Design Rule of Tetradentate Ligand-Based Pt(II) Complex for Efficient Singlet Exciton Harvesting in Fluorescent Organic Light-Emitting Diodes

Controlling intermolecular interactions, such as triplet–triplet annihilation (TTA) and triplet–polaron annihilation (TPA), is crucial for achieving high quantum efficiency in organic light-emitting diodes (OLEDs) by suppressing exciton loss. This study investigates the molecular design of tetradentate Pt(II) complexes used for singlet exciton harvesting in fluorescent OLEDs to elucidate the relationship between the chemical structure of the ligands and exciton quenching mechanisms. It was discovered that the bulkiness of substituents is pivotal for maximizing quantum efficiency in these devices. An exciton dynamics study conducted during device operation quantitatively analyzed the contribution of substituents to the OLED operation mechanism, demonstrating that complexes with bulky 2,6-diisopropylphenyl and tert -butyl substituents enhance singlet exciton harvesting by suppressing TTA and TPA, thereby facilitating Förster energy transfer.