Krzysztof Kledzik

Spectral properties of bis-9-anthryl derivatives immobilised in silica xerogel

Abstract Three bis-9-anthryl derivatives of the type Ant - R - Ant , where Ant is anthryl group and R is receptor spacer consisting of such donor atoms as N or N and O, were encapsulated in silica xerogel by the sol–gel method. Our recent studies in methanol solution show that these materials could be used as fluorosensors in chemical recognition phases for optical chemical sensor. Optical absorption spectra of the bis-anthryl derivatives are nearly the same in the solution and silica matrix. However, the free species entrapped in silica exhibit fluorescence emission spectra with a long wavelength tail, which is probably due to the presence of excimers in the excited state and/or heterogeneous environment of the emission centres in the amorphous silica matrix. The studied bis-anthryl derivatives undergo photochemical degradation during UV irradiation.

Azacrown-CH2-bipyridine receptors in silica xerogel.Optical and coordination properties

Samples of silica xerogel doped with encapsulated series of three receptors of the type (aza-3n-crown-n)-CH2-(2,2′-bipyridine), where n=4, 5 and 6, were prepared by the sol–gel process. Fluorescence excitation spectra of the encapsulated receptors differ from the absorption spectra. Emission of the samples can be quenched specifically owing to the coordination reaction with transition metal ions. Emission decays can be described by a double exponential, the lifetime values being short at room temperature. EPR spectra of CuII ions complexed on the surface of the receptor doped xerogel have fairly well resolved hyperfine structure and show an elongated rhombic octahedral environment for the receptors with 2,2′-bipyridine groups.

Fluorosensor action of bis-9-anthryl derivatives immobilised in silica xerogel

Abstract Silica xerogel samples with entrapped series of three fluorescent chemosensors of the Ant-R-Ant type, where Ant is an anthryl group and R is a receptor (spacer) with donor atoms, were prepared by the sol–gel process as chemical recognition phases. The absorption spectra characteristic of alkylanthracene are nearly the same for the free and complexed chemosensors in solution and those encapsulated in the silica xerogels. The fluorescence emission of the samples is specifically enhanced owing to the coordination reaction, with Cu II ions in particular. Emission decays can be described by a triple exponential; the lifetimes at room temperature are short. EPR spectra of Cu II ions complexed by chemisorption with the fluorosensors immobilised in silica have a fairly well resolved hyperfine structure and show the tetragonal–octahedral environment of the central ion. The recognition phase with fluorosensor 1 of the type Ant-NOON-Ant (where N and O are donor atoms) in silica can undergo cycles chemisorption–desorption many times.

A New Fluorescent Chemosensor for Cu2+ Based on a Dianthracene-Derivative

Abstract Besides being of interest in photochemistry, photoinduced electron transfer (PET) is a process largely used in the design of fluorescent ion sensing molecules. One of the simplest systems is based on fluorescent aromatic groups linked to amino groups and proposed as possible fluorescent transition metal ion chemosensor [1]. In this case, the fluorescence of the fluorophore “ligths on” when the amino group is complexed. On the other hand, in the absence of metal ions, the fluorescence is quenched by a PET originating from the nitrogen lone electron pairs [2]. We prepared a new fluorescent chemosensor, abbreviated as Ant-NH-O-O-NH-Ant (shown in Fig. 1) in which the intramolecular PET is expected to be efficient. The chemosensor consists of a metal-binding dioxodiamino unit linked to two light-emitting anthracene fragments. This type of supramolecules when irradiated in methanol solution (conc. 1.89—10−5 M.) at 368 nm displays a characteristic fluorescence spectrum for anthracene group with the most intensive band at 415 nm [Fig. 2(a)]. The emission is slightly enhanced upon coordination of such metal ions as Ni2+ and Zn2+ by the ligand fragment of the Ant-NH-O-O-NH-Ant molecule [Fig. 2(b) and (d)]. However, much higher intensity of emission is observed in the case of Cu2+ complex [see Fig 2(c)]. The fluorescence enhancement is presumably due to suppression of photoinduced fluorophore-to-metal electron-transfer mechanism.

A chemical recognition element for lithium ions based on optical electronic absorption

Xerogel samples with entrapped series of four optical absorption chemosensors were prepared by sol-gel process. These materials are proposed as chemical recognition elements of an optical chemical sensor. The roles of the chemosensors play proton-dissociable chromogenic azocrown ethers bearing phenol and two azo groups as parts of macrocycles. Occurrence of the alkali ion—receptor interaction is signalled by the chemosensors changing their electronic absorption spectra. By this way chemosensor 4O-CH3 is able to distinguish Li+ ions from other alkali metal ions present in aqueous solution, if the chemosensor is entrapped in Glymo-silica (1:1) xerogel matrix. The proposed recognition element for Li+ has been exposed to the cycles chemisorption—desorption many times. Besides DRIFT spectra of the used xerogel matrices were analyzed.

Chemical recognition phase of the fluorescence chemical sensor for copper (II) ions in aqueous solution

We review the principles of optical sensor based on the use of the sol-gel technique, in particular their fabrication. We also report on potential applications of the recognition phases prepared by encapsulation of fluorescent chemosensors which have been designed by means of a supramolecular approach: two anthryl groups linked to diaminodiethero group. Occurrence of the metal ion-receptor interaction is signaled through the enhancement of anthryl fluorescence. The enhancement takes place when the receptor is able to promote a photoinduced electron transfer mechanism. Cu(II) ions can be distinguished form other transition metal ions in aqueous solution by the recognition phase.