Oxabora[6]helicene 50 was prepared in 2016 by Hatakeyama and coworkers
and revealed deep and almost pure blue fluorescence with Commission
Internationale de l
0 Eclairage coordinates of (0.15, 0.08) [44]. Its enantiomers
showed CPL high fluorescence quantum yields of 0.65 at 436 nm activity with
g lum of 1.7 Â 10
À3 . Achiral structural analogues of 50 have proven efficient
B-containing PAH dopants in organic OLEDs and in field-effect transistors
[45]. These compounds are indeed known to display good carrier mobilities. Note
also that such BN and BO aromatic compounds display increasing interest in the
domain of thermally activated delayed fluorescence (TADF) [46].
4.6 CPL-Active Silahelicenes
Silylated π-conjugated molecules also display strong blue emission. In 2013,
Nozaki and coworkers reported the synthesis of enantiopure sila[7]helicene 51,
bearing a silole as the central cycle (Fig. 4.17) [47]. The UV-vis absorption spectrum
of (rac)-51 showed longest absorption at 412 nm, which is much longer than pristine
phenanthrene (293 nm) and dibenzosilole (286 nm), due to extended delocalization
of the π-electrons over the molecule. The absorption edge of (rac)-51 at 431 nm is
similar to that of λ
5 -phospha[7]helicene (432 nm) and red-shifted compared to the
related aza- and oxa-[7]helicenes (425 nm for aza[7]helicene and 409 nm for oxa[7]
helicene). Upon excitation at 320 nm, compound (rac)-51 exhibited a strong
blue fluorescence with λ max at 450 nm and good quantum yields in solution and
Si
Me
OH
0.6
UV
PL
51
ECD
CPL
0.5
0.4
0.3
0.2
0.1
100
50
0
–50
–100
–150
240 300 360 420 480 540 600
wavelenth (nm)
De (M –1
•cm –1
)
e (10 5
M –1
•cm –1
)
Intensity (au)
I
L
–l
R
(au)
Me
Me
Si
OH
Me
(P)–51
(M)–51
(P)–52
(P)–51
Fig. 4.17 Chemical structures of silahelicenes (P)-51 and (P)-52. UV-vis/fluorescence spectra and
ECD/CPL spectra of sila[7]helicene 51 in CH 2 Cl 2 . Blue lines in ECD and CPL spectra: (M )-isomer.
Red lines: (P)-isomer. The blue and red bars show the calculated ECD spectra. Reproduced with
permission [47]. Copyright 2013, American Chemical Society
72
J. Crassous
and revealed deep and almost pure blue fluorescence with Commission
Internationale de l
0 Eclairage coordinates of (0.15, 0.08) [44]. Its enantiomers
showed CPL high fluorescence quantum yields of 0.65 at 436 nm activity with
g lum of 1.7 Â 10
À3 . Achiral structural analogues of 50 have proven efficient
B-containing PAH dopants in organic OLEDs and in field-effect transistors
[45]. These compounds are indeed known to display good carrier mobilities. Note
also that such BN and BO aromatic compounds display increasing interest in the
domain of thermally activated delayed fluorescence (TADF) [46].
4.6 CPL-Active Silahelicenes
Silylated π-conjugated molecules also display strong blue emission. In 2013,
Nozaki and coworkers reported the synthesis of enantiopure sila[7]helicene 51,
bearing a silole as the central cycle (Fig. 4.17) [47]. The UV-vis absorption spectrum
of (rac)-51 showed longest absorption at 412 nm, which is much longer than pristine
phenanthrene (293 nm) and dibenzosilole (286 nm), due to extended delocalization
of the π-electrons over the molecule. The absorption edge of (rac)-51 at 431 nm is
similar to that of λ
5 -phospha[7]helicene (432 nm) and red-shifted compared to the
related aza- and oxa-[7]helicenes (425 nm for aza[7]helicene and 409 nm for oxa[7]
helicene). Upon excitation at 320 nm, compound (rac)-51 exhibited a strong
blue fluorescence with λ max at 450 nm and good quantum yields in solution and
Si
Me
OH
0.6
UV
PL
51
ECD
CPL
0.5
0.4
0.3
0.2
0.1
100
50
0
–50
–100
–150
240 300 360 420 480 540 600
wavelenth (nm)
De (M –1
•cm –1
)
e (10 5
M –1
•cm –1
)
Intensity (au)
I
L
–l
R
(au)
Me
Me
Si
OH
Me
(P)–51
(M)–51
(P)–52
(P)–51
Fig. 4.17 Chemical structures of silahelicenes (P)-51 and (P)-52. UV-vis/fluorescence spectra and
ECD/CPL spectra of sila[7]helicene 51 in CH 2 Cl 2 . Blue lines in ECD and CPL spectra: (M )-isomer.
Red lines: (P)-isomer. The blue and red bars show the calculated ECD spectra. Reproduced with
permission [47]. Copyright 2013, American Chemical Society
72
J. Crassous