Amplified anion sensing by conducting polymers

Inorganic anions play active roles in a wide variety of natural, medical, and industrial processes. To be able to monitor the concentration of these anions is, therefore, of great importance in modern science and technology. Reliable sensing of anions is a more challenging area of research than cation sensing for several reasons: anions have lower surface charge concentration than isoelectric cations; they display a wide range of geometries and delocalization of the charge. These factors make sensing of anions a difficult task.; Anion sensing can be performed by chemosensors. The performance of chemosensors can be improved through improved signal transduction of the sensors to generate reliable substrate-specific response. It was demonstrated that it could be achieved by extension of the conjugation of the sensor. There have been examples of cation and neutral substrate sensing by polymer sensors reported, while to-date little data have been presented describing a polymer sensor aimed at anion recognition and sensing. Beside that, application of sensors with dual mode of transduction may provide for more reliable signal response.; In order to obtain anion sensors with improved performance, we have decided to implement two new design features: (i) to use aromatic chromophores as sensor subunits, and (ii) to integrate these sensor subunits directly into the backbone of a conjugated polymer. 2,3-Di(pyrrole-2-yl)quinoxaline (DPQ), an aromatic compound known to undergo changes in color and emission in the presence of a fluoride anion, was used as a core anion receptor. Various aromatic moieties were attached to its 5- and 8-positions to extend the DPQ conjugation. This modification resulted in the increase of the emission intensity, quantum yield, and the anion affinity of the sensors compared to the parent DPQ precursor. Additionally, such a modification allowed for wavelength tuning thus providing a broader spectral region available for efficient anion sensing.; A molecular wire approach to anion sensing was studied in the second part of the project. A previously synthesized oligomer sensor was used as a precursor for the conducting polymer material capable of anion sensing. The polymer film was studied by a variety of methods including electrovoltammetry, electrochemical quartz crystal microbalance (EQCM), conductometry, and vis-NIR spectroscopy. The experiments performed present an unambiguous proof that the synthesized conjugated polymer is capable of efficient anion sensing. Utilization of both optical (absorption) and electrical (conductivity) transduction mechanisms allowed for increased reliability of the anion sensing. The use of synergy between p-doping and hydrogen bonding during the sensing process resulted in the augmented sensitivity of the polymer.