Although typical organic molecules are simply composed of carbon (C), hydrogen (H), nitrogen (N) and oxygen (O) atoms, carbon's unique bonding manners based on sp3, sp2and sp hybrid orbitals enable very complicated molecular architectures, leading to amazing functions in a wide variety of creatures and industrial products. In the last two decades, the allure of unlimited freedom of design with organic molecules has shifted a significant part of the research effort on electronics from inorganic into organic materials. In particular, great progress has been achieved in the development of organic light-emitting diodes (OLEDs). The successive progress of 1st generation OLEDs using fluorescent molecules and 2nd generation OLEDs using phosphorescent molecules solidified organic materials as a very attractive system for practical electronics.In this study, we designed new advanced electroluminescent (EL) molecules composed of only conventional CHN atoms without any precious metals. With proper molecular design, the energy gap between the two excited states, i.e., singlet (S1) and triplet (T1) excited states, are minimized, promoting very efficient spin up-conversion from T1 to S1 states (reverse intersystem crossing (ISC)) while maintaining a rather high radiative decay rate of >106/s, leading to a very high fluorescence efficiency. Using these unique molecules, we realized a very high external EL efficiency that is comparable with those of high-efficiency phosphorescence-based OLEDs. Thus, these molecules harvest both singlet and triplet excitons for light emission under electrical excitation through fluorescence decay channels.

High efficiency OLED based on delayed fluorescence

246th National Meeting (2013)

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