Chemistry Reference
In-Depth Information
TMS
OTf
steps
CpCo(CO)
2
(1.1 eq)
o
-xylene, h
+
,
OTf
OH
61%
40
ArCH
2
O
2
CCH
2
CO
2
H
D
CC, DMAP
TMS
TMS
O
O
Ar
OH
CH
2
Cl
2
,0 C
82%
42
O
O
41
O
O
Ar
O
O
TMS
C
60
,I
2
PhCH
3
rt
52%
OC
12
H
25
43
Ar =
OC
12
H
25
Scheme 12 Synthesis of benzo[3]phenylene-C
60
dyad 43 [
59
]
similar, it is difficult to determine whether or not emission in 38 is the result of an
excimer-like phane-state. However, the authors suggest that the longer lifetime of
38 implies participation of the phane state. Cyclophane 38 is more easily oxidized
than both 39 and 20.
To investigate the use of [N]phenylenes for photovoltaic applications, the
synthesis of linear benzo[3]phenylene-C
60
dyad 43 was reported in 2005 [
59
].
The synthesis employed iterative Co-catalyzed [2
2] cyclizations, using
3-trimethylsilylpropargyl alcohol to install a tether in the final cyclization to yield
41. Finally, diester 42 was reacted with C
60
using the Bingel conditions [
60
,
61
]to
give the desired dyad. The absorption spectrum of dyad 43 closely resembles the
sum of its constituents, signifying that there are not significant ground state
interactions between the [N]phenylene and fullerene which could otherwise inhibit
charge separation (Scheme
12
).
As with other linear [3]phenylenes, 41 and 42 are reportedly not fluorescent.
This is likely due to high rates of IC, which would make the donor portion of this
particular dyad not a good candidate for photovoltaic applications [
62
]. This led
researchers to investigate the photoinduced electron transfer of angular phenylenes,
with much slower rates of IC, in dyads. The fluorescence and quantum yield of
triangular [4]phenylene dyad 44 displays a solvent polarity dependence character-
istic of intramolecular charge transfer; however, levels of the charge-transfer
complex are low at equilibrium (Fig.
7
).
The small HOMO-LUMO gap of antiaromatics led researchers to investigate the
use of biphenylene as a molecular wire in a single molecule device [
63
]. Research on
single molecule devices made from acenes has shown that increasing conductivity
can be correlated to decreasing HOMO-LUMO gap and increasing quinoidal stability
[
64
]. Thioether-substituted biphenylene 47 was synthesized according to the
procedure outline in Scheme
13
and its conductance compared with that of fluorenes
þ
2
þ
