Fluorescent sensors transition metal ions

Most PET fluorescent sensors for cations are based on the principle displayed in Figure 10.7, but other photoinduced electron transfer mechanisms can take place with transition metal ions (Fabbrizzi et al., 1996 Bergonzi et al., 1998). In fact, 3d metals exhibit redox activity and electron transfer can occur from the fluorophore... 

An anthracene-based fluorescent sensor for transition metal ions (Figure 93) has been developed by Fabbrizzi et al. [120]. They have shown that at an appropriate pH (6-8), the addition of Mn " ", Co or Zn2+ does not affect the fluorescence. However, the addition of Cu or Ni ions results in a sharp... 

Rurack, K. Flipping the light switch ON —The design of sensor molecules that show cation-induced fluorescence enhancement with heavy and transition metal ions. Spec-trochim. Acta, Part A Mol. Biomol. Spectrosc. 2001. 57. 2161-2195. 

Fabbrizzi, L. Licchelli, M. Pallavicini, P. Perotti, A. Sacchi, D. A fluorescence sensor for transition metal ions based on anthracene. Angew. Chem.,Int. Ed. Engl. 1994, 33 (19). 1975-1977. 

From the point of view of the supramolecular design, the dioxotetramine subunit in the system 1 can be considered as a rather complicated pH switch, whose sensitivity is activated by a further external agent Cu or Ni. From the point of view of the molecular recognition and of the analytical applications, the supramolecule 1 can be considered as a novel example of a fluorescent sensor for transition metal ions. In particular, 1 is able to recognize Cu and Ni among many other metal ions present in the same solution, as illustrated by Figure 5. 

The sensor covalently joined a bithiophene unit with a crown ether macrocycle as the monomeric unit for polymerization (Scheme 1). The spatial distribution of oxygen coordination sites around a metal ion causes planarization of the backbone in the bithiophene, eliciting a red-shift upon metal coordination. They expanded upon this bithiophene structure by replacing the crown ether macrocycle with a calixarene-based ion receptor, and worked with both a monomeric model and a polymeric version to compare ion-binding specificity and behavior [13]. The monomer exhibited less specificity for Na+ than the polymer. However, with the gradual addition of Na+, the monomer underwent a steady blue shift in fluorescence emission whereas the polymer appeared to reach a critical concentration where the spectra rapidly transitioned to a shorter wavelength. Scheme 2 illustrates the proposed explanation for blue shift with increasing ion concentration. 

Many interferences occur, including those of transition metals (quenching) and of other ions sensitive to 8-HQS and EDTA. The fluorescence polarization of the ligand as a function of chelation has also been ocploited for a selective sensor based quinolin-8-ol to determine Ai( i), Mg<">, Zn< ), Be< >, Ca<">, Cd<"> and Pd<"> [81]. 

PPEs and PAEs have come a long way from the first synthesis in 1990 to sophisticated sensory and photonic materials PAEs and PPEs are very different from PPVs—despite their obviously close structural relation. PPEs are oxidatively more stable than PPVs, which makes them less suitable for some organic semiconductor applications, but PPEs, high fluorescence coupled with their great environmental stability makes them attractive as parts for sensors that detect biogenic and toxigenic materials, transition and alkali metal ions, and vapors exuding from land mines. 

The spectroscopic method is based on pressure-induced changes in absorption or/and emission spectra. The idea is to relate the pressme-induced shift of the fluorescence lines of the specific material to the value of the pressure. The material selected for the luminescence pressure sensor should be characterized by strong intensity of the emission line(s), which should be stable at a broad range of pressures and temperatures and the energy of which is possibly related linearly to pressure. It is also important that the emission of the sensor does not overlap the emission of the sample. Considering the above-mentioned requirements, the Raman fluorescence and photoluminescence of transition-metal and rare-earth ions were used. Raman modes of nitrogen [49], which is the pressure-transmitting medium, and Raman frequencies of diamond chips [51] have been used. Recently, a pressure-induced shift of the Raman line 1332 cm of the face of the DAC culet was proposed to estimate pressure < 1,000 kbar [50, 52]. 

The term upconversion describes an effect [1] related to the emission of anti-Stokes fluorescence in the visible spectral range following excitation of certain (doped) luminophores in the near infrared (NIR). It mainly occurs with rare-earth doped solids, but also with doped transition-metal systems and combinations of both [2, 3], and relies on the sequential absorption of two or more NIR photons by the dopants. Following its discovery [1] it has been extensively studied for bulk materials both theoretically and in context with uses in solid-state lasers, infrared quantum counters, lighting or displays, and physical sensors, for example [4, 5]. Substantial efforts also have been made to prepare nanoscale materials that show more efficient upconversion emission. Meanwhile, numerous protocols are available for making nanoparticles, nanorods, nanoplates, and nanotubes. These include thermal decomposition, co-precipitation, solvothermal synthesis, combustion, and sol-gel processes [6], synthesis in liquid-solid-solutions [7, 8], and ionothermal synthesis [9]. Nanocrystal materials include oxides of zirconium and titanium, the fluorides, oxides, phosphates, oxysulfates, and oxyfluoiides of the trivalent lanthanides (Ln ), and similar compounds that may additionally contain alkaline earth ions. Wang and Liu [6] have recently reviewed the theory of upconversion and the common materials and methods used. 

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