Three diphenylamino modified cationic cyclometalated platinum(II) complexes Ⅰ-Ⅲ have been designed and synthesized with 1,10-phenanthroline as an auxiliary ligand. The photophysical, electro-chemical and oxygen sensing properties of the complexes were investigated systematically. The results show that the introduction of different groups at the 5-position of the pyridine ring of 2-(4-diphenylamino) phenylpyridine can tune the emission wavelength of the platinum(II) complexes from 544 nm to 583 nm. The maximum emission wavelength of the trifluoromethyl-substituted complex Ⅲ is 583 nm. The results of oxygen sensing tests show that the oxygen sensitivity of the complex Ⅲ is remarkably improved, with a value of I0/I2.17 up to 6.4 in DMF.