Chemistry Reference
In-Depth Information
Fig. 28 Structures of periacenes
Periacenes refer to those PAHs with constant armchair edges and growing
zigzag edges, for example,
peri
-fusion of tetracene leads to peritetracene 121 and
peri
-fusion of pentacene results in peripentacene 122 (Fig.
28
). Perylene and
bisanthene can also be regarded as members of this family. Theoretical calculations
by Jiang pointed out a crossover from nonmagnetic phase to antiferromagnetic
phase starting from peritetracene, and an open-shell ground state is therefore
expected (Fig.
28
)[
91
]. Unfortunately, as the inverse dependence of stability
with conjugation length is remarkably larger compared to anthenes and rylenes,
the preparation of periacenes has not yet been achieved. The only experimental
evidence of peripentacene was the mass spectroscopic peak of gas-phase dispro-
portionation products [
92
].
On the way to making stable and characterizable peripentacene derivatives,
some preliminary results were achieved in our group. The synthetic concept is
based on nucleophilic addition followed by aromatization, as well as ring closing
reactions, which is similar to the preparation of stable bisanthenes. For this purpose,
the bispentacenequinone 124, obtained from dimerization of pentacenyl
monoketone 123, was subjected to nucleophilic addition of triisopropylsilylethynyl
lithium reagent followed by reductive aromatization with NaI/NaH
2
PO
2
to give the
cruciform 6,6
0
-dipentacenyl 125 (Scheme
13
)[
93
]. Interestingly, compound 125
exhibits two face-to-face
-stacking axes in a single crystal and this allows two-
directional isotropic charge transport, representing a new concept in semiconductor
design. FET mobilities up to 0.11 cm
2
V
1
s
1
were obtained based on vapor-
deposited thin films. Subsequent study was conducted by applying oxidative
photocyclization of 124 to obtain fused bispentacenequinone 126 [
94
]. However,
the subsequent nucleophilic reaction of compound 126 with excess Grignard reagent
of 1-bromo-3,5-di-
tert
-butylbenzene in anhydrous THF followed by acidification in
air did not generate the desired 1,2-addition adduct. Alternatively, an unexpected 1,4-
Michael addition product 127 was obtained and confirmed by X-ray single-crystal
analysis. Further treatment of 127 with excess Grignard reagent followed by acidifi-
cation in air gave the tetraaryl-substituted fused bispentacenequinone 128. Single-
crystal analysis revealed that there are
p
-unsaturated ketone structures in the fused
bispentacenequinones 126 and 127, which may explain the unusual Michael
additions. So far, synthesis of peritetracene derivatives was not reported and only
one potential precursor, i.e., monobromo-tetracene dicarboximide, was reported by
our group [
95
].
a
,
b
