New substituted tetrathiafulvalene - Quinone dyads: The influences of electron accepting abilities of quinone units on the metal ion-promoted electron-transfer processes

Article abstract of DOI:10.1021/jo800581t

(Chemical Equation Presented) The metal ion-promoted electron transfer occurs to all new dyads 1, 2, 3, and 4, even one of them, dyad 4, which has a rather weak electron acceptor unit. The results also indicate that the metal ion-promoted electron transfer within the dyads is influenced by the electron accepting abilities of quinone units; dyad 2 with the strongest electron acceptor among the four dyads shows the strongest absorption and ESR signals attributed to TTF^?+ in the presence of metal ions.

Full text of DOI:10.1021/jo800581t

by alternating UV and visible light irradiations in the presence
of spiropyran. It would be interesting to see whether the metal
ion-promoted electron transfer can occur to TTF-A dyads with
electron acceptor units showing different redox potentials, and
examine the influence of the electron-accepting abilities on the
metal ion-promoted electron transfer processes. For these
purposes, substituted TTF-quinone dyads 1, 2, 3, 4, and 56
(Scheme 1), whose quinone units exhibit different electron-
accepting behaviors, were synthesized and their electron transfer
properties were investigated in the presence of metal ions. The
TTF and quinone units are linked by the oligoethylene glycol
chain.7,8 Substituted quinones 12, 13, 14, and 15 (Scheme 1)
were synthesized and dyad 5 was also included for comparison.
The synthesis of substituted TTF-quinone dyads 1, 2, 3, and
4 started from compound 6. After reaction with p-toluenesulfo-
nyl chloride in the presence of triethylamine, compound 6 was
transformed into compound 7 in 86% yield, which was further
reacted with potassium thioacetate to make compound 8.
Reduction of compound 8 with LiAlH4 yielded compound 9,
New Substituted Tetrathiafulvalene-Quinone
Dyads: The Influences of Electron Accepting
Abilities of Quinone Units on the Metal
Ion-Promoted Electron-Transfer Processes
Hui Wu,†,‡ Deqing Zhang,*,† Guanxin Zhang,† and
Daoben Zhu*,†
Beijing National Laboratory for Molecular Sciences,
Organic Solids Laboratory, Institute of Chemistry, Chinese
Academy of Sciences, Beijing 100080, and Graduate School
of Chinese Academy of Sciences, Beijing 100080, China
dqzhang@iccas.ac.cn
ReceiVed March 14, 2008
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2001, 40, 1372–1409, and further references cited therein. (d) Farren, C.;
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67, 9130–9139. (e) Nielsen, M. B.; Nielsen, S. B.; Becher, J. Chem. Commun.
1998, 475–476. (f) Li, H.; Jeppesen, J. O.; Levillain, E.; Becher, J. Chem.
Commun. 2003, 846–847. (g) Liu, Y.; Flood, A. H.; Stoddart, J. F. J. Am. Chem.
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Zhu, D. J. Mater. Chem. 2005, 15, 2557–2561. (i) Zhou, Y.; Zhang, D.; Zhu,
L.; Shuai, Z.; Zhu, D. J. Org. Chem. 2006, 71, 2123–2130.
The metal ion-promoted electron transfer occurs to all new
dyads 1, 2, 3, and 4, even one of them, dyad 4, which has a
rather weak electron acceptor unit. The results also indicate
that the metal ion-promoted electron transfer within the dyads
is influenced by the electron accepting abilities of quinone
units; dyad 2 with the strongest electron acceptor among the
four dyads shows the strongest absorption and ESR signals
attributed to TTF·+ in the presence of metal ions.
Tetrathiafulvalene (TTF) and its derivatives are strong
electron donors (D). Various electron acceptors (A) have been
connected to TTF to afford electron donor-acceptor (D-A)
dyads or triads for investigations of charge-transfer interactions
and building molecular level devices, such as molecular
rectifiers1 and molecular switches.2 For instance, a new redox
fluorescence switch and some chemical sensors based on the
TTF-anthracene dyad were reported;3 the excited property of
anthracene within the TTF-anthracene dyad can be tuned by
assembly on the surfaces of gold nanoparticles.4 D-A dyads
with TTF and perylene diimide analogues were synthesized and
their fluorescence intensities varied with the oxidation states of
TTF units.5
(3) (a) Zhang, G.; Zhang, D.; Guo, X.; Zhu, D. Org. Lett. 2004, 6, 1209–
1212. (b) Li, X.; Zhang, G.; Ma, H.; Zhang, D.; Li, J.; Zhu, D. J. Am. Chem.
Soc. 2004, 126, 11543–11548. (c) Zhang, G.; Li, X.; Ma, H.; Zhang, D.; Li, J.;
Zhu, D. Chem. Commun. 2004, 2072–2073. (d) Feng, M.; Guo, X.; Lin, X.; He,
X.; Ji, W.; Du, S.; Zhang, D.; Zhu, D.; Gao, H. J. J. Am. Chem. Soc. 2005, 127,
15338–15339. (e) Lu, H.; Xu, W.; Zhang, D.; Chen, C.; Zhu, D. Org. Lett. 2005,
7, 4629–4632. (f) Zhang, G.; Zhang, D.; Zhou, Y.; Zhu, D. J. Org. Chem. 2006,
71, 3970–3972. (g) Wen, G.; Zhang, D.; Huang, Y.; Zhao, R.; Zhu, L.; Shuai,
Z.; Zhu, D. J. Org. Chem. 2007, 72, 6247–6250.
(4) Zhang, G.; Zhang, D.; Zhao, X.; Ai, X.; Zhang, J.; Zhu, D. Chem. Eur.
J. 2006, 12, 1067–1073.
(5) (a) Guo, X.; Zhang, D.; Zhang, H.; Fan, Q.; Xu, W.; Ai, X.; Fan, L.;
Zhu, D. Tetrahedron 2003, 59, 4843–4850. (b) Leroy-Lhez, S.; Baffreau, J.;
Perrin, L.; Levillain, E.; Allain, M.; Blesa, M.-J.; Hudhomme, P. J. Org. Chem.
2005, 70, 6313–6320. (c) Zheng, X.; Zhang, D.; Zhu, D. Tetrahedron Lett. 2006,
47, 9083–9087. (d) Guo, X.; Gan, Z.; Luo, H.; Araki, Y.; Zhang, D.; Zhu, D.;
Ito, O. J. Phys. Chem. A 2003, 107, 9747–9753.
We have recently reported a TTF-trichloroquinone dyad
linked by an oligoethylene glycol chain.6 For this D-A dyad,
the metal ion-promoted electron transfer was observed and
moreover the electron transfer process can be reversibly tuned
(6) Wu, H.; Zhang, D.; Su, L.; Ohkubo, K.; Zhang, C.; Yin, S.; Mao, L.;
Shuai, Z.; Fukuzumi, S.; Zhu, D. J. Am. Chem. Soc. 2007, 129, 6839–6846.
(7) For other examples of TTF-quinone systems, see: (a) Dumur, F.; Gautier,
N.; Gallego-Planas, N.; Sahin, Y.; Levillain, E.; Mercier, N.; Hudhomme, P.;
Masino, M.; Girlando, A.; Lloveras, V.; Vidal-Gancedo, J.; Veciana, J.; Rovira,
C. J. Org. Chem. 2004, 69, 2164–2177, and further references therein. (b) Scheib,
S.; Cava, M. P.; Baldwin, J. W.; Metzger, R. M. J. Org. Chem. 1998, 63, 1198–
1204.
† Chinese Academy of Sciences.
‡ Graduate School of Chinese Academy of Sciences.
10.1021/jo800581t CCC: $40.75
Published on Web 04/30/2008
2008 American Chemical Society
J. Org. Chem. 2008, 73, 4271–4274 4271

TABLE 1. The Redox Potentials (vs. Ag/AgCl) of Dyads 1, 2, 3, 4,
and 5, Oxidation Potentials of 6, and Reduction Potentials of
Reference Quinone Compounds 12, 13, 14, and 15a
SCHEME 1. The Chemical Structures of Dyads 1, 2, 3, 4,
and 5 and the Reference Compounds 12-15 as Well as the
Synthetic Scheme
compd
E1/2ox1, V
E1/2ox2, V
E1/2red1, V
1
2
3
4
5
6
0.50
0.49
0.50
0.50
0.50
0.50
0.84
0.84
0.83
0.83
0.84
0.83
-0.32
-0.06
-0.47
-0.60
-0.09
12
13
14
15
-0.32
-0.06
-0.48
-0.59
a Cyclic voltammetric measurements were performed with platinum
wires as working and counter electrodes, and Ag/AgCl electrode
(saturated KCl) as the reference electrode, respectively. The scan rate
was 100 mV S-1. n-Bu4NPF6 (0.1 M) was used as the supporting
electrolyte. The concentration of each compound was 1.0 × 10-3 . in a
mixture of CH2Cl2 and CH3CN (1:1, v/v).
which reacted with tetrachloro-1,4-benzoquinone and 1,4-
benzoquinone directly to afford dyad 2 and dyad 3 in 41% and
52% yields, respectively. For the synthesis of dyad 1, compound
7 was converted to compound 10 after reaction with NaN3.
Compound 11 was obtained by reaction of compound 10 with
PPh3, and further reaction of compound 11 with tetrachloro-
1,4-benzoquinone yielded dyad 1 in 31% yield. Dyad 4 was
obtained by direct reaction of compound 6 with 2,3-dichloro-
1,4-nathphoquinone in the presence of NaH. The detailed
synthetic procedures and characterizations are provided in the
Supporting Information. Reference quinone compounds 12, 13,
14, and 15 were also synthesized according to reported
procedures (see the Supporting Information).
FIGURE 1. Absorption spectra of dyad 1 recorded in a mixture of
CH2Cl2 and CH3CN (1:1, v/v; 5.0 × 10-5 M) in the presence of
increasing amounts of Pb2+ [Pb(ClO4)2]; the inset shows the 600-1200
nm part of the absorption spectra of dyads 1, 2, 3, 4, and 5 in the
presence of 1.0 equiv of Pb2+ [Pb(ClO4)2].
absorptions around 450 and 845 nm (see Figures S1-S11 of
the Supporting Information) were observed. For instance, Figure
1 shows the absorption spectrum of dyad 1 and those in the
presence of different amounts of Pb2+. Before the addition of
Pb2+, dyad 1 exhibits no absorption above 600 nm. However,
new absorptions around 450 and 845 nm appear in the presence
of Pb2+; moreover, the absorption intensities at 450 and 845
nm increased with increasing amounts of Pb2+ as shown in
Figure 1. According to previous studies,2i,6,10 the absorption
bands around 450 and 845 nm could be ascribed to the radical
cation of TTF (TTF•+) units of D-A dyads. This assumption
was supported by the control experiments with compound 6;
both chemical oxidation of 6 by addition Fe3+ and electro-
chemical oxidations of 6 by applying an oxidation potential at
+0.65 V (vs Ag/AgCl) led to new absorption bands at 450 and
845 nm (see Figures S13 and S14 of the Supporting Informa-
tion). The possibility that these new absorptions of dyads 1, 2,
3, and 4 in the presence of metal ions are due to the charge
transfer from the TTF to quinone units can be ruled out on the
The redox potentials were measured and the results are listed
in Table 1. The oxidation potentials of dyads 1, 2, 3, and 4 are
almost the same as those of dyad 5, and their reduction potentials
are almost the same as those of reference quinone compounds
12, 13, 14, and 15.9 These cyclic voltammtric data show that
there is no detectable interaction between TTF and quninone
units within these D-A dyads. The electron-accepting abilities
of the quinone units within dyads 1, 2, 3, 4, and 56 decreased
in the following order: 2 > 5 > 1 > 3 > 4.
The absorption spectra of dyads 1, 2, 3, and 4 were measured
in the presence of Pb2+, Zn2+, and Sc3+. In all cases, new
(8) For recent examples of metal complexation of polyether-TTFs, see: (a)
Trippe´, G.; Le Derf, F.; Lyskawa, J.; Mazari, M.; Roncali, J.; Gorgues, A.;
Levillain, E.; Salle´, M. Chem. Eur. J. 2004, 10, 6497–6509. (b) Lyskawa, J.; Le
Derf, F.; Levillain, E.; Mazari, M.; Salle´, M.; Dubois, L.; Viel, P.; Bureau, C.;
Palacin, S. J. Am. Chem. Soc. 2004, 126, 12194–12195. (c) Delogu, G.; Fabbri,
D.; Dettori, M. A.; Salle´, M.; Le Derf, F.; Blesa, M.-J.; Allain, M. J. Org. Chem.
2006, 71, 9096–9103. (d) Lyskawa, J.; Le Derf, F.; Levillain, E.; Mazari, M.;
Salle´, M. Eur. J. Org. Chem. 2006, 2322–2328. (e) Blesa, M.-J.; Zhao, B.-T.;
Allain, M.; Le Derf, F.; Salle´, M. Chem. Eur. J. 2006, 12, 1906–1914.
(9) The reduction potentials are referred to the first reduction waves of
substituted quinones.
(10) (a) Ashton, P. R.; Balzani, V.; Becher, J.; Credi, A.; Fyfe, M. C. T.;
Mattersteig, G.; Menzer, S.; Nielsen, M. B.; Raymo, F. M.; Stoddart, J. F.;
Venturi, M.; Williams, D. J. J. Am. Chem. Soc. 1999, 121, 3951–3957. (b)
Spanggaard, H.; Prehn, J.; Nielsen, M. B.; Levillain, E.; Allain, M.; Becher, J.
J. Am. Chem. Soc. 2000, 122, 9486–9494. (c) Ribera, E.; Veciana, J.; Molins,
E.; Mata, I.; Wurst, K.; Rovira, C. Eur. J. Org. Chem. 2000, 2867–2875. (d)
Khodorkovsky, V.; Shapiro, L.; Krief, P.; Shames, A.; Mabon, G.; Gorgues, A.;
Giffard, M. Chem. Commun. 2001, 2736–2737.
4272 J. Org. Chem. Vol. 73, No. 11, 2008

FIGURE 2. ESR spectrum of dyad 1 (1.0 × 10-4 M) in CH2Cl2/CH3CN
(1:1, v/v) in the presence of 1.0 equiv of Pb2+ [Pb(ClO4)2] recorded at
room temperature; the solution was degassed before measurement.
FIGURE 3. Cyclic voltammograms of dyad 12 (5.0 × 10-4 M) (a,
black) before and (b, red) after addition of 2 equiv of Pb2+ in CH2Cl2/
CH3CN (1:1, v/v) at a scan rate of 100 mV S-1. The inset shows the
cyclic voltammograms of compound 12 (5.0 × 10-4 M) before (c,
green) and after addition of 2.0 equiv of Pb(ClO4)2 (d, blue) at a scan
basis of the following considerations: (1) Intermolecular charge-
transfer absorption bands were not detected for the mixture
solutions of 6 (1.5 × 10-2 M) and 12/13/14 (2.5 × 10-2 M)
(see Figure S15 of the Supporting Information). These results
indicate that charge-transfer interactions between TTF and
quinone units within dyads 1, 2, 3, and 4 should be rather weak.
(2) If these new absorption bands observed for dyads 1, 2, 3,
and 4 were due to the charge-transfer interactions, the corre-
sponding charge-transfer absorption bands should be different
since the electron accepting abilities of the quinone units within
dyads 1, 2, 3, and 4 are different. But, dyads 1, 2, 3, and 4
exhibit the same new absorption bands at 450 and 845 nm upon
addition of metal ions. The following ESR studies also indicate
the formation of TTF•+ for these D-A dyads in the presence
of metal ions. In short, these absorption spectral results clearly
indicate the formation of TTF•+ in the presence of these metal
ions (Pb2+, Zn2+, and Sc3+), as a result of the electron transfer
within these TTF-quinone dyads.11
rate of 100 mV S-1
.
disproportionated into the corresponding Q2- and neutral Q in
the presence of metal ion at room temperature, which accounts
for the absence of ESR signals related to the radical anion of
the quinone (Q•-) unit of dyad 1.6,12 Similar ESR spectra were
observed for dyads 2, 3, and 4 after addition of Pb2+ (see Figures
S16-S18 of the Supporting Information). These ESR spectral
results also indicate that intramolecular electron transfer occurs
between the TTF and quinone units within dyads 1, 2, 3, and 4
in the presence of metal ions. For each substituted TTF-quinone
dyad, the ESR signal intensity was higher in the presence of
Pb2+/Sc3+ than that in the presence of Zn2+ under the same
conditions. Among these substituted TTF-quinone dyads, dyad
2 exhibits the strongest ESR signal in the presence of metal
ions under the same conditions. The ESR signal intensity of
the solution of dyads 1, 2, 3, 4, and 5 decreases in the following
order under the same conditions: 2 > 5 > 1 > 3 > 4.
For each substituted TTF-quinone dyad, the absorption
intensities at 450 and 845 nm (due to TTF·+) are rather weak
in the presence of Zn2+ compared to those containing Pb2+
/
Both absorption and ESR spectral studies indicate that the
metal ion-promoted electron transfer occurs within the substi-
tuted TTF-quinone dyads 1, 2, and 3, even for dyad 4, which
features a rather weak electron acceptor unit. The metal ion-
promoted electron transfer can be ascribed to the positive shift
of reduction potentials of quinones in the presence of metal ions
and the synergic coordination of oligoethylene glycol chain and
the radical anion of quinone with metal ions. The cyclic
voltammograms of dyads 1, 2, 3, and 4 and reference quinones
Sc3+. This result implies that Pb2+/Sc3+ can promote more
efficiently the electron transfer between TTF and quinone units
within these dyads, which is in agreement with the previous
observation.6 Among these substituted TTF-quinone dyads,
dyad 2 exhibits the strongest absorptions at 450 and 845 nm in
the presence of metal ions under the same conditions. The
absorption intensity at 845 nm decreases in the following order:
2 > 5 > 1 > 3 > 4, as indicated in the inset of Figure 1 where
the partial absorption spectra of dyads 1, 2, 3, 4, and 5 (5.0 ×
10-5 M in a mixture of CH2Cl2 and CH3CN (1:1, v/v))
containing 1.0 equiv of Pb2+ were displayed. A similar pattern
of the difference in absorption intensity at 845 nm was observed
in the presence of Sc3+/Zn2+ (see Figure S12 of the Supporting
Information).
12, 13, 14, and 15 were measured in the presence of Pb2+/Sc3+
/
Zn2+ (see Figures S20-S34 of the Supporting Information). By
employing the Fukuzumi’s method,12,13 the reduction potentials
of reference compounds 12, 13, 14, and 15 were estimated to
be 0.22, 0.28, 0.19, and 0.06 V, respectively, in the presence
of 4.0 equiv of Pb2+. As an example, Figure 3 shows the cyclic
voltammogram of dyad 1 containing 2.0 equiv of Pb2+. The
reduction wave around -0.36 V due to the redox reaction
(Q/Q•-) disappeared after addition of Pb2+, and the anodic
current around 0.48 V increased. It is probable that the reduction
ESR signals were detected for dyads 1, 2, 3, and 4 when
metal ions were present. As an example, Figure 2 shows the
ESR spectrum of dyad 1 in the presence of 1.0 equiv of Pb2+
.
On the basis of previous reports,6 the doublet ESR signals were
ascribed to the splitting of one H atom of the TTF unit in the
potential of the quinone unit of dyad 1 was shifted from -0.36
radical cation of the TTF unit of dyad 1 (g ) 2.0085, aH
)
14
to 0.48 V in the presence of Pb2+
.
On the basis of these
1.15 G). The radical anion of quinone (Q•-) can be easily
electrochemical data, it can be concluded that the electron
(11) The disproportionation reaction of Q•- into the corresponding Q2- and
neutral Q unit may occur easily in the presence of metal ions at room temperature
(see ref 10). This is in agreement with the fact that no ESR signals due to the
Q•- were detected for the solutions of dyad 1 after addition of metal ions at
room temperature.
(12) Fukuzumi, S.; Nishizawa, N.; Tanaka, T. J. Chem. Soc., Perkin Trans.
II 1985, 371–378.
(13) Fukuzumi, S.; Hironaka, K.; Nishizawa, N.; Tanaka, T. Bull. Chem.
Soc. Jpn. 1983, 56, 2220–2227.
J. Org. Chem. Vol. 73, No. 11, 2008 4273

SCHEME 2. The Proposed Mechanism for the Metal
Ion-Promoted Electron Transfer within Dyad 1
promoted electron transfer occurs to all new dyads including
dyad 4, which features a rather weak electron acceptor unit,
and (2) the metal ion-promoted electron transfer within the dayds
1, 2, 3, and 4 is influenced by the electron-accepting abilities
of quinone units: dyad 2 with a strong electron acceptor shows
strong absorption and ESR signals due to TTF•+ in the presence
of metal ions, compared to dyad 4 with a weak electron acceptor
under the same conditions. Moreover, the fact that metal ion-
promoted electron transfer occurs to dyad 4 with a rather weak
electron acceptor supports the assumption that the synergic
coordination of oligoethylene glycol chain and the radical anion
of the quinone unit with the metal ion may contribute to
stabilizing the corresponding charge-separation state and thus
facilitate the electron-transfer process.
transfer between TTF and quinone units of dyads 1, 2, 3, and
4 would become thermodynamically more feasible in the
presence of these metal ions (Pb2+, Sc3+, and Zn2+). The
reduction potential of reference compound 13 is higher than
those of 12, 14, and 15 in the presence of Pb2+/Sc3+/Zn2+. Their
differences in reduction potentials in the presence of metal ions
may explain why dyad 2 showed the strongest absorption and
ESR signals as mentioned above.
Experimental Section
Synthesis of Dyad 1. A solution of 10 (0.5 g, 0.81 mmol) in
THF (60 mL) was treated with PPh3 (0.43 g, 1.62 mmol) and H2O
(0.2 mL, 11.1 mmol) at 25 °C under N2. The resulting reaction
mixture was warmed at 45 °C for 10 h. The reaction mixture was
diluted with water and extracted with CH2Cl2. The organic phase
was dried over MgSO4 and concentrated in vacuo to give crude 11
as a yellow oil that was used directly without further purification.
The crude product of 11 was dissolved in dry THF and the
solution was cooled to 0 °C. Tetrachloro-1,4-benzoquinone (0.37
g, 1.5 mmol) was added. After being stirred for 30 min at this
temperature the reaction mixture was concentrated in vacuo.
Column chromatography of the residue on silica gel with CH2Cl2/
EtOAc (6:1, v/v) as eluant afforded dyad 1 as a purple oil (0.20 g)
The electron transfer processes within dyads 1, 2, 3, and 4
are still endothermic by just considering the redox potentials
of the TTF (E1/2(ox1) ) 0.50V, E1/2(ox2) ) 0.84 V as discussed
above) and quinone units in the presence of metal ion (Pb2+
,
Sc3+, Zn2+). Particularly, the quinone unit of dyad 4 exhibited
rather low reduction potential. Therefore, other mechanisms
must also contribute to the observed electron transfer in the
dyads, which could be the synergic coordination of oligoethylene
glycol chain and the radical anion of the quinone unit with metal
ion (see Scheme 2). This explains why electron transfer can be
observed for dyad 4, which contains a rather weak electron
acceptor. The observation that Pb2+/Sc3+ can promote the
electron transfer within TTF-quinone dyads efficiently may be
understood this way: (1) Sc3+ shows a preference for oxygen
coordination and (2) apart from the oxygen atoms of the
oligoethylene glycol chains, the sulfur atoms of the TTF unit
also may be involved in the coordination with metal ions, in
particular for Pb2+, which is a very poor oxyophile and prefers
the much softer sulfur ligands.
1
in 31% yield: H NMR (400 MHz, CDCl3) δ 6.42 (1H, s), 4.00
(2H, m), 3.71 (2H, t, J ) 5.1 Hz), 3.66-3.62 (18H, m), 3.29 (4H,
s), 2.93 (2H, t, J ) 6.4 Hz); 13C NMR (100 MHz, CDCl3) δ 174.3,
170.0, 143.6, 142.8, 135.9, 126.8, 123.1, 114.1, 106.9, 70.9, 70.8,
70.77, 70.74, 70.67, 69.8, 69.7, 44.9, 35.5, 30.4; HR-MS (MALDI-
TOF) calcd for C26H30Cl3NO7S7 796.9133, found 796.9092. Due
to overlapping signals, the total number of 13C NMR signals
deviates from the total carbon number within dyad 1. This also
holds true for dyads 2, 3, and 4.
The synthesis and characterization of dyads 2, 3, and 4 are
provided in theSupporting Information.
In summary, four new substituted TTF-quinone dyads were
synthesized and investigated in the presence of metal ions with
a view to understanding the influences of the electron-accepting
abilities of quinone units on the metal ion-promoted electron-
transfer process. The results indicate that (1) the metal ion-
Supporting Information Available: Synthesis of dyads 2,
3, and 4 and compounds 12-15, absorption and ESR spectra
of dyads 1, 2, 3, and 4 in the presence of metal ions, cyclic
voltammograms of 1, 2, 3, and 4, and compounds 12-15, and
those in the presence of metal ions, 1H NMR and 13C NMR of
dyads 1, 2, 3, and 4 and compounds 7, 8, 10, 12, and 15. This
material is available free of charge via the Internet at
http://pubs.acs.org.
(14) Compared to compound 12, the reduction potential of the quinone unit
of dyad 1 was further shifted anodically. This is likely due to the synergic
coordination of oligoethylene glycol chain and the radical anion of quinone with
metal ions as shown in Scheme 2, which would further facilitate the electron
transfer process within dyad 1.
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4274 J. Org. Chem. Vol. 73, No. 11, 2008