chiroptical properties. Fluorescence dissymmetry factors of Æ0.001 were obtained in
chloroform. For the longer and more π-conjugated helicenes (P,S)-2a and (M,S)-2b,
the maximum emission occurred at longer wavelength, i.e., 478 nm, and slightly
smaller fluorescence dissymmetry factors (Æ0.0008) were obtained. For both
compounds 1 and 2, and for the same transition, g abs and g lum have essentially the
same value showing no significant geometry change upon population of the emitting
state. This is corroborated by the small Stokes shifts of the emission maxima.
In 2016, the CPL activity of sulfurated systems 3 and 4 was measured by Longhi
et al. [14] who found a g lum as high 0.9 Â 10
À2 at ~510 nm (positive for (M ) and
vice versa, Table 4.1) for 4 while racemization was observed upon excitation of 3.
Post-functionalization of heterohelicene 5 with formyl (6) and diacyanovinyl (7)
groups enabled to extend the π-conjugation [15]. The tails of UV-vis and ECD
spectra together with emission and CPL bands in CH 2 Cl 2 are highlighted in Fig. 4.2.
Fig. 4.1 (a) Chemical structures of helical bridged triarylamines 1a,b; 2a,b; and 3–4. (b) UV-vis
(A), ECD (B), fluorescence (C), and CPL (D) spectra of (P,S)-1a and (M,S)-1b in CHCl 3 .
Reproduced with permission [13]. Copyright 2003, American Chemical Society
4 Circularly Polarized Luminescence in Helicene and Helicenoid Derivatives
55
chloroform. For the longer and more π-conjugated helicenes (P,S)-2a and (M,S)-2b,
the maximum emission occurred at longer wavelength, i.e., 478 nm, and slightly
smaller fluorescence dissymmetry factors (Æ0.0008) were obtained. For both
compounds 1 and 2, and for the same transition, g abs and g lum have essentially the
same value showing no significant geometry change upon population of the emitting
state. This is corroborated by the small Stokes shifts of the emission maxima.
In 2016, the CPL activity of sulfurated systems 3 and 4 was measured by Longhi
et al. [14] who found a g lum as high 0.9 Â 10
À2 at ~510 nm (positive for (M ) and
vice versa, Table 4.1) for 4 while racemization was observed upon excitation of 3.
Post-functionalization of heterohelicene 5 with formyl (6) and diacyanovinyl (7)
groups enabled to extend the π-conjugation [15]. The tails of UV-vis and ECD
spectra together with emission and CPL bands in CH 2 Cl 2 are highlighted in Fig. 4.2.
Fig. 4.1 (a) Chemical structures of helical bridged triarylamines 1a,b; 2a,b; and 3–4. (b) UV-vis
(A), ECD (B), fluorescence (C), and CPL (D) spectra of (P,S)-1a and (M,S)-1b in CHCl 3 .
Reproduced with permission [13]. Copyright 2003, American Chemical Society
4 Circularly Polarized Luminescence in Helicene and Helicenoid Derivatives
55