pyrene units transform themselves into a chirally π-stacked arrangement. These
changes in configuration are responsible for the cryptochiral behavior observed,
namely, the ultra-weak CD and intense CPL bands of excimer origin that are due to
the two floppy pyrene units that sandwich the octahydrobinaphthyl moiety.
In conclusion, a CD-silent/CPL-active cryptochiral binaphthyl fluorophore was
successfully created by connecting an axially chiral binaphthyl and two fluorescent
pyrene units through flexible tethers. This system can concurrently control two chiral
points (binaphthyl and pyrene) in the photoexcited state.
2.8 Controlling Circularly Polarized Luminescence (CPL)
of Binaphthyl-Pyrene Fluorophores Using Fluidic
and Glassy Media [27]
In Sects. 2.3 and 2.5, the CPL signs of chiral binaphthyl fluorophores with the same
axial chirality were reported to be controllable, both in solution and in the solid state,
by manipulating their external environments. In this section, a non-classical
approach for the dual control of the λ CPL and the CPL sign of a chiral organic
fluorophore, by varying the external environment, e.g., by choosing CHCl 3 solution
as the fluidic medium and PMMA film as the glassy solid medium, is reported. To
that end, chiral binaphthyl-pyrene fluorophore 7 with oligoether tethers was used
again as the model system (Fig. 2.20).
Interestingly, although the CHCl 3 solution-state PL of (R)-7 shows the typical
excimeric emission of its pyrene units, the PL of (R)-7 dispersed in PMMA film
shows a λ PL shifted to a significantly shorter wavelength (λ PL ¼ 393 nm), while its
Ф F value was higher, at 46%, due to the suppression of thermal vibrational deactivation (Fig. 2.21, lower).
As expected, (R)-7 exhibited CPL signals in CHCl 3 and PMMA film (Fig. 2.21,
upper panel). The CPL wavelength also changed, as was observed for PL. In
addition, (R)-7 exhibited CPL signs that depended on the fluidic and glassy states;
it was negative (À) in CHCl 3 solution (Fig. 2.15) and positive (+) in the PMMA film.
O
O
(R)-7
O
O
O
O
O
O
Fig. 2.20 Chiral
binaphthyl-pyrene
fluorophore (R)-7
2 Circularly Polarized Luminescence of Axially Chiral Binaphthyl Fluorophores
25
changes in configuration are responsible for the cryptochiral behavior observed,
namely, the ultra-weak CD and intense CPL bands of excimer origin that are due to
the two floppy pyrene units that sandwich the octahydrobinaphthyl moiety.
In conclusion, a CD-silent/CPL-active cryptochiral binaphthyl fluorophore was
successfully created by connecting an axially chiral binaphthyl and two fluorescent
pyrene units through flexible tethers. This system can concurrently control two chiral
points (binaphthyl and pyrene) in the photoexcited state.
2.8 Controlling Circularly Polarized Luminescence (CPL)
of Binaphthyl-Pyrene Fluorophores Using Fluidic
and Glassy Media [27]
In Sects. 2.3 and 2.5, the CPL signs of chiral binaphthyl fluorophores with the same
axial chirality were reported to be controllable, both in solution and in the solid state,
by manipulating their external environments. In this section, a non-classical
approach for the dual control of the λ CPL and the CPL sign of a chiral organic
fluorophore, by varying the external environment, e.g., by choosing CHCl 3 solution
as the fluidic medium and PMMA film as the glassy solid medium, is reported. To
that end, chiral binaphthyl-pyrene fluorophore 7 with oligoether tethers was used
again as the model system (Fig. 2.20).
Interestingly, although the CHCl 3 solution-state PL of (R)-7 shows the typical
excimeric emission of its pyrene units, the PL of (R)-7 dispersed in PMMA film
shows a λ PL shifted to a significantly shorter wavelength (λ PL ¼ 393 nm), while its
Ф F value was higher, at 46%, due to the suppression of thermal vibrational deactivation (Fig. 2.21, lower).
As expected, (R)-7 exhibited CPL signals in CHCl 3 and PMMA film (Fig. 2.21,
upper panel). The CPL wavelength also changed, as was observed for PL. In
addition, (R)-7 exhibited CPL signs that depended on the fluidic and glassy states;
it was negative (À) in CHCl 3 solution (Fig. 2.15) and positive (+) in the PMMA film.
O
O
(R)-7
O
O
O
O
O
O
Fig. 2.20 Chiral
binaphthyl-pyrene
fluorophore (R)-7
2 Circularly Polarized Luminescence of Axially Chiral Binaphthyl Fluorophores
25