These compounds are strongly emissive, with quantum yields up to 0.86 for
5 in CH 2 Cl 2 (Table 4.1). A clear red shift of absorption and emission was observed
upon increasing the conjugation. The strong charge transfer and high polarity of
these molecules were evidenced experimentally through the high solvent polarity
dependence of the emission properties (emission wavelength and quantum yield).
Regarding the chiroptics, similar g abs and g lum magnitudes were found for
each compound with g abs /g lum of +5.6 Â 10
À3 /+4.7 Â 10
À3 for (M)-5,
+2.1 Â 10
À3 /+1.4 Â 10
À3 for (M)-6, and + 0.9 Â 10
À3 /+0.9 Â 10
À3 for (M)-7.
These properties were also compared in liquid state/solid state and in nanoparticles
obtained by rapid precipitation in water. Respective g lum values of 4.5 Â 10
À3 ,
1.5 Â 10
À3 , and 2.8 Â 10
À3 were measured for nanoparticles of 5, 6, and 7 dispersed
in water, showing that CPL activity was conserved. Note that the influence of
solvent polarity was studied on the quantum yields but not on the absolute CPL
values.
4.2.2 Emission Properties and CPL Activity of Azahelicenes
In 2014, Abbate et al. reported the CPL activity of blue-fluorescent 5-aza[6]helicene
(8) enantiomers in relation to their ECD spectrum (Figs. 4.3 and 4.4) [20]. The sign
of the CPL signal was controlled by the sign of the lower energy ECD named S-type
Table 4.1 Photophysical data of helical triarylamines and of azahelicenes
Compound
λ Abs
max a
(nm)
λ Em
(nm)
Φ F
(%)
Solvent
(CPL)
10
3
g abs
10
3
g lum
Ref.
(P,S)-1a
434
453
–
CHCl 3
+1.1
+0.9
[13]
(M,S)-1b
434
453
–
CHCl 3
À1.1
À1.1
[13]
(P,S)-2a
442
478
–
CHCl 3
+1.0
+0.8
[13]
(M,S)-2b
442
478
–
CHCl 3
À1.0
À0.7
[13]
(M )-4
400
510
1.6
CHCl 3
~7.3
b
9
[ 14]
(M )-5
395
488
86
CH 2 Cl 2
+5.6
+4.7
[15]
(M )-6
461
584
44
CH 2 Cl 2
+2.1
+1.4
[15]
(M )-7
552
685
9
CH 2 Cl 2
+0.9
+0.9
[15]
(M )-8
411
444
–
CHCl 3
+5.16 +5.9
[16]
(M )-12
381
467
5.1
CHCl 3
0.09
b
<1
[ 17]
(M )-13
325
467
2.1
CHCl 3
0.02
b
<1
[ 17]
(P)-14
442
477,509 1.4
CHCl 3
4.5
~0
[18]
(P,P)-15
448
471,492 19
CHCl 3
~1
b
28 Æ 2 [17]
(P,P)-16
445
454,480 9.4
CHCl 3
6.5
11 Æ 2 [17]
(+)-17
416
473
39
CH 2 Cl 2
~13
b
9
[ 19]
(+)-17+TFA
(200 eq.)
416
514
80
CH 2 Cl 2
–
8
[ 19]
a Lowest-energy absorption band
b
Taken from [12]
56
J. Crassous
5 in CH 2 Cl 2 (Table 4.1). A clear red shift of absorption and emission was observed
upon increasing the conjugation. The strong charge transfer and high polarity of
these molecules were evidenced experimentally through the high solvent polarity
dependence of the emission properties (emission wavelength and quantum yield).
Regarding the chiroptics, similar g abs and g lum magnitudes were found for
each compound with g abs /g lum of +5.6 Â 10
À3 /+4.7 Â 10
À3 for (M)-5,
+2.1 Â 10
À3 /+1.4 Â 10
À3 for (M)-6, and + 0.9 Â 10
À3 /+0.9 Â 10
À3 for (M)-7.
These properties were also compared in liquid state/solid state and in nanoparticles
obtained by rapid precipitation in water. Respective g lum values of 4.5 Â 10
À3 ,
1.5 Â 10
À3 , and 2.8 Â 10
À3 were measured for nanoparticles of 5, 6, and 7 dispersed
in water, showing that CPL activity was conserved. Note that the influence of
solvent polarity was studied on the quantum yields but not on the absolute CPL
values.
4.2.2 Emission Properties and CPL Activity of Azahelicenes
In 2014, Abbate et al. reported the CPL activity of blue-fluorescent 5-aza[6]helicene
(8) enantiomers in relation to their ECD spectrum (Figs. 4.3 and 4.4) [20]. The sign
of the CPL signal was controlled by the sign of the lower energy ECD named S-type
Table 4.1 Photophysical data of helical triarylamines and of azahelicenes
Compound
λ Abs
max a
(nm)
λ Em
(nm)
Φ F
(%)
Solvent
(CPL)
10
3
g abs
10
3
g lum
Ref.
(P,S)-1a
434
453
–
CHCl 3
+1.1
+0.9
[13]
(M,S)-1b
434
453
–
CHCl 3
À1.1
À1.1
[13]
(P,S)-2a
442
478
–
CHCl 3
+1.0
+0.8
[13]
(M,S)-2b
442
478
–
CHCl 3
À1.0
À0.7
[13]
(M )-4
400
510
1.6
CHCl 3
~7.3
b
9
[ 14]
(M )-5
395
488
86
CH 2 Cl 2
+5.6
+4.7
[15]
(M )-6
461
584
44
CH 2 Cl 2
+2.1
+1.4
[15]
(M )-7
552
685
9
CH 2 Cl 2
+0.9
+0.9
[15]
(M )-8
411
444
–
CHCl 3
+5.16 +5.9
[16]
(M )-12
381
467
5.1
CHCl 3
0.09
b
<1
[ 17]
(M )-13
325
467
2.1
CHCl 3
0.02
b
<1
[ 17]
(P)-14
442
477,509 1.4
CHCl 3
4.5
~0
[18]
(P,P)-15
448
471,492 19
CHCl 3
~1
b
28 Æ 2 [17]
(P,P)-16
445
454,480 9.4
CHCl 3
6.5
11 Æ 2 [17]
(+)-17
416
473
39
CH 2 Cl 2
~13
b
9
[ 19]
(+)-17+TFA
(200 eq.)
416
514
80
CH 2 Cl 2
–
8
[ 19]
a Lowest-energy absorption band
b
Taken from [12]
56
J. Crassous