Integration of Exciton Donor and Acceptor in a Blue-Emitting Molecule with Zero Radius of Intramolecular Energy Transfer Mechanism for Highly Efficient and Stable Fluorescent OLEDs

Abstract

Multimaterial emission layer (EML) with host and dopant is known for its advantages in efficiency and lifetime for organic light-emitting diodes (OLEDs). However, as the compositions and the mixing ratio in the EML diversify, complex device physics and photophysics and complicated fabrication processes become challenging issues. Herein, a new concept to integrate exciton donor (host) and acceptor (dopant) into a single emitting molecule is suggested. 9-(8,9,10,11-Tetradeuterospiro[benzo[de]anthracene-7,9 '-fluoren]-2'-yl)-9H-carbazole (SBAF-Cz) and 8,9,10,11-tetradeutero-N-(9,9-dimethyl-9H-fluoren-2-yl)-N-phenylspiro[benzo[de]anthracene-7,9 '-fluoren]-3-amine (FPA-SBAF) are used as host and dopant, respectively. By integrating two units, 8,9,10,11-tetradeutero-2 '-(9H-carbazol-9-yl)-N-(9,9-dimethyl-9H-fluoren-2-yl)-N-phenylspiro[benzo[de]anthracene-7,9 '-fluoren]-3-amine (FPA-SBAF-Cz) is synthesized, and photophysical and electrical properties are characterized. Density functional theory and experimental results consistently reveal that SBAF-Cz and FPA-SBAF are photophysically and electrically independent. The electrical properties of FPA-SBAF-Cz behave independently, while the photophysical properties are the sum of those of SBAF-Cz and FPA-SBAF, which is attributed to the zero radius of intramolecular energy transfer (ZRIET) between donor and acceptor in FPA-SBAF-Cz. The single-component blue OLED with FPA-SBAF-Cz exhibits a maximum external quantum efficiency of 4.18%, which is higher than those of OLEDs with SBAF-CZ:FPA-SBAF multicomponent EMLs. Surprisingly, the device lifetime to 50% decrease from initial luminance is 114 h in FPA-SBAF-Cz OLED, which is 2.2 times longer than that of SBAF-Cz:FPA-SBAF OLEDs.