Hybridized local and charge-transfer excited states of blue OLEDs based on phenanthroimidazole derivates with a narrow FWHM of 24 nm

Abstract

Designing OLEDs with high efficiency deep-blue emission has always been a research topic that researchers are committed to pursuing. It is a long-standing challenge to realize HLCT materials with a Commission Internationale de L’éclairage (CIE_y) < 0.08 and narrow width at half maximum (FWHM). Here, six phenanthroimidazole derivatives (PT series) incorporating 3a,11b-dihydro-1H-phenanthroimidazole (PI) as the acceptor and triphenylamine (TPA) as the donor have been designed. The impact of introducing various functional groups in the minor axis of the entire molecule is investigated. The molecules were successfully synthesized and systematically investigated. Me-PT and TfMe-PT demonstrate exceptional photoluminescence quantum yields (PLQYs) of 80.10% and 87.64% and a narrow FWHM in neat films, respectively. Therefore, doped devices based on Me-PT and TfMe-PT were fabricated, with maximum external quantum efficiency (EQE_max) values of 5.52% and 5.47%, respectively. Both devices exhibit blue emission centered around a peak wavelength (λ_PL) of 465 nm and 466 nm, accompanied by a narrow FWHM of 24 nm and 25 nm, respectively. These findings underscore a streamlined and effective approach in HLCT materials, providing significant guidance for the development of high purity blue emission OLEDs.