Structural and photophysical properties of lathanide(III) complexes with a novel octadentate iminophenolate bibracchial lariat ether

We report here a structural and photophysical study of lanthanide complexes with the di-deprotonated form of the bibracchial lariat ether N,N'-bis(2-salicylaldiminobenzyl)-4,10-diaza-12-crown-4 (L(3)) (Ln = Ho(III)-Lu(III)). The X-ray crystal structures of [Ho(L(3)-2H)](ClO(4)) (1) and [Er(L(3)()-2H)](ClO(4)) (2) show the metal ion being eight-coordinate and deeply buried in the cavity of the dianionic receptor. Both sidearms of L(3) are on the same side of the crown moiety, resulting in a syn conformation. Likewise, the lone pair of both pivotal nitrogen atoms is directed inward of the receptor cavity in an endo-endo arrangement and the coordination polyhedron around the lanthanide ion may be described as a distorted square antiprism that shows a deformation toward a square prism by ca. 11 degrees . Attempts to isolate complexes of the lightest members of the lanthanide series were unsuccessful, which suggests a certain degree of selectivity of L(3) toward the heaviest Ln(III) ions. This was evaluated and rationalized on the basis of theoretical calculations performed in vacuo at the HF level, by using the 3-21G basis set for the ligand atoms and a 46+4f(n) effective core potential for lanthanides. For the [Ln(L(3)()-2H)](+) systems, the calculated bond distances between the metal ion and the coordinated donor atoms decrease along the lanthanide series, as usually observed for Ln(III) complexes. However, for the related [Ln(L(1)-2H)](+) and [Ln(L(2)()-2H)](+) systems our ab initio calculations provide geometries in which some of the bond distances of the metal coordination environment increase across the lanthanide series. Thus, thanks to the variation of the ionic radii of the lanthanide ions, receptors L(1)() (N,N'-bis(2-salicylaldiminobenzyl)-4,13-diaza-18-crown-6) and L(2) (N,N'-bis(2-salicylaldiminobenzyl)-1,10-diaza-15-crown-5) are specially adapted for the complexation of the lighter lanthanide ions. On the other hand, the erbium and ytterbium complexes of L(3) have been shown to be emissive in the near-IR. Time-resolved studies of complexes confirm that solvent is excluded from the inner coordination sphere in solution. The luminescence properties of the complexes make them ideally suited for use as luminescent tags and suggest that q = 0 complexes of erbium may, after all, be useful as luminescent tags in protic media.     

Dependence of the photophysical properties on the number of 2,2'-bipyridine units in a series of luminescent europium and terbium cryptates

The luminescence properties of a series of lanthanoid cryptates with an increasing number of 2,2'-bipyridine units have been investigated for the lanthanoids Eu and Tb in aqueous solution. The trends in important parameters that influence the photophysics in these complexes have been determined. With increasing bipyridine content, an increase is observed for the intersystem crossing efficiencies and the number of inner-sphere water molecules. In contrast, a decrease is found in the same direction for overall quantum yields, triplet energies, and sensitization efficiencies.     

Structural characterisation and photophysical properties of lanthanoid complexes of a tetra-amide functionalised calix[4]arene

Abstract

Lanthanoid complexes of a tetra-amide substituted calix[4]arene in the cone conformation are characterised by single crystal X-ray structure determination. The structural analysis shows that the metal ions are coordinated to the calixarene through the eight O donor atoms, along with one aqua ligand which is located within the cavity of the calixarene. The calixarene ligand was covalently incorporated into a polymethylmethacrylate monolith through p-allyl functional groups, followed by loading with a range of lanthanoid cations giving rise to light-emitting materials. The emission from the hydrid materials was found to be comparable to the solution phase emission.     

Structural, photophysical, and catalytic properties of Au(I) complexes with 4-substituted pyridines

Ionic gold(I) complexes with general formula of [Au(Py)2][AuCl2] and [Au(Py)2][PF6] (Py = 4-substituted pyridines) have been synthesized. Structures of five Au(I) complexes and a Ag(I) complex were determined by single crystal X-ray diffraction. Evidence for cationic aggregation of [Au(py)2][PF6] complexes in solution was obtained by conductivity measurements and by the isosbestic point observed from variable temperature UV-visible absorption spectra. All compounds were luminous in the solid state. Calculations employing density functional theory were performed to shed light on the nature of the electronic transitions. While the [Au(4-dmapy)2][AuCl2] (4-dmapy = 4-dimethylaminopyridine) and [Au(4-pic)2][AuCl2] (4-pic = 4-picoline) emissions were found to be mainly ligand in nature, their [PF6](-) counterparts involved a Au...Au-interaction imbedded in the highest occupied molecular orbital. [Au(4-dmapy)2][AuCl2] was found to be an efficient catalyst for Suzuki cross-coupling of aryl bromide and phenylboronic acid.     

Synthesis and photophysical properties of 2-styrylquinazolin-4-ones

trans-2-Styryl-substituted 3H-, 3-phenyl-, and 3-naphthylquinazolin-4-ones and their 6,7-difluoro derivatives were synthesized by condensation of appropriate 2-methylquinazolin-4-ones with aromatic aldehydes or by the transformation of the heterocycle of 2-methyl-3,1-benzoxazin-4-one under the action of benzylidenephenylamines.     

Syntheses and photophysical properties of some 4‐arylpyridinium salts

A number of 4‐arylpyridines, many methoxy substituted, were prepared by an efficient two‐step method involving aryl Grignard addition to 1‐methyl‐4‐piperidone and direct aromatization of the resulting 4‐aryl‐4‐piperidinols. The pyridines were N‐alkylated to give sulfonate salts desired for their fluorescent properties. Study of selected compounds as laser dyes revealed several structures to be efficient dyes lasing in the 530‐550 nm range. Two new diazaquaterphenyls were prepared and were quaternized. These salts exhibited intense fluorescence in the 420‐450 nm range, but would not lase. A phenolic azaterphenyl suitably substituted for excited state intramolecular proton transfer (ESIPT) did not fluoresce at all.     

Syntheses and photophysical properties of fluorescent 2-aryl-3-hydroxy-4-chromenones

The particle detectors proposed for the Super-conducting Super Collider contain polystyrene scintillation fibers as a component. Scintillation fluors soluble in styrene are required which have improved light output and response time. New 2-aryl-3-hydroxy-4-chromenones related to 3-hydroxyflavone were prepared which displayed these improved properties. Improved solvent systems for chromenone formation were essential in the synthesis of two of the chromenones. One chromenone produced fluorescence emission at 560 nm with a quantum yield of 0.53 and a scintillation decay time of 5 nsec.     

Solvent influence on the photophysical properties of 4-methoxy-N-methyl-1,8-naphthalimide

4-Methoxy-N-methyl-1,8-naphthalimide (1) exhibits considerable solvatochromism and its UV-vis spectral properties have been studied in several polar/non-polar and protic/aprotic solvents, as well as in ethanol-water mixtures. The results reveal a strong influence of the solvent's polarity and its hydrogen-bond donor (HBD) capability on the photophysical properties of 1. For binary ethanol/water mixtures, preferential solvation models describe the band shifts in the probe's visible absorption spectrum well, but they fail to describe the corresponding shifts of the emission maxima. Pseudolinear approximations between solvent composition and molecule's transition energies, E(T), can be used to study the composition of ethanol-water mixtures, simplifying the mathematical treatment for eventual analytical applications.     

Influence of solvent properties on cation-macrocycle complexation: Cesium cryptates

The chemical shift of the¹³³Cs resonance has been measured as a function of the mole ratio of cryptands C222, C222B, C221, and C211 to the Cs⁺ ion inN-methylformamide and dimethylacetamide solutions. The overall formation constants of the cesium cryptates were calculated from the NMR titration curves. From these and previously reported data it is clear that solvent properties such as dipole moment, donicity, dielectric constant and hydrogen bonding ability affect macrocyclic ligand-cation complexation equilibria through specific solvation of the cation, the ligand and the complex. A model of M⁺ · L bonding in solution, involving a rather intimate electrostatic attraction between the cation and the local electron distribution of the macrocycle accompanied by little perturbation of the charge distributions of the separated partners, is presented. In addition to the specific interactions previously noted, the presence of the solvent mitigates the ion-multipole forces which would otherwise govern the long-range attraction.This paper is dedicated to the memory of the late Dr C. J. Pedersen.Deceased.     

Photochemical and photophysical properties of indoprofen

The photophysical properties and photochemistry of indoprofen (INP) have been investigated. Absorption and emission spectroscopies in phosphate buffer, ethanol and ether show that INP photophysics is dominated by a singlet-singlet transition of pipi* character. INP fluoresces at room temperature, with a quantum yield approximately 0.04. Flash photolysis experiments together with the lack of phosphorescence at room temperature point to a very weak intersystem crossing. The photoreactivity of INP is centered on the propionic acid chain and gives rise to photoproducts similar to those obtained with other arylpropionic acids (ethyl, hydroxyethyl and acetyl derivatives). Thus, irradiation of INP in aqueous buffer results in photodecarboxylation and leads mainly to oxidative compounds whose proportions increase with increasing oxygen concentration. These data suggest a photoreactivity occurring from the excited singlet state.     

A new approach to 4-arylstyrenes: microwave-assisted synthesis and photophysical properties

Russian Chemical Bulletin - A convenient method was developed for the synthesis of 4-arylstyrenes containing residues of polycyclic aromatics or triphenylamine. The method is based on the...     

Primary photophysical properties of ofloxacin

Steady-state fluorescence has been used to study the excited singlet state of ofloxacin (OFLX) in aqueous solutions. Fluorescence emission was found to be pH dependent, with a maximum quantum yield of 0.17 at pH 7. Two pKa*s of around 2 and 8.5 were obtained for the excited singlet state. Laser flash photolysis and pulse radiolysis have been used to study the excited states and free radicals of OFLX in aqueous solutions. OFLX undergoes monophotonic photoionization from the excited singlet state with a quantum yield of 0.2. The cation radical so produced absorbs maximally at 770 nm with an extinction coefficient of 5000 +/- 500 dm3 mol-1 cm-1. This is confirmed by one-electron oxidation in the pulse radiolysis experiments. The hydrated electron produced in the photoionization process reacts with ground state OFLX with a rate constant of 2.0 +/- 0.2 x 10(10) dm3 mol-1 s-1, and the anion thus produced has two absorption bands at 410 nm (extinction coefficient = 3000 +/- 300 dm3 mol-1 cm-1) and at 530 nm. Triplet-triplet absorption has a maximum at 610 nm with an extinction coefficient of 11,000 +/- 1500 dm3 mol-1 cm-1. The quantum yield of triplet formation has been determined to be 0.33 +/- 0.05. In the presence of oxygen, the triplet reacts to form both excited singlet oxygen and superoxide anion with quantum yields of 0.13 and < or = 0.2, respectively. Moreover, superoxide anion is also formed by the reaction of oxygen with the hydrated electron from photoionization. Hence the photosensitivity due to OFLX could be initiated by the oxygen radicals and/or by OFLX radicals acting as haptens.     

Arylethynylacridines: electrochemiluminescence and photophysical properties

Electrogenerated chemiluminescence (ECL) of six new ethyne-based acridine derivatives (1-6) has been studied. The new acridine derivatives were synthesized by cross-coupling of 9-chloroacridine and corresponding donor-substituted phenylethynes under modified Sonogashira conditions. The donor groups were varied in the order of increasing steric hindrance and donor strength at the donor site. The solution phase photophysical properties and ECL of these compounds were studied comparatively in acetonitrile solvent. The UV-Visible spectra of compounds 1-5 exhibit closely the same maxima. Density functional theory (DFT) has been invoked to analyze and understand the unexpected UV-Visible absorption behavior. Compounds with weak electron donors produce excimer ECL irrespective of steric hindrance at the donor site, while the compound with a stronger donor gives rise to ECL that is blue-shifted with respect to its photoluminescence spectrum. All except one of these compounds also exhibit solid state fluorescence which may be useful for solid state devices such as organic light emitting diodes (OLEDs) and as laser dyes. The observed properties are discussed with reference to the structure of the compounds synthesized.     

Synthesis and photophysical properties of ferrocene-oligothiophene-fullerene triads

To promote photoinduced charge separation previously observed for the oligothiophene-fullerene dyads (nT-C60), we have designed an additional attachment with a strongly electron-donating ferrocene at the unsubstituted terminal site of the oligothiophene and synthesized two types of the ferrocene-oligothiophene-fullerene triads, Fc-nT-C60 directly linking the ferrocene to the oligothiophene and Fc-tm-nT-C60 inserting a trimethylene spacer between the ferrocene and the oligothiophene. For the central oligothiophene of the triads, a homologous series of quaterthiophene (4T), octithiophene (8T), and duodecithiophene (12T) are systematically examined. The cyclic voltammograms and electronic absorption spectra of Fc-nT-C60 indicate conjugation between the ferrocene and oligothiophene components. The emission spectra of Fc-nT-C60 measured in toluene demonstrate that the fluorescence of the oligothiophene is markedly quenched, as compared to that observed for the dyads nT-C60. This quenching is explained in terms of the involvement of intramolecular electron transfer in the photophysical decay process. The additionally conjugated ferrocene evidently contributes to the stabilization of charge separation states, thus promoting intramolecular electron transfer. This is corroborated by the observation that the emission spectra of the nonconjugated triads Fc-tm-nT-C60 are essentially similar to the corresponding dyads nT-C60.     

Synthesis and photophysical properties of lead phthalocyanines

This work reports on the synthesis and photophysical parameters of tetra-and octa-substituted new lead phthalocyanines. The complexes synthesized are: 1,4-(tetraphenoxyphthalocyaninato)lead (7a), 1,4-(tetra-tert-butylphenoxyphthalocyaninato)lead (7b), 2,3-(tetraphenoxyphthalocyaninato)lead (8a), 2,3-(tetra-tert-butylphenoxyphthalocyaninato)lead (8b), 2,3-octaphenoxyphthalocyaninatolead (9a) 2,3-[octakis(4-t-butylphenoxyphthalocyaninato)]lead (9b). Photophysical properties were studied for these complexes in a dimethylsulfoxide, dimethylformamide, toluene, tetrahydrofuran and chloroform. The fluorescence spectra were different from excitation spectra due to demetallation upon excitation. High triplet quantum yields ranging from 0.70 to 0.88 (in DMSO, DMF and toluene) and low triplet lifetimes (20–50 μs in DMSO, and <10 μs in the rest of the solvents) were observed due to the presence of heavy atom.     

Optical and photophysical properties of indolocarbazole derivatives

We present a study of the optical and photophysical properties of five ladder indolo[3,2-b]carbazoles, namely, M1, M2, M3, M4, and M5. The ground-state optimized structures were obtained by B3LYP/6-31G* density functional theory (DFT) calculations, whereas the optimization (relaxation) of the first singlet excited electronic state (S1) was performed using the restricted configuration interaction (singles) (RCIS/6-31G*) approach. The excitation to the S1 state does not cause important changes in the geometrical parameters of the compounds, as corroborated by the small Stokes shifts. The excitation and emission energies have been obtained by employing the time-dependent density functional theory (TDDFT). For all the compounds, excitation to the S1 state is weakly allowed, whereas the S2 <-- S0 electronic transition of each oligomer possesses a much larger oscillator strength. The absorption and fluorescence spectra of the compounds have been recorded in chloroform. A reasonable agreement is obtained between TDDFT vertical transition energies and the (0,0) absorption and fluorescence bands. On one hand, the pattern of the aliphatic side chains does not affect the absorption and fluorescence maxima of the compounds. On the other hand, the replacement of aliphatic chains by phenyl or thiophene rings induces hypsochromic shifts in the absorption and fluorescence spectra. Finally, the fluorescence quantum yield and lifetime of the compounds in chloroform have been obtained. From these data, the radiative and nonradiative rate constants of the deactivation of the S1 state have been determined.     

Characterization and photophysical properties of sulfur-oxidized diarylethenes

Controlled oxidation of sulfur atoms in benzothiophene rings of a photochromic diarylethene, 1,2-bis(2-methyl-1-benzothiophene-3-yl)perfluorocyclopentene (BTF6) by 3-chloroperbenzoic acid afforded various oxidation products such as BTFO1, BTFO2, and BTFO4. Upon irradiation with UV light, colorless o-BTFO1 and o-BTFO2 turned to red color, whereas colorless o-BTFO4 turned to yellow color. Theoretical calculation was performed to understand the absorption spectra of closed-ring isomers. All of those compounds returned back to their open-ring isomers upon irradiation with visible light. The cyclization conversions of BTFOn (n=1, 2, and 4) at the photostationary state are higher than that of BTF6. Interestingly, in the case of BTFO1, because of the unsymmetrical environment around the sulfoxide subunit in the molecule, the diastereoselective photocyclization was observed in 25% de. In addition, c-BTFO2 and c-BTFO4 also exhibited a marked fatigue resistance and strong fluorescence, respectively. Oxidation state of sulfur atom in a diarylethene can play an important role in determining its photophysical and photochromic properties.     

Synthesis and photophysical properties of phosphole-cored dendrimers

Phosphole-cored dendrimers having poly(benzyl ether) units through the third generation have been synthesized. The dendrimers display intense blue photoluminescence, the quantum yield increasing with the increasing generation of the dendron units. The optical properties are easily tuned by oxidation of the phosphorus atom of the phosphole ring.     

4-二羟基硼酰苯丙氨酸与果糖结合物的结构特性研究

使用密度泛函方法对4-二羟基硼酰苯丙氨酸与果糖结合物的结构特性进行了理论计算,确定了3种稳定构型,分析了该结构具有良好水溶性的原因.计算结果表明,前2种结构的反应活性较强,而第3种结构中果糖的加入并未过多影响其化学活性,3种结构中果糖的加入只是改变了原有分子的极性,果糖部分容易从复合结构上脱落,因而起到了一个很好的类似催化剂的作用.     

Cobaltacarborane-phthalocyanine conjugates: Syntheses and photophysical properties

Syntheses of two new cobaltacarborane-phthalocyanine conjugates, one anionic (Pc 6) and one zwitterionic (Pc 7), were accomplished via cyclotetramerization of the corresponding cobaltacarborane-substituted phthalonitriles (4 or 5) with excess phthalonitrile in quinoline. X-ray structures of two phthalonitrile precursors (2 and 3) were obtained and are discussed, and the absorption and emission properties of the two cobaltacarborane-phthalocyanine conjugates in several solvents were investigated. The anionic conjugate 6 exists mainly as a monomer in polar organic solvents and has fluorescence quantum yields in the region 0.2-0.3. The zwitterionic conjugate 7 aggregates in solution and displays lower quantum yields ∼0.1 in organic solvents.