Donatella Sacchi

A two-channel molecular dosimeter for the optical detection of copper(II)

A cyclam-like macrocycle with an integrated push-pull chromophore selectively detects Cu2+ inclusion through both orange-to-yellow colour change and quenching of the green fluorescence.

Sensing of transition metals through fluorescence quenching or enhancement. A review

A series of fluorescent sensors for transition metal ions were synthesized by linking a light-emitting subunit, anthracene, to a polyaza chelating subunit, either a dioxotetraamine or a tetraamine. Sensing of the divalent cations CuII, NiII and ZnII was investigated through spectrofluorimetric titrations in acetonitrile–N water (4:1) solutions. The selective recognition of CuII and NiII among other transition and non-transition metal ions is signalled through full quenching of fluorescence; discrimination between the two ions can be achieved by performing titrations at controlled pH. The system containing the tetraamine fragment, whose interaction with CuII and NiII induces fluorescence quenching, is also sensitive to ZnII, but in this case the recognition is signalled through a fluorescence enhancement.

A FLUORESCENT CHEMOSENSOR FOR THE COPPER(II) ION

Abstract The two-component system anthracene-9-carboxylic acid 1,4,8,11-tetrathia-cyclotetradecan-6-ylester ( 1 ) has been synthesized, structurally characterized and investigated as a fluorescent chemosensor for the Cu 11 ion. Crystallographic details for 1 : space group P 2 1 / c with α = 9.894(2), b = 24.608(2), c = 10.759(2) A , α = 90, β = 105.88, γ = 90°; V = 2519.7 A 3 , Z = 4 (R = 0.088, R w = 0.066) . In ethanolic solution 1 selectively incorporates Cu 11 into its tetrathia crown component in the presence of other 3d metal ions and signals the recognition through the quenching of the fluorescence of the anthracene fragment. Quenching of the photo-excited state (which has a charge transfer nature) takes place through a photo-induced electron transfer from the fluorophore to the metal center and involves the Cu II /Cu I couple. The d 10 cation Ag 1 competes successfully with Cu 11 for the tetrathia cavity of 1 in an ethanolic solution (not in an acetonitrile solution), but the occurrence of the metal/receptor interaction cannot be signalled, due to the poor redox activity of the non-transition cation Ag 1 .

A two-channel chemosensor for the optical detection of carboxylic acids, including cholic acid

A neutral receptor, in which a urea fragment has been equipped with two naphthaleneimide subunits, on interaction with acetate, in a DMSO solution, undergoes deprotonation of one of the N–H fragments; an event which is signalled by a yellow-to-red colour change and by the quenching of the blue fluorescence of the naphthalneimide subunit, with no competition by a number of anions (phosphate, nitrate, sulfate, chloride or bromide). This procedure can be employed for the visual and spectroscopic detection of cholic acid, even in presence of the other competing bile acids, such as glycocholic and taurocholic.

Light-emitting molecular machines: pH-induced intramolecular motions in a fluorescent nickel(II) scorpionate complex.

A cyclam-like macrocycle has been synthesized with a pendant arm containing a dansylamide group. In the corresponding nickel(II) complex, binding of the pendant arm to the metal is pH controlled. In particular, at pH 4.3, the sulfonamide group deprotonates and coordinates the NiII center, giving rise to a complex of trigonal bipyramidal stereochemistry, as shown by X-ray diffraction studies performed on the crystalline complex salt. At pH 7.5, an OH- ion binds the metal and a six-coordinate species forms. The binding-detachment of the pendant arm to/from the NiII center is signaled by changes in the emission properties of the dansyl subunit in the side chain; the fluorescence of this side chain is high when the pendant arm is not coordinated and low when the sulfonamide group is bound to the metal. The system investigated represents the prototype of a light-emitting molecular machine, driven by a pH change.

Supramolecular Functions Related to the Redox Activity of Transition Metals

Abstract The combination of the properties of different subunits in a multicomponent system may give rise to a function which is defined supramolecular. The presence of transition metals in one or more subunits may induce inter-component processes related to their redox and electron transfer (eT) properties, which trigger the supramolecular function (SF). The following examples are considered: (1) a receptor for transition metals is covalently linked to a fluorescent fragment; following recognition, a metal-to-fluorophore eT process quenches the fluorescence. SF: fluorosensing. (2) an azacyclam macrocycle, hosting the NiII/NiIII redox couple, is covalently linked to a photoactive fragment: the NiIII state quenches the neighboring fluorophore through an eT mechanism, the NiII state does not. SF: redox switching of a fluorescent signal. (3) a CuII ion is coordinated by two 2,2′-bipyridine molecules, each bearing a cyclam subunit containing a nickel centre; when nickel is in the divalent state, an inorganic anion X− (N3 −,NCO−,NCS−) is bound to CuII; on oxidation, X− moves to the NiIII centre. SF: electrochemically triggered translocation of X− from copper to nickel and vice versa.

Metal-induced assembling/disassembling of fluorescent naphthalenediimide derivatives signalled by excimer emission

The new quadridentate bischelating ligands 2 and 3 display in solution the typical absorption and emission properties expected for naphthalenediimide derivatives. Spectrophotometric studies show that systems 2 and 3 interact with Zn(II), Cd(II) and Cu(I) in CHCl3 or MeCN according to an apparent 1:1 stoichiometry. Molecular modelling, ESI-MS and 1H NMR experiments indicate that the complex species formed in the presence of stoichiometric amounts of metal ion are nonhelical [2 + 2] adducts. The metal-induced self-assembling process is signalled by an intense excimer-type emission caused by the intramolecular interaction of two naphthalenediimide subunits that face each other in the [2 + 2] adduct, as shown by molecular modelling studies. In the presence of excess metal ion, a disassembling process takes place, leading to a dinuclear complex with a 2:1 metal/ligand stoichiometry, in which the intramolecular excimer is no longer allowed to form because the interaction between the naphthalenediimide subunits has been lost. Thus, the overall metal-induced assembling/disassembling process is signalled by the appearance and disappearance of the excimer band in the emission spectrum.

A fluorescent molecular thermometer based on the nickel(II) high-spin/low-spin interconversion

The temperature of a fluid can be measured through a variation of the fluorescence emission intensity of a naphthalene fragment covalently linked to a NiII tetraaza-macrocyclic complex, which undergoes a temperature dependent spin interconversion equilibrium.

Origin of the blue fluorescence in Dominican amber

We report on optical absorption, fluorescence, and time-resolved fluorescence measurements in Dominican ambers. The “blue” variety reveals an intense fluorescence emission in the visible wavelength region, between 430 and 530nm, with spectral features typical of aromatic hydrocarbons. On the contrary, the “red” and “yellow” varieties have a much weaker and featureless emission. The data for blue amber, including fluorescence lifetime, allow the identification of perylene as the compound responsible for its distinctive showy fluorescence.

Excimer emission induced by metal ion coordination in 1,8-naphthalimide-tethered iminopyridine ligands

Ligands 2–5, containing the light-emitting subunit 1,8-naphthalimide, have been prepared and their photophysical properties studied by absorption and emission spectroscopy. Ligand 2 interacts in solution with several cations according to a 1 ∶ 2 (metal ∶ ligand) stoichiometry, the 1 ∶ 3 species being not favoured probably because of steric hindrance, while ligands 3–5 form 1 ∶ 3 adducts with all the investigated metal ions. The interaction of ligands 2–5 with metal ions induces considerable variations on the photophysical properties of the light-emitting subunit. The coordination of genuine transition metal ions (FeII, CoII, NiII, CuII) causes the emission intensity to decrease in all the investigated systems, while ZnII or CdII induce a fluorescence enhancement (system 2) or the formation of a new band in the emission spectra (systems 3–5) which can be ascribed to an intramolecular excimeric species. Excimeric emission is not observed in the complexes of 2, possibly because the ethylenic chain bridging the naphthalimide and the iminopyridine units is too short to allow the intramolecular interaction. The excimeric species disappears on increasing the metal ion (ZnII or CdII) concentration, as a result of the “disassembling” of the 1 ∶ 3 complexes and the consecutive formation of 1 ∶ 2 and 1 ∶ 1 species, in which the intramolecular interaction is less probable or no longer possible. The appearance and disappearance of an excimer band in the emission spectrum can be described as a convenient way to monitor a metal-driven assembling/disassembling process.