Hydrogen sulfide (H 2 S) is one of the endogenous gasotransmitters that has been recently reported to play a variety of pathological and physiological roles in different tissues. Therefore, probes that can sense H 2 S generated by enzymes with good selectivity and sensitivity would be very useful for drug discovery efforts, as well as for fundamental biological studies. My work focuses on the design, synthesis and characterization of luminescent lanthanide complexes as probes for time-gated luminescence detection of H 2 S.