(compared to monomer band) with an associated g lum in the range of |10
À2 |. The
intensity of the excimer fluorescence is the result of the peculiar geometry of these
systems, which brings the pyrene units in close spatial proximity (see the X-ray
structure in Scheme 12.7). Moreover, upon cation addition (e.g., Ba
2+ or Na
+ in
acetonitrile or CH 2 Cl 2 , respectively), profound conformational changes occur. In
particular, the carbonyl groups of the amides turn inward and the two pyrene
moieties part away from each other. It results in a loss of excimer fluorescence and
in a total CPL quenching (Fig. 12.5). If the cation is removed, excimer CPL is fully
recovered. In the ECD spectra instead, a signature inversion of most bands is visible
O
O
MeO 2 C
O
O
CO 2 Me
n
n
or
O
O
O
O
O
O
CO 2 Me
MeO 2 C
aromatic amine (3 equiv)
t-BuOK (4 equiv)
THF, -100 °C (1 min)
then 25 °C, 3 h
O
O
O
O
O
O
HN
NH
Ar
Ar
Ar-18C6, Ar-18C4 or Ar-16C4
18C4 or 16C4
18C6
O
O
O
O
O
O
O
O
O
H
H
HN
NH
O
O
O
O
O
O
HN
NH
O
O
O
O
O
O
HN
NH
pyr-27
pyr-28
pyr-29
pyr-27, X-ray
Lacour 2018
n=2
n=1
Scheme 12.7 Straightforward synthesis of chiral functionalized macrocycles and structures of
pyrene-functionalized macrocycles
O
Na
+
O
O
O
O
O
O
HN
NH
O
O
O
O
Na
+
NH
O
HN
pyr-28
pyr-28 + Na
+
O
O O
O
O O
10 –2
5.10 –3
–5.10 –3
–1.10 –2
450
500
550
l/nm
lL-l
R
600
(–)-pyr-28
(+)-pyr-28
(–)-pyr-28 + Na +
(+)-pyr-28 + Na +
0
Fig. 12.5 Reversible complexation of sodium cations by pyr-28 and associated CPL spectra
recorded in CH 2 Cl 2 (10
À5 M). Adapted from reference [28]. Published by The Royal Society of
Chemistry
284
F. Zinna et al.