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Synthesis and characterization of novel diazenes bearing pyrrole, thiophene and...
Raposo, M. Manuela M.; Fonseca, A. Maurício C.; Castro, M. Cidália R.; Belsley, M.; Cardoso, M. Fátima S.; Carvalho, Luís M.; Coelho, Paulo J.Two series of novel thermally stable second-order nonlinear optical (NLO) and photochromic chromophores have been designed and synthesized. The two series of compounds were based on different combinations of donor groups (pyrrole or thienylpyrrole) which act simultaneously as Π-conjugated bridges, together with diazoaryl or diazothiazolyl as acceptor moieties. Their photochromic and electrochemical behavior wer...
Novel photochromic 2,2´-bithiophene azo dyes
Coelho, Paulo J.; Carvalho, Luís H. Melo de; Moura, João C. V. P.; Raposo, M. Manuela M.The photochromic behaviour of two series of 2,2’-bithiophene azo dyes in THF solutions was studied. The photochromic properties and colour constancy were strongly dependent on the substitution pattern of the dyes. Under visible irradiation (> 420 nm) while some dyes exhibited a significant change in the colour intensity others exhibited an almost stable absorption. The photokinetic parameters of these systems a...
Estudo do comportamento fotocrómico de um naftopirano: uma experiência simples ...
Coelho,Paulo J.An easy experiment on the synthesis of 3,3-diphenyl-3H-naphtho[2,1-b]pyran and characterization of its photochromic behaviour is reported. Upon irradiation of an uncoloured toluene solution of 3,3-diphenyl-3H-naphtho[2,1-b]pyran with near UV light, an intense yellow colouration is produced due to the formation of two coloured open forms. When the irradiation source is removed the coloured open forms return to t...
Photochromic properties of thienylpyrrole azo dyes in solution
Coelho, Paulo J.; Carvalho, Luís H. Melo de; Fonseca, A. Maurício C.; Raposo, M. Manuela M.The photochromic behaviour of thienylpyrrole azo dyes in THF solutions was studied for the first time. The photochromic properties are strongly dependent on the substitution pattern on the dyes. Nitro-substituted thienylpyrrole azo dyes are particularly interesting since they exhibit very fast colouration/decolouration processes. The activation energies of these compounds are among the lowest values reported fo...
Studies under Continuous Irradiation of Photochromic Spiro[fluorenopyran-thioxa...
Salvador, Maria A.; Coelho, Paulo J.; Burrows, Hugh D.; Oliveira, M. Manuel; Carvalho, Luís M.New indeno-fused spiro[benzopyran-thioxanthenes] were synthesized (see 3a-d in Scheme 3) and their photochromic properties evaluated under continuous irradiation (Table 1). When submitted to irradiation for several minutes with a Xe lamp, the system behaved as one constituted by two open colored forms with different thermal bleaching rates and different susceptibilities to degradation. An increase in irradiatio...
Synthesis and reactivity of photochromic 2H-chromenes based on 3-carboxylated c...
Cerqueira, N. M. F. S. A.; Rodrigues, Lígia M.; Campos, Ana M. F. Oliveira; Carvalho, Luís H. Melo de; Coelho, Paulo J.; Dubest, Roger; Aubard, JeanNew photochromic 2H-chromenes including a 3-carboxylated coumarin nucleus were synthesised from hydroxycoumarins, and, in one case, the corrresponding trimethoxysilylcarboxamide was prepared. The photochromic behaviour was studied under flash photolysis conditions. The introduction of electron-withdrawing substituents in this position of the coumarin nucleus led to a global and significant bathochromic shift in...
Structural elucidation of the red dye obtained from reaction of 1,8-naphthalene...
Campos, Ana M. F. Oliveira; Carvalho, Luís H. Melo de; Silva, Artur M. S.; Martins, Cristina I.; Coelho, Paulo J.The structure of the intensely coloured red product obtained through the reaction of 1,8-naphthalenediol with 1,1-diphenylprop-2-yn-1-ol was reinvestigated. Instead of the expected permanent open form of the naphthopyran, the dye presents the alpha,beta-unsaturated chain at a different position of the naphthalene nucleus. The structure of this compound was elucidated on the basis of detailed spectral analysis,...
Synthesis of fluorescent 3-benzoxazol-2-yl-coumarins
X. H. Luan; Cerqueira, N. M. F. S. A.; Oliveira, Ana M. A. G.; Raposo, M. Manuela M.; Rodrigues, Lígia M.; Coelho, Paulo J.; Campos, Ana M. F. OliveiraTwelve 3-benzoxazol-2-yl-coumarins (1-3) were synthesised by reacting various ortho-aminophenols with three coumarin-3-carboxylic acids either directly or by formation of the intermediate amide. The cyclodehydrating agent was polyphosphoric acid (PPA). The compounds were characterised by spectroscopic methods. Absorption and fluorescence spectra of the compounds have also been recorded.
First report of a permanent open form of a naphthopyran
Campos, Ana M. F. Oliveira; Martins, Cristina I.; Coelho, Paulo J.; Carvalho, Luís H. Melo deThe 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.
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