Conjugated polymers based on poly(fluorenylene ethynylene)s: Syntheses and sensing performance for nitroaromatics

Four conjugated polymers (P 1 , P 2 , P 3 and P 4 ) based on poly(fluorenylene ethynylene)s (PFEs) have been synthesized by introducing 9,9-diphenylfluorene units and/or thiophene units into the backbone of PFEs. These exotic units remarkably change the behaviors of polymer, such as the solubility, the peak wavelengths of the optical spectra , and the spectral red-shift of solid polymers, etc. As sensing materials for detecting nitroaromatics, all the four polymers show observable fluorescence quenching when DNT exists. For example, in DNT/THF solution, the quenching efficiencies ( η EP ) of P 2 and P 4 are 95% and 90% at quenching equilibrium respectively, which are much higher than those of P 1 (77%) and P 3 (72%). The high η EP of P 2 and P 4 may be ascribed to the electron-rich character of thiophenylene units which can facilitate the electron-transfer between polymer and DNT. However, in another case of polymer films in DNT vapor, P 3 shows higher quenching efficiency even than P 2 at quenching equilibrium, which may be attributed to the fact that the steric hinderance of 9,9-diphenylfluorene units in P 3 can improve the permeability of the film sensor. P 4 , which contains both thiophenylene and 9,9-diphenylfluorene units, shows the highest quenching efficiency of 91% in DNT vapor at quenching equilibrium.