846
Published on the web May 29, 2013
Heterotriangulene as an Electron-transfer Mediator in Reduction
of vic-Dibromide Compounds
Shinsuke Inagi,* Noriyuki Kaihatsu, Shunsuke Kuribayashi, and Toshio Fuchigami
Department of Electronic Chemistry, Tokyo Institute of Technology,
Nagatsuta, Midori-ku, Yokohama, Kanagawa 226-8502
(Received April 6, 2013; CL-130308; E-mail: inagi@echem.titech.ac.jp)
NH2
I
A novel heterotriangulene derivative and its nonfused
+
2
analogue were successfully prepared, and their electrochemical
and optical properties were studied by cyclic voltammetry
measurements and UV-vis and photoluminescence analyses.
The mediatory use of the heterotriangulene derivative for the
electrocatalytic reduction of dibromo compounds was also
investigated.
CO2Me
CO2Me
Cu, CuI, K2CO3
Ph2O
190 °C
1) KOH/MeOH, 50 °C
2) HCl
O
O
N
O
N
3
3) SOCl2, SnCl4/CH2Cl2, reflux
CO2Me
I2, Ag2SO4
Heterotriangulene, i.e., triangulene structure with a hetero-
atom center like a nitrogen atom, has been designed and
recognized as a planar molecule, which can assemble to form
one-dimensional (1D) columnar structures.1-3 Recently, there
have been reports on application of heterotriangulene units to
organic light-emitting diode4 and dye-sensitized solar cell.5 The
electrochemistry of heterotriangulene 1 (Scheme 1) could not be
investigated because of its poor solubility in organic solvents.1
Later, a solubilized moiety was introduced into 1, and this made
it possible to conduct electrochemical measurements in organic
solvent such as chloroform (CHCl3) and dichloromethane
(CH2Cl2).6,7 Although current responses were observed at
cathodic scan, they were irreversible.7
Heterotriangulene 1
EtOH
r.t.
I
1) KOH/MeOH, 50 °C
O
O
2) HCl
I
N
3
N
3) SOCl2, SnCl4/CH2Cl2, reflux
CO2Me
I
I
O
Pre-3
Pre-2
C8H17
C8H17
CuI, [PdCl2(PPh3)2]
CuI, [PdCl2(PPh3)2]
i-Pr2NH/toluene, 80 °C
i-Pr2NH/toluene, 80 °C
R
R
N
In this work, we synthesized a novel soluble heterotriangu-
lene derivative in organic solvents and investigated its optical
and electrochemical properties in detail. Moreover, its mediatory
application in electrocatalytic reaction of vic-dibromide com-
pounds was also demonstrated.
O
O
CO2Me
MeO2C
N
MeO2C
3
R
R
R
R
O
=
R
C8H17
2
Scheme 1 shows the synthetic outline of heterotriangulene 2
via Friedel-Crafts-type cyclization of a triphenylamine deriva-
tive (Pre-3 to Pre-2), followed by the introduction of terminal
alkynes with a long alkyl chain. Similarly, the corresponding
nonplanar triarylamine derivative 3 was also synthesized. These
compounds are readily soluble in organic solvents such as
CHCl3 and tetrahydrofuran (THF).
First, the cyclic voltammetry (CV) measurements of these
compounds were carried out in 0.1 M tetrabutylammonium
hexafluorophosphate (Bu4NPF6)/THF with a glassy carbon
(GC) working electrode, platinum counter electrode, and
saturated calomel electrode (SCE) as a reference electrode.
Figure 1a shows the cyclic voltammograms of 2 and 3 for
anodic scans. Heterotriangulene 2 showed the same voltammo-
gram as the background (THF), and no oxidation peak was
observed within the range of potential window of THF, whereas
a couple of oxidation and re-reduction peaks (Eo¤ = 1.44 V vs.
SCE) were observed in the voltammogram of 3. Three electron-
withdrawing esters on 3 seem to cause the significant positive
shift of the oxidation potential of 3 from that of pristine
triphenylamine (Epox = 1.04 V vs. SCE).8 Interestingly, a much
more positive shift was observed in the voltammogram of 2,
which seems to be due to the delocalization of lone-pair
Scheme 1. Synthetic outline of compounds 2 and 3.
electrons of the nitrogen center throughout the molecules. In
cathodic scans, there was an irreversible reduction peak at
¹2.26 V in the voltammogram of 3 (Figure 1b). In contrast, in
the voltammogram of 2, two reversible redox couples appeared
at Eo¤ = ¹0.98 and ¹1.29 V, unlike in the case of the previous
report on the electrochemistry of the similar molecule.7 These
redox behaviors are derived from the capture of electrons on the
carbonyl moieties, and they were stabilized by the delocalization
on the planar molecule. These electrochemical data are summa-
rized in Table 1.
Next, the optical properties of 2 and 3 were studied. The
UV-vis spectra and photoluminescence (PL) spectra are shown
in Figure S1,9 and the data are summarized in Table 1. The
significant expansion of conjugation in 2 was suggested by the
large bathochromic shift of its absorption maximum from that of
3. Interestingly, the emission peak of 2 was very sharp (full
width at half-maximum, FWHM = 24 nm) due to its rigid and
planar structure compared to 3.
To better understand the electrochemical behaviors describ-
ed above, we then conducted the density functional theory
Chem. Lett. 2013, 42, 846-848
© 2013 The Chemical Society of Japan