(À) Cotton signs (Fig. 2.16, upper), even though (R)-7 and (R)-8 display opposite
CPL signs (Fig. 2.15, upper). Characteristically, these g CD values are smaller than
the corresponding g CPL values.
In this system, intermolecular associations of (R)-7 and (R)-8 in the S 0 state are
neglected. In addition, an odd-even effect involving the number of atoms in the
tethers may be a crucial factor that defines the signs of the CD and CPL signals;
however, both tethers in 7 and 8 have odd numbers of atoms. These results lead to
the conclusion that, although the chirality-oriented conformations of the two pyrenes
in 7 and 8 in the S 0 states are similar, their relative orientations in the S 1 states may be
very different, possibly with opposite handedness, which causes opposite CPL signs
to be observed for 7 and 8.
In conclusion, in axially chiral binaphthyls that connect fluorescent units, the CPL
signs, which are generated by the two photoexcited fluorophores, can be controlled
through tethered structures involving the axially chiral binaphthyl.
2.7 Cryptochiral Circularly Polarized Luminophores Based
on Axially Chiral Binaphthyls [26]
In this section, the novel functional binaphthyl fluorophores designed using the
CPL-controlling concepts discussed in Sects. 2.2 and 2.6, involving the
5,5
0 ,6,6
0 ,7,7
0 ,8,8
0 -octahydro-1,1
0 -bi-2-naphthyl fluorophore 9 connected to two
pyrenes through flexible ester tethers, is reported (Fig. 2.17).
The PL and CPL spectra of (R)-9 and (S)-9 in CHCl 3 are shown in Fig. 2.18. (R)-9
exhibits an intense excimer PL band at 468 nm (λ PL ) of pyrene origin. In addition, a
weak monomeric PL band at 396 nm is observed, which is ascribable to the sterically
constrained intramolecular dimeric pyrene moieties in their S 0 states. (R)-9 and (S)-9
emit CPL and exhibit positive (+) and negative (À) CPL signs in their S 1 -state
structures, respectively. The absolute value of g CPL for (R)-9 in CHCl 3 is
+2.5 Â 10
À3 at 454 nm.
O
O
O
O
9
Fig. 2.17 Chiral
binaphthyl-pyrene
fluorophore 9
2 Circularly Polarized Luminescence of Axially Chiral Binaphthyl Fluorophores
23
CPL signs (Fig. 2.15, upper). Characteristically, these g CD values are smaller than
the corresponding g CPL values.
In this system, intermolecular associations of (R)-7 and (R)-8 in the S 0 state are
neglected. In addition, an odd-even effect involving the number of atoms in the
tethers may be a crucial factor that defines the signs of the CD and CPL signals;
however, both tethers in 7 and 8 have odd numbers of atoms. These results lead to
the conclusion that, although the chirality-oriented conformations of the two pyrenes
in 7 and 8 in the S 0 states are similar, their relative orientations in the S 1 states may be
very different, possibly with opposite handedness, which causes opposite CPL signs
to be observed for 7 and 8.
In conclusion, in axially chiral binaphthyls that connect fluorescent units, the CPL
signs, which are generated by the two photoexcited fluorophores, can be controlled
through tethered structures involving the axially chiral binaphthyl.
2.7 Cryptochiral Circularly Polarized Luminophores Based
on Axially Chiral Binaphthyls [26]
In this section, the novel functional binaphthyl fluorophores designed using the
CPL-controlling concepts discussed in Sects. 2.2 and 2.6, involving the
5,5
0 ,6,6
0 ,7,7
0 ,8,8
0 -octahydro-1,1
0 -bi-2-naphthyl fluorophore 9 connected to two
pyrenes through flexible ester tethers, is reported (Fig. 2.17).
The PL and CPL spectra of (R)-9 and (S)-9 in CHCl 3 are shown in Fig. 2.18. (R)-9
exhibits an intense excimer PL band at 468 nm (λ PL ) of pyrene origin. In addition, a
weak monomeric PL band at 396 nm is observed, which is ascribable to the sterically
constrained intramolecular dimeric pyrene moieties in their S 0 states. (R)-9 and (S)-9
emit CPL and exhibit positive (+) and negative (À) CPL signs in their S 1 -state
structures, respectively. The absolute value of g CPL for (R)-9 in CHCl 3 is
+2.5 Â 10
À3 at 454 nm.
O
O
O
O
9
Fig. 2.17 Chiral
binaphthyl-pyrene
fluorophore 9
2 Circularly Polarized Luminescence of Axially Chiral Binaphthyl Fluorophores
23