Synthesis And Luminescent Properties Investigation Of Novel Rhenium Complexes Based On 1,10-phenanthroline Derivatives

In flat panel display and solid-state lighting, organic light-emitting diodes(OLEDs) show important application prospects. Since the intersystem crossing from singlet state to triplet state is effectively promoted by strong spin-orbit coupling, phosphorescent transition-metal complexes are capable of utilizing both singlet and triplet excitons leading to an internal quantum efficiency of 100% theoretically, which have been the popular materials for OLEDs. Currently, though Re(I) complexes exhibit relatively short excited state lifetime, excellent thermal, chemical, and photochemical stability, and many other unique performances, the researches on them are relatively less than Ir complexes. In general, OLEDs have much more hole mobility than electron mobility. The unbalanced carrier injection causes the serious deterioration of device performances. Research suggests that 1,10-phenanthroline has a rigid plane framework, superb chelate ability and good electron-transportation ability.Consequently, ten N-arylimidazo[4,5-f][1,10]phenanthroline Re(I) complexes and one [1,2,5]thiadiazolo[3,4-f][1,10]phenanthroline Re(I) complex were successfully synthetized. Besides, the structure of these complexes were characterized by MS, IR and NMR. In this paper, the applications of these Re(I) complexes in OLEDs were considered as the starting point. The concrete work was as follows.(1) Firstly, three Re(I) complexes based on 1,2-diphenyl-1H-imidazo[4,5-f] [1,10]phenanthroline derivatives were synthetized. By introducing bulky steric groups to N-1, the luminous efficiency was effectively improved. The devices with the structure of ITO/TAPC(20 nm)/CBP: Re-complex(30 nm)/TPBi(50 nm)/Liq(2 nm)/Al(150 nm) were made and characterized. Especially, the Re-FPIP-doped device exhibited a maximum current efficiencies of 21.1 cd/A corresponding to a power efficiency of 18.9 lm/W. The excellent performances should be contributed to the bulky steric groups, short lifetime and good electron-transporting ability of these Re(I) complexes.(2) Series of imidazo[4,5-f][1,10]phenanthroline Re(I) complexes with bipolar carrier-transportation ability were designed and synthetized. These complexes showed excellent luminous efficiency and thermal stability. The devices with the structure of ITO/m-MTDATA(10 nm)/NPB(20 nm) /CBP: Re-complex(30 nm)/ TBPi(30 nm)/ Alq3(20 nm)/Liq(2 nm)/Al were made and characterized. It was found that the Re-MCIP-doped device showed a maximum current efficiencies of 21.1 cd/A and maximum external quantum efficiency of 7.0%.(3) A Re(I) complex based on [1,2,5]thiadiazolo[3,4-f][1,10]phenanthroline was designed and synthetized. Since the conjugation of the complex was increased by introducing [1,2,5]thiadiazolo with the rigid structure to [1,10]phenanthroline, the luminous color of Re(I) complex was successfully tuned. Its emission lifetime was only 0.04μs, which greatly reduced the triplet–triplet annihilation and efficiency roll-off. When made doped devices, its maximum EL wavelength was 590 nm, belonging to yellow light. Compared with index compound, the complex exhibited red shift optical emission spectra of 30 nm and the [1,2,5]thiadiazolo[3,4-f][1,10] phenanthroline group effectively adjusted the emission wavelength. The maximum luminance, current efficiency and external quantum efficiency were 4420 cd/m2, 16.8 cd/A and 5.4%, respectively. The results suggest that the complex has great potential development in OLEDs.