Organic electroluminescence is one of the most promising technology for next generation of flat panel display.Hole transporting layer represents the weakest link in the electroluminescent structure considering the thermal stability of the materials.The most widely used hole transporting material

N

N’-bis (1-naphthyl)-N

N’-diphenyl-1

1’-biphenyl-4

4’-diamine (NPB)

has a glass transition temperature (

T

g

) of 95℃

which is much lower than that of the electron transporting material

tris (8-hydroxyquinoline) aluminum (Alq

3

).Based on the good hole transporting property and suitable energy level matched with other materials of NPB

two new hole transporting materials: N

N’-bis(1-naphthyl)-N

N’-di(4-methylphenyl)-1

1’-biphenyl-4

4’-diamine (NTB) and N

N’-bis(1-naphthyl)-N

N’-di(4-tert-butylphenyl)-1

1’-biphenyl-4

4’-diamine (NBB) were synthesized by introducing methyl and tert-butyl groups into NPB to improve its thermal stability.The glass transition temperature (

T

g

) of NTB and NBB measured by DSC are 108℃ and 129℃ respectively

showing better thermal stability than that of NPB.The ionization energy obtained by ultraviolet photoemission spectroscopy is 5.2eV for all of NPB and its derivatives.The emission peak in the photoluminescent spectra of the solid films of NTB and NBB are at 455nm and 460nm

which are close to the emission peak of NPB at 440nm.The organic electroluminescent devices using NPB

NTB and NBB as hole transporting layer (HTM) were fabricated with the structure of ITO/CuPc(20nm)/HTM(50nm)/Alq

3

(60nm)/LiF(0.5nm)/Al(100nm).The emission spectra of the three devices are the same and the green color light was emitted from the Alq

3

layer.The turn-on voltages of the devices are 11

9

8V for NPB

NTB and NBB

respectively.The brightness of the devices at 15V are 1000

1300

1200cd/m

2

for NPB

NTB and NBB.The devices with NTB and NBB also show better longevity than that of NPB in a prelimin ary test.