**5. Conclusions**

which potentially make it a smart "green" metal. Combinations One of the biggest challenges of the modern era is sustainability. Over the last years, the high variety of *N*, *O*, *S* donor ligands moved a strong interest toward spectroscopic and applicative features of the related complexes. Tridentate ligands are simple, low cost, and easy synthesizable pincers able to guarantee good stability to the derived complexes. On the other hand, zinc cation has a unique mix of attractive properties, which potentially make it a smart "green" metal. Combinations of suitable tridentate ligands with zinc cation are the perfect union to achieve remarkable PL responses and targeted applications. As a d 10 closed shell cation, zinc(II) plays a quite innocent role in the electronic and therefore spectroscopic pattern of the ligand, often guaranteeing a relevant CHEF effect. For this reason, zinc is a key issue in developing an alternative class of environmentally friendly and highly efficient fluorophores for display and lighting technologies. On the other hand, zinc plays a crucial role in many important biological processes and is a structural key component of proteins and enzymes. Versatile molecules able in the zinc(II) detection or in the zinc binding of fluorescence markers to specific biological substrates are recently proposed chemo- and biosensors.

As scientists, we presented here some examples of zinc tridentate complexes in an attempt to highlight some of their unique properties. We examined the PL emission tuning due to coordination and stating the most interesting applications. As researchers, we are committed to continuing the study of novel systems for the new technological frontier and we expect our research to be the subject of further interesting discoveries.

**Author Contributions:** Conceptualization, B.P.; data curation and formal analysis, R.D.; methodology, R.D. and B.P.; writing—original draft, B.P., writing—review & editing, B.P. All authors have read and agreed to the published version of the manuscript.

— — **Funding:** This research was funded by the Italian Ministry of Education, University and Research (MIUR) under grants PON PANDION 01\_00375.

**Conflicts of Interest:** The authors declare no conflict of interest.
