A new tetrathiafulvalene-perylene diimide dyad with a pentaoxa-heptadecane chain as the spacer: metal-ions-induced aggregation

A new TTF-perylene diimide dyad 1 with a pentaoxa-heptadecane chain as the spacer was synthesized and characterized. Absorption and fluorescent spectral studies of dyad 1 and reference compounds 2 and 3 indicate that aggregation of dyad 1 and compound 2 occurs in the presence of metal ions. Such metal-ions-induced aggregation is likely due to the synergic action of the coordination of metal ions with the oligoethylene glycol unit and the π-π stacking of the perylene diimide unit.     

Ratiometric fluorescence probe for two-photon bioimaging of Cr in living cells

We presented a ratiometric fluorescent probe dansylamide–rhodamine dyad (DANS–RB) for selectively detecting Cr³⁺ in semi-aqueous solution. The detection mechanism relies on the fluorescent resonance energy transfer (FRET) process from the dansylamide (energy donor) to the rhodamine (energy acceptor) after the addition of Cr³⁺. The cell-permeability of DANS–RB was confirmed by the two-photon fluorescence microscopy experiments, which demonstrated DANS–RB was a good candidate for monitoring the intracellular Cr³⁺ level with the ratiometric fluorescent method. Combining the excellent selectivity, the ratiometric quantitative detection, and the cell-permeability, DANS–RB may find a broad application in the investigation on biologically relevant species in living cells.     

Ratiometric fluorescent and colorimetric sensors for Cu based on 4,5-disubstituted-1,8-naphthalimide and sensing cyanide via Cu displacement approach

Two 4,5-disubstituted-1,8-naphthalimide derivatives 1 and 2 were synthesized as ratiometric fluorescent and colorimetric sensors for Cu²⁺, respectively. In 100% aqueous solutions of 1, the presence of Cu²⁺ induces a strong and increasing fluorescent emission centered at 478 nm at the expense of the fluorescent emission of 1 centered at 534 nm. Compound 2 senses Cu²⁺ by means of a colorimetric (primrose yellow to pink) method with a thorough quench in emission attributed to the deprotonation of the secondary amine conjugated to the naphthalimide fluorophore. 1-Cu²⁺ and 2-Cu²⁺ sense cyanide in ratiometric way via colorimetric and fluorescent changes.     

Control of the CT interaction between electron-donor and -acceptor moieties of a 1,4-dicyanonaphthalene-arene dyad for intermolecular exciplex or excimer formation in crystals

Colorless crystals of 1,4-dicyano-2-(4′-methoxybenzyloxy)methylnaphthalene (2), which is a 1,4-dicyano-2-methylnaphthalene (DCMN)-4-methylanisole (MA) dyad linked by an ether unit, selectively form a fluorescent intermolecular DCMN-MA exciplex (greenish blue, ). In contrast, 1,4-dicyano-2-(4′-methylbenzyloxy)methylnaphthalene (3), which is a DCMN-p-xylene dyad, forms a fluorescent intermolecular DCMN-DCMN excimer in the crystalline state (blue, ). These findings demonstrate that a moderate charge transfer interaction takes place between the DCMN moiety of 2 and MA moieties of the adjacent molecules of 2, which successfully facilitates the preparation of light-emissive organic crystals.     

Distinguishing normal cells from cancer cells via lysosome-targetable pH biomarkers with benzo[a]phenoxazine skeleton

In this paper, the design of a lysosome-targetable pH probe that has a fluorescent OFF (pH = 4) to ON (pH = 5–6) response is described to identify lysosomes in normal cells. The mechanism of photoinduced electron transfer with a fluorophore-based reaction (FBR-PET) was proposed. Benzo[a]phenoxazines with electro-donating aryl groups were selected, its (2,5-dimethoxyphenyl)imino-, (2-hydroxyphenyl)imino- and (2-hydroxy-5-methoxyphenyl)- imino-derivatives (probes 1a−c) were prepared and their optical responses towards pH were evaluated; their fluorescence pH titration experiments gave regularly changes with the increasing electro-donating abilities at the linked aryl groups, the (2-hydroxy-5-methoxyphenyl)iminobenzo[a]phenoxazine (probe 1c) exhibited a nearly OFF−ON response at 580–800 nm. All probes were reversible, and they showed excellent selectivity toward the proton over other competitive species. Fluorescence confocal images were performed with HeLa, KB cancer cells and V79 normal cells, probes 1a−c are all lysosome-targetable pH probes, and benzo[a]phenoxazine with (2-hydroxy-5-methoxyphenyl)imino-group (probe 1c) has potential applications in selective differentiation of normal cells from cancer cells.     

Study on fluorescent switching of naphthopyran with carbazole and pyrene dyad immobilized on SBA-15

A naphthopyran-bridge-carbazole dyad (CzNP), which exhibits both fluorescence and photochromism was synthesized. Then the CzNP was grafted into SBA-15-NH₂, with particular focus on how the SBA-15-NH₂ affects the photoswitching fluorescence change properties. A double fluorescence photochromic material, which was prepared by reacting 1-Pyrenecardboxaldehyde(PY-CHO):naphthopyran-carbazole(CzNP)=1:1 (molar ratio) with SBA-15-NH₂ was also synthesized. Naphthopyran in this two systems displayed excellent photochromic performance. The fluorescent emission was modulated between ‘on’ and ‘off’ via the photoisomerization of naphthopyran in high-degree, especially in PY-CzNP-SBA-15-NH₂ (>90%) due to the photoinduced energy transfer from pyrene excimers to the opened-form naphthopyran and the photoinduced electron transfer between carbazoles and the opened-form naphthopyran moiety. Both the fluorescence photoswitching CzNP-SBA-15-NH₂ and PY-CzNP-SBA-15-NH₂ in CH₃CN/H₂O (v/v, 1:1) solution displayed excellent fatigue resistance. The structural characteristics of CzNP-SBA-15-NH₂ and PY-CzNP-SBA-15-NH₂ were measured by FTIR spectra, X-ray diffraction (XRD), and Elemental analysis.     

Selection of synthetic receptors capable of sensing the difference in binding of d-Ala-d-Ala or d-Ala-d-Lac ligands by screening of a combinatorial CTV-based library

Screening of a combinatorial CTV-based artificial, synthetic receptor library 1 {1-13, 1-13, 1-13} for binding of a variety d-Ala-d-Ala and d-Ala-d-Lac containing ligands (6-11) was carried out in phosphate buffer (0.1 N, pH=7.0). After screening and Edman sequencing, synthetic receptors were found containing amino acid sequences, which are either characteristic for binding dye labeled d-Ala-d-Ala or d-Ala-d-Lac containing ligands. For example, receptors capable of binding d-Ala-d-Ala containing ligands 6, 7, 9 and 11 contained—almost in all cases—at least one basic amino acid residue—predominantly Lys—in their arms. This was really a striking difference with the arms of the receptors capable of binding d-Ala-d-Lac containing ligands 8 and 10, which usually contained a significant number of polar amino acids (Gln and Ser), especially in ligand 8, but hardly any basic amino acids. Use of different (fluorescent) dye labels showed that the label has a profound, albeit not decisive, influence on the binding by the receptor. A hit from the screening of the CTV-library with FITC-peptidoglycan (6) was selected for resynthesis and validation.     

Synthesis and photochemistry of pH-sensitive GFP chromophore analogs

GFP chromophore analogs (7a-e, 8, and 10a,b) containing 2-thienyl-, 5-methyl-2-furyl-, 2-pyrryl, and 6-methyl-2-pyridyl-groups were synthesized and their fluorescence spectra recorded in the pH range 1-7. NMR studies showed that protonation of 8 (2-thienyl system) inhibited photoisomerization (Z-E) about the exocyclic double bond but that protonation of 7c (E + Z) (2-pyrryl system) gave only 7cE. Fluorescence studies revealed enhancement of fluorescence intensity of 7c and 7b,e (furyl system) below pH 2.5 and gave a similar result for 10a (pyridyl system) below pH 6. Quantum yields at pH 1 were low, probably due to excited state proton transfer (ESPT).     

A “turn-on” fluorescent chemosensor for zinc ion with facile synthesis and application in live cell imaging

Compound 1 was facilely synthesized through a one step reaction from commercially available materials. As a sensitive and selective “turn-on” fluorescent chemosensor for Zn(II), 1 exhibits a 40-fold fluorescence enhancement response to Zn(II) over other physiological relevant metal ions in aqueous solution at neutral pH. Furthermore, 1 could be efficiently delivered to live cells for bioimaging of Zn(II).     

Spectrofluorimetric determination of serotonin and 5-hydroxyindoleacetic acid in urine with different cyclodextrin media

Alternative and sensitive spectrofluorimetric methods for the determination of hydroxyindoles, such as serotonin (5HT) and 5-hydroxyindoleacetic acid (5HIA), were developed on the basis of supramolecular interaction with cyclodextrin (CD) nanocavities (βCD and hydroxypropyl-βCD, HPCD) at different pH values. Both substrates and receptors have acidic protons, therefore the interactions produced in different systems were considered. The effects of neutral CD at pH 2.00 and 6.994, and of anionic CD at pH 13.00 on the specific acid-base species of the compounds at each pH were determined. In all the conditions studied, the fluorescence of the substrates in the presence of CD increased. The association constants (K_A, mol⁻¹ L) between the substrates and CD were determined (30-300) and interpreted. A zero-crossing first-derivative spectrofluorimetric method with and without HPCD was developed for the simultaneous determination of 5HT and 5HIA. The limits of detection (L_D, ng mL⁻¹) for the best conditions were 0.37 for 5HT and 0.50 for 5HIA at pH 2.00 with HPCD. These L_D proved to be better than others reported. The applicability of the direct and derivative spectrofluorimetric methods to urine samples was demonstrated with good recoveries 92-110% and R.S.D. 1-10%.     

6,6′-Bis-substituted BINOL boronic acids as enantioselective and chemoselective fluorescent chemosensors for d-sorbitol

A new chiral fluorescent BINOL boronic acid 1 has been synthesized. The chiral recognition properties of 1 are drastically different from BINOL boronic acid c. Sensor 1 shows improved enantioselectivity as well as chemoselectivity toward sugar alcohols, such as d-sorbitol and d-mannitol.The enantioselectivity of sensor 1 toward d-sorbitol (K_R/K_S) is 1:35 (pH 9.0), and the chemoselectivity for d-sorbitol/d-mannitol is 20:1.     

Synthesis and spectroscopic investigation of trifluoroethoxy-coated phthalocyanine linked with fullerene

Synthesis and spectroscopic investigation of trifluoroethoxy-coated phthalocyanine-fullerene dyad 2 has been described. While nonfluorinated phthalocyanine-fullerene dyad 1 showed an efficient property of intramolecular photoinduced electron transfer, dyad 2, regardless of its covalently linked dyad system, appears not to show any electronic communication between fullerene and phthalocyanine. This observation is presumably due to the strong electron withdrawing nature of 12 trifluoroethoxy groups; fluorine leads phthalocyanine to become an acceptor whose electronic accepting property is equivalent to that of fullerene. This is a unique example that fluorine can terminate electronic communication in the covalently fullerene-phthalocyanine dyad system.     

Salicylaldehyde fluorescein hydrazone: a colorimetric logic chemosensor for pH and Cu(II)

In this work, salicylaldehyde fluorescein hydrazone (1) was synthesized and characterized. Exhibiting reversible color changes responding to different pH in the presence of Cu(II) in buffered media, 1 could be applied as a colorimetric chemosensor for the detection of pH and Cu(II) bi-functionally. It presented a tunable system integrated with a Cu(II)-driven YES logic gate as well as an INHIBIT logic gate, with pH and Cu(II) as its chemical inputs based on encoding binary digits of logical conventions.     

1-(4-Nitrophenoxycarbonyl)-7-pyridin-4-yl indolizine: a new versatile fluorescent building block. Application to the synthesis of a series of fluorescent β-cyclodextrins

The synthesis of a series of new fluorescent building blocks 1a-d incorporating a pyridinoindolizine unit and two potentially reactive sites is described. The reaction of 1a-d with the mono-6-amino-6-deoxy-β-cyclodextrin provides the corresponding fluorescent water soluble hosts 2a-d in good yield. The sensor properties of 2a-d in the presence of 1-adamantanol is described.     

Intramolecular charge transfer dual fluorescent sensors from 4-(dialkylamino)benzanilides with metal binding site within electron acceptor

Three fluoroionophores (2a-c) were designed as the intramolecular charge transfer (CT) dual fluorescent sensors for metal cations with metal binding site within the electron acceptor. These sensors were derived from 4-dialkylaminobenzanilides (alkyl=methyl, ethyl, and n-butyl) with the amido phenyl ring being an arm of 15-crown-5 thus bearing binding site for alkaline and alkaline earth metal cations. Compounds 2a-c were expected to have two possible CT channels of opposite direction. The absorption and fluorescence spectra of 2a-c and their crown-ether free model molecules 3a-c in a variety of solvents were recorded. Dual fluorescence was observed with 2a-c and was assigned to the LE and the CT states, respectively. In nonpolar or less polar solvents the CT occurring with 2a-c was identified as that occurred with benzanilides (BA) with the amido anilines being the electron donor (the BA-like CT), while in polar solvents such as acetonitrile (ACN), the CT was still mainly the BA-like. In the presence of alkali and alkaline earth metal cations in ACN, the CT dual fluorescence underwent substantial changes so as increased total quantum yield, red-shifted LE band and enhanced CT to LE intensity ratio. Binding of the metal cations at the 15-crown-5 moiety of 2a-c was shown to turn the CT direction that the dialkylamino group in the binding complexes being the electron donor while the benzo-15-crown-5 moiety now being within the electron acceptor. The occurrence of this CT enhances metal cation binding to 15-crown-5 ether in 2a-c, which was confirmed by the observed higher metal binding constants. Compounds 2a-c as the CT dual fluorescent sensors were shown to operate under the mechanism of the metal cation binding induced switching of the CT character from the BA-like to that occurred with 4-(dimethylamino)benzamides (the DMABA-like). Compounds 2a-c therefore represent successful examples for the CT dual fluorescent sensors for cations with the metal binding site within the electron acceptor and can be employed as sensitive ratiometric fluorescent sensors for metal cations of improved sensing performance.     

Selective photoswitching of a dyad with diarylethene and spiropyran units

A dyad bearing diarylethene and spiropyran units were synthesized. Ultraviolet light, visible light, H⁺, and Fe³⁺ inputs induce the multiple interconversion among the colorless diarylethene with spiropyran form (3), the colored closed form of diarylethene with spiropyran form (4), ME (5), MEH (6, 7) and MEH·Fe³⁺ (8). The efficient energy transfer from the anthracene emission to MEH·Fe³⁺ or ME·Fe³⁺ form was achieved. Using multi-mode photo switching in a dyad 3, logic gates may be built.     

Structure modulation of metal–organic frameworks via reaction pH: Self-assembly of a new carboxylate containing ligand N-(3-carboxyphenyl)iminodiacetic acid with cadmium(II) and cobalt(II) salts

Self-assembly of a new carboxylate containing ligand, N-(3-carboxyphenyl)iminodiacetic acid (H₃L), with Cd(II) and Co(II) salts under different reaction pH results in the formation of four new coordination polymers, namely [Cd(HL)(H₂O)] (1), [Co(HL)(H₂O)] (2), [Cd(HL)(H₂O)₄] (3) and [Cd₃(L)₂(H₂O)₉] · 7H₂O (4). Single crystal X-ray diffraction analysis indicates that 1 and 2 are isomorphous and isostructural with a 2D wave-like network structure, while 3 has a 1D zigzag chain structure. The complexes 1–3 were obtained at low pH (<7) which makes the ligands only partly deprotonated. However, complex 4, obtained at pH 7 with all the carboxylate groups deprotonated, exhibits a 2D network structure. The results suggest that the reaction pH is one of the key factors in the formation of the coordination architectures. In addition, the photoluminescence properties of the free ligand (H₃L) and complexes 1, 3 and 4 were studied in the solid state at room temperature. Moreover, the magnetic property of complex 2 was investigated.     

Synthesis of environmentally sensitive 2′-deoxyguanosine containing solvatochromic pyrene fluorophore

The synthesis and photophysical property of novel solvatochromic pyrene derivative, Apa5 and fluorescent guanine ^ApaG8 were described. These newly synthesized fluorescent pyrene derivatives exhibited solvent polarity dependent fluorescence at longer wavelengths. Such environmentally sensitive pyrene derivatives can be used as a reporter probe that is sensitive to the changes in the microenvironment around DNA either in vitro or in vivo.     

Characterization of 2-phenylbenzo[g]quinoxaline derivatives as viscosity-sensitive fluorescent probes

To develop viscosity-sensitive fluorescent probes, five different substituted 2-phenylbenzo[g]quinoxaline derivatives (3a-e) were designed and synthesized by using benzo[g]quinoxaline as a fluorophore and phenyl ring bearing a rotatable single bond as a viscosity-sensitive unit. The fluorescence properties of these compounds were investigated in the media of the ethylene glycol-glycerol mixture with varied viscosity. It is found that 2-(4-hydroxyphenyl)benzo[g]quinoxaline (3d) and 2-(4-dimethylaminophenyl)-benzo[g]quinoxaline (3e) carrying stronger electron-donating groups in the phenyl ring show more sensitive fluorescence response to viscosity, revealing their potential use in viscosity detection and the key role of the substituted groups. The effects of solvent polarity and pH on the fluorescent properties of 3d and 3e were also discussed. The present study might be useful in developing viscosity-sensitive fluorescent probes.