Magnetic Field Effect on Optical and Electrical Properties of Organic Semiconductor Device

organic semiconductor have no heavy atom effect, so the lifetime of carrier spin in it can reach up to ms, due to the long lifetime, we have opportunity to manipulate the spin interaction between hole and electron.In OLED device, the ratio of singlet and triplet exciton comes from current injection is 1:3. Magnetism can disturb the interaction between electrons and holes exciton, as a result, the ratio of singlet and triplet exciton would change, the effect is called magnetic field effect(MFE). MFE is usually made of two effect:1.magnetic electroluminescence(MEL); 2. organic magnetoresistance (OMAR). With the help of equipment we build by ourselves, we can measure the luminescence and electrical properties of OLEDs under low temperature and magnetic field. By studying the MEL and OMAR effects of OLEDs, we can understand the spin-related processes in organic semiconductors more profoundly.

Magnetic Field Effect on Excited state Chemical Reaction  

The excited molecule can generate two different spin state radical pairs with weak interaction (Singlet state & Triplet state) in excited state chemical reaction, in which the radical pairs with different spin state can transform by intersystem crossing (ISC). The different spin state radical pairs have significantly different chemical and physical properties in nature including bond length, molecule geometry and electron configuration, which will form the different products in photochemical process. Due to the low energy difference between the singlet and triplet RPs (E_ST), the external magnetic field can change the ISC in singlet and triplet spin state, which will change the reaction rate and final product yield in photochemical reaction. The researches on magnetic field affecting excited state chemical reaction will help people understand the mechanism in chemical reaction more clearly.

         

Magnetic Field Effect on Luminescence Properties

Magnetic field effect on molecular excited state, mainly means the  evolution of the singlet and triplet state intermixing under external magnetic field. Magnetic field can affect the luminescence properties(lifetime, polarization, intensity.etc) of molecules because of the influence on dynamic equilibrium of singlet and triplet state. Therefore, we explore the dynamic process of spin polarized excited state luminescence to understand spin relaxation, spin transformation and other related physical and chemical processes by means of characterization and measurement of advanced optical, electrical and magnetic instruments and methods. We are able to further understand the fluorescence kinetics and reveal their physical and chemical nature from different perspectives with the help of the homemade HBT (Hanbury-Brown-Twiss) device and temperature-dependant fluorescence spectroscopy.