Luminescent Iridium(III) Cyclometalated Complexes: Host-Guest Chemistry and Application as Sensors

In this thesis, known and new iridium(III) cyclometalated complexes have been synthesized and investigated in a host-guest chemical context and in studies towards an application in the detection of peroxide-based explosives in fingerprints. The complexes [Ir(ppy-R)2(bpy)]n+ studied here contain two cyclometalated ligands (ppy-R: R-substituted 2-phenylpyridine), and one polypyridine ligand (bpy=2,2 -bipyridine). Substituent groups R included: R=H (Ir-H); R=CHO (Ir-CHO); R=CH2NH-Bu, Bu=n-butylamine, (Ir-CH2NH-Bu); R=CH2NH-Oct, Oct=n-octylamine (Ir-CH2NH-Oct); and R=CH2N-(Oct)2 (Ir-CH2N-(Oct)2).Chapter 2 demonstrated that the R group in the iridium(III) complexes significantly affects the photophysical properties. Luminescence and electrochemical studies confirmed that the CHO group acts as a strong electron withdrawing group (EWG), while Ir-CH2NH-Bu was more like Ir-H, as the n-butyl group (Bu) behaved as a mild EWG rather than an electron donating group (EDG). Ir-CHO and Ir-H both showed similar responses to solvent polarity, but the response of Ir-CH2NH-Bu was opposite to that observed for Ir-CHO and Ir-H. In the iridium alkylamine complexes, Ir-CH2N-(Oct)2 displayed different emission properties from Ir-CH2NH-Bu and Ir-CH2NH-Oct.In the host-guest study reported in Chapter 3, all complexes (Ir-CHO, Ir-H and Ir-CH2NH2+-Bu) showed a similar accommodation mode within Q[10], where the ppy-R ligands sat deep within the cavity while the bpy ligand sat on the portal. In the presence of Q[10] the emission profiles of these complexes showed enhanced intensity with blue shifts and became more structured. The titration study showed that both Ir-CHO and Ir-H had similar binding behavior (1:2 portal bound and 1:1 cavity bound) while Ir-CH2NH2+-Bu only displayed 1:1 cavity bound associations. The emissions of encapsulated complexes were found to be very sensitive to temperature. In Chapter 4 this type of Ir(III) cyclometalated complex was applied toward a detection application for both fingerprints and peroxide-based explosives in the oil of fingerprints. Ir-CH2N-(Oct)2 displayed the highest solubility in oleic acid (as an example of fatty acid that present in fingerprints). A boronic acid group (B(OH)2) was introduced to the bpy ligand to form B(OH)2-Ir-H, which was used as a sensor for peroxide detection, based on the ability of hydrogen peroxide (H2O2) to oxidize a boronic acid group and hence induce a change in the luminescence