Derivatives of triphenyltriazine and di-tert-butylcarbazole as TADF emitters for sky-blue OLEDs

The phenomena of triplet exciton up-conversion by thermally activated delayed fluorescence (TADF) and hybridized local and charge transfer states (HLCT) are approached to extend the internal quantum efficiency (IQE) of emitters potentially to 100%. Here, the series of newly designed and synthesized triphenyltriazines substituted by tert-butylcarbazolyl moieties were investigated. The compounds exhibited good charge-injecting abilities, and bipolar well-balanced charge transport mobility values reaching 10^-3 cm²/Vs at electric fields higher than 3.6 × 10⁵ V/s. The compounds were found to exhibit TADF properties in guest–host systems. Series of organic light emitting diodes (OLEDs) were fabricated exhibiting sky-blue electroluminescence with the intensity maxima at ca. 480 nm. Optimization of the OLEDs by the introduction of the host material with a HLCT resulted in the increase of EQE up to 5.8% for the device containing derivative of methoxy-substituted triphenyl triazine and di-tert-butylcarbazole as TADF emitter.