Photoactive thin films of terphenylene-based amorphous polymers. Synthesis, electrooptical properties, and role of photoquenching and inner filter effects in the chemosensing of nitroaromatics

Abstract

New photoactive segmented conjugated polymers with terphenylene chromophores were synthesized, and the chemosensing abilities to detect nitroaromatics compounds (NACs) of the polymeric thin films were evaluated in aqueous media. The thin films are strongly fluorescent, amorphous with no aggregation of the chromophores in the solid state and sensitive towards NACs in water. Though true quenching occurring after diffusion of the NACs into the amorphous films contributes to the total response of these polymer films, quenching efficiencies of nitroaromatics are strongly influenced by additional inner filter effect contributions that could be used to increase the film response. Thus, to maximize the response of these polymers, it is convenient to use the shortest feasible λexc for trinitritoluene (TNT) and the longest feasible λexc for picric acid (PA). In the micromolar concentration region, the highly absorbing PA frequently has a stronger response than TNT due to the inner filter effects (IFE) contributions. However, we observed that the properties of the material, such as exciton mobility or quencher-polymer compatibilities, become more relevant to define the quenching efficiency at the nanomolar range; though the electron-donor capabilities of the chromophores have no bearing on quenching efficiency. So, the tuning of morphology and photophysical properties of the polymer by structural design should be complemented with a rational selection of experimental conditions, e.g., λexc, in order to enhance the response towards the NAC of interest.