RESUMEN
It is important to attain red hot exciton materials applicable in highly efficient organic light-emitting diodes with low-efficiency roll-off, but their development is restricted by the energy gap law. Herein, the sulfur atom was replaced by a heavier selenium atom based on benzothiadiazole to obtain a new benzoselenadiazole acceptor with a heavy atom effect and stronger electron-withdrawing ability. Two novel red hot exciton materials named BSe-DtBuTPA and BSe-2PhCz-d24 were designed and synthesized based on the benzoselenadiazole unit. Benefiting from the heavy-atom effect of selenium and the small ΔES1T2, both emitters exhibited ultrafast high-lying reverse intersystem crossing rate constants (7.00 × 107 and 1.17 × 107 s-1). The devices based on BSe-DtBuTPA and BSe-2PhCz-d24 demonstrated maximum external quantum efficiencies of 4.81 and 7.15% with emission peaks at 653 and 596 nm, respectively. The device based on deep-red BSe-DtBuTPA exhibited negligible efficiency roll-off of 18.5% at 10000 cd/m2.
RESUMEN
Developing highly efficient blue thermally activated delayed fluorescence (TADF) emitters with a narrowband emission is still a challenge. Here, novel ultrapure blue TADF emitters of TSBA-Cz and TSBA-PhCz were designed and synthesized for organic light-emitting diodes (OLEDs). Photophysical and time-dependent density functional theory calculation results simultaneously show the similar intramolecular charge-transfer character of MR-type TADF emitters. Benefiting from the symmetrical and rigid molecular configuration, compounds TSBA-Cz and TSBA-PhCz emit a pure blue emission peak at 463 and 470 nm, a narrow full width at half-maximum (FWHM) of 30 and 36 nm, and a small singlet-triplet energy gap (ΔEST) of 0.21 and 0.18 eV, respectively, facilitating their excellent TADF behavior in doped films. Furthermore, highly efficient TADF-OLED devices using the TSBA-Cz and TSBA-PhCz with external quantum efficiencies of 23.4 and 21.3% emit ultrapure blue electroluminescence (EL) at 464 and 472 nm with a narrow FWHM of about 35 nm and CIE color coordinates of (0.14, 0.11) and (0.12, 0.18). This work provides novel TADF emitters for blue OLEDs with narrowband EL.
RESUMEN
Organic light-emitting diodes (OLEDs) still face a significant challenge in finding blue thermally activated delayed fluorescence (TADF) emitters that can achieve narrowband emission and high efficiency. In this work, we successfully design and synthesize a novel kind of TADF emitters based on rigid sulfur/oxygen-bridged triarylboron acceptor for ultrapure blue with narrowband electroluminescence. Time-dependent density functional theory (TD-DFT) calculations and photophysical results indicate the different intramolecular charge-transfer (ICT) character of two emitters. Benefiting from the rigid aromatic framework, both emitters exhibited deep-blue emission at 444 and 447 nm with a small full-width at half-maximum (fwhm) of about 33 nm, and a small singlet (S1)-triplet (T1) energy gap (ΔEST) of 0.23 and 0.36 eV. Consequently, OLEDs based on PhCz-TOSBA and TPA-TOSBA exhibit deep blue electroluminescence at 456 nm with fwhm of about 55 nm, affording high external quantum efficiencies (EQEs) of 16.69% with CIE coordinates of (0.14, 0.15) and 16.65% with CIE coordinates of (0.14, 0.12), respectively. These findings show that PhCz-TOSBA and TPA-TOSBA are superior emitters in ultrapure blue TADF devices.
