phosphorescence at room temperature, but no CPL activity was detected. This can be
explained by the weakly chiral environment around the two Pt centers and the high
sensitivity to oxygen. Note also that the precursor 1-(2-pyridyl)-hexahelicene 67
displayed fluorescence emission and CPL activity (see Table 4.12). Recently,
polyfluorinated platina[6]helicene 66e was prepared by Zheng et al. [66] It displayed
similar molecular behavior as 66a–c, namely red phosphorescence, and CPL activity
with a g lum of À3.7 Â 10
À3 in dichloromethane solution for the (P)-(+) enantiomer.
The same compound displayed a g lum of À4.1 Â 10
À3 when incorporated in a
DCzppy film (DCzppy: 2,6-bis(3-(9H-carbazol-9-yl)phenyl)pyridine). Interestingly,
compounds 66a and 66e were used as chiral dopants in OLED devices to conceive
efficient circularly polarized OLEDs (CP-OLEDs; see Sect. 4.10).
4.9.2 Coordination of Helicene-Bipyridine Ligands
Our group also prepared complexes bearing a helicene-bipyridine-type ligand.
Bipyridine ligands are classical N^N chelate ligands but can also act as C^N ones
toward different transition metal ions such as platinum. In 2015, we reported
the preparation of enantiopure helical cycloplatinated complexes (P)- and (M)-69
from a [6]helicene-bipyridine-type ligand, namely, 3-(2-pyridyl)-4-aza[6]helicene
((P)- and (M)-68 in Fig. 4.27) [67]. Due to the presence of an additional N atom in
organometallic species (P)- and (M )-69, the acid-base triggering of UV-vis, ECD,
Table 4.12 Photophysical data of platinahelicenes and helicene-bipy rhenium complexes
Compound
λ Abs
max a
(nm)
λ Em
(nm)
Φ
(%)
Solvent
(CPL)
10
3
g abs
10
3 g lum
Ref.
(P)-(+)-66a
452
644
10
CH 2 Cl 2
~3.5
b
+13
[65]
(P)-(+)-67
422
430
–
CH 2 Cl 2
~7.3
b
+0.8
[65]
(P)-(+)-66b
467
648
5.6
CH 2 Cl 2
~12
b
+0.5
[65]
(P)-(+)-66c
471
633
13
CH 2 Cl 2
~3.2
b
+0.4
[65]
(P)-(+)-66d
479
639
6.6
CH 2 Cl 2
–
~0
[65]
(P)-(+)-66e
463
612
27
CH 2 Cl 2
–
À3.7
(À4.1)
c
[66]
(M )-(À)-68
417
421
8.4
CH 2 Cl 2
~À4.1
b
À3.2
[67]
(M )-(À)68.2H
+
418
590
8.2
CH 2 Cl 2
~À5.3
b
À2.9
[67]
(M )-(À)-69
430
547
0.38
CH 2 Cl 2
~À5.2 À1.1
[67]
(M )-(À)-69.
H
+
450
555
2.7
CH 2 Cl 2
~À10
À2
[ 67]
((M,C Re )-70a
2
445
673
0.16
CH 2 Cl 2
~À2
À3
[ 68]
(M )-71a
1,2
444
598
6
CH 2 Cl 2
~À0.4 À1.5
[68]
a Lowest-energy UV-vis band
b
Taken from [12]
c Fluorescence quantum yield measured in a DCzppy film
84
J. Crassous
explained by the weakly chiral environment around the two Pt centers and the high
sensitivity to oxygen. Note also that the precursor 1-(2-pyridyl)-hexahelicene 67
displayed fluorescence emission and CPL activity (see Table 4.12). Recently,
polyfluorinated platina[6]helicene 66e was prepared by Zheng et al. [66] It displayed
similar molecular behavior as 66a–c, namely red phosphorescence, and CPL activity
with a g lum of À3.7 Â 10
À3 in dichloromethane solution for the (P)-(+) enantiomer.
The same compound displayed a g lum of À4.1 Â 10
À3 when incorporated in a
DCzppy film (DCzppy: 2,6-bis(3-(9H-carbazol-9-yl)phenyl)pyridine). Interestingly,
compounds 66a and 66e were used as chiral dopants in OLED devices to conceive
efficient circularly polarized OLEDs (CP-OLEDs; see Sect. 4.10).
4.9.2 Coordination of Helicene-Bipyridine Ligands
Our group also prepared complexes bearing a helicene-bipyridine-type ligand.
Bipyridine ligands are classical N^N chelate ligands but can also act as C^N ones
toward different transition metal ions such as platinum. In 2015, we reported
the preparation of enantiopure helical cycloplatinated complexes (P)- and (M)-69
from a [6]helicene-bipyridine-type ligand, namely, 3-(2-pyridyl)-4-aza[6]helicene
((P)- and (M)-68 in Fig. 4.27) [67]. Due to the presence of an additional N atom in
organometallic species (P)- and (M )-69, the acid-base triggering of UV-vis, ECD,
Table 4.12 Photophysical data of platinahelicenes and helicene-bipy rhenium complexes
Compound
λ Abs
max a
(nm)
λ Em
(nm)
Φ
(%)
Solvent
(CPL)
10
3
g abs
10
3 g lum
Ref.
(P)-(+)-66a
452
644
10
CH 2 Cl 2
~3.5
b
+13
[65]
(P)-(+)-67
422
430
–
CH 2 Cl 2
~7.3
b
+0.8
[65]
(P)-(+)-66b
467
648
5.6
CH 2 Cl 2
~12
b
+0.5
[65]
(P)-(+)-66c
471
633
13
CH 2 Cl 2
~3.2
b
+0.4
[65]
(P)-(+)-66d
479
639
6.6
CH 2 Cl 2
–
~0
[65]
(P)-(+)-66e
463
612
27
CH 2 Cl 2
–
À3.7
(À4.1)
c
[66]
(M )-(À)-68
417
421
8.4
CH 2 Cl 2
~À4.1
b
À3.2
[67]
(M )-(À)68.2H
+
418
590
8.2
CH 2 Cl 2
~À5.3
b
À2.9
[67]
(M )-(À)-69
430
547
0.38
CH 2 Cl 2
~À5.2 À1.1
[67]
(M )-(À)-69.
H
+
450
555
2.7
CH 2 Cl 2
~À10
À2
[ 67]
((M,C Re )-70a
2
445
673
0.16
CH 2 Cl 2
~À2
À3
[ 68]
(M )-71a
1,2
444
598
6
CH 2 Cl 2
~À0.4 À1.5
[68]
a Lowest-energy UV-vis band
b
Taken from [12]
c Fluorescence quantum yield measured in a DCzppy film
84
J. Crassous