New smart functional fluorophores based on stable spirocyclic zwitterionic Meisenheimer compounds

Molecules and materials showing stimulus-induced modulation of their optical properties are of interest in a large variety of areas. In this paper, we focus on fluorescent switches based on stable spirocyclic zwitterionic Meisenheimer compounds (SZMC), which are composed of a 2,4,6-trisubstituted cyclohexadienyl anion chromophore fused with a triazene ring via a spiro carbon atom. By exploiting a facile one-pot synthetic strategy, new SZMC switches have been prepared with halo-, electro- and thermochromic properties. These properties can be controlled by modifying the substituents on their two constituting units. In particular, the optical properties, the sensitivity to different chemical stimuli, and the range of thermal response of these systems can be tailored by varying (a) the nature of the electron-withdrawing groups in their 2,4,6-trisubstituted cyclohexadienyl anion chromophore, and (b) the bulkiness of the pending chains in their triazene ring. In combination with their versatile optical switching behavior, this synthetic tunability makes SZMC switches very promising functional molecules for applications in chemistry, materials science, and biosciences.