Stimuli-Responsive Colorimetric Sensors Based on Supramolecular Polydiacetylene

Abstract

Owing to the distinct blue-to-red color change and the fluorescence ‘turn-on’ feature in response to various physical (heat, pressure, electric current etc) and chemical (pH, solvent, ligand-receptor interactions, etc) stimuli, polydiacetylenes (PDAs) have been extensively investigated as stimulus-responsive colorimetric materials. Mechanical energy transferred to the PDA causes distortion of the π-conjugated backbone, resulting in the changes in the blue-shift in the absorption spectrum along with generation of a red fluorescence.

In this dissertation research, two PDA sensor systems that undergoes a colorimetric change upon mechanical strain and specific molecular recognition, are describe. Firstly, we demonstrate a reversibly mechanochromic PDA system. PDA, generated by polymerization of a bis-diacetylene PCDA-4APDS which contains an amidophenyl disulfide moiety, undergoes a blue to green chromatic change under mechanical stress. Furthermore, the original blue color was recovered via a metastable red-color state by anealing (heating-cooling) process. Interestingly, the reversibly mechanochromic property can be repeated more than 10 times. The results of control experiments using structural analogues demonstrate the significance of the unique design of PCDA-4APDS for producing for the reversible mechanochromic polymer. Secondly, we developed a new selective and sensitive colorimetric and fluorometric biothiol chemo sensor that is comprised of a merucry-complexed, pyridine contating PDA. Biothiols promote decomposition of the pyridine-mercury complex in the PDA due to the its high affinity toward sulfur. Specifically, upon addition of biothiols the sensor undergoes a blue to red color transition and generates red fluorescence. Furthermore, incorporation of the chemosensor in electrospun PEO nanofibers leads to an enhanced sensitivity for biothiol detection. The strategy developed in this study should be applicable to the design of other thiol-specific sensors that utilize pyridine-containing conjugated molecules.