nanosecond-order prompt fluorescence (lifetimes from 11.3 to 162 ns) and
microsecond-order delayed fluorescence (lifetimes from 0.04 to 24 μs). Chiroptical
properties were also investigated in toluene solution. Compounds 3–6 possess g lum
values in the same order of magnitude than compound 2 (from 0.5 Â 10
À3 to
1.2 Â 10
À3 ).
Importantly, Ben Zhong Tang and coworkers have demonstrated the Aggregation
Induced Enhancement Emission (AIEE) properties of such chiral compounds by
studying their fluorescence emissions in THF-H 2 O mixtures with different water
fractions ( f w ). Here, upon the formation of aggregates in water, the intramolecular
rotational and vibrational motions occurring in solution state are limited and
nonradiative decay processes from the excited states are decreased, leading to an
important increase in the fluorescence upon aggregation.
The authors have also evidenced a strong amplification of the chiroptical properties of this kind of emitters in thin films. Indeed, analyzing CD responses of neat
and doped films fabricated by CVD, a slight enhancement of Kuhn’s dimensionless
anisotropy factors (g abs multiplied by 2 up to 5 depending on the compound) was
observed for all emitters 3–6. Surprisingly, the enhancement of the g lum values was
found to be much higher, with an impressive 40-fold increase in the case of
compound 3, exhibiting a g lum value of 1.3 Â 10
À3 in toluene solution compared
to a value of 4.1 Â 10
À2 in neat film state (see Fig. 13.5). The authors have explained
this important amplification of the dissymmetry factors by the formation of chiral
aggregates during the formation of the thin film. Interestingly, this amplification also
occurs when the molecules 3–6 are used as emissive dopants in a mCP matrix. In
order to understand the origin of this amplification, more detailed characterization of
the postulated chiral aggregates would be necessary.
Nevertheless, based on those impressive chiroptical properties in thin film state,
CP-OLED were fabricated through CVD using neat and doped film involving
molecules 3–6 as emissive layers. This has led to the fabrication of the most
performant CP-OLEDs reported so far using CPL-SOMs in terms of circular polarization with g el up to 0.08 and External Quantum Efficiency (EQE) up to 3.5% for
OLED using neat films as emissive layers.
The third example of molecular design allowing the synthesis of molecules
merging CPL and TADF properties has been described by the group of
Man-Keung Fung and Chuan-Feng Chen [18]. Their original approach relies on
the linkage of two active TADF units, composed of a D-A-D system involving
carbazoles as donors and an aromatic-imide as acceptors, by chiral unit derived from
the commercially available trans-1,2-diaminocyclohexane (see Fig. 13.6).
Both enantiomers of this molecule were prepared in two steps starting from
commercially available (À)-(R,R)- or (+)-(S,S)-diaminocyclohexane F (see Scheme
13.3). This straightforward synthesis involved the lactamization of
4,5-difluorophthalic anhydride G with the chiral diamine F in AcOH as a first
step, followed by a nucleophilic aromatic substitution reaction on the fluoroaromatic
imide intermediate H with carbazole anions formed in THF using NaH as base.
Overall, the target molecule was obtained with a high enantiomeric excess
(ee > 99% measured using chiral HPLC) in almost 40% yield over the two synthetic
steps.
300
G. Pieters and L. Frederic
microsecond-order delayed fluorescence (lifetimes from 0.04 to 24 μs). Chiroptical
properties were also investigated in toluene solution. Compounds 3–6 possess g lum
values in the same order of magnitude than compound 2 (from 0.5 Â 10
À3 to
1.2 Â 10
À3 ).
Importantly, Ben Zhong Tang and coworkers have demonstrated the Aggregation
Induced Enhancement Emission (AIEE) properties of such chiral compounds by
studying their fluorescence emissions in THF-H 2 O mixtures with different water
fractions ( f w ). Here, upon the formation of aggregates in water, the intramolecular
rotational and vibrational motions occurring in solution state are limited and
nonradiative decay processes from the excited states are decreased, leading to an
important increase in the fluorescence upon aggregation.
The authors have also evidenced a strong amplification of the chiroptical properties of this kind of emitters in thin films. Indeed, analyzing CD responses of neat
and doped films fabricated by CVD, a slight enhancement of Kuhn’s dimensionless
anisotropy factors (g abs multiplied by 2 up to 5 depending on the compound) was
observed for all emitters 3–6. Surprisingly, the enhancement of the g lum values was
found to be much higher, with an impressive 40-fold increase in the case of
compound 3, exhibiting a g lum value of 1.3 Â 10
À3 in toluene solution compared
to a value of 4.1 Â 10
À2 in neat film state (see Fig. 13.5). The authors have explained
this important amplification of the dissymmetry factors by the formation of chiral
aggregates during the formation of the thin film. Interestingly, this amplification also
occurs when the molecules 3–6 are used as emissive dopants in a mCP matrix. In
order to understand the origin of this amplification, more detailed characterization of
the postulated chiral aggregates would be necessary.
Nevertheless, based on those impressive chiroptical properties in thin film state,
CP-OLED were fabricated through CVD using neat and doped film involving
molecules 3–6 as emissive layers. This has led to the fabrication of the most
performant CP-OLEDs reported so far using CPL-SOMs in terms of circular polarization with g el up to 0.08 and External Quantum Efficiency (EQE) up to 3.5% for
OLED using neat films as emissive layers.
The third example of molecular design allowing the synthesis of molecules
merging CPL and TADF properties has been described by the group of
Man-Keung Fung and Chuan-Feng Chen [18]. Their original approach relies on
the linkage of two active TADF units, composed of a D-A-D system involving
carbazoles as donors and an aromatic-imide as acceptors, by chiral unit derived from
the commercially available trans-1,2-diaminocyclohexane (see Fig. 13.6).
Both enantiomers of this molecule were prepared in two steps starting from
commercially available (À)-(R,R)- or (+)-(S,S)-diaminocyclohexane F (see Scheme
13.3). This straightforward synthesis involved the lactamization of
4,5-difluorophthalic anhydride G with the chiral diamine F in AcOH as a first
step, followed by a nucleophilic aromatic substitution reaction on the fluoroaromatic
imide intermediate H with carbazole anions formed in THF using NaH as base.
Overall, the target molecule was obtained with a high enantiomeric excess
(ee > 99% measured using chiral HPLC) in almost 40% yield over the two synthetic
steps.
300
G. Pieters and L. Frederic