quantum yields were rather low in solution (0.18 in toluene), they were found to be
much higher in thin film state, with values up to 0.78 in doped film using 3,3
0 -di
(9H-carbazol-9-yl)biphenyl (mCBP) as the host matrix. By studying temperaturedependent transient photoluminescence characteristics of the co-doped films, the
authors confirmed that these chiral compounds were TADF active and measured a
very small ΔE ST value of 0.06 eV. The transient photoluminescence decays of
molecule 7 in the co-doped film under vacuum show an expected biexponential
distribution. The fitting gave a short lifetime of 44 ns and a long one of 130 μs which
confirms that 7 emits both prompt and delayed fluorescence. The efficient induction
of chiroptical properties from the chiral 1.2-diaminocyclohexane unit to the TADF
active chromophores was next confirmed by the study of the chiroptical properties in
thin film state. Indeed, circular dichroism spectra show a clear CD signal for the band
centered on 400 nm corresponding to the ICT transition of the TADF active
chromophores. At the excited state, the induction of chiroptical properties was
also demonstrated with the measurement of luminescence dissymmetry factors of
+/À1.1 Â 10
À3 . Using 7 as dopant in the emitting layers (15 wt % (+)-(S,S)-7 or (À)(R,R)-7 in mCBP matrix), CP-OLED possessing a high maximum EQE of 19.7%
and electroluminescent dissymmetry factors (g El ) of 2.2 Â 10
À3 (close to the
photoluminescence dissymmetry factor measured in the thin film state,
1.1 Â 10
À3 ) was fabricated. Based on the same molecular design, Chen’s research
group has also synthesized the red emitting CPTADF molecule 8 (see Fig. 13.7) [19] .
In molecule 8, the red emitting TADF active units are composed of a
1,8-naphthalimide moiety as electron acceptor (in blue Fig. 13.7) and a
9,9-dimethyl-9,10-dihydroacridine (DMAC, in red) as electron donor. The tethering
Fig. 13.6 Design of CPTADF molecules described by Fung and Chen
N
N
O
O
O
O
N
N
N
N
NH 2
NH 2
O
O
O
F
F
AcOH, reflux
N
N
O
O
O
O
F
F
F
F
Carbazole, NaH
THF
H 75%
(+)-(S,S)-7
53%
G
F
Scheme 13.3 Synthesis of the CP-TADF molecules based on TADF aromatic imide
302
G. Pieters and L. Frederic
much higher in thin film state, with values up to 0.78 in doped film using 3,3
0 -di
(9H-carbazol-9-yl)biphenyl (mCBP) as the host matrix. By studying temperaturedependent transient photoluminescence characteristics of the co-doped films, the
authors confirmed that these chiral compounds were TADF active and measured a
very small ΔE ST value of 0.06 eV. The transient photoluminescence decays of
molecule 7 in the co-doped film under vacuum show an expected biexponential
distribution. The fitting gave a short lifetime of 44 ns and a long one of 130 μs which
confirms that 7 emits both prompt and delayed fluorescence. The efficient induction
of chiroptical properties from the chiral 1.2-diaminocyclohexane unit to the TADF
active chromophores was next confirmed by the study of the chiroptical properties in
thin film state. Indeed, circular dichroism spectra show a clear CD signal for the band
centered on 400 nm corresponding to the ICT transition of the TADF active
chromophores. At the excited state, the induction of chiroptical properties was
also demonstrated with the measurement of luminescence dissymmetry factors of
+/À1.1 Â 10
À3 . Using 7 as dopant in the emitting layers (15 wt % (+)-(S,S)-7 or (À)(R,R)-7 in mCBP matrix), CP-OLED possessing a high maximum EQE of 19.7%
and electroluminescent dissymmetry factors (g El ) of 2.2 Â 10
À3 (close to the
photoluminescence dissymmetry factor measured in the thin film state,
1.1 Â 10
À3 ) was fabricated. Based on the same molecular design, Chen’s research
group has also synthesized the red emitting CPTADF molecule 8 (see Fig. 13.7) [19] .
In molecule 8, the red emitting TADF active units are composed of a
1,8-naphthalimide moiety as electron acceptor (in blue Fig. 13.7) and a
9,9-dimethyl-9,10-dihydroacridine (DMAC, in red) as electron donor. The tethering
Fig. 13.6 Design of CPTADF molecules described by Fung and Chen
N
N
O
O
O
O
N
N
N
N
NH 2
NH 2
O
O
O
F
F
AcOH, reflux
N
N
O
O
O
O
F
F
F
F
Carbazole, NaH
THF
H 75%
(+)-(S,S)-7
53%
G
F
Scheme 13.3 Synthesis of the CP-TADF molecules based on TADF aromatic imide
302
G. Pieters and L. Frederic