binaphthyl fluorophore in solution is demonstrated. As axially chiral
binaphthyl fluorophore models, (R)-1,1
0 -binaphthyl-2,2
0 -dicarboxylic acid [(R)-3]
and (R)-2,2
0 -(1,1
0 -binaphthyl-2,2
0 -diylbis(oxy))diacetic acid [(R)-4] were examined
(Fig. 2.5).
The PL spectra of (R)-3 and (R)-4 were acquired in CHCl 3 and
dimethylformamide (DMF) solutions, owing to their differing polarities. Dicarboxylic acid (R)-3 did not exhibit PL in CHCl 3 and DMF solutions. On the other hand,
(R)-4 exhibited PL in both CHCl 3 and DMF, with PL maxima (λ PL ) observed at
356 and 361 nm, respectively, as shown in Fig. 2.6 (lower panel, black lines for
CHCl 3 and red lines for DMF). The PL quantum yield (Ф F ) of (R)-4 in CHCl 3 was
found to be 25%. On the other hand, its Ф F value increased to 39% in DMF, possibly
due to the suppression of the rotational freedom of the binaphthyl unit as a result of
hydrogen-bonding interactions with DMF. (R)-4 exhibited a CPL signal in CHCl 3
and DMF, as shown in Fig. 2.6 (upper). Interestingly, although significant changes
in λ em were not observed in the two solvents, (R)-4 exhibited opposite CPL signs in
the two solvents: negative (À) in CHCl 3 and positive (+) in DMF. Their g CPL values
were found to be similar at about À0.18 Â 10
–3 for CHCl 3 and about +0.19 Â 10
–3
for DMF.
In order to elucidate the ground state chirality of 4, CD and UV-Vis absorption
spectra in CHCl 3 and DMF were acquired, as shown in Fig. 2.7a, b, respectively.
The CD spectra of 4 exhibited significant differences in the first Cotton CD bands in
COOH
COOH
(R)-3
OCH 2 COOH
OCH 2 COOH
(R)-4
Fig. 2.5 Chiral binaphthyl
fluorophores (R)-3 and (R)-4
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
250 300 350 400 450 500
-12
-9
-6
-3
0
3
6
DC / V
g
e
d
m
/
L
P
C
Wavelength / nm
Fig. 2.6 CPL (upper) and
PL (lower) spectra of (R)-4
in CHCl 3 (black) and DMF
(red) (1.0 Â 10
À4 M)
2 Circularly Polarized Luminescence of Axially Chiral Binaphthyl Fluorophores
15