Syntheses and characterization of amplified fluorescence poly(aryleneethynylene)s based on 3,4-propylenedioxythiophenes and their application in TNT sensing

A series of electron rich dialkylated 3,4-propylenedioxythiophenes (ProDOT) based poly(aryleneethynylene), PAE, were synthesized and characterized in order to increase the absorption and emission maxima as compared to the their wholly phenylene based counterparts. As planned, these new polymers showed absorption maximum in the range of 397–432 nm with emission wavelength in the range of 511–559 nm which is significantly red shifted compared to the phenylene based PAE. Though, the absorption and emission maxima in this new series of PAEs was significantly red shifted, the quantum yields were found to be much lower as compared to the wholly phenylene based PAEs. The quantum yields were improved by the incorporation of bulky pentiptycene moiety which also resulted in fluorescence in solid state thin films. Furthermore, incorporation of pentiptycene units results in the binding of small aromatic compounds such as TNT resulting in the detection of TNT in thin films by fluorescence quenching. It was interesting to note that these pentiptycene based polymers on incorporation of ProDOTs exhibited lower quantum yields when compared with corresponding wholly phenylene based counterparts. This was attributed to the heavy atom effect due to the presence of sulphur in ProDOT. A series of copolymers were synthesized incorporating various amounts of ProDOT in order to explore if it is possible to increase quantum yield while retaining ProDOT in the final copolymer. However, results indicated that the incorporation of even small amount of ProDOT results in significant lowering of the quantum yields. All these polymers were characterized using NMR, FTIR, GPC, UV–Vis and fluorescence spectroscopy.