 (s, 9H), 0.14 (s, 6H). C NMR (100 MHz, CDCl ): δ (ppm) 182.1, 155.3, 152.6, 146.6,
3
39.0, 137.9, 137.0, 132.8, 132.5, 132.5, 130.2, 129.7, 128.9, 128.8, 125.3, 124.7, 109.0, 104.7, 102.9, 59.7,
+
+
+
6.0, 18.4, −5.2. HRMS (ESI ): m/z calcd for [C H O SSi] : 501.1914, found: 501.1914 [M+H] ; calcd for
3
0
33
3
+
+
[
C H NaO SSi] : 523.1734, found: 523.1721 [M+Na] .
30 32 3
4-((tert-butyldimethylsilyloxy)methyl)-5-((4,5-dimethyl-1,3-dithiol-2ylidene)methyl)thiophene-2-
carbaldehyde (10)
A solution of tributyl(4,5-dimethyl-1,3-dithiol-2-yl)phosphonium hexafluorophosphate 8 (317.7 mg, 0.66
mmol) and 3-((tert-butyldimethylsilyloxy)methyl)thiophene-2-carbaldehyde 4 (131.0 mg, 0.51 mmol) in
anhydrous THF (16 mL) was prepared, purged with argon and cooled to −78ºC. To this solution, Et N (352.4
3
µL, 2.51 mmol) was added dropwise and the resulting mixture was stirred for 15 min. After the removal of
the solvent, the residue was dissolved in EtOAc/hexanes (1:9) and filtered over neutral aluminum oxide to
give compound 9 as an intermediate. Then, a solution of 9 in THF (10 mL) was prepared, purged with argon

ACCEPTED MANUSCRIPT
and cooled to −45 ºC. To this solution, n-BuLi (1.6 M in hexanes) (0.53 mL, 0.85 mmol) was added
dropwise and the resulting mixture was stirred for 1h. DMF (0.09 mL, 1.2 mmol) was added dropwise and
then, the mixture was warmed to room temperature over 24h. Saturated NH Cl solution was added to quench
4
the reaction and the solvent was evaporated under reduced pressure. The organic layer was extracted with
CH Cl and dried over anhydrous MgSO . After the removal of the solvent, the aldehyde 10 was purified by
2
2
4
silica gel column chromatography (20% ethyl acetate in hexanes). Yield: red oil (136.2 mg, 0.34 mmol;
6
7%).
IR (neat): cm 1649 (C=O), 1492 (C=C). H NMR (400 MHz, CDCl ): δ (ppm) 9.80 (s, 1H), 7.65 (s,
-1
1
3
1
3
1
H), 6.82 (s, 1H), 4.69 (s, 2H), 2.09 (s, 3H), 2.03 (s, 3H), 0.92 (s, 9H), 0.09 (s, 6H). C NMR (100 MHz,
CDCl ): δ (ppm) 181.9, 146.6, 142.5, 137.9, 137.3, 135.8, 124.4, 123.4, 102.9, 59.6, 25.9, 18.3, 13.8, 13.1,
3
+
+
+
−
[
5.2. HRMS (ESI ): m/z calcd for [C H O S Si] : 399.0937, found: 399.0961 [M+H] ; calcd for
18 27 2 3
+
+
C H NaO S Si] : 421.0756, found: 421.0784 [M+Na] .
18 26 2 3
4-(3-((tert-butyldimethylsilyloxy)methyl)thiophen-2-yl)-N,N-diphenylaniline (13)
A solution of the stannyl derivative 12 (990.0 mg, 1.87 mmol) and compound 11 (668.2 mg, 1.87 mmol)
in anhydrous toluene (24 mL) was prepared, purged with argon for 15 min before addition of Pd(PPh3)4
112.3 mg, 0.10 mmol). The reaction mixture was refluxed for 15 h under an argon atmosphere. After
(
addition of water (30 mL), the mixture was extracted with toluene (2 × 30 mL). The organic phase was
washed with a saturated aqueous solution of NH Cl (30 mL) and water (3 × 10 mL) and dried over
4
anhydrous MgSO . After the removal of the solvent, the compound was purified by silica gel column
4
chromatography (2% diethyl ether in hexanes). Yield: light yellow oil (392.4 mg, 0.83 mmol; 44%).
-
1
1
IR (neat): cm 1592 (C=C). H NMR (300 MHz, CD Cl ): δ (ppm) 7.39−7.33 (m, 2H), 7.32−7.24 (m,
2
2
1
3
4
H), 7.21 (d, J = 5.2 Hz, 1H), 7.15−7.02 (m, 9H), 4.68 (s, 2H), 0.89 (s, 9H), 0.05 (s, 6H). C NMR (100
MHz, CD Cl ): δ (ppm) 148.1, 148.0, 140.6, 137.6, 130.4, 130.3, 129.9, 128.4, 125.2, 123.7, 59.9, 26.3,
2
2
+
+
+
1
[
8.8, −5.02. HRMS (ESI ): m/z calcd for [C H NOSSi] : 472.2125, found: 472.2109 [M+H] ; calcd for
29 34
+
+
C H NNaOSSi] : 494.1944, found: 494.1930 [M+Na] .
29 33
4-((tert-butyldimethylsilyloxy)methyl)-5-(4-(diphenylamino)phenyl)thiophene-2-carbaldehyde (14)
A solution of 13 (352.4 mg, 0.75 mmol) in anhydrous THF (17 mL) was prepared, purged with argon and
cooled to −30 ºC. To this solution, n-BuLi (1.6 M in hexanes) (0.78 mL, 1.25 mmol) was added dropwise
and the resulting mixture was stirred for 1 hour. Then, DMF (173 µL, 2 mmol) was added dropwise and the
mixture was warmed to room temperature (TLC monitoring using 2% diethyl ether in hexanes). Saturated
NH Cl solution was added to quench the reaction and the solvent was evaporated under reduced pressure.
4
The organic layer was extracted with diethyl ether (15 × 3 mL) and dried over anhydrous MgSO . After
4
removal of the solvent, the aldehyde 14 was purified by column chromatography on silica gel (2% ethylic
ether in hexanes). Yield: yellow oil (298.6 mg, 0.50 mmol; 80%).
-
1
1
IR (neat): cm 1670 (C=O), 1445 (C=C). H NMR (400 MHz, CD Cl ): δ (ppm) 9.84 (s, 1H), 7.80 (s,
2
2
1
3
1
H), 7.41−7.38 (m, 2H), 7.33−7.29 (m, 4H), 7.16−7.05 (m, 8H), 4.72 (s, 2H), 0.91 (s, 9H), 0.08 (s, 6H). C
NMR (100 MHz, CD Cl ): δ (ppm) 183.2, 150.3, 149.4, 147.7, 141.0, 139.5, 139.2, 130.4, 130.0, 126.5,
2
2
+
+
1
5
25.7, 124.4, 122.7, 60.0, 26.3, 18.8, −4.5. HRMS (ESI ): m/z calcd for [C H NO SSi] : 500.2074, found:
30 34 2
00.2045 [M+H] .
+
3-(4-((tert-butyldimethylsilyloxy)methyl)-5-((2,6-diphenyl-4H-pyran-4-ylidene)methyl) thiophen-2-
yl)-2-cyanoacrylic acid (1)
To a solution of aldehyde 7 (122 mg, 0.24 mmol) and 2-cyanoacetic acid (33 mg, 0.38 mmol) in
chloroform (5 mL) was added piperidine (160 µL; 1.62 mmol). The mixture was refluxed for 24 hours under
an argon atmosphere and then cooled down to room temperature. HCl (1N) was added until pH=3, the
organic phase was dried over MgSO and concentrated under reduced pressure. Then, hexane was added and
4

ACCEPTED MANUSCRIPT
a solid appeared. This compound was filtered under reduced pressure and washed with a mixture
hexane/CH Cl (9/1) to afford 1 Yield: dark purple solid (134 mg, 0.24 mmol; 96%).
2
2
-1
1
Mp 215−218 ºC. IR (KBr): cm 3100−2600 (COO−H), 2210 (C≡N), 1672 (C=O), 1652 (C=C). H NMR
(
=
400 MHz, dmso-d ): δ (ppm) 8.33 (s, 1H), 8.02−7.89 (m, 4H), 7.86 (s, 1H), 7.63−7.45 (m, 6H), 7.37 (d, J
1.5 Hz, 1H), 7.11 (d, J = 1.5 Hz, 1H), 6.37 (s, 1H), 4.76 (s, 2H), 0.90 (s, 9H), 0.11 (s, 6H). C NMR (75
6
1
3
MHz, dmso-d ): δ (ppm) 164.1, 154.8, 151.9, 145.7, 144.9, 139.3, 132.2, 131.6, 131.5, 130.5, 130.0, 129.9,
6
+
1
29.1, 128.9, 124.8, 124.5, 117.7, 109.1, 105.3, 102.4, 58.7, 25.7, 17.9, −5.4. HRMS (ESI ): m/z calcd for
+
+
[
C H NO SSi] : 568.1972, found: 568.1945 [M+H] .
33 34 4
3-(4-((tert-butyldimethylsilyloxy)methyl)-5-((4,5-dimethyl-1,3-dithiol-2-ylidene)methyl)thiophen-2-
yl)-2-cyanoacrylic acid (2)
To a solution of aldehyde 10 (136.4 mg, 0.34 mmol) and 2-cyanoacetic acid (45.4 mg, 0.53 mmol) in
chloroform (32 mL) was added piperidine (226.4 µL, 2.25 mmol). The mixture was refluxed for 85h under
an argon atmosphere and then cooled down to room temperature. The reaction crude was chromatographied
on reverse C18 silica gel (50 % AcONH (20 mM) in acetonitrile). After the addition of acetic acid a solid
4
appeared. This compound was filtered under reduced pressure to afford 2. Yield: dark purple solid (68.7 mg,
0
.15 mmol; 43%).
Mp 170−174 ºC. IR (KBr): cm 2211 (C≡N), 1673 (C=O), 1531 (C=C). H NMR (300 MHz, CDCl ): δ
-1
1
3
(
ppm) 8.21 (s, 1H), 7.68 (s, 1H), 6.84 (s, 1H), 4.69 (s, 2H), 2.14 (s, 3H), 2.07 (s, 3H), 0.92 (s, 9H), 0.09 (s,
13
6
1
4
4
H). C NMR (75 MHz, CDCl ): δ (ppm) 169.1, 149.1, 146.5, 145.5, 139.8, 136.6, 130.9, 125.6, 124.5,
3
+
+
16.9, 103.1, 91.5, 59.5, 25.9, 18.3, 14.0, 13.1, −5.3. HRMS (ESI ): m/z calcd for [C H NO S Si] :
2
1
28
3 3
+
+
+
66.0995, found: 466.1040 [M+H] . HRMS (ESI ): m/z calcd for [C H NNaO S Si] : 488.0815, found:
2
1
27
3 3
+
88.0793 [M+Na] .
3-(4-((tert-butyldimethylsilyloxy)methyl)-5-(4-(diphenylamino)phenyl)thiophen-2-yl)-2-
cyanoacrylic acid (3)
To a solution of aldehyde 14 (139.2 mg; 0.29 mmol) and 2-cyanoacetic acid (45.4 mg; 0.53 mmol) in
chloroform (26 mL) was added piperidine (200.6 µL; 1.90 mmol). The mixture was refluxed for 5 days
under an argon atmosphere and then cooled down to room temperature. The reaction crude was
chromatographied on reverse C18 silica gel (50 % AcONH (20 mM) in acetonitrile). After the addition of
4
acetic acid a solid appeared. This compound was filtered under reduced pressure to afford 3. Yield: pinkish
solid (113.1 mg, 0.20 mmol; 70%).
-
1
1
Mp 196−200 ºC. IR (KBr): cm 2223 (C≡N), 1679 (C=O), 1566 (C=C). H NMR (400 MHz, acetone-d ):
6
δ (ppm) 8.42 (s, 1H), 8.05 (s, 1H), 7.58−7.53 (m, 2H), 7.39−7.33 (m, 4H), 7.18−7.11 (m, 6H) 7.11−7.06 (m,
1
3
2
1
−
H), 4.83 (s, 2H), 0.91 (s, 9H), 0.11 (s, 6H). C NMR (100 MHz, acetone-d ): δ (ppm) 167.8, 151.5, 150.9,
6
48.9, 148.3, 143.4, 140.7, 134.9, 131.8, 131.5, 127.4, 127.2, 126.0, 123.6, 117.8, 100.1, 60.9, 27.3, 19.8,
4.1. HRMS (ESI ): m/z calcd for [C H N O SSi] : 565.1987, found: 565.2014 [M−H] .
-
-
-
3
3
33
2
3
3-((tert-butyldiphenylsilyloxy)methyl)thiophene-2-carbaldehyde (18)
A solution of tert-butyldiphenyl(thiophen-3-ylmethoxy)silane 17 (2.2 g, 6.2 mmol) in anhydrous diethyl
ether (10 mL) was prepared, purged with argon and cooled to −10 ºC. To this solution, t-BuLi (1.7 M in
pentane) (4 mL, 6.2 mmol) was added dropwise for a period of 20 min and the resulting mixture was stirred
at −10 ºC for 1h. Then, DMF (0.75 mL, 9.6 mmol) was added dropwise and the mixture was warmed to 0 ºC
and stirred at this temperature overnight (TLC monitoring using 20% hexanes in dichloromethane). Saturated
NH Cl solution was added to quench the reaction and the solvent was evaporated under reduced pressure.
4
The organic layer was extracted with diethyl ether (10 × 3 mL) and dried over anhydrous MgSO . After
4
removal of the solvent, the aldehyde 18 was purified by silica gel column chromatography (20% hexanes in
dichloromethane). Yield: yellow oil (454.9 mg, 1.20 mmol; 20%).

ACCEPTED MANUSCRIPT
-
1
1
IR (neat): cm 1664 (C=O), 1588 (C=C). H NMR (400 MHz, CD Cl ): δ (ppm) 9.95 (d, J = 0.9 Hz,
2
2
1
3
1
H), 7.68−7.66 (m, 5H), 7.48−7.37 (m, 6H), 7.25 (d, J = 5.0 Hz, 1H), 5.06 (s, 2H), 1.08 (s, 9H). C NMR
(
100 MHz, CD Cl ): δ (ppm) 182.9, 150.9, 138.1, 136.1, 134.5, 133.5, 130.5, 130.0, 128.5, 61.4, 27.2, 19.7.
2
2
+
+
+
HRMS (ESI ): m/z calcd for [C H O SSi] : 381.1339, found: 381.1313 [M+H] ; calcd for
[
2
2
25
2
+
+
C H NaO SSi] : 403.1158, found: 403.1139 [M+Na] .
22 24 2
4-((tert-butyldiphenylsilyloxy)methyl)thiophene-2-carbaldehyde (19)
A solution of tert-butyldiphenyl(thiophen-3-ylmethoxy)silane 17 (1.6 g, 4.5 mmol) in anhydrous THF (39
mL) was prepared, purged with argon and cooled to −10 ºC. To this solution, n-BuLi (1.6 M in hexanes) (2.8
mL, 4.5 mmol) was added dropwise and the resulting mixture was stirred at −10 ºC for 1h and 30 min. Then,
DMF (0.54 mL, 6.9 mmol) was added dropwise and the mixture was warmed to 0 ºC and stirred at this
temperature overnight (TLC monitoring using 20% ethyl acetate in hexanes). Saturated NH Cl solution was
4
added to quench the reaction and the solvent was evaporated under reduced pressure. The organic layer was
extracted with diethyl ether (15 × 2 mL) and dried over anhydrous MgSO . After removal of the solvent, the
4
aldehyde 19 was purified by silica gel column chromatography (20% ethyl acetate in hexanes). Yield: white
solid (465.3 mg, 1.22 mmol; 21%).
-1
1
Mp 76−78 ºC. IR (KBr): cm 1666 (C=O), 1466 (C=C). H NMR (400 MHz, CD Cl ): δ (ppm) 9.86 (d,
2
2
J = 1.3 Hz, 1H), 7.69−7.65 (m, 5H), 7.59−7.58 (m, 1H), 7.47−7.37 (m, 6H), 4.77 (d, J = 0.6 Hz, 2H), 1.08 (s,
1
3
9
6
[
H). C NMR (100 MHz, CD Cl ): δ (ppm) 183.5, 144.7, 144.5, 136.1, 135.8, 133.7, 130.8, 130.4, 128.4,
2 2
+
+
+
2.2, 27.1, 19.7. HRMS (ESI ): m/z calcd for [C H O SSi] : 381.1339, found: 381.1320 [M+H] ; calcd for
2
2
25
2
+
+
C H NaO SSi] : 403.1158, found: 403.1144 [M+Na] .
22
24
2
4-((tert-butyldiphenylsilyloxy)methyl)-5-((2,6-diphenyl-4H-pyran-4-ylidene)methyl)thiophene-2-
carbaldehyde (21)
A solution of 5 (22.6 mg, 0.51 mmol) in anhydrous THF (5 mL) was prepared, purged with argon and
cooled to −78ºC. To this solution, n-BuLi (1.6 M in hexanes) (0.32 mL, 0.51 mmol) was added dropwise and
the resulting mixture was stirred for 20 min. Then 3-((tert-butyldiphenylsilyloxy)methyl)thiophene-2-
carbaldehyde 18 (151.1 mg; 0.40 mmol) in anhydrous THF (5 mL) was added dropwise and the mixture was
warmed to room temperature for 21 hours (TLC monitoring using 10% dichloromethane in hexanes).
Saturated NH Cl solution was added to quench the reaction and the solvent was evaporated under reduced
4
pressure. The organic layer was extracted with hexanes (25 × 2 mL) and dried over anhydrous MgSO . After
4
the removal of the solvent, the residue was dissolved in hexanes/CH Cl (9/1) and filtered over silica gel to
2
2
give the compound 20 as an intermediate. A solution of 20 in THF (10 mL) was prepared, purged with argon
and cooled to −78 ºC. To this solution, n-BuLi (1.6 M in hexanes) (0.36 mL, 0.58 mmol) was added
dropwise and the resulting mixture was stirred for 1h and 30 min. DMF (0.08 mL, 1.03 mmol) was added
dropwise and the mixture stirred for 2h. Saturated NH Cl solution was added to quench the reaction and the
4
solvent was evaporated under reduced pressure. The organic layer was extracted with hexanes (15 × 2 mL)
and dried over anhydrous MgSO . After the removal of the solvent, the aldehyde 21 was purified by silica
4
gel column chromatography (20% ethyl acetate in hexanes). Yield: red oil (136.4 mg, 0.22 mmol; 55%).
-1
1
IR (neat): cm 1643 (C=O), 1518 (C=C). H NMR (400 MHz, CD Cl ): δ (ppm) 9.77 (s, 1H), 7.92−7.89
2
2
(
m, 2H), 7.80−7.78 (m, 2H), 7.75−7.67 (m, 4H), 7.64 (s, 1H), 7.55−7.38 (m, 12H), 7.27 (d, J = 2.0 Hz, 1H),
1
3
6
1
1
.47 (d, J = 2.0 Hz, 1H), 6.00 (s, 1H), 4.81 (s, 2H), 1.09 (s, 9H). C NMR (100 MHz, CD Cl ): δ (ppm)
2 2
82.4, 155.8, 153.0, 147.1, 139.1, 138.5, 137.8, 136.2, 133.8, 133.2, 133.1, 133.0, 130.7, 130.4, 130.2, 129.4,
+
29.3, 128.4, 125.9, 125.2, 109.5, 105.4, 103.3, 60.9, 27.2, 19.7. HRMS (ESI ): m/z calcd for
+
+
[
C H O SSi] : 625.2227, found: 625.2235 [M+H] .
40 37 3
3-((tert-butyldiphenylsilyloxy)methyl)-5-((2,6-diphenyl-4H-pyran-4-ylidene)methyl)thiophene-2-
carbaldehyde (23)

ACCEPTED MANUSCRIPT
A solution of 2,6-diphenyl(4H-pyran-4ylidene)diphenylphosphine oxide 5 (222.6 mg, 0.51 mmol) in
anhydrous THF (5 ml) was prepared, purged with argon and cooled to −78ºC. To the solution, n-BuLi (1.6 M
in hexanes) (0.32 mL, 0.51 mmol) was added dropwise and the resulting mixture was stirred for 20 min.
Then 4-((tert-butyldiphenylsilyloxy)methyl)thiophene-2-carbaldehyde 19 (150.0 mg; 0.39 mmol) in
anhydrous THF (5 mL) was added dropwise and the mixture was warmed to room temperature for 21 h
(
TLC monitoring using 20% ethyl acetate in hexanes). Saturated NH Cl solution was added to quench the
4
reaction and the solvent was evaporated under reduced pressure. The organic layer was extracted with
EtOAc and dried over anhydrous MgSO . After the removal of the solvent, the residue was dissolved in
4
EtOAc/hexanes (2:8) and filtered over silica gel to give the crude tert-butyl((5-((2,6-diphenyl-4H-pyran-4-
ylidene)methyl)thiophen-3-yl)methoxy)diphenylsilane 22 as an intermediate. A solution of 22 in THF (10
mL) was prepared, purged with argon and cooled to −78 ºC. To this solution, n-BuLi (1.6 M in hexanes)
(
0.42 mL, 0.68 mmol) was added dropwise and the resulting mixture was stirred for 2h. DMF (0.09 mL, 1.2
mmol) was added dropwise and the mixture stirred for 2h. Saturated NH Cl solution was added to quench the
4
reaction and the solvent was evaporated under reduced pressure. The organic layer was extracted with
EtOAc (15 × 3 mL) and dried over anhydrous MgSO . After the removal of the solvent, the aldehyde 23 was
4
purified by silica gel column chromatography (20% ethyl acetate in hexanes). Yield: dark red oil (138.9 mg,
0
.22 mmol; 56%).
-1
1
IR (neat): cm 1643 (C=O), 1579 (C=C). H NMR (400 MHz, CD Cl ): δ (ppm) 9.86 (s, 1H), 7.90−7.88
2
2
(
m, 2H), 7.82−7.80 (m, 2H), 7.73−7.70 (m, 4H), 7.50−7.41 (m, 12H), 7.22 (d, J = 1.9 Hz, 1H), 7.05 (s, 1H),
1
3
6
1
1
.55 (d, J = 1.9 Hz, 1H), 6.14 (s, 1H), 5.02 (s, 2H), 1.11 (s, 9H). C NMR (100 MHz, CD Cl ): δ (ppm)
2 2
81.4, 155.6, 153.1, 151.5, 151.3, 136.1, 133.7, 133.5, 133.3, 133.2, 133.1, 130.7, 130.5, 130.2, 129.4, 129.3,
+
28.4, 127.8, 125.9, 125.3, 109.1, 107.6, 103.2, 61.2, 27.2, 19.7. HRMS (ESI ): m/z calcd for
+
+
[
C H O SSi] : 625.2227, found: 625.2244 [M+H] .
40 37 3
3-(4-((tert-butyldiphenylsilyloxy)methyl)-5-((2,6-diphenyl-4H-pyran-4-ylidene)methyl)thiophen-2-
yl)-2-cyanoacrylic acid (15)
To a solution of aldehyde 21 (97.9 mg, 0.157 mmol) and 2-cyanoacetic acid (20.8 mg, 0.24 mmol) in
chloroform (16 mL) was added piperidine (109.9 µL, 1.04 mmol). The mixture was refluxed for 72h under
an argon atmosphere and then cooled down to room temperature. The reaction crude was chromatographied
on reverse C18 silica gel (started 50 % AcONH (20 Mm) in acetonitrile and finished 30%). After the
4
addition of acetic acid a solid appeared. This compound was filtered under reduced pressure to afford 15.
Yield: dark purple solid (83.4 mg, 0.12 mmol; 77%).
-1
1
Mp 208−211 ºC. IR (KBr): cm 2207 (C≡N), 1652 (C=O), 1539 (C=C). H NMR (300 MHz, THF-d ): δ
8
(
ppm) 8.29 (s, 1H), 8.01−7.98 (m, 2H), 7.88−7.85 (m, 2H), 7.79 (s, 1H), 7.76−7.70 (m, 4H), 7.59−7.32 (m,
1
3
1
3H), 6.76 (d, J = 1.6 Hz, 1H), 6.12 (s, 1H), 4.87 (s, 2H), 1.09 (s, 9H). C NMR (100 MHz, THF-d ): δ
8
(
1
ppm) 164.9, 156.6, 153.8, 147.8, 146.1, 139.8, 139.8, 136.6, 134.3, 134.0, 133.7, 133.5, 131.9, 130.9, 130.6,
+
30.0, 129.7, 128.8, 126.2, 125.7, 117.9, 110.2, 106.2, 104.0, 96.6, 61.3, 27.4, 20.1. HRMS (ESI ): m/z calcd
+
+
+
for [C H NO SSi] : 692.2285, found: 692.2248 [M+H] ; calcd for [C H NNaO SSi] : 714.2105, found:
7
43
38
4
43 37
4
+
14.2066 [M+Na] .
3-(3-((tert-butyldiphenylsilyloxy)methyl)-5-((2,6-diphenyl-4H-pyran-4-ylidene)methyl)thiophen-2-
yl)-2-cyanoacrylic acid (16)
To a solution of aldehyde 23 (120.4 mg, 0.192 mmol) and 2-cyanoacetic acid (25.6 mg, 0.30 mmol) in
chloroform (18 mL) was added piperidine (134.6 µL, 1.28 mmol). The mixture was refluxed for 20h under
an argon atmosphere, then cooled down to room temperature. The reaction crude was chromatographed on
reverse C18 silica gel (started 50 % AcONH (20 mM) in acetonitrile and finished 33%). After the addition
4
of acetic acid a solid appeared. This compound was filtered under reduced pressure to afford 16. Yield: dark
purple solid (86.0 mg, 0.12 mmol; 65%).

ACCEPTED MANUSCRIPT
-1
1
Mp 219−226 ºC. IR (KBr): cm 2209 (C≡N), 1651 (C=O), 1541 (C=C). H NMR (400 MHz, THF-d ): δ
8
(
ppm) 8.51 (s, 1H), 7.99−7.88 (m, 4H), 7.74−7.72 (m, 4H), 7.49−7.34 (m, 14H), 6.99 (s, 1H), 6.81 (br s, 1H),
1
3
4
1
1
6
.92 (s, 2H), 1.08 (s, 9H). C NMR (100 MHz, THF-d ): δ (ppm) 164.9, 156.4, 154.0, 152.5, 151.7, 143.7,
8
36.6, 134.3, 134.0, 133.7, 133.5, 131.9, 131.2, 130.9, 130.7, 130.0, 129.8, 128.8, 128.1, 126.2, 125.8, 118.1,
+
+
09.8, 108.4, 103.9, 95.8, 61.3, 27.4, 20.0. HRMS (ESI ): m/z calcd for [C H NO SSi] : 692.2285, found:
4
3
38
4
92.2313
2
.3. Device preparation and characterization
The working and counter electrodes consisted of TiO and thermalized platinum films, respectively, and
2
−
1
were deposited onto F-doped tin oxide (FTO, Pilkington Glass Inc., with 15 Ω sq sheet resistance)
conducting glass substrates. Efficient DSC devices were made using 9 µm thick films consisting of 20 nm
TiO nanoparticles (Dyesol© paste) and a scattering layer of 4 µm of 400 nm TiO particles (Dyesol© paste).
2
2
Prior to the deposition of the TiO paste, the conducting glass substrates were immersed in a solution of
2
TiCl (40 mM) for 30 minutes and then dried. The TiO nanoparticle paste was deposited onto a conducting
4
2
glass substrate using the screen printing technique. The TiO electrodes were gradually heated under an air
2
flow at 325 ºC for 5 min, 375 ºC for 5 min, 450 ºC for 15 min and 500 ºC for 15 min. The heated TiO2
electrodes were immersed again in a solution of TiCl (40 mM) at 70 ºC for 30 min and then washed with
4
ethanol. The electrodes were heated again at 500 ºC for 30 min and cooled before dye adsorption. The active
2
area for devices was 0.16 cm . The counter electrode was made by spreading a 5 mM solution of H PtCl in
2
6
isopropyl alcohol onto a conducting glass substrate containing a small hole to allow the introduction of the
liquid electrolyte using vacuum, followed by heating at 390 ºC for 15 minutes. All films were sensitized in
0
.3 mM dye solutions in dichloromethane for 2 hours at room temperature (optimized dye loading
conditions). The sensitized electrodes were washed with dichloromethane and dried under air. Finally, the
working and counter electrodes were sandwiched together using a thin thermoplastic (Surlyn) frame that
melts at 100 ºC. Electrolyte LP1 was used: consisted of 0.5 M 1-butyl-3-methylimidazolium iodide (BMII),
0
.1 M lithium iodide, 0.05 M iodine and 0.5 M tert-butylpyridine in acetonitrile.
The J/V curves of the cells were measured using a Sun 2000 solar simulator equipped with a 150W xenon
−
2
lamp. The illumination intensity was measured to be 100 mW cm with a calibrated silicon photodiode. The
appropriate filters were utilized to faithfully simulate the AM 1.5G spectrum. The applied potential and cell
current were measured using a Keithley 2400 digital source meter. The IPCE (incident photon to current
conversion efficiency) was measured using a home-made set up consisting of a 150 W Oriel xenon lamp, a
motorized monochromator and a Keithley 2400 digital source meter.
Transient photovoltage (TPV) and charge extraction (CE) measurements were carried out alike reported
36
before. In CE measurements, white light from a series of LEDs was used as the light source. When the
LEDs are turned off, the cell is immediately short-circuited and the charge is extracted allowing the electron
density in the cells to be calculated. By changing the intensity of the LEDs, the electron density can be
estimated as a function of cell voltage. In TPV measurements, in addition to the white light applied by the
LEDS, a diode pulse (660 nm, 10 mW) is applied to the sample inducing a change of 2–3 mV within the cell.
The resulting photovoltage decay transients are collected and the τ values are determined by fitting the data
to the equation exp(−t/τ).
2
.4. Computational details
3
7
Density Functional Theory (DFT) calculations were performed using Gaussian 09 with the ultrafine
integration grid. Solvent effects were estimated using a Conductor-like Polarizable Continuum Model
38, 39
(
CPCM).
Equilibrium geometries were optimized using the M06-2x hybrid meta-GGA exchange

ACCEPTED MANUSCRIPT
4
0
41
correlation functional and the medium size 6-31G* base. Ground state geometries were characterized as
minima by frequency calculations. Excitation energies were calculated by time-dependent single point
calculations using the M06-2x/6-311+G (2d,p) model chemistry. Absorption spectra were estimated through
the calculation of vertical excitations at the ground state geometry and emission spectra, through the
calculation of vertical excitations at the excited state geometry. Due to the large computational cost required
to calculate excited state vibrational energies, E0-0 were approached to adiabatic excitation energies (EAdia).
Ground state oxidation potentials (E ) were calculated using the M06-2x/6-311+G (2d,p) energies and
OX
calculating the thermal corrections to Gibbs free energy at the M06-2x/6-31G* level. Excited state oxidation
potentials (E* ) were estimated substracting E from Eox.
Molecular Orbital contour plots were obtained using the Avogadro software at 0.04 isosurface value.
OX
0-0
4
2
3
.
Results and discussion
3.1. Synthesis
The target compounds 1, 2, and 3 were prepared via condensation of the corresponding aldehyde
derivative (7, 10, 14) and cyanoacetic acid in the presence of piperidine (Scheme 1).
Scheme 1. Synthesis of dyes 1−3

ACCEPTED MANUSCRIPT
Scheme 2. Synthesis of aldehydes 7, 10
Aldehydes 7 and 10 were synthesized by a Wittig-Horner or Wittig reaction of the diphenylphosphine
43
44
45
oxide 5 or the phosphonium salt 8 with aldehyde 4, followed by lithiation of the resulting intermediates
6
1
1
and 9 and reaction with anhydrous DMF (Scheme 2). A different approach was adopted for the aldehyde
4
6
4 (Scheme 3) which was prepared through a Stille reaction between the stannane 12 and the compound
4
7
1, followed by lithiation and formylation with DMF.
Scheme 3. Synthesis of aldehyde 14
3
.2. Optical properties
-5
The absorption spectra of the synthesized dyes were studied in 10 M CH Cl solution (Fig. 3) and the
2
2
relevant optical data are listed in Table 1. Two absorption bands can be observed for all dyes, one between
00−400 nm assigned to a π−π* transition and the main band between 400−700 nm due to the ICT among
3
the donor and the acceptor units. The inclusion of a proaromatic donor like 4H-pyranylidene or dithiafulvene
results in a red-shift of the absorption when compared to the triarylamine dye. The molar extinction
coefficients of the dyes increase in the order triarylamine < 4H-pyranylidene < dithiafulvene, being for the
-1
-1
last one 37108 M cm . When the dyes are attached to TiO surface, they present broader bands than in
2
solution and the maximum absorption peaks are around 30 nm blue-shifted. In general, the blue shifts of the
absorption spectra on TiO are ascribed to the deprotonation of the carboxylic acid when anchored on the
2
4
8
titanium surface and/or to the formation of H-aggregates.

ACCEPTED MANUSCRIPT
0
0
0
0
0
.4
.3
.2
.1
.0
(
(
(
1)
2)
3)
3
00
400
500
600
700
800
Wavelenght (nm)
Fig. 3. Normalized UV-vis absorption of compounds 1−3
Table 1. Optical and electrochemical properties of dyes 1−3.
d
e
*
f
dye
λab s- , nm
λabs
(nm)
522
518
432
λem c
(nm)
659
630
611
b
Eox
E0-0
E
ox
1
-1 a
b
V (vs. NHE)
(eV)
V (vs. NHE)
(ε, M cm )
1
2
3
570 (30370)
568 (37108)
460 (23958)
0.87
0.93
1.22
1.97
2.06
2.29
−1.10
−1.12
−1.08
a
c
Absorption maxima in CH Cl solution. Absorption maxima on TiO films. Emission spectra
were recorded in CH Cl . First oxidation potentials were measured from three electrode
2
2
2
d
2
2
electrochemical cell in CH Cl containing 0.1 M TBAPF . A glassy carbon, Ag/AgCl (KCl 3M),
2
2
6
e
and Pt were used as working, reference, and counter electrode respectively. Zeroth-zeroth
transition energies estimated from the intersection of normalized absorption and emission spectra
in CH Cl solution. Excited-state oxidation potentials of the dyes obtained from E – E0-0.
f
2
2
ox
3
.3. Electrochemical Properties
The oxidation potential (E ) of each dye was determined in solution by differential pulse voltammetry
ox
*
(
DPV) methods. E ox was estimated from E −E (Table 1, see also energy diagram shown in SI Figure
ox
0-0
S-33).
The donor unit affects significantly the oxidation potential values, with an increase on the ease of
oxidation in the order 3 < 2 < 1, pointing to the superior donor ability of the 4H-pyranylidene moiety. The
regeneration of the oxidized dye after electron injection into the conduction band of TiO is guaranteed in all
2
cases, as the E values are more positive than the potential of the iodide/triiodide redox couple (+0.42 vs
ox
NHE), indicating that the oxidized dyes formed after the electron injection into the TiO electrode could
2
-
thermodynamically accept electrons from I ions.
The resulting E * values for all the dyes were almost similar and sufficiently more negative than the
ox
energy conduction band edge energy level of TiO (−0.5 V vs NHE), indicating an efficient injection of
2
electrons into the TiO from the excited dyes.
2
3
.4. Photovoltaic properties of DSSCs
The device performance (with an effective area of 0.16 cm ) were measured under sun-simulated AM 1.5
2
2
G irradiation (100 mW/cm ). The optimized conditions for these dyes are determined to be 0.3 mM of dye in
dichloromethane solution, 2 h of immersion and LP1 (0.5 M BMII/ 0.05M I / 0.5M TBP/ 0.1M LiI in
2
acetonitrile) as electrolyte. The relevant photovoltaic parameters V , J , ff, and solar-to-electrical energy
oc
sc

ACCEPTED MANUSCRIPT
conversion efficiencies (
η
) are collected in Table 2. Moreover, current density-voltage (J-V) curves and
incident photon- to- current conversion efficiencies (IPCE) of devices based on these dyes are represented in
Fig. 4.
Table 2. Photovoltaic properties of DSSCs constructed using the dyes 1−3.
-2
dye
J (mA cm )
Voc (V)
0.644
0.609
0.759
ff
η (%)
sc
1
2
3
11.74
6.99
7.26
74
69
74
5.56
2.91
4.09
The IPCE tendencies of these dyes are in accordance with their UV-vis absorption spectra on the TiO2
film. The onset of the IPCE spectra for dyes 1 and 2 are significantly broadened compared with the obtained
for dye 3. These results confirm the higher J value obtained for devices based on dye 1, with a broad and
sc
roughly constant photoresponse (~ 60%) in the range 450−600 nm. Dye 3 presents a maximum IPCE value
of 93% at 475 nm and the highest V value (0.759V) of all the molecules studied, suggesting a decrease in
oc
the charge recombination processes for this molecule. However, its J is 60% lower than obtained for
sc
compound 1, probably due to the narrower IPCE observed band.
Data in Table 2 indicate that the more efficient donor system is the 4H-pyranylidene (η = 5.56%),
followed by the triarylamine system (
η
= 4.09%) and finally the 1,3-dithiole (η = 2.91%).
1
5
0
5
0
5
100
1
1
2
3
80
60
40
-
1
2
3
Dark
Dark
Dark
-10
-15
-20
20
0
0
0,2
0,4
0,6
0,8
400 450 500 550 600 650 700 750 800
Wavelength (nm)
Voltage (V)
Fig. 4. J-V curves of compounds 1−3 (left) and IPCE curves of 1−3 (right)
3
.5. Structural modification of the thiophene ring and physical properties
With the aim of understanding the influence of a different bulky silyl ether group and its
position in the thiophene ring, dyes 15 and 16 were synthesized by a Knoevenagel condensation
of the unreported aldehydes 21 and 23 with 2-cyanoacetic acid (Scheme 4). We have chosen the
pyranylidene system as donor group due to the best results obtained in the previous section.
These precursors were obtained in a three-step synthetic route starting in both cases from
4
9
compound 17. Lithiation conditions (base and solvent) were finely tuned in order to activate

ACCEPTED MANUSCRIPT
position 2 (tert-BuLi, Et O) or position 5 (BuLi, THF) (Scheme 5). Finally, compounds 18 and
2
1
9 were obtained by reaction of the organolithium intermediates with DMF. Next, a Horner
reaction of diphenylphosphine oxide 5 with 18 or 19 afforded the corresponding pyranylidene-
thiophene derivatives 20 and 22, which by lithiation and reaction with DMF yielded final
aldehydes 21 and 23 respectively (Scheme 6).
Scheme 4. Synthesis of dyes 15, 16
Scheme 5. Synthesis of thiophene-aldehydes 18, 19
Scheme 6. Synthesis of aldehydes 21, 23
The substitution of a TBDMS group (1) by a tert-butyldiphenylsilyl (TBDPS (15)) does not
change significantly the maximum absorption peak (570 nm for 1 and 573 nm for 15). By
contrast, the molar extinction coefficient (
(
ε
) is enhanced on passing from TBDMS to TBDPS
30370 M cm (1) to 33618 M cm (15)), probably due to the incorporation of two additional
phenyl groups. Moreover, a bigger enhancement of the is found when the silyloxy substituent
-1
-1
-1
-1
ε

ACCEPTED MANUSCRIPT
is located at the position 3 of the thiophene ring instead of the position 4 (from 33618 (15) to
-1
-1
3
9963 M cm (16)).
Regarding the electrochemical properties, it has to be pointed that the E values for systems
ox
1
, 15 and 16 are very similar (+0.87, +0.90, and +0.88V respectively, measured in conditions
indicated in Table 1) and hence, the influence of the bulky substituent and its position is fairly
null (See SI Figure S-34).
We have tested the photovoltaic response of dyes 15 and 16 (Figure 5) in DSSCs and their
results were compared with those of compound 1 (Table 3). The substitution of a TBDMS
group (1) by the bulkier group (TBDPS) (15) improve slightly the efficiency (from 5.56% to
5
.86%), mostly due to a better value of the V for the last one. This result suggests that a
oc
TBDPS group retards the recombination of TiO conduction band electrons with the electrolyte
2
as it has been shown from charge extraction and transient photovoltage experiments (see
50
below).
The influence of the position of the silyl ether group was also studied and we have found that
the solar cell based on dye 16 (with a higher molecular extinction coefficient) shows an
efficiency of 3.42%, 42% lower that obtained for dye 15. The decrease in the efficiency is
mainly due to a lower J and V , to a lesser extent. The remarkable decrease of J was
sc
oc
sc
attributed to the lower injection efficiency, probably affected by the amount of dye absorbed to
the TiO surface.
2
Desorption experiments (0.1M NaOH, EtOH:H O (1:1)) determined that dye 16 is less
2
2
2
adsorbed (106 nmol/cm ) than dye 15 (140 nmol/cm ) and this observation was attributed to the
steric hindrance of the TBDPS group which is closer to the anchor group. Moreover, a lower
-
amount of dye absorbed could result in higher I concentration in the interface TiO /electrolyte,
3
2
increasing the recombination processes.
Table 3. Photovoltaic properties of DSSCs constructed using the dyes 1, 15 and 16
-2
dye
1
J (mA cm )
Voc (V)
0.644
0.689
0.624
ff
η (%)
sc
11.74
11.44
7.71
74
74
71
5.56
5.86
3.42
1
1
5
6
1
5
0
5
0
5
1
-
1
-10
-15
-20
15
1
6
Dark
Dark
Dark
0
0.2
0.4
Voltage (V)
0.6
0.8
Fig. 5- J-V curves of compounds 1, 15 and 16

ACCEPTED MANUSCRIPT
Figure 6 illustrates the charge density (charge accumulated at the device under different light
bias) and the charge lifetime at a given charge. As it can be seen, the solar cells made using dye
1
5 have the slowest charge recombination under working conditions. Moreover, it is worthy to
mention that a shift on the measured charge vs voltage is observed for the solar cells made using
dye 16. This shift can be attributed to the lower coverage of dyes at the surface of the TiO2,
which has as a consequence the lower concentration of protons at the surface of the TiO . In
2
fact, this is also in good agreement with the lower photocurrent measured.
1
1
1
1
1
1
1
1
8
8
8
8
7
7
7
7
0,1
0,01
,001
1
1
1
,6 x 10
,4 x 10
,2 x 10
1
15
1
1
1
16
5
6
1
8
6
4
2
x 10
x 10
x 10
x 10
x 10
0
0
1e+17
1e+18
1e+19
0
0,1 0,2 0,3 0,4 0,5 0,6 0,7
Voc_CH (V)
-
-
3
e density(e /cm )
Fig. 6- Charge Extraction (left) and Transient Photovoltage (right) curves of compounds 1, 15 and 16
3
.6. Theoretical calculations
The electronic structures of the new synthesized compounds have been studied using density
functional theory methods and the most relevant parameters derived from these calculations are
gathered in table 4. There is a good agreement with the experimental values described above,
with estimated error of less than 0.25 eV in the excitation energies, less than 0.1 V in EOX and
*
less than 0.2 V in E OX.
Table 4. Results of DFT Calculations.
a
*
EHOMO
ELUMO
(eV)
λAbs
(nm)
f
λem
E0-0
EOX
E
OX
(
eV)
(nm) (eV) V (vs. NHE) V (vs. NHE)
1
2
3
−6.38
−6.38
−6.58
−6.39
−6.40
−2.29
−2.13
−2.11
−2.30
−2.33
558 1.24
528 1.00
431 1.23
559 1.23
564 1.25
666
605
565
666
663
2.03
2.18
2.50
2.03
2.03
0.95
1.00
1.24
0.93
0.95
−1.08
−1.18
−1.26
−1.10
−1.08
1
5
6
1
a
Oscillator strength
Calculations describe the first excited state as the consequence of a one-electron transition
from the HOMO to the LUMO (see Figure 7). Excitation involves some charge transfer from
the donor to the cyanoacetic acid acceptor, with a large HOMO-LUMO overlap that gives rise
to large oscillator strengths and therefore to great molar extinction coefficients.

ACCEPTED MANUSCRIPT
Figure 7. HOMO (left) and LUMO (right) for compound 15.
Unfortunately, a direct correlation between the oscillator strengths (proportional to the peak
area) and the molar extinction coefficients (related to peak height) is not possible for
compounds giving rise to absorption bands of different width. Thus, compound 2 having the
largest
ε gives rise to the narrowest absorption band and also the lowest f.
4
H-pyranylidene compounds 1, 15 and 16 display similar HOMO and LUMO energies and
therefore their excitation energies and oxidation potentials are also similar. Compound 2, with a
weak donor group has a lower HOMO energy compared to the other studied dyes and, therefore,
displays higher excitation energies and EOX.
Conclusions
A series of five new metal free sensitizers (D-π-A) for DSSC with a trialkylsilyl ether group
in the spacer have been synthesized and characterized. Several donor unities have been studied,
obtaining the best performances with 4H-pyranylidene, followed by triphenylamine (TPA) and
dithiafulvene moieties respectively. Two trialkylsilyl ether groups (TBDMS and TBDPS) were
compared in order to study the influence of their molecular size in the photovoltaic properties.
The best efficiencies values were obtained for a TBDPS group at the position 4 of the thiophene
ring. This observation indicates that trialkylsilyl ethers can be promising substituents for future
more efficient sensitizers.
Acknowledgements
We gratefully acknowledge the financial support from the Spanish Ministry of Science
and Innovation, MICINN-FEDER (project CTQ2011-22727), MINECO (project
CTQ2014-52331-R) and the Gobierno de Aragón-Fondo Social Europeo (E39). A
predoctoral fellowship to R. Pérez-Tejada (CSIC, JAE 2011) is also acknowledged. The
authors thank Prof. Emilio Palomares for the use of the equipment at ICIQ and the
helpful comments on the results. Dr. Laia Pellejà thanks MICINN for the Severo Ochoa
Excellence Accreditation 2014.2018 (SEV-2013-0319).
Appendix. Supplementary material
Supplementary data associated with this article can be found, in the online version at

ACCEPTED MANUSCRIPT
References
1.
2.
3.
4.
5.
Ragoussi, M.-E.; Torres, T., New generation solar cells: concepts, trends and perspectives.
Chem. Commun. 2015, 51, 3957-3972.
Huang, Y.; Kramer, E. J.; Heeger, A. J.; Bazan, G. C., Bulk Heterojunction Solar Cells:
Morphology and Performance Relationships. Chem. Rev. 2014, 114, 7006-7043.
Hagfeldt, A.; Boschloo, G.; Sun, L. C.; Kloo, L.; Pettersson, H., Dye-Sensitized Solar
Cells. Chem. Rev. 2010, 110, 6595-6663.
Hardin, B. E.; Snaith, H. J.; McGehee, M. D., The renaissance of dye-sensitized solar cells.
Nature Photon. 2012, 6, 162-169.
Mishra, A.; Fischer, M. K. R.; Bäuerle, P., Metal-Free Organic Dyes for Dye-Sensitized
Solar Cells: From Structure: Property Relationships to Design Rules. Angew. Chem., Int.
Ed. 2009, 48, 2474-2499.
6.
7.
8.
Ning, Z. J.; Tian, H., Triarylamine: a promising core unit for efficient photovoltaic
materials. Chem. Commun. 2009, 5483-5495.
Liang, M.; Chen, J., Arylamine organic dyes for dye-sensitized solar cells. Chem. Soc. Rev.
2
013, 42, 3453-3488.
Tang, J.; Hua, J.; Wu, W.; Li, J.; Jin, Z.; Long, Y.; Tian, H., New starburst sensitizer with
carbazole antennas for efficient and stable dye-sensitized solar cells. Energy Environ. Sci.
2
010, 3, 1736-1745.
9
1
1
1
1
.
Liang, M.; Lu, M.; Wang, Q.-L.; Chen, W.-Y.; Han, H.-Y.; Sun, Z.; Xue, S., Efficient dye-
sensitized solar cells with triarylamine organic dyes featuring functionalized-truxene unit.
J. Power Sources 2011, 196, 1657-1664.
0. Cai, S.; Hu, X.; Zhang, Z.; Su, J.; Li, X.; Islam, A.; Han, L.; Tian, H., Rigid triarylamine-
based efficient DSSC sensitizers with high molar extinction coefficients. J. Mater. Chem. A
2
013, 1, 4763-4772.
1. Bonnier, C.; Machin, D. D.; Abdi, O. K.; Robson, K. C. D.; Koivisto, B. D., The effect of
donor-modification in organic light-harvesting motifs: triphenylamine donors appended
with polymerizable thienyl subunits. Org. Biomol. Chem. 2013, 11, 7011-7015.
2. Wang, Z.; Liang, M.; Wang, H.; Wang, P.; Cheng, F.; Sun, Z.; Song, X., Joint Electrical,
Photophysical, and Photovoltaic Studies on Truxene Dye-Sensitized Solar Cells: Impact of
Arylamine Electron Donors. ChemSusChem 2014, 7, 795-803.
3. Kim, S. H.; Choi, J.; Sakong, C.; Namgoong, J. W.; Lee, W.; Kim, D. H.; Kim, B.; Ko, M.
J.; Kim, J. P., The effect of the number, position, and shape of methoxy groups in
triphenylamine donors on the performance of dye-sensitized solar cells. Dyes Pigm. 2015,
1
13, 390-401.
1
1
1
1
4. Franco, S.; Garín, J.; Martínez de Baroja, N.; Pérez-Tejada, R.; Orduna, J.; Yu, Y.; Lira-
Cantú, M., New D−π–A-Conjugated Organic Sensitizers Based on 4H-Pyran-4-ylidene
Donors for Highly Efficient Dye-Sensitized Solar Cells. Org. Lett. 2012, 14, 752-755.
5. Pérez-Tejada, R.; Pellejà, L.; Palomares, E.; Franco, S.; Orduna, J.; Garín, J.; Andreu, R.,
Novel 4H-pyranylidene organic dyes for dye-sensitized solar cells: Effect of different
heteroaromatic rings on the photovoltaic properties. Org. Electron. 2014, 15, 3237-3250.
6. Bolag, A.; Nishida, J.-i.; Hara, K.; Yamashita, Y., Enhanced performance of dye-sensitized
solar cells with novel 2,6-diphenyl-4H-pyranylidene dyes. Org. Electron. 2012, 13, 425-
4
31.
7. Gauthier, S.; Caro, B.; Robin-Le Guen, F.; Bhuvanesh, N.; Gladysz, J. A.; Wojcik, L.; Le
Poul, N.; Planchat, A.; Pellegrin, Y.; Blart, E.; Jacquemin, D.; Odobel, F., Synthesis,
photovoltaic performances and TD-DFT modeling of push-pull diacetylide platinum
complexes in TiO2 based dye-sensitized solar cells. Dalton Trans. 2014, 43, 11233-11242.
8. Guo, K.; Yan, K.; Lu, X.; Qiu, Y.; Liu, Z.; Sun, J.; Yan, F.; Guo, W.; Yang, S.,
Dithiafulvenyl Unit as a New Donor for High-Efficiency Dye-Sensitized Solar Cells:
Synthesis and Demonstration of a Family of Metal-Free Organic Sensitizers. Org. Lett.
1
2
012, 14, 2214-2217.

ACCEPTED MANUSCRIPT
1
2
2
2
2
2
2
2
9. Wan, Z.; Jia, C.; Duan, Y.; Chen, X.; Lin, Y.; Shi, Y., Novel organic dye employing
dithiafulvenyl-substituted arylamine hybrid donor unit for dye-sensitized solar cells. Org.
Electron. 2013, 14, 2132-2138.
0. Wan, Z.; Jia, C.; Duan, Y.; Chen, X.; Li, Z.; Lin, Y., Novel organic sensitizers containing
dithiafulvenyl units as additional donors for efficient dye-sensitized solar cells. RSC Adv.
2
014, 4, 34896-34903.
1. Hara, K.; Dan-oh, Y.; Kasada, C.; Ohga, Y.; Shinpo, A.; Suga, S.; Sayama, K.; Arakawa,
H., Effect of Additives on the Photovoltaic Performance of Coumarin-Dye-Sensitized
Nanocrystalline TiO2 Solar Cells. Langmuir 2004, 20, 4205-4210.
2. Ren, X. M.; Feng, Q. Y.; Zhou, G.; Huang, C. H.; Wang, Z. S., Effect of Cations in
Coadsorbate on Charge Recombination and Conduction Band Edge Movement in Dye-
Sensitized Solar Cells. J. Phys. Chem. C 2010, 114, 7190-7195.
3. Choi, H.; Baik, C.; Kang, S. O.; Ko, J.; Kang, M. S.; Nazeeruddin, M. K.; Gratzel, M.,
Highly efficient and thermally stable organic sensitizers for solvent-free dye-sensitized
solar cells. Angew. Chem., Int. Ed. 2008, 47, 327-330.
4. Xu, M.; Zhang, M.; Pastore, M.; Li, R.; De Angelis, F.; Wang, P., Joint electrical,
photophysical and computational studies on D-pi-A dye sensitized solar cells: the impacts
of dithiophene rigidification. Chem. Sci. 2012, 3, 976-983.
5. Cai, L.; Tsao, H. N.; Zhang, W.; Wang, L.; Xue, Z.; Gratzel, M.; Liu, B., Organic
sensitizers with bridged triphenylamine donor units for efficient dye-sensitized solar cells.
Adv. Energy Mater. 2013, 3, 200-205.
6. Shi, J.; Chai, Z.; Zhong, C.; Wu, W.; Hua, J.; Dong, Y.; Qin, J.; Li, Q.; Li, Z., New
efficient dyes containing tert-butyl in donor for dye-sensitized solar cells. Dyes Pigm.
2
012, 95, 244-251.
2
7. Zhan, X.; Barlow, S.; Marder, S. R., Substituent effects on the electronic structure of
siloles. Chem. Commun. 2009, 1948-1955.
2
8. Lu, G.; Usta, H.; Risko, C.; Wang, L.; Facchetti, A.; Ratner, M. A.; Marks, T. J., Synthesis,
Characterization, and Transistor Response of Semiconducting Silole Polymers with
Substantial Hole Mobility and Air Stability. Experiment and Theory. J. Am. Chem. Soc.
2
008, 130, 7670-7685.
2
3
3
9. Akhtaruzzaman, M.; Seya, Y.; Asao, N.; Islam, A.; Kwon, E.; El-Shafei, A.; Han, L.;
Yamamoto, Y., Donor-acceptor dyes incorporating a stable dibenzosilole π-conjugated
spacer for dye-sensitized solar cells. J. Mater. Chem. 2012, 22, 10771-10778.
0. Ko, S.; Choi, H.; Kang, M. S.; Hwang, H.; Ji, H.; Kim, J.; Ko, J.; Kang, Y., Silole-spaced
triarylamine derivatives as highly efficient organic sensitizers in dye-sensitized solar cells
(
DSSCs). J. Mater. Chem. 2010, 20, 2391-2399.
1. Lin, L. Y.; Tsai, C. H.; Wong, K. T.; Huang, T. W.; Hsieh, L.; Liu, S. H.; Lin, H. W.; Wu,
C. C.; Chou, S. H.; Chen, S. H.; Tsai, A. I., Organic Dyes Containing Coplanar Diphenyl-
Substituted Dithienosilole Core for Efficient Dye-Sensitized Solar Cells. J. Org. Chem.
2
010, 75, 4778-4785.
3
2. Zeng, W. D.; Cao, Y. M.; Bai, Y.; Wang, Y. H.; Shi, Y. S.; Zhang, M.; Wang, F. F.; Pan,
C. Y.; Wang, P., Efficient Dye-Sensitized Solar Cells with an Organic Photosensitizer
Featuring Orderly Conjugated Ethylenedioxythiophene and Dithienosilole Blocks. Chem.
Mater. 2010, 22, 1915-1925.
3
3. Minaev, B. F.; Baryshnikov, G. V.; Minaeva, V. A., Electronic structure and spectral
properties of the triarylamine-dithienosilole dyes for efficient organic solar cells. Dyes
Pigm. 2012, 92, 531-536.
3
4. Park, J.; Lee, E.; Kim, J.; Kang, Y., Dithienosilole based organic sensitizers for efficient
dye-sensitized solar cells. Bull. Korean Chem. Soc. 2013, 34, 979-982.
3
5. Wuts, P. G. M.; Greene, T. W., Protection for the Hydroxyl Group, Including 1,2- and 1,3-
Diols. In Greene's Protective Groups in Organic Synthesis, John Wiley & Sons, Inc.2006
th
(
4 Ed).
3
6. Zewdu, T.; Clifford, J. N.; Hernandez, J. P.; Palomares, E., Photo-induced charge transfer
dynamics in efficient TiO2/CdS/CdSe sensitized solar cells. Energy Environ. Sci. 2011, 4,
4
633-4638.

ACCEPTED MANUSCRIPT
3
7. Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J.
R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.;
Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada,
M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.;
Kitao, O.; Nakai, H.; Vreven, T.; Montgomery Jr., J. A.; Peralta, J. E.; Ogliaro, F.;
Bearpark, M. J.; Heyd, J.; Brothers, E. N.; Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.;
Normand, J.; Raghavachari, K.; Rendell, A. P.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.;
Cossi, M.; Rega, N.; Millam, N. J.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.;
Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.;
Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V.
G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, Ö.;
Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09, Gaussian 09 Revision
A.02: Gaussian, Inc.: Wallingford, CT, USA, 2009.
3
8. Barone, V.; Cossi, M., Quantum Calculation of Molecular Energies and Energy Gradients
in Solution by a Conductor Solvent Model. J. Phys. Chem. A 1998, 102, 1995-2001.
9. Cossi, M.; Rega, N.; Scalmani, G.; Barone, V., Energies, structures, and electronic
properties of molecules in solution with the C-PCM solvation model. J. Comput. Chem.
3
2
003, 24, 669-681.
4
0. Zhao, Y.; Truhlar, D. G., The M06 suite of density functionals for main group
thermochemistry, thermochemical kinetics, noncovalent interactions, excited states, and
transition elements: two new functionals and systematic testing of four M06-class
functionals and 12 other functionals. Theor. Chem. Acc. 2008, 120, 215-241.
1. Hariharan, P. C.; Pople, J. A., Influence of polarization functions on MO hydrogenation
energies. Theor. Chim. Acta 1973, 28, 213-22.
4
4
2. Hanwell, M. D.; Curtis, D. E.; Lonie, D. C.; Vandermeersch, T.; Zurek, E.; Hutchison, G.
R., Avogadro: an advanced semantic chemical editor, visualization, and analysis platform.
J. Cheminf. 2012, 4, 17.
4
4
4
3. Abaev, V. T.; Karsanov, I. V.; Urtaeva, Z. K.; Blinokhvatov, A. F.; Bumber, A. A.;
Okhlobystin, O. Y., Preparation and properties of (4H-pyran-4-yl)diphenylphosphine
oxides. Zh. Obshch. Khim. 1990, 60, 1012-19.
4. Andreu, R.; Cerdán, M. A.; Franco, S.; Garín, J.; Marco, A. B.; Orduna, J.; Palomas, D.;
Villacampa, B.; Alicante, R.; Allain, M., Decreased Optical Nonlinearities upon CF3
Substitution on Tricyanofuran Acceptors. Org. Lett. 2008, 10, 4963-4966.
5. Posner, G. H.; Li, Z.; White, M. C.; Vinader, V.; Takeuchi, K.; Guggino, S. E.; Dolan, P.;
Kensler, T. W., 1α,25-Dihydroxyvitamin D3 Analogs Featuring Aromatic and
Heteroaromatic Rings: Design, Synthesis, and Preliminary Biological Testing. J. Med.
Chem. 1995, 38, 4529-37.
4
6. Leliège, A.; Le Regent, C.-H.; Allain, M.; Blanchard, P.; Roncali, J., Structural modulation
of internal charge transfer in small molecular donors for organic solar cells. Chem.
Commun. 2012, 48, 8907-8909.
4
4
4
7. Jen, K.-Y.; Ma, H.; Liu, S.; Dalton, L. R. Nonlinear optical compounds and methods for
their preparation. US20040135130A1, 2004.
8. Eisfeld, A.; Briggs, J. S., The J- and H-bands of organic dye aggregates. Chem. Phys. 2006,
3
24, 376-384.
9. Khatuya, H.; Pulito, V. L.; Jolliffe, L. K.; Li, X.; Murray, W. V., Novel thiophene
derivatives for the treatment of benign prostatic hyperplasia. Bioorg. Med. Chem. Lett.
2
002, 12, 2145-2148.
5
0. Mori, S. N.; Kubo, W.; Kanzaki, T.; Masaki, N.; Wada, Y.; Yanagida, S., Investigation of
the Effect of Alkyl Chain Length on Charge Transfer at TiO2/Dye/Electrolyte Interface. J.
Phys. Chem. C 2007, 111, 3522-3527.

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Synthesis and characterization of organic sensitizers with a trialkylsilyloxy group on the
π-spacer
DSSC efficiency was highly dependent on the size and position of the silyloxy group
Best efficiencies were obtained with the 4H-pyranylidene, followed by TPA and dithiafulvene
systems

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Organic sensitizers bearing a trialkylsilylether group for liquid dye
sensitized solar cells
a
a
a
b
Raquel Pérez-Tejada , Natalia Martínez de Baroja , Santiago Franco* , Laia Pellejà* ,
a
a
a
Jesús Orduna , Raquel Andreu , Javier Garín ,
a
Departamento de Química Orgánica-Instituto de Ciencia de Materiales de Aragón (ICMA), Universidad de
Zaragoza-CSIC, E-50009 Zaragoza, Spain.
b
Institute of Chemical Research of Catalonia ( ICIQ). Avda. Països Catalans, 16. Tarragona. E-43007.
Spain.
*
Corresponding author. Tel.: +34 976762283; E-mail address: sfranco@unizar.es
TABLE OF CONTENTS
General experimental methods
page S2
page S2
page S3
page S4
page S5
page S6
page S7
page S9
page S10
page S11
page S13
page S14
page S15
page S16
page S17
page S18
Figures S-1 to S-2 (NMR spectra of compound 7)
Figures S-3 to S-4 (NMR spectra of compound 10)
Figures S-5 to S-6 (NMR spectra of compound 13)
Figures S-7 to S-8 (NMR spectra of compound 14)
Figures S-9 to S-10 (NMR spectra of compound 1)
Figures S-11 to S-13 (NMR spectra of compound 2)
Figures S-14 to S-15 (NMR spectra of compound 3)
Figures S-16 to S-18 (NMR spectra of compound 18)
Figures S-19 to S-21 (NMR spectra of compound 19)
Figures S-22 to S-23 (NMR spectra of compound 21)
Figures S-24 to S-25 (NMR spectra of compound 23)
Figures S-26 to S-28 (NMR spectra of compound 15)
Figures S-29 to S-30 (NMR spectra of compound 16)
Figures S-31 (Normalized UV-vis absorption of compounds 1-3)
Figures S-32 (Normalized UV-vis absorption of compounds 1, 15 and 16)
Figures S-33 (Energy diagram of compounds 1-3)
Figures S-34 (Energy diagram of compounds 1, 15 and 16)
Calculated molecular geometries and energies
page S18
page S19
page S20
S1

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General Experimental Methods:
Infrared measurements were carried out in KBr or neat using a Perkin-Elmer Fourier Transform
Infrared 1600 spectrometer. Melting points were obtained on a Gallenkamp apparatus in open
1
13
capillaries and are uncorrected. H- and C-NMR spectra were recorded on a Bruker ARX300 or a
Bruker AV400 at 300 or 400 MHz and 75 or 100 MHz respectively; δ values are given in ppm
(relative to TMS) and J values in Hz. The apparent resonance multiplicity is described as s (singlet),
1
1
1
13
d (doublet), and m (multiplet). H- H COSY and H- C-HSQC experiments were recorded on a
Bruker ARX300 or a Bruker AV400 at 300 or 400 MHz in order to establish peaks assignment and
spatial relationships. Electrospray mass spectra were recorded on a Bruker Q-ToF spectrometer;
accurate mass measurements were achieved using sodium formate as external reference. UV-
Visible spectra were recorded with an UV-Vis UNICAM UV4 spectrophotometer. Pulse differential
voltammetry measurements were performed with a µ-Autolab type III potentiostat using a glassy
carbon working electrode, Pt counter electrode, and Ag/AgCl reference electrode. The experiments
-1
were carried out under argon in CH Cl , with Bu NPF as supporting electrolyte (0.1 mol L ). Scan
2
2
4
6
-1
-1
rate was 0.01V s , modulation amplitude 0.025V and modulation time 0.05 s .
10.0
5.0
0.0
ppm (f1)
1
Figure S-1: H NMR spectrum of compound 7 (400 MHz, CDCl ).
3
S2

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150
100
50
0
ppm (f1)
1
3
Figure S-2: C NMR (APT) spectrum of compound 7 (100 MHz, CDCl ).
3
1
0.0
5.0
0.0
ppm (t1)
1
Figure S-3: H NMR spectrum of compound 10 (400 MHz, CDCl ).
3
S3

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1
50
100
50
0
ppm (t1)
1
3
Figure S-4: C NMR (APT) spectrum of compound 10 (100 MHz, CDCl ).
3
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
ppm (f1)
1
Figure S-5: H NMR spectrum of compound 13 (300 MHz, CD Cl ).
2
2
S4

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150
100
50
0
ppm (f1)
1
3
Figure S-6: C NMR (APT) spectrum of compound 13 (100 MHz, CD Cl ).
2
2
5.0
0.0
ppm (f1)
1
Figure S-7: H NMR spectrum of compound 14 (400 MHz, CD Cl ).
2
2
S5

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1
50
100
50
0
ppm (t1)
1
3
Figure S-8: C NMR (APT) spectrum of compound 14 (100 MHz, CD Cl ).
2
2
8
.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
ppm (f1)
1
Figure S-9: H NMR spectrum of compound 1 (400 MHz, dmso-d ).
6
S6

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150
100
50
0
ppm (f1)
1
3
Figure S-10: C NMR (APT) spectrum of compound 1 (75 MHz, dmso-d ).
6
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
ppm (t1)
1
Figure S-11: H NMR spectrum of compound 2 (300 MHz, CDCl ).
3
S7

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150
100
50
0
ppm (t1)
1
3
Figure S-12: C NMR (APT) spectrum of compound 2 (75 MHz, CDCl ).
3
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
ppm (t2)
1
13
Figure S-13 H- C HSQC spectrum of compound 2.
S8