Synthesis of Silatrane-Containing Organic Sensitizers as Precursors for the Silyloxyl Anchoring Group in Dye-Sensitized Solar Cells

Article abstract of DOI:10.1055/s-0036-1588836

A series of organic D-π-A dyes, endowed with different silicon-based anchoring groups, has been prepared to assess the stability of such anchoring moieties on nanocrystalline TiO ₂ in dye-sensitized solar cells. Due to the difficulties encountered in finding a reliable and robust preparation protocol to obtain pure trialkoxysilanes, replacement with a silatrane moiety was evaluated. It was found that the silatrane group could be easily introduced on three different molecular scaffolds by using a simple amide coupling reaction mediated by EDC-Cl. Furthermore, the spectroscopic properties and anchoring mode on nanocrystalline TiO ₂ of the silatrane dyes were found to be nearly identical to those of the trialkoxysilane compounds, and both gave a much more stable attachment to the semiconductor compared with their cyanoacrylic acid counterpart, as shown by desorption experiments.

Full text of DOI:10.1055/s-0036-1588836

SYNTHESIS
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© Georg Thieme Verlag Stuttgart · New York
2017, 49, A–J
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en
M. Bessi et al.
Paper
Synthesis
Synthesis of Silatrane-Containing Organic Sensitizers as Precur-
sors for the Silyloxyl Anchoring Group in Dye-Sensitized Solar
Cells
Matteo Bessia,b
Marco Moninia
Massimo Calamantea,c
Alessandro Mordinia,c
Adalgisa Sinicropia,b
Riccardo Basosia,b
Mariangela Di Donatoc,d,f
Paolo Foggia,d,e,f
Alessandro Iagattid,f
Lorenzo Zania
Gianna Reginato*a
a Istituto di Chimica dei Composti Organometallici (CNR-ICCOM),
Via Madonna del Piano 10, 50019 Sesto Fiorentino, Italy
gianna.reginato@iccom.cnr.it
b Dipartimento di Biotecnologie, Chimica e Farmacia, Università
degli Studi di Siena, Via A. Moro 2, 53100 Siena, Italy
c Dipartimento di Chimica ‘U. Schiff’, Università degli Studi di
Firenze, Via della Lastruccia 13, 50019 Sesto Fiorentino, Italy
d INO, Istituto Nazionale di OtticaLargo Enrico Fermi 6, 50125
Florence, Italy
e Dipartmento di Chimica, Università degli studi di Perugia, via
Elce di Sotto 8, 06123 Perugia, Italy
f
LENS (European Laboratory for Non-Linear Spectroscopy), Via
N. Carrara 1, 50019 Sesto Fiorentino, Italy
Received: 14.03.2017
Accepted after revision: 28.04.2017
Published online: 07.06.2017
good power conversion efficiencies.1c,2 Most such organic
dyes possess a D-π-A structure, where D is generally a do-
nor group, π represents a conjugated scaffold, and A is an
acceptor group, which is designed to ensure an efficient at-
tachment of the sensitizer to the semiconductor layer
(most often constituted by TiO2). The most frequently used
anchors in DSSCs are cyanoacrylic acid or rhodanine-3-ace-
tic acid fragments; however, many other groups have been
tested such as carboxylate, phosphonate, sulfonate, cate-
chol, and pyridine groups.3 Indeed, the manner in which
the absorbing molecule is immobilized onto the semicon-
ducting metal oxide is crucial to achieve smooth electron
transfer between these two elements and to ensure a good
stability of the final devices; therefore, the search for new
anchors is a critical factor for the development of improved
DSSCs. Among others, a few series of D-π-A sensitizers with
silicon-based anchoring groups have been reported.4,5 Such
dyes, like gem-silanediols S1-4 (see Figure 1), were de-
signed with the aim of conferring increased stability on
dye-sensitized electrodes, due to the strong and especially
stable linkages to TiO2.
DOI: 10.1055/s-0036-1588836; Art ID: ss-2017-z0163-op
Abstract A series of organic D-π-A dyes, endowed with different sili-
con-based anchoring groups, has been prepared to assess the stability
of such anchoring moieties on nanocrystalline TiO2 in dye-sensitized so-
lar cells. Due to the difficulties encountered in finding a reliable and ro-
bust preparation protocol to obtain pure trialkoxysilanes, replacement
with a silatrane moiety was evaluated. It was found that the silatrane
group could be easily introduced on three different molecular scaffolds
by using a simple amide coupling reaction mediated by EDC-Cl. Fur-
thermore, the spectroscopic properties and anchoring mode on nano-
crystalline TiO2 of the silatrane dyes were found to be nearly identical to
those of the trialkoxysilane compounds, and both gave a much more
stable attachment to the semiconductor compared with their cyano-
acrylic acid counterpart, as shown by desorption experiments.
Key words organic dyes, trialkoxysilane, siltarane, UV/Vis spectrosco-
py, ATR-IR, dye-sensitized solar cells
In recent years, dye-sensitized solar cells (DSSCs) have
attracted much attention as an efficient and potentially
low-cost alternative to traditional silicon-based photovolta-
ic cells.1 A large number of metal-free organic dyes have
been employed in such devices, which have often displayed
Unfortunately, photovoltaic cells built using silanediol
dyes S1-4 showed conversion efficiencies much lower than
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2017, 49, A–J

B
M. Bessi et al.
Paper
Synthesis
C5H11C5H11
OH
CN
Si
OH
n
S
COOH
R
R
O
O
S
CN
R = Ph
R = t-Bu
n = 1,2
N
S1–4
COOH
N
R
S
OMe
OMe
N
Si
O
OMe
D5
R = H
MB25
S
DF15 R = OC6H13
N
H
N
CN
4
Figure 2 Reference dyes with a cyanoacrylic anchoring group
C6H13
ADEKA-1
Figure 1 D-π-A sensitizers with silicon-based anchoring groups
(ProDOT) moiety, which, because of electron donation from
the oxygen atoms, is more electron-rich and less aromatic
than a simple thiophene and was therefore anticipated to
alter the optoelectronic properties of the dyes; for example,
inducing a change in the width and intensity of visible light
absorption.11 Finally, in both cases, bulky substituents were
added to try to minimize the aggregation phenomena that
often occurs with this class of molecule, and to improve the
solubility and the photovoltaic performances.
Dyes DF15 and MB25 were then modified by using two
different organosilicon anchoring groups, namely a N-[3-
(trimethoxysilyl)propyl]acetamido group, having an alkyl
chain as the spacer, to obtain dye MM35, and a N-[4-(tri-
alkoxysilyl)phenyl]acetamido group, having an aromatic
ring as spacer, which gave dyes MM62 and MB56 (Figure 3).
those obtained by using the corresponding cyanoacrylic ac-
ids. However, this approach remains very interesting, as
shown in the case of alkoxysilyl derivative ADEKA-1 (Figure
1), in which the organosilicon tether for binding the metal
oxides is connected to the dye through a phenylamide moi-
ety.6 TiO2 photoelectrodes sensitized with ADEKA-1 were
shown to possesses good durability and to produce DSSCs
exceeding 12% power conversion efficiency, by using a
cobalt(III/II) tris(5-chloro-1,10-phenanthroline) complex
([Co(Cl-phen)3]3+/2+) as the redox electrolyte and applying a
hierarchical multi-capping treatment to the photoanode.
An even better efficiency was found when devices were
built in co-sensitization with LEG4 (a carboxy-anchor dye
with triphenylamine electron-donor group).7 Finally, spec-
troscopic and electrochemical studies concerning the fac-
tors affecting the performance of ADEKA-18 have helped to
establish the use of such silyl anchor groups as a very
promising approach.
CN
H
N
RO
S
O
Si(OEt)3
Inspired by these intriguing results, we decided to pre-
pare a series of new organic D-π-A sensitizers endowed
with an organosilicon anchoring group. Also in this case we
decided to introduce the silyloxy group through an amide
bond, to maintain the electron-withdrawing effect of the
cyanoacrylic moiety and ensure a good stability against hy-
drolytic degradation. Preparation of the desired dyes, how-
ever, was not straightforward and this prompted us to in-
vestigate the possibility of using a silatrane as an alterna-
tive. In this paper, we report the synthesis of some new
silyloxy- and silatrane-containing organic sensitizers and
discuss the possibility of using the latter as convenient pre-
cursors of a silyloxy anchoring group, for possible applica-
tion in DSSCs.
Two photosensitizers that are structurally related to the
triphenylamino-thienyl derivative D59 were selected as ref-
erence dyes (Figure 2).
The first dye, DF15, differs from D5 in the presence of
long-chain alkoxide substituents on the triarylamine group,
which was introduced to enhance the electron-donating
properties of the donor.10 In the second dye, MB25, the π-
scaffold was modified with a propylene-dioxythiophene
N
MM35
R = C6H13
OR
CN
H
N
RO
S
O
Si(OEt)3
N
MM62
R = C6H13
OR
H11C5 C5H11
O
O
CN
H
N
S
O
Si(OMe)3
N
MB56
Figure 3 Selected dyes with different organosilicon anchoring groups
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M. Bessi et al.
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Synthesis
The energies and shapes of MM35, MM62, and MB56
frontier molecular orbitals were calculated at the density
functional theory (DFT) level and compared with those
found for dye DF1510 and MB25, respectively (Figure 4).
In line with our expectations, the HOMO of all the com-
pounds was mainly localized on the conjugated scaffold of
the molecules, with a sizeable contribution coming from
the terminal diphenylamino donor groups. In contrast,
whereas with the reference dyes DF15 and MB25 the elec-
tron density of the LUMO is localized on the acceptor
group, which coincides with the linker, in all the silyloxy
dyes MM35, MM62, and MB56, the electron density of the
LUMO is mainly localized on the conjugated scaffold and on
the amide bond, and not on the silyloxy moiety, which is
the actual anchoring group of these compounds.
The bis-pentylpropylene-dioxythiophene (ProDOT)
substituted dye MB25 showed a larger HOMO–LUMO gap
than DF15 (2.45 vs. 2.27 eV), due to the destabilizing effect
of the alkoxide substituents on the triarylamine group,
which increases the energy of the HOMO. This effect leads
to a decrease of the HOMO–LUMO gap since the LUMO en-
ergies remain almost unchanged. A similar behavior is ob-
served comparing dyes MB56 and MM62 (2.45 vs. 2.33 eV).
On the other hand, dyes MB25 and MB56, as well as dyes
MM35 and MM62, display, respectively, equal and very
similar energy difference between frontier orbitals, which
supports the conclusion that the electron-withdrawing ef-
fect of the amide group is very similar to that of the carbox-
ylic acid moiety.
activated by using oxalyl chloride and then reacted with 3-
(triethoxysilyl)propylamine and triethylamine to give dye
MM35 in reasonable yield (Scheme 1). However, in our
hands, the same procedure was less efficient when 4-(tri-
methoxysilyl)aniline was used as the amine, leading to
compound MM62 in very low yield and purity. The use of
different coupling agents such as EDCCl/HOBt or TBTU/NEt3
did not improve the outcome of the reaction. Therefore, we
decided to use a different approach and reacted dye DF15
with 4-iodoaniline using EDCCl/HOBt as coupling agents.
After purification, 4-iodoamide 8 was recovered in good
yield and could be treated with triethoxysilane in the pres-
ence of Pd2(dba)3/JohnPhos catalyst.12 In this way, dye
MM62 was obtained in good yield (Scheme 1), albeit
through a difficult chromatographic purification. Unfortu-
nately, the latter procedure was once again not suitable to
prepare MB56, because, in this case, only the dehalogenat-
ed reaction product could be recovered after the silylation
step. Finally, we prepared dye MB56 in reasonable yields by
transforming 4-(trimethoxysilyl)aniline into the corre-
sponding 4-(trimethoxysilyl)phenylisocyanate, by reaction
in situ with triphosgene,13 and reacting the latter with dye
MB25 in the presence of Hunig’s base (Scheme 1).
Although we succeeded in obtaining the desired dyes,
we were disappointed by the difficulties encountered in
their synthesis and purification, as demonstrated by the
fact that accessing each of them required a different proce-
dure. Such behavior could be due to several factors. For in-
stance, it is known that alkoxysilane derivatives might be
unstable under hydrolytic conditions,14 and in the presence
of water might undergo polycondensation. Furthermore,
the tendency to be absorbed by silica strongly decreases the
yields when purification through silica gel is required, re-
Compounds DF15 and MB25 were prepared by follow-
ing a well-established procedure.10 To form the amide bond,
we initially followed the same procedure reported to pre-
pare compound ADEKA-1;6 thus, compound DF15 was first
Figure 4 Wave function plots and energies of the frontier molecular orbitals (FMOs) of compounds DF15, MB25, MB56, MM35, and MM62
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2017, 49, A–J

D
M. Bessi et al.
Paper
Synthesis
1) (COCl)2, CH2Cl2/DMF, 0 °C
2) (EtO)3Si(CH2)3NH2, CH2Cl2/Et3N, 0 °C, r.t.
OEt
Si
H
N
OEt
DF15
D
S
56%
OEt
O
MM35
I
NH2
EDCCl/HOBT
t-Bu
CH2Cl2, r.t.
70 %
P
t-Bu
HSi(OEt)3, NMP, DIPEA
Pd2dba3 (3 mol%), JohnPhos
H
H
N
N
JohnPhos =
Si(OEt)3
D
D
S
S
78%
O
O
I
8
MM62
X
C5H11C5H11
N
X
NH2
NCO
D =
CO(OCCl3)2
MB25
O
O
THF, DIPEA, 70 °C
CN
THF, DIPEA, r.t.
H
N
46%
D
MB56, X = H
MM62, X = OC6H13
S
O
Si(OMe)3
Si(OMe)3
Si(OMe)3
MB56
Scheme 1 Preparation of trialkoxysilane dyes MM35, MM62, and MB56
ducing the possibility of effectively obtaining pure com-
pounds in good yields.8 In view of these considerations, we
thought that a possible alternative might be to use a sila-
trane precursor to introduce siloxyl linkages to the metal
oxides.
Silatranes are relatively stable in acidic, neutral, and al-
kaline environment,15 can withstand many common syn-
thetic reaction conditions, and are resistant to silica gel
chromatography; nevertheless, they are still capable of be-
ing hydrolyzed on metal oxide surfaces to form strong, wa-
ter-stable, siloxane surface bonds.16 For these reasons, this
moiety has been successfully used for covalent attachment
to metal oxide semiconductor surfaces in the preparation of
heterogenized catalysts17 and, in some cases, for the attach-
ment on TiO2 of tetra-arylporphirin or organometallic
dyes.16,18 However, the use of a silatrane protecting group to
exploit the covalent metal oxide surface attachments of
metal-free organic dyes has not been reported so far.
The silatrane functional group can be introduced with
excellent yields from the simple reaction of trialkoxy sila-
nes with triethanolamine.15,19 Thus, silatrane 919b was ob-
tained in 90%yield by heating 4-(trimethoxysilyl)aniline to
reflux in toluene in the presence of NaOH and then simply
reacted with dyes DF15 and MB25 by using EDC-Cl as cou-
pling agent (Scheme 2). The reaction proceeded much more
cleanly than in the case of the corresponding trialkoxysi-
lane, and the corresponding pure dyes MB96 and MB113
could be easily obtained after flash column chromatogra-
phy in 66 and 43% yield, respectively. Furthermore, the
same approach could be applied to prepare the silatrane
DF15 or MB25 or MK-2
EDC-Cl (1.5 equiv)
CH2Cl2, r.t.
NC
H
N(CH2CH2OH)3
O
N
O
NaOH, toluene, 110 °C
N
H2N
Si
O
O
H2N
Si(OMe)3
Si
O
O
D-π−
N
O
90%
9
MB96, MB113, MB104
C6H13
CN
H
CN
C6H11O
N
OH
S
S
O
4
O
O
N
N
MB96 (66%)
C5H
Si
O
MK-2
O
11C5H11
N
C6H13
CN
H
N
O
O
OC6H11
CN
H
S
N
4
O
N
S
O
Si
O
O
O
MB104 (60%)
MB113 (43%)
Si
N
O
O
O
N
N
Scheme 2 Preparation of silatrane-containing dyes
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E
M. Bessi et al.
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Synthesis
analogue of alkoxysilane dye ADEKA-16 (see Scheme 2):
commercially available carboxylic sensitizer MK-220 was
treated with compound 9 under the same conditions de-
scribed above for DF15 and MB25, providing compound
MB104 in 60% yield.
UV/Vis spectra of silatrane dyes MB96 and MB113 were
recorded in CH2Cl2 solution, and compared with those of
the corresponding carboxylic acids (DF15 and MB25) and
trialkoxysilane dyes (MM62 and MB56). Relevant data are
reported in Table 1 and the spectra are shown in Figure 5 a.
It can be seen that very similar values were observed for the
absorption maximum; always showing a slight blueshift
going from the carboxylic acid (DF15 and MB25) to the tri-
alkoxysilane (MM62 and MB56) to the silatrane (MB96 and
MB113).
solution and heating at 70 °C for several hours. As an exam-
ple, the stained films obtained with dyes DF15, MM62, and
MB96 together with the original untreated TiO2 layer are
shown in Figure 6.
The UV/Vis spectra of the dyes adsorbed on TiO2 are
shown in Figure 5 b (DF15 and derivatives, MB25 and de-
rivatives) and Figure S2 (MB104). In all cases, much broader
Table 1 Relevant UV/Vis Spectroscopic Data of the Investigated Dyes
in Solution and Adsorbed on TiO2
Compd
λ
max (nm)
Solvent
ε (M−1 cm−1
)
λ
max (TiO2) (nm)
DF15a
530
523
518
515
511
506
491
507c
491
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CHCl3
CHCl3
CHCl3
35038
22917
42500
27925
22762
27300
35800
43500c
37200
457
493
490
457
475
476
441b
512c
478
MM62
MB96
MB25
MB56
MB113
MK-2
ADEKA-1
MB104
a Taken from the literature.10
b Taken from the literature.22
c Taken from the literature.7
The molar extinction coefficient, on the other hand, de-
creased on going from the carboxylic acid to the trialkoxysi-
lane, but increased again when moving to the silatrane (in
the case of MB96 reaching a value even higher than that of
the corresponding carboxylic acid DF15).21 These results
suggest that, in all the silicon-containing dyes, the electron-
ic and structural properties remain stable and, in particular,
silatranes appear to have optical properties comparable to
those of the already established siloxane dyes.
Figure 5 UV/Vis spectra of carboxylic acid, siloxane, and silatrane dyes
in solution (a) and adsorbed on TiO2 (b). DF15: solid red line; MM62:
dashed red line; MB96: dotted red line; MB25: solid blue line; MB56:
dashed blue line; MB113: dotted blue line.
To verify that silatrane is indeed a suitable functional
group to anchor the organic dyes on TiO2, compounds
MB96, MB113, and MB104 were adsorbed on nanocrystal-
line TiO2 films deposed on glass sheets, and the properties
of the resulting samples were compared with those of the
sensitized films obtained by using the other dyes.
Staining conditions were not the same for all com-
pounds: indeed, whereas carboxylic acid derivatives were
adsorbed by immersing the films overnight in a toluene
solution of the dyes at room temperature, attachment of
the silylated dyes to TiO2 required immersion in a toluene
Figure 6 From left to right: untreated TiO2 film; TiO2 film sensitized with
dye DF15; TiO2 film sensitized with dye MM62; TiO2 film sensitized with
dye MB96
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2017, 49, A–J

F
M. Bessi et al.
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Synthesis
absorptions were obtained than those recorded in solution.
Interestingly, and contrary to what was observed in solu-
tion, the carboxylic compounds showed an ipsochromic
shift compared with the corresponding silyloxy species,
which could be due to deprotonation of the acidic function
(necessary for adsorption on the semiconductor), but also
to the less pronounced formation of aggregates, due to the
reduced amount of adsorbed dye molecules (see below).
Significantly, the absorption characteristics of the silatranes
were almost identical to those of the corresponding tri-
alkoxysilanes, consistent with the hypothesis that the spe-
cies formed by the silatrane dyes upon absorption on the
semiconductor are analogous to those obtained starting
from the corresponding siloxanes (see the ATR-IR experi-
ments below for a further discussion).
Excellent stability on the TiO2 surface of both silylated
anchoring groups was proven by desorption studies in
aqueous environment.6 Semiconductor films sensitized
with the series of dyes DF15, MM62, and MB96 were im-
mersed into an acetonitrile/water 1:1 mixture at 60 °C, and
their relative absorbance was measured before immersion
and after fixed time intervals (Figure 7). After just 30 min-
utes, a loss greater than 40% of the dye absorbed on the film
could be observed for DF15, whereas in the case of the si-
lylated dyes the initial amount was almost completely re-
tained. The difference became more pronounced during the
course of the experiment, and after 3 hours only 20% of the
initial amount of cyanoacrylic acid DF15 was still anchored
on the TiO2 film, whereas almost no absorbance drop could
be observed for both the films sensitized with compounds
MM62 and MB96, which showed an essentially identical
behavior.
tative desorption method. Due to the strong nature of the
Si-O-Ti bond formed during adsorption, quantitative de-
tachment of the dyes was possible only by exposing the
film to a basic solution for several days and at 70 °C tem-
perature. We found that the estimated amount of attached
MM62 (0.48 × 10–7 mol cm–2) was almost eight times lower
than that reported for DF15 (3.70 × 10–7 mol cm–2),10 per-
haps because of the relatively bulky phenyltriethoxysilyl
anchoring group compared with a simple carboxylic acid.
On the other hand, the density of silatrane MB96
(1.01 × 10–7 mol cm–2) was more than double that of alkox-
ysilane MM62, possibly due its lower tendency to oligomer-
ize on the semiconductor surface compared with the tri-
alkoxysilyl moiety, as well as to the more compact ‘cage’
structure of the silatrane group, favoring a closer packing of
the molecules.
The nature of the bond formed by dyes DF15, MM62,
and MB96 with the semiconductor surface was also investi-
gated by means of ATR (attenuated total reflectance) FTIR
studies (see Figure S3–S4 in the Supporting Information).
Selected frequencies of diagnostic peaks are reported in Ta-
ble 2. In particular, the characteristic band at 1685 cm–1,
present in the spectrum of the pristine dye DF15 and at-
tributed to C=O stretching, disappeared upon absorption on
TiO2 and was replaced by a peak at 1387 cm–1, which could
be related to the symmetric stretching of the newly formed
COO– group.18 Instead, in the case of compound MM62, the
two sets of diagnostic peaks of the isolated dye located at
1468 cm–1 (C–H bending of the CH2 units of the alkoxysi-
lane group) and 1190–1160 cm–1 (four peaks, C–O stretch-
ing of the alkoxysilane group)18 disappeared in the FTIR
spectrum after absorption on TiO2, indicating the release of
the ethyl moieties and the likely formation of the Si–O–Ti
bonds.
Finally, the amount of dyes MM62 and MB96 adsorbed
on a 1.44 cm2 TiO2 film was measured by using the quanti-
Table 2 Diagnostic Peaks in the ATR FTIR Spectra of Isolated and Ad-
sorbed Dyes DF5, MM62, and MB96
Compd.
Isolated ν (cm–1
)
Adsorbed on TiO2 ν (cm–1
)
DF15
1685 (C=O str.)
1387 (COO– symm. str.)
MM62
1468 (C–H bend.),
1190–1160 (four peaks, C–O str.)
not present
not present
MB96
1130–1090 (four peaks, C–O str.)
not present
A similar situation occurred with dye MB96, with total
disappearance of the group of four peaks at 1130–1090 cm–1
(C–O stretching of the silatrane group). Unfortunately, in
the spectrum of the isolated compound, the peak at around
1450 cm–1 (C–H bending of the CH2 units of the silatrane
group) was almost completely concealed by a strong signal
at ca. 1500 cm–1, and thus its disappearance in the spec-
trum of the adsorbed compound could only be inferred by
the relative thinning of that peak. Notably, the spectra of
adsorbed dyes MM62 and MB96 were very similar (as can
Figure 7 Variation of the relative absorbance of TiO2 films sensitized
with compounds DF15 (red squares), MM62 (blue circles) and MB96
(green triangles) upon exposure to a 1:1 mixture of MeCN and H2O at
60 °C. Curves were fitted with a generic exponential decay function, but
no attempt was made to determine a rigorous kinetic law for desorp-
tion.
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2017, 49, A–J

G
M. Bessi et al.
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Synthesis
be seen from their superimposition, Figure S4), thus sug-
gesting that the anchoring group effectively formed upon
adsorption on TiO2 was the same for both dyes.
UV/Vis spectra of the compounds on TiO2 were recorded in transmis-
sion mode after sensitization of thin, transparent semiconductor
films. To this end, the titania paste (Dyesol 18NR-T) was screen-print-
ed on a 2 cm × 2 cm sodalime glass substrate, and the resulting films
(active area: 1.44 cm2) were sintered at 520 °C for 30 min. After sin-
tering, the titania films were sensitized by overnight immersion in
the appropriate dye solution (1.0 × 10–4 M in toluene), which took
place at r.t. for the carboxylic acid dyes and at 70 °C for the silicon-
containing dyes. After sensitization, the films were rinsed with EtOH
and deionized water, and dried.
In conclusion, a series of new organic D-π-A dyes en-
dowed with different trialkoxysilane anchoring groups was
prepared, in view of the recent successful application of
similar compounds as TiO2 sensitizers for dye-sensitized
solar cells. Introduction of the silicon-containing moieties
was accomplished by amide formation starting from the
corresponding cyanoacrylic acids DF15 and MB25. Howev-
er, preparation and purification of the products proved dif-
ficult, and specific reaction sequences had to be elaborated
to install the desired anchoring groups on each of the two
molecular scaffolds. The use of a silatrane anchoring group
proved to be a valid alternative, and the desired dyes could
be easily prepared from the corresponding carboxylic acids
by using a coupling procedure mediated by EDC-Cl. Fur-
thermore, purification of these compounds was much easi-
er than that of their siloxane counterparts. Silatranes pre-
pared in this study displayed optical and electronic proper-
ties almost identical to those of the corresponding
siloxanes, as highlighted by UV/Vis spectroscopic studies.
The possible anchoring to TiO2 of silatranes by formation of
a covalent bond with the semiconductor through Si–O–Ti
bridges was supported by ATR-IR experiments and by the
fact that both compounds showed excellent anchoring sta-
bility in desorption studies conducted under aqueous con-
ditions.
ATR-IR spectra of sensitized TiO2 powders were recorded with a Shi-
madzu model IRAffinity-1 in the range 4000–800 cm–1. To this end,
nc-TiO2 powder (Sigma–Aldrich, 50 mg) was sensitized by overnight
immersion in a 2.0 × 10–3 M solution in toluene of the dyes (at r.t. for
DF15, and at 70 °C for MM62 and MB96). After sensitization, the col-
ored powder was filtered, rinsed with petroluem ether and dried.
(E)-3-[5-((E)-4-{Bis[4-(hexyloxy)phenyl]amino}styryl)thiophen-2-
yl]-2-cyano-N-[3-(triethoxysilyl)propyl]acrylamide (MM35)
In a Schlenk tube under nitrogen atmosphere, acid DF15 (65 mg, 0.10
mmol, 1.0 equiv) was dissolved in anhydrous dichloromethane (1 mL)
and the solution was cooled to 0 °C, then oxalyl chloride (103 μL, 1.20
mmol, 12.0 equiv) and anhydrous DMF (0.8 μL, 0.012 mmol, 0.12
equiv) were added dropwise under nitrogen atmosphere. After the
end of gas evolution, the dark-blue mixture was allowed to reach r.t.
and was stirred for 4 h. Finally, the solution was diluted with di-
chloromethane (2 mL) and concentrated under reduced pressure for 1
h to remove the excess of oxalyl chloride. The resulting acyl chloride
was air-sensitive so it was used as such for the following step (65 mg).
1H NMR (CDCl3, 300 MHz): δ = 8.28 (s, 1 H), 7.63 (d, J = 3.8 Hz, 1 H),
7.74 (d, J = 8.4 Hz, 1 H), 7.32 (d, J = 8.6 Hz, 2 H), 7.26–6.83 (m, 13 H),
3.94 (m, 4 H), 1.85–1.80 (m, 4 H), 1.48–1.31 (m, 12 H), 0.91 (t, J =
6.5 Hz, 6 H).
In a Schlenk tube under nitrogen atmosphere, the acyl chloride ob-
tained in the previous step (65 mg, 0.10 mmol, 1.0 equiv) was dis-
solved in anhydrous dichloromethane (1.5 mL) and the solution was
cooled to 0 °C. In another Schlenk tube, 3-(triethoxysilyl)propylamine
(23 μL, 0.10 mmol, 1.0 equiv) and triethylamine (28 μL, 0.20 mmol,
2.0 equiv) were dissolved in anhydrous dichloromethane (1 mL), the
solution was then cooled to 0 °C and finally was added dropwise un-
der nitrogen atmosphere and strong stirring to the chloride solution.
During the addition, the temperature was maintained at 0 °C with an
ice bath. The mixture was left at 0 °C for 1 h, was then allowed to
reach r.t. (turning from blue to red) and was stirred for 16 h. Finally,
the solution was diluted with dichloromethane (20 mL) and was
washed first with 0.3 M aq HCl (20 mL) and then with H2O (3 × 20
mL). The organic phase was dried over Na2SO4 and the solvent was re-
moved under reduced pressure. The crude siloxane was purified by
silica gel column chromatography (pentane/EtOAc, 5:1) to yield pure
product MM35.
All reactions were performed under an inert nitrogen atmosphere in
a flame- or oven-dried apparatus, using Schlenk techniques. Tetrahy-
drofuran (THF) was purified by distillation over metallic sodium in
the presence of benzophenone, toluene was distilled over metallic so-
dium. CH2Cl2, 1,2-dichloroethane, N-methylpyrrolidone, and N,N-di-
methylformamide were dried by storing under nitrogen over 4 Å mo-
lecular sieves. 4-Iodoaniline,23 4-(trimethoxysilyl)phenylisocyanate,13
and 3-aminophenylsilatrane (9)24 were prepared as reported. Dye
DF15 and MB25 were prepared according to published proce-
dures.10,11 All other chemicals employed were commercially available
and were used as received. Petroleum ether was the 40–60 °C boiling
fraction. Thin-layer chromatography was carried out on aluminum-
supported Merck 60 F254 plates; detection was carried out using UV
light and permanganate solutions followed by heating. Flash column
chromatography was performed using Merck Kieselgel 60 (300–400
mesh) as the stationary phase. 1H NMR spectra were recorded at 200,
300 or 400 MHz, and 13C NMR{1H} spectra were recorded at 50.3, 75.5
or 100.6 MHz, with Bruker Avance or Varian Mercury series instru-
ments. Chemical shifts are referenced to the residual solvent peak
(CHCl3, δ = 7.26 ppm for 1H NMR and δ = 77.16 ppm for 13C NMR; C6D6
δ = 7.16 ppm for 1H NMR and δ = 128.1 ppm for 13C NMR). FTIR spec-
tra were recorded in the range 4000–400 cm–1 with a 2 cm–1 resolu-
tion with a Perkin–Elmer Spectrum BX instrument. ESI-MS spectra
were obtained by direct injection of the sample solution, with a Ther-
mo Scientific LCQ-FLEET instrument and are reported in the form
m/z. HRMS spectra were measured with a Thermo Scientific LTQ Or-
bitrap (FT-MS) instrument and are reported in the form m/z. UV/Vis
spectra were recorded with a Shimadzu UV-2600 spectrometer.
Yield: 48 mg (0.06 mmol, 56%); dark-red solid.
IR (KBr): 3366, 2924, 2202, 1656, 1578, 1505, 1239, 1102 cm–1
.
1H NMR (C6D6, 300 MHz): δ = 8.48 (s, 1 H), 7.14–7.11 (m, 4 H), 6.99–
6.94 (m, 2 H), 6.89–6.87 (m, 1 H), 6.85–6.80 (m, 4 H), 6.77–6.72 (m,
2 H), 6.45–6.43 (m, 2 H), 6.33 (t, J = 5.9 Hz, 1 H), 3.79 (q, J = 7.0 Hz,
6 H), 3.63 (t, J = 6.2 Hz, 4 H), 3.22 (t, J = 6.2 Hz, 2 H), 1.69–1.57 (m,
8 H), 1.36–1.13 (m, 25 H), 0.88 (t, J = 6.5 Hz, 6 H).
13C NMR (C6D6, 75 MHz): δ = 160.6, 156.6, 152.2, 149.9, 144.1, 140.7,
138.4, 134.7, 132.9, 128.5, 127.5, 126.0, 120.1, 118.2, 118.0, 115.8,
99.9, 68.2, 58.6, 42.9, 31.9, 29.7, 26.1, 23.5, 23.0, 18.6, 14.3, 8.1.
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2017, 49, A–J

H
M. Bessi et al.
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Synthesis
ESI-MS: m/z = 874.29 [M + Na]+. In the MS-spectrum, the peaks be-
longing to the compound having one methoxy and two ethoxy groups
are also present (due to exchange with MeOH used as the solvent for
the analysis): m/z = 838.21 [M + 1]+, 860.35 [M + Na]+.
13C NMR (C6D6, 75 MHz): δ = 157.9, 156.7, 152.8, 150.1, 144.9, 140.6,
139.1, 138.1, 136.1, 133.5, 132.0, 129.2, 127.6, 127.4, 126.1, 121.1,
120.7, 120.0, 119.6, 118.0, 115.9, 101.7, 68.2, 59.0, 31.9, 30.1, 29.7,
26.1, 23.0, 18.6, 14.3.
ESI-MS: m/z = 844.21 [M]+; the observed value is related to the mole-
cule having three methoxy groups instead of the ethoxy groups due
to exchange with MeOH used as the solvent for the analysis.
(E)-3-[5-((E)-4-{Bis[4-(hexyloxy)phenyl]amino}styryl)thiophen-2-
yl]-2-cyano-N-(4-iodophenyl)acrylamide (8)
HRMS: m/z [M]+ calcd for C52H63N3 O6SSi: 885.4201; found: 885.4195.
In a Schlenk tube under nitrogen atmosphere, dye DF15 (65 mg, 0.10
mmol, 1.0 equiv) was dissolved in anhydrous dichloromethane (1
mL), then EDC-Cl (29 mg, 0.15 mmol, 1.5 equiv) and HOBt (20 mg,
0.15 mmol, 1.5 equiv) were added. The solution was left under vigor-
ous stirring for 30 min, during which it turned blue, then 4-iodoani-
line (33 mg, 0.15 mmol, 1.5 equiv) was added and the mixture was
stirred at r.t. for 16 h. The solution was diluted with dichloromethane
(10 mL), and was washed with 0.3 M aq HCl (3 × 20 mL) and H2O
(3 × 20 mL). The organic phase was dried over Na2SO4 and the solvent
was removed under reduced pressure. Finally, the crude material was
purified by silica gel column chromatography (PE/EtOAc, 20:1 to 2:1)
to give pure product 1,
(E)-2-Cyano-3-{8-[(E)-4-(diphenylamino)styryl]-3,3-dipentyl-3,4-
dihydro-2H-thieno[3,4-b][1,4]dioxepin-6-yl}-N-[4-(trimethoxysi-
lyl)phenyl]acrylamide (MB56)
In a Schlenk tube under nitrogen atmosphere, triphosgene (59 mg,
0.20 mmol, 3.2 equiv) was dissolved in anhydrous THF (0.8 mL) and
the solution was cooled to 0 °C. In another tube, trimethoxysilylani-
line (85 mg, 0.40 mg, 2.1 equiv) and anhydrous DIPEA (160 μL, 0.88
mmol, 4.6 equiv) were dissolved in anhydrous THF (0.9 mL) and the
resulting mixture was added dropwise under vigorous stirring to the
triphosgene solution; a white precipitate was immediately observed.
The suspension was then warmed to 70 °C. After 3.5 h, no more tri-
methoxysilylaniline was detected by TLC, so the mixture was cooled
to r.t. and dye MB25 (125 mg, 0.19 mmol, 1.0 equiv), more anhydrous
DIPEA (67 μL, 0.38 mmol, 2.0 equiv) and anhydrous THF (0.5 mL) were
added. The suspension was warmed to 50 °C and stirred overnight.
The mixture was diluted with EtOAc (100 mL), and was washed with
H2O (2 × 100 mL) and brine (130 mL). The organic phase was dried
over Na2SO4 and the solvent was removed under reduced pressure.
The crude product was then washed with pentane (4 × 10 mL) and
MeOH (4 × 10 mL) to obtain purified siloxane MB56.
Yield: 57 mg (0.07 mmol, 68%); brown amorphous solid.
IR (KBr): 3311, 2924, 2207, 1678, 1592, 1561, 1502, 1236 cm–1
.
1H NMR (C6D6, 300 MHz): δ = 8.37 (s, 1 H), 7.48 (s, 1 H), 7.37–7.35 (m,
2 H), 7.12–7.04 (m, 8 H), 6.99–6.96 (m, 2 H), 6.88–6.81 (m, 7 H), 6.75–
6.72 (m, 1 H), 6.47–6.44 (m, 1 H), 3.64 (t, J = 6.2 Hz, 4 H), 1.64–1.59
(m, 8 H), 1.34–1.22 (m, 12 H), 0.88 (t, J = 6.5 Hz, 6 H).
13C NMR (C6D6, 75 MHz): δ = 158.7, 156.8, 153.6, 150.2, 145.0, 140.6,
139.4, 138.1, 137.7, 134.5, 133.7, 128.7, 127.6, 127.4, 126.1, 122.1,
120.0, 117.9, 117.8, 115.9, 98.9, 88.3, 68.3, 31.9, 29.7, 26.1, 23.0, 14.3.
ESI-MS: m/z = 850.15 [M + H]+.
Yield: 75 mg (0.088 mmol, 46%); dark-red amorphous solid.
IR (KBr): 2924, 2196, 1583, 1497, 1276 cm–1
.
(E)-3-[5-((E)-4-{Bis[4-(hexyloxy)phenyl]amino}styryl)thiophen-2-
yl]-2-cyano-N-[(4-triethoxysilyl)phenyl]acrylamide (MM62)
1H NMR (CDCl3, 300 MHz): δ = 8.57 (s, 1 H), 7.88 (s, 1 H), 7.67–7.65
(m, 2 H), 7.40–7.25 (m, 6 H), 7.15–6.90 (m, 12 H), 4.07 (s, 2 H), 3.98 (s,
2 H), 3.63 (s, 2 H), 1.39–1.26 (m, 16 H), 0.92–0.89 (m, 6 H).
13C NMR (CDCl3, 75 MHz): δ = 159.9, 156.3, 148.6, 147.3, 145.8, 141.4,
139.8, 136.0, 135.8, 133.0, 131.7, 129.9, 129.5, 128.2, 125.2, 123.7,
122.7, 119.5, 118.5, 115.5, 113.4, 94.1, 78.3, 78.1, 51.0, 43.8, 32.7,
32.2, 29.8, 22.7, 14.2.
Compound 8 (47 mg, 0.055 mmol, 1.0 equiv) was placed inside a dry
Schlenk tube under a nitrogen atmosphere. In two other Schlenk
tubes, stock solutions of Pd2(dba)3·CHCl3 (15 mg/mL, in anhydrous di-
chloromethane) and JohnPhos (10 mg/mL, in anhydrous dichloro-
methane) were prepared, and then the desired quantities of
Pd2(dba)3·CHCl3 (150 μL, 1.5 × 10–3 mmol, 0.03 equiv) and JohnPhos
(90 μL, 3.0 × 10–3 mmol, 0.06 equiv) were added to amide 8. The sol-
vent was evaporated, the solid was dissolved again in anhydrous N-
methylpyrrolidone (1 mL), and then HSi(OEt)3 (15 μL, 0.075 mmol, 1.5
equiv) and anhydrous DIPEA (26 μL, 0.15 mmol, 3.0 equiv) were add-
ed. The dark-red solution was left under vigorous stirring at r.t. for 16
h. The mixture was diluted with dichloromethane (10 mL), filtered on
Celite and finally washed with H2O (3 × 20 mL). The organic phase
was dried over Na2SO4 and the solvent was removed under reduced
pressure. The crude material was purified by flash column chroma-
tography on silica gel (from PE/toluene, 1:3 to toluene 100%, then tol-
uene/Et2O, 25:1) to give pure product MM62.
ESI-MS: m/z = 856.41 [M + H]+.
HRMS: m/z [M + H]+ calcd for C50H57O6N3SSi: 856.3816; found:
856.3807.
Preparation of Silatrane Dyes; General Procedure
The appropriate acid DF15, MB25, or MK-2 (0.045 mmol, 1.00 equiv)
was dissolved in anhydrous 1,2-dichloroethane (1 mL), then EDC-Cl
(13 mg, 0.069 mmol, 1.5 equiv) was added. The solution was left un-
der vigorous stirring for 30 min, during which it turned blue. 3-Amin-
ophenyl silatrane (9; 19 mg, 0.069 mmol, 1.5 equiv) was then added,
and the mixture was allowed to react at 50 °C for 16 h. The solution
was diluted with dichloromethane (10 mL) and washed with 0.3 M aq
HCl (3 × 30 mL) and H2O (2 × 30 mL). The organic phase was dried
over Na2SO4 and the solvent was removed under reduced pressure.
The crude product was then purified by silica gel flash column chro-
matography to give the pure silatrane product.
Yield: 34 mg (0.023 mmol, 78%); purple amorphous solid.
IR (KBr): 3322, 2924, 2202, 1678, 1592, 1569, 1502, 1239 cm–1
.
1H NMR (CDCl3, 300 MHz): δ = 8.42 (s, 1 H), 7.90 (s, 1 H), 7.71–7.60
(m, 6 H), 7.32–7.29 (m, 2 H), 7.12–7.02 (m, 6 H), 6.89–6.81 (m, 6 H),
3.98–3.91 (m, 4 H), 3.87 (q, J = 7.0 Hz, 6 H), 1.83–1.63 (m, 4 H), 1.51–
1.42 (m, 4 H), 1.37–1.32 (m, 8 H), 1.25 (t, J = 7.0 Hz, 9 H), 0.91 (t, J =
7.0 Hz, 6 H).
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2017, 49, A–J

I
M. Bessi et al.
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Synthesis
(E)-N-[4-(2,8,9-Trioxa-5-aza-1-silabicyclo[3.3.3]undecan-1-yl)phe-
nyl]-3-[5-((E)-4-{bis[4-(hexyloxy)phenyl]amino}styryl)thiophen-
2-yl]-2-cyanoacrylamide (MB96)
13C NMR (CDCl3, 75 MHz): δ = 159.0, 155.0, 144.2, 143.6, 143.1, 142.3,
141.0, 140.8, 140.5, 139.7, 139.2, 137.0, 136.6, 135.3, 135.2, 130.1,
129.4, 129.0, 128.7, 128.4, 127.4, 126.2, 125.3, 125.2, 124.0, 123.5,
123.0, 120.7, 119.3, 119.0, 118.1, 117.6, 108.9, 108.8, 97.5, 57.9, 51.2,
37.8, 31.9, 31.8, 31.7, 31.4, 30.7, 30.5, 30.2, 29.9, 29.7, 29.5, 29.4, 29.2,
22.8, 22.7, 14.3, 14.0.
ESI-MS: m/z = 1203.06 [M + H]+
HRMS: m/z [M]+ calcd for C70H86N4O4S4Si: 1202.5301; found:
Prepared starting from dye DF15 (29 mg). Purified by silica gel flash
column chromatography (toluene/EtOAc, 10:1 to 2:1).
Yield: 27 mg (0.030 mmol, 66%); dark-red amorphous solid.
IR (KBr): 3390, 2923, 2199, 1671, 1575, 1506, 1239 cm–1
.
1H NMR (C6D6, 400 MHz): δ = 8.38 (s, 1 H), 8.22 (d, J = 8.3 Hz, 2 H),
7.73 (br. s, 1 H), 7.60 (d, J = 8.4 Hz, 2 H), 7.14–7.05 (m, 8 H), 6.99 (d, J =
16.0 Hz, 1 H), 6.93 (d, J = 3.9 Hz, 1 H), 6.84–6.77 (m, 5 H), 6.51 (d, J =
3.9 Hz, 1 H), 3.65 (t, J = 6.4 Hz, 4 H), 3.47 (t, J = 5.7 Hz, 6 H), 1.99 (t, J =
5.7 Hz, 6 H), 1.65–1.59 (m, 4 H), 1.38–1.31 (m, 4 H), 1.28–1.18 (m,
8 H), 0.88 (t, J = 7.0 Hz, 6 H).
13C NMR (C6D6, 100 MHz): δ = 158.4, 156.6, 152.5, 149.9, 144.3, 140.7,
140.3, 138.7, 137.5, 136.0, 134.8, 133.0, 128.6, 128.5, 127.5, 126.1,
120.1, 119.0, 118.3, 117.9, 115.9, 100.2, 68.2, 57.9, 50.8, 31.9, 29.7,
26.1, 23.0, 14.3.
1202.5298.
Measurement of Density of Adsorbed Dye Molecules on TiO2
The TiO2 films, sensitized with MM62 and MB96 according to the
procedure described above, were placed in flasks containing 15 mL of
a 0.1 M solution of KOH in EtOH/THF 9:1. After 3 days at r.t. followed
by 4 days at 50 °C under gyroscopic stirring, full decoloration of the
films was observed. The absorbance of the resulting solutions was
measured by UV/Vis spectroscopy and compared to that of a standard
2.5 × 10–5 solution of the compounds in the same solvent/base mix-
ture. The amount of dye present in the unknown solution was calcu-
lated and divided by the film surface area, yielding density values in
the 1.0–0.5 × 10–7 mol cm–2 range.
ESI-MS: m/z = 896.58 [M]+.
HRMS: m/z [M]+ calcd for C52H60N4O6SSi: 896.4003; found: 896.3995.
(E)-N-[4-(2,8,9-Trioxa-5-aza-1-silabicyclo[3.3.3]undecan-1-yl)phe-
nyl]-2-cyano-3-{8-[(E)-4-(diphenylamino)styryl]-3,3-dipentyl-
3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepin-6-yl}acrylamide
(MB113)
Dye Desorption Kinetics
The TiO2 sensitized films were placed in 50 mL flasks containing 20
mL of a CH3CN/H2O, 1:1 mixture (v/v), which was then heated at
60 °C. At defined times (after 5, 15, 30, 60, and 120 min immersion),
the films were removed from the solvent mixture, rinsed with EtOH
and dried, and the absorbance of the films at the dye λmax was record-
ed with a UV/Vis spectrometer. After the measurement, the films
were placed back in the solution and the desorption reaction was
continued for a total of 3 h.
Prepared starting from dye MB25 (30 mg). Purified by silica gel flash
column chromatography (toluene/EtOAc, 10:1 to 2:1).
Yield: 18 mg (0.020 mmol, 43%); dark-red amorphous solid.
IR (KBr): 3420, 2923, 2194, 1666, 1577, 1496, 1271 cm–1
.
1H NMR (CDCl3, 400 MHz): δ = 8.56 (s, 1 H), 7.76 (br. s, 1 H), 7.74 (d, J
= 8.2 Hz, 2 H), 7.53 (d, J = 8.2 Hz, 2 H), 7.37 (d, J = 8.6 Hz, 2 H), 7.30–
7.28 (m, 2 H), 7.14–6.99 (m, 12 H), 4.03 (s, 2 H), 3.97 (s, 2 H), 3.91 (t, J
= 5.7 Hz, 6 H), 2.93 (t, J = 5.7 Hz, 6 H), 1.37–1.29 (m, 16 H), 0.91 (t, J =
6.8 Hz, 6 H).
13C NMR (CDCl3, 100 MHz): δ = 159.3, 155.9. 148.4, 147.4, 145.8,
141.0, 138.8, 137.1, 135.2, 132.1, 131.2, 130.2, 129.5, 128.1, 125.1,
123.6, 122.8, 119.0, 118.5, 115.6, 113.5, 95.1, 78.2, 77.9, 57.9, 51.2,
43.8, 32.7, 32.2, 29.8, 22.7, 14.2.
DFT Calculations
The structures of compounds DF15, MB25, MB56, MM35, and MM62
were optimized in vacuo based on the results of DFT calculations car-
ried out with the Gaussian09 program package25 at the B3LYP/6-31G*
level.26,27
ESI-MS: m/z = 908.58 [M]+.
HRMS: m/z [M]+ calcd for C53H60N4O6SSi: 908.4003; found: 908.3999.
Acknowledgment
The authors thank Ente Cassa di Risparmio di Firenze (‘ENERGYLAB’
project) and Regione Toscana (‘SELFIE Project’ FAR-FAS 2014 grant)
for financial support, as well as CINECA and CREA (Colle Val d’Elsa, It-
aly) for the availability of high-performance computing resources and
financial support.
(E)-N-[4-(2,8,9-Trioxa-5-aza-1-silabicyclo[3.3.3]undecan-1-yl)phe-
nyl]-2-cyano-3-{5′′′-(9-ethyl-9H-carbazol-3-yl)-3′,3′′,3′′′,4-tetra-
hexyl-[2,2′:5′,2′′:5′′,2′′′-quaterthiophen]-5-yl}acrylamide (MB104)
Prepared starting from dye MK-2 (43 mg). To promote the acid disso-
lution in the reaction mixture, MK-2 was first dissolved in anhydrous
THF (0.5 mL) and then anhydrous 1,2-dichloroethane was added. Pu-
rified by silica gel flash column chromatography (toluene/EtOAc, 20:1
to 2:1).
Supporting Information
Supporting information for this article is available online at
https://doi.org/10.1055/s-0036-1588836.
S
u
p
p
o
nrtogI
f
rmoaitn
S
u
p
p
ortiInfogrmoaitn
Yield: 33 mg (0.027 mmol, 61%); dark-red amorphous solid.
IR (KBr): 3409, 2923, 2194, 1671, 1572, 1506, 1422, 1231 cm–1
.
1H NMR (CDCl3, 300 MHz): δ = 8.57 (s, 1 H), 8.31 (d, J = 1.2 Hz, 1 H),
8.15 (d, J = 7.7 Hz, 1 H), 7.87 (br. s, 1 H), 7.77–7.71 (m, 3 H), 7.57–7.47
(m, 3 H), 7.43 (d, J = 4.3 Hz, 1 H), 7.40 (d, J = 4.9 Hz, 1 H), 7.29–7.17
(m, 2 H), 7.08 (s, 1 H), 7.02 (s, 2 H), 4.38 (q, J = 7.0 Hz, 2 H), 3.92 (t, J =
5.7 Hz, 6 H), 2.93 (t, J = 5.7 Hz, 6 H), 2.87–2.80 (m, 8 H), 1.78–1.64 (m,
8 H), 1.46 (t, J = 7.1 Hz, 3 H), 1.40–1.34 (m, 24 H), 0.92–0.90 (m, 12 H).
References
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Synthesis
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© Georg Thieme Verlag Stuttgart · New York — Synthesis 2017, 49, A–J