328
Y. Imai
16.3 Non-classical Control of CPL in Solid-State, Axially
Chiral Binaphthyl Luminophore Wrapped
with Inorganic KBr Crystal [12]
In Sect. 16.2, it was seen that the sign of CPL of a polymer-wrapped axially chiral
binaphthyl luminophore could be controlled by adjusting the dihedral angle of the
binaphthyl unit.
In this section, the effect of an inorganic KBr crystal, instead of an organic
polymer, on the CPL from a solid-state circularly polarized luminophore is
discussed. Two almost identical chiral binaphthyl derivatives with the same (R)axial chirality, open-type binaphthyl (R)-3,3
-bis(triphenylsilyl)-1,1
-bi-2-naphthol
[(R)-3] and closed-type binaphthyl (R)-3,3
-bis(triphenylsilyl)-1,1
-binaphthyl-2,2
-
diyl hydrogenphosphate [(R)-4], were used (Fig. 16.3). Chiral KBr-wrapped binaphthyl luminophores, (R)-3/KBr and (R)-4/KBr, were prepared by embedding (R)-3
and (R)-4 into KBr crystal, respectively.
(R)-3/KBr and (R)-4/KBr exhibited CPL at ≈ 372 and ≈ 365 nm (λ CPL ), with F F
= 0.08 and 0.29, respectively, without any significant quenching (Fig. 16.4a). The
reason for the absence of CPL from KBr-wrapped (R)-(+)-1,1
-binaphthyl-2,2
-diol
is not clearly understood. Besides, although (R)-3 and (R)-4 have the same axial
chirality, the CPL sign of (R)-3/KBr was negative (−) while that of (R)-4/KBr was
positive (+). The g CPL values for (R)-3/KBr and (R)-4/KBr were ≈ –2.5 × 10
−4 and
≈ +2.2 × 10
−4 , respectively.
The CD spectra of (R)-3/KBr and (R)-4/KBr show several peaks between 270 and
360 nm for vibronic π-π * transitions, which are characteristic of naphthyl groups
(Fig. 16.4b). The g CD values of (R)-3/KBr and (R)-4/KBr at the first Cotton CD bands
at 349 and 341 nm were ≈ –1.8 × 10
−4 and ≈ +4.4 × 10
−4 , respectively. (R)-3/KBr
and (R)-4/KBr also exhibited opposite CD signs for the first Cotton CD bands: The
CD sign for (R)-3/KBr was negative (−), while that for (R)-4/KBr was positive (+).
Fig. 16.3 Chiral binaphthyl
luminophores (R)-3 and
(R)-4
OH
OH
Si
Si
Ph
Ph
Ph
Ph
Ph
Ph
Si
Si
Ph
Ph
Ph
Ph
Ph
Ph
O
O
P
O
OH
(R)-3
(R)-4
Y. Imai
16.3 Non-classical Control of CPL in Solid-State, Axially
Chiral Binaphthyl Luminophore Wrapped
with Inorganic KBr Crystal [12]
In Sect. 16.2, it was seen that the sign of CPL of a polymer-wrapped axially chiral
binaphthyl luminophore could be controlled by adjusting the dihedral angle of the
binaphthyl unit.
In this section, the effect of an inorganic KBr crystal, instead of an organic
polymer, on the CPL from a solid-state circularly polarized luminophore is
discussed. Two almost identical chiral binaphthyl derivatives with the same (R)axial chirality, open-type binaphthyl (R)-3,3
-bis(triphenylsilyl)-1,1
-bi-2-naphthol
[(R)-3] and closed-type binaphthyl (R)-3,3
-bis(triphenylsilyl)-1,1
-binaphthyl-2,2
-
diyl hydrogenphosphate [(R)-4], were used (Fig. 16.3). Chiral KBr-wrapped binaphthyl luminophores, (R)-3/KBr and (R)-4/KBr, were prepared by embedding (R)-3
and (R)-4 into KBr crystal, respectively.
(R)-3/KBr and (R)-4/KBr exhibited CPL at ≈ 372 and ≈ 365 nm (λ CPL ), with F F
= 0.08 and 0.29, respectively, without any significant quenching (Fig. 16.4a). The
reason for the absence of CPL from KBr-wrapped (R)-(+)-1,1
-binaphthyl-2,2
-diol
is not clearly understood. Besides, although (R)-3 and (R)-4 have the same axial
chirality, the CPL sign of (R)-3/KBr was negative (−) while that of (R)-4/KBr was
positive (+). The g CPL values for (R)-3/KBr and (R)-4/KBr were ≈ –2.5 × 10
−4 and
≈ +2.2 × 10
−4 , respectively.
The CD spectra of (R)-3/KBr and (R)-4/KBr show several peaks between 270 and
360 nm for vibronic π-π * transitions, which are characteristic of naphthyl groups
(Fig. 16.4b). The g CD values of (R)-3/KBr and (R)-4/KBr at the first Cotton CD bands
at 349 and 341 nm were ≈ –1.8 × 10
−4 and ≈ +4.4 × 10
−4 , respectively. (R)-3/KBr
and (R)-4/KBr also exhibited opposite CD signs for the first Cotton CD bands: The
CD sign for (R)-3/KBr was negative (−), while that for (R)-4/KBr was positive (+).
Fig. 16.3 Chiral binaphthyl
luminophores (R)-3 and
(R)-4
OH
OH
Si
Si
Ph
Ph
Ph
Ph
Ph
Ph
Si
Si
Ph
Ph
Ph
Ph
Ph
Ph
O
O
P
O
OH
(R)-3
(R)-4