via one-electron reduction. To make the reduction process
stable and reversible, the generated negative charge should
be efficiently compensated for by the positive charge.
Ferrocene is well-known for its stable and reversible one
For preparation of the target compounds, the ferrocenyl
group was successfully introduced to the benzophenone or
anthraquinone via coupling of the corresponding aryl dia-
9
zonium salts with ferrocene. As shown in Scheme 1,
7
electron oxidation reaction. Our research group has studied
the new stable organic and inorganic electrochromic materi-
8
als. In this work, we report the synthesis of bifunctional
and stable electrochromic systems through combination of
anthraquinones and ferrocenes (Figure 1a,b). It can be
Scheme 1
.
Synthetic Pathway for Ferrocenylbenzophenones
FB) and Ferrocenylanthraquinones (FA)
(
Figure 1. Redox reactions of anthraquinone (a) and ferrocene (b);
diazonium salts were prepared in situ from the corresponding
aryl amines via reaction with sodium nitrite under acidic
conditions. 1,8-Bisferrocenylanthraquinone is not available
commercially and was prepared from the corresponding
nitroarene by reduction using Na S. All compounds were
2
stable under air and purified by flash column chromatogra-
phy.
cartoon of a single-layer electrochromic device (c).
expected that in single-layer sandwich-type electrochromic
devices, via power supply, the ferrocenyl group will be
oxidized to assume the role of a counter material on the
anode as the anthraquinone portion will be reduced to show
electrochromism on the cathode and the charges compensated
for by each other (Figure 1c).
1
0
Next, the electrochemical behavior of each compound was
investigated by cyclicvoltammetry using a conventional
three-electrode cell assembly. Each compound (5 mM) was
dissolved in N-methylpyrrolidone (NMP) containing 0.10 M
tetrabutylammonium tetrafluoroborate. The working and
counting electrodes were glassy carbon and platinum wire,
Figure 2 shows the compounds used in this work. Actually,
we started from the combination of ferrocene systems with
+
respectively. An Ag/Ag reference electrode was used. Table
1
summarizes the electrochemical properties of the all
compounds studied in this work.
Ferrocenylbenzophenones (FB1-3) showed irreVersible
reduction peaks between -2.08 and -2.17 V (versus Ag/
+
Ag ) and reversible oxidation peaks at +0.27 V. The
unstability of the generated ketyl radicals resulted in poor
1
1
electrochromic performance. In contrast, ferrocenylan-
thraquinones showed stable electrochemical properties. As
revealed in cyclovoltammograms in Figure 3a,c, 1-ferroce-
(
6) (a) Qiao, W.; Zheng, J.; Wang., Y.; Zheng, Y.; Song, N.; Wan, X.;
Wang, Z. Y. Org. Lett. 2008, 10, 641. (b) Zheng, Y.; Zheng, J.; Dou, L.;
Qiao, W.; Wan, X. J. Mater. Chem. 2009, 19, 8470. (c) Thum, C. C. L.;
Khairallah, G. N.; O’Hair, R. A. J. Angew. Chem., Int. Ed. 2008, 47, 9118,
and references cited therein.
(
(
7) Togni, A.; Hayashi, T. Ferrocenes; Wiley-VCH: Weinheim, 1995.
8) (a) Sharmoukh, W.; Ko, K. C.; Ko, J. H.; Nam, H. J.; Jung, D.-Y.;
Figure 2
.
Compounds used in this work.
Noh, C.; Lee, J. Y.; Son, S. U. J. Mater. Chem. 2008, 18, 4408. (b)
Sharmoukh, W.; Ko, K. C.; Park, S. Y.; Ko, J. H.; Lee, J. M.; Noh, C.;
Lee, J. Y.; Son, S. U. Org. Lett. 2008, 10, 5365. (c) Park, S. Y.; Lee, J. M.;
Noh, C.; Son, S. U. J. Mater. Chem. 2009, 19, 7959.
(
9) C aˆ rlescu, I.; Scutaru, A. M.; Apreutesei, D.; Alupei, V.; Scutaru, D.
a well-known ketyl radical system based on diaryl ketone.
Three benzophenone derivatives having ferrocenyl groups
at the 3-, 4-, or the 4,4′-position were designed. In addition,
two monoferrocenylanthraquinones and three bisferrocenyl-
anthraquionones were designed.
Appl. Organomet. Chem. 2007, 21, 661.
(
10) Dahan, A.; Ashkenazi, T.; Kuznetsov, V.; Makievski, S.; Drug,
E.; Fadeev, L.; Bramson, M.; Schokoroy, S.; Rozenshine-Kemelmakher,
E.; Gozin, M. J. Org. Chem. 2007, 72, 2289.
(
11) It should be noted that electrochromism has been defined in
reversible electrochemical systems.
Org. Lett., Vol. 12, No. 14, 2010
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