Chemistry Reference
In-Depth Information
Table 6.11 High-resolution analysis of the Eu(
5
D
0
7
F
0
) and Eu(
5
D
0
!
7
F
1
) transitions for
[MLnL
3
]
n
þ
n
þ
and [MEuML
3
]
helicates.
5
D
0
!
7
F
0
E
(cm
1
)
5
D
0
!
7
F
1
Ligand
M
State
T
/K
Ref.
DE
(A
2
-E)
(cm
1
)
DE
(E-E)
(cm
1
)
Zn
II
L24
MeCN
10
17 224
94
43
[8]
Zn
II
MeCN
295
12 236
n.a.
n.a.
Zn
II
L25
Solid
10
17 220
127
21
[61]
Zn
II
Solid
295
17 229
140
55
Zn
II
a
Solid
295
17 226
134
63
Cr
III
Solid
10
17 216
100
48
[90]
Zn
II
HL27
Solid
10
17 224
138
42
[94]
Zn
II
Solid
295
17 235
145
35
Zn
II
MeCN
295
17 237
149
n.a.
Zn
II
L26
Solid
10
17 221
118
37
[95]
Zn
II
Solid
295
17 225
117
n.a.
Zn
II
MeCN
295
17 224
82
49
Zn
II
L28
Solid
13
17 221
146
35
[96]
Zn
II
MeCN
295
17 232
147
n.a.
Fe
II
Solid
13
17 221
144
37
Zn
II
Zn
II
L29
Solid
10
17 221
98
32
[11]
Cr
III
Cr
III
Solid
10
17 218
80
34
a
Eu-doped (2%) [GdZn(L25)
3
]
5
þ
.
Quantum yields have only been determined for Eu
III
helicates (Table 6.12). They
span a wide range, from 0.01% in [EuZn(L24)
3
]
5þ
, because the N
9
environment
made up of benzimidazolepyridine units is known to generate a rather low-lying and
quenching LMCT state (see above), to a high 32% for the sparingly soluble carbox-
ylate [EuZn(L27)
3
]
2þ
. The robustness of the triple helical edifices is exemplified by
the fact that adding up to 0.93M water to [EuZn(L25)
3
]
5þ
does not alter either the
5
D
0
lifetime or the quantum yield [61]. Similarly, the quantum yield of [EuCr
(L25)
3
]
5þ
in acetonitrile (3.2%) remains unchanged up to 3M of added water [90].
If the same experiment is conducted on the even more robust [EuZn(L27)
3
]
2þ
heli-
cate, the quantum yield drops to 87% of its initial value when 2M of water are
added, probably in view of the second sphere effect of fast diffusing O-H vibrators
and then further decreases slowly to reach about 80% of its initial value for a water
concentration of 10M. The quantum yield in pure water is about half that in acetoni-
trile but the lifetime is still long, 2.43ms. With
(D
2
O)
¼
4.48ms, one calculates a
t
hydration number
q
0, using the equation of Supkowski and Horrocks (Equation
6.15) [97], a remarkable result in that, even in pure water, there is no inner sphere
interaction with the solvent [94].
1
1
q
¼
1
:
11
Þ
Þ
0
:
31
ð
6
:
15
Þ
tð
H
2
O
tð
D
2
O
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