following the same design rules, they have synthesized four novel chiral TADF
emitters, involving carbazole, 3,6-ditertbutylcarbazole and 9,10-Dihydro-9,9dimethylacridine as electron donors units (see Fig. 13.4). Those compounds were
synthesized using the same synthetic procedure described for compound 2, except
for compound 6, another couple base-solvent was used (
t BuOK as base and ACN as
solvent). In terms of photophysical properties, molecules 3–6 exhibit broad and
relatively weak absorption bands centered at 400, 420, 440, and 450 nm, respectively, which can be associated with intramolecular charge transfer (ICT) process
derived from the Donor-Acceptor (D-A) active chromophore units. Emission spectra
were measured in toluene solution and maximum emissions were observed between
495 nm and 595 nm depending on the nature of electron donor moiety (see
Table 13.1). Low to good quantum yields from 0.05 for compound 6 to 0.4 for
compound 3 were determined in neat thin film fabricated by CVD. Fluorescence
decays were also investigated for each molecule in thin film. All compounds were
found to be TADF emitters and show bi-exponential fluorescent decays with
O
O
N
N
N
F
(R)-3
N
O
O
N
N
N
t-Bu
t-Bu
N
O
O
N
N
N
t-Bu
t-Bu
t-Bu
t-Bu
O
O
N
N
N
F
(R)-4
(R)-5
(R)-6
Fig. 13.4 Structure of CPTADF emitters synthetized by Tang et al
Table 13.1 Photophysical properties of compounds 3–6
3
4
5
6
λabs CT (nm)
400
420
440
450
λem max (nm)
493
530
531
585
λem max (nm) in neat film
520
538
553
580
Quantum yield in neat film
0.4
0.2
0.2
0.05
13 Design of Circularly Polarized Thermally Activated Delayed Fluorescence Emitters
299