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Herein, we report the design and synthesis of a red luminescent ruthenium (Ru) complex with imidazophenanthroline as the chelating ligand. The metal complex showed a unique concentration-dependent distinct optical response in the presence of the target analyte, Na2S. At the lower concentration (micromolar range), the addition of Na2S resulted in the decrease of absorption maximum with a diminution of luminescence intensity. On the contrary, a bathochromic shift in the UV–visible spectrum with a turn-on luminescence response was noticed upon the addition of excess Na2S (millimolar range). The detailed mechanistic investigation indicated the formation of a hydrogen-bonded complex with sulfide (HS̅) ions at lower concentrations involving imidazole nitrogen ends. On the other hand, excess Na2S led to the reduction of nitro to amino group, which facilitated the extent of intramolecular charge transfer. Furthermore, we used the Ru(II) complex for analyzing H2S in toilet water samples, as it is the indicator of fecal contamination. Also, it was observed that chemically modified paper strips could detect H2S in contaminated water samples without involving any sophisticated instruments (sustainable approach). Finally, the imaging of H2S inside living breast cancer cells (MCF-7) was achieved under various stimulated conditions. Moreover, H2S-induced, concentration-dependent alternation in the luminescence signal was also noticed under intracellular conditions.
Fernandes et al. (Tue,) studied this question.