Chemistry Reference
In-Depth Information
Fig. 19 Redox species of trioxytriangulene
Scheme 5 Synthesis of biradical trianion 60 [
62
,
63
]
radical 57 possesses a similar electronic structure with 6-oxophenalenoxyl radical
mentioned above, in contrast to the diradical trianion 60 with a triplet biradical
ground state.
The triplet ground state trioxytriangulene biradical compounds were prepared by
Bushby by reduction of the corresponding ketones (Scheme
5
). The biradical
trianion species 60 exhibited high stability in degassed solution even at room
temperature, due to the extension of delocalization and protection from dimeriza-
tion [
62
,
63
]. Compound 60 was triplet in the ground state as determined by ESR
spectroscopy, while other unsymmetric derivatives appeared to be ESR silent and
singlet in the ground state [
64
]. The introduction of heteroatoms was believed to lift
the degeneracy of the NBMOs, causing a kinetic exchange interaction that
dominates over dynamic spin polarization in the parent
systems.
Organic open-shell compounds have shown some promise as electrode-active
materials in secondary batteries. Since oxophenalenoxyl systems have already
shown a high performance to this end, some trioxytriangulene neutral radical
systems, such as
tert
-butyl and bromo-substituted derivatives 68 and 69, were
recently prepared by Morita et al. [
65
]. Such molecules possessed a SOMO and
two degenerate LUMOs as shown in Fig.
20
. Compound 68 gave a high capacity of
311 Ahkg
1
, exceeding those of Li-ion batteries in the first discharge process.
Compared to 68, the bromo-substituted 69 showed improved output voltage and
cycle performance, indicating a tunable performance on the basis of chemical
modification. These results pointed out a high potentiality of organic open-shell
systems for applications in superbatteries with high energy densities.
p
