الفهرس 
Merocyanine dyesOnly 14 pages are availabe for public view
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Abstract
Merocyanine dyes of stilbazdium betaines have been found to be of more interest than other merocyanine dyes owing to their extreme 4- solvatochromic properties. The protonated trans form MH tr is photochemically active and isomerizes to give the cis form under the effect of light. In contrast, the unprotonated trans form Mtr is photochemically $table and does not show photoisomerization. This behaviour was explained in terms of the presence of a predominant non-polar quinonoid structure in which the central double bond is absent. The unprotonated cis form is thermally active and isomerizes to the trans form Mtr . Owing to the irreversibility of the thermal reaction, a complete molecular reaction cycle is performed in oce + + +direction: Mtr MH tr& MH;, -- * MCi, ”~Mtr To give more informations about the solvatochromism of the dye (M) the studies are concerned with the effect of the medium on the spectroscopic properties, protolytic equilibrium and the thermal cis/trans isomerization not only in homogeneous media but also in heterogeneous media such as aqueous micelles , reversed micelles and microemulsions. This thesis comprises six chapters. In chapter one : a general introduction for the subject under investigation is given. The introduction includes the solvatochromism of some betaine compounds and the importance of merocyanine dyes as the subject of many reported studies, and the importance of the solvent effect on the spectroscopic properties of organic molecules. There is also a general introduction for anthracene derivatives including some reactions which were studied before. Mechamism of fluorescence quenching and organized assemblies such as micelles, reversed micelles and microemulsions are another part of the introduction. In cha~tertw o; the experimental work such as the chemicals and solvents used, the method of preparation of merocyanine dyes are given. This chapter includes all instrumentations used such as the spectrophotometer, spectrofluorometer and crison digital pHmeter. Finally it gives more information about the methods used for the determination of the fluorescence quantunr yield, photochemical isomerization quantum yields, the rate costant of the thermal isomerization, the fluorescence quenching rate constant and measurements of light intensity ”actinometry” In cha~terth ree : the protolytic properties of the dye (M) were studied. The dissociation constants in both the ground and excited state were determined in cationic and anionic aqueous micelle of cetyltrimethylammonium bromide CTAB and sodium dodecyl sulphate SDS respectively at different concentrations in different pH values. The results obtained suggest that specific hydrogen bonding in CTAB occurs by donating the MH+ proton to the surrounding water molecules. In SDS micelles, MH+ interacts by a specific hydrogen bonding mechanism in which the micelle surface can behave as hydrogen bond acceptor. In chapter four : the rate constant of the thermal reaction were measured and the activation parameters of (M) dye were calculated in different media. The kinetic results for the dye (M) in ethylene glycol and methanol1 water at different ratios are collected in this chapter, which also contains the discussion of the solvatochromism of the merocyanine dye and the role of the solvent used in the thermal cisltrans isomerization. This chapter includes also the kinetic studies of the thermal reaction in aqueous micelles of CTAB and SDS at different concentrations. The effect of water pool in oil-water (olw) microemulsion on the rate constant of the thermal reaction and on the activation parameters were also studied In cha~tefri ve : the quantum yields Qct, $ic of the photochemical isomerization reaction were determined in homogeneous and heterogeneous media by using Gauglitz’s method. All the results of the quantum yield measurements predict that the heterogeneous medium as aqueous micelle, reversed micelles + + and microemulsions led to catalyze the MHc+MH reaction. The results also predict that the isomerization reaction in pure water and cationic micelle (CTAB) could be considered as a side reaction in the deactivation while it remains the main channel of deactivation in other media. The fluorescence quantum yield Qf is also measured in different media. It was found that Qf values are higher in the heterogeneous media than that of pure water. This is ascribed to the polarity effect. In cha~ter six : this chapter is devided into two parts, the quenching of the fluorescence of the merocyanine dye and quenching of 9- methylanthracene using two quenchers from the halogenated p-benzoquinones . This chapter includes the study of the effect of these etectron acceptors as quenchers and micelles on the observed quenching rate constant, the fluorescence intensity and illustrate the type of quenching mechanisa which was achieved by studying the Stern-Volmer plots.