Luis M. Carvalho

Synthesis and spectrokinetic studies of spiro[thioxanthene-naphthopyrans]

Abstract Several new spiro[thioxanthene-naphthopyrans] were prepared from substituted naphthols using a one step reaction. The photochromic properties of the new compounds were studied under flash photolysis and continuous irradiation. Compared to reference compounds general significant bathochromic shifts in the absorption spectra of the open forms, faster thermal bleaching kinetics and interesting fatigue resistances were observed.

Characteristics of p-hydroxybenzoic acid oxidation using Fenton's reagent.

Abstract The objective of this work was to investigate the oxidation of p-hydroxybenzoic acid by the Fentons reagent. Batch experiments were carried out to investigate the influence of the most important process variables: hydrogen peroxide and ferrous salt concentrations, pH, and temperature. The optimal results obtained indicate that p-hydroxybenzoic acid can be effectively degraded using Fentons oxidation within 10-min reaction time by using a molar ratio H2O2: p-hydroxybenzoic acid of 4:1 and H2O2:Fe2+ of 15:1, at 30°C and pH = 3.0. The behavior of ORP and pH along the reaction time for different values of R (molar ratio H2O2: p-hydroxybenzoic acid) was also discussed. A pseudo-first order model was applied to describe the oxidation kinetics of p-hydroxybenzoic acid by Fentons reagent.

Synthesis and photochromic behaviour of novel 2H-chromenes derived from fluorenone

Abstract The synthesis of 2 H -chromenes based on a fluorenone nucleus is described. Whereas 2,2-diphenyl-2 H -pyranofluorenones 4 – 7 and dicyanomethylidene-2 H -pyranofluorenes 8 – 10 do not exhibit photochromism, 2,2-diphenyl-2 H -pyranofluorenols exhibit photochromic behaviour. The spectrokinetic properties of these compounds in solution are reported.

Synthesis of photochromic dyes based on annulated coumarin systems

Novel 2H-chromenes derived from hydroxycoumarins were synthesized, and their photochromic behaviour was studied under flash-photolysis conditions, showing a wide absorption range in the visible region. All the compounds exhibit low fluorescence, which apparently has no negative effect on their photochromic properties.

A new xanthone from Hedychium gardnerianum.

A new xanthone (2), 3-(2-hydroxyethoxy)xanthone, and three known compounds, 1-hydroxyxanthone, salicylic acid and the sesquiterpene oplopanone, were isolated for the first time from the rhizomes of Hedychium gardnerianum Rosc. The structures of these compounds were elucidated on the basis of detailed spectral analysis, including 2D NMR experiments.

Synthesis and Photochromic Behaviour of Novel 2H-1-Benzopyrans (=2H-Chromenes) Derived from Carbazololes

The synthesis and photochromic properties of new 2,2-diphenyl-2H-1-benzopyrans, fused to an indole moiety, are described. All compounds exhibit photochromic behaviour in solution at room temperature. The heteroanellation effects are variable and depend on the position and geometry of the fused indole moiety. A general bathochromic shift in the spectra of the open forms is observed. The presence of a N-methyl group prevents the broadening of the absorption spectra and promotes the instability of some photoinduced forms of compounds with the indole moiety fused at the 5,6 positions of the 2H-1-benzopyran skeleton. The enhanced photocolouration efficiency in the near-UV and the kinetics of thermal bleaching indicate that the novel compounds with an indole moiety fused at the 6,7 positions, particularly those with a linked thiophene moiety, are very interesting molecules for applications in the field of variable optical absorption systems.

Synthesis and photochromic behaviour under flash photolysis and continuous irradiation of novel 2H-chromenes derived from hydroxydibenzothiophenes

The synthesis and photochromic properties, under flash photolysis and continuous irradiation, of new 2,2-diphenyl-2H-1-benzopyrans including a dibenzothiophene nucleus are described. Under flash photolysis, all compounds exhibit photochromic behaviour in solution at room temperature, but under continuous irradiation the same was not perceived. Compared to reference compounds, a general bathochromic shift and the existence of two absorption bands in the Vis spectra of the open forms, leading to a boardening in the absorption range, is observed. The heteroannellation effects on the spectrokinetic parameters are variable and depend on the position and geometry of the fused benzothiophene moiety. The effect of electron-withdrawing substituents in C(6) of the 2H-1-benzopyran skeleton, with the benzothiophene nucleus fused at the 7,8 positions, are analyzed.

Jatrophane and lathyrane diterpenoids from Euphorbia hyberna L.

A new diterpene tetraester, from the jatrophane family, and two new diterpene triesters, with a lathyrane skeleton, have been isolated from the chloroform extract of the roots of Euphorbia hyberna L. The structures of these compounds have been established by spectroscopic methods, including 2D NMR experiments.

Synthesis and Photochromic Behavior of Novel Annelated 2H‐Chromenes Derived from Hydroxy‐9H‐xanthen‐9‐ones

The synthesis of four novel pyrano-xanthenones derived from hydroxy-9H-xanthen-9-ones is described, and their photochromic properties in solution are reported. All compounds synthesized exhibit a good colorability, making them good potential dyes. The presence of the chromone system fused in the 7,8-position seems to lead to more stabilized colored forms.

First report of a permanent open form of a naphthopyran

The synthesis of a permanent open form of a naphthopyran is described for the first time. The open form of the 10-hydroxy-2H-naphtho[1,2-b]pyran, obtained by reaction of 1,8-dihydroxy-naphthalene with 1,1-diphenylprop-2-yn-1-ol under acid catalysis, is stable due to the establishment of an intramolecular hydrogen bond.