The Colorimetric and Fluorescent Sensors Based on Heterocycle Containing Polydiacetylene (PDA)

Abstract

Polydiacetylenes (PDAs) are structurally and optically unique conjugated polymers that are derived from topochemical polymerization of the self-assembled diacetylene (DA) monomers. External stimuli including heat, solvent, PH, mechanical stress, ligand-receptor interaction, etc) afford distortion in the π-conjugated backbone of the polymer, resulting in the color changes (typically blue-to-red) of the polymer. These optical changes typically accompany by the generation of bright red fluorescence. In this thesis research, two PDA systems were developed using heterocycle-containing DA monomers. First, a colorimetric PDA sensor was explored for the detection of adenosine triphosphate (ATP). A PDA which was functionalized with pyridine-cadmium complexes displayed a blue-to-red color upon exposure to ATP in a THF-HEPES mixture solution. Close inspection of the mechanism revealed that the ATP-promoted color change is due to the combination of ATP-initiated decomposition of the pyridine-cadmium complex and THF-induced solvatochromism. The unique feature of this method allowed a sequence selective molecular logic gate. Second, a colorimetric and fluorescence turn-on PDA sensor was designed that is specific to Fe(III) ions. An imidazole-containing PDA displayed a blue-to-red color change with a red fluorescence emission upon exposure to Fe(III) ions. The sensor system was found to be selective and sensitive for Fe(III) ions and revealed both amide and imidazole moieties are involved in the metal-binding event. The strategies in this study with PDAs that are derived from heterocycle-containing DA monomers for the ATP and Fe(III) ion sensors should be useful in the design of new PDA-based colorimetric and fluorescent sensors.