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A simple and rapid liquid chromatographic method with diode-array UV-vis spectrophotometric detection has been developed for the authentication of dragon's blood resins from Dracaena and Daemonorops trees. Using this method it was discovered that the flavylium chromophores, which contribute to the red colour of these resins, differ among the species and could be used as markers to differentiate among species. A study of parameters, such as time of extraction, proportion of MeOH and pH, was undertaken to optimise the extraction of the flavyliums. This method was then used to make extracts from samples of dragon's blood resin obtained from material of known provenance. From the samples analysed 7,6-dihydroxy-5-methoxyflavylium (dracorhodin), 7,4'-dihydroxy-5-methoxyflavylium (dracoflavylium) and 7,4'-dihydroxyflavylium were selected as species markers for Daemonorops spp., Dracaena draco and Dracaena cinnabari, respectively. The chromatograms from these samples were used to build an HPLC-DAD database. The ability to discriminate among species of dragon's blood using the single marker compounds was compared with a principal components analysis of the chromatograms in the HPLC-DAD database. The results from the HPLC-DAD method based on the presence of these flavylium markers was unequivocal. The HPLC-DAD method was subsequently applied to 37 samples of dragon blood resins from the historical samples in the Economic Botany Collection, Royal Botanic Gardens, Kew. The method identified anomalies in how samples in this collection had been labelled. It is clear that the method can be used to evaluate the provenance of samples used in different areas of cultural heritage. It also could be used to monitor the trade of endangered species of dragon's blood and the species being used in complex formulations of traditional Chinese medicine.

The performance of flavylium-based photochromic systems is increased by their incorporation into Pluronic F-127 matrixes, which switch from polymeric solutions to micelles to gels with changes in temperature depending on copolymer concentration. Two flavylium compounds, 7,4'-dihydroxyflavylium and 7-(N,N-diethylamino)-4-hydroxyflavylium, both exhibiting a small thermal cis-trans isomerization barrier in water were investigated. In the first system the flavylium in the gel photoswitches from the colorless trans-chalcone (Ct) species to the yellow flavylium cation (AH+) with quantum yield Phi=0.04 (25 degrees C) at pH 2.2 or to the orange quinoidal base (A) with quantum yield Phi=0.015 (25 degrees C) at pH 5.2. The photoproducts revert back to their initial form by a thermal process characterized by first-order kinetics; the rate constants exhibit a bell shape variation with pH, with a maximum at pH 4.3 (lifetime 4.2 min). The second system, 7-(N,N-diethylamino)-4-hydroxyflavylium, does not exhibit photochemistry in water but, when incorporated into the Pluronic F-127 gel, switches from yellow to red with a quantum yield of Phi=0.01 at pH 4.9. The respective thermal back reaction takes place with a lifetime of 66.7 min1. The flavylium network of chemical reactions is a good sensor for the detection of not only the critical micelle temperature but also the gelation temperature of Pluronic and like solutions and, in some instances, the exposure to UV and visible radiation.

Spectrophotometric measurements in the region of the ion pair charge transfer band of the Co(Sepulchrate) 3+ I − system were used to assess the role played by the adducts between the complex cation and iodide anion in the photochemical behaviour of the system. No clear evidence was obtained for the presence or absence of 1:2 or higher adducts and the association constant and molar absorptivity of the 1:1 adduct (ion pair) could not be determined with a satisfactory accuracy. Nevertheless, reliable values were evaluated for the fraction of the exciting light absorbed by the ion pair in the photochemical experiments, and these values were used to correct the previously reported quantum yields, which were based on the total amount of light absorbed by the solutions. The “true” quantum yields for the ion pair are discussed in relation to the proposed reaction mechanism.

A strategy to obtain photochromism from the network of chemical reactions originated by flavylium compounds in solution is described. This strategy is particularly useful for flavylium salts bearing amino groups which give rise to a variety of beautiful colors but lack photochemistry in water. The trans-chalcone of 7-(N,N-diethylamino)-4'-hydroxyflavylium interacts strongly with CTAB micelles defining a yellow dark state. Upon irradiation, the system switches to a pink-red state emerging from the flavylium cation that is formed inside the micelle and ejected to the bulk aqueous phase. The photochemical product reverts back to the trans-chalcone adduct with the micelle in the dark. The thermodynamics as well as the kinetics of the photochromic system were studied in detail. The best color contrast is obtained at pH = 4.25 with Phi = 0.001 and a recovery lifetime of approximately 3 h. This photochromic system works with no need of changing the pH, which constitutes an important improvement over previously described systems dependent on pH jumps.

Differently from water, efficient photochromism with a strong colour contrast has been observed for the multistate compound 7,4'-dihydroxyflavylium in the presence of cetyl trimethylammonium bromide (CTAB) micelles. Two states are responsible for the photochromism: trans-chalcone (inside the micelle) in the dark, and flavylium cation, AH(+), (in bulk water) upon irradiation. The kinetics of the system was characterized by flash photolysis and pH jumps. Evidence that the photochemical process leading to AH(+) occurs in the micelle was achieved. The best colour contrast is obtained at pH = 1.5, from a solution practically colourless in the dark, to an intense yellow upon irradiation (quantum yield 0.4). The system is completely reversible with a lifetime of 38 min at room temperature, and exhibits a reasonable stability. A kinetic model capable of fitting the data from thermal entrance of the compound into the micelle, its ejection to bulk water upon irradiation and quantum yields of the photochemical process is proposed.

Photochromism of trans-4-(N,N-diethylamino)-2,4′-dihydroxychalcone, with formation of the photoproduct 7-(N,N-diethylamino)-4′-hydroxyflavylium, is promoted in the ionic liquid phase of a water/[bmim][PF6] biphasic system.

The complex network of chemical reactions of the compound 6-hydroxyflavylium perchlorate was studied by different techniques including UV-vis absorption spectrophotometry, stopped-flow, electrochemistry, and photochemistry. The network is characterized by the formation of a very reactive zwitterionic base as well as by p-quinoidal chalcones. The trans-chalcone is metastable in very acidic solutions and exhibits reversible redox reactions, allowing to introduce for the first time in the flavylium network an electrochemical input.

Useful application of photochromic compounds as optical memories implies the existence of a large kinetic barrier between the forms interconverted by light. In the case of flavylium salts, the ground state isomerization barrier between the photoisomerizable chalcone isomers is shown to correlate with the electron donating ability of the substituents, measured by their effects in the (1)H NMR chemical shifts of the aromatic protons. Substitution with electron donating groups in ring A lowers the barrier while substitution at ring B has the opposite effect. However, in water, the observed increase is higher than expected in the case of compound 4',9-dihydroxychalcone when compared with the analogous 4'-dimethylamino-9-hydroxychalcone, containing a better electron donating group in the same position. Our interpretation is that the water network is providing an efficient pathway to form tautomers. In acetonitrile, unlike water, the expected order is indeed observed: E(a)(4',9-dihydroxychalcone) = 60 kJ mol(-1)E(a) (4'-dimethylamino-9-hydroxychalcone) = 69 kJ mol(-1).

Development of fluorescent chemosensors able to bind and signal either cations or anions in aqueous media is reviewed. Abundant examples in the literature support the versatility of polyamine-based chemosensors towards applications in water. The chemosensors described have a common structure consisting of a binding polyamine motif linked to a fluorophoric unit. Different sensing mechanisms are explored: photoinduced electron transfer from the amine lone pairs to the fluorophoric unit(s), photoinduced electron transfer between fluorophoric units, energy transfer, excimer and exciplex formation. The protonation equilibria of the polyamine chains render great versatility to the chemosensors since they are at the basis of the different sensing mechanisms and also allows the tuning between cation and anion binding regime.

O VI Encontro do Fórum Nacional de Cursos de Geologia foi promovido entre os dias 30 de maio e 2 de junho de 2006, pelas seguintes universidades: Federal do Rio de Janeiro (UFRJ), Univ. Federal Rural do Rio de Janeiro (UFRRJ) e do Estado do Rio de Janeiro (UERJ) e pela Sociedade Brasileira de Geologia (SBGeo), nos institutos aos quais estão vinculados os cursos de Geologia das três instituições.

O notavel incremento, verificado nas ultimas decadas, nas demandas sociais sobre o ambiente e sobre os recursos naturais, bem como as significativas mudancas na producao e transmissao do conhecimento cientifico e tecnologico tornam inadiavel a realizacao de amplo diagnostico sobre a formacao dos geologos nas Universidades Brasileiras. Esse cenario permitiu que, no ano de 2001, o Instituto de Geociencias da Universidade Federal da Bahia e, no ano de 2002, o Instituto de Geociencias da Universidade Estadual de Campinas, com apoio da Sociedade Brasileira de Geologia e outras entidades, organizassem duas reunioes sucessivas, denominadas de Seminario Nacional sobre Cursos de Graduacao em Geologia, com o objetivo de analisar os rumos do ensino na Geologia no Brasil, com vistas a enfrentar os desafios do seculo XXI. Os resultados do primeiro evento foram sintetizados por Mesquita et. al. (2001).

The synthesis of the new terpyridine-containing macrocycle 2,6,10,14-tetraaza[15](6,6'')cyclo(2,2':6',2'')terpyridinophane (L) is reported. The ligand contains a tetraamine chain linking the 6,6'' positions of a terpyridine unit. A potentiometric, (1)H NMR, UV-vis spectrophotometric and fluorescence emission study on the basicity properties of in aqueous solutions shows that the first four protonation steps occur on the polyamine chain, while the terpyridine nitrogens are involved in proton binding only in the last protonation step at strongly acidic pH values. Cu(II), Zn(II), Cd(II) and Pb(II) complexation was studied in aqueous solution by means of potentiometric, spectrophotometric and spectrofluorimetric measurements. Cu(II) and Zn(II) can form both mono- and dinuclear complexes in solution, while the larger Cd(II) and Pb(II) give only mononuclear complexes. In the [ML](2+) complexes (M = Zn(II) or Cd(II)) the metal is unequivocally bound to the terpyridine unit. Some amine groups are not coordinated and can quench the fluorescence emission of the terpyridine unit thanks to an electron transfer process. Protonation of the unbound amine groups inhibits the eT process, affording fluorescent [MLH(x)]((2+x)+) complexes.

The compound 7,4'-dihydroxy-5-methoxyflavylium (dracoflavylium) was identified as the major red colorant in samples of the resin "dragon's blood", extracted from the tree Dracaena draco. The complex network of reversible chemical reactions that dracoflavylium undergoes in aqueous solution is fully described; for the first time, all the equilibrium constants that enable a complete characterisation of the system have been obtained (K'(a)=1.6 x 10(-4), K(a1)=1.0 x 10(-4), K(a2)=3.2 x 10(-8), K(Ct1)=1.0 x 10(-7), K(Ct2)=1.3 x 10(-10)). It is concluded that the red colour is due to a stable quinoid base, A, which is the major species at pH 4-7. It is further shown that this compound does not fit the commonly accepted definitions of anthocyanidin nor 3-deoxyanthocyanidin. Similarly to synthetic flavylium salts, the natural compound 7,4'-dihydroxy-5-methoxyflavylium gives rise to several species (multistate system) reversibly interconverted by external stimuli, such as pH.

Clares Garcia, M. Paz, M.Paz.Clares@uv.es ; Garcia-España Monsonis, Enrique, Enrique.Garcia-Es@uv.es ; Soriano Soto, Concepcion, Concepcion.Soriano@uv.es ; Tejero Toquero, Roberto, Roberto.Tejero@uv.es

Their basic idea consisted of the connec-tion of an amine to a fluorophoric anthracene unit on oneside and to a pyridine moiety on the other. At acidic pHvalues the amino and the pyridine groups are protonatedand a photoinduced electron transfer (PET) occurs fromthe π-π* excited state of the anthracene to the protonatedpyridinium unit, leading to quenching of the fluorescence.However, at high pH values, where the amino group is notprotonated, PET alternatively takes place from the aminelone pair to the same excited state of the fluorophore, yield-ing the same inhibitory effect on the fluorescence. Betweenthese two pH values, there is a pH window where PET doesnot take place and fluorescence emission is observed. Basedon this idea, A. P. de Silva et al. have developed several re-lated “off-on-off” fluorescent systems combining anthra-cene, pyridine and amino groups.

The synthetic flavylium salt 7-(N,N-diethylamino)-4′-hydroxyflavylium tetrafluoroborate gives rise in aqueous solution to a complex network of chemical reactions driven by pH. The system was studied by 1H NMR, single crystal X-ray diffraction, steady state and transient UV-Vis spectrophotometry as well as stopped flow. The crystal structure shows a high degree of coplanarity between the pyrylium system and the phenyl group in position 2. Thermodynamic and kinetic constants for the pH dependent network of chemical reactions were obtained. The introduction of an amino group in position 7 allows formation of protonated species leading, in particular, to a tautomeric form of the protonated cis-chalcone, CcH+, whose absorption spectra is rather red shifted, in comparison with the correspondent protonated trans-chalcone, CtH+. The CcH+ species can be rapidly converted into the flavylium cation through a first order process with lifetime of 0.2 s at pH = 2.35. This new reaction channel confers this compound a peculiar behaviour in acidic media, allowing to define an unidirectional pH driven reaction cycle.

The synthesis, protonation behavior, and Cu2+ and Zn2+ coordination chemistry of the novel bibrachial aza lariat ether (naphthalen-1-ylmethyl)[2-(20-[2-[(naphthalen-1-ylmethyl)amino]ethyl]-3,6,9,17,20,23,29,30-octaazatricyclo[23.3.1.1*11,15*]triaconta-1(29),11(30),12,14,25,27-hexaen-6-yl)ethyl]amine (L) are discussed. The macrocycle, which has two aminoethyl naphthyl moieties symmetrically appended to a 2:2 azapyridinophane structure, displays, in the pH range 2-11, six protonation steps that correspond to the protonation of the secondary amino groups. Steady-state fluorescence measurements show emissions due to the monomer and to the excimer formed between the two naphthalene fragments of the macrocycle. The time-resolved fluorescence data, obtained by the time-correlated single photon counting technique, show that a significant percentage of excimer is preformed as ground-state dimers. The ligand L forms with the metal ions Cu2+ and Zn2+ mono- and dinuclear complexes in aqueous solution. The influence of metal coordination in the fluorescence emission of L is analyzed. The acid-base, coordination capabilities, and emissive behavior of L are compared with those presented by its synthetic precursor L1, which has a tripodal tris(2-aminoethyl)amine structure functionalized at one of its terminal amino groups with a naphthyl moiety.

The macrocyclic phenanthrolinophane 2,9-[2,5,8-triaza-5-(N-anthracene-9-methylamino)ethyl]-[9]-1,10-phenanthrolinophane (L) bearing a pendant arm containing a coordinating amine and an anthracene group forms stable complexes with Zn(II), Cd(II) and Hg(II) in solution. Stability constants of these complexes were determined in 0.10 mol dm(-3) NMe(4)Cl H(2)O-MeCN (1:1, v/v) solution at 298.1 +/- 0.1 K by means of potentiometric (pH metric) titration. The fluorescence emission properties of these complexes were studied in this solvent. For the Zn(II) complex, steady-state and time-resolved fluorescence studies were performed in ethanol solution and in the solid state. In solution, intramolecular pi-stacking interaction between phenanthroline and anthracene in the ground state and exciplex emission in the excited state were observed. From the temperature dependence of the photostationary ratio (I(Exc)/I(M)), the activation energy for the exciplex formation (E(a)) and the binding energy of the exciplex (-DeltaH) were determined. The crystal structure of the [ZnLBr](ClO(4)).H(2)O compound was resolved, showing that in the solid state both intra- and inter-molecular pi-stacking interactions are present. Such interactions were also evidenced by UV-vis absorption and emission spectra in the solid state. The absorption spectrum of a thin film of the solid complex is red-shifted compared with the solution spectra, whereas its emission spectrum reveals the unique featureless exciplex band, blue shifted compared with the solution. In conjunction with X-ray data the solid-state data was interpreted as being due to a new exciplex where no pi-stacking (full overlap of the pi-electron cloud of the two chromophores - anthracene and phenanthroline) is observed. L is a fluorescent chemosensor able to signal Zn(II) in presence of Cd(II) and Hg(II), since the last two metal ions do not give rise either to the formation of pi-stacking complexes or to exciplex emission in solution.

We report the absorption spectra and the photophysical properties (fluarescence spectrum, quantum yield, and lifetime) of four dendrimers of the polylpropylene amine) family (POPAMs) functionalized at the periphery with naphthylsuffonamide (hereafter called naphthyl) units. Each dendrimer Gn, where n = 1 to 4 is the generation number, comprises 2n -1 (i.e., 32 for G4) naphthyl functions in the periphery and 2 n-1 - 2 (i.e., 30 for G4) tertiory amine units in the branches. All the experiments have been carried out in acetonitrile solutions. Comparison with two reference compounds (N-methyl-nophthalene-2-sulfonamide, A, and N-(3-dimethylamino-propyl)-2-naphthalene-1-sulfonamide, B), has shown that the absorption spectra of the dendrimers are significantly different from those expected from the component units. Furthermore, the intense, fluorescence band of the naphthyl unit (λ max = 343 nm; Φ = 0.15, τ = 8.5 ns) is strongly guenched in the dendrimers. The quenching effect increases with increasing generation and is accompanied by the appearance of a weak and broad emission tall at lower energy. Protonation of the amine units of the dendrimers by addition fo CF 3 SO 3 H (triflic acid causes a strong increase in the intensity of the naphthyl luminescence and a change in the form of the emission tail. The shapes of the titration curves depend on dendrimer generation, but in any cose, the effect of the acid can be fully reversed by sucoessive addition of a base (tributylamine). The results obtained show that in the dendrimers there are interactions (both in the ground and excited states) between naphthyl units as well as between naphthyl units and amine units of the branches; this gives rise to dimer/excimer and charge-transfer/exciplex excited states. Titration with Zn(CF 3 SO 3 ) 2 has the same effect as acid titration, as far as the final emission spectrum is concerned, but a much higher concentration of Zn(CF 3 SO 3 ) 2 has to be used and the shapes of the titration plots are very different. Titration with Co(NO 3 ) 2 .6H 2 O causes a much smaller increase in the intensity of the naphthyl fluorescence compared with Zn(CF 3 SO 3 ) 2 . The results obtaine have shown that protonation and metal coordination can reveal the presence of ground and excired state electronic interactions in functionalized poly(propylene amine) dendrimers, and that the presence of photoactive units in the dendrimers can be useful to reveal some peculiar aspects of the protonation and metal coordination processes.

Two new fluorescent macrocyclic structures bearing two naphthalene (Np) units at both ends of a cyclic polyaminic chain were investigated with potentiometric, fluorescence (steady-state and time-resolved) and laser flash photolysis techniques. The fluorescence emission studies show the presence of an excimer species whose formation depends on the protonation state of the polyamine chains implying the existence of a bending movement (occurring in both the ground and in the first singlet excited state), which allows the two naphthalene units to approach and interact. For comparison purposes, one bis-chromophoric compound containing a rigid chain (piperazine unit) was also investigated. Its emission spectra shows a unique band decaying single exponentially thus showing that no excimer is formed. With the two new ligands, excimer formation occurs in all situations even at very acidic pH values when the protonation of the polyamine bridges is extensive. Coexistence of ground-state dimers with dynamic excimers was established based on steady-state and time-resolved fluorescence data. The energetics of excimer formation and dissociation were determined in ethanol and water. Different methods of decay analysis (independent decay deconvolution, global analysis and excimer deconvolution with monomer) were used to extract the kinetic (rate constants for excimer formation, dissociation, and decay) and thermodynamic parameters. In ethanol and acidified ethanol:water mixtures, an additional short decay time was found to exist and assigned to a dimer, whose presence is assumed to be responsible by the decrease in activation energy for excimer formation in this solvent. The results are globally discussed in terms of the small architectural differences that can induce significant changes in the photophysical behavior of the three studied compounds.

The 4'-dimethylaminoflavylium ion in aqueous solution undergoes an intricate network of chemical reactions controlled by pH and light excitation. It is shown that nine different forms are involved, including two species that are not present in previously investigated compounds of the flavylium family. The thermodynamic and kinetic constants of the equilibria and interconversion processes have been obtained by pH jump (included stopped-flow) experiments. The photochromic properties exhibited by the trans/cis chalcone forms have been investigated. The peculiar aspect of 4'-dimethylaminoflavylium, as compared to previously investigated compounds of the same family, is a close to planarity structure, as demonstrated by the X-ray analysis on the parent 4'-aminoflavylium compound (2.3 degrees torsion angle between the benzopyrylium and benzene ring). The results obtained show that the flavylium cation is strongly stabilized by the electron-donor character of the dimethylamino substituent on the benzene ring. The donor-acceptor interaction makes both the protonation of the amino group and the hydration of the flavylium cation difficult, with consequences on the tautomerization and cis/trans isomerization reactions. The multistate/multifunctional properties of 4'-dimethylaminoflavylium have been discussed in the frame of write-lock-read-unlock-erase cycles.

The fluorescence emission of a naphthalene unit attached to a polyamine chain is quenched by intramolecular electron transfer from the deprotonated amines to the excited fluorophore. Measurements of the respective quenching rate constants as a function of the distance, reveal an exponential dependence with β = 0.45 A-1. Identical measurements carried out in deuterated water have shown a similar dependence with the distance β = 0.49 A-1 but an average reduction of the absolute values of the rate constants of ca. 1.2. The polyamine chains seem to constitute a bridge through which the electron can find a route to its movement, more efficiently than through space.

In this work a new water-soluble long-lifetime chemosensor, containing a polyamine unit connected to a complexed Ru(II) metal center, is described. Its crystal structure has been characterized by X-ray analysis. The polyamine macrocyclic unit is capable of anchoring cationic or anionic substrates, according to its protonation state. Examples of electron transfer involving the ruthenium complex core and the bound substrate are presented. The photocatalytic ability of such a system is illustrated by the oxidation of iodide to iodine promoted by light absorption at 436 nm.

The synthesis of the macrocyclic ligand 4,4'-(2,5,8,11,14-pentaaza[15])-2,2'-bipyridylophane (L3), which contains a pentaamine chain linking the 4,4'-positions of a 2,2'-dipyridine moiety, is reported. Protonation and Zn(II) complexation by L3 and by macrocycle L2, containing the same pentaamine chain connecting the 6,6'-positions of 2,2'-dipyridine, were studied by means of potentiometric, UV-vis, and fluorescent emission measurements. While in L2 all the nitrogen donor atoms are convergent inside the macrocyclic cavity, in L3 the heteroaromatic nitrogen atoms are located outside. Both ligands form mono- and dinuclear Zn(II) complexes in aqueous solution. In the mononuclear Zn(II) complexes with L2, the metal is coordinated inside the macrocyclic cavity, bound to the heteroaromatic nitrogen donors and three amine groups of the aliphatic chain. As shown by the crystal structure of the [ZnL2](2+) complex, the two benzylic nitrogens are not coordinated and facile protonation of the complex takes place at slightly acidic pH values. Considering the mononuclear [ZnL3](2+) complex, the metal is encapsulated inside the cavity, not coordinated by the dipyridine unit. Protonation of the complex occurs on the aliphatic polyamine chain and gives rise to translocation of the metal outside the cavity, bound to the heteroaromatic nitrogens.

Chemosensors have attracted interest in many different scientific fields, such as environmental chemistry, medicine, and the processing and storage of information. These molecular-scale devices have the advantage of working on the same spatial scale as the chemical structures that are responsible for macroscopic behaviour observed in the environment or those associated with health problems. Moreover, they allow the construction of molecular-scale devices for information storage. In this review, we describe a family of chemosensors based on a polyamine receptor and a fluorescent signalling unit. Polyamine receptors are water-soluble ambidentate receptors; they are able to coordinate either metal ions, when sufficient deprotonated amino groups are available, or anionic species, when there are sufficient protonated amino groups. On the other hand, the use of fluorescent signalling units confers the advantage of an immediate visual response/signal.

Coordination/detachment of a pendent functionality in the Zn(II) complex with a macrocyclic ligand L gives rise to on/off switching of exciplex emission, defining an elementary molecular machine whose movements are driven by both pH and light.

Association constants for the ion pairs formed between [Co(Sep)]3+ and the anions fluoride, chloride, bromide, iodide, perchlorate, and oxalate were obtained from the chemical shifts of the 59Co resonance that occur upon addition of such anions to solutions of the cobalt complex. The usefulness of 59Co NMR to obtain formation constants, in order to calculate the "true" quantum yields for the ion pairs, is discussed. Key words: association constant, cobalt sepulchrate, ion pair, 59Co NMR, quantum yield.

The formation of a supercomplex between the Ru(bpy)(CN)(4)(2-) (bpy = 2,2'-bipyridine) complex and the [32]ane-N(8)H(8)(8+) macrocycle (1) has been studied in water and in acetonitrile. In acetonitrile, supercomplex formation is accompanied by (i) large hypsochromic shifts in the absorption spectrum (color changes from deep violet to yellow) and in the emission spectrum, (ii) large anodic shifts in standard oxidation (0.73 V) and reduction (0.37 V) potentials, (iii) typical shifts of (1)H-NMR signals for the macrocycle N-bound protons and the complex bipyridine protons, and (iv) a large increase in the MLCT excited-state lifetime of the complex. In water, the spectral shifts and the changes in standard potential are much less pronounced, but supercomplex formation is evidenced by (13)C-NMR (and (1)H-NMR) and by emission lifetime changes. In both solvents, supercomplex formation is complete in 1:1, 1.0 x 10(-4) M solutions, indicating very large stability constant values. A structure of the supercomplex with the macrocycle bound in a "boat" conformation to the four cyanide ligands of the complex, plausible in terms of molecular models, is consistent with all the experimental data. In water, the supercomplex further associates with added negative species containing carboxylate functions, as shown by partial reversal of the lifetime changes. When the added species is also a potential electron transfer quencher (such as, e.g., Rh(dcb)(3)(3-), dcb = 4,4'-dicarboxy-2,2'-bipyridine), however, association is not accompanied by quenching. This behavior is attributed to the structure of the supercomplex-quencher adduct, in which the macrocycle acts as an insulating spacer between the excited complex and the quencher.

The pH dependence of the network of chemical reactions involving 3′,4′,7-trihydroxyflavylium was studied and all the rate and equilibrium constants were determined in the presence and absence of β-cyclodextrin. The β-cyclodextrin increases the rate constant of the flavylium cation hydration to give the hemiketal and decreases the reverse rate constant (de-hydration). The quantum yield of the flavylium cation formation from irradiation of the trans-chalcone increases from 0.023 to 0.055, respectively, in the absence and presence of β-cyclodextrin. NMR spectral characterization of the inclusion complex between 3′,4′,7-trihydroxyflavylium and β-cyclodextrin was performed by ROESY and suggests a structure in which the hydroxyl substituents at positions 3′ and 4′ interact with the internal surface of the β-cyclodextrin.

Five intrinsically electrochromic ionic liquids based on vanadium oxides are obtained by a simple and efficient acid base neutralization of the cation hydroxide and ammonium vanadate. These novel ionic liquids play the role of the electrochrome and electrolyte in liquid electrochromic cells.

2′-Hydroxyflavylium and 2′-hydroxyflavanone derivatives can be interconverted by a precise sequence of pH jumps, through the respective intermediate (mono) ionized trans-chalcones. In acidic and neutral media, the well known network of chemical reactions involving flavylium cation, quinoidal base, hemiketal, and cis and trans chalcones is established. In the pH range 8 < pH < 10, the chalcone (Ct) deprotonates and evolves to the formation of a flavanone (F). At higher pH values, the di-ionized trans-chalcone is the stable species, formed from the flavylium cation. Acidification of the di-ionized trans-chalcone gives the flavylium cation or the flavanone, via the mono-ionized trans-chalcone, respectively at pH < 1 and pH ≈ 9. In contrast with the chalcones, the flavanone once formed is stable even in acidic media. However, under strongly basic conditions, it leads back to the di-ionized trans-chalcone, the most stable species at more basic pH values, and the reactions leading to Ct−, F, Ct2−, Ct−, constitute a one direction cycle for interconversion of these species.

In moderately acidic water/ethanol solutions, 7-(naphthalen-2-ylmethyl)-5,6-dihydrobenzo[c]xanthen-12-ium perchlorate shows C–H proton acidity giving rise to an ethylenic base species, instead of the hydration products of the typical flavylium network of chemical reactions, hemiketal, cis-chalcone and trans-chalcone. The kinetics of this acid–base process is much slower, kobs(s−1) = 3.5 × 10−3 + 0.16[H+], than those commonly observed for O–H deprotonation. In the presence of the triblock copolymer Pluronic F-127, the ethylenic base is dramatically stabilized shifting the pKa from 1.35 (in ethanol : water (1 : 1) to −0.35. Taking profit from the well-described temperature dependence of this polymer, a phase transition thermochromic system was achieved. The system was cycled between 5 and 35 °C with negligible changes in absorbance after 20 cycles.

One- and two-dimensional NMR were used to characterize the several forms of malvin present in aqueous solution in the pH range 0.3–4.5 and to determine their molar fractions as a function of pH. In addition to the flavylium cation, two hemiacetal forms and both the cis and trans forms of chalcone were firmly identified. The pathways for the interconversion of the different forms were derived and the molar absorbances of the species calculated by coupling NMR and UV/Vis data. Equilibrium constants were determined at different temperatures, and enthalpy and entropy changes were calculated for the interconversion processes. The conclusions are supported by molecular orbital calculations.