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In this worl,we show that the spin dynamics of excitons can be dramatically altered by Maxwell magnetic field coupling,together with an ion-enhanced,low-inteal-splitting-energy organic semiconducting emitter.By employing a unique,alteating current (AC)-driven organic electroluminescent (OEL) device architecture that optimizes this magnetic field coupling,almost complete control over the singlet-to-triplet ratio (from fluorescent to phosphorescent emission in a single device) is realized.We attribute this spin population control to magnetically sensitive polaron-spin pair intersystem crossings (ISCs) that can be directly manipulated through exteal driving conditions.As an illustration of the utility of this approach to spin-tailoring,we demonstrate a simple hybrid (double-layer) fluorescence-phosphorescence (F-P) device using a polyfluorene-based emitter with a strong exteal Zeeman effect and ion-induced long carrier diffusion.Remarkable control over de-excitation pathways is achieved by controlling the device-driving frequency,resulting in complete emission blue-red color tunability.Picosecond photoluminescence (PL) spectroscopy directly confirms that this color control derives from the magnetic manipulation of the singlet-totriplet ratios.These results may pave the way to far more exotic organic devices with magnetic-field-coupled organic systems that are poised to usher in an era of dynamic spintronics at room temperature.