N-Acylureido functionality as acceptor substituent in solvatochromic fluorescence probes: detection of carboxylic acids, alcohols, and fluoride ions

An Anthracene and Indole-based Fluorescent Probe for the Detection of Chromium(III) Ions in Real Water Samples

A novel fluorescent probe possessing anthracene with an indole unit was designed and synthesized to detect chromium(III) ions (Cr³⁺) with high sensitivity and selectivity. The probe was synthesized in one step by mixing two commercially available chemicals, 2-aminoanthracene and Indole-5-carboxaldehyde. The probe molecule (ANT-In) demonstrates distinct properties, for instance, "turn-on" fluorescence response, high sensitivity and selectivity in less than one minute, and low detection limit (0.2 µM) via hydrolysis of the C = N bond. Additionally, the probe ANT-In was successfully used to identify the presence of chromium(III) ions in real water samples.

Fluorescence Sensors Based on Hydroxycarbazole for the Determination of Neurodegeneration-Related Halide Anions

The environmental presence of anions of natural origin or anthropogenic origin is gradually increasing. As a tool to tackle this problem, carbazole derivatives are an attractive gateway to the development of luminescent chemosensors. Considering the different mechanisms proposed for anion recognition, the fluorescence properties and anion-binding response of several newly synthesised carbazole derivatives were studied. Potential anion sensors were designed so that they combined the native fluorescence of carbazole with the presence of hydrogen bonding donor groups in critical positions for anion recognition. These compounds were synthesised by a feasible and non-expensive procedure using palladium-promoted cyclodehydrogenation of suitable diarylamine under microwave irradiation. In comparison to the other carbazole derivatives studied, 1-hydroxycarbazole proved to be useful as a fluorescent sensor for anions, as it was able to sensitively recognise fluoride and chloride anions by establishing hydrogen bond interactions through the hydrogen atoms on the pyrrolic nitrogen and the hydroxy group. Solvent effects and excited-state proton transfer (ESPT) of the carbazole derivatives are described to discard the role of the anions as Brönsted bases on the observed fluorescence behaviour of the sensors. The anion-sensor interaction was confirmed by 1H-NMR. Molecular modelling was employed to propose a mode of recognition of the sensor in terms of complex stability and interatomic distances. 1-hydroxycarbazole was employed for the quantitation of fluoride and chloride anions in commercially available medicinal spring water and mouthwash samples.

Isocyanide Insertion-Cyclization Reaction for Imidazoisoindol-5-imine Scaffold Synthesis: A Selective Solvatochromic Fluorescent Probe for Methanol Detection

An efficient, ligand-free, and Pd-catalyzed method for the synthesis of imidazoisoindole imine scaffolds with satisfactory yields via C-C and C-N bond formation has been developed. The synthesized scaffolds have unique potential for selective MeOH detection from other solvents, especially EtOH. The appealing features of this transformation are phosphinic ligand-free conditions, the use of a small amount of Pd(OAc)₂, and a practical procedure for the synthesis of imidazoisoindole imine scaffolds.

D-π-A-π-D type solvatochromic fluorescence probes based on triphenylamine: Synthesis, photophysical properties and application

Two D-π-A-π-D type solvatochromic fluorescence probes (JT1 and JT2) based on triphenylamine have been synthesized. The photophysical and electrochemical properties of these probes as well as their solvatochromic behavior were studied. The Stokes shifts of JT1 and JT2 reach 175 nm (6417.0 cm^-1) and 218.6 nm (9916.7 cm^-1) in the acetonitrile solution, respectively. There is an excellent linear correlation between the Stokes shifts and the E_T (30) solvent polarity values in different solvents. The high responsiveness of JT1 and JT2 to solvent polarity makes them promising candidates for solvatochromic fluorescence probes, especially for the detection of the polarity of non-proton solvents or the content of water in tetrahydrofuran.

An anthracene based fluorescent probe for the selective and sensitive detection of Chromium (III) ions in an aqueous medium and its practical application

An anthracene based fluorescent probe, integrated with thiophene moiety, exhibited selective and sensitive detection of chromium (III) ions over other metal ions. Its synthesis was achieved by simple mixing of two commercially available compounds, 2-aminoanthracene, and 2-thiophenecarboxaldehyde, in onestep without the needed complex purification process. The probe molecule ( ANT-Th ) offered exceptional features such as “turn-on” fluorescence response, low detection limit (0.4 μM), and fast response time (<1 min) via C=N bond hydrolysis. Also, a simple test paper system was developed for the rapid detection of chromium (III) ions with the naked eye.

Amphiphilic triphenylamine–benzothiadiazole dyes: preparation, fluorescence and aggregation behavior, and enzyme fluorescence detection

Change of aggregate stabilization based on removal of the galactopyranose moiety leads to an emission enhancement to detect β-galactosidase activity.

The Solvatochromic Materials: A Progress Review

Solvatochromic compounds attracted more and more attentions in the application of fluorescent probe, indicator, chromogenic reagent, molecular recognition field and so on. Although sovatochromic effects have been discovered for more than a century, they are still difficult to understand and even more difficult to predict. This review introduced organometallic complexes and organic compounds of solvatochromic materials and highlight the latest progress in recent years, and the molecular structure design and solvatochromic properties are discussed.

A NIR fluorescent probe for the detection of fluoride ions and its application in in vivo bioimaging

A near-infrared fluorescent probe has been developed, which is available for visualizing exogenous fluoride ions in vitro and in vivo.

Degradable Organically-Derivatized Polyoxometalate with Enhanced Activity against Glioblastoma Cell Line

High efficacy and low toxicity are critical for cancer treatment. Polyoxometalates (POMs) have been reported as potential candidates for cancer therapy. On accounts of the slow clearance of POMs, leading to long-term toxicity, the clinical application of POMs in cancer treatment is restricted. To address this problem, a degradable organoimido derivative of hexamolybdate is developed by modifying it with a cleavable organic group, leading to its degradation. Of note, this derivative exhibits favourable pharmacodynamics towards human malignant glioma cell (U251), the ability to penetrate across blood brain barrier and low toxicity towards rat pheochromocytoma cell (PC12). This line of research develops an effective POM-based agent for glioblastoma inhibition and will pave a new way to construct degradable anticancer agents for clinical cancer therapy.

The maiden report of a fluorescent-colorimetric sensor for expeditious detection of bifluoride ion in aqueous media

A fluorescent-colorimetric chemosensor L, for rapid detection of bifluoride ion has been developed based on a simple bis-Schiff base.

Turn-on-type emission enhancement and ratiometric emission color change based on the combination effect of aggregation and TICT found in the hexaazatriphenylene-triphenylamine dye in an aqueous environment

Turn-on-type emission enhancement and a ratiometric emission color change were achieved simultaneously due to the aggregation and TICT of a donor–acceptor-type dye.

New solvatochromic probes: performance enhancement via regulation of excited state structures

Regulation of excited state structures resulted in new fluorophores with much enhanced solvatochromic properties.

Cell and in vivo imaging of fluoride ion with highly selective bioluminescent probes

Two rapid bioluminescent probes for the detection of fluoride ion were developed on the basis of F-Si bond formation herein. It should be noted that probe 1 exhibited highly selective and sensitive detection toward fluoride ion over other anions and has been successfully applied in imaging fluoride ion in both living cells and animals.

Light-emitting properties of donor–acceptor and donor–acceptor–donor dyes in solution, solid, and aggregated states: structure–property relationship of emission behavior

In a polar aqueous environment, a series of triphenylamine-based donor–acceptor-type dyes showed efficient light emission upon the formation of aggregates.

Amphiphilic benzothiadiazole–triphenylamine-based aggregates that emit red light in water

An amphiphilic donor–acceptor dye can provide red light emission in water in an aggregate state.

A fluorescent probe for rapid aqueous fluoride detection and cell imaging

A stable and highly selective fluorescent probe has been designed and synthesized for the rapid detection of fluoride ions (F(-)) in aqueous solution and living cells. The design was based on the high reactivity of F(-) toward a silyl group.

Studies of the solvatochromic emission properties of N-aroylurea derivatives II: influence of hydrogen-bonding interactions

The solvatochromic emission properties of five naphthoylurea derivatives with different substitution patterns at the naphthoylurea functionality were investigated, with a particular focus on the influence of inter- and intramolecular H-bonding interactions. The bathochromic shifts of the emission maxima correlate well with the acceptor number or Catalán's acidity of the solvent (Δλ = 47-86 nm), indicating an excited species with a pronounced negative charge that is stabilized by H-bond donating (HBD) solvents. In media with restricted free volume the formation of the charged species is not favored, because the required conformational change to establish an intramolecular charge transfer (ICT) between the fluorophore and the acylurea substituent is hindered, and the emission mainly originates from the locally excited state. This relationship between the alignment of the naphthoyl carbonyl functionality relative to the naphthyl ring and the spectroscopic shift was confirmed by the comparison of the ground state conformation and the emission spectra of the naphthoylurea derivatives in the solid state. Time-resolved experiments revealed different excited entities, whose lifetimes are significantly influenced by the HBD properties and the temperature of the environment. With few exceptions the naphthoylurea derivatives exhibit only two emissive species in the nanosecond range. All experimental data point to conformational relaxation and solvent reorganization leading to the cis and trans isomers of one preferential conformer with respect to the acylurea unit. The structure of the preferred conformation is mainly determined by the possible inter- or intramolecular H-bonds and is therefore also strongly influenced by the HBD and H-bond accepting (HBA) properties of the polar solvents. As the NH groups of the acylurea functionality contribute mainly to the entire inter- and intramolecular H-bond arrangement the variation of the substitution pattern of the urea unit, specifically the presence and position of the NH groups, leads to derivatives with significantly different steady-state and time-resolved emission properties.

The synthesis and spectral properties of a stimuli-responsive D-π-A charge transfer dye based on indole donor and dicyanomethylene acceptor moiety

A dual mode chemosensor dye 3 for detection of fluoride ion, based on the D-π-A molecular framework by one-step condensation, presents high selectivity and sensitivity both in colorimetric and fluorometric analyses. Upon the addition of F(-) anion, the absorption band shows a remarkable red shift along with fluorescent intensity decreasing. The absorption and fluorescent intensities of the dye 3 can be reversibly selected by deprotonation/protonation of the amine moiety via control of intramolecular charge transfer (ICT), leading to a molecular switch with "on" and "off" states. (1)H NMR titration analysis and DMol(3) calculation were employed to reveal the intermolecular charge transfer system of dye 3-F(-) complex.

Highly brominated anthracenes as precursors for the convenient synthesis of 2,9,10-trisubstituted anthracene derivatives

When 9,10-dibromoanthracene was treated with bromine in CCl₄ without a catalyst, 1,2,3,4,9,10-hexabromo-1,2,3,4-tetrahydroanthracene (3) was obtained in 95% yield in the absence of other stereoisomers or rearomatization products. We investigated the base-induced elimination reaction of hexabromide 3 under various conditions. Pyridine-induced elimination of hexabromide 3 afforded 2,9,10-tribromoanthracene (12) in 75% yield, and tribromide 12 was transformed to trimethoxy compound 13 and trinitrile 14 by copper-assisted nucleophilic substitution reactions.

N-(4-Bromo-benzo-yl)-N,N'-dicyclo-hexyl-urea

In the title compound, C(20)H(27)BrN(2)O(2), mol-ecules are linked into one-dimensional chains through (amide)N-H⋯O=C(amide) inter-molecular hydrogen bonds.

Donor-and-Acceptor Substituted Truxenes as Multifunctional Fluorescent Probes

A series of dimesitylboryl acceptor (mesityl=2,4,6-trimethylphenyl) and/or diphenylamino donor (-N(Ph)2)-substituted truxene derivatives, classified as D-or-A substituted compounds and D-and-A substituted charge-transfer compounds, have been synthesized. Two D-and-A substituted truxene compounds, namely, 2-dimesitylboryl-7,12-di(N,N-diphenylamino)-5,5',10,10',15,15'-hexaethyltruxene (BN2) and 2,7-di(dimesitylboryl)-12-(N,N-diphenylamino)-5,5',10,10',15,15'-hexaethyltruxene (B2N), exhibit extraordinarily large solvatochromism ranging from 420 nm (in hexane) to 580 nm (in acetonitrile) in aprotic solvents, which can be used to probe the polarity of the solution environment. Due to proton-donor interactions, the solvatochromic red shift of BN2 and B2N in protic solvents has been significantly decreased, and this effect can be used to identify local protic and aprotic environment. Furthermore, because of the interaction between F- and acceptor, BN2 and B2N show sharp spectral response to fluoride ion concentration. The simultaneous "turn-off" at 500 nm and "turn-on" at 380 nm of the fluorescence signal have provided a good example of a fluorescent ratiometric method, which can greatly enhance the sensitivity of the fluoride ion probe. Underlying these interesting spectral phenomena and multifunctional probe properties is the charge-transfer strategy of grafting donor and acceptor moieties, as A-pi-D2 or A2-pi-D style, to the triangular truxene.

Simple bis-thiocarbono-hydrazones as sensitive, selective, colorimetric, and switch-on fluorescent chemosensors for fluoride anions

Bis-thiocarbono-hydrazones are found to be a class of sensitive, selective, ratiometric, and colorimetric chemosensors for anions such as fluoride (F(-)) or acetate (Ac(-)). The sensitivities, or the binding constants of the sensors with anions, were found to be strongly dependent on the substituents appended on the pi-conjugation framework, the delocalization bridge CH==N, the aromatic moiety, and the hetero atom in the C==X group (X=O, S) of the sensors. Single-crystal structures and (1)H NMR titration analysis shows that the --CH==N-- moiety is a hydrogen-bond donor, and it is proposed that an additional CHF hydrogen bond is formed for the sensors in the presence F(-). A sensor bearing anthracenyl groups is demonstrated as a switch-on fluorescent chemosensor for F(-) and Ac(-). The recognition of F(-) in acetonitrile (MeCN) by a sensor with nitrophenyl substituents is tolerant to MeOH (MeCN/MeOH=10:1, v/v) and water (MeCN/H(2)O=30:1, v/v); at these solvent ratios the absorption intensity of the sensor-F(-) complex solution at maximal absorption wavelength was attenuated to half of the original value in pure MeCN.

Long-wavelength analogue of PRODAN: synthesis and properties of Anthradan, a fluorophore with a 2,6-donor-acceptor anthracene structure

We have synthesized the environment-sensitive fluorophores 2-cyano-6-dihexylaminoanthracene and 2-propionyl-6-dihexylaminoanthracene (Anthradan) starting from 2,6-diaminoanthraquinone. Anthradan is the benzologue of the well-known family of naphthalene 2-propionyl-6-dimethylaminonaphthalene (PRODAN) fluorophores. The additional spectral red shift of the anthracene avoids the autofluorescence of many biological systems and provides for more favorable excitation wavelengths for fluorescence applications. Furthermore, Anthradan exhibits polarity-sensitive emission comparable to that of PRODAN and displays high quantum yields in a range of solvents. Single molecules of these anthracene-containing fluorophores have been imaged in polymer hosts as a proof-of-principle.