14 documents found, page 1 of 2
Luminescent halogen-substituted 2-(N-arylimino)pyrrolyl boron complexes: the in...
Rodrigues, Ana I.; Krishnamoorthy, Paramasivam; Gomes, Clara S. B.; Carmona, Nicolas; Di Paolo, Roberto E.; Pander, Piotr; Pina, JoãoA group of new boron complexes [BPh2{κ2N,N′-NC4H3-2-C(H)[double bond, length as m-dash]N-C6H4X}] (X = 4-Cl 4c, 4-Br 4d, 4-I 4e, 3-Br 4f, 2-Br 4g, 2-I 4h) containing different halogens as substituents in the N-aryl ring have been synthesized and characterized in terms of their molecular properties. Their photophysical characteristics have been thoroughly studied in order to understand whether these complexes exh...
Fluorescence spectra and decays of malvidin 3,5-diglucoside in aqueous solutions
Figueiredo, Paulo; Pina, Fernando; Vilas-Boas, Luis; Maçanita, António L.The fluorescence properties of malvidin 3,5-diglucoside in aqueous solutions at various pH values were investigated using steady state and time-resolved fluorescence techniques. Fluorescence emission bands were assigned to the flavylium cation (AH+) (λmax = 620 nm), hemiacetal (B) (λmax = 370 nm), chalcone (C) (λmax = 435 nm), ionized chalcone (C−) (λmax = 495 nm), quinonoidal base (A) (λmax = 660 nm) and ioniz...
Elucidation of the multiple equilibria of malvin in aqueous solution by One- an...
Santos, Helena; Turner, David L.; Lima, João C.; Figueiredo, Paulo; Pina, Fernando S.; Maçanita, António L.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 absor...
Photochromism of the Synthetic 4',7-Dihydroxyflavylium Chloride
Figueiredo, Paulo; Lima, João C.; Santos, Helena; Wigand, Marie Claude; Brouillard, Raymond; Maçanita, António L.; Pina, FernandoThe synthetic compound 4',7-dihydroxyflavylium chloride shows an interesting photochromic effect at moderately acidic pH values. Pale yellow solutions of this compound, equilibrated in the dark at pH 3.4, become bright yellow upon irradiation with 313-nm light. Switching off the light, gives back the initial pale yellow solution. Photochemical methods, *H NMR, and molecular orbital calculations were used to elu...
Interaction between Poly(9,9-bis(6′-N,N,N-trimethylammonium)hexyl)fluorene phen...
Monteserín, María; Burrows, Hugh D.; Valente, Artur J. M.; Mallavia, Ricardo; Paolo, Roberto E. Di; Maçanita, António L.; Tapia, María J.The interaction between three poly(9,9-bis(6-N,N,N-trimethylammonium)hexyl)fluorene phenylene) bromide (HTMA-PFP) samples of different molecular weights (Mn = 14.5, 30.1 and 61.3 kg/mol) and both dsDNA and ssDNA secondary structures has been studied using UV−visible absorption and fluorescence spectroscopies (including steady-state, time-resolved, and anisotropy measurements for the latter), viscosity, and elec...
Picosecond Structural Relaxation of Abietic Acid Based Amine End Capped Para-Ph...
Paolo, Roberto E. Di; Gigante, Barbara; Esteves, Maria A.; Pires, Natércia; Santos, Célia; Lameiro, Maria H.; Melo, João Seixas de; Burrows, Hugh D.The synthesis and photophysical properties of six new abietic acid based amine end-capped p-phenylenevinylene trimers (AECPV3) in their lowest excited singlet states are presented. The AECPV3 compounds show a large red-shift of both the absorption (25-30 nm) and emission (37-42 nm) maxima with respect to those of the corresponding trimers. Picosecond time-resolved fluorescence data reveal the presence of a fast...
Modulating the Emission Intensity of Poly-(9,9-bis(6‘-N,N,N-trimethylammonium)h...
Monteserín, María; Burrows, Hugh D.; Valente, Artur J. M.; Lobo, Victor M. M.; Mallavia, Ricardo; Tapia, María J.; García-Zubiri, Iñigo X.The interaction between the cationic HTMA-PFP (Poly-(9,9-bis(6‘-N,N,N-trimethylammonium)hexyl-fluorene phenylene) bromide) and oppositely charged sodium n-alkyl sulfonate surfactants of different chain lengths has been studied in DMSO−water solutions (4% v/v) by UV−visible absorption, fluorescence spectroscopy, fluorescence lifetimes, electrical conductivity, and 1H NMR spectroscopy. Polymer−surfactant interact...
Kinetics and Thermodynamics of Poly(9,9-dioctylfluorene) β-Phase Formation in D...
Dias, Fernando B.; Morgado, Jorge; Maçanita, António L.; Costa, Fernando P. da; Burrows, Hugh D.; Monkman, Andrew P.Poly(9,9-dioctylfluorene) (PFO) adopts a particular type of conformation in dilute solutions of the poor solvent methylcyclohexane (MCH) below 273 K, which is revealed by the appearance of a red-shifted absorption peak at 437−438 nm. The formation of this ordered conformation depends on the temperature but is independent of polymer concentration over the range studied (3−25 μg/mL). On the basis of absorption, s...
Kinetics and thermodynamics of poly (9,9-dioctylfluorene) beta-phase formation ...
Costa, Fernando Pestana da; Maçanita, António L.; Morgado, Jorge; Dias, Fernando B.; Burrows, Hugh D.; Monkman, Andrew P.Poly(9,9-dioctylfluorene) (PFO) adopts a particular type of conformation in dilute solutions of the poor solvent methylcyclohexane (MCH) below 273 K, which is revealed by the appearance of a red-shifted absorption peak at 437−438 nm. The formation of this ordered conformation depends on the temperature but is independent of polymer concentration over the range studied (3−25 μg/mL). On the basis of absorption, s...
Comprehensive Evaluation of the Absorption, Photophysical, Energy Transfer, Str...
Becker, Ralph S.; Melo, J. Seixas de; Maçanita, António L.; Elisei, FaustoA large basis set of R-oligothiophenes with two to seven rings (R2-R7), also including thiophene, R1, have been investigated in five solvents regarding absorption, fluorescence and phosphorescence, quantum yields of fluorescence ( F) and triplet formation ( T), lifetimes of fluorescence and the triplet state, quantum yields of singlet oxygen production ( ¢), all rate constants kF, kIC, kISC, and several of the ...