Solvent-Regulated Fluorimetric Differentiation of Al³⁺ and Zn²⁺ Using an AIE-Active Single Sensor

Abstract

The absence of d-orbital electrons or presence of full-filled d-orbital electrons in metal ions is a well-known Achilles' heel problem for the detection of these metal ions by a simple UV-visible study. For this reason, detection of metal ions such as Al 3+ with no d-orbital electrons or Zn 2+ with filled d-orbital electrons is a challenging task. Herein, we report a 2-naphthol-based fluorescent probe [1-((E)-((E)-(5-bromo-2-hydroxybenzylidene)hydrazono)methyl)naphthalen-2-ol] (H 2 L) that has been used to sense and discriminate Al 3+ and Zn 2+ via solvent regulation. The probe exhibits excellent selectivity and swift sensitivity toward Al 3+ in MeOH− water (9:1, v/v) and toward Zn 2+ in dimethyl sulfoxide (DMSO)−water (9:1, v/v) among various metal ions. The respective detection limit is found to be 9.78 and 3.65 μM. The sensing mechanism is attributed to multiple processes, viz., the inhibition of photo-induced electron transfer (PET) along with the introduction of chelation-enhanced emission (CHEF) and excited-state intramolecular proton transfer (ESIPT) inhibition, which are experimentally well verified by UV−vis absorption spectroscopy, emission spectroscopy, and NMR spectroscopy. The probe shows aggregation-induced emissive (AIE) response in ≥70% aqueous media as well as in the solid state. The experimental results are well corroborated by time-resolved photoluminescence (TRPL) and density functional theory (DFT) calculations. An advanced-level OR-AND-NOT logic gate has been constructed from a different chemical combinational input and emission output. The reversible recognition of both Al 3+ in MeOH−water (9:1, v/v) and Zn 2+ in DMSO−water (9:1, v/v) is also ascertained in the presence of Na 2 EDTA, enabling the construction of a molecular memory device. The probe H 2 L also detects intracellular Al 3+ /Zn 2+ ions in Hela cells. Altogether, our fundamental findings will pave the way for designing and synthesis of unique chemosensors that could be used for cell imaging studies as well as constructing molecular logic gates.

A naphthalene-based azo armed molecular framework for selective sensing of Al3+

“…At the same time, this highly stable rigid planar complex involving diamagnetic oxophilic Al 3+ efficiently reduces the nonradiative decay to induce greenish-yellow emission. 60,61 This spectral choice is further confirmed by the help of other physical and spectroscopic studies.…”

Copper(II) Ion Promoted Reverse Solvatochromic Response of the Silatrane Probe to Spectral Shifts: Preferential Solvation and Computational Approach

“…Development of an organic receptor with unique photophysical attributes for the selective recognition of metal ions whose sensitivity depends upon solvent media and surrounding circumstances is scientifically exciting and highly desirable for practical applications. − Moreover, a single probe having different responses toward multiple analytes in a single solvent is common in the literature, − but a unimolecular system having a change in sensing response toward a single analyte on account of different solvents is still rare. Such systems are of deep interest in solvent-responsive supramolecular systems because they can differentiate and detect analytes of interest in the presence of other interfering solvent counterparts .…”

Activation of apoptosis by rationally constructing NIR amphiphilic AIEgens: surmounting the shackle of mitochondrial membrane potential for amplified tumor ablation

“…33 In this phenomenon, molecules fluoresce strongly when aggregated or in a solid state, but faintly when dispersed in solution. 19,[34][35][36][37][38][39] Considering their advantages, such as high photostability, a large Stokes shift, and easy preparation, some impressive AIE luminogens (AIEgens) have been extensively explored by Tang, Liu and other groups, especially in the fields of bioimaging, sensing, and therapy. 13,20,37,[40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57] However, undesirable aggregations of most AIEgens in aqueous environments with "always on" fluorescence is not conducive to high signal-to-noise ratio (SNR) imaging of other cellular suborganelles and targets of interest owing to their high hydrophobicity.…”