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Y.-L. Chen et al. / Tetrahedron Letters 48 (2007) 2421–2425
benzo[b]triphenylene (10). Consistently, the oxadisilole
fused benzo[b]triphenylenes (9a and 9b) also exhibit a
References and notes
2
0
red shift of the emission (i.e., D 7–9 nm). In general,
the more the oxadisilole substitution, the longer are
the absorption and emission wavelengths shifted. The
more the oxadisiole substitution, the fluorescence quan-
tum yields of these benzo[b]triphenylene derivatives was
enhanced.
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As silyl group is known to play the roles of r-donating
2
1
and p-withdrawing, the position and the number of
oxadisiole substitution therefore show profound effect
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the potentials reported are referenced to Fc/Fc stan-
dard and the results are tabulated in Table 1. Mono-
oxadisiole fused benzo[b]triphenylene 9a exhibits an
irreversible one-electron oxidation corresponding to
the formation of cation, with Epa at 1.07 V, which is
slightly lower than that of the parent benzo[b]triphenyl-
ene 10. This suggests that oxadisiole substituted at the
2
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e) Yoshida, H.; Watanable, M.; Ohshita, J.; Kunai, A.
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,7-position of benzo[b]triphenylene ring acting as a
r-electron donor stabilizes the formation of the cat-
ion. In contrast, the bis-5,6,7,8-oxadisiole substituted
benzo[b]triphenylene 9b, which exhibits a irreversible
one-electron oxidation with E1/2 at 1.25 V, did not show
an enhanced stabilization of the cation as compared to
that of parent benzo[b]triphenylene 10. This indicates
that the p-electron withdrawing role of oxadisiole group
in such a substitution pattern becomes significant. These
results suggest that the r-donating or p-withdrawing
role of oxadisiole group can easily be tuned by the num-
ber and the position of oxadisiole substitution on the
aromatic ring.
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Two new oxadisilole substituted benzo[b]triphenylenes
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In summary, two new mono- and bis-oxadisilole fused
benzo[b]triphenylene 9a and 9b were synthesized via pal-
ladium-catalyzed [2+2+2] cyclotrimerization reaction
followed by deoxyaromatization. These benzo[b]tri-
phenylene derivatives were characterized. The r-donat-
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greatly affected by the number and the position of oxa-
disiole substitution on the aromatic ring. In general, as
compared with the parent benzo[b]triphenylene, the
quantum yields of these oxadisilole substituted deriva-
tives were increased. Further study of the potential
applications of these newly synthesized oxadisilole fused
benzo[b]triphenylenes in optoelectronics is in progress.
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1
Acknowledgments
Financial support from the Faculty Research Grant
FRG/06-07/II-05) and CALM are gratefully
(
acknowledged.