New Phosphorescent Materials Iridium Complexes: Synthesis, Photopysical And Electrochemical Characterization

In order to modulate luminescence color of iridium complexes, new series of heteroleptic cyclometalated iridium complexes which have the general formula (ppz)2Ir(LX) (ppz=1-phenylpyrazole, LX =2-(2′-hydroxyphenyl) benz- othiazole(BTZ), 2-(3 -methyl-2′-hydroxy-phenyl) benzothiazole (3-MeBTZ), 2- (4- methyl - 2′- hydroxyphenyl) benzothiazole (4-MeBTZ), 2- (4-trifluorometh -yl- 2′- hydroxyphenyl) benzothiazole (4-tfmBTZ)) and blue phosphorescence iridium complex which is (dfppy)2Ir(pic)(dfppy=2-(2,4-difluorophenyl) pyridine, pic=2-picolinic acid) were synthesized. Their molecular structure, photophysical and electrochemical properties were tested and analyzed comparatively, and the relationship between their chemical structures and properties were discussed preliminary.1. BTZ and BTZ-based derivatives, 3-MeBTZ, 4-MeBTZ, 4-tfmBTZ, were synthesized. The yield of these ligands was improved visa changed reaction time and temperature. A new series of iridium complexes coordinated with ppz and BTZ, 3-MeBTZ, 4-MeBTZ, 4-tfmBTZ, (ppz)2Ir(LX) (LX= BTZ, 3-MeBTZ, 4-MeBTZ, 4-tfmBTZ) were synthesized. These complexes'structures were characterized by 1H NMR and IR absorption spectra.2. Blue phosphorescence iridium complex which is (dfppy)2Ir(pic) was synthesized using the traditional method, structure of this iridium complex was characterized by 1HNMR and IR absorption spectra.3. UV-vis absorption spectra and fluorescence spectra of (ppz)2Ir(LX) were measured. The results show that the four complexes have basically similar UV-Vis absorption spectra, fluorescence excitation and emission spectra. Their maximum emission peaks are located at 583nm-615nm, and accompanied by a lower intensity emission band around 400nm. Emissions primarily come from light absorption of ligands, not the transition of 3MLCT and 3π-π*. Compared with Ir(ppz)3, these complexes have not only stronger phosphorescence at room temperature but also their emission color can be tuned by modifying ancillary ligand. This indicates that there is energy transfer from cyclometalated ligand to ancillary ligand in complexes. The weak emission around 400nm is ascribed to the radiation transition of single state excition from ancillary ligand BTZ perturbed by metallic ion, and light emission around long-wavelength to the radiation transition of triplet state 3MLCT of Ir(BTZ) fragment. The oxidation-reduction potentials of complexes are obtained from C-V curves. By comparing, we find that the complex incorporating an electron donating substituent, is more easy to be oxidized, while the complex incorporating an electron withdrawing substituent is more difficult to be oxidized, but the complex introducing whether electron donating substituent or electron withdrawing substituent is more difficult to be reduced.4. UV-vis absorption spectra and fluorescence spectra of (dfppy)2Ir(pic) were measured. From the UV-vis absorption spectra, we find that the coupling between highest occupied molecular orbital (HOMO) of cyclometalated ligand and the d orbital of Ir3+ ion is weakened owing to introducing two fluorine with electron withdrawing effect so that the triplet state transition from metal to cyclometalated ligand charge transfer (3MLCT) is weak. So, there isn't obvious absorption peak beyond the wavelength range of 400nm. Because fluorescence excitation spectra is similar to UV-vis absorption spectra, so all the photo-absorption make a contribution to emitting. The maximum emission peak (dfppy)2Ir(pic) is located on 494nm, testifying that we have realized blue phosphorescence emitting.