Spectroscopic behavior on the formation complex of three double-armed calix[4]arene derivatives with lanthanoid nitrates in acetonitrile

The complexation spectroscopic behavior of three p-tert-butylcalix[4]arene Schiff bases i.e. 5,11,17,23-tetra-tert-butyl-25,27-bis[2-[N-(3-nitrobenzylidene)amino]ethoxy]-26,28-dihydroxycalix[4]arene (1), 5,11,17,23-tetra-tert-butyl-25,27-bis[2-[N-(2-hydroxybenzylidene)amino]ethoxy]-26,28-dihydroxycalix[4]arene (2), and 5,11,17,23-tetra-tert-butyl-25,27-bis[2-[N-(2-hydroxy-3-methoxybenzylidene)amino]ethoxy]-26,28-dihydroxycalix[4]arene (3) with lanthanoid nitrates (Tb3+ and Eu3+) has been investigated in anhydrous acetonitrile at 25 degrees C by using UV-vis and FT-IR as well as fluorescence spectra. The results obtained indicated that the spectroscopic behavior of compounds 1-2 upon complexation with lanthanoid ions did not show any significant larger difference in comparison with free compounds 1 and 2, which may be contributed to the poor binding ability. Contrary to compounds 1 and 2, the lower rim functional groups in compound 3 can form two large pi electron conjugate system with lanthanide ion and encapsulate lanthanide ions tightly, displaying the novel spectroscopic behavior upon complexation with lanthanide ions. As compared with compound 3, the formation complexes of compound 3 with Tb3+ and Eu3+ showed new broad intense absorption at 398 nm, respectively, and IR spectra showed that O-H stretching vibration at 3413.40 cm(-1) displayed a large drop. It is interestingly noted that the narrow emission line spectra were observed only for 3 complex with Tb3+, but did not for 3-Eu3+ complex. In the 3-Eu3+ complex, the broad-band emission at lambda(max) = 534 nm was obtained at the excitation of 398 nm. The spectroscopic behavior of three calix[4]arene derivatives upon complexation with lanthanoids was discussed from the relationship between the host structure and the properties of guest lanthanide ions.     

Nitro-substituted stilbeneboronate pinacol esters and their fluoro-adducts. Fluoride ion induced polarity enhancement of arylboronate esters

A series of stilbeneboronate pinacol cyclic esters, containing none to three nitro groups, have been synthesized by various olefination reactions and characterized by X-ray single-crystal structure analysis. A stilbeneboronate ester bearing electron-acceptor groups experiences transition to a push-pull pi-electron system upon complexation with one fluoride ion at the boron atom. The UV-vis absorption maxima of the presented nitro-substituted stilbeneboronate esters are red-shifted upon addition of fluoride ions, indicating this binding event. The enhancement of the polarity of the investigated compounds and the changes in the electronic system were investigated by UV-vis absorption spectroscopy and solvatochromism. Additionally, studies were performed by natural bond orbital (NBO) analysis and RI-CC2 calculations of the vertical excitation energies. The synergism of fluoride ion complexation and solvation upon the UV-vis band shift is interpreted in terms of linear solvation energy relationships (LSERs) using the Kamlet-Taft solvent parameter set. It is found that the UV-vis absorption of the fluoro-boronates is strongly dependent on the solvents hydrogen-bond donating ability.     

A fluorescent fluoride ion probe based on a self-organized ensemble of 5-hydroxyflavone-Al(III) complex

In the presence of Al(III) ions, 5-hydroxyflavone (5HF) through a complexation reaction in MeOH, shows dual fluorescence, characterized by a newly developed peak at 554nm upon excitation at 363nm. In this communication, the subsequent ligand exchange reaction of the complex with fluoride ion causing a fluorescence enhancement followed by a decrease in fluorescence intensity involving an intermediate mechanistic pathway, delivering a quantitative estimation route for fluoride ion in the concentration range from 5x10(-5) to 7x10(-4)M, has been reported. The ligand exchange reaction, without interference from other common anions, has been investigated by UV-vis and fluorescence spectroscopies combined with the AM1 semi-empirical self-consistent field quantum chemical calculations within UHF formalism in their ground state.     

双吲哚啉螺吡喃化合物的合成及其酸和金属离子致变色性能

设计、合成了一种新型双吲哚啉螺吡喃化合物1,用核磁、红外及质谱等技术手段表征了其结构。 利用紫外可见吸收光谱研究了化合物1的酸致变色和金属离子变色性能。 结果表明,化合物1能够在氢离子或金属离子的作用下发生可逆的开环与闭环反应。 当氢离子或金属离子加入到化合物1的异丙醇溶液中,溶液颜色从无色变为红色,同时产生460 nm新吸收峰。 进一步加入氢氧根离子或EDTA溶液后,溶液颜色变回无色,460 nm处的吸收峰又消失。 该化合物的酸和金属离子致变色性质在分子传感和离子识别等领域有潜在的应用价值。     

Calix[4]pyrrole virtuous sensor: a selective and sensitive recognition for Pb(II) ions by spectroscopic and computational study

A novel supramolecular sensor derived from calix[4]pyrrole system i.e. calix[4]pyrrole bearing aminoanthraquinone derivative (CAAQ) have been designed and synthesized. The complexation behavior of metal cations [Ag(I), Ba(II), Ca(II), Ni(II), Co(II), Fe(III), Hg(II), Cu(II), Cr(II), Pb(II), Zn(II), (1 × 10^?4 M)] with CAAQ (1 × 10^?6 M) was studied by spectrophotometry and spectrofluorometry. Metal ion like Pb(II) produces red shift in absorption spectra and quenching in emission spectra likelihood of strong complexation of Pb(II) ions with CAAQ. Fluorescence cell imaging also supports the complexation of Pb(II) ions with CAAQ. The binding constants, quantum yield, stoichiometry of complex, mechanism of quenching by Stern–Volmer equation and Density functional theory calculation have been determined.     

Fluoride ion detection by 8-hydroxyquinoline-Zr(IV)-EDTA complex

A simple fluorescent detection based on the ligand exchange mechanism is proposed for the fluoride ion in aqueous media. This procedure is based on the exchange of 8-hydroxyquinoline (oxine) coordinated to Zr(IV) by fluoride ion without interference from other common anions. The ternary complex of oxine with [Zr(H(2)O)(2)EDTA].2H(2)O formed by replacing two water molecules in aqueous solution provides a sensitive signalling system for fluoride ion in the concentration range from 6 x 10(-7)M to 8 x 10(-4)M. The green fluorescence (lambda(max)=532 nm) exhibited by the complex upon excitation at 247 nm decreases in intensity with fluoride addition with a detection limit of 12 ppb. The complexation reaction between oxine and Zr(IV)-EDTA and the ligand exchange reaction with fluoride ion has been investigated by UV-vis and fluorescence spectroscopies combined with the PM3 semi-empirical quantum chemical calculations. Job's method of continuous variation and the molar ratio method ascertain a 1:1 stoichiometry composition of the chelate in aqueous media.     

Synthesis and ion sensing properties of new colorimetric and fluorimetric chemosensors based on bithienyl-imidazo-anthraquinone chromophores

Novel colorimetric receptors for fluoride ion sensing containing anthraquinone as a chromogenic signaling unit and imidazo-2,2'-bithiophene binding sites are reported. Well-defined color change was observed upon addition of fluoride ions to acetonitrile solutions of receptors 2. Compounds 2a-c, deprotonated after fluoride ion addition, were studied as metal ion chemosensors in the presence of Zn(II), Hg(II), and Cu(II) in acetonitrile solutions, especially compound 2a which displayed a marked change from pink to yellow-gold colors upon complexation.     

PHOTOPHYSICS and PHOTOCHEMISTRY OF BIS-2-(9-ANTHRYL)ETHYL GLUTARATE

Abstract— The photochemistry and photophysics of bis-(2-(9-anthryl)ethyl glutarate 2 and 2-(9-anthryl) ethyl pivalate 3 have been examined as monomeric models for poly-2-(9-anthryl)ethyl methacrylate 1. The absorption and excitation spectra of 2 show no ground state interaction, but appreciable monomer (51%) and excimer (49%) emission. Delayed monomer and excimer fluorescence are also observed in fluid solution at room temperature. Photolysis of 2 at low temperature produces a photoproduct (44% yield) which is unstable at room temperature and presumably is the head-to-head (H-H) dimer. Steady state irradiation of 2 at room temperature (Λ 350 nm) cleanly produces a head-to-tail (H-T) dimer (6) derived from the singlet state and an additional unidentified adduct (7). The product distribution is concentration dependent, with 6 predominating at high concentrations (> 10⁻³ M ). The fluorescence spectra of the broken dimers derived from 6 and 7 indicate that substantial ir overlap exists in the transition state leading to each product.     

Investigation of the spectral properties of a squarylium near-infrared dye and its complexation with Fe(III) and Co(II) ions.

The spectral features of the squarylium dye NN525 in different solutions and its complexation with several metal ions were investigated. The absorbance maximum of the dye is at 669 nm in tetrahydrofuran. This value matches the output of a commercially available laser diode (650 nm), thus making use of such a source practical for excitation. The emission maximum of the dye in tetrahydrofuran is at 676 nm. The addition of either Fe(III) ion or Co(II) ion resulted in fluorescence quenching of the dye. The detection limit is 6.24 x 10(-8) M for Fe(III) ion and 1.55 x 10(-8) M for Co(II) ion. The molar ratio of the metal to the dye was established to be 1:1 for both metal ions. The stability constant Ks of the metal-dye complex was calculated to be 3.14 x 10(6) M(-1) for the Fe-dye complex and 2.64 x 10(5) M(-1) for the Co-dye complex.     

1,5-二芳基-3-(2-羟基-4,6-二甲氧基苯基)-2-吡唑啉的合成及氟离子荧光探针行为

设计合成了8个1,5-二芳基-3-(2-羟基-4,6-二甲氧基苯基)-2-吡唑啉化合物4a~4h. 它们的结构经由IR、1H NMR、MS和元素分析确认. 测定了它们的紫外光谱和荧光光谱, 研究了它们对氟离子的选择性识别作用, 发现化合物4a,4c和4d均可选择性地识别氟离子, 其中4a和4c作为识别氟离子的荧光探针, 受常见离子干扰较小, 选择性较高.     

Charge‐Transfer Interactions in Tris‐Donor–Tris‐Acceptor Hexaarylbenzene Redox Chromophores

Symmetric‐ and asymmetric hexaarylbenzenes (HABs), each substituted with three electron‐donor triarylamine redox centers and three electron‐acceptor triarylborane redox centers, were synthesized by cobalt‐catalyzed cyclotrimerization, thereby forming compounds with six‐ and four donor–acceptor interactions, respectively. The electrochemical‐ and photophysical properties of these systems were investigated by cyclovoltammetry (CV), as well as by absorption‐ and fluorescence spectroscopy, and compared to a HAB that only contained one neighboring donor–acceptor pair. CV measurements of the asymmetric HAB show three oxidation peaks and three reduction peaks, whose peak‐separation is greatly influenced by the conducting salt, owing to ion‐pairing and shielding effects. Consequently, the peak‐separations cannot be interpreted in terms of the electronic couplings in the generated mixed‐valence species. Transient‐absorption spectra, fluorescence‐solvatochromism, and absorption spectra show that charge‐transfer states from the amine‐ to the boron centers are generated after optical excitation. The electronic donor–acceptor interactions are weak because the charge transfer has to occur predominantly through space. Moreover, the excitation energy of the localized excited charge‐transfer states can be redistributed between the aryl substituents of these multidimensional chromophores within the fluorescence lifetime (about 60 ns). This result was confirmed by steady‐state fluorescence‐anisotropy measurements, which further indicated symmetry‐breaking in the superficially symmetric HAB. Adding fluoride ions causes the boron centers to lose their accepting ability owing to complexation. Consequently, the charge‐transfer character in the donor–acceptor chromophores vanishes, as observed in both the absorption‐ and fluorescence spectra. However, the ability of the boron center as a fluoride sensor is strongly influenced by the moisture content of the solvent, possibly owing to the formation of hydrogen‐bonding interactions between water molecules and the fluoride anions.     

Cyanide ion complexation by a cationic borane

While we have previously reported that [1-(Mes2B)-8-(Me3NCH2)-C10H6]+ ([2]+) complexes fluoride ions to form [1-(Mes2FB)-8-(Me3NCH2)-C10H6] (2-F), we now show that this cationic borane also complexes cyanide to form [1-(Mes2(NC)B)-8-(Me3NCH2)-C10H6] (2-CN). This reaction also occurs under biphasic conditions (H2O-CHCl3) and may serve to transport cyanide in organic phases. The zwitterionic cyanoborate 2-CN has been fully characterized and its crystal structure determined. UV-vis titration experiments carried out in THF indicate that [2]+ has a higher affinity for fluoride (K > 10(8) M(-1)) than cyanide (K = 8.0 (+/-0.5) x 10(5) M(-1)). Steric effects which impede cyanide binding to the sterically congested boron center of [2]+ are most likely at the origin of this selectivity. Finally, electrochemical studies indicate that [2]+ is significantly more electrophilic than its neutral precursor 1-(Mes2B)-8-(Me2NCH2)-(C10H6) (1). These studies also show that reduction of [2]+ is irreversible, possibly because of elimination of the NMe3 moiety under reductive conditions. In fact, [2]OTf reacts with NaBH4 to afford 1-(Mes2B)-8-(CH3)-(C10H6) (4) which has also been fully characterized.     

Sensitive and selective PET-based diimidazole luminophore for Zn(II) ions: a structure-activity correlation

3-(3-Ethoxymethyl-1H-imidazol-2-yl)-3-(1-ethoxymethyl-1H-imidazol-2-yl)-3H-benzo[de]isochromen-1-one, 4, is a novel photoinduced electron transfer (PET) chemosensor that becomes fluorescent upon binding metal ions and shows a strong preference toward Zn(II) ions. The new bisimidazol PET sensor and its zinc complex were prepared and characterized in terms of their crystal structures, absorption and emission spectra, and orbital energy diagrams. Free 4 is a weakly luminescent species. On the basis of detailed DFT calculations, we suggest that the poor luminescence yield of free 4 originates from its orbital structure in which two pi-orbitals of the two imidazole rings, HOMO and HOMO-1, are situated between two pi-orbitals of the isochromene-one system, HOMO-2 and LUMO. The absorption and emission processes occur between the two pi-orbitals of the isochromene-one system, HOMO-2 and LUMO, and the two pi-imidazole orbitals serve as quenchers for the excited state of the molecule through nonradiative processes. Upon binding Zn(II) ions, 4 becomes a highly luminescent species having a luminescence maximum peaking at 375 nm (lambda(ex) = 329 nm). The significant 900-fold enhancement in luminescence upon binding of the Zn(II) ions is attributed to the stabilization of the pi-orbitals of the imidazole rings upon their engagement in new bonds with the zinc ion. The affinity of 4 to zinc ions in acetonitrile is found to be very high, Ka > 3 x 10(6) M(-1), while with other metals ions, the association constants are considerably weaker.     

A highly Lewis acidic triarylborane bearing peripheral o-carborane cages

A triarylborane (2) bearing three o-carborane cages at peripheral positions on the aryl groups was prepared and its crystal structure was determined from X-ray diffraction study. Treatment of 2 with KF in the presence of 18-crown-6 led to the potassium salt, [2F](-). A UV-vis titration experiment carried out in THF/H(2)O (9/1 v/v) showed that 2 binds fluoride ions with a binding constant (K) of 4.8 × 10(4) M(-1), which is an order-of-magnitude greater than K for the mono-carborane substituted triarylborane. The enhanced fluoride ion affinity of 2 indicates an apparent additive effect of multiple carborane substitutions on the Lewis acidity enhancement of the triarylborane. The highly Lewis acidic nature of 2 was further utilized in evaluating the fluoride ion affinity of tris(pentafluorophenyl)borane (B(C(6)F(5))(3)). A fluoride exchange reaction between [2F](-) and B(C(6)F(5))(3) resulted in 15 times higher fluorophilicity for B(C(6)F(5))(3) than for 2. The lower Lewis acidity of 2 compared with B(C(6)F(5))(3) was confirmed from its greater cathodic reduction potential.     

Construction of subphthalocyanine-porphyrin and subphthalocyanine-phthalocyanine heterodyads through axial coordination

The treatment of boron(III) subphthalocyanine chloride (SPcCl) with 3- or 4-hydroxypyridine in the presence of pyridine in toluene gave the corresponding boron(III) subphthalocyanine pyridinolates SPc(3-OPy) ( 1) or SPc(4-OPy) ( 2). Having a pyridyl group, these compounds could axially complex with a series of zinc(II) and ruthenium(II) porphyrins and phthalocyanines to form the corresponding subphthalocyanine-porphyrin and subphthalocyanine-phthalocyanine heterodyads. As revealed by UV-vis spectroscopy, the ground-state interaction between the two chromophores in these dyads is insignificant. The complexation processes were also studied by (1)H NMR and fluorescence spectroscopic methods, which confirmed the 1:1 binding stoichiometry. The association constants, as determined by fluorescence titration, were generally higher for the ruthenium(II) tetrapyrroles [(2.5-4.7) x 10 (4) M (-1)] than for the zinc(II) counterparts [(0.3-1.8) x 10 (4) M (-1)]. The molecular structures of the two pyridyl subphthalocyanines 1 and 2, together with three novel subphthalocyanine-porphyrin heterodyads, were also determined by X-ray diffraction analyses.     

Fluoride ion capture from water with a cationic borane

The reaction of the [Li(THF)4]+ salt of dimesityl-1,8-naphthalenediylborate with [Me2NCH2]I affords a borane (1-(Mes2B)-8-(Me2NCH2)-C10H6) which can be converted into a cationic borane [3]+ ([1-(Mes2B)-8-(Me3NCH2)-C10H6]+) by methylation with MeOTf. This cationic borane promptly complexes fluoride to afford the corresponding zwitterionic ammonium/fluoroborate 3-F (1-(Mes2FB)-8-(Me3NCH2)-C10H6). Cation [3]+ fails to react with chloride, bromide, and iodide indicating that fluoride complexation is selective. Structural, spectroscopic, and computational studies carried out on 3-F show the existence of an unusual C-H...F-B hydrogen bond. Remarkably, [3]+ captures fluoride from water under biphasic conditions (H2O/CHCl3) to form 3-F. The high fluoride affinity of [3]+ can be correlated to the Coulombic forces which stabilize the B-F bond against heterolysis.     

Multistage complexation of fluoride ions by a fluorescent triphenylamine bearing three dimesitylboryl groups: controlling intramolecular charge transfer

A propeller-shaped boron-nitrogen compound (NB(3)) with three binding sites for fluoride anions was synthesized and investigated by optical absorption, luminescence, and ((1)H, (11)B, (13)C, (19)F) NMR spectroscopy. Binding of fluoride in dichloromethane solution occurs in three clearly identifiable steps and leads to stepwise blocking of the three initially present nitrogen-to-boron charge transfer pathways. As a consequence, the initially bright blue charge transfer emission is red-shifted and decreases in intensity, until it is quenched completely in presence of large fluoride excess. Fluoride binding constants were determined from global fits to optical absorption and luminescence titration data and were found to be K(a1) = 4 × 10(7) M(-1), K(a2) = 2.5 × 10(6) M(-1), and K(a3) = 3.2 × 10(4) M(-1) in room temperature dichloromethane solution. Complexation of fluoride to a given dimesitylboryl site increases the electron density at the central nitrogen atom of NB(3), and this leads to red shifts of the remaining nitrogen-to-boron charge transfer transitions involving yet unfluorinated dimesitylboryl groups.     

A highly selective and sensitive BODIPY-based colourimetric and turn-on fluorescent sensor for Hg2+ ions

A series of monostyryl boron dipyrromethenes appended with an NO(4), NO(2)S(2), N(3)O(4), or N(3)O(2)S(2)-type ligand have been prepared and characterised. While the UV-Vis spectra of the former three compounds in CH(3)CN/H(2)O (2?:?3 v/v) do not respond towards a wide range of metal ions, the derivative with an N(3)O(2)S(2)-ligand exhibits a highly selective and sensitive spectral response towards Hg(2+) ions. The absorption band is blue-shifted by 40 nm due to inhibition of the intramolecular charge transfer process upon metal complexation. The fluorescence is also turned on giving a strong emission band at 572 nm. The colour changes can be easily detected by the naked eye. The results suggest that this compound serves as a promising colourimetric and fluorescent sensor for Hg(2+) ions in this mixed aqueous medium.     

A highly emissive cruciform triarylborane as a ratiometric and solid state fluorescence sensor for fluoride ions

We disclosed a novel cruciform tri-coordinate organoboron compound, 2′,5′-bis{[(4-dimesitylboryl)phenyl]ethynyl}-1′,4′-bis[(4-N,N-diphenylamino)phenyl]-[1,1′:4′,1′]terphenyls, which displays a characteristic intramolecular charge transfer transition and is highly emissive both in solutions and solid state. The complexation with fluoride ions induces a large blue shift in fluorescence, enabling ratiometric fluorescence sensing of fluoride. In addition, its prompt response to fluoride ions was also observed even in the solid state.     

Ammonium boranes for the selective complexation of cyanide or fluoride ions in water

With the recognition of aqueous fluoride and cyanide ions as an objective, we have investigated the anion binding properties of two isomeric ammonium boranes, namely [p-(Mes2B)C6H4(NMe3)]+ ([1]+) and [o-(Mes2B)C6H4(NMe3)]+ ([2]+). These cationic boranes, which could be obtained by reaction of the known 4- and 2-dimesitylboryl-N,N-dimethylaniline with MeOTf, have been investigated both experimentally and computationally. They both react with fluoride and cyanide ions in organic solvents to afford the corresponding fluoroborate/ or cyanoborate/ammonium zwitterions 1F, 1CN, 2F, and 2CN. In aqueous solution, however, these cationic boranes behave as remarkably selective receptors. Indeed, [1]+ only complexes cyanide ions while [2]+ only complexes fluoride ions. In H2O/DMSO 60:40 vol (HEPES 6 mM, pH 7), the cyanide binding constant of [1]+ and the fluoride binding constant of [2]+ are respectively equal to 3.9 (+/-0.1) x 108 and 910 (+/-50) M-1. Structural and computational studies indicate that both steric and electronic effects contribute to the unusual selectivity displayed by these cationic boranes. Owing to favorable Coulombic effects, the para-derivative [1]+ has a very high affinity for cyanide; yet these effects are not sufficiently intense to allow complexation of the more efficiently hydrated and less basic fluoride anion. In the case of the ortho-derivative [2]+, the proximity of the ammonium moiety leads to an increase in the Lewis acidity of the boron center thus making fluoride binding possible. However, steric effects prevent cyanide coordination to the boron center of [2]+. Finally, cation [1]+ and [2]+ bind their dedicated anions reversibly and show a negligible response in the presence of other common anions including Cl-, Br-, I-, NO3-, OAc-, H2PO4-, and HSO4-.