Investigation of the effects of microwave electromagnetic field on the reaction dynamics of radical ion pairs

2004 Fiscal Year Final Research Report Summary

• Project/Area Number: 15550022
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Physical chemistry
• Research Institution: RIKEN (The Institute of Physical and Chemical Research)
• Principal Investigator: SAKAGUCHI Yoshio RIKEN (The Institute of Physical and Chemical Research), Surface Chemistry Laboratory, Senior Scientist, 川合表面化学研究室, 副主任研究員 (30167423)
• Project Period (FY): 2003 – 2004
• Keywords: microwave irradiation / radical ion pair / rectangular cavity / Electric-mode / Magnetic-mode / electron transfer reaction / RYDMR / OLED materials

Research Abstract

The reaction dynamics of radical pair is affected by the irradiation of microwave which can induce the electron spin resonance of the component radicals. This is due to the effect of magnetic component of microwave. On the other hand, the effect of electric field to materials is generally much larger than that of magnetic field. Therefore, the microwave irradiation to the radical ion pair may induce both of the effects of electric and magnetic components of electromagnetic wave. This is also an example of the chemical effect of electromagnetic field, which is now occupying the public interest. To investigate the independent contribution of electric and magnetic component to the reaction, we developed a dual mode cavity which can apply each of the components to samples. For the photoreaction of 2-methyl-1,4-naphthoquinone in sodium dodecylsulfate micellar solution, forming a neutral (changeless) radical pair, we reconfirmed the contribution of the magnetic component with the dual cavity . At the same condition, we could not find significant effect of the electric component. For the photoreaction of 10-methylphenothiazine with 1,4-dicyanobenzene, forming a radical ion pair, we found 〜2% increase of the retardation of the disappearance of escaped radical ions at the irradiation of the microwave pulse in a kW range power. This effect was independent of the magnetic field, excluding the possibility of electron spin resonance.
In order to generate a radical ion pair without initial spin correlation, we investigated the emission process of the organic electroluminescence materials(OLED). We found a clear magnetic field effect on the emission intensify of these fluorescent EL materials. The analysis of this dependence revealed that the main origin of this fluorescence of is not the direct emission due to the recombination of singlet radical ion pair but the delayed fluorescence due to the collision of triplet excitons formed in the recombination of triplet radical ion pair at high operating voltages. The irradiation of resonant microwave reduced the emission intensity, which shows the contribution of magnetic component to the emission process.