Chemistry Reference
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Fig. 10 Solid state packing of 96a (
left
) and 96h (
right
)[
55
]
Scheme 26 Synthesis of 6,12-diaryl IFs 87a-m [
77
,
78
]
Like 92a,b, the absorption spectra of 96a-i showed three low energy transitions
with the
l
max
values between 561 and 577 nm, corresponding to a band gap of
2.08
2.15 eV [
55
]. Cyclic voltammetry measurements exhibited first reduction
potentials between
0.7 and
0.5 V and second reduction potentials between
1.2
and
4.1 V.
Explanation for the lack of HOMO and LUMO energy level variation was due to
low orbital density on the 2- and 8-positions, where only weak inductive electronic
effects could be invoked.
While removal of ethynyl groups on the 5- and 11-positions did reduce steric
hindrance, substitution had a significant impact on the crystal morphology of
96 [
55
]. Parent 96a packed without any
1.0 V, correlating to LUMO energies that range between
4.0 and
-interactions (Fig.
10
) where the closest
intermolecular distance was an edge to face contact of 3.85
˚
. Alternatively,
96h exhibited one-dimensional columnar stacks with an intermolecular distance
of 3.40
˚
.
The next series of fully-conjugated indeno[1,2-
b
]fluorenes synthesized by Haley
et al. was 6,12-diarylindeno[1,2-
b
]fluorenes (Scheme
26
)[
77
]. Similar to 96a-i,
lithium-halogen exchange with the appropriate aryl halide and reaction with 22
afforded mixtures of stereoisomers 97a-i. Reduction using anhydrous SnCl
2
at
elevated temperatures provided 87a-j in 36-59% yield. The electron-withdrawing
p
