Achieving efficient deep-blue TADF in carbazole-pyrimidine compounds

Diazine-based thermally activated delayed fluorescence chromophores

“…52 Serevičius and coworkers have designed a couple of 4,6-di(9H-carbazol-9-yl)pyrimidine derivatives 1 (Chart 1). 49 These chromophores exhibit DE ST significantly higher than 0.1 eV (Table 1) and do not show any TADF properties in solution but TADF can be observed when doped in 1 wt% polymethylmetacrylate (PMMA) thin films for compound 2, as shown by O 2 sensibility and temperature activation experiments. DFT calculations indicate that the methyl group at the C5 position of the pyrimidine ring (Figure 2) clearly increased the twisting angle between ED and EA units, thereby reducing the DE ST value.…”

“…In this case, however, the central pyrrole ring of carbazole is not always able to induce sufficiently large steric effect to maintain a quasi-perpendicular arrangement with the EA part of the push-pull structure upon excitation necessary to observe spatially separated HOMO and LUMO orbitals and small enough DE ST . 47,48 The carbazole fragments can be connected directly to the pyrimidine core by simple nucleophilic substitution or by Buchwald-Hartwig Pd-catalyzed cross-coupling reaction from chloropyrimidine derivatives, 49 whereas 9-phenyl-9H-carbazole fragments can be grafted onto the pyrimidine core by Pd-catalyzed Suzuki cross-coupling reaction from chloropyrimidine derivatives and the corresponding boronic acids/esters, 50 by Ullman coupling from the corresponding bromophenylpyrimidine 51 or by nucleophilic substitution from the corresponding fluorophenylpyrimidine. 52 Serevičius and coworkers have designed a couple of 4,6-di(9H-carbazol-9-yl)pyrimidine derivatives 1 (Chart 1).…”

Realization of deep-blue TADF in sterically controlled naphthyridines for vacuum- and solution-processed OLEDs

“…Compared to the performance of currently state-of-the-art narrow-band deep-blue (o460 nm) OLEDs based on conventional D-A-type TADF emitters, these ND-based (particularly tCz-ND-based) OLEDs are among the best devices in terms of the EQE and efficiency roll-off properties (see Table S5 in the ESI †). 8,12,[23][24][25][26][27][28] The results imply that sterically controlled CT interactions combined with H-bonding can indeed be promising in attaining narrow deep-blue TADF by employing ND acceptors.…”

TD-DFT and Experimental Methods for Unraveling the Energy Distribution of Charge-Transfer Triplet/Singlet States of a TADF Molecule in a Frozen Matrix

“…36 In addition, it has been pointed out by several reports that multiexponential decay and spectral shift over time are the evidence of the conformational distribution of TADF molecules in solids. 28,[37][38][39][40][41][42][43] However, the relation of conformational distribution, configurations of excited state transition orbitals, and excited state energies have not been clearly explained. Moreover, while 1 CT states are widely investigated through time-resolved spectroscopy of photoluminescence (PL) in the full time range of fluorescence, triplet states are mostly investigated by PL measurement at a fixed delay time due to difficulties in phosphorescence measurement at room temperature and long-lasting phosphorescence emission up to several tens of seconds.…”