Rational Molecular Design Strategy for High-Efficiency Ultrapure Blue TADF Emitters: Symmetrical and Rigid Sulfur-Bridged Boron- Based Acceptors

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 (Delta EST) of 0.21 and 0.18 eV, respectively, facilitating their excellent TADF behavior in doped films. Furthermore, highly efficient TADFOLED 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.

Automated summary

Novel ultrapure blue TADF emitters of TSBA-Cz and TSBA-PhCz were designed and synthesized for high-efficiency OLEDs. These emitters exhibited a pure blue emission peak, narrow FWHM, and small Delta EST, showcasing excellent TADF behavior. The TADFOLED devices using these emitters achieved ultrapure blue EL with narrow FWHM and high external quantum efficiencies.