Synthesis Of Fluorenyl Oxadiazole Iridium Complexes And Their Applications In Electroluminescence And Chemical Sensing

The iridium complexes have many excellent photophysical properties,such as large stoke displacement,long luminescence lifetimes,high efficiency,etc.They have been widely used in electroluminescent devices,chemical sensing,and biological imaging in recent years.The luminescence properties of the iridium complexes can be easily regulated by modification of the ligands.In this paper,we have selected fluorenyl oxadiazole ligands as ring metal C^N ligands to synthesize a series of iridium complexes.1,3,4-oxadiazole has good electron affinity,which can improve the electron transport performance of OLED devices.At the same time,we introduced further groups such as electron donating and electron withdrawing to the ligands structure for exploring the impact on device performance.The specific research contents of this paper are as follows:(1)The fluorenyl oxadiazole ligand molecule was designed,and six phosphorescent iridium complexes were synthesized by modified the ligand in terms of introducing groups such as carbazole and 1,3,4-oxadiazole to the fluorenyl group.The property of photophysics,electrochemistry and OLED devices were characterized.The results show that the luminescence of the complexes is in the range of yellow orange range(537-566 nm),and the introduction of electron donating groups or extension of the conjugated chain on the ligands will cause the absorption and emission wavelengths to shift red.The introduction of sterically hindered biphenylamino group can effectively inhibit concentration quenching.At the same time,the introduction of carbazole,oxadiazole and other groups on the basis of the original structure can effectively reduce the turn on voltage of the devices,and greatly improve the luminescence brightness.(2)The F atom is introduced on the basis of the ligand molecule of the previous chapter,and the structure of the complex is further modified by introducing different hole transporting groups or replacing the auxiliary ligand.The results of characterization show that the luminescence of the complexes is in the range of yellow orange range(534-571 nm).The replacement of the fluorine atom to the para position or using 2-pyridine tetrazolium as an auxiliary ligand will cause the emission wavelength to shift blue,and introducing electron groups causes the luminescence wavelength to be red-shifted.In the device characterization,the performance of devices based on Ir-F at different doping concentrations is better than that of Ir-Hex.In addition,the performance of devices will get worse with the electron-donating ability of the groups increasing in the complexes.(3)The photophysical properties of the synthesized neutral iridium complexes were studied in detail.It was found that they have significantly enhanced luminescence in the aggregate state compared with the solution,which is characterized by AIPE properties.By analyzing the single crystal structure and crystal packing pattern of the complex,we believe the possible reason for this phenomenon is that the rotation of the benzene ring connected to the oxadiazole limited when the molecules are aggregated.Meanwhile,we found that the complex Ir-F has piezochromism,which may be related to the destruction of the original crystal packing structure after the complex is pressed.Finally,Ir-Hex,Ir-OXD,Ir-F and Ir-PtzF were selected for the detection of nitroexplosives.The selected complexes have good selectivity and detection sensitivity for PA.The main mechanism of detection should be attributable to photoelectron transfer(PET).(4)Four ionic iridium complexes were synthesized with L-F as the main ligand and using bipyridine and 1,10-phenanthroline as auxiliary ligands.Their structure and photophysical properties were characterized.The results showed that the luminescence of the complexes in dimethyl sulfoxide(DMSO)was significantly enhanced.The complex Ir-POP+was blue-shifted in the toluene solution compared with other solutions.It may be because the solvent effect of toluene that inhibits ~3LLCT transition.In addition,complex Ir-POP+was selected for the detection of nitroexplosives.It has good selectivity and detection sensitivity to PA.The detection limit is estimated as 0.22?M.