Fluorescence of diimidazo[1,2-a:2',1'-c]quinoxalinium salts under various conditions

The synthesis and photophysical properties of diimidazo[1,2-a:2',1'-c]quinoxalinium salts were examined for different counteranions. The ethyl-substituted diimidazo[1,2-a:2',1'-c]quinoxalinium salt with tosylate anion (categolized in ionic liquid) showed good fluorescence (ΦF = 0.77) in organic solvent. The 3,10-diphenyldiimidazo[1,2-a:2',1'-c]quinoxalinium salts showed absorption and fluorescence peaks resembling those of the former diimidazoquinoxaline. The salt also emitted under various conditions such as in organic solvents, water, and even in the solid state, while retaining a good fluorescence quantum yield (ΦF = 0.5-0.8). Furthermore, the fluorescence was quenched efficiently through the introduction of an electron-donating substituent on the alkyl side chain.