ABSTRACT.

The work performed during this Ph. D. is divided in two groups. The first one is dedicated to the study of known dyes as sensors for certain ions and neutral molecules. Most of the studies were done in organics solvents, but some of the dyes were incorporated into polymeric films, in order to use them in water. The second part of the work describes the synthesis and characterization of new chromo-/fluorogenic systems based on five-membered heterocycles, which could be used as chemosensors in the future.
2,4,6-trisusbtituted pyrylium salts were used as molecular sensors for the recognition of anionic and nucleophilic species. The 2,6-diphenyl-4-(p-metacriloxi)phenyl pyrylium monomers were synthesized for the preparation of polymers with different hydrophilic properties. Anions such as carbonate and cyanide could be detected with these materials. The selectivity of these polymeric materials is function of the pH of the solution. At pH 11 the polymeric materials showed selectivity toward cyanide. The nucleophilic attack of cyanide to the pyrylium ring induced a color change from yellow to red caused by the ring opening. The presence of carbonate at pH 7.5 induced the same color change. The diffusion of the carbonate anion inside the polymeric film induced a local increase in the concentration of the hydroxide anion, which is able to open the pyrylium ring through out a nucleophilic attack, resulting in the color changes observed.
4-arylvinyl-2,6-aryl substituted derivatives were employed in the selective detection of amines. When a primary amine is added to solutions of one of these dyes, a pyridinium salt is formed, due to the nucleophilic attack of the amino to the pyrylium ring. We took advantage of the greater nucleophilicity of the amino group in an amines compare to the amino group in the amino acids, for carrying out the selective recognition of biogenic amines in food. 
4-(p-phenylamino)-2,6-diphenylpyridines, with the N of the amino group substituted with crown ethers of different size and with different heteroatom, were studied as donor-acceptor systems for the recognition of ionic species. These receptors form two types of complexes with metal cations, one of them when the coordination occurs with the anilinium unit (donor group), and the other one, upon coordination with the pyridine unit (acceptor group). These complexes have different colors properties: yellow (coordination with the pyridine) and colorless (coordination with the aniline). The coordination behavior of these receptors was studied through UV-Vis titrations. Three kinds of responses were observed: (i) dual coordination, (ii) selective coordination and (iii) no coordination. The receptor 10-[4-(2,6-diphenylpyridin-4-yl)-phenyl]-10-aza-1,4-dioxa-7,13-dithia-cyclopenta-decane (3b) form, in a selective way, an uncolored complex with Hg(II), due to the fact that 10-aza-1,4-dioxa-7,13-dithiaciclopentadecane macrocycle presented a high affinity for this cation. 
These receptor-metal cation complexes were further employed for differential anion sensing. Addition of an anion to a weakly coordinated complex can lead to the formation of a ternary ion pair complex, change the preference for coordination, induce dissociation of the complex or have no effect. The colour changes depend on the effect of the anion. Various patterns of spectral changes were obtained and analysis of the data yielded clear differential recognition patterns for acetate, fluoride, iodide and cyanide anions.
In the second part of this Thesis a serial of heterocyclic compounds with chromo-/fluorogenic properties are synthesized, most of them containing a thiophene ring. The bithiophenes with macrocyclic rings can be used for the detection of metal cations. Triheterocycles with p-aminobencene N-substituted pyrrol as central ring were also synthesized. The terminal amino group of these heterocycles can be easily transformed in ureas, thioureas, guanidinium salts, amides and quaternary ammonium salts, moieties that have been extensively used in the design of anion receptors. We used thiosemicarbazones as a novel coordinative subunit for the development of receptors for anions. A family of N-phenylthiosemicarbazones of 2'-thiophenes functionalized in the 5' position has been synthesized for this purpose. These receptors contain N-H and C-H moieties that will be able to form coordination complexes with anions through out hydrogen bonding interactions. Most of the heterocycles were spectroscopically characterized, considering that they have never been synthesized.