units is difficult to achieve upon photoexcitation; as a result, (R)-7 exhibits
monomer-like excimer CPL in PMMA film.
In conclusion, the CPL/PL characteristics of an axially chiral binaphthyl
fluorophore connected to fluorescent units can be doubly controlled by selecting a
fluidic CHCl 3 solution and a glassy PMMA film.
2.9 The Appearance of Circularly Polarized Luminescence
(CPL) from a Chiral Binaphthyl-Terthiophene
Fluorophore in the Solid State [28]
If chirality transfer from the chiral binaphthyl to a remote achiral fluorescent unit in a
fluorescent binaphthyl system is not efficient in the solution state, CPL signals due to
two remote fluorescent moieties may be not observed. In this section, the appearance
of CPL from a dual-tandem fluorophoric molecular system, namely, (R)-10 and (S)10 (Fig. 2.23), which consist of an axially chiral binaphthyl and two achiral
terthiophenes, is reported. Terthiophene is a basic π-conjugated thiophene unit
with superior fluorescence properties due to its long wavelength emission.
(R)-10 exhibited the marked PL associated with terthiophene units in CHCl 3
solution, with a PL maximum (λ PL ) observed at 437 nm. Unfortunately, neither (R)nor (S)-10 exhibited any meaningful CPL spectrum in CHCl 3 , presumably due to the
highly flexible linkers between the terthiophenes and binaphthyl.
On the other hand, (R)-10 exhibited marked PL with a λ PL at 413 nm in the KBr
solid state (Fig. 2.24, lower). Expectedly, (R)-10 in KBr exhibited CPL with a g lum
value of about +5.0 Â 10
–4 .
The solid-state CD and UV-Vis absorption spectra of (R)-10 in the KBr pelletdispersed state are shown in Fig. 2.25. Several π-πà transitions associated with the
terthiophene groups of 10, in the 260–360 nm region are observed. The g CD value at
the Cotton CD band (λ CD ¼ 342 nm) of (R)-10 is about À3.2 Â 10
–5 . The difference
in the values of g CD and g CPL is possible ascribable to conformational changes in the
ground and photoexcited states.
10
O
O
S
S
S
S
S
S
Fig. 2.23 Chiral
binaphthyl-terthiophene
fluorophore 10
2 Circularly Polarized Luminescence of Axially Chiral Binaphthyl Fluorophores
27
monomer-like excimer CPL in PMMA film.
In conclusion, the CPL/PL characteristics of an axially chiral binaphthyl
fluorophore connected to fluorescent units can be doubly controlled by selecting a
fluidic CHCl 3 solution and a glassy PMMA film.
2.9 The Appearance of Circularly Polarized Luminescence
(CPL) from a Chiral Binaphthyl-Terthiophene
Fluorophore in the Solid State [28]
If chirality transfer from the chiral binaphthyl to a remote achiral fluorescent unit in a
fluorescent binaphthyl system is not efficient in the solution state, CPL signals due to
two remote fluorescent moieties may be not observed. In this section, the appearance
of CPL from a dual-tandem fluorophoric molecular system, namely, (R)-10 and (S)10 (Fig. 2.23), which consist of an axially chiral binaphthyl and two achiral
terthiophenes, is reported. Terthiophene is a basic π-conjugated thiophene unit
with superior fluorescence properties due to its long wavelength emission.
(R)-10 exhibited the marked PL associated with terthiophene units in CHCl 3
solution, with a PL maximum (λ PL ) observed at 437 nm. Unfortunately, neither (R)nor (S)-10 exhibited any meaningful CPL spectrum in CHCl 3 , presumably due to the
highly flexible linkers between the terthiophenes and binaphthyl.
On the other hand, (R)-10 exhibited marked PL with a λ PL at 413 nm in the KBr
solid state (Fig. 2.24, lower). Expectedly, (R)-10 in KBr exhibited CPL with a g lum
value of about +5.0 Â 10
–4 .
The solid-state CD and UV-Vis absorption spectra of (R)-10 in the KBr pelletdispersed state are shown in Fig. 2.25. Several π-πà transitions associated with the
terthiophene groups of 10, in the 260–360 nm region are observed. The g CD value at
the Cotton CD band (λ CD ¼ 342 nm) of (R)-10 is about À3.2 Â 10
–5 . The difference
in the values of g CD and g CPL is possible ascribable to conformational changes in the
ground and photoexcited states.
10
O
O
S
S
S
S
S
S
Fig. 2.23 Chiral
binaphthyl-terthiophene
fluorophore 10
2 Circularly Polarized Luminescence of Axially Chiral Binaphthyl Fluorophores
27