The goal of this PhD was to explore the reactivity of a novel N-aminoacridinium salt. This derivative has been used for the preparation of pH-sensitive and fluorescent diaza [4]helicene dyes thanks to particularly facile N-N bond cleavage reactions. This compound has also been used as nitrogen source for the stereospecific aziridination and sulfoximination of unfunctionalized olefins and sulfoxides under metal-free oxidative conditions respectively. The corresponding NH aziridines and sulfoximines were then obtained using mild photoreductive conditions. Moreover, N-aminoacridinium salt was utilized for the preparation of the fisrt small fluorophore (pKa 5.3) which specifically stains for late endosome compartments (pH 4.8-6) and for the synthesis of chiral (helical) BODIPY and azobenzene derivatives.