Aza-BODIPY dyes with enhanced hydrophilicity

Attempts to make a diamino disulfonic acid derivative of an aza-BODIPY showed it was difficult to add BF2 to a disulfonated azadipyrromethene, and sulfonation of an aza-BODIPY resulted in loss of the BF2 fragment. We conclude the electron-deficient character of aza-BODIPY dyes destabilizes them relative to BODIPY dyes. Consequently, sulfonation of the aza-BODIPY core is not a viable strategy to increase water solubility. This assertion was indirectly supported via stability studies of a BODIPY and an aza-BODIPY in aqueous media. To afford the desired compound type, an aza-BODIPY with two amino and two sulfonic acid groups was prepared via modification of the aryl substituents with cysteic acid.