Charge transfer(CT) states or charge transfer complexes(CTCs) have been shown to have critical influenceson the operations of different organic optoelectronic devices including organic light-emitting devices(OLEDs)[1-3],organic field effect transistors and organic photovoltaic(OPV) devices [4-6].In this talk,relationshipbetween CT state and exciplex emission in OLED will be discussed.