Fluorinated 9,9′-bianthracene derivatives with twisted intramolecular charge-transfer excited states as blue host materials for high-performance fluorescent electroluminescence

We report the electroluminescent (EL) performance of a series of fluorinated 9,9′-bianthracene derivatives (BAnFs) to serve as host materials for selected dopants in organic light-emitting diodes (OLEDs). Different F substitution patterns strongly affect the EL performances. In particular, 10,10′-bis(4-fluorophenyl)-9,9′-bianthracene (BAn-(4)-F) works as an excellent fluorescent host for N,N-diphenylamino phenyl vinyl biphenyl (DPAVBi) and 10-(2-benzothiazolyl)-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H,11H-benzo[l]pyrano(6,7,8-ij)quinolizin-11-one (C545T) dopants to obtain high-performance OLEDs with excellent external quantum efficiencies (EQEs) of 5.43% and 5.20%, respectively. We demonstrate that the improved EQEs are due to the enhanced occurrence of singlet excitons in BAn-(4)-F-based EL devices. The BAn-(4)-F host molecule with a particular twisted intramolecular charge-transfer (TICT) excited state, which participates in a charge-transfer (CT) intersystem crossing mechanism, realizes transitions from the triplet to singlet CT-states. At the dopant site, the available singlet excitons formed via Förster energy transfer from host BAn-(4)-F to dopant are greatly increased. We conclude that the BAn-(4)-F host based on 9,9′-bianthracene can significantly enhance the singlet generation fraction in EL devices.