Fabrizio Bolletta

Luminescent chemosensors for transition metal ions

Abstract The need for selective and sensitive sensors able to monitor in real-time and real-space the concentration of analytes of biological, clinical, and environmental interest is nowadays generally accepted. Of the various kinds of chemosensors, luminescence-based chemosensors present many advantages, since they can take profit of the high sensitivity and versatility typical of photoluminescence spectroscopy. In this contest, special interest has been devoted to the development of luminescent chemosensors for transition metal ions, since some of them are present in biological systems in trace amounts and, at the same time, they all can represent an environmental concern when present in uncontrolled amounts. In this contribution we review the chemical systems able to act as luminescent chemosensors for this class of metal ions.

Rate Constants for the Quenching of Excited States of Metal Complexes in Fluid Solution

The rate constants for the quenching of the excited states of metal ions and complexes in homogeneous fluid solution are reported in this compilation. Values of kq for dynamic, collisional processes between excited species and quenchers have been critically evaluated, and are presented with the following information, among others, from the original publications, when available: description of the solution medium, temperature at which kq was determined, experimental method, range of quencher concentration used, lifetime of the excited state in the absence of quencher, activation parameters, quenching mechanism. Data collection is complete through the end of 1986, and covers the coordination compounds of 26 metals, including the ions and complexes of the inner‐ and outer‐transition metals, and porphyrin complexes of nontransition metals. Data for 261 excited states quenched by more than 400 inorganic quenchers and 600 organic quenchers have been extracted from almost 500 publications. The introduction to th...

Searching for New Luminescent Sensors: Synthesis and Photophysical Properties of a Tripodal Ligand Incorporating the Dansyl Chromophore and of Its Metal Complexes

The new tripodal ligand 1 containing the dansyl chromophore has been synthesized and characterized. The intense luminescence characteristic of the chromophore is maintained in the ligand structure, showing that no intramolecular interactions are present. This ligand has been shown to complex in acetonitrile/water solutions only with Cu2+, Co2+, Zn2+, and Cd2+ ions, with concomitant pronounced changes in the fluorescence spectra. The complexation is controlled by pH conditions: at neutral pH this ligand shows a remarkable selectivity towards Cu2+ ions, suggesting a possible use for 1 as a luminescent chemosensor for this ion.

Photophysical Behaviour of Corrole and its Symmetrical and Unsymmetrical Dyads

The luminescence properties at room temperature and 77 K of octamethylcorrole are reported for the first time, together with the photophysical behaviour of corrole-corrole and porphyrin-corrole dyads covalently linked through the 10-position with a phenyl bridge. The photophysical properties of corrole free base are very similar to those of the porphyrin analogues, whereas the dimeric systems show luminescence bands different from those of the parent monomers, indicating an unexpectedly high degree of interaction between the chromophores. The porphyrin-corrole dyad undergoes photocatalysed ring opening of the corrole moiety to give the corresponding porphyrin-biliverdin species.

A fluorescent sensor for magnesium ions

Diaza-18-crown-6 appended with two 5-chloro-8-hydroxyquinoline groups can serve as an effective chemosensor for Mg2+. The modified macrocycle will fluoresce in the presence of Mg2+ but not with other alkaline earth ions at pH 7.2. Mg2+ concentrations can be measured in the presence of Na2+, K+, Ca2+, Sr2+ and Ba2+.

A New Family of Luminescent Sensors for Alkaline Earth Metal Ions

The fluorescence of the crown ethers 1 (n=3–5) is enhanced by more than one hundred times on addition of Ba2+, Sr2+, and Ca2+ metal ions, showing in this way an off/on response. This behavior, together with the range of selectivities displayed by this family of crowns toward alkaline earth metal ions, makes them suitable for sensor applications. The appearance of a delayed fluorescence after complexation can be used to increase the signal-to-noise ratio in analysis applications.

Luminescence signalled enantiomeric recognition of chiral organic ammonium ions by an enantiomerically pure dimethylacridino-18-crown-6 ligand

Acridino-18-crown-6 ligands 1 and 2 are able to bind organic ammonium salts in acetonitrile with high affinity, causing pronounced changes in the luminescence properties of the two partners. Furthermore, enantiomerically pure chiral ligand 2 shows a high enantioselectivity towards chiral organic ammonium ions. The observed changes in the photophysical properties are also an important tool for understanding the interactions present in the adduct. The possibility of monitoring the binding process by means of such a sensitive technique as photoluminescence spectroscopy can gain ground for the design of very efficient enantioselective chemosensors for chiral species.

Photophysics of 1,3-alternate calix[4]arene-crowns and of their metal ion complexes: evidence for cation–π interactions in solution

The photophysical properties of the family of calix[4]arene-crowns and of their metal complexes are reported here for the first time. Among different observed perturbations, addition of alkali metal ions causes monitorable, and sometimes pronounced, changes in fluorescence intensities and in the wavelength maxima of the hosts. All together, the observed results strongly suggest that the cation–π interactions play a major role in tuning the luminescence properties of the host. The utility of photoluminescence spectroscopy for the determination of association constants between calixarene derivatives and metal ions is also demonstrated.

From a molecular to a supramolecular photochemistry

Abstract Following a current trend of chemical research, photochemical investigations are moving from molecular to supramolecular species. Some of the results obtained by the authors with supramolecular species containing metal complexes are briefly reviewed, with particular emphasis on (i) cage-type complexes, (ii) host-guest systems, (iii) metal catenates, and (iv) oligonuclear metal complexes.

Chemiluminescence and electrochemiluminescence of coordination compounds

Chemiluminescence and electrochemiluminescence reactions involving coordination compounds represent an interesting class of reactions which nay offer useful information on the mechanism of outer—sphere electron transfer processes. Most studies have concentrated on the Ru—polypyridine complexes but examples of different complexes, including binuclear species and clusters, have also been reported. Some important examples of such processes are briefly discussed and some general theoretical and experimental considerations on comproportionation reactions leading to the formation of metal—to—ligand charge transfer excited states are presented.