Pina, F, Parola AJ, SaintMaurice A, Manfrin MF, Moggi L, Indelli T, Scandola F.
1997.
Electron transfer between Fe(CN)(6)(3-) and iodide promoted by supercomplexation with a polyammonium macrocycle, 1997. Journal of the Chemical Society-Dalton Transactions. :2327-2330.
AbstractSome new properties promoted by the formation of a supercomplex between iron hexacyanometallates and the polyazamacrocycle [32]aneN(8) (1,5,9,13,17,21,25,29-octaazacyclodotrane) are described. In the presence of the polyazamacrocycle, thermal and photoinduced electron transfer from iodide to Fe(CN)(6)(3-) were observed in moderately acidic media. The thermal reaction is slow (k(obs) = 8.9 x 10(-4) s(-1), at 25 degrees C) and proceeds to an equilibrium (K = 7 M-2, at 25 degrees C). The reaction is almost isoergonic, with favorable enthalpy and unfavorable entropy changes (Delta G degrees = -4.8 kJ mol(-1), Delta H degrees = -160 kJ mol(-1), Delta S degrees = -0.54 kJ mol(-1) K-1). A photoinduced electron-transfer process, leading to additional iodide oxidation, was observed upon flash irradiation of equilibrated solutions. Following the photoinduced process, the system reverts to the thermal equilibrium in the dark. The promoting role of the macrocycle is thermodynamic for the thermal process (anodic shift in the Fe-II/III potential upon supercomplex formation) and kinetic for the photoinduced process [formation of ion-paired species between hexacyanoferrate(III) and iodide upon supercomplex formation]. The thermal reaction is reversible in basic media (where the macrocycle deprotonates and supercomplex formation is prevented), providing an example of on/off switching by pH changes of an electron-transfer reaction.
de Melo, JS, Pina J, Pina F, Lodeiro C, Parola AJ, Lima JC, Albelda MT, Clares MP, Garcia-Espana E, Soriano C.
2003.
Energetics and dynamics of naphthalene polyaminic derivatives. Influence of structural design in the balance static vs dynamic excimer formation, 2003. Journal of Physical Chemistry A. 107:11307-11318.
AbstractTwo 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.
Valente, AA, Petrovski Z, Branco LC, Afonso CAM, Pillinger M, Lopes AD, Romao CC, Nunes CD, Goncalves IS.
2004.
Epoxidation of cyclooctene catalyzed by dioxomolybdenum(VI) complexes in ionic liquids. Journal of Molecular Catalysis a-Chemical. 218:5-11., Number 1
Abstractn/a
Gomes, AC, Bruno SM, Gago S, Lopes RP, Machado DA, Carminatti AP, Valente AA, Pillinger M, Goncalves IS.
2011.
Epoxidation of cyclooctene using soluble or MCM-41-supported molybdenum tetracarbonyl-pyridylimine complexes as catalyst precursors. Journal of Organometallic Chemistry. 696:3543-3550., Number 22
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Nascimento, SMC, Linhares JMM, Joao CAR, Amano K, Montagner C, Melo MJ, Vilarigues M.
2015.
Estimating the Colors of Paintings. Computational Color Imaging, Cciw 2015. 9016(
Tremeau, A., Schettini, R., Tominaga, S., Eds.).:236-242.
Abstractn/a
Nascimento, SMC, Linhares JMM, Joao CAR, Amano K, Montagner C, Melo MJ, Vilarigues M.
2015.
Estimating the Colors of Paintings, 2015. Computational Color Imaging, Cciw 2015. 9016(
Tremeau, A., Schettini, R., Tominaga, S., Eds.).:236-242.
Abstractn/a
Neves, CS, Granadeiro CM, Cunha-Silva L, Ananias D, Gago S, Feio G, Carvalho PA, Eaton P, Balula SS, Pereira E.
2013.
Europium Polyoxometalates Encapsulated in Silica Nanoparticles Characterization and Photoluminescence Studies. European Journal of Inorganic Chemistry. :2877-2886., Number 16
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Rondao, R, de Melo JS, Melo MJ, Parola AJ.
2012.
Excited-State Isomerization of Leuco Indigo, 2012. Journal of Physical Chemistry A. 116:2826-2832.
AbstractThe photoreaction of indigo and two other derivatives in its reduced (leuco) form was investigated by absorption and fluorescence (steady-state and time-resolved) techniques. The fluorescence quantum yield (phi(F)) dependence with the UV irradiation time was found to increase up to a value of phi(F) approximate to 0.2-0.3 (after 16 min) for indigo and phi(F) = 0.2 (at similar to 150 min) for its derivative 4,4'-dibutoxy-7,7'-dimethoxy-5,5'-dinitroindigo (DBMNI). With a model compound, where rotation around the central C-C bond is blocked, the phi(F) value was found constant with the UV irradiation time. Time-resolved fluorescence revealed that initially the decays are fitted with a biexponential law (with 0.12 and 2.17 ns), ending with an almost monoexponential decay (similar to 2.17 ns). Quantum yields for the isomerization photoreaction (phi(R)) were also obtained for indigo and DBMNI with values of 0.9 and 0.007, respectively. The results are rationalized in terms of a photoisomerization (conversion) reaction occurring in the first excited singlet state of trans to cis forms of leuco indigo.