symmetrical helically chiral mono(BODIPY) 27 did indeed show a slight decrease in
μ (from 7.6 to 6.0Á10
À1 ); however a concurrent decrease in m (from 1.4Á10
À3 to
7.3Á10
À4 ) coupled with an unfavourable shift in τ (from 65 to 70
) resulted in an
overall decrease in |g lum | for 32 vs. 27. However examination of this system may
provide useful lessons for the rational control of m, μ, and τ as an important design
paradigm for future CPL-SOMs.
Propeller-like PolyarylBODIPYs
Propeller chirality has been also explored to gain CPL activity in BODIPYs. Thus,
Mori et al. have recently reported a heptaarylBODIPY 33 having quasi propeller
chirality (Fig. 6.23) [58]. Although the arylic propeller blades have pendant chiral
groups, almost-complete one-directional propeller chirality is unfortunately not
achieved, even by using non-polar solvents (e.g. cyclohexane) and low temperatures
[58]. This fact is attributed to the computed small energy difference between the
corresponding propeller diastereomers (0.8 kcalÁmol
À1 ), in combination with a
computed barrier for the P-to-M propeller flipping of 3.8 kcalÁmol
À1 [58]. Nonetheless, decreasing the temperature below À70
C results in the detection of a visible
(above 600 nm) clearly bisignalized dichroic CD signal corresponding to the emission maxima of the BODIPY chromophore and attributed to the formation of headto-tail propeller dimers which induce an efficient chiral perturbation of the involved
BODIPY chromophores. Interestingly, such an efficient perturbation also allows the
detection of a visible CPL signal from the said BODIPY dimers (maximum
g lum ¼ +2.0Á10
À3 at À120
C) combined with a high fluorescence quantum yield
(ϕ ¼ 0.45) [58].
O
O
O
O
O
O
O
F F
N B
N
O
O
O
O
O
O
O
F
F
N
B
N
Propeller
flipping
(P)-33
(M)-33
Fig. 6.23 BODIPY 33 with propeller-like chirality. At low temperature, efficient chiral perturbation of the BODIPY chromophore, detected by CD and CPL signalization, is attributed to the
formation of head-to-tail dimers
136
M. J. Hall and S. de la Moya
μ (from 7.6 to 6.0Á10
À1 ); however a concurrent decrease in m (from 1.4Á10
À3 to
7.3Á10
À4 ) coupled with an unfavourable shift in τ (from 65 to 70
) resulted in an
overall decrease in |g lum | for 32 vs. 27. However examination of this system may
provide useful lessons for the rational control of m, μ, and τ as an important design
paradigm for future CPL-SOMs.
Propeller-like PolyarylBODIPYs
Propeller chirality has been also explored to gain CPL activity in BODIPYs. Thus,
Mori et al. have recently reported a heptaarylBODIPY 33 having quasi propeller
chirality (Fig. 6.23) [58]. Although the arylic propeller blades have pendant chiral
groups, almost-complete one-directional propeller chirality is unfortunately not
achieved, even by using non-polar solvents (e.g. cyclohexane) and low temperatures
[58]. This fact is attributed to the computed small energy difference between the
corresponding propeller diastereomers (0.8 kcalÁmol
À1 ), in combination with a
computed barrier for the P-to-M propeller flipping of 3.8 kcalÁmol
À1 [58]. Nonetheless, decreasing the temperature below À70
C results in the detection of a visible
(above 600 nm) clearly bisignalized dichroic CD signal corresponding to the emission maxima of the BODIPY chromophore and attributed to the formation of headto-tail propeller dimers which induce an efficient chiral perturbation of the involved
BODIPY chromophores. Interestingly, such an efficient perturbation also allows the
detection of a visible CPL signal from the said BODIPY dimers (maximum
g lum ¼ +2.0Á10
À3 at À120
C) combined with a high fluorescence quantum yield
(ϕ ¼ 0.45) [58].
O
O
O
O
O
O
O
F F
N B
N
O
O
O
O
O
O
O
F
F
N
B
N
Propeller
flipping
(P)-33
(M)-33
Fig. 6.23 BODIPY 33 with propeller-like chirality. At low temperature, efficient chiral perturbation of the BODIPY chromophore, detected by CD and CPL signalization, is attributed to the
formation of head-to-tail dimers
136
M. J. Hall and S. de la Moya