The possibility of replacing volatile and toxic organic solvents by ionic liquids (ILs) could contribute to safer procedures for conservation and restoration. This study introduces the use of ILs in varnish removal from paintings. The efficacy of this new procedure was assessed by applying different types of ILs in mock-ups of several painting materials and varnishes. The removal of IL residues from the surface of paintings was assessed mainly by FTIR-ATR. The application of ILs to a real painting is illustrated.

The acid-base properties as well as the photochemical reactivity of the co-ordination compound K-4[Co(CN)(5)(SO3)] in the presence of three polyammonium macrocyclic receptors were studied in aqueous solution. The pK(a) of the free complex (3.9) (sulfite deprotonation) changed to pK(a) <0.5 upon complexation with the receptors. The quantum yield for sulfite photoaquation of the free complex in the basic form (Phi = 0.85 +/- 0.09) decreased to 0.05 +/- 0.01, 0.12 +/- 0.03 and 0.45 +/- 0.09 in the presence of[24]aneN(8)H(8)(8+), [30]aneN(10)H(10)(10+) and [32]aneN(8)H(8)(8+), respectively. For the acidic form of the free complex (Phi = 0.40 +/- 0.05) the quantum yield was not affected by supercomplexation with [32]aneN(8)H(8)(8+). For the adducts formed from the other two macrocyclic receptors it was not possible to evaluate the quantum yields of the acidic forms, because protonation was not complete even at very high proton concentrations. The results were interpreted in terms of second-sphere interactions involving hydrogen bonding between the complex and the macrocycles. In the case of [32]aneN(8)H(8)(8+) the experimental results are compatible with a structure in which the cyanides are involved in hydrogen bonding but the sulfite ligand is not. In the two other supercomplexes the sulfite ligand seems to be involved in hydrogen bonding.

The photochemistry of aqueous solutions of [Co(CN)5H2O]2- in the presence of the polyammonium macrocyclic receptor [32]ane-N8H88+ was studied. The quantum yield for cyanide release in free [Co(CN)5H2O]2- (PHI = 0.003 at 313 nm, pH 1.5) is reduced approximately threefold in the presence of the protonated macrocycle, which provides evidence for the formation of a supramolecular structure. Further evidence for the supramolecular structure is obtained from the thermal anation of [Co(CN)5H2O]2- with Br- (40-degrees-C, pH 1.0), the rate of which is increased in the presence of [32]ane-N8H88+, suggesting that the ligand water is not involved in hydrogen bonds with the macrocycle. These results are interpreted in terms of possible supramolecular structures.

The energy- and electron-transfer quenching processes of the lowest triplet excited state of biacetyl (2,3-butanedione) imprisoned in a hemicarcerand have been systematically investigated in CH2Cl2 solution at room temperature. Twenty potential quenchers have been used, including ten triplet energy accepters (mostly, aromatic hydrocarbons) and nine electron donors (mostly, aromatic amines). Bimolecular rate constants for the quenching processes were obtained by Stern-Volmer analysis and compared with those found for the quenching of free biacetyl. In the electron-transfer processes, aromatic amines with oxidation potential from +0.015 V (N,N,N',N'-tetramethyl-p-phenylenediamine) to +0.83 V (diphenylamine) quench free biacetyl at the diffusion-controlled limit, whereas for imprisoned biacetyl the rate constant decreases (roughly in a linear manner) from 4.0 x 10(8) to 1.2 x 10(5) M(-1) s(-1) As far as energy-transfer is concerned, the rate constant for the quenching of free biacetyl increases with decreasing Delta G degrees and reaches the diffusion-controlled plateau value (k(q) similar to 10(10) M(-1) s(-1)) for Delta G degrees similar to 0.1 eV, whereas for imprisoned biacetyl a scattered, bell-shaped log k(q) vs Delta G degrees plot is obtained, with a maximum value (similar to 10(6) M(-1) s(-1)) much below the diffusion-controlled limit. The results obtained show that the walls of the hemicarcerand allow only very weak electronic interaction between incarcerated triplet biacetyl and external quenchers. A brief discussion of the results obtained in the light of current energy- and electron-transfer theories is presented.

The synthesis, potentiometric studies and photophysical properties of two new polyamine ligands (L1 and L2) possessing the dansyl chromophore were studied in aqueous 0.15 M NaCl. The compounds show the absorption and emissions bands characteristic of the dansylamide fluorophore and both present intramolecular excited state proton transfer at intermediate pH ranges. One of the ligands (L2) strongly coordinates Zn(II) leading to fluorescence quenching. A model compound (L3) of the dansyl moiety was also investigated. (c) 2006 Elsevier B.V. All rights reserved.

The absorption and excited state properties of 9-cyanoanthracene are strongly modified upon inclusion into an octaimine hemicarcerand; the walls of the host do not transfer excitation to the guest and quench its fluorescent excited state.

The network of chemical reactions of the compound 4'-methoxyflavylium was studied in the presence of SDS micelles, using stopped-flow, UV-vis absorption and flash photolysis techniques. The results were compared with analogous experiments carried out in water. The large stabilization of the flavylium cation onto the micelles was proven to be due to an increase in the rate of the dehydration reaction, rather than a decrease of the hydration reaction; the cis-trans isomerisation of the chalcone was not affected by the micelles. It is shown that SDS micelles can be considered as an external stimulus capable of changing the system from one state to another. (c) 2006 Elsevier B.V. All rights reserved.

We show photorheology in aqueous solutions of weakly entangled wormlike micelles prepared with cetyltrimethylammonium bromide (CTAB), salicylic acid (HSal), and dilute amounts of the photochromic multistate compound trans-2,4,4'-trihydroxychalcone (Ct). Different chemical species of Ct are associated with different colorations and propensities to reside within or outside CTAB micelles. A light-induced transfer between the intra- and intermicellar space is used to alter the mean length of wormlike micelles and hence the rheological properties of the fluid, studied in steady-state shear Bow and in dynamic rheological measurements. Light-induced changes of fluid rheology are reversible by a the relaxation process. at relaxation rates which depend on pH and which are consistent with photochromic reversion rates measured by UV-vis absorption spectroscopy. Parameterizing viscoelostic rheological states by their effective relaxation time tau(c) and corresponding response modulus G(c), we find the light and dark states of the system to fall onto a characteristic state curve defined by comparable experiments conducted without photosensitive components. These reference experiments were prepared with the same concentration of CTAB, but different concentrations of HSal or sodium salicylote (NaSal), and tested at different temperatures.

Chalcones possessing a hydroxyl group in position 2 cyclize to form flavylium salts in acidic media, this reaction being reversible under neutral-basic conditions. On the other hand, chalcones possessing a hydroxyl group in position 2' cyclize to form flavanones in basic media. By synthesizing 2'-hydroxyflavylium tetrafluoroborate, it was possible to obtain trans-2,2'-dihydroxychalcone that in solution can evolve to 2'-hydroxyflavanone or back to 2'-hydroxyflavylium depending on the pH. The several equilibria established in aqueous solution were fully characterized. The importance of including flavanones into the flavylitun network of chemical reactions is briefly exploited. (C) 2007 Elsevier Ltd. All rights reserved.

The rate and equilibrium constants of the network of chemical species involving the dye 2'-methoxyflavylium tetrafluoroborate were characterized using stopped flow and flash photolysis in both acidic and alkaline aqueous solution. The trans-chalcone is the thermodynamic stable species in acidic solutions 2 < pH < 7; irradiation of trans-chalcone at low pH leads to the corresponding coloured flavylium cation. The system reverts to its initial state in a few hours, in the dark. The kinetics of the various steps in the system were determined; flash photolysis revealed that the rate determining process of flavylium formation is the ring closure to give the corresponding hemiketal. In alkaline medium the ionized transchalcone is the stable form and clear evidence for the existence of a hemiketal species was obtained. A write-read-erase cycle can be performed with this compound. (c) 2008 Elsevier Ltd. All rights reserved.