Tetrathiafulvalene–Polychlorotriphenylmethyl Dyads: Influence of Bridge and Open-Shell Characteristics on Linear and Nonlinear Optical Properties

Article abstract of DOI:10.1002/chem.201701623

Three conjugated donor-π-acceptor radical systems (1 a–1 c) were prepared by bridging a tetrathiafulvalene (TTF) electron-donor unit to a polychlorotriphenylmethyl (PTM) electron-acceptor radical through vinylene units of different lengths. The dependence

Full text of DOI:10.1002/chem.201701623

A Journal of
Accepted Article
Title: TTF-PTM dyads: The role of the bridge and open-shell character
on the linear and nonlinear optical properties
Authors: Jaume Veciana, Manuel Souto, Joaquin Calbo, Imma Ratera,
and Enrique Ortí
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To be cited as: Chem. Eur. J. 10.1002/chem.201701623
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TTF-PTM dyads: The role of the bridge and open-shell character
on the linear and nonlinear optical properties
[a],†
[b],†
[a]
[b]
[a]
Manuel Souto,
Joaquín Calbo,
Imma Ratera,* Enrique Ortí,* and Jaume Veciana*
Abstract: In this article, three conjugated donor-π-acceptor radical
systems (1a-1c) based on a tetrathiafulvalene (TTF) unit, as
electron-donor, connected to a polychlorotriphenylmethyl (PTM)
radical, as electron-acceptor, through different vinylene units as
bridge have been synthesized. The dependence of the
intramolecular charge transfer on the length of the conjugated bridge
has been analysed by different electrochemical and spectroscopic
techniques. In addition, linear optical properties and the second-
order non-linear optical (NLO) response of these derivatives have
been theoretically calculated by comparing with their non-radical
analogues (2a-2c). Interestingly, an enhanced NLO response is
predicted when the PTM is in its radical form as well as when the
length of the bridge becomes longer. Theoretical calculations
confirm the active role of the bridge in the electronic communication
between the donor TTF and the acceptor PTM units.
ago, some of us reported the second-order non-linear optical
(SONLO) response of a family of polychlorotriphenylmethyl
(PTM) radical derivatives showing large β hyperpolarizability
[
25–27]
values.
Interestingly, PTM radical derivatives can act as
[
28]
efficient electron acceptors in front of many donor molecules.
In view of the donor and acceptor capabilities of both TTF
and radical PTM molecules, it is of high interest to combine both
units in a D-π-A molecule and theoretically evaluate its NLO
response. Recently, we have reported different D-π-A systems
based on a PTM radical electron-acceptor linked to a TTF
electron-donor through conjugated vinylene bridges that exhibit a
reversible switching between a neutral and a zwitterionic state in
[
29–32]
solution through the application of external stimuli
conductivity in solid state.
or
[33–35]
In order to study the optical
properties of this kind of radical dyads and evaluate the
influence of the open-shell character and the length of the bridge,
we have synthesized and characterized a family of TTF-π-PTM
radical derivatives (1a-1c) and their non-radical analogues (2a-
Introduction
2
c) (Scheme 1). In this article, we present a detailed study of the
The design and synthesis of novel organic materials exhibiting
nonlinear optical (NLO) properties is an interesting field due to
intramolecular charge-transfer dependence on the open-shell
structure and the bridge length of this family of compounds.
Moreover, in order to study the electronic, geometrical and
optical (linear and non-linear) properties of such dyads,
theoretical calculations have been carried out demonstrating
larger β values for the radical dyads, compared with the non-
radical ones, and upon increasing the spacer conjugation length.
[
1–5]
their potential applications in optoelectronic technologies.
In
particular, organic molecules which contain electron-donor (D)
and electron-acceptor (A) units linked by a π-conjugated bridge
(
D-π-A molecules as push-pull systems) have been the subject
of considerable effort for the development of electro-optic
switching elements for telecommunications and optical
[
6–8]
information processing.
Remarkable characteristics of such
push-pull systems are their large β hyperpolarizabilites and the
possibility of tuning this property by changing the nature of the
bridge and the strengths of the donor and acceptor units.
Regarding the building blocks, the tetrathiafulvalene (TTF)
moiety has been widely used as an efficient electron-donor unit
for synthesizing TTF-π-A structures with appealing NLO
properties. Indeed, after the first example reported in 1998 by N.
[
9]
Martín, J. Garín and coworkers, many other TTF-based push-
pull derivatives with closed-shell electronic structure exhibiting
Scheme 1. Molecular structures of D-π-A radical dyads (1a, 1b and 1c) and
their non-radical derivatives (2a, 2b and 2c).
[
10–18]
large NLO responses have been described.
On the other
hand, molecular materials with open-shell electronic structures
have also aroused the interest of many researchers because of
[
19–24]
their high potentiality as NLO-phores.
Thus, a few years
Results and Discussion
Synthesis
[
a]
b]
Dr. Manuel Souto, Dr. Imma Ratera, Prof. Jaume Veciana
Institut de Ciència de Materials de Barcelona (ICMAB-
CSIC)/CIBER-BBN
Campus Universitari de la UAB, 08193, Bellaterra, Spain
E-mail: vecianaj@icmab.es
The synthesis of the formyl-TTF precursor 3a was carried out by
reaction of monolithio-TTF with dimethylformamide with a yield
of 69 % (Scheme 2).
reported by González et al.
monolithio-TTF with N,N-dimethylacrolein to yield the trans-
vinylogue amide according to the coupling constants in the H-
[36,37]
The improved synthesis of 3b was
[
Dr. Joaquín Calbo, Prof. Enrique Ortí
Instituto de Ciencia Molecular, Universidad de Valencia
[11]
and involves the reaction of the
46980 Paterna, Spain
1
†
These authors contributed equally.
NMR spectra. Finally, the larger formyl-TTF vinylogue 3c was
obtained by a Wittig reaction of 3b with the phosphorane 4 in a
40 % yield.
Supporting information for this article is given via a link at the end of
the document.
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+
•
2+
of the TTF moiety to TTF and TTF with similar redox
potentials (vs. Ag/AgCl) of around 0.45 and 0.96 V, respectively.
As expected, the CV of radicals 1a-1c exhibits three waves
–
•
+•
related to the following redox pairs: PTM /PTM , TTF/TTF , and
+
•
2+
TTF /TTF . The value of ∆E
p
(= Epa - Epc) was in the range of
80-100 mV. The oxidation potentials of the TTF moiety remain
mostly unaltered for closed-shell compounds 2a-2c and equal to
those of TTF. In contrast, for open-shell compounds 1a-1c, the
oxidations of TTF are shifted towards more anodic values as the
length of the spacer shortens, indicating a stronger interaction
between the donor and acceptor groups when they become
closer. The more positive values measured for 1a (0.50 and 1.01
V) compared with 2a (0.45 and 0.95 V) suggest that the radical
dyad exhibits a stronger interaction between the donor and the
acceptor due to the enhanced electron-acceptor character of the
PTM radical moiety. On the other hand, the reduction peak
Scheme 2. Synthesis of the formyl-TTF derivatives 3a-3c.
The synthesis of all non-radical TTF-π-PTM derivatives 2a-
–
•
assigned to the PTM /PTM process shifts toward more negative
values when the bridge becomes longer, which contradicts the
larger charge transfer expected for the shorter systems. This
apparent discrepancy is explained below with the help of
theoretical calculations on the basis of the active role played by
the π-conjugated bridge in the charge-transfer process between
the donor and the acceptor.
2
c was carried out by a Horner-Wadsworth-Emmons reaction of
[
38]
the phosphonated-functionalized non-radical PTM derivative 5
with the formyl-TTF derivatives 3a-3c (Scheme 3). Compounds
a and 2b were obtained in 70 % yield whereas 2c was obtained
2
in moderate yield (40 %). All-trans vinylogues were obtained
according to the coupling constants in the H-NMR spectra (see
the Supporting Information).
1
Scheme 3. Synthesis of the non-radical dyads 2a-2c.
Finally, the synthesis of radicals 1a-1c involves the
subsequent deprotonation of the non-radical TTF-π-PTM
derivatives 2a-2c with tetrabutylammonium hydroxide (TBAOH)
followed by oxidation of the formed carbanion with silver nitrate
(
3
AgNO ), affording the final radical dyads 1a-1c with yields
Figure 1. Cyclic voltammetry of radical compounds 1a-1c in CH
Ag/AgCl under Argon (n-Bu PF (0.1 M) as electrolyte, 300 K, scan rate of 0.1
4 6
V/s).
2
Cl
2
vs.
between 73 and 78 % (Scheme 4). The radical compounds were
obtained as black solids which are stable under atmospheric
conditions.
Table 1. Electrochemical data of dyads 1a-1c and 2a-2c.
red [a]
ox1 [a]
1/2
ox2 [a]
1/2
[b]
[c]
Dyad
E
1/2
-
E
E
∆Eel1(V)
∆Eel2(V)
-
-
(1e )
(1e )
(1e )
1
a
-0.16
-0.20
-0.22
0.50
0.44
0.40
1.01
0.96
0.92
0.66
0.64
0.62
0.51
0.52
0.52
1b
1
2
c
Scheme 4. Synthesis of the radical dyads 1a-1c.
a
-
-
-
0.45
0.45
0.46
0.95
0.96
0.97
-
-
-
0.50
0.51
0.51
Electrochemical properties
2b
Cyclic voltammetry (CV) of radicals 1a-1c, as well as their non-
radical precursors 2a-2c, was performed in CH
2
Cl
2
at room
2c
temperature (Figure and Figure S4 in the Supporting
1
Information, and Table 1). The CV of compounds 2a-2c show
two quasi-reversible redox waves due to the stepwise oxidation
[a] In Volts vs Ag/AgCl; CH
rate of 0.1 V/s. [b] ∆Eel1 (V) = E 1/2 - E 1/2. [c] ∆Eel2(V) = E 1/2 - E 1/2
2 2 6
Cl as solvent, TBAPF as electrolyte and scan
ox1 red ox2 ox1
.
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Optical properties
2 2
UV-vis spectra of non-radical dyads 2a-2c in CH Cl are showed
in the Supporting information (Figure S5). All spectra exhibit two
principal bands in the 300‒350 and 400‒500 nm regions that
shift towards longer wavelengths as the bridge lengthens (Table
2). The optical gaps inferred from the lowest-energy band are
larger than 2 eV and slightly shift to the red when increasing the
bridge length.
2 2
More interesting are the UV-Vis-NIR spectra in CH Cl of
radical dyads 1a-1c at 300 K (Figure 2 and Table 2), which can
be deconvoluted in five principal peaks (Figures S6-S8). All
spectra show a well-defined, intense band at 385 nm that is
[28]
characteristic of chromophores incorporating the PTM radical.
Two less-resolved peaks appear at lower energies for 1a (426
and 518 nm), 1b (456 and 568 nm) and 1c (475 and 607 nm),
which are attributed to the electronic conjugation of the unpaired
electron into the π-conjugated framework. The tendency of these
bands to shift towards lower energies when increasing the
2 2
Figure 2. UV-vis-NIR spectra of a solution 0.05 mM of dyads 1a-1c in CH Cl .
Inset shows an amplification of the low-energy range of the spectra.
Magnetic properties
bridge length is in agreement with
a
higher electron
delocalization over the vinylene units. Finally, the appearance of
a broad band is observed in the 900‒1100 nm range, which is
assigned to an intramolecular charge-transfer (ICT) process
from the TTF unit to the PTM radical. The optical gaps
calculated from the lowest-energy band (~1 eV) are smaller than
those obtained for the non-radical analogues, in agreement with
the stronger electron-acceptor character of the PTM radical unit
and the presence of the semi-occupied molecular orbital
The ESR spectra of radicals 1a, 1b and 1c in toluene/CH Cl2
(0.05 mM at 220 K) show three partially overlapped main lines
centred at different g-values (Figure 3 and Table 3). The shift of
the g factor to higher values recorded from 1a to 1c indicates
larger delocalization of the α-SOMO over the π-conjugated
framework. The three overlapped lines observed at 220 K with
2
1
slightly different hyperfine coupling constants (a (H), Table 3)
can be ascribed to the coupling of the unpaired electron with two
1
(
SOMO) which appear at lower energies (see the theoretical
H atoms of the vinylene bridges (Figure 3).
calculations below).
Table 3. ESR parameters used for the simulation of the experimental X-band
spectra of 1a-1c radicals.
Table 2. UV-vis-NIR data for compounds 1a-1c and 2a-2c in CH
2 2
Cl .
Experimental and theoretical optical gap (∆Eopt).
Dyad
g-value
2.0025
2.0026
2.0028
a
1
(H) (G)
‒3
‒1
‒1
∆Eopt,exp
∆Eopt,theor
b
Dyad
λ
max/nm (10 × ε/M cm
)
a
(eV)
(eV)
1a
1.10
1
b
c
1.07
2
4
95 (20.6); 323 (sh); 385 (26);
26 (15); 518 (4.3); 957 (0.6)
73 (sh); 326 (21.8); 385 (29.3);
56 (12.3); 568 (4.5); 942 (0.6)
1
a
b
1.07
1.08
1.13
1.09
1
1.04
2
4
1
3
40 (24.9); 385 (30.1); 475
1c
1.09
1.07
(15.9); 607 (7.4); 918 (0.7)
2a
2b
2c
290 (sh); 322 (28.4); 456 (5.4)
289 (sh); 332 (26.4); 463 (5.4)
278 (sh); 355 (24.8); 471 (6.4)
2.20
2.15
2.10
2.74
2.55
2.43
a
Experimental optical gaps are calculated from the onset of the lowest-energy
b
absorption band.
Theoretical optical gaps are calculated as the energy
difference between the SOMO and HOMO in radical 1a-1c, and between the
LUMO and HOMO in non-radical 2a-2c.
2 2
Figure 3. ESR spectra of 0.05 mM solutions of dyads 1a-1c in toluene/CH Cl
at 220 K.
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Theoretical calculations
(Table 2) is attributed to the HOMO→LUMO transition, which is
calculated at lower energies upon increasing the bridge length
(Figure S14). This transition implies a certain degree of charge
transfer from the TTF unit to the bridge+PTM region (Figure 4a).
The intense electronic transition observed in the 320‒350 nm
range is assigned to the π-π* HOMO-1→LUMO monoexcitation
and mainly implies the vinylene bridge (Figure 4a). It is predicted
at lower energies going from 2a to 2c (Figure S14) in good
agreement with the experimental observations.
Frontier molecular orbitals. Theoretical calculations were
performed for the family of both radical and non-radical donor-π-
acceptor TTF-π-PTM derivatives under the density functional
theory (DFT) framework. Geometry optimizations were carried
out at the B3LYP/6-31G** level of theory including solvent
effects (see the Supporting Information for full computational
details). Minimum-energy structures of 2a-2c show the TTF unit,
which exhibits the typical boat shape, nearly coplanar to the
conjugated vinylene bridge, whereas the benzene ring
connecting the PTM unit with the bridge presents a dihedral
angle of ~43º with respect to the plane of the bridge (Figure
S11). Minimum-energy geometries of the radical analogues 1a-
1c show similar structural characteristics. Note that two main
conformers arise from the relative orientation of the TTF unit
with respect to the π-conjugated bridge: the s-cis and s-trans
isomers (Figure S12). Theoretical calculations predict the s-trans
isomer 3 kcal/mol more stable than the s-cis for both 1a-c and
2a-c. Hence, the following analysis refers only to the s-trans
isomers.
Figure 4. a) Isovalue contours (±0.03 a.u.) calculated for the frontier molecular
orbitals of 2c at the B3LYP/6-31G** level in CH
frontier molecular orbitals for 2a-c.
2 2
Cl . b) Energy diagram of the
Figure 5. a) Isovalue contours (±0.03 a.u.) calculated for the frontier molecular
orbitals of 1c at the B3LYP/6-31G** level in CH
showing the frontier molecular orbitals for 1a-c.
2 2
Cl . b) Energy diagram
Figure 4a displays the isovalue contours calculated for the
frontier molecular orbitals of 2c as a representative example.
Similar contours are obtained for 2a and 2b (Figure S13). The
highest-occupied molecular orbital (HOMO) is calculated to be
mostly localized on the TTF unit, whereas the second lowest-
unoccupied molecular orbital, the LUMO+1, is centred on the
PTM fragment. Otherwise, the HOMO-1 and the LUMO spread
mainly over the π-conjugated bridge and contain important
contributions from the TTF and PTM fragments, respectively.
Therefore, upon increasing the length of the bridge, the HOMO-
The topologies calculated for the frontier molecular orbitals
of the radical species 1a-c are comparable to those obtained for
the non-radical analogues. Figure 5a shows those computed for
1c as a representative example (see Figure S15 for 1a). As for
2a-c, the α and β HOMOs are located on the TTF unit. In
contrast, the SOMO is essentially localized over the acceptor
PTM fragment. The lowest energy gap in the radical compounds
1a-c therefore corresponds to the HOMO−SOMO β gap, which
is computed nearly constant (~1.1 eV) along the 1a-c family due
to the negligible participation of the bridge in both the HOMO
and the SOMO (Figure 5). The HOMO→SOMO excitation
implies a charge transfer from the TTF unit to the PTM moiety
and gives rise to the low-lying broad ICT absorption band
experimentally recorded in the 950 nm region (Figure 2). The
values predicted theoretically for the HOMO−SOMO gap are in
very good accord with the optical gap deduced from the UV-vis-
NIR spectra (Table 2).
1
and LUMO increase and decrease in energy, respectively,
whereas the HOMO and LUMO+1 energies are barely affected
due to their more localized character (Figure 4b). As
a
consequence, the HOMO−LUMO energy gap of the non-radical
species is systematically reduced upon increasing the bridge
length, going from 2.74 eV in 2a to 2.43 eV in 2c. Based on
time-dependent DFT (TDDFT) calculations, the lowest-energy
UV-vis band experimentally recorded in the 450‒470 nm region
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Charge and spin-density distributions. To scrutinize the effect
that the length of the bridge has on the electron transfer
between the TTF and PTM fragments, the electronic distribution
was analysed by performing a natural population analysis (NPA)
at the B3LYP/6-31G** level. For 1a-c, theoretical calculations
indicate that the TTF fragment has a large positive charge that
increases upon shortening the bridge length (from +0.24e in 1c
to +0.27e in 1a; Figure 6), evidencing the enhanced electron
communication between TTF and PTM for short-length bridges.
Logically, the NPA charge accumulated by the bridge plus the
acceptor PTM unit has the same trend but with opposite sign
(
Figure 6). However, by analysing the bridge and the PTM
fragments separately, we predict that the acceptor PTM contains
an absolute negative charge that becomes slightly larger upon
increasing the bridge length (Figure 6). This amount of charge
does not come from the TTF fragment, which is further from
PTM along the a-c series, but from the π-conjugated bridge,
which redistributes its charge with a partial electron donation to
the PTM. The same trends are qualitatively reproduced for the
closed-shell analogues 2a-2c, but with a global reduced electron
acceptor ability of PTM (Figure 6). Theoretical results therefore
confirm the active role of the π-conjugated bridge, suggesting
that it does not only impact on the donor-acceptor separation but
directly participates in the charge-transfer process.
Figure 6. Accumulated NPA charges calculated for molecular fragments of 1a-
c and 2a-c at the B3LYP/6-31G** level including solvent effects. Molecular
fragments definition and atomic charges identification with colours are
included in the upper part for the representative 1c dyad.
Figure 7 shows the spin-density distributions calculated for
the neutral and charged species of 1c and 2c as representative
examples. Calculations indicate that the unpaired electron in the
1a-c systems is located on the PTM unit, slightly spreading over
the π-conjugated bridge (Figure 7 and S18). The spin-density
distribution computed for the charged species allows for the
assignment of the redox processes taking place in the cyclic
voltammetry experiments. For the non-radical systems 2a-2c,
the first and second oxidations take place on the donor TTF
moiety, with a significant contribution of the π-conjugated bridge,
and a closed-shell dication is obtained (Figure 7). For the cation,
the TTF core evolves to a planar structure as it is the case for
+
•
2+
isolated TTF , whereas the TTF unit presents an inter-ring
Figure 7. Spin densities calculated for neutral and charged species of
representative compounds 1c and 2c at the CAM-B3LYP/6-31G** level of
theory in CH Cl .
2 2
2
+
twisting of 36º for 2c . Likewise, a similar picture is predicted for
the radical analogues. In 1a-1c, the first oxidation takes place in
the TTF moiety, and a triplet cation with one unpaired electron
localized on each moiety (PTM and TTF) is generated (Figure 7).
The second oxidation in the 1a-1c compounds takes place again
on the TTF unit, forming a radical dication with one unpaired
electron in the PTM fragment. As expected, the reduction
process in 1a-c originates in the PTM unit and gives rise to a
negatively charged closed-shell species.
NLO properties. Theoretical first hyperpolarizabilities were
finally computed for the radical 1a-c and non-radical 2a-c
derivatives at the BH&HLYP/6-31G** level of theory (Figure 8) to
assess the NLO response in our D-π-A dyads (see the
Supporting Information for full computational details). Non-
radical 2a-c dyads are predicted with β values ranging 73‒225 ×
‒
30
10
esu. Calculations demonstrate that radical push-pull
derivatives provide larger hyperpolarizabilities compared to the
non-radical analogues, with β values in the range of 202‒601 ×
‒
30
10
esu. Moreover, a systematic enhancement of the NLO
response is achieved by increasing the bridge length (Figure 8).
It is important to note that the β hyperpolarizabilities calculated
for our radical D-π-A dyads surpass those reported for similar
closed-shell TTF-A dyads, which are in the order of 200‒500 ×
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‒
‒
30
30
[11,17,18]
[26]
1
1
0
0
esu,
esu).
and for the unsubstituted PTM radical (362 ×
1.00 g (4.9 mmol) of tetrathiafulvalene, previously recrystallized from
heptane, was dissolved in 60 mL of anhydrous THF under an inert
atmosphere. Then, it was cooled down to -78 ºC with an acetone/N bath
2
and 3.13 mL of LDA (1.8 M) were added and stirred for 90 minutes to
obtain the lithiated TTF-derivative. After that, 1.20 mL (15.5 mmol) of
anhydrous N,N-dimethylformamide (DMF) were added to the solution,
which was stirred for 2 extra hours. Then, the mixture was acidified with
2 2
hydrochloridric acid (2 M), extracted with CH Cl , and washed with water.
The organic phase was dried with anhydrous magnesium sulfate, filtrated,
and the solvent was evaporated under reduced pressure. The product
was purified by column chromatography of silica gel using a mixture of
hexane and CH
2 2
Cl as eluent (1:1). 0.79 g (69%) of the final product
-
were obtained. Characterization: LDI-TOF (positive mode): m/z (amu/e ):
+
· 1
2
33.37 (M ) H-RMN (250MHz, CDCl3, δ(ppm)): 9.48 (s, 1H, CHO); 7.43
‒1
(s, 1H, CH); 6.33 (s, 2H, CH). FT-IR (ν (cm )): 3267 (w); 3063 (w); 3038
(
w); 2920 (w); 2281 (w); 2114 (w); 1786 (w); 1713 (w); 1662 (s); 1645 (s);
1
1
561 (m); 1550 (m); 1532 (s); 1515 (s); 1472 (m); 1368 (m); 1287 (m);
252 (m); 1228 (m); 1143 (s); 1075 (m); 1000 (m); 983 (m); 866 (w); 829
(m); 788 (s); 775 (s); 737 (m); 697 (m).
Figure 8. Theoretical β hyperpolarizabilities calculated at the BH&HLYP/
-31G** level of theory in CH Cl
6
2
2
.
Compound 3b
5
50 mg (2.70 mmol) of tetrathiafulvalene were dissolved in 40 mL of
anhydrous THF under Ar atmosphere. Then it was cooled to -78 °C and
.70 mL of solution of lithium diisopropylamide (LDA) in
tetrahydrofuran were added to the solution and stirred for 60 minutes.
Then, 0.5 mL (5.2 mmol) of 3-(dimethylamino)-acrolein were added and
the solution was stirred for two hours. Afterwards, the mixture was
Conclusions
1
a 2 M
In summary, we have reported the synthesis of a new family of
TTF-π-PTM dyads that have been fully characterized by multiple
spectroscopic techniques in order to analyse the intramolecular
charge transfer between the electron-donor TTF and the
electron-acceptor PTM radical. DFT calculations allowed
understand the geometrical and electronic properties of such
dyads, indicating an active role of the bridge as well as of the
radical/non-radical nature of PTM in the charge-transfer process.
The second-order non-linear optical (NLO) properties of the
TTF-π-PTM derivatives have been theoretically calculated,
demonstrating a direct dependence on the bridge length and an
enhancement of the NLO response for the open-shell dyads.
2 2
acidified with hydrochloric acid (2 M), extracted with CH Cl and washed
with water. The organic phase was dried with anhydrous magnesium
sulfate, filtrated and the solvent was evaporated under reduced pressure.
The product was purified by column chromatography of silica gel using a
mixture of hexane and ether to yield 430 mg (62%) of TTF-CH=CH-CHO
1
(
3b) as a dark red-brownish solid. Characterization: H-NMR (250 MHz,
3
CDCl , δ(ppm)): 9.58 (d, 1H, J = 7.4 Hz, CHO); 7,17 (d, 1H, J = 15.4 Hz,
CH-CHO); 6.87 (s, 1H); 6.35 (s, 2H); 5.96 (dd, 1H, J = 15.4, 7.4 Hz,
‒1
CH=CH-CHO). FT-IR (ν (cm )): 3063 (w); 2955 (w); 2921 (m); 2851 (m);
1
(
8
738 (w); 1660 (s, C=O); 1600 (s, CH=CH); 1522 (m); 1511 (m); 1458
w); 1382 (w); 1252 (w); 1216 (w); 1157 (w); 1112 (s); 1001 (w); 953 (s);
30 (m); 795 (m) 754 (s); 728 (m); 669 (m). LDI-TOF (positive mode):
-
+·
m/z (amu/e ): 257.722 (M ).
Experimental Section
Compound 3c
General Methods
1
A solution of triphenylphosphoranylidene-acetaldehyde (212 mg, 0.7
mmol) and 3b (90 mg, 0.35 mmol) in benzene (20 mL) was refluxed
under Ar for 3 hours. After cooling, hexane (30 mL) was added and the
H NMR spectra were recorded using Bruker Avance 250, 400, 500
instruments and Me4Si as an internal standard. Infrared spectra were
recorded with a Spectrum One FT-IR Spectroscopy instrument and
UV/Vis/NIR spectra were measured using a Cary 5000E Varian. ESR
spectra were performed with a Bruker ESP 300 E equipped with a
rectangular cavity T102 that works with an X-band (9.5 GHz). The
solutions were degassed by argon bubbling before the measurements.
LDI/TOF MS were recorded in a Bruker Ultraflex LDI-TOF spectrometer.
Cyclic voltammetry measurements were obtained with a potentiostat
precipitated Ph
product was purified by column chromatography using hexane/Et
90:10) to obtain 40 mg (40 %) of TTF-CH=CH-CH=CH-CHO (3c) as a
3
PO was filtered. The solvent was evaporated and the
2
O
(
1
red solid. Characterization: H-NMR (250 MHz, CDCl
1
1
3
, δ(ppm)): 9.57 (d,
H, J = 7.9 Hz, CHO); 7,10 (dd, 1H, J = 15.2, 11.0 Hz); 6.73 (d, 1H, J =
5.1 Hz); 6.59 (s, 1H); 6.33 (s, 2H); 6,26 (dd, 1H, J = 14.5, 11.2 Hz); 6,20
‒1
(dd, 1H, J = 14.5, 7.6 Hz). FT-IR (ν (cm )): 3063 (w); 2981 (w); 2848 (w);
2
63a from EG&G Princeton Applied Research in a standard 3 electrodes
1660 (s, C=O); 1602 (s, CH=CH); 1582 (s, CH=CH); 1504 (s); 1392 (w);
cell. All reagents and solvents employed for the syntheses were of high
purity grade and were purchased from Sigma-Aldrich Co., Merck, and
SDS. Dry solvents were used in the chemical reactions and in the cyclic
voltammetries. The solvents used for optical spectroscopy and ESR
measurements were of HPLC grade (ROMIL-SpS). In addition, for cyclic
1
289 (w); 1246 (w); 1140 (s); 1108 (s); 1006 (m); 975 (s); 830 (w); 795
-
(m); 776 (m); 750 (m). LDI-TOF (positive mode): m/z (amu/e ): 283.352
+
·
(M ).
voltammetry experiments, CH
eliminate the acidic residues.
2
Cl
2
was filtered over basic alumina to
Compound 2a
1000 mg (1.14 mmol) of the phosphonate PTM derivative (4-
Compound 3a
[bis(2,3,4,5,6-pentachlorophenylmethyl)methyl]-2,3,4,6-tetrachlorobenzyl
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Chemistry - A European Journal
10.1002/chem.201701623
FULL PAPER
phosphonate) were dissolved in 40 mL of anhydrous THF under strict
inert conditions. The solution was cooled down to -78 ºC by means of an
1138 (m); 992 (s); 951 (w); 859 (w); 808 (s); 778 (m); 735 (w); 716 (w);
682 (m). LDI-TOF (negative mode): m/z (amu/e ): 1004.488 (M );
-
-·
-
-·
acetone/CO
2
(s) bath. Next, 384 mg (3.42 mmol) of potassium tert-
(positive mode): m/z (amu/e ): 1003.931 (M ). UV-VIS-NIR (CH
2
Cl
2
, λmax
‒3
‒1
‒1
butoxide were added and stirred for 20 minutes to form the yellow ylide
under an inert argon atmosphere. After that, 141 mg (1.25 mmol) of
formyl-TTF were added and the reaction was kept at a low temperature
under argon for 3 days. Then, the solution was slowly warmed up to
room temperature and acidified with 1.7 mL of a 2 M solution of HCl and
in nm, 10 × ε in M ·cm ): 278 (sh); 355 (24.8); 471 (6.4). Cyclic
1
4 6 2 2 ½
voltammetry (Bu NPF 0.15 M in CH Cl as electrolyte): E = 0.462 V;
2
½
E
= 0.970 V.
Compound 1a
00 mg (0.1 mmol) of 2a were dissolved in 30 mL of anhydrous THF. 150
2 2
the product was extracted with 3 portions of 40 ml of CH Cl . The organic
phase was washed with water, dried with anhydrous magnesium sulfate
and the solvent was evaporated under reduced pressure. Finally, the
product was purified by flash column chromatography of silica gel using a
1
µL (0.15 mmol) of tetrabutylammonium hydroxide 1.0 M in methanol were
added and the purple solution was stirred for 1 hour. Then, 32 mg (0.18
mmol) of silver nitrate dissolved in 5 mL of acetonitrile were added to the
solution and stirred for 5 minutes. The solution changes from purple to
mixture of hexane/diethyl ether (50:50) as eluent. 778 mg (80%) of
1
product 2a were obtained. Characterization: H-NMR (250 MHz, C
6 6
D ,
δ(ppm)): 7.21 (s, 1H; PTM-H), 6.29 (d, 1H, J = 16.0 Hz); 6.13 (d, 1H, J =
0
dark brown with silver (Ag ) precipitated. Then, the solution was filtered
‒
1
1
(
6.2 Hz); 5.52 (s, 1H); 5.39 (s, 2H). FT-IR (KBr, ν (cm )): 2925 (s), 2850
s), (C-H TTF); 1610 (s) (vinylene bridge); 1530 (m), 1513 (m) (C=C
TTF); 1463 (m); 1356 (s); 1336 (s); 1296 (s); 1134 (m); 1120 (m); 943
through silica and the solvent was evaporated under reduced pressure.
Finally, the product was precipitated with MeOH to produce 73 mg of
dyad 1a (73 %) as brownish powder. Characterization: FT-IR (KBr, ν
‒
(
m); 794(s), 779 (s) (C-Cl); 752 (m). UV-VIS-NIR (CH
2
Cl
2
, λmax in nm, 10
‒1
(
cm )): 2915 (w), 2889 (w), 1603 (w) (vinylene bridge); 1502 (w), 1474
w) (C=C TTF); 1375 (m); 1351 (m); 1334 (s); 1284 (m); 1260 (m); 1250
m); 1163 (m); 1134 (m); 1102 (s); 940 (s); 798(w), 780 (w) (C-Cl). UV-
3
‒1
‒1
×
ε in M ·cm ): 290 (sh); 322 (28.4); 456 (5.4). LDI-TOF (negative
mode): m/z (amu/e ): 953.705 (M ). Cyclic voltammetry (Bu
(
(
-
-·
4 6
NPF 0.15 M
1
2
½
in CH
2
Cl
2
as electrolyte): E
½
= 0.448 V and E
= 0,965 V vs. Ag/AgCl.
‒3
‒1
‒1
2 2
VIS-NIR (CH Cl , λmax in nm, 10 × ε in M ·cm ): 295 (20.6); 323 (sh);
3
85 (26); 426 (15); 518 (4.3); 957 (0.6). LDI/TOF (positive mode): m/z
Compound 2b
-
+•
+
(
C
amu/e ): 952 [M ], 882 [M-2Cl] . Elemental Analysis: Anal. Calcd. for
(C 14): C, 38.11; H, 1.84; S, 12.33. Found: C, 38.88; H, 1,7;
½
S, 12.20. CV (Bu = ‒0.16 V;
27
H
5
Cl14
S
4
6
H
1
454 mg (0.52 mmol) of the phosphonated PTM derivative were dissolved
4
NPF
= 1.01 V vs. Ag/AgCl. ESR (CH
(H) = 1.10 G.
6
0.15 M in CH
2
Cl
2
as electrolyte): E
2
3
½
in 40 mL of anhydrous THF under inert conditions. The solution was
cooled down to -78 ºC and 116 mg (1.03 mmol) of potassium tert-
butoxide were added and stirred for 20 minutes to form the yellow-orange
ylide. After 20 minutes, 147 mg (0.57 mmol) of the aldehyde 3b were
added and the reaction was warmed up to room temperature and stirred
for 2 days. Then the mixture was extracted with CH
water, dried with anhydrous MgSO and solvents were evaporated under
reduced pressure. Finally, the product was purified by column
chromatography of silica gel using a mixture of ether and hexane (1:1) to
obtain to obtain 362 mg (71 %) of 2b as a dark reddish powder.
E
½
= 0.50; E
2
Cl /toluene, 220 K): g =
2
2.0025, a
1
Compound 1b
0 mg (0.08 mmol) of 2b were dissolved in 20 mL of anhydrous THF. 120
2 2
Cl , washed with
8
4
µL (0.12 mmol) of tetrabutylammonium hydroxide 1.0 M in methanol were
added and the purple solution was stirred for 1 hour. Then, 25 mg (0.14
mmol) of silver nitrate dissolved in 5 mL of acetonitrile were added to the
solution and stirred for 5 minutes. The solution changes from purple to
dark brown with silver (Ag ) precipitated. Then, the solution was filtered
through silica and the solvent was evaporated under reduced pressure.
Finally, the product was precipitated with MeOH to produce 60 mg of
1
Characterization: H-NMR (250 MHz, C
6
D
6
, δ(ppm)): 7.23 (s, 1H); 6.49
0
(dd, 1H, J = 15.7, 10.5 Hz); 6,30 (d, 1H, J = 15.7 Hz); 6.09 (dd, 1H, J =
1
5.2, 10.0 Hz); 5.87 (d, 1H, J = 15.1 Hz); 5.50 (s, 1H); 5.41 (s, 2H). FT-IR
‒1
(
ν (cm )): 2951 (w); 2922 (m); 2851 (m); 1727 (w); 1597 (m, CH=CH);
dyad 1b (73 %) as brownish powder. Characterization: FT-IR (KBr, ν
1
1
7
×
526 (m); 1513 (m); 1458 (w); 1369 (w); 1337 (m); 1294 (s); 1239 (w);
190 (w); 1136 (m); 979 (s); 922 (w); 859 (w); 828 (w); 806 (s); 793 (s);
‒1
(
(
(
cm )): 2955 (m); 2922 (m); 2851 (m); 1594 (w, CH=CH); 1525 (w); 1508
m); 1458 (w); 1376 (w); 1333 (s); 1259 (m); 1163 (w); 1136 (m); 1117
m); 1066 (m); 971 (s); 923 (w); 865 (w); 815 (s); 795 (s); 778 (s); 735 (s);
‒3
78 (m); 746 (w); 734 (w); 685 (m). UV-VIS-NIR (CH
2
Cl
2
, λmax in nm, 10
‒1
‒1
ε in M ·cm ): 289 (sh); 332 (26.4); 463 (5.4). LDI-TOF (positive
‒3
‒1
‒1
708 (m). UV-VIS-NIR (CH
2 2
Cl , λmax in nm, 10 × ε in M ·cm ): 273 (sh);
-
+·
4 6
mode): m/z (amu/e ): 981.705 (M ). Cyclic voltammetry (Bu NPF 0.15 M
326 (21.8); 385 (29.3); 456 (12.3); 568 (4.5); 942 (0.6). LDI/TOF (positive
1
½
2
2
in CH Cl
2
as electrolyte): E
= 0.447 V; E
½
= 0.958 V.
-
+·
mode): m/z (amu/e ): 979.711 (M ). Elemental Analysis: Anal. Calcd. for
(C 14): C, 39.43; H, 2.06; S, 12.03. Found: C, 38.8; H, 2.00;
S, 11.67. CV (Bu
C
29
H
7
Cl14
S
4
6
H
1
Compound 2c
30 mg (0.26 mmol) of the phosphonated PTM derivative were dissolved
4
NPF
= 0.96 V vs. Ag/AgCl. ESR (CH
1
(H) = 1.07 G.
6
0.15 M in CH
2
Cl
2
as electrolyte): E
½
= ‒0.20 V;
2
3
½
E
½
= 0.44; E
2
Cl /toluene, 220 K): g =
2
2
2.0026, a
in 30 mL of anhydrous THF under inert conditions. The solution was
cooled down to -78 ºC and 60 mg (0.52 mmol) of potassium tert-butoxide
were added and stirred for 20 minutes to form the yellow-orange ylide.
After 20 minutes, 85 mg (0.30 mmol) of the aldehyde 3c were added and
the reaction was warmed up to room temperature and stirred for 2 days.
Compound 1c
0 mg (0.07 mmol) of 2c were dissolved in 20 mL of anhydrous THF. 100
7
µL (0.10 mmol) of tetrabutylammonium hydroxide 1.0 M in methanol were
added and the purple solution was stirred for 1 hour. Then, 21 mg (0.12
mmol) of silver nitrate dissolved in 5 mL of acetonitrile were added to the
solution and stirred for 5 minutes. The solution changes from purple to
2 2
Then the mixture was extracted with CH Cl , washed with water, dried
with anhydrous MgSO and solvents were evaporated under reduced
4
pressure. Finally, the product was purified by column chromatography of
silica gel using a mixture of ether and hexane (1:1) to obtain to obtain
0
dark brown with silver (Ag ) precipitated. Then, the solution was filtered
1
1
05 mg (40 %) of 2c as a dark reddish powder. Characterization: H-
through silica and the solvent was evaporated under reduced pressure.
Finally, the product was precipitated with MeOH to produce 55 mg of
6 6
NMR (250 MHz, C D , δ(ppm)): 7.23 (s 1H); 6.64 (dd, 1H, J = 15.6, 9.6
Hz,); 6.36 (d, 1H, J = 15.5 Hz); 6.1-5.8 (m, 4H); 5.51 (s, 1H); 5.42 (SM
dyad 1c (78 %) as brownish powder. Characterization: FT-IR (KBr, ν
‒1
2
H). FT-IR (ν (cm )): 2955 (w); 2922 (w); 2855 (w); 1575 (m, CH=CH);
‒1
(
cm )): 2953 (w); 2922 (w); 2850 (w); 1571 (m, CH=CH); 1508 (m); 1459
1525 (m); 1510 (m); 1459 (m); 1370 (w); 1337 (m); 1294 (s); 1237 (w);
This article is protected by copyright. All rights reserved.

Chemistry - A European Journal
10.1002/chem.201701623
FULL PAPER
(
9
(
m); 1377 (w); 1333 (s); 1318 (s); 1257 (s); 1157 (w); 1137 (m); 116 (w);
Organic Molecules and Crystals, Academic Press, Inc.,
Orlando, 1987.
89 (s); 941 (m); 913 (w); 816 (s); 808 (s); 795 (m); 779 (w); 735 (m); 708
‒3
‒1
‒1
m). UV-VIS-NIR (CH
2
Cl
2
, λmax in nm, 10 × ε in M ·cm ): 340 (24.9);
3
85 (30.1); 475 (15.9); 607 (7.4); 918 (0.7). LDI/TOF (positive mode):
[2]
[3]
J. Zyss, Molecular Nonlinear Optics, Academic Press, Inc.,
New York, 1993.
-
-·
(negative mode): m/z (amu/e ): 1004.734 (M ); (positive mode): m/z
-
-·
(
C
amu/e ): 1003.203 (M ). Elemental Analysis: Anal. Calcd. for
(C 14): C, 40.69; H, 2.12; S, 11.74. Found: C, 40.9; H, 2.5;
S, 11.83. CV (Bu
31
H
9
Cl14
S
4
6
H
N. O. Prassad, D. J. Williams, Introduction to Nonlinear
Optical Effects in Molecules and Polymers, Wiley-
Interscience, 1991.
1
4
NPF
= 0.92 V vs. Ag/AgCl. ESR (CH
1
(H) = 1.04 G.
6
0.15 M in CH
2
Cl
2
as electrolyte): E
½
= ‒0.22 V;
2
3
E
½
= 0.40; E
½
2
Cl /toluene, 220 K): g =
2
2.0028, a
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BBN), the Generalitat de Catalunya (grant 2014-SGR-17), the
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Chemistry - A European Journal
10.1002/chem.201701623
FULL PAPER
Entry for the Table of Contents
FULL PAPER
Manuel Souto, Joaquín Calbo, Imma
Ratera, Enrique Ortí, Jaume Veciana*
Page No. – Page No.
TTF-PTM dyads: The role of the
bridge and open-shell character on
the linear and nonlinear optical
properties
Three conjugated donor-π-acceptor radical systems based on a tetrathiafulvalene (TTF)
unit, as electron-donor, connected to a polychlorotriphenylmethyl (PTM) radical, as
electron-acceptor, through different vinylene units as bridge have been synthesized and
characterized. The linear and non-linear optical properties of these derivatives have been
theoretically calculated by comparing with their non-radical analogues.
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