CD spectra. Both enantiomers of mono(BODIPY) 32 were also CPL active, with
|g lum | ¼ 3.7Á10
À3 (Fig. 6.22) [57].
Cyclic voltammetry of racemic 32 suggested that the process of symmetry
breaking had resulted in an increase in charge transfer character in the excited
state [57]. This is of interest in the design of CPL-SOMs as the typically low |g lum |
values observed arise as a consequence of the mismatch in the magnitude of the
magnetic (m) and electric (μ) transition dipole moments, since |g lum | ¼ 4(|μ|Á|m|Á
cosτ)/(|μ|
2 + |m|
2 ) where τ is the angle between the two transition dipole moments. In
CPL-SOMs the electric transition dipole moment is commonly several orders of
magnitude greater than the corresponding magnetic transition dipole moment. However, an increase in charge transfer character in the excited state would be expected
to decrease the electric transition dipole moment. Calculation of these parameters for
both the unsymmetrical helically chiral mono(BODIPY) 32 and the comparable
Fig. 6.22 Unsymmetrical helically chiral mono(BODIPY) 32 and their visible CPL activity upon
visible irradiation in solution. (a) Experimental CD (red ¼ (M )-32, blue ¼ (P)-32) and UV-Vis
absorption spectra (black). (b) Calculated Boltzmann-weighted spectra, CD (red ¼ (M )-32) and
UV-Vis absorption spectra (black). (c) CPL (red ¼ (M )-32, blue ¼ (P)-32) and fluorescence spectra
(black) [adapted with permission from [57], copyright 2017 WILEY-VCH Verlag GmbH]
6 BODIPY Based Emitters of Circularly Polarized Luminescence
135
|g lum | ¼ 3.7Á10
À3 (Fig. 6.22) [57].
Cyclic voltammetry of racemic 32 suggested that the process of symmetry
breaking had resulted in an increase in charge transfer character in the excited
state [57]. This is of interest in the design of CPL-SOMs as the typically low |g lum |
values observed arise as a consequence of the mismatch in the magnitude of the
magnetic (m) and electric (μ) transition dipole moments, since |g lum | ¼ 4(|μ|Á|m|Á
cosτ)/(|μ|
2 + |m|
2 ) where τ is the angle between the two transition dipole moments. In
CPL-SOMs the electric transition dipole moment is commonly several orders of
magnitude greater than the corresponding magnetic transition dipole moment. However, an increase in charge transfer character in the excited state would be expected
to decrease the electric transition dipole moment. Calculation of these parameters for
both the unsymmetrical helically chiral mono(BODIPY) 32 and the comparable
Fig. 6.22 Unsymmetrical helically chiral mono(BODIPY) 32 and their visible CPL activity upon
visible irradiation in solution. (a) Experimental CD (red ¼ (M )-32, blue ¼ (P)-32) and UV-Vis
absorption spectra (black). (b) Calculated Boltzmann-weighted spectra, CD (red ¼ (M )-32) and
UV-Vis absorption spectra (black). (c) CPL (red ¼ (M )-32, blue ¼ (P)-32) and fluorescence spectra
(black) [adapted with permission from [57], copyright 2017 WILEY-VCH Verlag GmbH]
6 BODIPY Based Emitters of Circularly Polarized Luminescence
135