Reaching the 5% theoretical limit of fluorescent OLEDs with push–pull benzophospholes

Abstract

We report the synthesis and characterization of benzophosphole oxides featuring an ethoxy substituent on the P atom and electro-donating amino groups on the lateral phenyl groups. The optical and redox properties of these compounds are studied experimentally and computationally (TD-DFT). In particular, we show how the nature of the donor allows fine-tuning the internal charge transfer (ICT) and, thus, the optical properties. Considering the intense fluorescence in the solid state (powder or thin film) and the favorable redox and thermal properties, these compounds were introduced in multilayered organic light emitting devices. All compounds display high efficiency and one compound even exhibits an external quantum efficiency (EQE) of 5%, which represents the theoretical limit of the EQE of purely fluorescent emitters. These results highlight the potential of this novel family of fluorophores to develop next generation optoelectronic/photonic devices.