Bioorthogonal chemistry emerged as a powerful tool in luminescent bioimaging that relies of the use of luminescent click reagents. Some of these probes demonstrate 'switch-on' luminescence following a conjugation Luminogenic probes are highly desirable, as the non-conjugated probe generates no luminescent background, ensuring high sensitivity of the probe without the need for laborious washing protocols. Phosphorescent cyclometallated iridium(III) complexes enrich the field of luminescent bioimaging by offering unique characteristics and several advantages over traditional organic probes. They are easy to prepare, highly tuneable, photostable, and their long lived excited states provide opportunity for time-delayed elimination of the background luminescence as well as for luminescence lifetime imaging. Interaction of the complexes in the exited state with oxygen is of interest for intracellular and in vivo oxygen sensing due to their oxygen-dependent emissions , while sensitisation of singlet oxygen is utilised in photodynamic therapy. In addition to luminescence, the presence of the heavy metal centre allows the use of additional complementary detection techniques such as X-ray fluorescence, ICP-MS and electron microscopy. Phosphorescent cyclometallated iridium(III) complexes were developed as bioorthogonal reagents incorporating a variety of click groups. Inverse electron demand Diels-Alder reaction (IEDDA) is the fastest in the repertoire of bioorthogonal chemistry and several examples of metal complexes were reported in the literature. Of particular interest are complexes in which coordination of the Ir(III) metal centre to the diene facilitates the reaction kinetics. For example, Lo et al. demonstrated this effect in tetrazine complexes, while we describesimilar behaviour of Ir(III) complexes of 1,2,4triazines. Importantly, both the tetrazine and the triazine systems also show luminogenic behaviour in reactions with BCN derivatives. We report the synthesis and evaluation of novel iridium(III) complexes that can participate in IEDDA reaction. The novelty of these complexes arises from the 1,2,4-triazine fragment that is annealed to phenanthroline-type ligand through C5-C6 bond. This feature distinguishes the 1,2,4triazine from 1,2,4,5-tetrazines as there is no possibility for annealing phenanthroline or any other units to the tetrazine ring due to the absence of carbon-carbon bonds.