6.3.2 Poly(BODIPY)S
6.3.2.1 Axially Chiral Bis(BODIPY)S
Bruhn et al. examined the synthesis of axially chiral 1,1
0 - and 3,3
0 -linked bis
(BODIPY)s 34 and 35, through the oxidative C–C coupling of the corresponding
1- and 3- unsubstituted mono(BODIPY)s [59, 60]. Steric crowding around the bis
(BODIPY) axis of both 34 and 35 prevents free rotation resulting in configurationally stable atropisomers (Fig. 6.24).
Axially chiral 1,1
0 - and 3,3
0 -linked bis(BODIPY)s 34 and 35 were resolved by
chiral HPLC (Chirex (S)-Val, CH 2 Cl 2 /n-hexane 3:7 (34); Chiralpak IA, CH 2 Cl 2 /nhexane 8:2 (35)) and showed near mirror-image CD spectra. 3,3
0 -linked bis
(BODIPY) 35 gave an intense CD couplet arising from a strong coupling of the
transition dipole moments of the two BODIPY fluorophores, whilst also giving a
maximum g lum of 3.8Á10
À3 (Fig. 6.25). Interestingly, 34 is one of the rare examples
in which exciton rule fails due to non-negligible μ-m coupling, resulting in an
inverted and weaker CD couplet with respect to that of compound 35 (with same
absolute configuration) as well as CPL. The demonstration of CPL from these
directly linked atropisomeric BODIPYs provided some evidence that the coupling
of the transition dipole moments of two (or more) BODIPY cores may be an
interesting strategy for the creation of future efficient CPL-SOMs.
6.3.2.2 Helically Chiral Poly(BODIPYs)
Helically Labile Bis(BODIPYs)
The group of de la Moya has shown that nucleophilic aromatic substitution reaction
of accessible 3,5-dichloroBODIPY with commercial 1,2-diphenyl-1,2ethanediamine provides facile access to bis(haloBODIPY) 36 (Fig. 6.26) where
two identical BODIPY cores are covalently linked by a conformationally flexible
chiral centre containing bridge [61]. The synthesis of bis(haloBODIPY) 36 is
straightforward (ca. 50% chemical yield) and allows the direct preparation of
enantiopure chiral bis(BODIPY)s via the corresponding enantiopure diamines.
g lum = 3.8·10 -3
N
N
N
B
F 2
F 2
B
N
N
N
F 2
B
N
N B
F 2
g lum = 4·10 -4
35
34
1'
1
3'
3
Fig. 6.24 Axially chiral
1,1
0 -linked bis(BODIPY) 34
and axially chiral 3,3
0 -linked
bis(BODIPY) 35 (one
enantiomer shown in each
case), as well as their visible
CPL signatures upon visible
light irradiation in solution
(no data on fluorescence
efficiency available)
6 BODIPY Based Emitters of Circularly Polarized Luminescence
137
6.3.2.1 Axially Chiral Bis(BODIPY)S
Bruhn et al. examined the synthesis of axially chiral 1,1
0 - and 3,3
0 -linked bis
(BODIPY)s 34 and 35, through the oxidative C–C coupling of the corresponding
1- and 3- unsubstituted mono(BODIPY)s [59, 60]. Steric crowding around the bis
(BODIPY) axis of both 34 and 35 prevents free rotation resulting in configurationally stable atropisomers (Fig. 6.24).
Axially chiral 1,1
0 - and 3,3
0 -linked bis(BODIPY)s 34 and 35 were resolved by
chiral HPLC (Chirex (S)-Val, CH 2 Cl 2 /n-hexane 3:7 (34); Chiralpak IA, CH 2 Cl 2 /nhexane 8:2 (35)) and showed near mirror-image CD spectra. 3,3
0 -linked bis
(BODIPY) 35 gave an intense CD couplet arising from a strong coupling of the
transition dipole moments of the two BODIPY fluorophores, whilst also giving a
maximum g lum of 3.8Á10
À3 (Fig. 6.25). Interestingly, 34 is one of the rare examples
in which exciton rule fails due to non-negligible μ-m coupling, resulting in an
inverted and weaker CD couplet with respect to that of compound 35 (with same
absolute configuration) as well as CPL. The demonstration of CPL from these
directly linked atropisomeric BODIPYs provided some evidence that the coupling
of the transition dipole moments of two (or more) BODIPY cores may be an
interesting strategy for the creation of future efficient CPL-SOMs.
6.3.2.2 Helically Chiral Poly(BODIPYs)
Helically Labile Bis(BODIPYs)
The group of de la Moya has shown that nucleophilic aromatic substitution reaction
of accessible 3,5-dichloroBODIPY with commercial 1,2-diphenyl-1,2ethanediamine provides facile access to bis(haloBODIPY) 36 (Fig. 6.26) where
two identical BODIPY cores are covalently linked by a conformationally flexible
chiral centre containing bridge [61]. The synthesis of bis(haloBODIPY) 36 is
straightforward (ca. 50% chemical yield) and allows the direct preparation of
enantiopure chiral bis(BODIPY)s via the corresponding enantiopure diamines.
g lum = 3.8·10 -3
N
N
N
B
F 2
F 2
B
N
N
N
F 2
B
N
N B
F 2
g lum = 4·10 -4
35
34
1'
1
3'
3
Fig. 6.24 Axially chiral
1,1
0 -linked bis(BODIPY) 34
and axially chiral 3,3
0 -linked
bis(BODIPY) 35 (one
enantiomer shown in each
case), as well as their visible
CPL signatures upon visible
light irradiation in solution
(no data on fluorescence
efficiency available)
6 BODIPY Based Emitters of Circularly Polarized Luminescence
137