Abstract
	
	The present Thesis entitled “Chromo-fluorogenic sensors for the detection of potentially hazardous materials” is related to the design and synthesis of chromogenic chemodosimeters and to the preparation of organic-inorganic hybrid silica nanoparticles for the visual detection of nerve agent simulants and, by extension, for the real nerve agents. The high toxicity of the nerve agents and the fact that several terrorist groups have used them very recently in indiscriminate attacks underscores the need to detect these lethal compounds with quick, reliable procedures. In recent years, and as alternative a to the usual physical measurements employed for the detection of nerve agents, fluorescent dosimeters and sensors has been developed. However, these fluorescent sensors required the use of relatively sophisticated equipment in order to detect these lethal chemicals. Bearing in mind these facts we focused this Thesis in the preparation of highly selective and sensitive chromogenic sensors that allowed a visual detection of nerve agent simulants. Nerve agents are highly toxic organophosphorous compounds that presented an electrophilic character and are prone to react with nucleophilic species. 
	As a first part of this Thesis three reactive sites, bearing nucleophilic moieties, coupled with several donor-acceptor chromophores were designed, synthesized and evaluated as colorimetric probes against nerve agent simulants. The first two families of chromogenic reagents developed in this Thesis are based in azo dyes. 
      In the first family, the mechanism of action of the reactive site is based in two consecutive reactions; (i) a primary aliphatic alcohol phosphorylation and (ii) subsequent intramolecular cyclization with a tertiary amine (N,N-dimethylaniline), that yielded a quaternary ammonium salt as a final product. In this family, this reactive site the N,N-dimethylaniline acts as donor group in the final azo dye. When the cyclization reaction takes place the quaternary nitrogen atom changes its character to electron acceptor with a subsequent colour change. Bearing in mind these facts, we prepared three chromogenic reagents that were able to give colour changes in the presence of nerve agent simulants allowing their visual detection in organic solvents and in water-acetonitrile mixtures. Also the final chromogenic reagents were included in an inorganic support for the sensing of nerve agent simulants in the vapour phase.
      The second family of chromogenic reagents is based on azo dyes containing pyridine rings. The nitrogen atom in the pyridine ring has nucleophilic character and is able to react with the nerve agent simulants giving pyridinium cations. This phosphorylation reaction changes the electronic properties of the nitrogen atom from donor (in the pyridine form) to acceptor (in the pyridinium salt). Making use of this reactivity several azo dyes containing pyridine rings were synthesized. These receptors were able to react with nerve agent simulants leading to remarkable colour changes that allowed their colorimetric detection. Also these pyridine-based receptors were tested for the colorimetric recognition of nerve agent simulants in the vapour phase.
      The last family of chromogenic reagents developed in this Thesis is based in diarylmethanol and triarylmethanol (carbinols) derivatives. This family of receptors allowed a visual detection of nerve agent simulants by the formation of a coloured product from a colourless one. The mechanism of the chromogenic response is related with the phosphorylation of a secondary or tertiary aliphatic alcohol followed by the elimination of a phosphate fragment that yielded a coloured carbocation. Both consecutive reactions induced the appearance of an absorption band in the visible zone that allowed the detection of the nerve agent simulants.
      Finally, a new optical test for the detection of nerve agent simulants based on nerve agent control of mass transport to the surface of bifunctionalised silica nanoparticles was also prepared. The chromogenic paradigm involves the use of silica nanoparticles that are functionalized with two different subunits; thiol groups and aliphatic alcohols. The role of thiol moieties is to act as a reactive subunit towards a squaraine dye. The reaction of thiols with the central electron-deficient four-membered ring of the squaraine induces a loss of aromaticity, coupled with a bleaching of the blue squaraine solution. Additionally, aliphatic alcohols are known to give acylation reactions with phosphonate substrates. The sensing protocol relies on the fact that the phosphorylation reaction of the hydroxyl groups with certain nerve agent simulants would inhibit the reaction between thiols and squaraine dye, resulting in chromogenic signalling. Chromogenic detection of nerve agent simulants was achieved in solution and in vapour phase by using these bifunctionalized nanoparticles.