promote ICT upon the excitation [62]. Thus, it is known that the fluorescent
behaviour of BODIPY chromophores functionalized with both an efficient
electron-donating group and an efficient electron-withdrawing group (push-pull
effect) is ruled by the population of an ICT state upon excitation [63–65]. In this
context, the differential ability of 36 and 37 to promote ICT (which is expected to be
higher for nitrogenated 36) could cause significant differences in the charge distribution upon excitation, which would explain the observed CPL reversal [62]. Indeed,
the promotion of an ICT state upon excitation is demonstrated to be acting in these
bis(BODIPY)s [66]. Other than by structural changes, ICT modulation can be
achieved by alteration in solvent polarity, alongside the finely tuning other key
fluorescent signatures such as the fluorescent quantum yield (e.g. ϕ up to 0.30 for
37 in less polar cyclohexane) [62]. The demonstrated capability for modulating ICT,
together with synthetic accessibility, capability for reversing the polarization handedness, and configurational lability, is likely to make the helically labile bis
(BODIPY) design a key element in the development of future tunable CPL-SOMs.
Figure-of-Eight Bis(BODIPY)S
The figure-of-eight geometry involves a peculiar helicity, which is expected to
provide unique and interesting chiroptical properties. However, few examples of
enantiopure figure-of-eight compounds have been described, and CPL-SOMs based
on this geometry are limited [67–69]. Nonetheless, Nabeshima et al. have reported a
CPL-enabling macrocyclic bis(BODIPY) 38 with a figure-of-eight design
N B
N
N
B
N
O
O
Cl
Cl
F F
F
F
(R,R)-37
R
R
N B
N
N
B
N
O
O
Cl
Cl
F F
F
F
S
S
(S,S)-37
g lum = -1·10 -3
f = 0.17
g lum = +1·10 -3
f = 0.17
Fig. 6.29 Helically labile bis(haloBODIPY)s (R,R)- and (S,S)-37 and their visible CPL signatures
upon visible wavelength irradiation in solution
6 BODIPY Based Emitters of Circularly Polarized Luminescence
141
behaviour of BODIPY chromophores functionalized with both an efficient
electron-donating group and an efficient electron-withdrawing group (push-pull
effect) is ruled by the population of an ICT state upon excitation [63–65]. In this
context, the differential ability of 36 and 37 to promote ICT (which is expected to be
higher for nitrogenated 36) could cause significant differences in the charge distribution upon excitation, which would explain the observed CPL reversal [62]. Indeed,
the promotion of an ICT state upon excitation is demonstrated to be acting in these
bis(BODIPY)s [66]. Other than by structural changes, ICT modulation can be
achieved by alteration in solvent polarity, alongside the finely tuning other key
fluorescent signatures such as the fluorescent quantum yield (e.g. ϕ up to 0.30 for
37 in less polar cyclohexane) [62]. The demonstrated capability for modulating ICT,
together with synthetic accessibility, capability for reversing the polarization handedness, and configurational lability, is likely to make the helically labile bis
(BODIPY) design a key element in the development of future tunable CPL-SOMs.
Figure-of-Eight Bis(BODIPY)S
The figure-of-eight geometry involves a peculiar helicity, which is expected to
provide unique and interesting chiroptical properties. However, few examples of
enantiopure figure-of-eight compounds have been described, and CPL-SOMs based
on this geometry are limited [67–69]. Nonetheless, Nabeshima et al. have reported a
CPL-enabling macrocyclic bis(BODIPY) 38 with a figure-of-eight design
N B
N
N
B
N
O
O
Cl
Cl
F F
F
F
(R,R)-37
R
R
N B
N
N
B
N
O
O
Cl
Cl
F F
F
F
S
S
(S,S)-37
g lum = -1·10 -3
f = 0.17
g lum = +1·10 -3
f = 0.17
Fig. 6.29 Helically labile bis(haloBODIPY)s (R,R)- and (S,S)-37 and their visible CPL signatures
upon visible wavelength irradiation in solution
6 BODIPY Based Emitters of Circularly Polarized Luminescence
141