Random Copolymers of Styrene with Pendant Fluorophore Moieties: Synthesis and Applications as Fluorescence Sensors for Nitroaromatics

Abstract

Five random copolymers comprising styrene and styrene with pendant fluorophore moieties, namely pyrene, naphthalene, phenanthrene, and triphenylamine, in molar ratios of 10:1, were synthesized and employed as fluorescent sensors. Their photophysical properties were investigated using absorption and emission spectral analyses in dichloromethane solution and in solid state. All copolymers possessed relative quantum yields up to 0.3 in solution and absolute quantum yields up to 0.93 in solid state, depending on their fluorophore components. Fluorescence studies showed that the emission of these copolymers is highly sensitive towards various nitroaromatic compounds, both in solution and in the vapor phase. The detection limits of these fluorophores for nitroaromatic compounds in dichloromethane solution proved to be in the range of 10−6 to 10−7 mol/L. The sensor materials for new hand-made sniffers based on these fluorophores were prepared by electrospinning and applied for the reliable detection of nitrobenzene vapors at 1 ppm in less than 5 min.

Synthesis of random copolymers of styrene and arylamino substituted styrenes and their sensitivities towards nitroaromatics

“…Fabricated sensor elements were employed in a previously reported fluorescence recorder 36 (Figure S104). Briefly, the fluorescence recorder, equipped with a compact camera, was used to register in real time the fluorescence attenuation caused by contact of fluorescent materials with a gas mixture contaminated with the analyte vapor.…”

“…In our previous work, it has been demonstrated that the optimal conditions for polymerization of styrene with 4-arylstyrenes proved to be as follows: 1.5 mol% of 2,2 0azobis(isobutyronitrile) (AIBN) in 0.5 mL of THF, the reaction temperature 80 C, the reaction time 3 h, thus providing the best yields of copolymers and the lowest polydispersity PDI. 36 The same conditions have been applied successfully for copolymerization of styrene and the corresponding N-arylaminostyrenes (3a-h) (Scheme 3). Copolymers P1-P8 were obtained in good yields, and their thermal stabilities were studied (Table 2).…”

“…Fluorescent materials M3, M6, and M7 were prepared by electrospraying tetrahydrofuran (THF) solutions of copolymers P3, P6, and P7, respectively, onto sheets of melamineformaldehyde foam substrate according to the previously described technique. 36 In brief, commercially available melamine-formaldehyde foam is cut into thin sheets that are utilized as an air-permeable inert substrate supporting electrospun fluorescent probes. For further details about the fabrication of materials see "Preparation and employment of electrospun fluorescent materials" section (Supplementary Material).…”

“…These results are similar to those previously reported for copolymers with pendant fluorophore moieties. 36 The sorptive capacity of PS linked to π-π interactions allows the retention of analytes with electron affinity towards the benzene rings, especially the retention of aromatic analytes. 48 Incomplete fluorescence recovery after exposure to vapors can be observed for aromatic analytes, such as nitrobenzene and toluene, while fluorescence attenuation from aliphatic compounds, such as ethanol and acetone, is reversible.…”

“…Responses of materials M3 and M7 towards saturated vapor of nitrobenzene are higher compared to previously described polymers with fluorescent moieties that do not contain amino groups between the polymer backbone and fluorescent moieties. 36 The incorporation of amino groups also causes a fluorescence enhancement on exposure to ethanol and acetone for all fluorescent materials, and these phenomena can potentially mask the quenching signal from nitrobenzene. However, the fluorescence quenching by nitrobenzene is scarcely reversible compared to highly reversible fluorescence enhancement from acetone and ethanol, suggesting that on simultaneous action of nitrobenzene and ethanol/acetone, the quenching of the material's fluorescence can be detected during the post-exposure interval of the measurement.…”