Donor Extension on Spiro‐Acridine Enables Highly Efficient TADF‐OLEDs with Relieved Efficiency Roll‐Off

Abstract

Organic light emitting diodes based on thermally activated delayed fluorescent (TADF) emitters with both high external quantum efficiency (EQE) and low efficiency roll-off are under urgent pursuing. Three TADF emitters based on fluorene-spiro-acridine derivatives as donors are developed. Composing of rigid donor and acceptor, all emitters exhibit high PLQYs of 96-99%. Direct conjugation attached on acridine offers an enhanced reverse intersystem crossing (k RISC ) in IA-TRZ, while the extension via spiro-junction accelerates the radiative decay rate (k r ) in 2S-TRZ and IT-TRZ. Remarkably, all emitters enable high electroluminescent performance with EQE of 35.6% for 2S-TRZ, 36.1% for IT-TRZ and 32.0% for IA-TRZ, respectively, and very high luminance of up to 100 000 cd m −2 . Surprisingly, 2S-TRZ and IT-TRZ that hold larger k r and smaller k RISC than that of IA-TRZ exhibit more relieved efficiency roll-off, indicating the significance of k r . More importantly, IT-TRZ with a moderate k r and k RISC among these emitters shows the lowest roll-off which demonstrates that the comprehensive consideration of all photophysical processes is important to attain excellent devices. It also emphasizes the molecular modulation method through side group that can induce elaborate control on decay channels for finely optimizing emitters. This study can provide a useful perspective in designing practical emitters.

Multi-spiro junctions enable efficient thermally activated delayed fluorescent emitter

“…As a result, compounds based on TSBA may exhibit a good capability of resisting aggregation-caused quenching. Moreover, the decomposition temperature ( T d , related to 5 wt% loss) is 496 °C, which is higher than that previously reported for D2T-TRZ (437 °C) 23 and 2S-TRZ (479 °C), 24 which suggests a better thermal stability of the trispiro-junction.…”

“…By combining the PLQY, the rate constants of radiative decay ( k r ), intersystem crossing ( k ISC ) and reverse intersystem crossing ( k RISC ) are calculated to be 1.25 × 10 7 s −1 , 2.48 × 10 7 s −1 and 9.04 × 10 5 s −1 , respectively, which are similar to those of 2S-TRZ ( k r = 1.74 × 10 7 s −1 , k RISC = 9.71 × 10 5 s −1 ). 24 The similar photophysical properties between TSBA-TR and 2S-TRZ may hint at an excellent EL performance of TSBA-TR .…”

“…This led to the achievement of a high EQE of 36.1% with a small efficiency roll-off of 11% under 1000 cd m À2 . 23,24 Multi spiro-junction based donors hold significant potential for useful TADF emitters. Building upon these successful designs, a new donor with tri-spiro geometry is developed to further explore the application of SAs in TADF emitters (Fig.…”

Imidazophenothiazine-Based Thermally Activated Delayed Fluorescence Materials with Ultra-Long-Lived Excited States for Energy Transfer Photocatalysis

“…The selection of ACR, SACR, and TerCz was based on their weak donating ability, which results in blue emission and high E T . , Both SACR’s spiro-junction and TerCz’s dendritic nature enhance solubility, and prevent π–π stacking. PTZ and SMAT were chosen as sulfur-containing donors to further induce SOC and ISC in IPTZ donor–acceptor dyads …”

Dihydroindenofluorenes as building units in organic semiconductors for organic electronics

“…Based on these observations and in order to decrease the conjugation, the same group recently synthesized two new TADF emitters also constructed on the [2,1- b ]-DHIF core with however only one acridine unit between this core and the acceptor unit (triphenyltriazine) and either a fluorene (in [2,1- b ]-101 ) or two methyl units (in [2,1- b ]-102 ) decorating the second bridge of the [2,1- b ]-DHIF core. 217 Both OSCs were doped in DPEPO as the EML in TADF-OLEDs. The EQEs surpassed those previously reached and the four devices are in the top 10 of the more efficient bluish green TADF-OLEDs, 200,201,210 especially TADF-OLED20 using [2,1- b ]-102 as the dopant which reaches an extremely high EQE of 36.1%.…”