Improved synthesis dimethylhomoecoerdianthrone (HOCD) and its functionalization through facile amination reactions

• Improved synthesis of dimethylhomoecoerdianthrone (HOCD), a 1O2 sensitive dye.
• Functionalized HOCD with sulfonate and develop novel nanoprobe for 1O2 detection.
• Uncovered facile reaction of HOCD with aliphatic amines.
• Prepared a number of amine functionalized HOCD with potential 1O2 sensing application.
• Understood reaction mechanism between HOCD and amines with DFT calculations.

An improved synthesis of dimethylhomoecoerdianthrone (HOCD), a dye used for singlet oxygen detection, was reported by isolation of a key intermediate followed by cyclization reaction. Moreover, dehydrogenative amination reaction between HOCD and alkyl amines and diamines resulted in amine functionalized HOCD derivatives with good yield. The observed reactivity depends on the nucleophilicity of amine and electrophilicity of HOCD. DFT calculations suggest that the reaction involves 1,4-Michael addition followed by migration of hydrogen atom due to aromatization. Under the aerated conditions, dehydrogenation occurs to restore the ketone structure. This C-N coupling reaction can be utilized to construct molecular materials with near infrared photonic properties. Finally, we illustrated that the HOCD derives, HOCD-SO3−, can be grafted to semiconductor nanocrystals (quantum dots) to give turn-on fluorescent nanoprobe for highly selective detection of singlet oxygen.