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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...
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...
Electrospray tandem mass spectrometry of 2H-chromenes
Campos, Ana M. F. Oliveira; Domingues, M. R. M.; Domingues, Pedro; Oliveira, M. Manuel; Carvalho, Luís H. Melo de; Correia, António J. FerrerSeveral 2H-chromenes, derived from carbazoles, were analyzed by electrospray tandem mass spectrometry. The 2H-chromenes constitute an important class of compounds that exhibit photochromic activity. The fragmentation pathways of the protonated molecular species [M+H]+ were studied and main fragmentation pathways of these compounds were identified. Fragmentation pathways of [M+D]+ ions were also studied in orde...
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,...
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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