Spiranic O-BODIPYs
The group of de la Moya demonstrated that simple fluorine-substitution reactions of
accessible F-BODIPYs with enantiopure 1,1
0 -binapth-2-ol (BINOL) allowed the
easy preparation of spiranic C 2 -symmetric mono(BODIPY)s endowed with CPL
activity, as exemplified by the straightforward preparation (ca. 60% chemical yield)
and CPL behaviour of enantiomers 20 (Fig. 6.16) [50]. Thus, (R)-20 and (S)-20
exhibit visible spectrum CPL (BODIPY emission) upon irradiation with visible light
(BODIPY excitation) in CHCl 3 solution, the recorded CPL spectra appearing as
mirror images with a maximum |g lum | value ca. 10
À3 (positive g lum for the
R enantiomer). The CPL maxima observed match those of the visible light emission
maxima of the involved BODIPY chromophore (λ max ca. 570 nm; ϕ ca. 0.45),
clearly indicating that the observed CPL arises from BODIPY not BINOL emission.
Thus spiranic C 2 -symmetric mono(BODIPY)s (R)-20 and (S)-20 represent the first
reported examples of CPL from a BODIPY chromophore following direct
excitation.
The CPL-enabling design of 20 is interesting since it involves the use of a single
chiral moiety (the 1,1
0 -biphen-2-ol-based BINOL unit) to chirally perturb the
N B
N
O
O
(S)-20
N B
N
O
O
(R)-20
R
S
g lum = +0.7·10 -3
f = 0.46
g lum = -0.8·10 -3
f = 0.44
N B
N
O
O
(S)-21
N B
N
O
O
(R)-21
R
S
g lum = -0.6·10 -3
f = 0.69
g lum = +0.8·10 -3
f = 0.69
Br
Br
Br
Br
Fig. 6.16 Molecular structures and visible CPL signatures (upon visible light irradiation in
solution) of the first CPL-SOMs based on spiranic C 2 -symmetric mono(BODIPY)s 20 and 21
N B
N
F F
HN
NH
N B
N
F F
O
O
N
N
H
H
O
O
19 in CH 2 Cl 2
19 in DMF
7 0
6 0
5 0
4 0
3 0
2 0
1 0
–1 0
–2 0
–3 0
400
450
500
550
600
Wavelength (nm)
0
Fig. 6.15 Molecular structure of difluoroboron-chelated urobilin derivative 19 showing postulated
conformational change on solvation (left CH 2 Cl 2 ; right DMF) and CD spectra (in CH 2 Cl 2 (broken
line) and DMF (solid line)) [adapted with permission from [49], copyright 1997 American Chemical Society]
6 BODIPY Based Emitters of Circularly Polarized Luminescence
129
The group of de la Moya demonstrated that simple fluorine-substitution reactions of
accessible F-BODIPYs with enantiopure 1,1
0 -binapth-2-ol (BINOL) allowed the
easy preparation of spiranic C 2 -symmetric mono(BODIPY)s endowed with CPL
activity, as exemplified by the straightforward preparation (ca. 60% chemical yield)
and CPL behaviour of enantiomers 20 (Fig. 6.16) [50]. Thus, (R)-20 and (S)-20
exhibit visible spectrum CPL (BODIPY emission) upon irradiation with visible light
(BODIPY excitation) in CHCl 3 solution, the recorded CPL spectra appearing as
mirror images with a maximum |g lum | value ca. 10
À3 (positive g lum for the
R enantiomer). The CPL maxima observed match those of the visible light emission
maxima of the involved BODIPY chromophore (λ max ca. 570 nm; ϕ ca. 0.45),
clearly indicating that the observed CPL arises from BODIPY not BINOL emission.
Thus spiranic C 2 -symmetric mono(BODIPY)s (R)-20 and (S)-20 represent the first
reported examples of CPL from a BODIPY chromophore following direct
excitation.
The CPL-enabling design of 20 is interesting since it involves the use of a single
chiral moiety (the 1,1
0 -biphen-2-ol-based BINOL unit) to chirally perturb the
N B
N
O
O
(S)-20
N B
N
O
O
(R)-20
R
S
g lum = +0.7·10 -3
f = 0.46
g lum = -0.8·10 -3
f = 0.44
N B
N
O
O
(S)-21
N B
N
O
O
(R)-21
R
S
g lum = -0.6·10 -3
f = 0.69
g lum = +0.8·10 -3
f = 0.69
Br
Br
Br
Br
Fig. 6.16 Molecular structures and visible CPL signatures (upon visible light irradiation in
solution) of the first CPL-SOMs based on spiranic C 2 -symmetric mono(BODIPY)s 20 and 21
N B
N
F F
HN
NH
N B
N
F F
O
O
N
N
H
H
O
O
19 in CH 2 Cl 2
19 in DMF
7 0
6 0
5 0
4 0
3 0
2 0
1 0
–1 0
–2 0
–3 0
400
450
500
550
600
Wavelength (nm)
0
Fig. 6.15 Molecular structure of difluoroboron-chelated urobilin derivative 19 showing postulated
conformational change on solvation (left CH 2 Cl 2 ; right DMF) and CD spectra (in CH 2 Cl 2 (broken
line) and DMF (solid line)) [adapted with permission from [49], copyright 1997 American Chemical Society]
6 BODIPY Based Emitters of Circularly Polarized Luminescence
129