Design And Synthesis Of Cationic Bis-cyclometalated Iridium (?) Complexes And Their Oxygen Sensing Properties

At present,cyclometalated Ir(?)complexes have attracted much attention due to their high quantum yields,photo-and thermal stabilities as well as easy tunability of the properties.Therefore,cyclometalated Ir(?)complexes have been widely studied for their potential applications in organic electroluminescence devices,photocatalysis,cell imaging,analytical probing and so on.The dynamic quenching of phosphorescence(or fluorescence)of oxygen-sensitive probes(OSPs)by molecular oxygen is the most widely accepted sensing mechanism for the optical detection of this gas.Optical oxygen sensors have become popular because of features such as the absence of oxygen consumption,good reversibility,high sensitivity,and fast response.Up to now,Ru(?)complexes and Pt(?)/Pd(?)porphyrin complexes have often been reported as OSPs in the field of optical oxygen sensing.However,relatively little attention has been paid to the cyclometalated Ir(?)complexes as the OSPs.In order to rationally construct cyclometalated Ir(?)complexes with excellent oxygen sensing performance,it is necessary to well understand the structure-property relationship(including photophysical property,electrochemical property,photostability,oxygen sensitivity and reversibility)of the OSPs.In this dissertation,a series of new cationic bis-cyclometalated Ir(?)complexes based on 2-phenylpyridine derivatives were designed and synthesized,and their properties were investigated in detail.The main contents and results of this study are as follows:1.A new class of diphenylphosphoryl-substituted cationic bis-cyclometalated Ir(?)complexes[Ir(POFdFppy)2(N^N)]+PF6-(dFppy = 2-(2,4-difluorophenyl)pyridine)(Ir1-Ir6)with different N^N ancillary ligands were synthesized and characterized.The influence of N^N ancillary ligands(phen = 1,10-phenanthroline,bpy = 2,2'-bipyridine,dMebpy =5,5'-dimethyl-2,2'-bipyridine.biim = 2,2'-biimidazole,dMebiim = 1,1'-dimethyl-2,2'-biimidazole,dPhbiim = 1,1'-diphenyl-2,2'-biimidazole)on the photophysical,electrochemical properties and oxygen sensing properties of these Ir(?)complexes was investigated.The results show that phen-and bpy-type Ir(?)complexes Irl-Ir3 emit greenish-blue colors at 465-497 nm with high ?PL values of 56%-61%in CH2Cl2.When the biim ancillary ligand is used,Ir4(?emmax at 451 nm)with a ?PL of 45%exhibits a blue-shifted emission compared to other complexes.Ir5(?PL=5%)with the dMebiim ancillary ligand shows a significant decrease in ?PL relative to Ir4.The ?PL of Ir6 with the dPhbiim ancillary ligand in CH2Cl2 is also extremely low(<3%).However,the photoluminescent quantum yields of Ir5 and Ir6 in solid state increase remarkably in comparison to those in solution.Among them,Irl bearing a phen moiety exhibits the highest oxygen sensitivity.2.Based on the results mentioned-above,a series of cationic bis-cyclometalated Ir(?)complexes Ir7-Ir12 using 2-phenylpyridine(ppy)derivatives with a 2,4-difluorophenyl moiety as the cyclometalating ligands and the phen as ancillary ligand were designed and prepared.The influence of the alteration of CAN cyclometalating ligands with different conjugation systems and substituents on the photophysical,electrochemical properties and oxygen sensing properties of the corresponding Ir(?)complexes was studied.Enlarging the conjugated systems of the cyclometalating ligands results in red-shifts in absorption and emission maxima,prolonged phosphorescence lifetimes and enhanced oxygen sensitivity of the corresponding complexes.On the other hand,introducing a trifluoromethyl group at the 5-position of the pyridyl ring of cyclometalating ligands can improve the photostability of the corresponding Ir(?)complexes.The complex Ir12 with an increased conjugate system and a trifluoromethyl group exhibits the highest oxygen sensitivity.3.Three cationic bis-cyclometalated Ir(?)complexes Ir14-Ir16 with an ester substituent(-COOEt)at the 4-position of the phenyl ring on the ppy derivatives and the phen as ancillary ligand were synthesized and characterized.The photophysical and electrochemical properties of these Ir(?)complexes were studied in detail.In addition,the influence of an ester group(-COOEt)on the oxygen sensing properties of the Ir(?)complexes was also investigated.The results reveal that the emission maxima of ester-substituted Ir(?)complexes Ir14-Ir16 show notably blue-shifts relative to the model complex[Ir(ppy)2(phen)]+PF6-(Ir13).Ir14-Ir16 demonstrate extended phosphorescence lifetimes and better oxygen sensitivity compared to Ir13.Ir(?)complexes Ir13-Ir16 exhibit excellent operational stability and high photostability.Among them,the ester-substituted Ir(?)complex Ir16 with a methyl group in the pyridine unit shows the highest oxygen sensitivity.