bisignalizated visible wavelength dichroic signal (negative Cotton effect for polymers based on (R)-BINOL moiety) matching with the visible absorption spectra of
the involved π-extended BODIPY chromophores (maximum |g abs | values up to
ca. 3 Â 10
À3 for 39c; negative values for the R polymers) [72]. The observed
bisignalization suggests exciton coupling between the neighbouring BODIPY chromophores, disposed in a helically chiral architecture. Moreover, these BODIPY
polymers show CPL activity in the red range of the spectra, upon excitation with
visible light in THF solution, the CPL spectra for enantiomers being mirror images
(maximum |g lum | values up to ca. 2Á10
À3 at 611 nm for 39c; negative values for the
R polymers) [72]. Interestingly, both the |g abs | and |g lum | values were demonstrated to
depend on the dihedral angle of the involved BINOL-based moiety: as the angle
increases, the corresponding size of CD or CPL signal decreases [72].
6.4 Summary and Outlook
Despite the inherently planar, achiral nature of the BODIPY fluorophore, a diverse
array of strategies have been explored in an effort to induce efficient chiral perturbation directed towards the gain of CPL activity. The key twisting deformation
postulated to be a requirement for an efficient CPL emission (in terms of |g lum | value)
[32], has been demonstrated in mono(BODIPY)s through embedding the BODIPY
core in an helicene-like architecture (e.g. by fusing π-conjugated rings to the
BODIPY core [30], by intramolecular FÁÁÁH bonding in chiral-urobilin derivatives
[49], or by constrained N,N,O,- and N,N,O,O-boron chelation [55, 57]). Beyond
N B
N
Cl
F F
39
g lum = -0.9·10 -3
f = 0.23
R
O
O
[
]n
Ar
C 8 H 17 -n
R
O
O
C 4 H 9 -n
C 4 H 9 -n
R
O
O
a
b
c
39a
g lum = -1.8·10 -3
f = 0.21
39b
g lum = -2.0·10 -3
f = 0.26
39c
Ar:
Fig. 6.32 BINOL-based BODIPY polymers 39 and visible CPL signatures (upon visible light
irradiation in THF solution)
144
M. J. Hall and S. de la Moya
the involved π-extended BODIPY chromophores (maximum |g abs | values up to
ca. 3 Â 10
À3 for 39c; negative values for the R polymers) [72]. The observed
bisignalization suggests exciton coupling between the neighbouring BODIPY chromophores, disposed in a helically chiral architecture. Moreover, these BODIPY
polymers show CPL activity in the red range of the spectra, upon excitation with
visible light in THF solution, the CPL spectra for enantiomers being mirror images
(maximum |g lum | values up to ca. 2Á10
À3 at 611 nm for 39c; negative values for the
R polymers) [72]. Interestingly, both the |g abs | and |g lum | values were demonstrated to
depend on the dihedral angle of the involved BINOL-based moiety: as the angle
increases, the corresponding size of CD or CPL signal decreases [72].
6.4 Summary and Outlook
Despite the inherently planar, achiral nature of the BODIPY fluorophore, a diverse
array of strategies have been explored in an effort to induce efficient chiral perturbation directed towards the gain of CPL activity. The key twisting deformation
postulated to be a requirement for an efficient CPL emission (in terms of |g lum | value)
[32], has been demonstrated in mono(BODIPY)s through embedding the BODIPY
core in an helicene-like architecture (e.g. by fusing π-conjugated rings to the
BODIPY core [30], by intramolecular FÁÁÁH bonding in chiral-urobilin derivatives
[49], or by constrained N,N,O,- and N,N,O,O-boron chelation [55, 57]). Beyond
N B
N
Cl
F F
39
g lum = -0.9·10 -3
f = 0.23
R
O
O
[
]n
Ar
C 8 H 17 -n
R
O
O
C 4 H 9 -n
C 4 H 9 -n
R
O
O
a
b
c
39a
g lum = -1.8·10 -3
f = 0.21
39b
g lum = -2.0·10 -3
f = 0.26
39c
Ar:
Fig. 6.32 BINOL-based BODIPY polymers 39 and visible CPL signatures (upon visible light
irradiation in THF solution)
144
M. J. Hall and S. de la Moya