*Review* **Zinc (II) and AIEgens: The "Clip Approach" for a Novel Fluorophore Family. A Review**

**Rosita Diana and Barbara Panunzi \***

Department of Agricultural Sciences, University of Naples Federico II, 80055 Portici, Italy; rosita.diana@unina.it **\*** Correspondence: barbara.panunzi@unina.it; Tel.: +39-081-674-170

**Abstract:** Aggregation-induced emission (AIE) compounds display a photophysical phenomenon in which the aggregate state exhibits stronger emission than the isolated units. The common term of "AIEgens" was coined to describe compounds undergoing the AIE effect. Due to the recent interest in AIEgens, the search for novel hybrid organic–inorganic compounds with unique luminescence properties in the aggregate phase is a relevant goal. In this perspective, the abundant, inexpensive, and nontoxic d<sup>10</sup> zinc cation offers unique opportunities for building AIE active fluorophores, sensing probes, and bioimaging tools. Considering the novelty of the topic, relevant examples collected in the last 5 years (2016–2021) through scientific production can be considered fully representative of the state-of-the-art. Starting from the simple phenomenological approach and considering different typological and chemical units and structures, we focused on zinc-based AIEgens offering synthetic novelty, research completeness, and relevant applications. A special section was devoted to Zn(II) based AIEgens for living cell imaging as the novel technological frontier in biology and medicine.

**Keywords:** AIE; zinc complex; fluorescence

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**Citation:** Diana, R.; Panunzi, B. Zinc (II) and AIEgens: The "Clip Approach" for a Novel Fluorophore Family. A Review. *Molecules* **2021**, *26*, 4176. https://doi.org/10.3390/ molecules26144176

Academic Editors: Jorge Bañuelos Prieto and Ugo Caruso

Received: 16 June 2021 Accepted: 6 July 2021 Published: 9 July 2021

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