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

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 d10 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.

Recent Advances in Aggregation-Induced Emission Active Materials for Sensing of Biologically Important Molecules and Drug Delivery System

“…More recently, Maity et al developed an antipyrine fluorescent probe 4-[(2-hydroxy-3-methoxy-benzylidene)-amino-1,5-dimethyl-2-phenyl-1,2-dihydro-pyrazole-3-one (OVAP) for selective detection of Al 3+ and Zn 2+ detection [ 47 ]. Diana and Panunzi in their review described several AIE active fluorescent probes for sensing of Zn 2+ ions [ 48 ]. Moreover, Sun et al developed a multifunctional AIE active Schiff base fluorescent probe (TPESB) combined with AIE and ESIPT.…”

Luminescent Zn (II)-Based Nanoprobes: A Highly Symmetric Supramolecular Platform for Sensing of Biological Targets and Living Cell Imaging

“…The structural versatility of the zinc coordination core can be exploited in building tailored nanosized architecture. On the other hand, the desired PL properties of the nano-tools can be modulated by the optically innocent "clip approach" (Diana and Panunzi, 2021) due to zinc cation. Finally, in the live observations cells and tissues can be both deeply penetrated and preserved thanks to the small non-toxic zinc ion.…”

“…UCNPs are known for their applications in bioimaging, biosensing, and nanomedicine thanks to their highly efficient cellular uptake, high optical penetrating power, and little background noise at the deep tissue level. Yu Tang and coworkers in 2017 (Cai et al, 2017) produced a core-shell MOF-based nanocomposite UCNPs/MB@ The employ of fluorescence AIE (aggregation induced enhancement) active markers state exhibit stronger emission in the concentred solution (Caruso et al, 2018;Diana and Panunzi, 2021) than in diluted ones. AIE undergoing probes can solve problems due to fluorescence quenching of the aggregates in aqueous physiologic media and are very useful in bioimaging (Fan et al, 2020b;Ying et al, 2021).…”

A Novel L-Shaped Fluorescent Probe for AIE Sensing of Zinc (II) Ion by a DR/NIR Response

“…As a closed-shell cation, it acts as a constraint, locking the ligand into an emissive conformation mainly due to LCT (ligand charge transfer) transitions, even altering intensity and/or position of the photoluminescence (PL) pattern [ 25 , 28 , 29 , 30 , 31 , 32 , 33 , 34 ]. With an AIE probe, zinc cation can recover and/or modulate the emission [ 25 , 35 , 36 , 37 , 38 , 39 , 40 ] by reformulating the orbital separation between HOMO and LUMO regions. Interestingly, zinc (II) has a potential in enhancing and red-shifting the emission of DR/NIR probes [ 1 , 2 , 3 , 41 , 42 ].…”