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

We report the synthesis and characterization of benzophospholes oxides featuring 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 to fine tune the Internal Charge Transfer (ICT) and, thus, the optical properties. Considering the intense fluorescence in the solid-state, the favorable redox and thermal properties, compounds were inserted in multilayered Organic Light Emitting Devices. All compounds display high efficiency and one compound even reaches 5% of external quantum efficiency (EQE), which represents the theoretical limit of EQE of purely fluorescent emitters. These results highlight the potential of this novel family of fluorophores to develop optoelectronic/photonic devices of next generation.