Fluorescent Nanoaggregates of Pentacenequinone Derivative for Selective Sensing of Picric acid in Aqueous Media

Synthesis of pyridyl functionalized 3-pyrrolyl BODIPY based fluoroprobes and application towards highly selective detection of picric acid

A series of pyridyl-coupled 3-pyrrolyl BODIPY fluoroprobes were synthesized by varying the position of the pyridyl/N-methylated pyridyl group at the α-/meso-position of the 3-pyrrolyl BODIPY scaffold and thoroughly characterized by HRMS and 1D/2D NMR techniques. Our studies indicated that only the water-soluble N-methylated p-pyridyl 3-pyrrolyl BODIPY among various pyridyl-coupled 3-pyrrolyl BODIPYs synthesized here showed an effective and exclusive sensing for picric acid (HPA). The N-methylated p-pyridyl 3-pyrrolyl BODIPY rapidly detects HPA in an aqueous medium with exceptional selectivity, sensitivity (LOD = 7.90 pM), and high binding affinity (Ka = 4·94 × 108 M-1) through both chromogenic and fluorogenic signalling modes. Our studies support the formation of a charge transfer complex between cationic N-methylated p-pyridyl 3-pyrrolyl BODIPY and picrate as verified by absorption, fluorescence, electrochemical, and NMR techniques. DFT and TD-DFT studies further support the structural and experimental observations, including the sensing mechanism of HPA.

Curcumin-derivatives as fluorescence-electrochemical dual probe for ultrasensitive detections of picric acid in aqueous media

We are reporting the two curcumin derivatives, ferrocenyl curcumin (Fc-cur) and 4-nitro-benzylidene curcumin (NBC), as a probe through dual modalities, i.e., fluorescence and electrochemical methods, for the detection of nitro-analytes, such as picric acid (PA). The probes exhibited aggregation-induced enhanced emission (AIEE), and the addition of picric acid (PA) demonstrated good and specific fluorimetric identification of PA in the aggregated state. By using density functional theory (DFT), the mechanism of picric acid's (PA) interactions with the probes was further investigated. DFT studies shows evidence of charge transfer from curcumin derivatives probe to picric acid resulting into the formation of an adduct. The reduction of trinitrophenol (PA) to 2, 4, 6-trinitrosophenol was investigated utilizing a probe-modified glassy carbon electrode (GCE) with a good detection limit of 9.63 ± 0.001 pM and 41.01 ± 0.002 pM, respectively, for Fc-cur@GCE and NBC@GCE, taking into account the redox behavior of the probe. The applicability of the designed sensor has been utilized for real-time application in the estimation of picric acid in several water samples collected from the different source.

Pyrazoline-Based Fluorescent Probe: Synthesis, Characterization, Theoretical Simulation, and Detection of Picric Acid

2-Pyrazoline containing benzothiazole ring 2-[1-(1,3-benzothiazol-2-yl)-5-(4-methoxyphenyl)-4,5-dihydro-1H-pyrazol-3-yl]phenol (BP) have been synthesized for the effective identification of picric acid over other competing nitro compounds using fluorescence technique. The pyrazoline BP showed quenching efficiency as high as 82% comparative to other nitro aromatics. The limit of detection and limit of quantification were found to be 1.1 μM and 3.3 μM. The possible mechanism with the quenched PA detection efficiency was based on fluorescence energy transfer and photoinduced electron transfer. Moreover, the observed results were supported by the optimized structures of the compounds using the DFT/B3LYP/6-311G/LanL2DZ method. Eventually, the pyrazoline derivative BP was further utilized for natural water samples, showing recoveries in the 87.62-101.09% and RSD was less than 3%.

Dual-Channel Imine-Amine Photoisomerization in a Benzoimidazole and Benzothiazole Coupled System: Photophysics and Applications

A molecule, namely 2-(1H-benzo[d]imidazol-2-yl)-6-(benzo[d]thiazol-2-yl)-4-bromophenol (BIBTB), having a two-way proton transfer unit of thiazole and imidazole moieties was synthesized and characterized by NMR, electrospray ionization mass spectrometry (ESI-MS), and single-crystal diffraction studies. Steady state and time-resolved spectral studies of BIBTB support excited state intramolecular proton transfer (ESIPT), causing imine-amine tautomerization through a two-way 6-membered H-bonded ring, where the N atoms of benzothiazole and the benzoimidazole unit are involved as proton acceptor sites. Interestingly, in a nonpolar and moderately polar solvent, photoisomerization in BIBTB is found to be favored toward the thiazole ring, whereas in a highly polar solvent, it is favored toward the imidazole ring. A spectral comparison of BIBTB with judicially designed molecules 2-(benzo[d]thiazol-2-yl)-4-bromophenol (HBT) and 2-(1H-benzo[d]imidazol-2-yl)-4-bromophenol (BIB) supports these inferences. Theoretical calculation using the Density Functional Theory (DFT) at CAM-B3LYP/6-311+G(d,p) level supports the existence of two low-energy 6-membered hydrogen-bonded planar conformers in the ground state in the gas phase and in solvents of different dielectrics. The potential energy curves (PECs) calculated along the proton transfer (PT) coordinate are found to have a high energy barrier in the ground state and to be barrierless or have a low energy barrier in the excited state for both the forms. The calculated vertical excitation and the emission energy from the relaxed excited and PT states show good correlation with the experimental spectral data. Aggregation of BIBTB in water with red shifted emission was established from X-ray single-crystal structure analysis, solid state emission, and Dynamic Light Scattering (DLS) measurement. The molecule BIBTB also acts as a fluorescence probe for sensing the explosive picric acid in the subnano scale and can be used to determine the proportion of water in dimethyl sulfoxide (DMSO) solvent.

Label-Free Detection of Unbound Bilirubin and Nitrophenol Explosives in Water by a Mechanosynthesized Dual Functional Zinc Complex: Recognition of Picric Acid in Various Common Organic Media

High levels of unconjugated bilirubin (UB) in serum lead to asymptomatic and neonatal jaundice and brain dysfunctions. Herein, we have reported the detection of UB at as low as 1 μM in an aqueous alkaline medium using a Zn(II) complex. The specificity of the complex has been validated by the HPLC in the concentration window 6-90 μM, which is rare. The sensory response of the probe at physiological pH against nitro explosives developed it as an instant-acting fluorosensor for picric acid (PA) and 2,4-dinitrophenol (2,4-DNP). Spectroscopic titration provided a binding constant of 4×105  M-1 with PA. The naked eye detection was found to be 15 μM. The solid-state photoluminescent nature of the complex enabled it for PA sensing in the solid phase. Interestingly, the probe remained fluorescent in various volatile and non-volatile organic solvents. As a result, it can also detect PA and 2,4-DNP in a wide range of common organic media. NMR studies revealed the coordination of PA, 2,4-DNP, and UB to the Zn(II) center of the probe, which is responsible for the observed quenching of the probe with the analytes.

Histotoxicity of AIEgen Based on Triphenylamine for the Simultaneous and Discriminatory Sensing of Hg2+ and Ag+ Directly in Aqueous Media for Environmental Applications

A newly synthesized AIEgen based on triphenylamine is fully characterized and coded as BRA for the simultaneous and discriminatory selective detection of Hg2+ and Ag+ ions directly in mixed aqueous media for the identification and purification of water with a low detection limit. Moreover, we employed BRA in histotoxicity in that when compared to the control group, fish exposed to the "novel synthesized luminogen (BRA)" that demonstrated photophysical phenomena during the "sensing of mercury and silver (heavy metals) in aqueous media" did not show any major distinguishing changes in the architecture of their gills, liver, muscle, brain, kidney, and heart tissues.

Simple and efficient PET and AIEE mechanism-based fluorescent probes for sensing Tabun mimic DCNP

The highly sensitive, selective, easy-to-prepare, aqueous media based on two novel probes 2-(pyren-1-yl)imidazo[1,2-a]pyridine (IMP-Py) and (2-(pyren-1-yl)imidazo[1,2-a]pyridin-3-yl)methanol (IMP-Py-OH) are synthesized for the detection of toxic chemical warfare nerve agent mimic diethylcyanochlorophosphonate (DCNP). Both probes are found effective in the detection of DCNP but comparatively, IMP-Py shows better properties in terms of instantaneous response, specificity, selectivity and a low detection limit of 16.9 nM. A significant enhancement of fluorescence intensity of IMP-Py due to aggregation-induced emission enhancement (AIEE) and photoinduced electron transfer (PET) phenomenon was inhibited due to phosphorylation of the hydroxy group of IMP-Py-OH in presence of DCNP has been observed. Taking the advantages of good sensitivity and fast response, probe IMP-Py has been fabricated into a viable paper strips portable product, tested for its potential for the detection of DCNP in tap water as well as with its vapor and response is visible under a UV lamp of 365 nm wavelength.

Dualistic Fluorescence as Well as Portable Smartphone-Assisted RGB-Relied Sensing Assay for the Ultra-Sensitive Determination of Pendimethalin in Food and Water Samples by AIEE Active Organic Probes

Herein, a peculiar fluorometric as well as smartphone-assisted RGB-relied sensing assay is introduced for determining pendimethalin (PDM) herbicide contents (in parts per trillion level) based on the anthracene-incorporated pyrimidinone/thione probes (S1 to S4). These compounds offered a unique and impressive aggregation-induced emission enhancement (AIEE) behavior by aggregation in H₂O-dimethylformamide medium. Furthermore, these AIEE active compounds were found to display superior selectivity and extraordinary sensitivity for PDM detection via fluorescence quenching response. The extent of quenching degree was found to be linearly varied with the PDM concentration ranging from 0 to 20 nM, with a lower limit of detection of 367.8 pM (103.4 ppt) by S3 nanoaggregates. The detailed investigation revealed that such a high sensitivity of the designed sensor toward PDM is attributable to the existence of dual "photoinduced charge transfer and Förster resonance energy transfer process mechanisms". The Stern-Volmer plots, Job's plot, Benesi-Hildebrand plot, and ¹H NMR titrations as well indicated the existence of substantial interactions between the sensor and PDM. The conducted selectivity tests provided distinguishable selectivity for PDM detection over various other insecticides/pesticides as well as other structural nitro analogues. Additionally, the presented sensing assay was also applied to quantify the PDM residues in spiked food (vegetables, fruits, and grains) and water samples. In addition, the sensor-coated fluorescent paper test strips were also fabricated for on-site detection of PDM. The applicability of smartphone-relied RGB analysis significantly streamlined the operation process, speeds up the detection procedure, and also offered a novel methodology for real-time analysis of PDM in real samples.

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.

A New Compound for Sequential Sensing of Picric Acid and Aliphatic Amines: Physicochemical Details and Construction of Molecular Logic Gates

Picric acid (PA) at low concentration is a serious water pollutant. Alongside, aliphatic amines (AAs) add to the queue to pollute surface water. Plenty of reports are available to sense PA with an ultralow limit of detection (LOD). However, only a handful of works are testified to detect AAs. A new fluorescent donor-acceptor compound has been synthesized with inherent intramolecular charge transfer (ICT) character that enables selective and sensitive colorimetric quantitative detection of PA and AAs with low LODs in non-aqueous as well as aqueous solutions. The synthesized compound is based on a hemicyanine skeleton containing two pyridenylmethylamino groups at the donor and a benzothiazole moiety at the acceptor ends. The detailed mechanisms and reaction dynamics are explained spectroscopically along with computational support. The fluorescence property of the detecting compound changes due to protonation of its pyridinyl centers by PA leading to quenching of fluorescence and subsequently de-protonation by AAs to revive the signal. We have further designed logic circuits from the acquired optical responses by sequential interactions.

Fluorescence modulation of naphthalene containing salicyl hydrazide-based receptor through aggregation-induced emission enhancement approach: Dual detection of lanthanum and cyanide ions in semi-aqueous medium

The sensing activity of naphthalene containing salicyl hydrazide-based fluorescence receptor has been improved through aggregation-induced enhanced emission mechanism approach in semi-aqueous medium. The receptor has been found to be selective toward La³⁺ with approximately 70-fold fluorescence enhancement due to a combined effect of keto-enol tautomerism inhibition and chelation enhanced fluorescence with a detection limit of 3.91 × 10^-6 M. In addition, the receptor is also able to sense CN^- with a detection limit of 3.55 × 10^-6 M via deprotonation effect, justifying its multiple analyte sensing behaviour. Hence, the current analytical methodology improves the sensing activity of the probe and also provides a greener alternative for La³⁺ and CN^- detection.

Charge transfer complexes: Emerging and promising colorimetric real-time chemosensors for hazardous materials

After introducing the concept of charge transfer (CT) complex formation by Mulliken and the discovery of crystalline picrate (association of picric acid and aromatic hydrocarbons) by Fritzsches, a large interest has been drawn in this field. CT complexes have been explored and exploited for different applications for several decades. The research has been aimed mostly for discovering and characterizing new CT materials and exploring applications mainly in the field of optoelectronic properties, antimicrobial activities and DNA/protein binding properties for the last six years. However, nowadays, CT complexes are exploited for their photocatalytic activities and designing chemosensors for the colorimetric real-time detection of hazardous materials like nitro explosives, anions and toxic heavy metal ions in an aqueous medium. This review sheds light on updates on CT complexes, their types, synthesis and applications. The brief discussion on the emergence of CT complexes as highly potential chemosensors along with the explanation of sensing mechanism through article summarization is the centerpiece of this review. The final outcomes are discussed and concluded.

'Light-Up' AIE-Active Materials: Self-Assembly, Molecular Recognition and Catalytic Applications

Aggregation induced emission enhancement (AIEE) is one of the most widely explored phenomena to develop 'light up' (fluorescent) materials having potential applications in the field of supramolecular chemistry, analytical chemistry and material chemistry. By applying the principles of host-guest chemistry, we have developed a variety of aggregation induced emission (AIE/AEE) active materials having specific affinity for metal ions, electron deficient/electron rich analytes. The interactions between AIE active assemblies and metal ions are further tuned to prepare nanohybrids having potential applications as catalytic/photocatalytic systems in various organic transformations under eco-friendly conditions. This account summarizes various design strategies developed in our labortary for the preparation of AIE/AEE active building blocks having sensing and catalytic applications.

Polyhydroquinoline nanoaggregates: A dual fluorescent probe for detection of 2,4,6-trinitrophenol and chromium (VI)

Fluorescent polyhydroquinoline (PHQ) derivative was fabricated utilizing one-pot engineered course. The PHQ derivative indicated aggregation induced emission enhancement (AIEE) with arrangement of nanoaggregates of size 11-13 nm in 95% watery DMF medium. The fluorescence emission of PHQ nanoaggregates was extinguished by including TNP and Cr (VI). They indicated prevalent fluorescence quenching towards both TNP and Cr (VI) over other meddling nitro-compounds and metal particles. In light of results got we presumed that both photo-induced fluorescence quenching of PHQ nanoaggregates by TNP, while Inner Filter Effect (IFE) was in charge of fluorescence quenching of PHQ nanoaggregates by Cr (VI). The PHQ nanoaggregates empowered identification of TNP and Cr (VI) down to 0.66 μM (TNP) and 0.28 μM (Cr (VI)). The use of PHQ nanoaggregates were reached out for location of TNP and Cr (VI) in genuine water tests.

The high selective chemo-sensors for TNP based on the mono- and di-substituted multifarene[2,2] with different fluorescence quenching mechanism

The chem-sensors, based on the triazole-CH₂-anthracene-functionalized multifarene[2,2] were successfully synthesized, which could efficiently and rapidly detect 2,4,6-trinitrophenol (TNP). The high specificities of the proposed macrocyclic sensors were achieved by selective response for TNP in the existence of other competing phenolic compounds, and the limits of detection in ∼10^-8 mol/L range were produced to confirm the high sensitivities of the chem-sensors, which could be attributed to the mechanism of electron and resonance energy transfer processes in the complexes with the supramolecular interactions. ¹H NMR titration analysis revealed the actual binding position should be the triazole rings of sensors with the hydroxyl group on TNP to offer a hydrogen bonding. The extraordinary sensing properties endued the compounds as sensitive fluorometric chem-sensors for the potential application of TNP detection.

Gel Formed by Self-Assembly of a Urea-Modified Monopyrrolotetrathiafulvalene Derivative Displays Multi-Stimuli Responsiveness and Absorption of Rhodamine B

A new monopyrrolotetrathiafulvalene-based derivative containing a urea group was designed, synthesized and thoroughly characterized. It proved to be a non-gelator in a single solvent even when heated or sonicated. However, it could self-assemble in a CHCl₃ (CH₂ Cl₂ )/n-hexane mixture to form a thermo-responsive supramolecular organogel. SEM, FT-IR spectroscopy, UV/Vis absorption spectroscopy, and SAXS revealed that in the organogel system, the gelators self-assembled into supramolecular networks with a J-type aggregation mode under the joint effect of π-π stacking, intermolecular hydrogen-bonding, and van der Waals forces. Interestingly, the gel phase was shown to undergo reversible gel-sol transformation induced by Fe³⁺ -Vitamin C (Vc), trifluoroacetic acid-triethylamine (TFA-TEA) and picric acid (PA)-NaOH. In particular, in the presence of picric acid, the experimental results proposed that charge transfer occurred from the electron-donor gelator to the electron-acceptor picric acid due to the possibility of complex formation. Furthermore, the formed organogel could behave as the matrix for encapsulating cationic fluorescent dye from wastewater, and the adsorption efficiency was directly proportional to the concentration of the gelator.

An antipyrine based fluorescence "turn-on" dual sensor for Zn2+ and Al3+ and its selective fluorescence "turn-off" sensing towards 2,4,6-trinitrophenol (TNP) in the aggregated state

A 2,6-diformyl-p-cresol (DFC)-4-amino antipyrine (AP) based dual signaling fluorescent Schiff base ligand (DFCAP) is found to exhibit colorimetric and fluorescence turn on selective sensing towards metal ions, Zn2+ and Al3+. It also exhibits a significant aggregation induced emission (AIE) phenomenon by controlling the water-THF solvent ratio which provides robust green emissive fluorogenic aggregates with well-defined morphologies. Turn-on fluorescence enhancements as high as 195 fold and 168 fold in methanol for Al3+ and Zn2+ at 480 nm and 508 nm, respectively, were noticed. The binding constants and stoichiometry determined from the fluorescence titration data are K = 7.63 × 104 M-1 and 3.42 × 104 M-1 and 1 : 1 complexation for both Al3+ and Zn2+ respectively, supported by Job's method. DFCAP shows high sensitivity towards the detection of Zn2+ and Al3+ ions with very low detection limit values of ca. ∼21 nM and 30 nM respectively. Besides by applying its attractive AIE feature, the green emissive hydrosol functions as a good chemosensor with high sensitivity for a selected explosive TNP through ground state complexation with a LOD value of ca. ∼1.74 μM and especially a high Stern-Volmer quenching constant of ca. ∼4.14 × 105 M-1. For instant 'naked eye' response for the trace detection of TNP in the solution state, we fabricated a simple paper strip that could detect TNP on-site in a fast, inexpensive and simple way.

A tripodal supramolecular sensor to successively detect picric acid and CN− through guest competitive controlled AIE

Herein, we report a simple and efficient method for the selective and sensitive detection of picric acid (PA) and CN⁻via a novel guest competitive controlled aggregation-induced emission (AIE) mechanism based on a tris-naphthalimide derivative TG.

Nanostructured Graphene Oxide Dots: Synthesis, Characterization, Photoinduced Electron Transfer Studies, and Detection of Explosives/Biomolecules

Herein, we report the preparation of graphene oxide dots (GO dots) by fine-tuning the carbonization degree of citric acid. The structure of GO dots was characterized by absorption spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, as well as high-resolution scanning electron microscopy and transmission electron microscopy analyses. The typical particle size of the GO dots was 42 nm. The fluorescent characteristics of the GO dots were analyzed by fluorescence spectroscopy. Once excited at 360 nm, the GO dots were fluorescent in the range of 450-550 nm, which was dependent on the excitation wavelength. Further, GO dots were effectively utilized for multifarious applications such as photoinduced electron transfer and detection of explosives and biomolecules. The emission property of GO dots was competently quenched by viologens, picric acid (PA), and bilirubin (BR). The mechanism of quenching by viologens and explosives/biomolecules was found to be due to photoinduced electron transfer and the internal filter effect, respectively. Intriguingly, the detection minimum of PA is in the nanomolar level. Toward commercialization, the economic test strips have also been introduced for the identification of PA. Furthermore, the GO dots have been applied as an efficient luminescent bioprobe for a selective and perceptive finding of BR.

Fluorescence chemical sensor for determining trace levels of nitroaromatic explosives in water based on conjugated polymer with guanidinium side groups

A novel fluorescent conjugated polymer (poly(2-amino-N-(2-((4-ethynylphenyl) ethynyl) phenyl)-5-guanidinopentanamide)-1,4-phenylethynylene-1,4-phenyleneethynylene, PPE-Arg) was synthesized in this paper. We found that PPE-Arg could be quenched by picric acid (PA). Photoinduced electron transfer (PET) mechanism can be used to describe the fluorescence quenching of PPE-Arg. It could be speculated that the photo-induced electrons may be transferred from PPE-Arg to nitroaromatic explosives. In this paper, the experiment conditions and detection performance of PPE-Arg were systematically studied. The experiment results demonstrate PPE-Arg as a sensor for PA has a good linear range from 5 × 10^-7 to 6 × 10^-5 mol L^-1 with the calculated limit of detection (LOD) to be 1.0 × 10^-7 mol L^-1. Meanwhile, reaction time between PPE-Arg and PA is less than 1 min. This proposed sensor was applied to rapidly detect nitroaromatic explosives in environmental water samples and satisfactory results were obtained.

Different self-assemblies and absorption–emission properties of the picrate salts of aromatic amine or heterocycle linked oximes

Different sub-assemblies and fluorescence quenching in picrate salts of an aromatic amine and of three different heterocycle tethered aldoximes are described.

Proton triggered emission and selective sensing of 2,4,6-trinitrophenol using a fluorescent hydrosol of 2-phenylquinoline

Compound 2-phenylquinoline (PhQ) displayed novel aggregation induced emission enhancement (AIEE) characteristics in its aggregate/solid state. It allows reversible fluorescence switching in acidic and basic media and ‘turn off’ fluorescence sensor for TNP.

Inner filter effect based selective detection of picric acid in aqueous solution using green luminescent copper nanoclusters

Designing superior probes to detect trace amounts of picric acid (PA) is of huge importance for homeland security and environmental protection.

A sensitive and selective sensor for picric acid detection with a fluorescence switching response

Low molecular weight organogelator for the detection of picric acid.

High Solid Fluorescence of a Pyrazoline Derivative through Hydrogen Bonding

Pyrazoline and its derivatives often exhibit strong emissions in dilute solutions, but their emission intensity is often dramatically reduced in the solid state due to strong intermolecular interactions between neighboring molecules. In this report, we successfully synthesized a new pyrazoline 4-(3-(4-(decyloxy)phenyl)-1-(2,3,5,6-tetrafluoro-4-(trifluoromethyl)phenyl)-4,5-dihydro-1H-pyrazol-5-yl)-N,N-diethylaniline (PPDPD), into which seven fluorine (F) atoms were incorporated. In the solid state, PPDPD emits a strong blue light at λ_max 430 nm with a fluorescence quantum yield of up to 41.3%. Single-crystal analysis showed the presence of intra/intermolecular C-H···F bonds that may impede molecular motion and block the non-radiative decay channel. Compound PPDPD therefore shows high emission efficiency in the solid state.

Simple Bisthiocarbonohydrazone as a Sensitive, Selective, Colorimetric, and Ratiometric Fluorescent Chemosensor for Picric Acids

A bisthiocarbonohydrazone-based chemosensor molecule (R1) containing a tetrahydro-8-hydroxyquinolizine-9-carboxaldehyde moiety has been synthesized and characterized as a new ratiometric fluorescent probe for picric acid (PA). The ratiometric probe R1 is a highly selective and sensitive colorimetric chemosensor for PA. The association between the chemosensor and PA and the ratiometric performance enabled by the key role of excited state intramolecular proton transfer in the detection process are demonstrated. Selectivity experiments proved that R1 has excellent selectivity to PA over other nitroaromatic chemicals. Importantly, the ratiometric probe exhibited a noteworthy change in both colorimetric and emission color, and this key feature enables R1 to be employed for detection of PA by simple visual inspection in silica-gel-coated thin-layer chromatography plates. Probe R1 has been shown to detect PA up to 3.2 nM at pH 7.4. Microstructural features of R1 and its PA complex have been measured by a field emission scanning electron microscope, and it clearly proves that their morphological features differ dramatically both in shape and size. Density function theory and time-dependent density function theory calculations were performed to establish the sensing mechanism and the electronic properties of probe R1. Furthermore, we have demonstrated the utility of probe R1 for the detection of PA in live Vero cells for ratiometric fluorescence imaging.