The Study Of Magnetic Field Effects Based On Free-Radical Reactions In Solution

Magnetic fields can alter the rate, yield or product distribution of chemical reactions, which brings about the advent of a new research field, named as "spin chemistry". Spin chemistry is an area of research centered around the influence of electron and nuclear spins on chemical reactivity. Spin chemistry has made contributions in diverse areas of science, such as in chemistry, physics, biology and materials science.In this thesis, we report magnetic field effects based on three most recent systems in spin chemistry:the Ru(bpy)32+system, the tertiary amines system and the fluorographene system. The magnetic field effects (MFE) on electrogenerated chemiluminescence (MFEECl), electrical current (MC) and photoluminescence (MFEPL) based on the above systems are studied and the generation mechanism of MFE is investigated. It mainly includes:Firstly, abnormal MFEECL based on the common Ru(bpy)32+-electrochemiluminescence system is reported for the first time. The abnormal MFEECLl suggests that the activated charge-transfer [Ru(bpy)33+...TPrA.] complexes may become magnetized states in solution during the application of magnetic field at room tempreture. In addition, the sweeping rate effect of magnetic field and the distinct behavior between MFEECL and MC provide indirect evidence to support the existence of the magnetized charge-transfer [Ru(bpy)33+... TPrA.] complexes.Secondly, three different electrochemiluminescence systems:Ru(bpy)32+/TPrA, Ru(bpy)32+/TEA and Ru(bpy)32+/Na2C2O4are chosen to study the relationship between the sign of exchange interaction in radical pairs and the sign of MFEECL.Positive MFEECL are observed for Ru(bpy)32+/TPrA and Ru(bpy)32+/TEA systems, while a negative MFEECL is observed based on Ru(bpy)32+/Na2C2O4system. The significant difference on MFEECL is ascribed to the positive exchange interaction (J>0) in radical pairs [Ru(bpy)33+...TPrA·] and [Ru(bpy)33+…TEA·], while a negative exchange interaction (J<0) in radical pairs [Ru(bpy)33+…CO2·]. Due to different signs of exchange interaction, an applied magnetic field can enhance the singletâ†'triplet conversion rate in radical pairs [Ru(bpy)33+…TPrA·] and [Ru(bpy)33+…TEA·], 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 applied magnetic field leads to an increase/decrease on the density of light-emitting triplets of Ru(bpy)32+*. As a consequence, we can tune MFEECL between positive and negative values by changing the sign of exchange interaction in radical pairs during an electrochemical reaction.Thirdly, we report a giant magnetocurrent of>100%in the nonmagnetic electrochemical system based on the oxidation of tertiary amines at room temperature. Combining the electrochemical oxidation mechanism of tertiary amines and magnetocurrent in different solvents with different deprotonation rates, we propose spin-dependent deprotonation is the key factor for the generation of giant magnetocurrent. Specifically, the a-C-H bond cleavage through deprotonation during the oxidation of tertiary amines generates singlet radical pairs. A magnetic field can cause a spin flipping from singlet to triplet in radical pairs by perturbing spin precessions. The singlet-*triplet interconversion can overwhelmingly suppress the reduction through a-C-H bond recovery due to Paul Exclusion Principle. This can significantly increase the electrical current by increasing the oxidation rate of amines, leading to a giant magnetocurrent. Here we show a new approach of using spin-dependent deprotonation to generate giant magnetocurrent in electrochemical reactions at room tempreture.Fourthly, due to the very few studies of MFEPL based on fluorographene, we investigated MFEPL of fluorographene dispersed in hexanol solution, and observed a positive MFEPL with a high magnitude of30%. Through the comparison of MFEPL on fluorographene dispersed in hexanol solution and fluorographene powder, we suggest that magnetic field-dependent intersystem crossing rate in inter-layer excited states is accountable for the MFEPL. In addition, we also demonstrated that the MFEPL of fluorographene dispersed in organic solvents can be tuned via controlling of the layer number of fluorographene and the dielectric constant of organic solvent. With appropriate layer numbers and dielectric constant, we can observe a much larger MFEPL. Therefore, our study presents a new approach to tune the magneto-optical properties of fluorographene by using a magnetic field.