Analysis of orientation of the transition dipole moment of phosphorescent dyes in the energy-transferring condition

Abstract

The dipole orientation of emitter is one of the key factors to enhance out-coupling efficiency in OLEDs. Polymers or small molecules with long chain structure have been known as being able to have preferred orientation. On the other hand, people conventionally have thought that the octahedral phosphorescent molecules do not have preferred orientation. However, there were reports that some phosphorescent molecules oriented to horizontal direction to interfaces. Therefore, it becomes important to analyze the dipole orientation of phosphorescent dyes. The dipole orientation could be determined by comparison of measurement and optical simulation. I studied the dipole orientation of phosphorescent dyes and factors that can affect to the dipole orientation by the angular dependent PL measurement. I improved the dipole orientation determining method of angular dependent photoluminescence measurement. Next, dipole orientation of 6 different phosphorescent dyes was determined by this method. Lastly, I found out that the dipole orientation could be changed by doping concentration and excitation condition.