An amphiphilic near-infrared Mn,O-chelated metallo-azadipyrromethene dye: Synthesis, acid-responsive properties, and aggregation pathway control

Abstract

A new amphiphilic Mn,O-chelated azadipyrromethene dye 1 bearing dodecyl chains at the 1,7-phenyls and oligo(ethylene glycol) chains at the 3,5-phenyls was synthesized and characterized. The dye 1 exhibited an absorption maximum in NIR at 823 nm, which is largely bathochromically shifted as compared with the known aza-BODIPY as well as the B,O-chelated aza-BODIPY dyes. Meanwhile, the electrochemical studies of this dye indicated a lower HOMO-LUMO gap in comparison with the boron-chelated analogues. This dye also displayed the acid-responsive properties, as indicated by the hypsochromical shift of ca. 94 nm of the absorption band as well as the occurrence of fluorescence emission at 751 nm upon adding trifluoroacetic acid (TFA) into the dye 1 solution. Moreover, in highly polar solvent MeOH the amphiphilic dye 1 self-assembled into H-type aggregates, which exhibited a fibrous morphology in AFM studies. Further temperature-dependent UV/Vis absorption spectroscopic studies revealed a cooperative aggregation mechanism of dye 1 in MeOH. Based on the acid-responsive properties of 1, a method of control of the aggregation pathway of dye 1 by using acid and base was proposed and demonstrated by UV/Vis spectroscopic studies.