Efficient blue thermally activated delayed fluorescence emitters showing very fast reverse intersystem crossing

Highly Efficient and Stable Blue Organic Light‐Emitting Diodes based on Thermally Activated Delayed Fluorophor with Donor‐Void‐Acceptor Motif

“…Previous reports usually adopted donors with high steric effect for Xo to obtain small Δ E ST , including 1,3,6,8‐tetramethyl‐9 H ‐carbazole, 9,9‐dimethyl‐9,10‐dihydroacridine, etc., which, however, induce large dihedral angles for a small f . [ 26 , 27 , 28 ] Here, the less steric effect between PhCz and Xo groups favors moderate dihedral angles to keep a large f while the delocalized HOMO into the two substituted phenyl rings facilitates a small Δ E ST . The frontier energy levels of both groups were calculated to be 1.789 and 5.238 eV for Xo LUMO and PhCz HOMO, respectively.…”

Promoting Reverse Intersystem Crossing in Thermally Activated Delayed Fluorescence via Heavy-Atom Effect

“…To solve the device lifetime and efficiency roll-off problems, acceleration of RISC is a prerequisite, and TADF molecules having very fast RISC have been developed recently; the RISC rate constant (kRISC) of metal-free TADF molecules has been increased up to 10 7 -10 8 s −1 . [12][13][14][15][16][17][18] Regarding the above, it is essential to understand the mechanism of RISC to provide new guidelines for designing TADF molecules with large kRISC. In the first phase of the TADF study, RISC has been considered to occur via a direct transi-tion from the lowest triplet state (T1) to the lowest excited singlet state (S1).…”

“…15,20,[22][23][24][25][26][27] Recently, we have reported on the S-containing TADF molecule 3-(1,3,6,8-tetramethyl-9H-carbazol-9-yl)-9H-thioxanthen-9-one (MCz-TXO, Figure 1a). 18 , where S0 denotes the ground state. For the molecules in this study, we can reasonably neglect the contribution of energy levels higher than S2 and T3 on the toRISC process (see also later).…”

Decisive role of heavy-atom orientation for efficient enhancement of spin–orbit coupling in organic thermally activated delayed fluorescence emitters

“…As correlation ( 1) is caused by different indirect electronic reasons, the presence of HAs can increase SOC, but hypothetically should not affect the fluorescence rate. However, in spite of the rapidly growing interest in such materials, [14][15][16][17] very scarce knowledge on the mechanism of HA action on organic TADF emitters prevents their targeted rational molecular design. Taking into account the complex nature of TADF, the effect of a particular heavy atom on the nature of electronic states and other parameters connected with f 1CT-S0 (k r ) and k rISC (SOC) is highly unintuitive and should be extensively investigated.…”

“…However, in contrast to the all-organic phosphorescent materials, some of their TADF analogues are capable of 100% quantum yields of luminescence within micro-and submicrosecond regimes. 13 Taking into account the most recent achievements, [14][15][16][17] development of organic and hybrid TADF materials seems to be the most promising direction for environment friendly multifunctional optoelectronics.…”