Efficient Polaron Recombination and Fast Energy Transfer in a Deep Blue Phosphorescent Pt(II) Complex via Covalently Fused p‐Type Host

ABSTRACT

Achieving high‐efficiency deep‐blue phosphorescent organic light‐emitting diodes is fundamentally hindered by intermolecular kinetic bottlenecks in polaron recombination and exciton‐transfer dynamics. We overcome these limits through a fused emitter architecture where a p‐type host and a tetradentate Pt(II) dopant are covalently integrated into a single molecule, Pt‐SP‐tCz. Despite direct chemical integration, two units retain fully independent photophysical and electrochemical identities, establishing dual recombination sites within a single molecule, significantly enhancing radiative probability. The fused geometry collapses energy donor–acceptor separation to the molecular length scale, enabling exceptionally fast intramolecular energy‐transfer pathway—zero‐radius intramolecular energy transfer (ZRIET). When paired with an n‐type host, the intramolecular p‐type host facilitates exciplex formation, creating a second zero‐radius pathway that transfers excitons directly to the Pt center—namely, the ZETPLEX mechanism. This dual short‐range transfer framework produces a record‐high Förster resonance energy transfer rate of 3.64 × 10 ⁸ s ^{− 1} , and a recombination coefficient of 1.12 × 10 ⁻⁷ cm ³ s ⁻¹ unattainable in conventional exciplex systems. A simplified two‐component EML achieves an external quantum efficiency of 23.6% with deeper‐blue emission and stability comparable to the optimized three‐component devices. Our results demonstrate that molecular fusion provides a powerful strategy to simultaneously transcend intermolecular kinetic limits, establishing a new paradigm for high‐performance deep‐blue emission.