Nucleophilic addition of CN− ion to C N bond of aza-BODIPY leading to turn-on fluorescence sensor

We report for the first time that 1,3,5,7-tetraaryl aza-BODIPYs can be used as an exclusive chemodosimetric, colorimetric and turn-on fluorescence sensor for CN− ion. We demonstrated that CN− ion attacks the CN bond of aza-BODIPY core via nucleophilic addition reaction and the resultant compound show significant alteration in electronic properties because of disruption of conjugation as verified by spectral and electrochemical studies. Specially, the aza-BODIPY which exhibit moderate fluorescence in NIR region changes to fluorescent compound which emits strongly in the visible region and thus the 1,3,5,7-tetraaryl aza-BODIPY can be used as turn-on fluorescence sensor for CN− ion. We also used 2-formyl-1,3,5,7-tetraaryl aza-BODIPY which has both CN and CHO active sites for nucleophilic attack by CN− ion and showed that CN− ion prefer CN over CHO as demonstrated here.