Chemistry Reference
In-Depth Information
4 10
3
10
1.9 10
3
b
1.7 10
3
8
3 10
3
1.5 10
3
g
1.3 10
3
6
i
h
2 10
3
1.0 10
3
1800
g
1880
1960
2040
2120
2200
h
4
f
g
e
1 10
3
d
2
e
c
b
c
a
a
0 10
0
0
1000
1400
1800
Wavelength (nm)
2200
2600
3000
250
350
450
550
650
750
Wavelength (nm)
Figure2.19
Evolution of the electronic absorption spectra during the course of the electrochemicalreduction
of triradical
3
. Left: Different traces in the visible range corresponding to distinct average reduction states of:
(a)0.00;(b)0.29;(c)0.56;(d)0.73;(e)0.90;(f)1.17;(g)1.49;(h)1.71;and(i)2.10e
−
/molecule.Right:Selected
spectral traces observed in the NIR region. (Reprinted with permission from [13b]. Copyright 1996 Wiley-VCH
VerlagGmbH&Co.KGaA.)
To study longer range IET phenomena, diradical
14
, consisting of two PTM units connected by a 1,4-
bis(1-ethynylphenyl) benzene bridge, was obtained together with its radical anion derivative
14
−
•
.
73
The
bridge of
14
not only ensures a long distance between the two PTM units and a high degree of molecular
rigidity, but also a suitable electronic structure to promote an electronic coupling between the two PTM
ends separated by a significantly large through-space radical-to-radical distance of 3.2 nm, as revealed by
semiempirical AM1 calculations.
74
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
14
Cl
Cl
Magnetic susceptibility measurements on
14
show that the magnetic moment of this compound decreases
with decreasing temperature, indicating that the ground state is a singlet with a thermally accessible triplet
state. A separation of 1.5 K between both states was obtained from the fitting to the Bleaney - Bowers
equation of the experimental
T versus T data.
75
The EPR spectrum of
14
at room temperature was in
agreement with such an electronic structure. Thus, it shows three overlapped lines that correspond to the
coupling of each of the two unpaired electrons with two equivalent
1
H nuclei, along with other satellite
lines that correspond to the coupling of the two unpaired electrons with the naturally abundant
13
C nuclei of
χ
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