Asymmetric Diphosphane Dioxides With A–π–A–π’–D Scaffolds for High‐Purity Deep‐Blue Luminescence

Phosphane oxides represent a cornerstone unit in modern optoelectronic materials due to their strong electron‐withdrawing character, high thermal stability, and ability to tune excited‐state properties. Herein, we report a streamlined design strategy toward donor–π–acceptor–π’–acceptor ( Γ –type) systems incorporating dual phosphane oxide units as both intermediate and terminal acceptors. A series of diphosphane dioxides ( 1 – 3 ) was synthesized and characterized, revealing pronounced deep‐blue fluorescence ( λ em = 385–418 nm in toluene, λ em = 415–457 nm in solid) that stems from charge‐transfer and locally excited states with high photoluminescence yields up to 95%. Structure–property relationships demonstrate that subtle variations in π‐conjugation (π = phenyl, biphenyl) and donor strength govern optical bandgap, oscillator strength, excited‐state dipole moments, and intersystem crossing pathways. Notably, 2 and 3 exhibit favorable thermal stability and high triplet energies, enabling their application as emitters in deep‐blue OLEDs. Devices based on 2 exhibit a maximum external quantum efficiency (EQE) of 4.86%, delivering high blue color purity with CIE coordinates of (0.15, 0.07), while maintaining low turn‐on voltages and minimal efficiency roll‐off. Transient electroluminescence studies indicate a significant contribution from triplet–triplet annihilation, enhancing exciton utilization beyond the conventional singlet limit.