Organic light emitting diodes (OLEDs) have attracted considerable attention due to their potential applications in fiat-panel displays since the first report [1] of C W Tang and S A VanSlyke in this field.In flat-panel display applications the three colors of red,green,blue (RGB) of OLEDs with good color purity and stability are required,especially the red one.Much progress has been made in the development of red color OLEDs display.Many materials have been synthesized and used in red OLEDs,such as pyran-containing compounds [2,3],bipolar-characteristic materials [4-6],Europium Complexes[7-9],porphyrin compounds[10,11] However,OLED devices based on above mentioned materials have been shown to have low luminance efficiency,and are not free from the current induced quenching phenomenon under high-current driving conditions.This is a disadvantage,especially for passive matrix displays which would be required to operate at high current densities in order to achieve the desired brightness for certain applications.Resently,Z H Kafafi et al have developed OLEDs based on pentacene derivatives substituted with alkynl or aryl moieties at 6,13 position of the pentacene skeleton[12-15].These OLED devices based on pentacene derivatives have a good stability which can remain quantum efficiency constant at high current density due to singlet-singlet exciton emission,and saturated red emission was obtained.The combination of stable devices efficiency over a wide range of current densities and a saturated red color,make pentacene derivatives-based devices ideal for passive and active display applications.A doping EL system,based on the principle of guest-host energy transfer to effect the spectral shift from tris-(8-hydroxyquinolinato) aluminum (Alq3) to the dopant molecules,has been adopted by C W Tang et al [2].Alq3 is a suitable host for red EL emitters since its emission at 530nm is adequate to sensitize guest EL emission in the red spectral region.However,the emission obtained from such a doping system is generally not red but orange due to an emitting peak of Alq3 in addition to the red peak in this doping system.Therefore,the orange emission was the result of a mixture of the two emitting peaks.Using an additional dopant which acts as an intermediary for more efficient energy transfer from host to emitting guest molecules can lead to better color chromaticity and improved device performance[16].Here,we report on a pentacene derivative,6,13-di-(3,5-diphenyl) phenylpentacene (PDT),which was firstly synthesized by molecular design in home.These OLED devices based on PDT as the red emitter emit pure red light.A stable red emission (chromaticity coordinate:x=0.61,y=0.37) was obtained in device within the luminance range of 180-2800cd/m2.The maximum luminance is 4400cd/m2 at 21V.The maximum luminance efficiency is 2.4cd/A at current density of 120 mA/cm2.The coordinates are of(0.6388,0.3499) at 0.4 mA/cm2.