Modulation of Optical Oxygen Sensing Properties of Iridium (III) Complexes By Changing Their Substitution Groups

The series of bis-cyclometalated iridium (III) complexes bearing different substituents (-H, -OCH3, -F, -CH3) at the aryl moiety (Ir-1, Ir-2, Ir-3 and Ir-4) have been synthesized and characterized by MASS and 1H NMR spectrometries, and IR, absorption and emission spectroscopies. The effects of the substituents on their oxygen sensing properties as well as optical properties and decay kinetics have been investigated systematically in tetrahydrofuran (THF) and ethyl cellulose (EC) thin films. The Ir (III) complexes embedded in EC-based thin films showed more advanced sensor dynamics, higher oxygen sensitivity, and superior relative signal changes when compared with their solution phase. The I0/I100 values of Ir-1, Ir-2, Ir-3 and Ir-4 immobilized in EC thin film were calculated as 11.3, 5.2, 7.0 and 25.6 for the concentration range of 0-100% pCO2, respectively. These results show that the weak electron-donating properties of the methyl groups at the aryl moiety improve remarkably the optical oxygen sensing abilities of the Ir (III) complexes.