Bis-cyclometalated Ir(III) complexes with carbazole/triphenylamine donor fragment for oxygen sensing

Bis-cyclometalated Ir(III) complexes Ir(ppy-Carbazole)2(acac) and Ir(ppy-NPh3)2(acac) (acac = acetylacetonate) based on the 2-phenylpyridine (ppy) with carbazole or triphenylamine moieties were prepared, characterized and tested as phosphorescent materials. The photophysical properties of the two complexes were investigated by comparing them with the unsubstituted parent Ir(III) complex Ir(ppy)2(acac). Complexes Ir(ppy-Carbazole)2(acac) and Ir(ppy-NPh3)2(acac) with carbazole/triphenylamine-appended C<^>N cyclometalating ligands exhibit larger molar extinction coefficients and longer luminescence lifetimes compared to the unsubstituted parent Ir(ppy)2(acac). Based on a rational design strategy by combining a ppy unit and electron-donating carbazole or triphenylamine segment, we investigated the merits of the carbazole or triphenylamine group substituted cyclometalated Ir(III) complexes for oxygen sensing. These probes demonstrate optimal luminescence dynamics for oxygen monitoring in the range of 0-100% oxygen levels when immobilized in an ethyl cellulose matrix. Importantly, the complex Ir(ppy-NPh3)2(acac) exhibits a longer luminescence lifetime (tau = 3.60 mu s) and a higher oxygen sensitivity (I0/I100 = 15.0, KSV = 0.02582 Torr-1) compared with the other complexes.