band in relation with Inoue and Mori’s nomenclature [22]. This effect was also
shown in carbo[6]helicenes (M )-10 and (M)-11 which exhibited positive CPL
signals at ~410 and 415 nm, respectively, in CHCl 3 (vide infra) [20]. In 2016,
Longhi and Santoro reported the vibronically resolved calculated UV-vis, ECD,
emission, and CPL spectra of 8. A CPL dissymmetry factor g lum of +0.59 Â 10
À3 at
444 nm was experimentally measured for (M )-8 in CHCl 3 (Table 4.1) and used
as a helically shaped chiral model to test the validity of advanced theoretical
calculations of chiroptical techniques [16]. Note that the g lum value of corresponding
1-aza[6]helicene 9 was evaluated to be between 10
À4 and 10
À3 by Fuchter,
Campbell, and coworkers who used this helicene as a chiral inducer in organic
light-emitting diodes (OLEDs, see Sect. 4.10) [21]
4.2.3 Double Vs. Single Azahelicenes
In 2014 Tanaka and coworkers reported the enantioselective synthesis of
azahelicenes 12 and 13 and of S-shaped double azahelicenes 15 and 16 (Fig. 4.5)
[17, 18]. Their photophysical properties are summarized in Table 4.1. Double
azahelicenes 15 and 16 showed red shifts of absorption and emission maxima
as compared with their corresponding single azahelicenes 12 and 13. They also
showed higher quantum yields in CHCl 3 solution. Interestingly, the CPL activity of
N
(M)-8
N
(M)-9
(M)-10
(M)-11
H 3 C
Fig. 4.3 Structures of aza[6]helicenes 8,9 and carbo[6]helicenes 10,11 [20, 21]
200
Δε
ΔΙ
300
H
H
S
S
350
450
550
400 nm
nm
Fig. 4.4 ECD and CPL spectra of 8 in CHCl 3 . Reproduced with permission [20]. Copyright 2014,
American Chemical Society
58
J. Crassous