Detection of volatile organic compounds in the vapor phase using solvatochromic dye-doped polymers

The solvatochromic dye, Reichardtʹs Betaine [2,6-diphenyl-4-(2,4,6-triphenylpyridinio)phenolate] (RDye), was investigated for use in chemical sensing applications. The polarity-sensitive dye was incorporated into several polymer films of differing polarity and sorbent characteristics, and exposed to the headspace above a variety of solvents. Reversible and reproducible changes in the absorption maximum (λmax) of RDye were observed for the series of vapors comprising a range of polarities. The polymers absorbed and concentrated the analyte vapors, thereby influencing the environment surrounding the dye embedded in the polymer. Comparison of the vapor/film results with those of RDye dissolved in the neat solvents were favorable. Methanol and ethanol vapors produced large blue shifts in λmax (avg ≈103 and 63 nm, respectively) for most of the polymer films tested, while isopropanol, acetone, and some chlorinated hydrocarbons produced varying responses in the different films. Water, the most polar vapor tested, did not have much influence on λmax in the films. This is attributed to RDyeʹs low solubility in water and the hydrogen-bonded clustering of water in the films. Exposure of the films to vapors of binary methanol-water mixtures demonstrated that the dye molecules were preferentially solvated by methanol, indicating the detectability of polar vapors in humid environments.