dodecane. The same behavior was observed by ECD spectroscopy showing
significant change for concentrated solutions in dodecane and for films obtained
by drop casting from nonane solutions. Interestingly, for a concentration higher
than 2 Â 10
À3 M, the solution was viscous and at 0.05 M it became a gel.
CPL measurement was carried out for a solution with 1 Â 10
À3 M in dodecane
(Fig. 4.13). Emission from enantiomer aggregates between 600 and 700 nm was
found to be mirror image for enantiomeric systems. Interestingly, aggregation
offered a strong dissymmetry factor (g lum ¼ 0.01 at around 630 nm). Likewise,
the g abs was large (g abs ¼ 0.01 between 500 and 550 nm); thus, the good similarity
Table 4.4 Photophysical data of oxahelicenic derivatives
Compound λ Abs
max a (nm) λ Em (nm) Φ F (%) Solvent (CPL) 10
3 g abs 10
3 g lum Ref.
(M )-34
400
476
–
CHCl 3
À0.22
b
À35
[32]
MeOH
–
À21
[32]
(P)-(+)-35
380
479
23
CHCl 3
+0.56
b
+0.95
[33]
(P)-(+)-36
388
514
18
CHCl 3
+1.3
b
+1.1
[33]
(P)-19
500
550
66
CH 2 Cl 2
-1.1
b
À1.2
[34]
(P)-(+)-37
323
421
–
DMSO
–
3
[ 35]
(P)-(+)-38
310
439
–
DMSO
–
5
[ 35]
(P)-(+)-39 ~360
430
–
CH 3 CN
~+1.2
b
+1.5
[36]
(P)-(+)-40 ~360
430
–
CH 3 CN
~+1.2
b
+1.4
[36]
a Lowest-energy absorption band
b
Taken form [12]
OC 12 H 25
OC 12 H 25
OC 12 H 25
OC 12 H 25
S
100
0.6
0.4
0.2
–0.2
–0.4
–0.6
500 550 600 650 700 750 800
80
60
40
20
500 550
I
L +I
R
I
L –I
R
600 650 700 750
(P )– (+)–41
(P)– (+)–41
(M )– (–)–41
(M )– (–)–41
800
S
(P)–(+)–41
O
OO
O
a
b
Wavelength (nm)
Fig. 4.13 Chemical structure of (P)-41. (a) Total luminescence and (b) CPL from solutions at
23
C of (P)-(+) and (M )-(À)-41 in dodecane (1 Â 10
À3 M) after excitation with unpolarized light
(λ ex ¼ 325 nm). Adapted with permission [37]. Copyright 2001, American Chemical Society
68
J. Crassous