CHANGE IN THE FLUORESCENCE OF 1,1′-DIARYL-2,2′-BIIMIDAZOLES UPON THE ADDITION OF ACID

The optical properties of a series of 1,1'-diaryl-2,2'-biimidazoles were examined. Different transitions were observed in their fluorescence spectra upon changing the electronic properties of the phenyl ring at the Cl and Cl' positions. The presence of a formyl group on the phenyl ring results in fluorescence via a CT transition with a solvent effect. A bathochromic change was observed when HCl was added to a solution of compound bearing a methoxy group in CH2Cl2, whereas a hypsochromic change was observed in compound bearing a formyl group. These observations were attributed to the protonation, which causes a characteristic change in their biimidazole moieties.