Chemistry Reference
In-Depth Information
Table 3 Reduction potentials of corannulene measured by cyclic voltammetry
a
Compound
Electrolyte/solvent
Reduction potential (V, vs ferronce)
References
1
TBAH/MeCN
2.33,
2.95
[
34
]
1
TBAH/MeCN (298 K)
2.32,
3.03
[
78
]
1
TBAP/MeCN
2.31
[
81
]
1
TMAB/DMF (213 K)
2.30,
2.84,
3.43
[
78
]
15
TBAH/MeCN
2.34,
3.05
[
78
]
23c
TBAH/THF
1.66
[
41
]
23d
TBAH/THF
1.48
[
40
]
28-F
2.38 [
40
]
28-Cl TBAH/THF
2.34 [
40
]
33 TBAH/MeCN
2.41,
3.01 [
34
]
43 TBAH/MeCN
2.43,
2.97 [
34
]
45-Me TBAH/MeCN
2.49,
3.04 [
34
]
45-CF
3
TBAP/MeCN
1.36 [
81
]
54 TBAH/DMF
2.58,
>
3.11 [
34
]
a
TBAH
tetrabutylammonium hexafluorophosphate;
TBAP
tetrabutylammonium perchlorate;
TMAB
tetramethylammonium tetrafluoroborate. In comparisons of reduction potentials, the fol-
lowing conversion factors are used: E(FeCp
2
+
/FeCp
2
)
¼
E(NHE) - 0.665
¼
E(SCE) - 0.424
¼
E
(Ag/AgNO
3
) - 0.105
TBAH/THF
The reduction potentials of corannulene and its derivatives are strongly
affected by the kind and number of the substituents (Table
3
). The methyl group
is a weak electron-donating substituent. The addition of methyl groups to the
corannulene nucleus shifted the reduction potentials to be more negative, especially
decamethylcorannulene 54-Me [
34
,
77
]. The halogen substituent in monohalo-
corannulenes, such as 28-F and 28-Cl, does not change the reduction potential
of corannulene significantly. Strong electron-withdrawing substituents,
trifluoromethyl groups, cause the reduction potential of trifluoromethyl-substituted
corannulene derivatives to make a large positive shift, compared to 1 [
40
,
41
,
81
].
Pentakis(trifluoromethyl)corannulene (45-CF
3
) is a representative example.
Synthesis of a series of multi(phenylthio)corannulenes via direct nucleophilic
substitution of corresponding halocorannulenes using sodium hydride as a base and
thiophenol as the pro-nucleophile enabled a systematic study of their optoelectric
properties as a function of substituent number and placement (Siegel et al.,
unpublished results). A linear dependence of the first reduction potential and
the photophysical properties on the number of substituents was observed (Table
4
).
The first reduction potential measured by the cyclic voltammetry suggests an
additivity factor of +0.10 V per phenylthio group on corannulene. Moreover, the
bathochromic shift observed for the longest wavelength absorption
ʻ
l,a
increases
with rising substitution around the rim of 1, with an additivity factor of
ca. 10-15 nm per phenylthio group.
