Generating Huge Magnetocurrent by Using Spin-Dependent Dehydrogenation Based on Electrochemical System

Systems featuring large magnetocurrent (MC) at room temperature are attractive owing to their potential for application in magnetic field sensing. Usually, the magnetic materials are exploited to achieve large MC effect. Here, we report a huge MC of up to 150% in a nonmagnetic system based on the electrochemical oxidation of hydrazine at room temperature. The huge MC is ascribed to the spin-dependent N–H bond cleavage and reformation through dehydrogenation during the oxidation of hydrazine. Specifically, the N–H bond cleavage generates singlet radical pairs. An external magnetic field can accelerate the spin evolution from singlet to triplet in spin-correlated radical pairs by perturbing spin precessions. Increasing the amount of triplet radical pairs can largely reduce the N–H bond recovery and significantly enhance the oxidation current of hydrazine. As a consequence, the spin-dependent bond formation through dehydrogenation can provide a new approach to generate huge MC in electrochemical cells

Changing the Sign of Exchange Interaction in Radical Pairs to Tune Magnetic Field Effect on Electrogenerated Chemiluminescence

Two different electrogenerated chemiluminescence (ECL) systems, Ru­(bpy)₃²⁺/TPrA and Ru­(bpy)₃²⁺/C₂O₄^2–, are chosen to study the relationship between the sign of exchange interaction in radical pairs and magnetic field effects (MFEs) on electrogenerated chemiluminescence intensity (MFE_ECL). A positive MFE_ECL up to 210% is observed for the Ru­(bpy)₃²⁺/TPrA system, while a negative MFE_ECL of only −33% is observed based on the Ru­(bpy)₃²⁺/C₂O₄^2– system. The significant difference on MFE_ECL is ascribed to different signs of exchange interaction in radical pairs [Ru­(bpy)₃³⁺···TPrA^•] and [Ru­(bpy)₃³⁺···CO₂^–•] because they have a distant and proximate separation distance between two radicals of a pair, which result in different magnetic-field-induced intersystem crossing directions between singlet and triplet states. The experimental results suggest that an applied magnetic field can enhance the singlet → triplet conversion rate in radical pairs [Ru­(bpy)₃³⁺···TPrA^•] while facilitating an inverse conversion of triplet → singlet in radical pairs [Ru­(bpy)₃³⁺···CO₂^–•]. The increase/decrease of triplet density in radical pairs stimulated by an applied magnetic field leads to an increase/decrease on the density of light-emitting triplets of Ru­(bpy)₃^2+*. As a consequence, we can tune MFE_ECL between positive and negative values by changing the sign of exchange interaction in radical pairs during an electrochemical reaction