Electrochemical mechanism of spiro and zwitterionic Meisenheimer compounds: A potential fluorescence molecular switching system

The reaction between picric acid and an excess of diisopropylcarbodiimide yields a stable red–orange fluorescent zwitterionic spiro Meisenheimer complex of 1,3,5-trinitrobenzene (ZW1). The acidic character of the iminium/guanidium moiety of the triazine ring in ZW1 permits to obtain the corresponding non-fluorescent spiro Meisenheimer Complex (MC2). The redox properties of both ZW1 and MC2 have been studied using electrochemical oxidation–reduction mechanism (established by cyclic voltammetry; classical and with ultramicroelectrodes) and controlled-potential electrolysis. A potential fluorescence switching system has been established, since fluorescent properties can be reversibly modulated by conversion of both states (ON, ZW1) and (OFF, MC2) upon reduction of ZW1 or oxidation of MC2.