Luminescent chemosensors for transition metal ions

Uncovering the sensing mechanism of a zinc ion sensor: Fluorescence enhancement induced by the elimination of the TICT state

Precise detection of zinc ion is of fundamental importance in the fields of environment protection and food safety. A comprehensive understanding of the sensing mechanism will help to the design of such sensors. The detailed photophysical process of a zinc ion sensor as well as the sensing mechanism are uncovered with the aid of density functional theory (DFT) and time-dependent density functional theory (TDDFT). Both the ground state and first excited state potential energy surfaces (PES) of the sensor are carefully explored to reveal the photo-physical process of the sensor. Excited state intramolecular proton transfer (ESIPT) is observed on the S1 state PES. Then, the twist motion of C=N double bond is triggered after the ESIPT process, which leads to a twisted intramolecular charge transfer (TICT) state. This TICT state is found to make the sensor non-emissive. With the addition of Zn2+, the TICT state is eliminated which greatly enhances the fluorescence of the sensor and achieves zinc ion detection. The interaction of the sensor with Cd2+ and Hg2+ are also explored, which well explains the good selectivity of the sensor.

A Review on Recent Development of Phenothiazine-Based Chromogenic and Fluorogenic Sensors for the Detection of Cations, Anions, and Neutral Analytes

This review provides an in-depth examination of recent progress in the development of chemosensors, with a particular emphasis on colorimetric and fluorescent probes. It systematically explores various sensing mechanisms, including metal-to-ligand charge transfer (MLCT), ligand-to-metal charge transfer (LMCT), photoinduced electron transfer (PET), intramolecular charge transfer (ICT), and fluorescence resonance energy transfer (FRET), and elucidates the mechanism of action for cation and anion chemosensors. Special attention is given to phenothiazine-based fluorescence probes, highlighting their exceptional sensitivity and rapid detection abilities for a broad spectrum of analytes, including cations, anions, and small molecules. Phenothiazine chemosensors have emerged as versatile tools widely employed in a multitude of applications, spanning environmental and biomedical fields. Furthermore, it addresses existing challenges and offers insights into future research directions, aiming to facilitate the continued advancement of phenothiazine-based fluorescent probes.

Repurposing an antimicrobial peptide for the development of a dual ion channel/molecular receptor-like platform for metal ion detection

The presence of non-essential metals in the environment as contaminants is prone to cause hazardous health problems following accumulation in the human body and the ensuing toxic effects. This calls for continuous discovery and innovation in the realm of developing easy-to-operate, cheap and sensitive sensors. Herein, we describe the proof of concept approach for designing a molecular receptor-like, chimeric sensor based on the pore-forming peptide alamethicin (Alm), tethered via a linker with an ultrashort peptide nucleic acid (PNA) moiety, capable of generating functional ion channel oligomers in planar lipid membranes. The working principle of the sensor exploits the ability of Hg2+ ions to complex mismatching thymine-thymine sequences between the PNA receptor moiety on Alm oligomers and free, thymine-based, single-stranded DNAs (ssDNAs) in solution, thus creating a stable base pair at the oligomer entrance. This generates a transducing mechanism which converts the metal ion complexation into a specific electrical signature of the self-assembled Alm oligomers, enabling selective Hg2+ ion detection. The platform is programmable, whereby the simple exchange of the PNA sequence and its ssDNA counterpart in solution rendered the system selective for Cu2+ ion detection. With further optimization, the presented solution has the potential to translate into miniaturized, cost-effective biosensors suitable for the real-time, label-free and continuous detection of metal ions or other biomolecules.

Recent applications of coinage metal nanoparticles passivated with salicylaldehyde and salicylaldehyde-based Schiff bases

Salicylaldehyde (SD) and its derivatives are effective precursors for generating coinage metal (gold, silver, and copper) nanoparticles (NPs). These NPs have a variety of potential environmental applications, such as in water purification and sensing, and those arising from their antibacterial activity. The use of SD and its derivatives for synthesizing coinage NPs is attractive due to several factors. First, SD is a relatively inexpensive and readily available starting material. Second, the synthetic procedures are typically simple and can be carried out under mild conditions. Finally, the resulting NPs can be tailored to have specific properties, such as size, shape, and surface functionality, by varying the reaction conditions. In an alkaline solution, the phenolate form of SD was converted to its quinone form, while ionic coinage metal salts were converted to zero-valent nanoparticles. The capping in situ produced quinone of coinage metal nanoparticles generated metal-enhanced fluorescence under suitable experimental conditions. The formation of iminic bonds during the formation of Schiff bases altered the properties (especially metal-enhanced fluorescence) and applications.

Role of silver nanoparticles and silver nanoclusters for the detection and removal of Hg(ii)

Silver metal, being a 3d transition metal in group 11 in the periodic table, is widely used in material science for its distinguished plasmonic properties. Nanoparticles (NPs) and nanoclusters (NCs) are widely used in sensing applications having a surface plasmon band and emissive properties, respectively. Mercury is one of the detrimental toxins and threats to various ecosystems. The distinction between nanoparticles and nanoclusters, the utility and toxicity of heavy metal mercury, fluorometric and colorimetric approaches to the recognition of mercury ions with NPs and NCs, the mechanism of detection, spot detection, and natural water sample analyses were illustrated in detail in this review article. Moreover, the sensing platform and analyte (Hg2+) fate were described for substantiating the mechanism. It was observed that NCs are mostly utilized for fluorometric approaches, while NPs are mostly employed for colorimetric approaches. Fluorometric detection is mainly quenching-based. However, sensing with enhancement was found in a few reports. Adulteration of other metals with silver particles often modifies the sensing platform.

Synthesis of Cu (II) and Zn (II) Complexes of a Quinoline Based Flexible Amide Receptor as Fluorescent Probe for Dihydrogen Phosphate and Hydrogen Sulphate and Their Antibacterial Activity

A novel 8-hydroxy quinoline-derived amide receptor, in conjunction with its Cu (II) and Zn (II) complexes, has been strategically developed to function as remarkably efficient fluorescent receptors with a distinct capability for anion sensing. The comprehensive characterization of the synthesized compounds were achieved through UV-Vis, IR, NMR, and HRMS spectroscopic techniques. Among the Cu (II) and Zn (II) complexes, the latter exhibits superior selectivity for anions, specifically dihydrogen phosphate and hydrogen sulfate, as their tetrabutylammonium salts in a 9:1 acetonitrile-water (v/v) mixture. The Cu (II) complex demonstrates enhanced anion binding compared to the amide ligand, albeit with reduced selectivity. Furthermore, the affinity was evaluated using the Benesi-Hildebrand plot. The binding constants and Limit of Detection (LOD) for both complexes were precisely quantified. The Job plot illustrates a clear 1:1 binding interaction between the metal complexes and the guest anions. Significantly, both metal-complex receptors display a broad spectrum of antibacterial activity, against both gram-positive and gram-negative bacteria. It is worth highlighting that the Zn (II) complexed receptor outperforms the Cu (II) complexed receptor, as evidenced by its considerably lower Minimum Inhibitory Concentration (MIC) value against both bacterial strains.

Luminescent Silicon Nanocrystals as Metal Ion Sensors

At relatively low concentrations in aqueous solution, Fe3+, Fe2+, Cu2+, and Ni2+ quench the photoluminescence (PL) of the undecenoic acid-capped silicon (Si) nanocrystals. The PL could be restored by adding a chelating agent, such as ethylenediaminetetraacetic acid (EDTA), to remove the ions. Fe3+ and Cu2+ also significantly increase the PL lifetime. Other metal ions, including Cd2+, Mn2+, Pb2+, Zn2+, In3+, K+, and Ca2+, had no effect on the Si nanocrystal PL. The limits of detection (LODs) for Fe3+ and Cu2+ of 370 and 150 nM, respectively, are low enough for metal ion sensing applications.

A Review on Small Organic Colorimetric and Fluorescent Hosts for the Detection of Cobalt and Nickel Ion

In recent years, there has been a notable increase in efforts to advance efficient hosts for detecting cobalt and nickel ions, driven by their extensive industrial applications and environmental significance. This review meticulously examines the progress made in small organic colorimetric and fluorescent hosts tailored specifically for the sensitive and selective detection of cobalt and nickel ions. It delves into a diverse range of molecular architectures, including organic ligands, elucidating their unique attributes such as sensitivity, selectivity, and response time. Moreover, the review precisely explores the underlying principles governing the colorimetric and fluorescent mechanisms employed by these hosts, shedding light on the intricate interactions between the sensing moieties and the target metal ions. Furthermore, it critically evaluates the practical applicability of these hosts, considering crucial factors such as detection limits, recyclability, and compatibility with complex sample matrices. Additionally, exploration extends to potential challenges and prospects in the field, emphasizing the imperative for ongoing innovation to address emerging environmental and analytical demands. Eventually, through this comprehensive examination, the review seeks to contribute to the ongoing endeavor to develop robust and efficient tools for monitoring and detecting cobalt and nickel metal ions in diverse analytical scenarios.

An Indole-based Chromofluorogenic Probe for Detection of Trivalent Al3+, Ga3+, In3+ and Fe3+ Ions

An easily synthesizable indole-derived chromofluorogenic probe InNS has been demonstrated for recognition of trivalent metal ions (i. e., Al3+, Ga3+, In3+ and Fe3+). Both UV-Vis and emission spectral studies have been employed to assess the cation sensing ability of InNS in semi-aqueous medium. This probe exhibited a chromogenic response for these metal ions, and the related change was accompanied with the appearance of a new absorption near 376 nm. An obvious color change from pale yellow to dark yellow could also be noticed upon addition of the aforementioned metal ions to the probe's solution. Distinctively from the UV-Vis analysis, the fluorescence behavior of InNS was completely different; it displayed a 'turn-on' fluorescence response for only Al3+ among all the studied cations. The detection limit and the association constant (Ka) for Al3+ were determined to be 12.5 nM and 6.85×106 M-1, respectively. A potential 1 : 1 binding mode of Al3+-InNS has been established based on Job's plot, 1H NMR and DFT analyses. The reversibility experiment was conducted using strongly chelating EDTA ion, and a corresponding logic gate has been devised. In terms of practical applications, the InNS has been utilized to detect Al3+ in human breast carcinoma (MCF-7) cell lines displaying promising 'turn-on' bioimaging experiments.

Chromene Carbohydrazide- Schiff Base as a Highly Selective Turn-Off Fluorescence Chemosensor for In3+ Ion and its Application

A new 7-(diethylamino)-2-oxo-2 H-chromene-3-carbohydrazide design to synthesize a simple Schiff-base condition. The synthesized molecules' (probe L) photophysical properties were investigated in various solvent systems and solvent-poor-solvent assays. Probe L exhibits the absorbance band at 440 nm and the emission band at 488 nm in DMSO: H2O (7:3, v/v). Further, probe L shows selective turn-off emission recognition of In3+ ions in DMSO: H2O (7:3, pH = 7.4). By Job's plot and ESI mass analysis, probe L forms a 1:2 stoichiometry complex with an estimated association constant of 4.04 × 104 M- 2 with In3+ ions. Metal induces CHEQ (chelation-caused fluorescence quenching) to reduce the intensity of probe L's emission, and the estimated quenching constant was 4.52 × 104 M- 1. The limit of detection was found to be 5.93 nM; the time response of the sensor is instantaneous, and its reversible nature was confirmed using EDTA additions. Solid substrates (test strips) were designed and tested for fast, reliable, user-friendly, and real-time sensing of In3+ ions for on-site applications. The binding mechanism of probe L with In3+ ions was investigated using 1H NMR titration and DFT/TD-DFT studies.

Chalcone-based Turn-Off Chemosensor for Selective and Susceptible Detection of Fe2+ Ions: Spectroscopic and DFT Investigations

Herein, in this report we are introducing newly synthesized chalcone derivative, "(E)-1-phenyl-3-(4-((5-(((Z)-thiophen-2-ylmethylene)amino)-1,3,4-thiadiazol-2-yl)thio)phenyl)prop-2-en-1-one" (5), as a chemosensor to detect Fe2+ metal ions in HEPES buffer solution of pH 7.5. Spectroscopic techniques were used to confirm the synthesized sensor. To determine the chemical reactivity and molecular stability of the probe, a frontier molecular orbitals investigation was carried out. A molecular electrostatic potential map was investigated to know the binding site of 5 for metal ion coordination. The theoretical absorption and fluorescence emission properties were estimated and correlated with the experimental observations. The sensor showed excellent selectivity for Fe2+ compared to all other studied metal ions. The fluorescence binding studies were carried out by adding different amounts of Fe2+ ions for a fixed concentration of probe 5. The inclusion of Fe2+ ions resulted in a decrease in fluorescence intensity with a bathochromic shift of emission wavelength of 5 due to the 5-Fe2+ complexation. The binding affinity value for the probe was found to be 576.2 M-1 with the help of the Stern-Volmer plot. The Job's plot and mass spectra supported the 2:1 (5: Fe2+) stoichiometry of complex formation. The detection limit and limit of quantification of 5 for Fe2+ were calculated to be 4.79 × 10-5 M and 14.54 × 10-5 M. Further, in addition to this, the photophysical parameters such as fluorescence lifetime of 5 and 5-Fe2+ complex measured to be 0.1439 and 0.1574 ns. The quantum yield of 5 and 5-Fe2+ was found to be 0.0398 and 0.0376. All these experimental findings revealed that probe 5 has excellent selectivity and sensitivity for Fe2+ ions.

A Naphthoquinoline-Dione-Based Cu2+ Sensing Probe with Visible Color Change and Fluorescence Quenching in an Aqueous Organic Solution

Copper metal ions (Cu2+) are widely used in various industries, and their salts are used as supplementary components in agriculture and medicine. As this metal ion is associated with various health issues, it is necessary to detect and monitor it in environmental and biological samples. In the present report, we synthesized a naphthoquinoline-dione-based probe 1 containing three ester groups to investigate its ability to detect metal ions in an aqueous solution. Among various metal ions, probe 1 showed a vivid color change from yellow to colorless in the presence of Cu2+, as observed by the naked eye. The ratiometric method using the absorbance ratio (A413/A476) resulted in a limit of detection (LOD) of 1 µM for Cu2+. In addition, the intense yellow-green fluorescence was quenched upon the addition of Cu2+, resulting in a calculated LOD of 5 nM. Thus, probe 1 has the potential for dual response toward Cu2+ detection through color change and fluorescence quenching. 1H-NMR investigation and density functional theory (DFT) calculations indicate 1:1 binding of the metal ion to the small cavity of the probe comprising four functional groups: the carbonyl group of the amide (O), the amino group (N), and two t-butyl ester groups (O). When adsorbed onto various solid surfaces, such as cotton, silica, and filter paper, the probe showed effective detection of Cu2+ via fluorescence quenching. Probe 1 was also useful for Cu2+ sensing in environmental samples (sea and drain water) and biological samples (live HeLa cells).

Nanoarchitectonics of highly dispersed polythiophene on paper for accurate quantitative detection of metal ions

π-Conjugated polymers such as polythiophene provide intramolecular wire effects upon analyte capture, which contribute to sensitive detection in chemical sensing. However, inherent aggregation-induced quenching causes difficulty in fluorescent chemical sensing in the solid state. Herein, we propose a solid-state fluorescent chemosensor array device made of a paper substrate (PCSAD) for the qualitative and quantitative detection of metal ions. A polythiophene derivative modified by dipicolylamine moieties (1poly), which shows optical changes upon the addition of target metal ions (i.e., Cu2+, Cd2+, Ni2+, Co2+, Pb2+, Zn2+, and Hg2+), was highly dispersed on the paper substrate using office apparatus. In this regard, morphological observation of the PCSAD after printing of 1poly suggested the contribution of the fiber structures of the paper substrate to the homogeneous dispersion of 1poly ink to suppress aggregation-induced quenching. The optical changes in the PCSAD upon the addition of metal ions was rapidly recorded using a smartphone, which was further applied to imaging analysis and pattern recognition techniques for high-throughput sensing. Indeed, the printed PCSAD embedded with 1poly achieved the accurate detection of metal ions at ppm levels contained in river water. The limit of detection of the PCSAD-based sensing system using a smartphone (48 ppb for Cu2+ ions) is comparable to that of a solution-based sensing system using a stationary spectrophotometer (16 ppb for Cu2+ ions). Therefore, the methodology based on a combination of a paper-based sensor array and a π-conjugated polymer will be a promising approach for solid-state fluorescent chemosensors.

Design of molecular sensors and switches based on luminescent ruthenium-terpyridine complexes bearing active methylene and triphenylphosphonium motifs as anion recognition sites: experimental and DFT/TD-DFT investigation

Synthesis, characterization and thorough investigation of the photophysical and electrochemical properties of a new category of emissive homo- and heteroleptic Ru(II)-complexes derived from the [4'-(p-triphenylphosphonium methyl phenyl)-2,2':6',2''-terpyridine]bromide (tpy-PhCH2PPh3Br) ligand have been executed in this work. Incorporation of the PhCH2PPh3+Br- group at the terpyridine motif appropriately adjusts the triplet metal-to-ligand charge transfer (3MLCT) and metal-centered (3MC) excited states so that the complexes luminesce at room temperature (RT) having lifetimes within the range of 6.82-9.63 ns. The RT emission characteristics of the complexes get further enhanced via aggregation phenomena through the use of different solvent/non-solvent mixtures (DMSO/H2O and DMSO/PhCH3 mixtures). Temperature dependent emission spectral measurements indicate that the emission intensity, quantum yield and lifetime increase upon dropping down the temperature, thereby designated as the on-state, while the increase of temperature causes a reduction of the said properties, indicating the off-state and the process is fully reversible. Taking advantage of the active methylene group coupled with a phosphonium motif, anion sensing characteristics of the complexes are investigated systematically in DMSO through the use of various optical channels and spectroscopic tools. The complexes are very much sensitive to fluoride and to a lesser extent acetate and dihydrogen phosphate among the studied anions. In essence, the complexes function as sensors for temperature and fluoride ion. Computational investigations were also executed via density functional theory (DFT) and time-dependent (TD)-DFT to obtain a clear understanding of the electronic structures of the metalloreceptors, appropriate assignment of the spectral bands and their mode of interaction with selected anions.

Pyrene Appendant Triazole-based Chemosensors for Sensing Applications

Over the last two decades, the design and development of fluorescent chemosensors for the targeted detection of Heavy Transition-metal (HTM) ions, anions, and biological analytes, have drawn much interest. Since the introduction of click chemistry in 2001, triazole moieties have become an increasingly prominent theme in chemosensors. Triazoles generated via click reactions are crucial for sensing various ions and biological analytes. Recently, the number of studies in the field of pyrene appendant triazole moieties has risen dramatically, with more sophisticated and reliable triazole-containing chemosensors for various analytes of interest described. This tutorial review provides a general overview of pyrene appendant-triazole-based chemosensors that can detect a variety of metal cations, anions, and neutral analytes by using modular click-derived triazoles.

An aggregation-induced emission-based ratiometric fluorescent chemosensor for Hg(II) and its application in Caenorhabditis elegans imaging

A chromone-based ratiometric fluorescent probe L2 was developed for the selective detection of Hg(II) in a semi-aqueous solution based on aggregation-induced emission (AIE) and chelation-enhanced fluorescence (CHEF) effect. The probe L2 fluoresced significantly at 498 nm in its aggregated state, and when chelated with Hg(II), the soluble state fluoresced 1-fold higher. In addition, Job's plot reveals that the probe forms a 1:1 stoichiometry complex with Hg(II) with an association constant of 9.10 × 103M-1 estimated by the BH plot. The probe L2 detects Hg(II) down to 22.47 nM without interference from other interfering ions. The FTIR, ESI mass, and DFT-based computational studies investigated the binding mechanism of probe L2 with Hg(II). Taking advantage of its AIE characteristics, the probe L2 was successfully applied for bio-capability analysis in Caenorhabditis elegans (a nematode worm) imaging of Hg(II) in a living model.

A terpyridyl-rhodamine hybrid fluorescent probe for discriminative sensing of Hg (II) and Cu (II) in water and applications for molecular logic gate and cell imaging

Sensitive and discriminative sensing of more than one analyte with a single fluorescent probe is significant and challenging. Herein a new terpyridyl-rhodamine hybrid, namely TRH, has been rationally designed and prepared with two responsive groups in the molecular structure, which facilitate the discriminative detection of Hg2+ and Cu2+ ions in water with detection limits of 4.9 and 53.3 nM by ratiometric fluorescence change (F595/F485) and fluorescence quenching, respectively. Investigations show that the selectivity to Hg2+ ions can be attributed to Hg2+-promoted spirolactam ring opening and further hydrolysis, followed by a through-bond energy transfer (TBET) process. The selective fluorescence quenching to Cu2+ ions probably can be ascribed to the binding Cu2+ to terpyridyl that triggers a ligand-to-metal charge transfer (LMCT) process, which can also efficiently inhibit the TBET process induced by Hg2+ ions and promotes the discriminative sensing of Cu (II) and Hg (II). In addition, the fluorescent responses to Hg2+ and Cu2+ ions cover a wide pH range. Moreover, a combinatorial logic gate with the functions of NOR and INHIBIT has been fabricated by using Hg2+ and Cu2+ ions as chemical input signals, and fluorescence at 485 and 595 nm as output signals. Besides, TRH also exhibits sensitive and discriminative sensing ability to Hg2+ and Cu2+ ions by the fluorescence of rhodamine fluorophore. Significantly, based on the fluorescence signal output of rhodamine moiety, TRH can be used as a tracer for the discriminative sensing of Hg2+ and Cu2+ ions by using living cells.

Development of a Ratiometric Fluorescent Cu(II) Indicator Based on Poly(N-isopropylacrylamide) Thermal Phase Transition and an Aminopyridyl Cu(II) Ligand

An aqueous Cu2+ and Zn2+ indicator is reported based on copolymerizing aminopyridine ligands and the environment-sensitive dansyl fluorophore into the responsive polymer poly(N-isopropylacrylamide) (PNIPAm). The metal ion binding creates charge and solvation that triggers PNIPAm's thermal phase transition from hydrophobic globule to hydrophilic open coil. As a basis for sensing the metal-binding, the dansyl fluorescence emission spectra provide a signal at ca. 530 nm and a signal at 500 nm for the hydrophobic and hydrophilic environment, respectively, that are ratiometrically interpreted. The synthesis of the title pyridylethyl-pyridylmethyl-amine ligand (acronym PEPMA) with a 3-carbon linker to the copolymerizable group, aminopropylacrylamide (PEPMA-C3-acrylamide), is reported, along with a nonpolymerizable model ligand derivative. The response of the polymer is validated by increasing temperature from 25 °C to 49 °C, which causes a shift in maximum emission wavelength from 536 nm to 505 nm, along with an increase in the ratio of emission intensity of 505 nm/536 nm from 0.77 to 1.22 (λex = 330 nm) as the polymer releases water. The addition of divalent Cu or Zn to the indicator resulted in a dansyl emission shift of 10 nm to a longer wavelength, accompanied by fluorescence quenching in the case of Cu2+. The addition of EDTA to the Cu2+-loaded indicator reversed the fluorescence shift at 25 °C to 35 °C. The affinities of Cu2+ and Zn2+ for the PEPMA derivatives are log Kf = 11.85 and log Kf = 5.67, respectively, as determined by potentiometric titration. The single-crystal X-ray structure of the Cu2+-PEPMA derivative is five-coordinate, of-geometry intermediate between square-pyramidal and trigonal-bipyramidal, and is comparable to that of Cu2+ complexes with similar formation constants.

A Novel Photoluminescent Ag/Cu Cluster Exhibits a Chromic Photoluminescence Response towards Volatile Organic Vapors

A new Ag/Cu bimetallic cluster [Ag₁₀Cu₆(bdppthi)₂(C≡CPh)₁₂(EtOH)₂](ClO₄)₄ (1, bdppthi = N,N'-bis(diphenylphosphanylmethyl)-tetrahydroimidazole) exhibited strong phosphorescent (PL) emission at 644 nm upon excitation at 400 nm. Removal of the coordinated EtOH molecules in 1 resulted in derivative 1a, which exhibited significant red-shifted emission at 678 nm. The structure and PL of 1 was restored on exposure to EtOH vapor. Cluster 1a also exhibited a vapor-chromic PL response towards other common organic solvent vapors including acetone, MeOH and MeCN. A PMMA film of 1a was developed as a reusable visible sensor for MeCN.

Multifunctional nanomaterials and nanocomposites for sensing and monitoring of environmentally hazardous heavy metal contaminants

The applications of conventional sensors are limited by the long response time, high cost, large detection limit, low sensitivity, complicated usage and low selectivity. These sensors are nowadays replaced by Nanocomposite-based modalities and nanomaterials which are known for their high selectivity and physical and chemical properties. These nanosensors effectively detect heavy metal contaminants in the environment as the discharge of heavy metals into natural water as a result of human activity has become a global epidemic. Exposure to these toxic metals might induce many health-related complications, including kidney failure, brain injury, immune disorders, muscle paleness, cardiac damage, nervous system impairment and limb paralysis. Therefore, designing and developing novel sensing systems for the detection and recognition of these harmful metals in various environmental matrices, particularly water, is of extremely important. Emerging nanotechnological approaches in the past two decades have played a key role in overcoming environmentally-related problems. Nanomaterial-based fabrication of chemical nanosensors has widely been applied as a powerful analytical tool for sensing heavy metals. Portability, high sensitivity, on-site detection capability, better device performance and selectivity are all advantages of these nanosensors. The detection and selectivity have been improved using molecular recognition probes for selective binding on different nanostructures. This study aims to evaluate the sensing properties of various nanomaterials such as metal-organic frameworks, fluorescent materials, metal-based nanoparticles, carbon-based nanomaterials and quantum dots and graphene-based nanomaterials and quantum dots for heavy metal ions recognition. All these nano-architectures are frequently served as effective fluorescence probes to directly (or by modification with some large or small biomolecules) sense heavy metal ions for improved selectivity. However, efforts are still needed for the simultaneous designing of multiple metal ion-based detection systems, exclusively in colorimetric or optical fluorescence nanosensors for heavy metal cations.

Argentivorous molecules with chromophores: dependence of their fluorescence intensities on the distance between a donor and an acceptor

We have prepared new argentivorous molecules (L2 and L3) having different linker lengths between cyclen and anthracene units. The structures of Ag⁺ complexes with the new ligands were investigated in solution and solid states. The silver(I) ion-induced ¹H NMR and UV-vis spectral changes of L2 and L3 showed the presence of 1 : 1 complexes. The solid-state structures of the Ag⁺ complexes with L2 and L3 are stable 1 : 1 complexes because four aromatic side-arms wrap the Ag⁺ incorporated in the cyclen unit. A photo-induced electron transfer (PET) effect that depends on the length of the linker connecting the nitrogen atoms of cyclen to the chromophore is also investigated. The result indicates a linear (log) correlation between the donor-chromophore average distances of the optimized structures calculated by DFT calculations and fluorescence intensities (log I), and the PET effect becomes ineffective at about 12 Å in this system.

Fashionable Co-operative Sensing of Bivalent Zn2+ and Cd2+ in Attendance of OAc- by Use of Simple Sensor: Exploration of Molecular Logic Gate and Docking Studies

The Schiff-base probe H₂VL [6,6'-((1E,1'E)-hydrazine-1,2 diylidenebis(methanylylidene))bis(2-methoxyphenol)] is synthesized and structurally characterized by single crystal X-ray diffraction (SCXRD). H₂VL is able to detect selectively acetate ion (OAc-) colorimetrically over other anions with 1:1 co-ordination. The detection limit is found to be 4.93 µM. On the other hand, fluorescence intensity of the receptor is drastically enhanced with Zn²⁺ and Cd²⁺ in the presence of acetate as counter anion. N, N-Dimethyl formamide (DMF) or Dimethylsulphoxide (DMSO) and acetate (OAc-) was the best solvent and counter anion for Zn²⁺/Cd²⁺ -sensing compared with other solvents and anions, respectively. Detection limit for Zn²⁺ and Cd²⁺ are calculated to be 1.94 µM and 1.99 µM, respectively. The strong selective emissive behavior could be attributed to the CHEF (chelation-enhanced fluorescence) process. According to the changes in output emission intensity in DMSO in response to the set of ions (Zn²⁺, Cd²⁺ and OAc¯) as input variables, the function of 3-input multifunctional molecular logic circuits has been demonstrated. The molecular docking studies of H₂VL with DNA and BSA are also performed to confirm its possible bioactivity.

Recent Development in Coordination Compounds as a Sensor for Cyanide Ions in Biological and Environmental Segments

Rapid detection of toxic ions has taken great attention in the last few decades due to its importance in maintaining a greener environment for human beings. The extreme toxicity of cyanide (CN-) ions is a great environmental concern as its continued industrial use generates interest in facile and sensitive methods for CN- ions detection. Since CN- ions act as a ligand in coordination chemistry which rapidly coordinates with suitable metals and forms complexes, this ability was mainly explored in its detection. It also attacks the central metal in coordination compounds and gives a fluorimetric response. Coordination compounds behave as a sensor for the detection of important ions like CN- ions and have gained great attention due to their facile synthesis, multianalyte detection, clear detection and low detection limit. Recently, considerable efforts have been devoted to the detection and quantification of hazardous multianalyte using a single probe. Cu2+ complexes are the main complexes used for CN- ions detection; however, the complexes of many other metals are also used as sensors. Four basic types of interaction have been discussed in coordination compound sensors for CN- detection. The performances of different sensors are compared with one another and the sensors which have the lowest detection limit are highlighted. This review comprises the progress made by coordination compounds as sensors for the detection of CN- ions in the last six years (2015-2021). To the best of our knowledge, there is no review on coordination compounds as a sensor for CN- ions during this period. [Figure: see text].

A ratiometric fluorescence probe for imaging endoplasmic reticulum (ER) hypochlorous acid in living cells undergoing excited state intramolecular proton transfer

Hypochlorous acid (HOCl), one of the most important ROS in living organisms, appears to serve an important role in the immune system in vivo. Endoplasmic reticulum (ER), the largest organelle in cells, manages many biological processes connected to vital activities. To better obtain insight into the relationship of ER stress and HOCl level, a ratiometric fluorescent probe RHE, based on rhodamine combined with HBT and ER-targeting group, was designed and synthesized for HOCl detection in the ER. Probe RHE shows a large stokes shift about 155 nm, which is derived to ESIPT principle. In addition, probe RHE exhibited excellent properties such as fast response (<80 s), high sensitivity with a low detection limit (40 nM), high selectivity and anti-interference. Moreover, probe RHE displayed an excellent ER-targeting ability and had been successfully applied for detection of exogenous and endogenous HOCl in HepG2 cells.

Synthesis of SBA-Pr-NHC as a selective fluorescent sensor for the detection of Ag+ ion in aqueous media

SBA-Pr-NHC as a novel silica-based chemosensor was synthesized through the functionalization of mesoporous silica SBA-15 material with 4-hydroxy-2-oxo-2H-chromene-3-carbaldehyde, which was successfully immobilized to the surface of mesoporous silica, and its hexagonal mesoporous structure has been preserved. Photoluminescence spectroscopy was applied to study the sensing behavior of SBA-Pr-NHC, which displayed high selectivity for sensing Ag⁺ ion in aqueous media. After the addition of trace amounts of Ag⁺ ions into the aqueous solution, a significant enhancement of fluorescence emission has occurred with the detection limits of 2.4 × 10^-5 M.

Are luminescent Ru2+ chelated complexes selective coordinative sensors for the detection of heavy cations?

The ability of [Ru(bpy)₂(bpym)]²⁺ (bpy = 2,2'-bipyridine; bpym = 2,2'-bipyrimidine) to probe specifically heavy cations has been investigated by means of density functional theory for transition metals, group 12 elements and Pb²⁺. On the basis of the calculated Gibbs free energies of complexation in water it is shown that all reactions are favorable with negative enthalpies except for Hg²⁺, with the transition metal cations forming stable bi-metallic complexes by coordination to the bpym ligand. Comparison between the optical and photophysical properties of the Ru²⁺ probe and those of the coordination compounds does not demonstrate a high selectivity due to very similar characteristics of the absorption and emission spectra. Whereas by complexation the lowest metal-to-ligand-charge-transfer (MLCT) shoulder of [Ru(bpy)₂(bpym)]²⁺ at 462 nm is more or less shifted to the red as a function of the cation, the second MLCT band at 415 nm, less sensitive to the complexation, gains in intensity and is slightly blue-shifted. The visible MLCT emission of [Ru(bpy)₂(bpym)]²⁺ at 706 nm is altered by complexation leading to near IR (800-900 nm) emission in most of the coordination compounds. Complexation to some transition metal cations (Fe, Co, Rh and Pd) generates low-lying metal-centered (MC) excited states that quench luminescence. In contrast to the conclusion of experimental findings by Kumar et al. (Chem. Commun. 2014, 50, 8488-8490), [Ru(bpy)₂(bpym)]²⁺ cannot be proposed as a fast and selective probe for monitoring Pd²⁺ in aqueous media. Indeed, it does not possess the optical and photophysical characteristics necessary to discriminate Pd²⁺ ions over a variety of other cations.

A Chromo-Fluorogenic Naphthoquinolinedione-Based Probe for Dual Detection of Cu2+ and Its Use for Various Water Samples

The presence of an abnormal amount of Cu²⁺ in the human body causes various health issues. In the current study, we synthesized a new naphthoquinolinedione-based probe (probe 1) to monitor Cu²⁺ in different water systems, such as tap water, lakes, and drain water. Two triazole units were introduced into the probe via a click reaction to increase the binding affinity to a metal ion. In day-light, probe 1 dissolved in a mixed solvent system (HEPES: EtOH = 1:4) showed a vivid color change from light greenish-yellow to pink in the presence of only Cu²⁺ among various metal ions. In addition, the green luminescence and fluorescence emission of the probe were effectively bleached out immediately after Cu²⁺ addition. The limit of detection (LOD) of the probe was 0.5 µM when a ratio-metric method was used for metal ion detection. The fluorescence titration data of the probe with Cu²⁺ showed a calculated LOD of 41.5 pM. Hence, probe 1 possesses the following dual response toward Cu²⁺ detection: color change and fluorescence quenching. Probe 1 was also useful for detecting Cu²⁺ spiked in tap/lake water as well as the cytoplasm of live HeLa cells. The current system was investigated using ultraviolet-visible and fluorescence spectroscopy as well as density functional theory calculations (DFT).

Theoretical Investigations on the Detecting Mechanism of a Typical 2,4,6-Trinitrophenol Fluorescence Sensor and Its Design Strategy

Fluorescence sensors based on small organic molecules are drawing increasing attention. In this contribution, the underlying detection mechanism of a typical fluorescence sensor for 2,4,6-trinitrophenol (TNP) based on fluorescence quenching is comprehensively investigated. The TNP molecule is proved to plant an intermolecular electron transfer state (dark state) below the bright state. Strong π-π interaction is observed between the sensor and TNP, which provides considerable orbital overlaps between the sensor and analyte. Electron transfer from the sensor to analyte is facilitated by such a strong interaction, which quenches the sensor's fluorescence. The design strategy for such TNP sensors is proposed based on the detection mechanism, and a series of new sensors is designed, which is likely to have better sensitivity than the original sensor.

Ni (II) detection by 2-amino-5-substituted-1,3,4-oxadiazole as a chemosensor using photo-physical method: Antifungal, antioxidant, DNA binding, and molecular docking studies

An oxadiazole derivative 2 was prepared by condensation reaction through cyclization of semicarbazone in the presence of bromine and the structural confirmation was supported by ¹ H and ¹³ C NMR, FT-IR spectroscopy, and LC-MS spectrometry. Its sensing ability was examined towards Ni²⁺ ion with binding constant 1.04 x 10⁵ over the other suitable metal cations (Ca²⁺ , Co²⁺ , Cr³⁺ , Ag⁺ , Pb²⁺ , Fe³⁺ , Mg²⁺ , and K⁺ ) by UV-visible and fluorescence spectroscopic studies and the minimum concentration of Ni²⁺ ion with LOD was found to be 9.4μM. Job's plot method gives the binding stoichiometry ratio of Ni²⁺ ion vs oxadiazole derivative 2 to be 2:1. Furthermore, the intercalative binding mode of oxadiazole derivative 2 with Calf Thymus DNA was supported by UV-Vis, fluorescence, viscosity, cyclic voltammetry, time-resolved fluorescence, and circular dichroism measurements. The molecular docking result gives the binding score for oxadiazole derivative 2 to be -6.5 kcal/mol, which further confirms the intercalative interaction. In addition, the anti-fungal activity of oxadiazole derivative 2 was also screened against fungal strains (C. albicans, C. glabrata, and C. tropicalis) by broth dilution and disc diffusion method. In the antioxidant studies, the oxadiazole derivative 2 showed potential scavenging activity against DPPH and H₂ O₂ free radicals.

A highly potential acyclic Schiff base fluorescent turn on sensor for Zn2+ ions and colorimetric chemosensor for Zn2+, Cu2+ and Co2+ ions and its applicability in live cell imaging

Herein, we report two acyclic Schiff base receptors CS-1 and CS-2 capable of being selective fluorescent turn on for Zn2+ions and colorimetric chemosensor for Zn2+, Cu2+, and Co2+ ions by showing a colour change from colourless to yellow in 1:1 ratio of acetonitrile and HEPES buffer (1:1, v/v, pH 7.4) without the interference from other metal ions screened (Cd2+, Hg2+, Sn2+, Ni2+, Cr3+, Mn2+, Pb2+, Ba2+, Al3+, Ca2+, Mg2+, K+ and Na+). The fluorescence turn on enhancement towards Zn2+ ions is ascribed to PET blocking, suppression of -C=N- isomerisation, and the ESIPT process. The selectivity, competitivity and reversibility of the synthesised probes (CS-1 and CS-2) made them promising chemosensors for the detection of Zn2+, Cu2+, and Co2+ ions. The density functional theory (DFT) calculations have theoretically endorsed the colorimetric changes in the examined absorption spectra and binding mode of both CS-1/CS-2 with metals ions. In addition, 1H NMR titrations were also consistent with the recognition mechanism of Zn2+ ions with the CS-1/CS-2. Further, the Jobs plot analysis infers a 1:1 stoichiometric ratio for both evaluating receptors CS-1 and CS-2 with Zn2+, Cu2+ and Co2+ ions and was supported by DFT, NMR (only for Zn2+ ions), UV-Visible, and fluorescence spectroscopic studies. Moreover, the detection limits of CS-1 and CS-2 for Zn2+ ions were determined to be 7.69 and 5.35 nM, respectively, which is less compared to the detection limit of Cu2+, Co2+ ions as well as the limit approved by the United State Environmental Protection Agency (US EPA). The probes CS-1 and CS-2 found to show high fluorescence quantum yields at pH = 7 during the titration with Zn2+ as compared with other pHs (5-6 and 8-11). Gratifyingly, fluorescence microscopy imaging in HeLa cells revealed that the pair of receptors can be employed as an excellent fluorescent probe for the detection of Zn2+ions in living cells, indicating that this facile chemosensor has a huge potential in cellular imaging.

Assembly of a Zn(II) coordination polymer of tetrapyridyl tetraene ligands for selective sensing of CrO42- and Fe3+ in water via luminescence quenching and enhancement

Four Zn(II)-based coordination polymers (CPs), [Zn(4-tkpvb)(FB)2] (CP1), [Zn(4-tkpvb)(CB)2] (CP2), [Zn(4-tkpvb)(BB)2] (CP3) and [Zn(4-tkpvb)(NTP)]n (CP4), were prepared from solvothermal reactions of Zn(NO3)2•6H2O with 1,2,4,5-tetrakis((E)-2-(pyridin-4-yl)vinyl)benzene (4-tkpvb) in the presence of 3-florobenzoic acid...

Bz-8HQ: a novel supramolecular fluorochrome exhibiting multiple stimuli-responsiveness

A novel multifunctional fluorescent molecule (Bz-8HQ) was synthesized from the linkage of benzimidazole (Bz) and 8-hydroxyquinoline (8HQ) molecules and its response to multiple stimuli was investigated spectroscopically.

Low-cost photo-switches based on stilbene-appended Zn(II)-terpyridine complexes

We report herein the synthesis, characterization, photophysics, and photo-isomerization behaviors of three Zn(II)-terpyridine complexes of the type [Zn(tpy-pvp-X)₂]²⁺ (X = H, Me, and NO₂) covalently tethered with stilbene moiety. The complexes exhibit absorption bands stretching up to the edge of the visible domain due to ligand → ligand charge transfer (LLCT) transitions and strong emission at room temperature in the visible due to radiative deactivation of ³LLCT state having lifetime within 1.0-3.0 ns. The stilbene motifs in the complexes undergo trans to cis isomerization upon irradiating with UV and visible light accompanied by significant alteration of their absorption, emission, and ¹H NMR spectral profiles. Apart from the variation of electron donating and electron withdrawing substituent (X), the isomerization studies were also carried out in three different solvents (DCM, MeCN, and DMSO) to further tune their kinetic and thermodynamic parameters. The rate, rate constant and quantum yield of isomerization were estimated in all the solvents. The reverse process (cis to trans) also occurs very slowly on keeping but could be accelerated upon heating. Trans to cis photoisomerization leads to quenching of emission in case of 1 and 2, whereas backward thermal cis to trans conversion leads to restoration of emission. By contrast, for the nitro-derivative (3) forward process induces emission enhancement, while backward process gives rise to emission quenching. In essence, "on-off" and "off-on" emission switching is feasible for 1 and 2, whereas "off-on" and "on-off" emission switching occurs in case of 3. Emission spectral responses upon successive action of photonic and thermal input lead to the fabrication of INHIBIT and IMPLICATION logic gates. DFT and TD-DFT computational investigations were also undertaken to visualize their electronic structures, correct assignment of the spectral bands, and mode of isomerization process.

Facile room temperature synthesis of ultra-small sized porous organic cages for fluorescent sensing of copper ion in aqueous solution

Facile synthesis of nano porous organic cages with small size and good fluorescence property is highly desirable, but still challenging and scarce for their sensing applications. Here we report a rapid room-temperature recrystallization method for the preparation of nano porous organic cages with ultra-small size as a fluorescent probe for copper ion. The prepared nano porous organic cages gave the diameter of 2.49 ± 0.04 nm, and exhibited stable emission at 535 nm with absolute quantum yield of 0.68%. On the basis of the coordination interaction and charge transfer between the nano porous organic cages and copper ion, a simple fluorescent probe for copper ion in aqueous solution was developed. The developed method gave a calibration function of QE = 0.4815lg[Cu²⁺] + 0.5847 (where QE is the quenching efficiency; [Cu²⁺] in μM) (R² = 0.9987) in a concentration range of 0.1-2 μM, the limit of detection (3s) of 8 nM, and the relative standard deviation of 0.36% for 10 replicate determinations of 0.5 μM copper ion. The recoveries of spiked copper ion in tap water samples ranged from 96.8% to 103.0%. The proposed method possesses good sensitivity, selectivity and accuracy.

Stimuli-Responsive Molecular Switches and Logic Devices Based on Ru(II)-Terpyridyl-Imidazole Coordination Motif

We report herein the synthesis, photophysics, and electrochemistry of three Ru(II)-terpyridine complexes derived from a new terpyridyl-imidazole ligand (tpy-HImzPh₃F₂) and study their pH- and temperature-responsive behaviors toward the fabrication of molecular switches. The complexes emitted at room temperature (RT) have a lifetime within the 4.5-49.0 ns domain, depending on the auxiliary ligand and the solvent used. In the acidic region, the complexes exhibit emission, indicating the "on-state", while in the basic condition, the emission is totally quenched, indicating the "off-state". Similarly, when the temperature is lowered, the emission intensity and lifetime are enhanced, demonstrating the on-state, while increase of temperature leads to quenching of the emission intensity and lifetime, designated as the off-state. In both cases, the process is reversible. The bathochromic shift of the spectral band together with the emission quenching and lowering of the Ru³⁺/Ru²⁺ potential is also observed upon deprotonation at elevated pH. In addition, systematic variation of the absorption spectral behaviors upon variation of pH helps in evaluation of the pK_a's of the complexes. In essence, the complexes can act as switches emanated from a huge change in their absorption, emission, and redox behaviors as a function of their acidity/basicity (pH) and temperature. Moreover, their emission spectral responses as a function of pH and temperature were utilized for the fabrication of two-input binary logic gates. Density-functional theory (DFT) and time-dependent density-functional theory (TD-DFT) computations are performed for appropriate interpretation of the spectral bands.

Ultrafast Excited-State Dynamics of CuBr3- Complex Studied with Sub-20 fs Resolution

Ultrafast excited-state dynamics of CuBr₃^- complex was studied in acetonitrile and dichloromethane solutions using femtosecond transient absorption spectroscopy with 18 fs temporal resolution and quantum-chemical DFT calculations. Upon 640 nm excitation, the CuBr₃^- complex is promoted to the ligand-to-metal charge transfer (LMCT) state, which then shortly undergoes internal conversion into the vibrationally hot ligand field (LF) excited state with time constants of 30 and 40 fs in acetonitrile and dichloromethane, respectively. The LF state nonradiatively relaxes into the ground state in 2.6 and 7.3 ps in acetonitrile and dichloromethane, respectively. Internal conversion of the LF state is accompanied by vibrational relaxation that occurs on the same time scale. Based on the analysis of coherent oscillations and quantum-chemical calculations, the predominant forms of the CuBr₃^- complex in acetonitrile and dichloromethane solutions were revealed. In acetonitrile, the CuBr₃^- complex exists as [CuBr₃(CH₃CN)₂]^-, whereas three forms of this complex, [CuBr₃CH₂Cl₂]^-, [CuBr₃(CH₂Cl₂)₂]^-, and [CuBr₃(CH₂Cl₂)₃]^-, are present in equilibrium in dichloromethane.

Functionalized Silver Nanoparticles as Colorimetric and Fluorimetric Sensor for Environmentally Toxic Mercury Ions: An Overview

Nanoscience is a multifaceted field which encompasses metal nanoparticles (MNPs) having novel and size-related optical properties significantly different from the bulk level as well as at the atomic level. Amongst noble MNPs, the silver nanoparticles (AgNPs) have unique properties for metal interaction. Presently, there have been expedite reports which are taken under the review in virtue of sensing the mercury ions in aqueous media. Mercury dissemination in various forms contaminates the ecosystem. Globally mercury is ranked as the most toxic element and an urgent threat to humans since it causes major health issues. Employing MNPs, especially AgNPs for the detection of mercury ions is the economic, handy and apt method in contrast to time-consuming methods that use expensive instrumentations. The review highlights a study of colorimetric and fluorimetric detection of the level of Hg (II) ions in aqueous media selectively with high sensitivity in different courses of conditions using AgNPs synthesized by various approaches. Graphical abstract.

Metal ion size profoundly affects H3glyox chelate chemistry

The bisoxine hexadentate chelating ligand, H₃glyox was investigated for its affinity for Mn²⁺, Cu²⁺ and Lu³⁺ ions; all three metal ions are relevant with applications in nuclear medicine and medicinal inorganic chemistry. The aqueous coordination chemistry and thermodynamic stability of all three metal complexes were thoroughly investigated by detailed DFT structure calculations and stability constant determination, by employing UV in-batch spectrophotometric titrations, giving pM values (pM = −log[Mⁿ⁺]_free when [Mⁿ⁺] = 1 μM, [L] = 10 μM at pH 7.4 and 25 °C) – pCu (25.2) > pLu (18.1) > pMn (12.0). DFT calculated structures revealed different geometries and coordination preferences of the three metal ions; notable was an inner sphere water molecule in the Mn²⁺ complex. H₃glyox labels [^52gMn]Mn²⁺, [⁶⁴Cu]Cu²⁺ and [¹⁷⁷Lu]Lu³⁺ at ambient conditions with apparent molar activities of 40 MBq μmol⁻¹, 500 MBq μmol⁻¹ and 25 GBq μmol⁻¹, respectively. Collectively, these initial investigations provide insight into the effects of metal ion size and charge on the chelation with the hexadentate H₃glyox and indicate that further investigations of the Mn²⁺–H₃glyox complex in ^52g/55Mn-based bimodal imaging might be worthwhile.

The bisoxine hexadentate chelating ligand, H₃glyox was investigated for its affinity for Mn²⁺, Cu²⁺ and Lu³⁺ ions; all three metal ions are relevant with applications in nuclear medicine and medicinal inorganic chemistry.

Emission Switching in the Near-Infrared by Reversible Trans-Cis Photoisomerization of Styrylbenzene-Conjugated Osmium Terpyridine Complexes

A new array of homoleptic osmium(II) complexes based on styrylbenzene-conjugated terpyridine ligands (tpy-pvp-X) were synthesized and their photophysical, electrochemical, and photoisomerization behaviors thoroughly investigated in this work. Both electron-donating and -withdrawing substituents were incorporated onto a tpy-pvp-X (X = H, Me, Cl, NO₂, and Ph) moiety to tune the optical properties and also the rate of photoisomerization behaviors in the complexes. All complexes display strong spin-allowed singlet metal-to-ligand charge-transfer bands in the visible (495-506 nm) and weak singlet ground state to triplet metal-to-ligand charge-transfer (³MLCT) broad bands within the 600-700 nm range. The complexes also exhibit strong phosphorescence emission from their ³MLCT state in the near-infrared domain (737-752 nm) at room temperature with excited-state lifetimes spanning between 107 and 165 ns. Two styrylbenzene units promote reversible trans-trans to trans-cis/cis-cis isomerization induced by light. The rate constants and quantum yields of photoisomerization were found to vary linearly with the Hammett σ_p parameters of the substituents. The rate and quantum yields were also found to decrease with increasing polarity of the solvents. Considerable modulation of the optical behavior along with luminescence switching in the complexes has been achieved upon photoisomerization. Moreover, the optical outputs as a function of two photonic stimuli inputs were used to demonstrate the binary function of a two-input IMPLICATION logic gate. In conjunction with the experimental study, computational investigations were also carried out in all three conformations of the complexes (trans-trans, trans-cis, and cis-cis) to have a perception of their electronic structures and for correct assignment of their absorption and emission spectral bands.