Unsymmetrically urea silatranes: Synthesis, characterization and a selective on-off fluorescence response to acetate anion

New unsymmetrically Substituted Urea enclosed Silatranes (USUS) 2-5 are prepared in good yield by nucleophilic attack of pyrrolidine, piperidine, 3-methylpyridine-2-amine and N-methylbenzenamine containing active hydrogen atom on newly synthesized 3-isocyanatopropylsilatrane 1. All the compounds have been characterized by elemental analysis, IR, multinuclear (1H and 13C) NMR and mass spectrometry. The single crystal X-ray crystallography technique facilitates the establishment of exact structures of silatranes 2, 3 and 4. The fluorescence titration results have revealed a selective on-off fluorescence response of silatranes toward acetate anion.