The Effect of Substituent Position on Photophysical Properties of Iridium Phosphorescent Complexes Based on Substituted 2,4-Diphenylpyridine
Phosphorescent iridium complexes are the electroluminescent materials with the best comprehensive performance.Phosphorescent iridium complexes have been employed in organic light-emitting diodes(OLEDs),electrochemical light-emitting cells(LECs),photocatalysis,tumour diagnosis and sensors owing to their various advantages such as high quantum efficiency,good thermal stability and tunable emission colors.The color tuning of the iridium phosphorescent complex can be realized by changing the chemical structure of the main ligands and auxiliary ligands such as changing the conjugation degree of ligand,electron-donating and with drawing ability of substituents and substituent position.The influence of substituent position on iridium phosphorescent complex's photophysical properties was rarely researched.In this paper,we propose studying the effect of different substitution positions of methyl groups on the photophysical properties of iridium phosphorescent complexes.Two new iridium phosphorescence complexes(2,4-2Me-2,4-dppy)2 Ir(tmd)and(3,5-2Me-dppy)2 Ir(tmd)were synthesized with 2,4-diphenylpyridine of different methyl substituent positions as the main ligand and 2,2,6,6-tetramethylheptanedione as the auxiliary ligands.Their composition and spatial structure were characterized by elemental analysis,nuclear magnetic resonance(1H NMR and 13 C NMR)and single-crystal X-ray diffraction.Bothcomplexes show slightly distorted octahedral configuration with space groups of C 12/C1 and P-1,with monoclinic and triclinic crystal systems,respectively.The thermal stability was tested by TG curves,the two complexes have good thermal stability with thermal decomposition temperatures of 307 ℃ and 318 ℃ respectively.UV-Vis spectra and photoluminescence spectra studied the photophysical properties of the complexes.The emission wavelengths of the two complexes in solution were 545 and 572 nm,respectively.The quantum yields in solution were 70％and 92％,respectively.The effect of substituent position on the photophysical properties of iridium phosphorescent complexes was further discussed.It was found that the position of the methyl group had a significant effect on the luminescence color and emission wavelength of 2,4-diphenylpyridine iridium phosphorescent complexes.Compared with the iridium phosphorescent complex obtained when the methyl group is at the 2 and 4 positions,the emission wavelength of the iridium complex obtained when the methyl group is at the 3 and 5 positions has a significant redshift,which is pure yellow light emission.It is a potential yellow light material expected to be applied in OLED lighting.
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