Dual-Mode Multiple Ion Sensing via Analyte-Specific Modulation of Keto-Enol Tautomerization of an ESIPT Active Pyrene Derivative: Experimental Findings and Computational Rationalization

Ultrafast conformation-dependent charge transfer in N, N, N', N'-tetramethyl-1,3-propanediamine: Effect of flexible carbon skeleton on electron lone pair interactions

Flexible three-carbon skeleton makes N, N, N', N'-tetramethyl-1,3-propanediamine (TMPDA) an important diamine system to investigate the conformation-dependent electron lone pair interactions and charge delocalization. The charge transfer process linked to structural motions of the three-carbon skeleton has been monitored in real time by the Rydberg electron binding energy (BE) spectra of TMPDA coupled with quantum chemical calculations. Optical excitation to the 3p state with a 200 nm pump pulse initially generated a localized charge on one of the two nitrogen atoms that may partially transfer to the other one. Rapid internal conversion (IC) from the 3p to 3s state occurred within 430 fs, resulting in an initial charge delocalized 3s_h/3s_l population ratio of 23.6 %/76.4 %. A final 3s_h/3s_l (51.9 %/48.1 %) equilibrium proceeded within about 2.64 ps. The 3s_h (TTTT+, GG'TG+ and G'GG'G+) and 3s_l (GG'GG'+ and GG'G'G+) (see text for structure definitions) are identified as the extended and folded conformers, respectively. Two types of electron lone pair interactions, i.e., through-space interaction (TSI) and through-bond interaction (TBI), are found to coexist in TMPDA to drive charge transfer. The GG'GG'+ and GG'G'G+ structures exhibit TSI, while the TTTT+ structure shows TBI. The GG'TG+ and G'GG'G+ structures exhibit both TSI and TBI. Flexible three-carbon skeleton provide more opportunities for the two N-electron lone pairs to overlap in space (i.e., TSI), making TMPDA to be favorable for the most stably folded conformation.

A highly selective and sensitive rhodamine B-based chemosensor for Sn4+ in water-bearing and biomaging and biosensing in zebrafish

A novel colorimetric-fluorescent dual-mode chemosensor (JT5) based on rhodamine B has been produced for monitoring Sn4+ in the DMSO/H2O (4:1, v/v) medium. It has high sensitivity, a low detection limit, a short response time (1 s) and high stability, and can still be maintained after two weeks with the red dual fluorescence/ colorimetric response. Enhancement of red fluorescence (591 nm) and red colorimetric (567 nm) response of JT5 by Sn4+ addition. The electrostatic potential of the sensor JT5 molecule was simulated to speculate on the sensing mechanism, and the IR, mass spectrometry and 1H NMR titration were utilized to further demonstrate that JT5 was coordinated to Sn4+ with a 1:1 type, the rhodamine spironolactam ring of JT5 opens up to form a penta-membered ring with Sn4+, meanwhile, its system may have chelation enhanced fluorescence (CHEF) effect. In addition, theoretical calculations were carried out to give the energy gaps of JT5 and [JT5 + Sn4+] as well as to simulate the electronic properties of the maximal absorption peaks. Notably, the sensor JT5 was successfully applied to monitoring Sn4+ in zebrafish, and the JT5-loaded filter paper provided a solid-state platform for detecting Sn4+ by both naked eye and fluorescent methods. In summary, this work contributes to monitoring Sn4+ in organisms and solid-state materials and promotes understanding of Sn4+ functions in biological systems, environments, and solid-state materials.

Construction of a novel fluorescent probe for sensitive determination of glyphosate in food and imaging living cells

Glyphosate is a widely used broad-spectrum herbicide in agriculture and horticulture to control a variety of weeds and undesirable plants. However, the excessive use of glyphosate has raised a number of environmental and human health concerns. It is urgent to develop tools to detect glyphosate. Herein, a novel dual-signal probe CCU-Cu2+ was designed and synthesized on the basis of CCU. CCU exhibited excellent selectivity and great sensitivity for Cu2+ which were based on both fluorescence "turn-off" reaction and comparative color visualisation methods. Due to the strong chelating ability of glyphosate on Cu2+, the CCU-Cu2+ complex was applied to glyphosate detection in practical samples. The experimental results in vitro showed that the CCU-Cu2+ complex was highly selective and rapid, with a low detection limit (1.6 μM), and could be recognised by the naked eye in the detection of glyphosate. Based on the excellent properties of the CCU-Cu2+ complex, we also constructed a smartphone-assisted detection sensing system for glyphosate detection, which has the advantages of precision, sensitivity, and high interference immunity. Moreover, the CCU-Cu2+ complex was also successfully employed for exogenous glyphosate imaging in living cells. These characteristics demonstrated that CCU-Cu2+ holds significant potential for detection and imaging of glyphosate in bio-systems.

Biogenic Polymer-Based Fluorescent Assemblies: Versatile Platforms for Ultrasensitive ATP Detection and Enzyme Assay

Here, we investigated the optical properties of biocompatible supramolecular assemblies formed through electrostatic interactions between anionic fluorescent dyes and biogenic polymers. The dynamic equilibrium between the monomeric form (fluorescent) and aggregates (nonfluorescent) of dye molecules is responsible for the stimuli-responsive behavior of these polymer composites, which can respond to changes in pH, temperature, and ionic strength. Furthermore, we employed supramolecular assemblies for the purpose of turn-on fluorescence sensing of adenosine triphosphate (ATP) at physiological pH. Notably, no interference was observed even in the presence of well-known competing analytes such as pyrophosphate. In addition to its outstanding selectivity, the present system can detect ATP at concentrations as low as 4.8 nM. The superior detection capabilities are achieved through multiple interactions with biogenic polymers, involving the adenine ring, ribose unit (through hydrogen bonding), and phosphate groups (via charge pairing) of ATP. Given the remarkable sensitivity to ATP, we have applied the present system for the detection of a dephosphorylating enzyme, alkaline phosphatase.

AIE active fluorescent organic nanoparticles based optical detection of Cu2+ ions in pure water: a case of aggregation-disaggregation reversibility

An AIE-active pyrene-terpyridine derivative, (4'-(pyren-1-yl)-2,2':6',2''-terpyridine) (1) was found to form nanoaggregate in an aqueous medium. The probe involved hydrogen bonding with solvent molecules that modulated the charge transfer behavior and consequently resulted in different spectroscopic behavior due to the formation of fluorescent organic nanoparticles (FONs). In the presence of Cu2+ ions, FONs displayed a ratiometric red shift of the absorption band (360 to 420 nm) accompanied by a prominent naked-eye color change from colorless to light yellow. With a gradual increase in water content, 1 displayed a huge red shift of the emission band (430 to 475 nm) denoting its switching from monomer to FONs. In the presence of Cu2+, the 475 nm emission band of FONs gradually diminished, facilitating the micromolar scale detection of Cu2+ (LOD = 8.57 μM) in a 100% aqueous medium with a fluorogenic color change from cyan to dark. The SEM and DLS data indicated the cation-induced disaggregation of FONs, which was further confirmed by mass spectral analysis and electron paramagnetic resonance measurement. In addition, the high selectivity of FONs towards Cu2+ ions over other potential cations and the 2 : 1 (1-Cu2+) binding stoichiometry were also determined. Moreover, the spectroscopic behavior of the monomeric amphiphilic probe was well supported by extensive DFT study. Such detection of Cu2+ ions in pure aqueous medium denoting an aggregation-disaggregation event is very rare in the literature.

Oxidized Bisindolyl-Based Amphiphilic Probe for Dual Mode Analysis of Heavy Metal Pollutants in Aqueous Medium

The oxidized bisindolyl-based amphiphilic, chromogenic probe has been synthesized that can form nanoscopic aggregates in the aqueous medium. Along with solvent polarity and pH of the medium, it was observed that the addition of heavy metal pollutants, like Hg2+ can cause significant alteration in the charge transfer state. This resulted in the immediate change in the solution color from yellow to orange. Additionally, we could excite either the monomer species or the aggregates of the probe by choosing the proper excitation wavelength. Upon exciting at 390 nm, the compound exhibited a broad fluorescence spectrum with maxima at 450 nm, presumably due to twisted state charge transfer. On the contrary, the aggregated species (λex = 465 nm) displayed a comparatively weaker fluorescence band centered at 565 nm. Interestingly, the fluorescence intensity at the 450 nm band experience fluorescence quenching in the presence of Hg2+ ion, while the aggregate emission band remained unaffected. Finally, the present system was utilized for detection of mercury ions in natural water samples.

A fluorescent Salamo-Salen-Salamo-Zn(II) sensor for bioimaging and biosensing H2PO4- in Zebrafish and plants

A newly designed and synthesized Salamo-Salen-Salamo-Zn(II) complex sensor (sensor ZT) was extensively explored for anion sensing studies. The selectivity and sensitivity of the sensor ZT towards H2PO4- ions were based on ICT and CHEF effects, and via displacement pathways in DMSO/H2O (9:1, v/v) medium in the presence of other anions like, PO43-, HPO42- and P2O74- in a short time, separately. The prepared ZT sensor has excellent association constant and low detection lines. The sensing mechanism and binding mode of the sensor were studied by UV-Vis spectroscopy, HR-MS, 1H NMR titration and theory calculations (DFT & TD-DFT) for analytes. The time response and stability of the sensor are also given. Meanwhile, the sensor ZT can be widely used as a simple and effective solid-state optical sensor to detect H2PO4- by intuitive fluorescence changes. In addition, besides the environment can be used as a powerful instrument for detecting H2PO4-, based on the good biocompatibility and tissue permeability of ZT, effectively monitoring H2PO4- in cellular distribution by confocal microscopy using Zebrafish and bean sprout.

Sequence-Specific Relay Recognition of Multiple Anions: An Interplay between Proton Donors and Acceptors

Ratiometric detection of analyte is highly deserving since the technique is free from background correction. This work reports the design and synthesis of a pyridine-end oligo p-phenylenevinylene (OPV) derivative, 1 and its application in ratiometric dual-mode (both colorimetric and fluorogenic) recognition of dual anions, bisulfate (LOD=12.5 ppb) followed by fluoride (LOD=18.2 ppb) by sequence-specific relay (SPR) technique. The colorless probe turns brown with addition of bisulfate and again becomes colorless with the sequential addition of fluoride ion. In addition to such naked-eye color change, interestingly the ratiometric spectroscopic signals are reversible and evidently, the probe is reusable for several cycles. Besides, in presence of bisulfate, the protonated probe molecules, owing to their larger amphiphilic characteristics, formed self-assembled nanostructures. In addition to colorimetric and fluorescent changes, 1 H NMR titration and systematic DFT study evidently establish the underneath proton transfer mechanisms. Such reusable OPV-based chemosensor particularly with the capability of naked-eye recognition of dual anions using the SPR technique is seminal and possibly the first report in the literature.