Phosphorescent heavy-metal complexes are one class of excellent photoluminescent materials. The heavy metal-induced spin–orbit coupling leads to singlet–triplet state mixing, thus decreases the “spin-forbidden” component of the radiative relaxation of the triplet state, and consequently improves the phosphorescence quantum efficiency and radiative emission lifetime. Moreover, the emission wavelength of metal complexes can be easily tuned through the ligand modification and the change of central metals.

Ruthenium(II) and Iridium(III)-based complexes have d6 electronic structures. The advantageous photophysical properties including long lifetime, large Stokes shift and long wavelength excitation provide them to be good candidates for chemosensors. This thesis focuses on the development of novel iridium and ruthenium complexes for small molecules sensing. Their long-lived photoluminescence lifetime allows detecting analytes even in the presence of short-lived background fluorescence by using time-gating techniques.

An overview of the developing trends in molecular beacon design and applications will be introduced in Chapter 1. In Chapter 2, the long-lived emission of Ir(III) and Ru(II) complexes are combined with time-resolved spectroscopic techniques for optimizing the sensitivity of molecular beacons. A novel iridium complex with long-lived photoluminescence will be discussed in Chapter 3, which can be used for the detection of thiol-containing amino acids in the presence of strong background fluorescence. In Chapter 4, pre-exponential factors derived from time-resolved experiments will be applied for quantifying free histidine in mixtures with histidine-containing proteins. The last Chapter is the development of the new application of Ruthenium complexes as a media for dispersion nanotubes in aqueous solution.