4.9 CPL-Active Transition Metal Complexes of Helicenes
4.9.1 Cycloplatinated Helicenes
Coordination chemistry offers a simple way to tune the optical and electronic
properties of the π-ligands since both the coordination sphere geometry and the
nature of the metal-ligand interaction can be readily modified by varying the metal
center. This will produce a great impact on the properties of the molecule
[62]. Recent studies have demonstrated many potential applications of
N-containing helicenes in coordination chemistry and in materials science
[63]. Indeed, their transition metal complexes may show interesting properties in
harvesting (visible) light and re-emitting it at a wavelength that depends on the
metallic ion used, thus allowing the development of light-emitting devices,
chemosensors, photovoltaic dye-sensitized devices, etc. In 2010, our group prepared
the first class of organometallic helicenes incorporating a metallic ion, i.e., Pt, within
their helical backbone, named platinahelicenes [64, 65]. Enantiopure platina[6]
helicene 66a, platina[8]helicene 66b, bisplatina[6]helicene 66c, and bisplatina[10]
helicene 66d (Fig. 4.26), displayed absorption spectra that were strongly red-shifted
compared to the starting ligands, with longer absorption wavelengths above 450 nm.
Furthermore, platinahelicenes 66a-d are efficient deep-red phosphors, with emission
maxima between 630 and 700 nm, quantum yields around 0.05–0.10 in deoxygenated solution at room temperature and luminescence lifetimes of 10–20 μs. Interestingly, platinahelicenes 66a–c displayed circularly polarized phosphorescence with
dissymmetry factors as high as 10
À2 , which is one order of magnitude bigger than for
most of organic helicenes. These g lum values appeared positive for the (P) enantiomers and negative for the (M ), which was not always the case in azaborahelicenes
analogues 46a–d [45]. Note that bis-platina[10]helicene 66d also exhibited red
N
N
Pt
Pt
O
O
O
O
OCH 3
N
Pt
O
O
N
Pt
N
Pt
F
F
O
O
O
O
(P)-(+)-66a
(P)-(+)-66c
(P)-(+)-66d
CF 3
N
Pt
O
O
(P)-(+)-66e
F
OCH 3
N
Pt
O
O
(P)-(+)-66b
OCH 3
N
(P)-(+)-67
Fig. 4.26 Chemical structures of platinahelicenes 66a–e and of precursor 67
4 Circularly Polarized Luminescence in Helicene and Helicenoid Derivatives
83
4.9.1 Cycloplatinated Helicenes
Coordination chemistry offers a simple way to tune the optical and electronic
properties of the π-ligands since both the coordination sphere geometry and the
nature of the metal-ligand interaction can be readily modified by varying the metal
center. This will produce a great impact on the properties of the molecule
[62]. Recent studies have demonstrated many potential applications of
N-containing helicenes in coordination chemistry and in materials science
[63]. Indeed, their transition metal complexes may show interesting properties in
harvesting (visible) light and re-emitting it at a wavelength that depends on the
metallic ion used, thus allowing the development of light-emitting devices,
chemosensors, photovoltaic dye-sensitized devices, etc. In 2010, our group prepared
the first class of organometallic helicenes incorporating a metallic ion, i.e., Pt, within
their helical backbone, named platinahelicenes [64, 65]. Enantiopure platina[6]
helicene 66a, platina[8]helicene 66b, bisplatina[6]helicene 66c, and bisplatina[10]
helicene 66d (Fig. 4.26), displayed absorption spectra that were strongly red-shifted
compared to the starting ligands, with longer absorption wavelengths above 450 nm.
Furthermore, platinahelicenes 66a-d are efficient deep-red phosphors, with emission
maxima between 630 and 700 nm, quantum yields around 0.05–0.10 in deoxygenated solution at room temperature and luminescence lifetimes of 10–20 μs. Interestingly, platinahelicenes 66a–c displayed circularly polarized phosphorescence with
dissymmetry factors as high as 10
À2 , which is one order of magnitude bigger than for
most of organic helicenes. These g lum values appeared positive for the (P) enantiomers and negative for the (M ), which was not always the case in azaborahelicenes
analogues 46a–d [45]. Note that bis-platina[10]helicene 66d also exhibited red
N
N
Pt
Pt
O
O
O
O
OCH 3
N
Pt
O
O
N
Pt
N
Pt
F
F
O
O
O
O
(P)-(+)-66a
(P)-(+)-66c
(P)-(+)-66d
CF 3
N
Pt
O
O
(P)-(+)-66e
F
OCH 3
N
Pt
O
O
(P)-(+)-66b
OCH 3
N
(P)-(+)-67
Fig. 4.26 Chemical structures of platinahelicenes 66a–e and of precursor 67
4 Circularly Polarized Luminescence in Helicene and Helicenoid Derivatives
83