Pb2+ coordination-driven self-assembly of amorphous amphiphilic aromatic block copolymer into semi-crystallized nanostructures with enhanced fluorescence emission

Abstract

Fabrication of luminescent soft nanostructures using non-conjugated polymers is still regarded as being a great challenge. In this work, we have synthesized, for the first time, a range of amphiphilic block copolymers of polyarylene ether nitrile (amPEN) containing pendent carboxylic and sulfonic groups in the hydrophilic segments, which were further self-assembled into nanospheres in an oil-in-water (O/W) microemulsion system. The size, as well as the morphology, of the generated nanospheres can be easily modulated by using the chemical structures of the amPEN. Interestingly, we have discovered that the initial amorphous amphiphilic aromatic block copolymer can be transformed into semi-crystallized polymeric nanospheres with obviously enhanced fluorescence emission when Pb²⁺ is introduced into the emulsion self-assembling process. On the basis of X-ray diffractometry, transmission electron microscopy, differential scanning calorimetry and fluorescence spectroscopy characterizations, we have confirmed that the enhanced emission of the semi-crystallized nanospheres can be attributed to the rigidification of macromolecular chains via the combination of the intermolecular hydrophobic interactions and the coordination of Pb²⁺ with the pendent carboxylic/sulfonic groups, which favors the radiative decay of the excited aromatic structures. Considering the facile synthesis, reliable self-assembly features and the enhanced fluorescence emission, the present work could open a pathway for the design of highly luminescent robust polymeric nanostructures using members of the non-conjugated polyarylene ethers family.