Chemistry Reference
In-Depth Information
Scheme 10 Synthesis of ovalene from bisanthene [
85
]
Fig. 26 Structures of substituted ovalenes [
86
-
88
]
bisanthenequinone 101 followed by reduction/aromatization of the as-formed diol.
The obtained compounds not only showed enhanced stability and solubility but also
exhibited absorption and emission in the NIR region as well as amphoteric redox
behavior, which qualified them as NIR dyes and hole/electron transporting
materials. The same synthetic strategy was also applied to prepare quinoidal
bisanthene 103, which can be regarded as a rare case of stable and soluble
nanographene with a quinoidal character [
84
]. An intense NIR absorption and
amphoteric redox behaviors were also observed for compound 103.
Since bisanthene has a diene character at the bay regions, Diels-Alder reaction
can take place which allows easy access to more extended aromatic systems. For
example, Diels-Alder cycloaddition reactions with maleic anhydride as dienophiles
followed by oxidative dehydrogenation and decarboxylation gave compound 105,
namely ovalene, as an insoluble material (Scheme
10
)[
85
]. As two more sextet
benzenoid rings can be drawn for ovalene compared to bisanthene, ovalene is more
stable than bisanthene with larger HOMO-LUMO gap, in spite of a larger molecular
size and more extended conjugation. One general approach towards soluble ovalene
derivatives is to attach solubilizing and/or bulky groups onto the rigid ovalene core.
A series of soluble ovalene derivatives 106 and 107 as shown in Fig.
26
was
obtained by twofold oxidative Diels-Alder reactions with different electron-
withdrawing dienophiles [
86
,
87
]. An interesting example is our recent report on
preparation of large disc-like 7,14-dicyano-ovalene diimide 108 [
88
]. Due to the
attachment of electron-withdrawing imide and cyano groups, 108 exhibited n-type
character and high electron mobilities of up to 1.0 cm
2
V
1
s
1
in N
2
and
0.51 cm
2
V
1
s
1
in air atmosphere were achieved in solution processing FET
devices. This device performance from 108 is better than most solution processible
n-type semiconductors reported so far.
