The effect of the phenylene linkage in poly(fluorene-alt-phenylene)s on the thermodynamics and kinetics of nitroaromatic and nitroaliphatic sensing

The preparation, photophysical characterization and sensing of a series of highly luminescent poly(fluorene-alt-phenylene)s (PFP) were studied. These PFP polymers varied the phenylene linkage in the 1,4 (PFP-p), 1,3 (PFP-m) and 1,2 (PFP-o) positions. The photoluminescence of these polymers ranged from ultraviolet to blue in color in both solution and film states by simply varying the linkage of the phenylene moiety. Photon Electron Spectroscopy in Air (PESA) revealed that the change in the emission was primarily attributed to the difference of the electron affinity of the polymer. Stern-Volmer quenching studies indicated that these poly(fluorene-alt-phenylene) polymers are highly sensitive towards nitroaromatic materials in solution, particularly in comparison to the reference poly(9,9-di-n-hexylflourene) (PDHF). These PFP polymers were found to be four to ten times more sensitive towards dinitrobenzene as compared to PDHF. In addition, PFP-o displayed the highest polymer-based Stern-Volmer quenching towards the taggant DMNB. The solid-state fluorescence quenching of the PFP-p and PFP-m films using DMNB was enhanced (up to 71.5%) compared to the reference PDHF (59.6%) and was attributed to both thermodynamic and diffusion kinetic factors.