Realizing green phosphorescent light-emitting materials from rhenium(i) pyrazolato diimine complexes.
Two neutral pyrazolato diimine rhenium(I) carbonyl complexes with formula [Re(CO)(3)(N-N)(btpz)] where N-N = 2,2'-bipyridine (1) and 1,10-phenanathroline (2), and btpz = 3,5-bis(trifluoromethyl) pyrazolate, were synthesized and characterized by elemental analysis, routine spectroscopic methods, and single-crystal X-ray diffraction study. Ground and excited state properties of these complexes were investigated by steady-state and time-resolved spectroscopies. Complexes 1 and 2 show photoluminescent emission in both solution and solid-state at room temperature, arising from metal to ligand charge-transfer (MLCT) transition with strong overlapping of intraligand pi --> pi transitions. The long-lived excited state lifetimes of complexes 1 and 2, which are on the order of microseconds, indicate the presence of phosphorescent emission. As these complexes hold the potential to serve as phosphors for organic light-emitting diodes (OLEDs), their electroluminescent performances were evaluated by employing them as dopants of various electron transport layer (ETL) or hole transport layer (HTL) hosts. For complex 1, a green electrophosphorescence emission centered at lambda(max) = 530 nm was observed at low turn-on voltage ( approximately 6 V) with luminous power efficiency of 0.72 lm/W, external quantum efficiency of 0.82%, and luminance of 2300 cd/m(2) at a current density of 100 mA/cm(2).
Ranjan
Sudhir
S
Department of Chemistry, National Tsing Hua University, Hsinchu 30013, Taiwan, Republic of China.
Lin
Shen-Yi
SY
Hwang
Kuo-Chu
KC
Chi
Yun
Y
Ching
Wei-Li
WL
Liu
Chao-Shiuan
CS
Tao
Yu-Tai
YT
Chien
Chin-Hsiung
CH
Peng
Shie-Ming
SM
Lee
Gene-Hsiang
GH