A 2,2'-bipyridyl-bridged tetrathiafulvalene-quinone dyad: Intramolecular electron-transfer promoted by metal ions

Article abstract of DOI:10.1002/cjoc.201090294

A 2,2'-bipyridyl-bridged tetrathiafulvalene (TTF)-quinone dyad (1) was synthesized and characterized. Both absorption and ESR spectroscopic studies clearly indicate that electron transfer occurs from TTF to the quinone unit for dyad 1 in the presence of m

Full text of DOI:10.1002/cjoc.201090294

FULL PAPER
A 2,2'-Bipyridyl-Bridged Tetrathiafulvalene-quinone Dyad:
Intramolecular Electron-Transfer Promoted by Metal Ions†
Huang, Guangxi(黄光熙)
Zhang, Guanxin(张关心)
Zhang, Deqing*(张德清)
Zhu, Daoben(朱道本)
Beijing National Laboratory for Molecular Sciences, Organic Solids Laboratory, Institute of Chemistry, Chinese
Academy of Sciences, Beijing 100190, China
A 2,2'-bipyridyl-bridged tetrathiafulvalene (TTF)-quinone dyad (1) was synthesized and characterized. Both
absorption and ESR spectroscopic studies clearly indicate that electron transfer occurs from TTF to the quinone unit
for dyad 1 in the presence of metal ions. The results manifest that the coordination of dyad 1 with metal ions plays a
key role in facilitating the intramolecular electron transfer.
Keywords donor-acceptor system, tetrathiafulvalene, quinone, electron transfer, 2,2'-bipyridine
Introduction
coordination with metal ions (Scheme 1). Thus, it is
interesting to examine whether the metal-ions promoted
intramolecular electron transfer within TTF-quinone
dyad can take place by using bipyridyl unit as a bridge
instead of oligoethylene glycol chain. In the ‘cisoid’
form the TTF and quinone units would be spatially ad-
jacent, and as a result the metal ion promoted electron
transfer would become more favorable.
Herein we report a new TTF-quinone dyad (dyad 1,
Scheme 2), in which TTF unit and quinone unit are
linked by bipyridyl unit at the 3- and 3'-postions, re-
spectively. The results show that intramolecular electron
transfer can take place effectively within dyad 1 in the
presence of metal ions.
Initially, tetrathiafulvalene (TTF) and its derivatives
as electron donors were designed and investigated for
organic conducting materials.1 However, during the past
decades, miscellaneous TTF-based functional molecules
have been constructed and examined in many fields.2-4
For example, a number of electron donor (D)-acceptor
(A) dyads with TTF units have been reported.3,4 These
TTF based D-A molecules are interesting as models for
studies of charge-transfer interactions, photoinduced
electron transfer processes and molecular level devices.
Recently, we have reported the metal-ions promoted
electron transfer within TTF-quinone dyads in which
the TTF and quinone units are covalently linked by the
oligoethylene glycol chain (Scheme 1).5a-5d The results
show that the coordination of oligoethylene glycol chain
and the radical anion of quinone with metal ions play
key role in promoting the intramolecular electron trans-
fer within TTF-oligoethylene glycol-quinone dyads. In
other words, coordination of oligoethylene glycol chain
with metal ions induces the conformation change for
TTF-quinone dyads; thus, TTF and quinone units within
the dyad become adjacent upon metal ion coordination,
which will facilitate the intramolecular electron transfer.
Besides glycol chain there are many other functional
units that can change molecular conformation upon ex-
ternal stimulus. For instance, 2,2'-bipyridyl, an impor-
tant building block in supramolecular chemistry and
material science, prefers ‘transoid’ formation in the ab-
sence of metal ions;6 however, if certain metal ions are
present, 2,2'-bipyridyl exists in the ‘cisoid’ form via
Experimental
Materials
CsOH•H2O and p-chloranil were purchased from
Acros and Alfa, respectively. Other reagents were used
as received unless otherwise stated. All solvents were
purified and dried following standard procedures unless
otherwise stated.
Characterization techniques
Melting points were measured with an XT4-100X
1
apparatus and uncorrected. H NMR, 13C NMR, MS
(including HRMS), absorption and ESR spectra were
measured with conventional spectrometers. Cyclic
voltammetric measurements were performed in a stan-
dard three-electrode cell, with glassy carbon as the
working electrode and platinum wire as auxiliary elec-
*
E-mail: dqzhang@iccas.ac.cn; Tel.: 0086-010-62639355; Fax: 0086-010-62569349
Received July 13, 2010; revised and accepted August 22.
Project supported by the National Natural Science Foundation of China (Nos. 20802081, 20721061), the State Basic Program (No. 2006CB806201),
Chinese Academy of Sciences, and Transregio Project (TRR61).
† Dedicated to the 60th Anniversary of Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences.
Chin. J. Chem. 2010, 28, 1743— 1750
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Huang et al.
FULL PAPER
Scheme 1 Illustration of the metal ions-promoted intramolecular electron transfer within TTF-oligoethylene glycol-quinone dyad and
the conformation change for 2,2'-bipyridyl unit upon binding metal ions
Scheme 2 Synthetic approach to dyad 1
trode, and Ag/AgCl electrode (saturated KCl) as the
reference electrode; n-Bu4NPF6 (0.1 mo/L) was used as
supporting electrolyte. Elemental analyses were per-
formed on a Carlo-Erba-1106 instrument.
Synthesis of compound 2 A mixture of 2-(2-hy-
droxyethoxy)ethyl 4-methyl benzenesulfonate (9.20 g,
35.4 mmol), 3,4-dihydro-2H-pyran (4.46 g, 53.1 mmol)
and pyridinium p-toluenesulfonate (0.44 g, 1.77 mmol)
was dissolved in 50 mL dry CH2Cl2. The solution was
stirred for 12.0 h at room temperature and then
quenched with 20 mL of diethyl ether. The resulting
solution was washed with saturated brine, dried with
Na2SO4, and then the solvent was removed. Separation
with column chromatography (silica gel, CH2Cl2) gave
compound 2 as pale yellow oil (10.2 g) in 83.8% yield.
1H NMR (CDCl3, 400 MHz) δ: 7.80 (d, J＝7.8 Hz, 2H),
7.34 (d, J＝7.7 Hz, 2H), 4.59 (s, 1H), 4.17—4.16 (m,
2H), 3.86—3.79 (m, 2H), 3.72—3.71 (m, 2H), 3.60—
3.59 (m, 2H), 3.55—3.47 (m, 2H), 2.44 (s, 3H), 1.82—
1.80 (m, 1H), 1.73—1.68 (m, 1H), 1.58—1.53 (m, 4H);
13C NMR (CDCl3, 100 MHz) δ: 144.8, 133.1, 129.8,
128.0, 99.0, 70.7, 69.3, 68.7, 66.6, 62.3, 30.6, 25.4, 21.6,
19.5; HRMS calcd for C16H24O6S 344.1294, found
344.1293.
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A 2,2'-Bipyridyl-Bridged Tetrathiafulvalene-quinone Dyad
Synthesis of compound 5 Under nitrogen, a mix-
ture of compound 4 (2.16 g, 10 mmol) and KH (3.20 g,
80 mmol) in 50 mL of anhydrous THF was heated to
reflux for 1.0 h. Compound 2 (12.4 g, 36 mmol) in 50
mL of anhydrous THF was then added. After refluxed
for 6.0 h, the reaction was quenched with saturated
brine. The whole mixture solution was extracted with
CH2Cl2 and dried with Na2SO4. The solvent was re-
moved by evaporation, and the residue was purified by
column chromatography (silica gel, EtOAc) to give
mixture was stirred for 30 min, followed by addition of
a solution of 7 (546 mg, 1.0 mmol) in 15 mL of anhy-
drous degassed THF. After being stirred overnight at
room temperature, the residue was purified by silica gel
column chromatography using the mixture of dichloro-
methane and methanol (40∶1, V/V) as eluant. Com-
pound 8 (500 mg) was obtained as an orange oil in
1
71.4% yield. H NMR (CDCl3, 400 MHz) δ: 8.55 (s,
2H), 8.01—7.97 (m, 2H), 7.36 (s, 2H), 6.40 (s, 1H),
4.54 (s, 4H), 3.68 (t, J＝4.3 Hz, 2H), 3.65—3.53 (m,
12H), 3.28 (s, 4H), 2.89 (t, J＝6.0 Hz, 2H), 2.51 (s, 1H);
13C NMR (CDCl3, 100 MHz) δ: 155.6, 155.5, 147.5,
147.4, 136.2, 133.4, 133.3, 126.5, 123.3, 123.0, 117.8,
113.9, 106.8, 72.5, 70.5, 70.4, 70.1, 69.6, 69.5, 61.7,
35.3, 30.2; HRMS calcd for C28H33N2O5S7 [M＋H]＋
701.0435, found 701.0400.
1
compound 5 (5.26 g) as a yellow oil in 93.9% yield. H
NMR (CDCl3, 400 MHz) δ: 8.54 (d, J＝4.0 Hz, 2H),
8.02 (d, J＝7.6 Hz, 2H), 7.36—7.33 (m, 2H), 4.62 (s,
2H), 4.53 (s, 4H), 3.88—3.83 (m, 4H), 3.64—3.45 (m,
16H), 1.83—1.52 (m, 12H); 13C NMR (CDCl3, 100
MHz) δ: 155.6, 147.5, 136.3, 133.7, 123.3, 99.1, 70.7,
70.6, 70.3, 69.5, 66.8, 62.4, 30.7, 25.6, 19.6; HRMS
calcd for C30H45N2O8 [M ＋ H] ＋ 561.3176, found
561.3167.
Synthesis of compound 1 To a solution of com-
pound 8 (180 mg, 0.26 mmol) in 5 mL dry THF was
added NaH (12.5 mg, 0.52 mmol). The mixture was
stirred for 30 min. Then tetrachloro-1,4-benzoquinone
(128 mg, 0.52 mmol) was added. After being stirred for
5 h, the reaction mixture was filtered. After removal of
solvents, the residue was subjected to column chroma-
tography on silica gel to give compound 1 (124 mg) as a
black green solid in 52.6% yield. 1H NMR (CDCl3, 400
MHz) δ: 8.55—8.53 (m, 2H), 7.80 (d, J＝7.4 Hz, 1H),
7.92 (d, J＝7.4 Hz, 1H), 7.37—7.33 (m, 2H), 6.39 (s,
1H), 4.66 (t, J＝4.1 Hz, 2H), 4.53 (s, 2H), 4.46 (s, 2H),
3.73 (t, J＝4.1 Hz, 2H), 3.62 (t, J＝6.4 Hz, 2H), 3.55—
3.51 (m, 6H), 3.43 (t, J＝4.3 Hz, 2H), 3.29 (s, 4H), 2.90
(t, J＝6.4 Hz, 2H); 13C NMR (CDCl3, 100 MHz) δ:
172.7, 171.9, 155.5, 155.3, 147.5, 140.3, 138.8, 136.3,
136.1, 133.5, 133.3, 126.6, 125.7, 123.4, 123.0, 117.8,
114.0, 106.8, 73.6, 70.9, 70.7, 70.5, 70.1, 70.0, 69.7,
69.5, 69.4, 35.4,＋ 30.3; HRMS calcd for
C34H31Cl3N2O7S7 [M] 907.9225, found 907.92364.
Synthesis of compound 6 To a solution of com-
pound 5 (5.66 g, 10.1 mmol) in methanol (100 mL) was
－1
added aqueous HCl (1 mol•L , 60 mL). After stirred
for 2.0 h at room temperature, NaOH aqueous was
added to neutralize excess HCl. The resulting solution
was extracted with CHCl3 (150 mL×10), and dried
with Na2SO4. After removal of solvents the residue was
subjected to column chromatography on silica gel to
give compound 6 (2.70 g) as a white solid in 68.1%
1
yield. M.p. 95—97 ℃; H NMR (CDCl3, 400 MHz) δ:
8.57 (d, J＝4.8 Hz, 2H), 7.95 (d, J＝7.8 Hz, 2H), 7.38
—7.35 (m, 2H), 4.56 (s, 4H), 3.63 (t, J＝4.8 Hz, 4H),
3.56—3.49 (m, 12H), 3.40 (s, 2H); 13C NMR (CDCl3,
100 MHz) δ: 156.1, 147.8, 136.4, 133.3, 123.4, 72.9,
70.5, 70.2, 69.8, 61.8. Anal. calcd for C20H28N2O6: C
61.21, H 7.19, N 7.14; found C 61.28, H 7.23, N 7.05.
Synthesis of compound 7 To a solution of com-
pound 6 (685 mg, 1.75 mmol), triethylamine (2.4 mL,
17.3 mmol) and catalytic amount of DMAP in 120 mL
of dry CH2Cl2 at －78 ℃, p-toluenesulfonyl chloride
(380 mg, 2.00 mmol) was added. The resulting mixture
was stirred for 12 h. Then the organic solution was
washed with NaHCO3 aqueous, dried with Na2SO4. Af-
ter removal of solvents, the residue was subjected to
column chromatography on silica gel to give compound
7 (560 mg) as a pale yellow oil in 58.6% yield. 1H NMR
(CDCl3, 400 MHz) δ: 8.55 (d, J＝3.2 Hz, 2H), 7.98 (d,
J＝7.5 Hz, 2H), 7.79 (d, J＝7.8 Hz, 2H), 7.36—7.31 (m,
4H), 4.54 (s, 2H), 4.51 (s, 2H), 4.14 (s, 2H), 3.66—3.49
(m, 14H), 2.43 (s, 4H); 13C NMR (CDCl3, 100 MHz) δ:
155.7, 155.6, 147.6, 147.5, 145.0, 136.4, 136.3, 133.4,
133.1, 130.0, 128.1, 123.4, 72.6, 70.7, 70.5, 70.2, 70.1,
69.6, 69.5, 69.4, 68.＋8, 61.8, 21.8; HRMS calcd for
C27H35N2O8S [M＋H] 547.2114, found 547.2130.
Synthesis of compound 8 Under N2 atmosphere, a
solution of CsOH•H2O (252 mg, 1.50 mmol) in 2 mL of
anhydrous degassed CH3OH was dropped into a solu-
tion of compound 37 (456 mg, 1.2 mmol) in 30 mL of
anhydrous degassed THF over a period of 10 min. The
Results and discussion
Synthesis and characterization
The synthetic approach to dyad 1 is shown in
Scheme 2. Reaction of compound 46a with compound 2
in the presence of KH afforded compound 5. Removal
of the tetrahydropyran group in compound 5 led to
compound 6, which was further transformed into com-
pound 7 after mono-tosylation. Reaction of compounds
7 and 37 in the presence of CsOH yielded compound 8.
Further reaction of compound 8 with tetrachloro-1,4-
benzoquinone in the presence of NaH afforded dyad 1
in 52.6% yield.
Absorption and ESR spectral studies
Figure 1 shows the absorption spectrum of dyad＋1
and those in the presence of different amount of Sc3 .
No absorption above 550 nm was detected for dyad 1
＋
before addition of Sc3 . This implies that the in-
tramolecular interaction between TTF and quinone unit
within dyad 1 can be neglected. However, after addition
Chin. J. Chem. 2010, 28, 1743— 1750
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Huang et al.
FULL PAPER
＋
of Sc3 to the solution of dyad 1, new absorption bands
around 450 and 850 nm emerged, and their absorption
＋
intensities increased by increasing the amount of Sc3 .
The maximum absorption reached after the addition of
＋
more than 1.5 equiv. of Sc3 (see inset A of Figure 1).
According to previous studies,5 the absorption bands
around 450 and 850 nm can be ascribed to the radical
cation of TTF unit of dyad 1. Therefore, the appearance
of these two absorptions indicates the formation of the
＋
＋
TTF• for dyad 1 in the presence of Sc3 . This is likely
due to the e＋lectron transfer within dyad 1 in the pres-
ence of Sc3 based on the previous investigations of
TTF-quinone dyads.5 The corresponding Job plot ＋(see
inset B of Figure 1) implies that dyad 1 binds Sc3 to
form a complex with 2∶3 stoichiometry.
－5
Figure 2 ESR spectrum of dyad 1 (5.0× 10 mol/L) in CH2Cl2
＋
in the presence of 5.0 equiv. of Sc3 [Sc(OTf)3] recorded at room
temperature; the solution was degassed before measurement.
＋
＋
Ni2 and Ba2 ). Obvious increasement of absorptions
around 450 and＋850 nm were observed for dyad 1 in the
presence of Pb2 (Figure 3), being simililar to those of
＋
dyad 1 with Sc3 . New absorptions around 450 and 850
nm ＋were also observ＋ed for dyad 1 in the presence of
＋
Zn2 , Cd2 and Co2 (Figure 3). In addition, strong
ESR signals were d＋etected for the solution of dyad 1
＋
containing Pb2 /Zn2 ＋ (Figure 4＋). Thus, it can be con-
＋
＋
cluded that Pb2 /Zn2 /Cd2 /Co2 can also promote the
electron transfer efficiently between TTF and quinone
units within dyad 1. The Job plots shown in insets of
Figure 3 indicate that the solutions exhibit maximum
absorbance at 850＋nm when the molar ratios of dyad 1
＋
vs. Pb2 and Zn2 were 1∶2 and 2∶3, respectively.
Figure 1 Absorption spectra of dyad 1 recorded in CH2Cl2 (5.＋0
Accordingly, it may be concluded that dyad 1 binds
－5
×
10 mol/L) in the presence of increasing amount of Sc3
＋
＋
Pb2 and Zn2 to form 1∶2 and 2∶3 complexes, re-
[Sc(OTf)3]; inset A shows the variation of absorb＋ance intensity at
spectively.
850 nm upon addition of different amounts of Sc3 , inset B shows
＋
Job plot for the binding of 1 with Sc3
.
Cyclic voltammetric studies
In order to understand the mechanism for metal ions
The solution of dyad 1 was ESR silent. However,
strong ESR signal was ob＋served for the solution of dyad
1 in the presence of Sc3 as shown in Figure 2. The
doublet ESR signals were likely due to the radical
cation of TTF unit of dyad 1, and the doublet signals
were ascribed to the splitting of one H atom of TTF unit.
However, the radical anion of quinone unit could not be
detected for the fast－disproportionation of the r－adical
anion of quinone (Q• ) into the corresponding Q2 and
neutral Q in the presence of metal ion at room tempera-
ture.8 Nevertheless, the emergence of ESR signal con-
firms that electro＋n transfer takes place for dyad 1 in the
presence of Sc3 . Accordingly, both absorption and
ESR spectroscopic investigations manifest that electron
promoted electron transfer within dyads 1, the redox
＋
potentials of 1 in the absence and presence of Sc3 /
＋
＋
Pb2 /Zn2 were measured. Figure 5 depicts the cyclic
voltammogra＋m of＋1 and that in the presence of 2.0
＋
equiv. of Sc3 /Pb2 /Zn2 . Three quasi-reversible redox
1/2
waves were detected for dyad 1, corresponding to E
ox1
1/2
ox2
1/2
red
＝0.50 V, E ＝0.89 V and E ＝－0.14 V. The two
oxidation potentials are close to those of compound 3
(see Scheme 2) ( E ＝0.49 V, E ＝0.88 V).7 Thus,
1/2
ox1
1/2
ox2
1/2
ox1
1/2
the oxidation waves with E ＝0.50 V and E
＝
ox2
＋
0.89 V should be due to the formation of TTF• and
2＋
1/2
red
TTF , respectively. The reduction wave with E
＝
－0.14 V is owing to the reduction of quinone unit in
dyad 1 according to previous study.5 These results can
reach the conclusions that the electron donor-acceptor
interaction within dyad 1 can be neglected in the ground
state, which agrees well with the absorption spectral
studies as discussed above. Therefore, the electron
transfer occurs between TTF and quinone units of dyad
＋
1 in the presence of Sc3 .
The absorption and ESR spectra of dyads 1 were
also measured in the＋prese＋nce of＋other metal ions (in-
＋
＋
＋
cluding Li＋, Na＋, K , Pb2 , Zn2 , Mg2 , Cd2 , Co2 ,
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Chin. J. Chem. 2010, 28, 1743— 1750

A 2,2'-Bipyridyl-Bridged Tetrathiafulvalene-quinone Dyad
＋
＋
－5
Figure 3 Absorption spectra of dyad 1 recorded in CH2Cl2 (5.0× 10 mol/L) in the presence o＋f increasin＋g amount of Pb2 (A), Zn2
＋
＋
(B), Cd2 (C) and Co2 (D); insets show the corresponding Job plots for the binding of 1 with Pb2 and Zn2
.
＋
＋
－5
Figure 4 ESR spectra of dyad 1 (5.0× 10 mol/L) in CH2Cl2 in the presence of 5.0 equiv. of Pb2 and Zn2 recorded at room tem-
perature; the solution was degassed before measurement.
transfer between the TTF and quinone units of dyads 1
By comparing the metal ion-promoted electron
transfer within TTF-oligoethylene glycol chain-quinone
is not thermodynami＋cally ＋feasible. However, in the
＋
＋
presence of Sc3 /Pb2 /Zn2 , the reduction wave was
dyads, we assume that sulfur atoms from TTF• , oxygen
positively shifted (see Figure 5). For instances, the re-
duction peak potential of the quinone unit in dyad 1 was
shifted from －0.18 to 0.05 a＋nd 0.02 V in the presence
atoms of biglycol chain and oxygen atoms of the radical
anion of＋quinone unit in dyad 1 may coordinate with
＋
＋
Sc3 /Pb2 /Zn2 to stabilize the electron-transfer state
by increasing the interaction between the corresponding
cation and anion (see Scheme 3). However, there is still
some difference in their coordination geometry for dyad
1 complex with different metal ions. For example, the
＋
of 2.0 equiv. of Sc3 and Pb2 , respectively (see Figure
5). On the basis of previous studies,5 positive shifts of
reduction potential of quinone unit in dyad 1 in the
presence of metal ions make the intramolecular electron
transfer from TTF unit to quinone unit more feasible.
＋
stoichiometry of complex formed between 1 and Sc3 /
Chin. J. Chem. 2010, 28, 1743— 1750
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www.cjc.wiley-vch.de
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Huang et al.
FULL PAPER
＋
－4
Figure 5＋ Cyclic voltammograms of dyad 1 (5.0× 10 mol/L) in CH2Cl2 before (solid) and after (dot) addition of 2.0 equiv. of Sc3
/
＋
Pb2 /Zn2
.
Scheme 3 The proposed mechanism for the metal ion-promoted electron transfer within dyad 1
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Chin. J. Chem. 2010, 28, 1743— 1750

A 2,2'-Bipyridyl-Bridged Tetrathiafulvalene-quinone Dyad
＋
Zn2 was estimated to be 2∶3 via the job plots (insets
2004, 104, 5115.
of Figu＋re 1 and Figure 3). As illustrated in Scheme 3,
(f) Martín, N.; Sánchez, L.; Herranz, M. A. Á.; Illescas, B.;
Guldi, D. M. Acc. Chem. Res. 2007, 40, 1015.
(g) Dichtel, W. R.; Miljanić, O. S.; Zhang, W.; Spruell, J.
M.; Patel, K.; Aprahamian, I.; Heath, J. R.; Stoddart, J. F.
Acc. Chem. Res. 2008, 41, 1750.
＋
one Sc3 /Zn2 may firstly coordinate with two 2,2'-bipy-
ridyl units leading to conformation change of 2,2'-bipy-
ridyl unit from ‘transoid’ to ‘cisoid’. The favorable
‘cisoid’ conformation would cause the TTF and quinone
units in dyad 1 to be spatially adjacent; further synergic
coordination of the radical anion＋of quinone and the
(h) Canevet, D.; Salle, M.; Zhang, G.; Zhang, D.; Zhu, D.
Chem. Commun. 2009, 2245; and reference herein.
(i) Stoddart, J. F. Chem. Soc. Rev. 2009, 38, 1802.
(a) Perepichka, D. F.; Bryce, M. R.; Pearson, C.; Petty, M.
C.; McInnes, E. J. L.; Zhao, J. P. Angew. Chem., Int. Ed.
2003, 42, 4636.
＋
diglycol chain with two Sc3 /Zn2 results in electron
＋
transfer efficiently in dyad 1. For Pb2 , however, the
3
＋
complex of dyad 1 with Pb2 adopts 1∶2 stoichiome-
try and the coordination mode is proposed as shown in
Scheme 3. Similarly, because of the ‘cisoid’ conforma-
(b) Tsiperman, E.; Becker, J. Y.; Khodorkovsky, V.;
Shames, A.; Shapiro, L. Angew. Chem., Int. Ed. 2005, 44,
4015.
＋
tion of 2,2'-bipyridyl unit after coordination with Pb2 ,
the TTF and quinone units in dyad 1 would be spatially
adjacent, which is favorable for the intramolecular elec-
(c) Baffreau, J.; Dumur, F.; Hudhomme, P. Org. Lett. 2006,
8, 1307.
＋
tron transfer in the presence of Pb2 .
(d) Molina-Ontoria, A. N.; Fernández, G.; Wielopolski, M.;
Atienza, C.; Sánchez, L.; Gouloumis, A.; Clark, T.; Martín,
N.; Guldi, D. M. J. Am. Chem. Soc. 2009, 131, 12218.
(a) Becher, J.; Brimert, T.; Jeppesen, J. O.; Pedersen, J. Z.;
Zubarev, R.; Bjørnholm, T.; Reitzel, N.; Jensen, T. R.;
Kjaer, K.; Levillain, E. Angew. Chem., Int. Ed. 2001, 40,
2497.
Conclusion
In summary, the 2,2'-bipyridyl linked TTF-quinone
dyad 1 was synthesized and characterized. Both absorp-
tion and ESR spectroscopic studies clearly indicate that
electron transfer occurs from TTF to the quinone unit
4
＋
＋
within dyad 1 in the presence of metal ions (Sc3 , Pb2 ,
(b) Leroy-Lhez, S.; Baffreau, J.; Perrin, L.; Levillain, E.;
Allain, M.; Blesa, M.-J.; Hudhomme, P. J. Org. Chem. 2005,
70, 6313.
＋
＋
＋
Zn2 , Cd2 and Co2 ). The coordination of dyad 1 with
metal ions plays a key role in facilitating the in-
tramolecular electron transfer: (1) the metal ion coordi-
nation induces the positive shift of the reduction poten-
tial of the quinone unit which makes the intramolecular
electron transfer from TTF unit to quinone unit more
feasible; (2) the coordination with metal ions induces
the conformation change of bipyridyl unit from
‘transoid’ to ‘cisoid’ which would be favorable for the
synergic coordination of the radical anion of quinone
and the diglycol chain with metal ions. These results
provide a new example of metal ions-promoted electron
transfer within TTF-quinone dyads. Further studies re-
garding the application of such metal ions-promoted
electron transfer are underway.
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